Coatings doi: 10.3390/coatings16091052

Authors: Emircan Dinçer Nesrin Korkmaz Osman Nuri Öcalan Onur Saraçoğlu

Postharvest quality losses limit the storage life of strawberries, highlighting the need for environmentally friendly preservation approaches. In this study, CaO-Based nanoparticles were green-synthesized using hemp (Cannabis sativa L.) leaf extract as a reducing and stabilizing agent, characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDX), and applied to Portola and Monterey strawberries at concentrations of 50, 100, 150, and 200 ppm. XRD analysis confirmed CaO as the main crystalline phase, with CaCO3 identified as a secondary crystalline phase, whereas the presence of metallic Ca could not be confirmed unambiguously. The fruit were stored at 1 ± 0.5 °C and approximately 90% relative humidity for 21 days. The effects of CaO-NP treatments varied according to cultivar, concentration, storage period, and the quality parameter evaluated. In Portola, the 100 ppm treatment resulted in the lowest weight loss, while the 50 ppm treatment maintained the highest firmness and total monomeric anthocyanin content at the end of storage. The 200 ppm treatment produced the lowest numerical decay rate, although it was statistically similar to the control and 100 ppm treatments. In Monterey, the 50 ppm treatment maintained the highest firmness and showed the lowest weight loss among the nanoparticle treatments; however, it did not reduce weight loss below the control and resulted in the highest decay rate. The 100, 150, and 200 ppm treatments maintained decay rates comparable to the control. The 150 ppm treatment maintained comparatively high soluble solids content in both cultivars, while the 200 ppm treatment resulted in the highest total phenolic content in Monterey. No sustained improvement in total antioxidant capacity was observed. Overall, no single CaO-NP concentration was consistently effective across all quality attributes or both cultivars, indicating that these coatings require cultivar- and quality-target-specific optimization.

Coatings doi: 10.3390/coatings16091051

Authors: Zhihao Geng Jingjie Zhang Hui Ma Xiaolan Bai Haiying Mao

This study addresses the unclear damage mechanisms of TiAlSiN-coated tools during high-speed milling of GH4169 by integrating milling experiments with finite element simulations, and establishes a thermo-mechanical coupled damage prediction model that accounts for the superposition effect of cyclic loads. Cutting experiments show that with increasing cutting speed, the rake face damage evolves from peeling and abrasive wear to comb-shaped thermal cracks, mechanical cracks, and large-area peeling, accompanied by a significant reduction in tool life. Simulations reveal that the superposition of residual thermal compressive stress during the idle-cutting phase with mechanical stress in the subsequent cutting cycle forms alternating loads, which is the fundamental cause of thermo-mechanical fatigue crack initiation. The XFEM-CEM coupled model indicates that at higher cutting speeds, the maximum principal stress increases, promoting easier coating crack initiation and greater interfacial debonding. The thermo-mechanical coupled damage prediction model, improved by incorporating a temperature-modified strength threshold and a thermal acceleration factor, yields predictions consistent with experimental results, providing a theoretical basis for process parameter optimization and tool life prediction.

Coatings doi: 10.3390/coatings16091050

Authors: Liangsong Cheng Fang Liu Nicolas Brosse

Waterborne polyurethane (WPU) has emerged as one of the most promising environmentally friendly coating materials owing to its low volatile organic compound (VOC) emissions, excellent film-forming ability, good adhesion, and versatility in formulation. However, WPU suffers from several intrinsic limitations including inadequate thermal stability, modest mechanical strength, poor flame retardancy, and a lack of inherent antibacterial activity. To address these deficiencies, phosphorylated microfibrillated cellulose (PMFC), prepared from beech wood sawdust via sequential steam explosion, phosphorylation, and superfine grinding, was employed as a substrate for in situ silver nanoparticle (AgNPs) synthesis and subsequent incorporation into WPU via aqueous blending and solvent casting. PMFC functions through a combined mechanism: the hydroxyl and phosphate groups coordinate Ag+ ions, providing nucleation sites, while the nanofibrillar network provides steric stabilization against post-synthesis aggregation. The influence of AgNPs loading (1–10 wt% relative to PMFC at a fixed 1 wt% PMFC content) on the morphology, antibacterial activity, silver release behavior, thermal stability, flame retardancy, and mechanical properties of the resulting composite films was comprehensively investigated using free-standing composite films as a model system. At the optimal Ag loading of 5 wt%, the composite exhibited strong antibacterial activity against Escherichia coli with silver release below 1.15 ppb after 96 h, while tensile strength and Young’s modulus increased by 80% and 298%, respectively, relative to neat WPU. At high Ag loadings (70–80 wt%), the composites achieved conductive-level surface resistivity (~3 log Ω) through percolation network formation, demonstrating antistatic functionality. This study provides an effective strategy for fabricating WPU composite films with combined antibacterial, mechanical reinforcement, and antistatic capabilities.

Coatings doi: 10.3390/coatings16091049

Authors: Nian Zhang Shuzhen Zhang Shijie Wu Yi Wang Yang Liu Zhendong Mao

The electrostatic rotary bell (ESRB) sprayer is widely used in the coating industry due to its ability to achieve uniform film thickness and reasonable paint transfer efficiency. However the efficiency of paint transfer and spraying coverage in ESRB systems remain highly sensitive to process parameters. Therefore, optimizing these parameters is essential to reducing paint consumption, energy use, and environmental impact. In this study, a simulation model of the ESRB spraying process was established using ANSYS/Fluent. The spraying flow field, paint deposition profile, and film thickness distribution were validated through the experiment. Based on a single-factor test and the Box–Behnken response surface method, a multi-parameter optimization framework was designed to investigate the effects of six spraying process parameters, including inner and outer shaping air flow rate, bell rotational speed, applied voltage, target distance, and paint flow rate, on coating pattern width and paint transfer efficiency. Based on the Z-score standardization, a mathematical model of the comprehensive score with six factors was established to evaluate spraying efficiency and paint transfer efficiency and predict optimal spraying process parameters. The results indicate that voltage and spray distance are significant factors affecting the comprehensive score, with the order of influence being voltage > spray distance. The optimal parameters were as follows: bell rotational speed X1, 40 kr/min; inner shaping air flow rate X2, 196 sl/min; outer shaping air flow rate X3, 298 sl/min; paint flow rate X4, 249 cc/min; applied voltage X5, 52 kV; and target distance X6, 154 mm. Validation tests showed deviation between the predicted comprehensive score and the actual value from simulation and experiment were 2.03% and 1.36%, respectively. These results demonstrate that the proposed optimization model has high reliability and can be used to optimize spraying process parameters.

Coatings doi: 10.3390/coatings16091048

Authors: Xia Wang Yufan Wang Hongliang Liu Xiaofeng Yuan Xiangang Cui Jiefeng Wang

A series of NixCo3−xO₄ (x = 0.75, 1, 1.5, 2, 2.25) catalysts with different Ni/Co molar ratios was fabricated via the co-precipitation method. The catalytic performance for CO oxidation and SO₂ resistance of the prepared catalysts was systematically investigated, and their physicochemical properties were characterized by XRD, SEM, BET, H₂-TPR, CO-TPD and in situ DRIFTS. The experimental results reveal that the Ni₂.₂₅Co₀.₇₅O₄ catalyst exhibits the optimal CO oxidation activity, achieving a CO conversion of 93.25% at 120 °C. The superior catalytic performance can be attributed to its large specific surface area, low reduction temperature, and easily activated lattice oxygen species. When exposed to SO₂ at a concentration 10 times the industrial emission limit, all catalysts exhibited varying degrees of activity loss. Among them, NiCo₂O₄ exhibited the slowest deactivation rate and showed the greatest recovery in CO conversion after SO₂ was cut off, suggesting relatively better sulfur tolerance and recoverability among the investigated catalysts. In conclusion, tuning the Ni/Co molar ratio can effectively optimize the low-temperature CO oxidation activity and sulfur resistance of Ni-Co composite oxides. This work provides a useful reference for the structural composition design and practical application of such catalysts in flue gas purification.

Coatings doi: 10.3390/coatings16091047

Authors: Daniela Stoeva Georgi Kotlarski Dimitar Dechev Edmon Lazarov Nikolay Ivanov Stefan Valkov Valentin Mateev Iliana Marinova Maria Ormanova

Tungsten nitride (WN) coatings were deposited on copper substrates by reactive direct current magnetron sputtering using deposition times of 15, 30, 45, and 60 min. The influence of deposition time on the structural, morphological, and electrical properties of the coatings was systematically investigated. WN coatings with thicknesses increasing from approximately 0.45 to 1.60 μm were obtained as the deposition time increased. Energy-dispersive X-ray spectroscopy confirmed the presence of W and N in the coating region, while X-ray diffraction showed diffraction features consistent with a crystalline hexagonal δ-WN phase with a dominant {110} preferred orientation for all samples. Increasing deposition time was accompanied by a decrease in the lattice parameter from 2.934 to 2.922 Å and in the relative lattice strain from 0.014 to 0.010. Atomic force microscopy showed that coatings deposited for 15 and 30 min reduced the initial surface roughness, whereas longer deposition times promoted the development of larger surface features and increased roughness. Electrical impedance measurements showed a strong frequency-dependent response. Electrical impedance exhibited a pronounced frequency dependence. At the 1000 kHz range, the impedance magnitude was approximately 0.54 Ω, 0.43 Ω, 0.45 Ω, and 0.43 Ω for coatings deposited for 15, 30, 45, and 60 min, respectively. The electrical response was correlated with the evolution of lattice strain and structural characteristics, although the present data not establish a unique charge-transport mechanism. These findings indicate that deposition time is an important parameter for tailoring the structural and electrical response of WN coatings for conductive and protective applications.

Coatings doi: 10.3390/coatings16091046

Authors: Ziqiao Tang Xiaoheng Zhou Yu Hu Desong Jiang Yihang Tu Won-Ho Kim Sung-Jin Song Haiyin Qing Tao Liu

Owing to their exceptional thermal insulation and protective capabilities, thermal barrier coatings (TBCs) are widely applied to critical hot-section components of aero-engines. However, under increasingly harsh service environments, internal defects such as delamination tend to form within the coatings, posing a severe threat to engine operational safety and service life. To effectively evaluate delamination defects in TBCs, this study employs the immersion ultrasonic pulse-echo technique to inspect specimens subjected to various thermal cycling treatments. Four specimens, subjected respectively to 21, 32, 43, and 54 thermal cycles at 1200 °C, were tested. Ultrasonic response data were systematically acquired via normal incidence scanning from both the superalloy substrate side and the ceramic top coat side. Combining Fast Fourier Transform (FFT), Continuous Wavelet Transform (CWT) based on the generalized Morse wavelet, Wavelet Packet Energy Entropy (WPEE), and peak-to-peak amplitude variations of the second echo, multi-dimensional features were extracted from ultrasonic signals across the frequency domain, joint time-frequency domain, and energy distribution profiles. Through comparative analysis, ultrasonic waveform and time-frequency characteristics representing defect evolution were obtained. A significant monotonically decreasing trend of WPEE with the aggravation of interfacial delamination was established, characterizing the acoustic energy confinement process induced by interfacial damage. Furthermore, a multilayer finite element (FE) model reasonably reproduced dynamic acoustic wave propagation; numerical results are in agreement with experimental data, validating the feasibility of the proposed detection method. The detection and evaluation framework established in this study provides a reference for safety monitoring and lifespan prediction of aero-engine TBCs.

Coatings doi: 10.3390/coatings16091045

Authors: Jie Yao Zhongming He Tangxin Xie

Low-activity copper tailings (CTs) were mechanochemically activated and used to develop a copper tailings–slag–metakaolin grouting material (CSM). Mechanical grinding and Na2SO4 addition were first optimized, after which single-factor experiments and response surface methodology were used to evaluate the effects of the water-to-solid ratio, alkali activator dosage, and MCCT content on slurry properties and compressive strength. Grinding for 40 min with 3 wt% Na2SO4 relative to the dry CT mass produced the highest activity index of 84.5%. The optimized CSM mixture had a water-to-solid ratio of 0.69, an alkali activator dosage of 6.7 wt%, and an MCCT content of 35.5 wt% of the dry solid precursor. Validation experiments yielded a fluidity of 235 mm, a bleeding rate of 2.8%, a setting time of 165 min, and a 28 d compressive strength of 8.62 MPa, with prediction errors below 5%. Microstructural characterization indicated that mechanochemical activation refined the CT particles, increased their structural disorder, and contributed to the formation of Ca–Si–Al–O-rich binding phases and AFt-like crystals in the hardened matrix. Within the defined preliminary material-level system boundary, the embodied energy, greenhouse gas emissions, and material cost of CSM were estimated to be 67.86%, 82.87%, and 27.28% lower, respectively, than those of the 1 kg ordinary Portland cement (OPC) binder benchmark. These results indicate the potential of CSM as a filling and consolidation grout with reduced material-level environmental burdens and cost within the adopted assessment boundary.

Coatings doi: 10.3390/coatings16091044

Authors: Xuelei Li Mingli Xiang Peng Wu Haobin Tian

Advanced composite materials have been widely applied in aerospace structures owing to their low weight, high strength, excellent fatigue resistance, and corrosion resistance. However, during the curing and molding processes of carbon-fiber composites, significant residual stresses are introduced within the components due to factors such as thermal contraction, resin curing shrinkage, and the mismatch in thermal expansion coefficients between the fibers and the matrix. This consequently compromises the performance and reliability of the composites, potentially leading to deformation, warpage, and even cracking, which in severe cases may result in component rejection. This paper aims to investigate the mechanisms by which different forms of prestress influence curing-induced residual stress and strain states, and to analyze their effects on the mechanical properties and microstructural evolution of the materials. In this study, embedded fiber Bragg grating sensors were used to monitor strain evolution during the heating, isothermal curing, and cooling stages of unidirectional carbon-fiber-reinforced polymer laminates subjected to no prestressing, uniaxial through-thickness compressive prestressing, or biaxial prestressing. Tensile tests and scanning electron microscopy were subsequently conducted to evaluate the mechanical response and fracture morphology. The fiber Bragg grating results showed that the strain response varied markedly with the prestressing mode and force level. The findings are expected to provide theoretical guidance and experimental references for mitigating curing-induced residual stresses and improving the molding quality of composite materials.

Coatings doi: 10.3390/coatings16091043

Authors: Jia Xu Wei Qiu Jingjing Yao

Co-based oxides are commonly introduced into porous ceramic membranes to add catalytic activity, but their attachment at the atomic scale remains unclear. We examined a buried Co3O4/Al2O3 interface formed by sol–gel deposition and thermal conversion. Site-specific focused-ion-beam (FIB) lift-out, scanning transmission electron microscopy with energy-dispersive X-ray spectroscopy (STEM-EDS), and high-resolution transmission electron microscopy (HRTEM) were used to access and characterize the interface. A Co-rich spinel-type domain with a (111) lattice spacing was observed next to Al2O3(012). The observations guided density functional theory (DFT) initial models. After structural relaxation, substrate-O-mediated Co-O contacts emerged from both starting geometries: the O-bridged-start model exhibited eight contacts across four Co sites, whereas the non-bridged-start model developed three contacts around one Co site. Around the Co-O-Al linkages, there is a clear manifertation of the interface polarization and charge redistribution, indicated by charge-density-difference and Bader analyses. In both models, projected density of states (PDOS) showed coupling between Co 3d and O 2p states, while integrated crystal orbital Hamilton population (ICOHP) analysis further indicated that O atoms retained Al-O bonds while forming occupied-state Co-O bonds. These results support a representative, laterally distributed Co-O-Al motif as an atomic-scale pathway for chemically attaching the functional oxide to porous alumina.

Coatings doi: 10.3390/coatings16091042

Authors: Xiantao Zhou Haoran Yan Zihao Wang Guanwen Xu Chonghui Ma Xinyou Liu

As a crucial intersection of flexible electronics and embodied intelligent robotics, electronic skin is evolving from single flexible sensors toward a skin-like intelligent system integrating flexible support, signal sensing, environmental protection, signal transmission, and intelligent feedback. With expanding application scenarios, materials must simultaneously meet requirements for softness, stretchability, high strength, self-healing, wear resistance, and long-term stability. Bio-based self-healing polyurethane, leveraging tunable soft–hard segment structures, a wide range of mechanical properties, facile dynamic bond formation, and renewable raw materials, offers a novel material design pathway for highly reliable electronic skin. This review examines the structural and performance modulation of bio-based components—such as castor oil, nanocellulose, lignin, chitosan, tannic acid, and vanillin—in polyurethane coatings, analyzes the mechanisms of non-covalent interactions, dynamic covalent bonds, and multi-dynamic networks in segment motion, energy dissipation, damage repair, and interface reconstruction, and further discusses their adaptation strategies in encapsulation layers, sensing layers, circuit layers, and base layers. Particular attention is paid to polyurethane coatings as protective and functional interface layers, where coating structure, adhesion, mechanical durability, and damage recovery determine the long-term reliability of electronic skin devices. Finally, this review summarizes current challenges in multi-performance synergy, conductive network stability, bio-based component consistency, long-term service, and large-scale fabrication, while envisioning future directions such as intelligent encapsulation, multi-layer synergy, and data-driven material design.

Coatings doi: 10.3390/coatings16091041

Authors: Hu Jin Yansong Zhang Qiang Jia Jianhao Wang Maoqi Ji Meng Zhang Jian Lu

The dust generated during coal mining poses a significant threat to miners’ health and safety. Surfactants, as effective agents for improving coal wettability, require a deeper exploration of their microscopic action mechanisms. This study systematically investigates the micro-interaction behaviors and wetting regulation mechanisms of four types of surfactants—anionic (SDBS), cationic (CTAB), zwitterionic (BS-12), and nonionic (AEO-9)—with lignite, bituminous coal, and anthracite through molecular simulations and dynamic contact angle experiments. To correlate the wettability differences with the physical and chemical properties of different coal ranks, XRD and SEM observations were employed to analyze the mineral composition and surface microstructure. The results demonstrate that SDBS has the strongest adsorption capacity on coal, with the wettability capacity ranked as follows: SDBS > CTAB > BS-12 >AEO-9. This research reveals the regulation mechanism of surfactants on coal wettability, providing a theoretical basis for optimizing dust prevention technologies and fostering the development of green mining.

Coatings doi: 10.3390/coatings16091040

Authors: Xin Wen Zhenhao Yu Yu He Ziteng Wang Xi Chen Kechen Song

With the rapid development of manufacturing, increasingly stringent requirements for material quality and inspection efficiency have promoted the widespread application of deep learning-based nondestructive testing technologies in industrial quality control. In recent years, steel surface defect detection has expanded from conventional inspection scenarios with controlled imaging conditions, such as steel strips, plates, and welds, to more challenging applications involving the inner surfaces of steel pipes, castings, and complex industrial components. This paper reviews recent advances in deep learning-based steel surface defect detection from an industrial application-oriented perspective, with particular emphasis on developments in application scenarios, datasets, methodological frameworks, and research trends. It analyzes representative reviews and their limitations, summarizes publicly available datasets covering conventional flat steel products, pipes, and castings, examines the defect characteristics of different inspection objects, and reviews the development of deep learning and its industrial applications. Furthermore, defect detection and segmentation methods are systematically organized according to practical requirements, including challenging imaging conditions, limited annotated data, small and low-contrast defects, real-time deployment, and cross-domain generalization. Finally, the key challenges, emerging trends, future research directions, and priorities for the next stage of development are discussed.

Coatings doi: 10.3390/coatings16091039

Authors: Jian Li Jun Yuan Shaoyang Wu Haitao Hao Xuchen Zhang Shanhui Liu

Stable tension is critical for the coating quality of lithium-ion battery electrodes. As the origin of tension control, the unwinding system’s control accuracy governs the stability of downstream processes and the final yield. To achieve the required precision, we propose a control strategy that combines reinforcement learning and fuzzy PID. We first derived a nonlinear time-varying dynamic model of the unwinding tension system based on the unwinding mechanism. Leveraging this model, we then designed a reinforcement-learning-based fuzzy PID controller. Finally, we validated the performance of the proposed control strategy through simulations and experiments. Simulations and experiments confirm that, under varying coil radius, the reinforcement-learning-based fuzzy PID controller outperforms both the conventional PID and fuzzy PID controllers in robustness, effectively accommodating the effects of time-varying tension system parameters. Moreover, this method substantially improves the dynamic performance of the unwinding system, with pronounced overshoot suppression, and demonstrates superior robustness and disturbance rejection capabilities.

Coatings doi: 10.3390/coatings16091038

Authors: Xuanhao Cao Anhua Xu Xin Zheng Yindong Xu Weipeng Gai Bowen Guan

High Friction Surface Treatment (HFST) relies heavily on wear-resistant aggregates to ensure roadway safety, yet the conventional evaluation of aggregate abrasion resistance is time-consuming and resource-intensive. In this study, a machine learning framework was developed to predict the abrasion-induced angularity evolution of recycled high-alumina aggregates from their initial morphological characteristics, thereby enabling rapid abrasion-resistance screening. Six regression models were compared under leave-one-group-out cross-validation, and an improved whale optimization algorithm (IWOA) was proposed to tune the Gaussian process regression (GPR) model, incorporating five enhancements and a regularized fitness function to restrain overfitting. The models were trained on 42 samples from six aggregates, whose angularity, Form 2D, micro-texture, sphericity, and F:E ratio were measured with the AIMS II device before and after successive abrasion cycles. The IWOA-GPR model achieved the best performance, with an R2 of 0.8909, an RMSE of 150.98, an MAE of 120.55, and a MAPE of 4.60%. The SHAP analysis identified the abrasion revolutions, the initial Form 2D, and the initial angularity as the dominant contributors to the worn angularity. Moreover, the early angularity loss after the first 500 revolutions correlated strongly with the measured Los Angeles abrasion value (r = 0.935), which allows the LAA of a candidate aggregate to be estimated after a single abrasion cycle. The proposed framework therefore provides a rapid and reliable tool for screening wear-resistant aggregates for HFST applications and supports the clean utilization of recycled solid wastes in anti-skid pavements.

Coatings doi: 10.3390/coatings16091037

Authors: Ligang Wang Xingxing Zhou Peng Guo Shengjie Cheng Guozhong Li

Accurate three-dimensional characterization of asphalt pavement texture requires both reliable surface reconstruction and quantitative interpretation of reconstructed geometry. This study evaluated a passive binocular stereo vision workflow integrating camera calibration, image preprocessing, AANet-based disparity estimation, point-cloud processing, reference-plane correction, surface reconstruction, and texture characterization. Calibration using 16 stereo checkerboard pairs yielded a mean reprojection error of 0.12 px and a baseline of 60.110 mm. On Scene Flow samples, AANet achieved an endpoint error of 2.37 px and a >1-px error rate of 9.2%, compared with 9.71 px and 28.7% for SGBM. Reference-block verification produced absolute height errors of 0.07–0.16 mm and a mean relative error of 4.57%. For nine representative pavement stereo pairs, valid-pixel ratios were 74.75%–87.66% and direct grid coverage was 77.86%–90.62%. Across six specimen series and eight loading stages, reconstructed MTD decreased by 38.9%, 37.7%, and 33.3% for AC-13, SMA-13, and OGFC-13, respectively. Mean specimen-level correlations between reconstructed MTD and measured TD reached 0.865, while fractal dimension–BPN correlations ranged from 0.454 to 0.940. These results demonstrate the potential of passive binocular vision for quantitative asphalt pavement texture characterization under controlled laboratory conditions.

Coatings doi: 10.3390/coatings16091036

Authors: Ruslana Pavukova Yi Mao Yu-Wei Cui Vladimir Uglov Sergey Zlotski

Ti-35Nb-2Ta-3Zr (TNTZ) β-titanium alloy is attractive for biomedical applications because of its relatively low elastic modulus and composition based on nominally non-cytotoxic alloying elements; however, its surface hardness and intrinsic bioactivity remain limited. In this study, Zn nanoparticles were incorporated into the near-surface region of TNTZ by friction stir processing (FSP), followed by compression plasma flow (CPF) treatment in nitrogen. Cross-sectional scanning electron microscopy and energy-dispersive X-ray spectroscopy, X-ray diffraction, microhardness testing, and inductively coupled plasma mass spectrometry after 60 days of immersion in simulated body fluid were used to characterize the modified layers. CPF treatment produced a distinct surface-modified layer approximately 10–15 μm thick, increased the Zn signal within the upper approximately 11 μm, and generated diffraction peaks assigned to Ti2N. The fitted β-phase lattice parameter decreased with nominal X-ray penetration depth, and tensile residual stresses were calculated for all CPF-treated conditions. Sample 1 exhibited the highest microhardness at the lowest applied load. After 60 days of immersion, the mean Zn concentration was 261.87 ± 0.0031 μg/L for FSP and 102.41 ± 0.0063 μg/L for FSP + CPF, corresponding to an approximately 60.9% lower mean cumulative Zn concentration after CPF treatment. Electrochemical, tribological, and biological testing is still required to establish corrosion, wear, and biological performance.

Coatings doi: 10.3390/coatings16091035

Authors: Zhimin Zhao Ping Zhang Junbao Zhang Hui Yang Youqiang Wang

The 7075-T6 aluminum alloy exhibits excellent specific strength due to the presence of precipitated η′ phase, but its surface mechanical performance under demanding conditions is often limited. In this study, a horizontal cylindrical magnetron sputtering system was used to deposit TiN coatings on the surface of 7075-T6 aluminum alloy to enhance its surface mechanical properties and structural performance. The effects of deposition temperature, substrate bias voltage, and N2/Ar flow ratio on the microstructure, surface morphology, phase composition, hardness, and residual stress of the coatings were systematically investigated. The results showed that at 80 °C, enhanced lateral atomic diffusion promoted the transformation of the coating growth mode from coarse columnar crystals to dense quasi-layered structures. The surface roughness decreased from 0.193 μm at room temperature to 0.077 μm, the (111) preferred orientation significantly increased, the hardness reached 383 HV, and the compressive stress was −2.8 GPa. However, when the temperature was raised to 120 °C, grain coarsening and TiN/7075Al interface thermal mismatch stress dominated, and the hardness decreased by approximately 19.3%. At −80 V bias, the atomic impact effect produced by ion bombardment made the coating densified optimally, with the lowest surface roughness of 0.068 μm, a hardness of 377 HV, and a compressive stress of −3.1 GPa; at −150 V, excessive bombardment led to severe re-sputtering and lattice distortion, resulting in a compressive stress of −6.8 GPa and a hardness of 351 HV. When N2/Ar = 10/25, the reaction sputtering kinetics and chemical thermodynamic conditions reached the optimal balance, achieving the highest diffraction peak signal-to-noise ratio and the narrowest full width at half maximum. These results reveal the temperature-dependent competitive relationship between thermally activated coating densification and thermal mismatch-induced structural degradation, providing insights into the optimization of TiN coating deposition parameters on aluminum alloys.

Coatings doi: 10.3390/coatings16091034

Authors: Hongqiong Zhang Hao Wu Yang Zhao Kun Zhang Jingren Dong

A rare carved lacquer (tixi) plate recovered from the Southern Song Dynasty Nanhai No. 1 shipwreck was examined to reconstruct its coating stratigraphy, raw materials, and manufacturing sequence. Detached fragments collected before conservation treatment were investigated by cross-sectional optical microscopy, micro-Raman spectroscopy, thermally assisted hydrolysis–methylation pyrolysis–gas chromatography/mass spectrometry (THM-Py-GC/MS), scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS), and wood-anatomical microscopy. The polished cross-section contains nine lacquer layers with a combined thickness of 387.3 μm above a heterogeneous ground, yielding ten visually distinguishable strata. Alternating dark, red, and yellow layers establish the technological basis for the carved polychrome effect. Raman bands identify cinnabar (HgS) in the red layer and orpiment (As2S3) in the yellow layer. THM-Py-GC/MS detected homologous alkenes, alkanes, and alkylbenzenes diagnostic of Chinese lacquer derived from Toxicodendron vernicifluum. Monocarboxylic acids were present, whereas no clear dicarboxylic-acid markers of a drying oil were observed; because the object was waterlogged and degraded, this absence is treated as a lack of positive evidence rather than proof that oil was never used. The ground is enriched in Ca and P and is therefore consistent with a bone-ash-based filler, although phase-specific confirmation remains necessary. Wood anatomy identifies the substrate as Chinese fir (Cunninghamia lanceolata, Cupressaceae). Together, the results document an organic–inorganic multilayer coating system and provide material evidence for Southern Song carved-lacquer technology, while defining conservation risks associated with a waterlogged wooden core and light-sensitive pigments. The marine archaeological context and the support-to-surface, layer-resolved design distinguish this case from most previous studies of Song-dynasty lacquerware. Beyond technological reconstruction, the findings identify conservation priorities for waterlogged wood, the wood–ground–lacquer interface, and light-sensitive pigmented layers, and provide a transferable evidence framework for comparative research on archaeological lacquer.

Coatings doi: 10.3390/coatings16091033

Authors: Xingkang Jia Yi Zhang Jianqiang Yin Lina Yan

The long-term preservation of earthen wall heritage in Shanxi largely depends on the stability of its rammed earth walls. In this study, the ancient city wall site of Guoyang in Shanxi is taken as a case study. Samples are collected from four directional sections (brick, mortar, and rammed earth), and a nonlinear dynamic finite element method (FEM) with horizontal impact loading is applied, combined with microscopic analyses (SEM, XRF, XRD), to investigate the deterioration mechanisms and structural responses of the brick wall surface. The results show that (1) under identical stress, the north wall exhibits smaller displacement (2.942 × 10−2 mm) than the south wall (4.058 × 10−2 mm), indicating greater lateral stiffness and deformation resistance; (2) the rammed earth particles on the north side show the highest uniformity (CV = 0.4981), while those on the west side display the greatest dispersion (CV = 0.9852), revealing pronounced differences in microscopic stability among the different wall orientations; (3) the north-side rammed earth exhibits a composition typical of high-quality traditional ternary lime–soil mixtures, characterized by high SiO2 (47.06%), high CO2 (19.73%), and low Na2O (2.358%); and (4) the durability of the four wall sections varies with distinct deterioration characteristics. Mineral composition and environmental factors jointly contribute to the differences in wall color and surface conditions. This study provides a reference for the conservation and restoration of similar rammed earth heritage sites.

Coatings doi: 10.3390/coatings16091032

Authors: Tao Zhang Ping Zheng Rui Hai Baoyu Dong Chao Pu Erdeng Ai Jiangao Zhang Peng Yin

To enhance the high-temperature rutting resistance, fatigue performance and low-temperature cracking resistance of base asphalt, and promote the resource utilization of industrial solid waste, this study took 70# asphalt as the base asphalt and selected nano-montmorillonite (MMT) and fly ash (FA) as composite modified fillers. A series of composite modified asphalt samples was prepared with MMT:FA mass ratios of 1:2, 1:3 and 1:4 and total filler contents of 3%, 5% and 7%, respectively. Conventional physical tests, dynamic shear rheometry (DSR), multiple stress creep recovery (MSCR), linear amplitude sweep (LAS) and bending beam rheometry (BBR) were adopted to systematically evaluate the pavement rheological properties. The microscopic modification mechanism was revealed by thin-layer chromatography with flame ionization detection (TLC-FID) and gel permeation chromatography (GPC). The results show that MMT-FA composite filler can significantly reduce the penetration, increase the softening point, and greatly enhance the high-temperature rutting factor, creep-recovery rate and fatigue life of asphalt, while its influence on low-temperature performance is controllable. For the optimal group, S5, the rutting factor rises by 42.6% at 64 °C, and the fatigue life increases by 58.3% under 5.0% strain compared with the base asphalt. With the increase in filler content, the high-temperature and fatigue performance of asphalt increases first and then slows down, while the low-temperature stiffness rises gradually. Microscopic analysis indicates that the intercalation and strong adsorption of MMT restrict the light components of asphalt and increase the proportion of macromolecules, and FA plays the roles of particle filling and skeleton support. The two fillers synergistically optimize the colloid structure and molecular distribution of asphalt. Based on rheological properties and microscopic mechanism, the optimal ratio is 1:3 for MMT:FA with a total content of 5%, under which the composite modified asphalt achieves the best comprehensive pavement performance and can meet the requirements of heavy-load traffic and areas with large temperature differences. The research results can provide experimental and theoretical support for the material design, performance optimization and engineering application of MMT-FA composite modified asphalt.

Coatings doi: 10.3390/coatings16091031

Authors: Jicheng Zhou Xingrong Zhu Jianyong Zhan Linzhao Hao Linfei Feng

Half-cell photovoltaic modules have been widely applied in distributed photovoltaic systems and building-integrated photovoltaic systems. Linear edge shading caused by buildings, guardrails, and adjacent modules is a key factor affecting their power generation performance. To address this problem, this paper establishes an equivalent prediction model for edge-shading of half-cell modules by combining the series–parallel topology of the module and the conduction behavior of bypass diodes. The genetic algorithm is employed to extract the model parameters, and the bisection method is used to solve the output current and obtain the corresponding I–V and P–V characteristics of the module under shading conditions. Simulation analysis is conducted by considering the edge-shading ratio and module installation orientation as variables, and the output characteristics and variation trends of PV modules under two configurations, namely long-edge shading with horizontal installation and short-edge shading with vertical installation, are investigated and compared. The results show that long-edge shading can cause current mismatch in cell strings and conduction of bypass diodes, leading to step features in the I–V curve, a multi-peak structure in the P–V curve, and rapid power attenuation. Short-edge shading only results in a linear decrease in photogenerated current, with smooth output curves and an approximately linear reduction in power along with the shading ratio, resulting in relatively smooth output characteristics. This study reveals the coupled effects of edge-shading and module installation orientation and provides a reference for evaluating shading-induced performance degradation and selecting suitable installation orientations for half-cell PV modules under the investigated shading conditions.

Coatings doi: 10.3390/coatings16091030

Authors: Yiyi Guo Miao Tian Yun Su Jun Li

With the continuous advancement of digital technology and intelligent algorithms, numerical simulation has become an important approach for investigating the thermal transport behavior and protective performance of thermal protective clothing (TPC). To provide a systematic understanding of the development and current research landscape of numerical simulation of thermal protective clothing (NSTPC), this study reviewed the development status of NSTPC through statistical analysis, bibliometric methods, and in-depth literature reading. The theoretical foundations, model construction, and development process of NSTPC were analyzed, with particular emphasis on heat transfer mechanisms, moisture transport, multilayer material structures, and fabric–air gap–skin interfaces. The results indicated that NSTPC has developed along multiple directions, with models ranging from one-dimensional to three-dimensional approaches, from material- and layer-level representations to garment-level simulations, and from single-physics heat transfer models to coupled multi-physics models. These approaches continue to coexist and are employed for different research purposes. Future research may further explore coupled multi-physics field simulation, dynamic simulations of the human body and heat exposure scenarios, the design and evaluation of novel high-performance thermal protective materials and coatings, and the integration of artificial intelligence and machine learning with numerical simulation. These findings provide a systematic knowledge base for understanding NSTPC development and support the design, performance evaluation, optimization, and safety assessment of TPC.

Coatings doi: 10.3390/coatings16091029

Authors: Shiqiang Luo Qitai Guo Dong Chen Tao Liu Yue Zhang Sude Ma

Conventional carbon-black-based low-resistance anti-corona coatings can exhibit electrical properties that are sensitive to filler dispersion, particle spacing, interfacial conditions, and temperature-induced structural rearrangement. In this study, nano antimony-doped tin oxide (ATO) was surface-modified with γ-aminopropyltriethoxysilane (KH550) and used to partially replace carbon black in an E-51 epoxy matrix. The total hybrid-filler loading was fixed at 10 wt% relative to the mass of E-51 epoxy resin, while the ATO/carbon black mass ratio was varied from 0:10 to 10:0. Fourier transform infrared spectroscopy was used to examine the introduction of KH550-derived organosilane species onto ATO, and the coating formulations were screened by measuring surface resistance and corona inception voltage (CIV) under a needle–plate electrode configuration. The selected A3C7 coating was further compared with a commercial carbon-black-based low-resistance anti-corona coating through scanning electron microscopy and thermal cycling between 25 and 150 °C. A3C7 exhibited a surface resistance of (1.17 ± 0.07) × 104 Ω and the highest CIV of 2.58 ± 0.04 kV, representing a 40.1% increase relative to the carbon-black-only A0C10 coating. Relatively uniform circular or elliptical micron-scale features were observed on the A3C7 surface; however, their chemical origin could not be determined by conventional SEM. After 50 thermal cycles, the relative resistance change in A3C7 was 12.62% ± 1.19%, markedly lower than the 63.95% ± 6.76% obtained for the commercial coating. The corresponding CIV retentions were 91.86% and 82.40%, respectively. These results demonstrate that partial replacement of carbon black with KH550-modified ATO can provide a favorable balance among low surface resistance, increased CIV, and improved thermal-cycling electrical stability. The microscopic origin of this behavior remains to be clarified by direct characterization of filler distribution and conductive pathways.

Coatings doi: 10.3390/coatings16091028

Authors: Luxi Li Xilin Wang Lei Zhang Yingzhi Shan Ming Tang

The corrosion of tin amalgam reflective coatings on Qing Dynasty reverse glass paintings has traditionally been attributed to oxidation pathways. No other corrosion types have been reported for this artifact class to date. This study investigated two reverse glass paintings using Scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) and micro-Raman spectroscopy (Raman). In one sample, the corrosion products are romarchite (SnO), tin tetroxide (Sn3O4), and cassiterite (SnO2), confirming the conventional oxidation pathway. In the other sample, abhurite (Sn21Cl16(OH)14O6) and hydroromarchite (Sn3O2(OH)2) are identified alongside tin oxides. This is the first report of chlorine-bearing corrosion products in Qing Dynasty reverse glass paintings. This finding indicates that the coating was exposed to a high-humidity, chloride-containing environment. The coexistence of chloride-mediated and oxidation-pathway products reflects microenvironmental heterogeneity on the coating surface. Preventive conservation for similar objects should prioritize maintaining a stable relative humidity at approximately 50%, excluding exogenous chloride sources, and avoiding acidic pollutants.

Coatings doi: 10.3390/coatings16091027

Authors: Jinlong Liu Guangrui Zhang Shiwei Wang Zhen Yan Jian Yin Conghua Lu

Passive daytime radiative cooling (PDRC) technology with high solar reflectance and high infrared emissivity has been increasingly applied in green buildings. However, current PDRC designs are either high-cost or require additional multi-step fabrication processes, and both factors hinder their broader industrial application. Here, we present a low-cost, easy-to-process, scalable and uncomplicated porous epoxy-based radiative cooling coating via a simple Pickering high-internal-phase-emulsion (HIPE) approach. The obtained porous epoxy-based coating has micro- and submicropores. These hierarchical porous microstructures enable a synergistic interaction between the filler and the porous microstructure, thus enhancing the radiative cooling performance. As a result, the obtained porous epoxy-base polymer with alumina as fillers (PEP-A) coating presents a high solar reflectance of 95.6% in the wavelength range of 0.3–2.5 μm and a high infrared emissivity of 96.3% in the wavelength range of 8–14 μm, as well as a maximum subambient cooling temperature of 3.4 °C and an average cooling power of 105.6 W·m−2 under solar shortwave radiation of 123.01–134.67 W·m−2. Furthermore, the PEP-A coating can be easily applied via roll-coating, blade-coating, or brush-coating, and self-cures on diverse substrates like aluminum sheets, steel plates, polypropylene sheets, bricks, and wall surfaces without any additional template-extraction process. In particular, the cost of the raw materials for the PEP-A coating is 0.2–1.3% of that of previously reported radiative cooling coatings (e.g., Poly(vinylidenefluoride-co-hexafluoropropylene) and polydimethylsiloxane). The extraction-free nature, easy processability, self-curing ability, and low cost of the PEP-A coating make it very promising for large-scale PDRC production and applications.

Coatings doi: 10.3390/coatings16091026

Authors: Lei Qiao Xiaoqiang Zhang Taotao Li Ruifeng Li

In this work, a Fe-based amorphous coating (Fe44Cr18Mo7Ni4Cu2B20Si3C2) was fabricated via high-velocity oxygen fuel (HVOF) spraying, and the effect of annealing temperature on its microstructure, phase composition, and corrosion resistance in 3.5 wt.% NaCl solution was investigated. The as-sprayed (AS) coating exhibits an amorphous content of 85.71% and a porosity of 1.37%. Annealing at 540 °C (H540) reduces porosity to 0.98% without significant crystallization, whereas annealing at 640 °C (H640) and 740 °C (H740) triggers extensive crystallization (amorphous content drops to 24.18% and 19.20%), and porosity increases to 1.82% and 2.17%. Electrochemical tests show that corrosion resistance deteriorates progressively with increasing temperature. icorr increases from 3.56 μA/cm2 (AS) to 50.0 μA/cm2 (H740), while Rp decreases from 8472 to 669 Ω·cm2. EIS reveals that the AS coating is dominated by the inner barrier layer (Rb >> Rt), whereas annealing causes a drastic collapse of Rb (from 8.374 × 104 to 5.011 Ω·cm2). This degradation is attributed to crystallization-induced grain boundaries and reduced effective Cr content, which impair passive film integrity and accelerate corrosion.

Coatings doi: 10.3390/coatings16091025

Authors: Shiquan Liu Jincheng Wei Fengchun Wang Xizhong Xu Zhizhong Chen Xiaomeng Zhang

This study compares the low-temperature responses of two SBS-based asphalt mixtures under progressive step loading: a 4% SBS-modified control mixture and a composite mixture containing 3% SBS + 1.0% Nano-SiO2. Progressive three-point bending creep tests were conducted at 0 °C, −10 °C, and −20 °C to evaluate their mechanical and time-dependent responses. Furthermore, a reduced offset-power-law equation motivated by the first-order small-argument expansion of the fractional-order representation was calibrated to the recorded within-stage creep curves and subsequently used for a model-based time-domain interpretation. The reduced equation captured the main features of the recorded within-stage curve shapes under the tested conditions and provided stage-specific descriptors for comparing the recorded time-dependent responses. In the retained records, the measured flexural tensile strength and maximum flexural tensile strain values were higher for the composite formulation than for the 4% SBS-modified control under the tested temperature conditions. Under the tested step-loading conditions, the retained stage curves showed formulation-dependent within-stage displacement responses. The observed differences are interpreted at the formulation-comparison level rather than as isolated Nano-SiO2 effects. The comparison is limited to the retained records for the two prescribed formulations at the common 5.2% asphalt-to-aggregate ratio and does not quantify between-specimen variability. Together, the measured flexural indicators and model-derived stress-retention responses describe a temperature-dependent balance among deformation accommodation, flexural resistance, and modeled stress retention.

Coatings doi: 10.3390/coatings16091024

Authors: Abdullah Aljamhan Fahad Alkhudhairy

This study evaluated and compared copper oxide (CuO) and titanium dioxide (TiO2) nanoparticles (NPs) incorporated into etch-and-rinse adhesives, with and without photoactivation, on microleakage (ML), resin tag length (RTL), micro tensile bond strength (μTBS), and degree of conversion (DC) in caries-affected dentin (CAD). One hundred thirty extracted permanent mandibular molars with occlusal caries (ICDAS 5) were randomly allocated into five groups (n = 26): unmodified adhesive (control); CuO NP-modified (1 wt%); CuO NP-modified with green-light activation; TiO2 NP-modified (1 wt%); and TiO2 NP-modified with UV pre-irradiation. Modified adhesives were applied in etch-and-rinse mode and LED-photopolymerized. Micro-hybrid composite build-ups were placed incrementally, and specimens were thermocycled. ML was assessed by dye penetration, RTL by SEM, μTBS by universal testing machine, and DC by ATR-FTIR; fracture modes were classified as adhesive, cohesive, or admixed. Data were analyzed using one-way ANOVA and post hoc Tukey’s. All experimental groups outperformed the control for ML, RTL, and μTBS (p < 0.05). For DC, only the photoactivated groups exceeded control (75.23% and 76.12% vs. 65.22%; p < 0.05); whereas, the non-activated nanoparticle groups did not differ from control. Pre-irradiation of NP-modified adhesives before photopolymerization produced better bonding and marginal sealing, a promising strategy for resin composite restorations.

Coatings doi: 10.3390/coatings16091023

Authors: Abdullah Aljamhan Fahad Alkhudhairy

This study evaluated and compared four irrigation activation protocols—conventional syringe irrigation (CSI), passive ultrasonic irrigation (PUI), photon-induced photoacoustic streaming (PIPS), and shock wave-enhanced emission photoacoustic streaming (SWEEPS)—with 17% EDTA as a final irrigant, with respect to smear layer (SL) removal and push-out bond strength (PBS) of root canal sealer in the apical third of curved root canals. One hundred and twenty extracted single-rooted human premolars with oval canals and moderate curvature (20–40°, Schneider’s method) were allocated into four groups randomly (n = 30 each). Canals were prepared crown-down under 2.5% NaOCl irrigation, followed by final 17% EDTA irrigation per the assigned protocol: CSI, PUI, PIPS, and SWEEPS. 10 specimens per group underwent SEM evaluation of SL removal using Hülsmann’s criteria; remaining specimens were obturated. In 10 samples, apical sealer adaptation was assessed via SEM. PBS of ten samples were evaluated using a universal testing machine, followed by failure mode assessment. Data were statistically evaluated using two-way mixed ANOVA, followed by Tukey’s post hoc test for PBS and Kruskal–Wallis test with Dunn’s multiple-comparison test with Bonferroni correction for SL scores (p < 0.05). Minimum SL removal was exhibited by the apical third of Group 1 (CSI-EDTA) samples. PIPS-EDTA and SWEEPS-EDTA presented comparable SL elimination outcomes in the cervical and middle thirds (p > 0.05). SL elimination between these two groups was significantly different in the apical third. The cervical section of Group 4 displayed the highest bond integrity. However, the lowest bond strength was exhibited by the apical third of Group 1 (CSI-EDTA). SWEEPS combined with EDTA demonstrated superior smear layer removal throughout curved root canals, including the apical third, and yielded the highest push-out bond strength among all tested irrigation protocols.

Coatings doi: 10.3390/coatings16091022

Authors: Xiangyang Xu Wenlong Wang Yaoqi Chang Xingfu Yu Kai Zhang Weijun Liu Wei Wang

To investigate the effect of femtosecond laser scanning path on the surface integrity of 7075 aluminum alloy after paint removal, parallel, Z-shape, and loop-shape scanning were compared in terms of surface morphology, microstructure, chemical composition, roughness, wettability, and corrosion resistance. Parallel scanning effectively removed the paint while maintaining a surface roughness of 0.27 μm, close to that of the original substrate. The resulting regular unidirectional laser-induced periodic surface structures (LIPSS) yielded a water contact angle of 85°, consistent with the Wenzel wetting model. X-ray photoelectron spectroscopy (XPS) showed the lowest C 1s and O 1s peak intensities, the lowest lattice-oxygen fraction in Al2O3, the strongest metallic Al0 signal, and limited thermal oxidation. Electrochemical measurements showed the most positive corrosion potential (−0.974 V), the highest film resistance and charge-transfer resistance, and the best corrosion resistance for parallel scanning. By contrast, energy accumulation at the ends during Z-shape scanning and thermal accumulation at the corners and center during loop-shape scanning increased pit and recast-defect densities, oxidation, and corrosion degradation. Loop-shape scanning produced a surface roughness of 3.60 μm and a contact angle of 140.7°, indicating superhydrophobicity, but also the highest corrosion current density and the poorest corrosion resistance, showing that superhydrophobicity does not necessarily correspond to high corrosion resistance. The results show that scanning path affects LIPSS evolution, oxide-film integrity, and corrosion resistance through the spatial distribution of laser energy and thermal accumulation. Among the three paths, parallel scanning provided the best combination of paint removal, low substrate damage, and corrosion resistance, supporting its use in femtosecond-laser paint removal from aircraft aluminum alloy skins.

Coatings doi: 10.3390/coatings16091021

Authors: Guanglong Chai Songyu Sun Yang Wu Lan Xu Ernian Zhao Zhaoyan Cui

Inorganic-bonded bamboo composite (InorgBam) combines the lightweight, high-strength nature of bamboo bundles with the heat resistance, low smoke emission, and environmental compatibility of inorganic binders. However, the inherent surface pores and inter-bundle gaps in this material may facilitate water ingress, and the protective role of waterborne coatings, along with their influence on mechanical performance, remains unclear. This study investigated these issues through short-term water absorption tests, dynamic water contact angle measurements, industrial X-ray computed tomography (CT), and mechanical evaluations. After 48 h of immersion, the coated specimens absorbed only 9.55% water, representing a 59.0% reduction relative to the uncoated group (23.29%). The coated surface exhibited minimal change in contact angle, indicating restricted droplet spreading. CT imaging further revealed a relatively continuous coating layer that sealed surface pores, inter-bundle gaps, and local depressions, with no evidence of deep penetration into the interior. Following coating application, the parallel-to-grain tensile, compressive, and flexural strengths exhibited marginal increases of 3.37%, 2.94%, and 3.27%, respectively, while the dominant failure modes remained unchanged. Collectively, these findings demonstrate that the waterborne coating delays moisture ingress primarily through surface sealing and barrier effects, rather than internal pore-filling, thereby preserving the basic mechanical properties of InorgBam under unaged conditions.

Coatings doi: 10.3390/coatings16091020

Authors: Zimu Li Jichen Zhang Wentang Zhang Baoxing Ren Yong Fan Jianing Xu

Metal corrosion shortens the service life of engineering materials and can cause structural failure and serious safety hazards. Conventional polymer coatings rely mainly on passive barrier protection and often provide limited protection after mechanical damage. Here, we developed a smart epoxy coating containing flake-like CeO2–melamine (CeO2-MA) composite fillers and systematically evaluated the effect of filler content on corrosion protection. Among the tested formulations, the 0.5 wt.% CeO2-MA/epoxy coating exhibited the best overall corrosion protection. Following 72 h of immersion under artificial-defect conditions, its low-frequency impedance modulus (|Z|0.01Hz) was approximately 3.3 times that of the epoxy control. This improved protection may be associated with the complementary effects of melamine adsorption and the formation of cerium-containing deposits in damaged regions. After thermal treatment at 60 °C for 10 min, the coating exhibited pronounced scratch narrowing with only minor residual grooves, along with partial recovery of electrochemical barrier performance. These findings support a multifunctional coating strategy, although direct validation of the inhibition mechanism and longer-term evaluation of the recovered barrier performance remains necessary.

Coatings doi: 10.3390/coatings16091019

Authors: Małgorzata Mizielińska Camille Lucas Wojciech Jankowski Magdalena Zdanowicz

The aim of this study was to impart antimicrobial activity to the surface of two types of polymeric films: biodegradable poly(butylene succinate)—PBS and recyclable biaxially oriented polypropylene—PP films against selected strains of mold and bacteria. The films were coated with a hydroxypropyl methylcellulose (HPMC) carrier containing scCO2 extracts of frankincense (F) and rosemary (R). The modified PP and PBS films, including both additives (FR), exhibited higher antibacterial activity than the coated materials containing exclusively F, and they were selected for storage tests of sliced, plant-based meat analog. The influence of the packaging on maintaining the quality of the tested product during 48 h and 96 h storage at 5 °C was evaluated. The gathered data revealed that functional layers containing mixed scCO2 extracts can be successfully applied on the surface of both types of foils to obtain active packaging, maintaining the microbial quality of vegan alternatives during their secondary storage.

Coatings doi: 10.3390/coatings16091018

Authors: Zhenliang Feng Nianyu Du Huasheng Mei Zihan Zheng Fangchao Zhao Jie Liu

The formation of anti-permeability is a critical step in the in-situ repair of organic anti-corrosion coatings under seawater, yet it is significantly influenced by the surrounding marine environment, particularly seawater temperature and applied cathodic polarization potential. In this study, we systematically investigated the effects of temperature and cathodic polarization potential on the permeability of curing epoxy coatings in simulated shallow seawater. Our results demonstrate that the anti-permeability formation process is governed by the competition between seawater penetration and coating curing. At lower temperatures, the EIS-derived evolution of coating resistance suggested heterogeneous electrolyte uptake across the coating surface, whereas at elevated temperatures, the electrochemical response indicated a more uniform progression of ionic ingress. Moreover, enhanced cathodic polarization accelerated both seawater penetration and the curing reaction of the epoxy coating. The underlying mechanisms of temperature- and polarization-dependent permeability formation were discussed in detail, providing theoretical insights into the top-down permeation process during underwater curing, which may inform the development of more effective in situ repair strategies for organic coatings.

Coatings doi: 10.3390/coatings16091017

Authors: Xingchang Zhuo Yichen Rong Baisheng Liu Juan Ding Yingwei Zhang Wenfeng Guo Guoan Hou

In cold and humid regions, icing events often occur on wind turbines. The phenomenon changes the profile of the aerodynamic airfoil and reduces the power generation efficiency of wind turbines. In the present study, icing tests were conducted in an icing wind tunnel based on NACA0018 airfoils made of fiber reinforced plastics (FRP) and aluminum alloy to investigate the effects of material type and wind speed on the characteristics of icing, including the icing area, the thickness of ice and the adhesive strength of ice. The experimental results indicated that the types of ice on the FRP airfoil and aluminum alloy airfoil were mixed ice and rime ice, respectively. The icing area increased linearly with icing time. The aluminum-alloy airfoil exhibited greater ice accretion at 6 and 10 m/s, whereas the FRP airfoil showed greater ice accretion and a broader ice-covered region at 14 m/s. The FRP airfoil also had a higher adhesive strength. The research in the present study provided an experimental foundation for anti- and de-icing technology development of wind turbine blades.

Coatings doi: 10.3390/coatings16091016

Authors: Jiakun Niu Jinjiang Wang Qing He Fuming Kuang Yusheng Zhang Huanyu Gu Xinyu Li

Ultra-fine zirconia-based powder used in thermal barrier coatings is a core raw material for high-performance coatings, but its small particle size causes clogging during discharge. The discrete element method (DEM) can simulate powder flow and is an effective numerical tool to study clogging, yet discrete element parameters of this powder are lacking. In this work, irregular particles were simplified as soft spheres and scaled from D50 = 1.2 µm to D50 = 240 µm using an improved scaling scheme derived from classical particle scaling and similarity principles. The Hertz-Mindlin with Johnson-Kendall-Roberts Version 2 (JKR V2) contact model in EDEM was adopted, with the angle of repose as the calibration response. The two-level fractional factorial design showed that the particle-particle coefficient of static friction had the largest absolute main effect, followed by JKR surface energy and the particle-stainless steel coefficient of static friction. Steepest ascent tests determined optimal ranges: 0.7–0.9 for particle-particle static friction and 0.17–0.27 for JKR surface energy; the particle-stainless steel friction was fixed at its median of 0.45. An orthogonal test combined with linear interpolation yielded the calibrated parameter combination: 0.8 and 0.19, respectively. The simulated angle of repose was 53.87°, which lies within the experimentally measured range of 50–56° and differs by 0.37% from the experimental mean of 53.67°, showing good agreement between the simulation and experiment under the present calibration condition. The calibrated parameters may provide reference values for DEM simulations of similar static or quasi-static conditions; however, their applicability to other granular flow conditions, including discharge, requires further independent validation.

Coatings doi: 10.3390/coatings16091015

Authors: Izabela Betlej Karolina Lipska Piotr Boruszewski

This study evaluated the effect of modifying pine and birch wood veneers with graphene oxide (GO) and the duration of UV irradiation on roughness parameters (Ra, Rz, Rq). Surface roughness was evaluated in directions both perpendicular and parallel to the grain after 0, 16, 32, and 48 h of photoageing exposure. The study showed that the measurement direction was the main factor determining the values of the roughness parameters. The interaction between impregnation and UV exposure time was significant, indicating that the effect of UV radiation depended on the impregnation used. The roughness parameters for birch were relatively stable. In contrast, for non-impregnated pine, UV radiation caused an increase in roughness, particularly in the direction perpendicular to the grain. Graphene oxide impregnation altered the ageing course of the pine surface, resulting in reduced roughness parameters at longer exposure times.

Coatings doi: 10.3390/coatings16091014

Authors: Daniel C. Ribu Rajamony Rajesh Duraisamy Thirumalaikumarasamy Chidambaram Seshadri Ramachandran C. Ahamed Saleel Abdul Aabid Muneer Baig Bahaa Saleh

The journal retracts the article entitled “Investigating the Water Jet Erosion Performance of HVOF-Sprayed WC-10Co Coatings on 35CrMo Steel Utilizing Design of Experiments” [...]

Coatings doi: 10.3390/coatings16091013

Authors: Ziheng Zhao Elmi Bin Abu Bakar Norizham Bin Abdul Razak Mohammad Nishat Akhtar Elvis Chun Sing Chui

Automated corrosion classification is crucial for industrial inspection. However, existing methods face severe class imbalance and strict computational constraints on edge devices. This study proposes a stepwise self-training framework for six-category corrosion classification. Leveraging a Vision Transformer and XGBoost classifier, this study proposes a class-aware proportional screening strategy that expands a small, labelled dataset with 19,964 unlabeled images to create a more balanced training set. Progressive training and knowledge distillation are then integrated to train a lightweight MobileNetV2 student model. The optimal fine-tuned model achieves a peak classification accuracy of 87.52%, improving upon the baseline MobileNetV2 by over 5%. Grad-CAM analysis confirms accurate focus on corroded regions, while mask-based fine-tuning demonstrates robustness, maintaining over 83% accuracy under 10% visual interference. This approach minimizes computational overhead without sacrificing accuracy, thereby offering a practical solution for real-world monitoring on resource-constrained devices.

Coatings doi: 10.3390/coatings16091012

Authors: Tomas Kačinskas Saulius Baskutis Valdas Grigaliūnas

Bearing-grade PEEK composites are intended to improve sliding performance, but filler addition does not necessarily reduce friction. This study compared the dry sliding tribological behaviour of neat PEEK and hybrid PEEK containing PTFE, graphite, and carbon fibre against 42CrMo4+QT steel. Ring-on-block tests were performed at nominal PV values of 0.3–3.2 MPa·m/s, contact pressures of 0.87–5.82 MPa, and sliding velocities of 0.26–0.55 m/s. Each material–condition combination was tested using three independent specimens. Coefficient of friction was calculated from simultaneously measured tangential and normal forces, and subsurface temperature was recorded continuously. Initial and post-test surfaces were examined using optical and extended depth-of-field microscopy. Group mean COF values ranged from 0.052 to 0.123. Hybrid PEEK exhibited a higher numerical mean COF than neat PEEK in all six operating conditions, with relative differences of approximately 1.53–8.36%. Two-factor ANOVA estimated an overall hybrid-minus-neat difference of +0.003388 COF units (95% CI 0.001279–0.005496; p = 0.0029), whereas none of the six condition-specific neat–hybrid comparisons was significant after Holm correction. Initial temperature, maximum temperature, and baseline-normalised temperature rise were reported for every specimen and treated descriptively. Both materials reached stable sliding states without seizure or uncontrolled thermal escalation. Post-test EDF observations showed a denser pattern of fine grooves on neat PEEK, whereas hybrid PEEK exhibited comparatively smoother intervening regions interrupted by fewer but locally deeper features. Mass changes remained close to the capability of the applied balance and did not permit quantitative wear-rate comparison. The results show that the investigated hybrid formulation did not provide a dry-friction reduction advantage over neat PEEK under the tested conditions.

Coatings doi: 10.3390/coatings16091011

Authors: Zhenhu Wang Lijun Dong Yajun Luo Erli Xia Sawei Qiu Junjiang Xun Xindong Liu Heman Wen

In the current manuscript, the hot deformation behavior and the thermal processing map of 6082-T6 rolled aluminum alloy sheet were studied. A series of compression tests were conducted using the Gleeble-3500 thermal simulation machine under the conditions of 200–350 °C and 0.001–1 s−1. In order to tackle the stress errors caused by friction and plastic deformation temperature rise, the friction correction model and the adiabatic temperature rise interpolation method were used, respectively, to correct the flow stress curve. Based on the corrected data, a strain-compensated Arrhenius constitutive equation was constructed. Through the 4th-order polynomial fitting of material parameters and strain, the measured and predicted stresses were compared, with the average relative error reaching 10.50%. The thermal processing map was drawn based on the dynamic material model, and the material instability region was concentrated in the low-temperature high-strain rate zone. Within the investigated temperature and strain rate range, the optimal processing window was 320–350 °C and 0.001–0.031 s−1. Combined with microscopic characterization by Optical microscope and transmission electron microscope, it was found that deformation at low temperature and high strain rate was mainly dynamic recovery, and dynamic recrystallization could fully occur at high-temperature low-strain rate. The research results can provide theoretical support for the optimization of the hot forging and hot stamping processes of this alloy.

Coatings doi: 10.3390/coatings16091010

Authors: Jibo Miao Ruizhi Peng Shu Feng Xue Liu

With rapid development of 5G/6G communication and high-power electronic devices, electromagnetic interference (EMI) shielding textiles are urgently required to mitigate electromagnetic pollution. Traditional metallic shielding suffered from heavy weight, poor corrosion resistance, and secondary electromagnetic reflection, while continuous basalt fibers (CBFs) exhibit excellent mechanical strength, lightweightness, thermal/chemical resistance, and electrical insulation, which makes CBFs ideal substrates for EMI devices. Herein, a multifunctional waterborne polyurethane (WPU) sizing agent (coating emulsion) integrated with Mn-Zn spinel ferrite was developed for in situ lubrication on the as-spun CBFs. The composite sizing agents consisted of a WPU matrix, water-soluble epoxy, mineral oil lubricant, CTAB surfactant, KH-570 coupling agent, and micro-sized Mn-Zn ferrites. Characterizations including particle size distribution, thermogravimetric analysis, water contact angle (WCA), water absorption, FTIR, XRD, and SEM were conducted to verify uniform anchoring of ferrites on the CBF surfaces. Increasing ferrite dosages induced slight particle aggregation, elevated surface hydrophobicity (WCA = 42.4° → 99.43°), and reduced water absorption (65% → 35%), which greatly improved the moisture resistance of the CBFs. The X-band EMI shielding tests revealed that the total shielding effectiveness (SET) of modified CBF fabrics increased from 0.11 dB (pristine fiber without ferrite) to 58.57 dB at a loading of 8.0 g/L ferrite. The absorption loss (SEA) dominated the shielding performance over reflection loss (SER). The low-to-moderate contents (1.5–3.0 g/L) of ferrite achieved ultra-high absorption, while higher ferrite loading (5.0–8.0 g/L) intensified the impedance mismatch and enhanced surface reflection. This work establishes a scalable fabrication of absorption-prioritized lightweight CBF shielding, which provides a feasible pathway for flexible EMI shielding textiles.

Coatings doi: 10.3390/coatings16091009

Authors: Gisela M. Calle Luz Quispe-Sanchez Segundo G. Chavez

The development of biodegradable materials from renewable sources represents a promising strategy to reduce the environmental impact associated with conventional plastics. This study aimed to optimize potato starch-based bioplastics incorporated with lemongrass essential oil (Cymbopogon citratus) using Response Surface Methodology (RSM) and to evaluate their application in fresh pineapple (Ananas comosus) preservation. A Box–Behnken experimental design with three factors and three levels was applied, considering potato starch concentration (4–8 g), essential oil content (100–300 µL), and glycerol volume (1–2 mL) as independent variables. The effects of these factors on tensile strength, elongation at break, and Young’s modulus were analyzed using a quadratic model. The optimized formulation exhibited a desirability value of 1.00, consisting of 4.13 g of starch, 131.59 µL of essential oil, and 1.43 mL of glycerol, with predicted values of 2.91 MPa tensile strength, 53.18% elongation at break, and 15.18 MPa Young’s modulus. Experimental validation showed good agreement with model predictions, with relative errors below 20%. The optimized bioplastic was subsequently applied as a coating for fresh-cut pineapple stored under refrigeration (4–8 °C), reducing weight loss and improving the stability of physicochemical and textural properties compared with the control treatment. The results demonstrate that potato starch-based bioplastics containing lemongrass essential oil have potential as active biodegradable coatings for extending the quality preservation of fresh pineapple.

Coatings doi: 10.3390/coatings16091008

Authors: Zhanfang Wu Peixin Tang Guirong Liu Xiangyang Li

Ni–Mo alloy claddings were fabricated on low-carbon steel substrates using powder metallurgy combined with hot isostatic pressing (PM-HIP). The interfacial microstructure, elemental interdiffusion, phase composition and microhardness distribution of the bimetallic composite were investigated systematically. The results show that sound metallurgical bonding without pores, cracks and element dilution is achieved under the HIP process of 1100 °C, 120 MPa and 4 h holding time. Interdiffusion of Fe, Ni and Mo atoms forms a 20–50 μm thick interfacial transition layer, and Mo exhibits a relatively low diffusion capacity due to its large atomic radius. Two intermetallic phases, Ni4Mo and NiMo, are formed in the cladding layer because of the inhomogeneous distribution of Mo. A prominent microhardness gradient is observed throughout the composite, and the interfacial layer presents the highest hardness of 905 HV resulting from multiple strengthening mechanisms. As an effective alternative to traditional welding and cladding technologies, the PM-HIP process exhibits great potential for manufacturing complex bimetallic components with prospective service prospects in severe corrosive environments.

Coatings doi: 10.3390/coatings16091007

Authors: Bauyrzhan Rakhadilov Aibol Mural Dauir Kakimzhanov Yernar Turabekov

This study investigates the effect of high-temperature hydrogen exposure on the structure and properties of Cr2O3/Al2O3-based detonation coatings deposited on AISI 316L stainless steel. Bilayer and gradient coatings were exposed to hydrogen at 1000 °C for 3, 4, and 5 h and subsequently characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDS), surface profilometry, and thermal desorption spectroscopy (TDS). One independent specimen was examined for each combination of coating architecture and hydrogen exposure duration. Therefore, the present study was designed as an exploratory comparative investigation rather than a statistically powered study. The principal α-Al2O3 and Cr2O3 phases remained detectable after all exposure durations, indicating preservation of the main oxide phases. SEM/EDS analysis revealed microcracks, local defects, and heterogeneous surface regions, with more pronounced localized damage in the bilayer coatings. The Ra values of the bilayer coatings were 1.385, 0.833, and 1.207 μm after 3, 4, and 5 h, respectively, whereas the corresponding values for the gradient coatings were 1.049, 1.337, and 1.049 μm. The minimum Ra of 0.833 μm after 4 h in the bilayer coating coincided with SEM/EDS evidence suggesting local coating damage and possible thinning. TDS showed the most intense hydrogen desorption for the gradient coating after 3 h. Overall, the observed results suggest that coating architecture influences surface evolution and hydrogen-retention behavior under the investigated high-temperature hydrogen exposure conditions.

Coatings doi: 10.3390/coatings16091006

Authors: Yuting Qin Fengqi Qiu Yibing Liu Zhenhua Xue

Wood and wood-based materials represent low-carbon sustainable alternatives to petroleum sound absorbers, yet their baseline sound absorption coefficient varies drastically with wood species, anatomical cutting orientation and pore connectivity due to strong structural anisotropy. This review systematically integrates multiscale structural regulation, porous acoustic theories and data-driven optimization into a unified framework, revealing that broadband high sound absorption relies on the synergistic coordination of impedance matching, thermo-viscous dissipation and low-frequency resonant mechanisms, rather than simply maximizing porosity. We quantitatively compare state-of-the-art wood absorbers: directionally frozen wood aerogels achieve near-perfect absorption (α = 0.95–1.00, NRC = 0.82) across 520–6300 Hz, marking the current performance benchmark, while multifunctional superhydrophobic wood aerogels deliver moderate absorption (α ≈ 0.40) but stand out as all-biomass weather-resistant composites. Rigid-frame JCA/JCAL and poroelastic Biot models are clarified for wood’s distinct stiffness characteristics, and existing data-driven approaches are categorized, highlighting that most neural surrogates rely solely on FEM simulation without physical impedance-tube validation. Critical unresolved challenges including poor moisture/fire durability, insufficient industrial scalability and incomplete material databases are summarized, and targeted research priorities covering gradient manufacturing, hybrid physics–machine learning models and lifecycle environmental evaluation are proposed.

Coatings doi: 10.3390/coatings16091005

Authors: Jiaolong Huang Changjun Qiu Tiyun Xiao Jia Gao Yong Li Ruiqing Li Pinghu Chen

22Cr12NiMoWV martensitic heat-resistant steel serves as a candidate material for underground coiler sector plates, whereas the coupling relationship between partial austenitization, precipitate/carbide evolution, martensitic interfaces and mechanical response under medium-temperature quenching–tempering conditions is still ambiguous. This work systematically explores four key heat treatment variables to clarify the microstructure–property correlation and strengthening rebalance mechanism. In the 790–830 °C partial austenitization interval, the austenite fraction increases from 36.49 wt.% to 72.32 wt.% with a concurrent decline of M23C6 carbides from 5.34 wt.% to 4.92 wt.%, demonstrating competitive evolution between austenite generation and carbide retention. Specimens quenched at 810 °C for 2 h deliver a yield strength of 1015.4 ± 13.8 MPa and tensile strength of 1192.9 ± 17.8 MPa, 24.9% and 19.9% higher than conventional QT samples, owing to synergistic reinforcement from α′ martensite matrix, orientation interfaces and Cr-Mo-W-V-rich precipitates. After 400 °C × 4 h tempering, the steel still maintains superior strength, and its average misorientation falls from 40.41° to 31.17°. Though its engineering ductility is inferior to the quenched state, the mixed dimple–quasi-cleavage fracture mode suggests a partial recovery of ductile fracture characteristics compared with over-treated samples. The uncovered strengthening mechanism provides microstructural theoretical support for process optimization. Compared with the conventional quenching and tempering process, the optimized medium-temperature process (810 °C × 2 h quenching + 400 °C × 4 h tempering) reduces energy consumption and the production cycle and provides solid theoretical and experimental data for a green and low-cost industrial heat treatment of coil plates.

Coatings doi: 10.3390/coatings16091004

Authors: Yılmaz Yurci Musa Kiliç Oktay Adiyaman Yahya Hışman Çelik

High-speed steel (HSS) substrates were coated with layers of CrC, NbC, TiC, and VC using thermo-reactive diffusion (TRD) at 900 and 1100 °C for 2 and 4 h. The experimental design was implemented according to the Taguchi L8 orthogonal array. Coating morphology was investigated using scanning electron microscopy (SEM) combined with energy-dispersive spectroscopy (EDS), while phase composition was determined by X-ray diffraction (XRD). The contributions of coating type, temperature, and time to coating thickness, microhardness, coefficient of friction, and specific wear rate were evaluated using analysis of variance (ANOVA). SEM and EDS analyses showed that coatings produced at lower temperatures and shorter times exhibited irregular layer thickness, localized porosity, and irregular carbide formation, while coatings applied at higher temperatures and longer times were associated with smoother layers, more homogeneous element distribution, and improved surface morphology. XRD analyses confirmed that the coatings consisted of dense carbide phases and that the chemical composition of the substrate affected the resulting coating phases. Phase composition analysis revealed the presence of phases such as Cr7C3 and Cr23C6 in the coatings. It was observed that coating thickness and hardness generally increased with increasing temperature and coating time. Variance analysis showed that the highest additive ratios in terms of coating thickness belonged to coating type (45.13%) and temperature (42.34%), while in terms of microhardness, temperature (39.92%) and coating type (37.77%) had higher additive ratios. The highest additive ratio in terms of friction coefficient was obtained with coating type (87.98%), while temperature (34.99%) and coating type (33.37%) were determined as the parameters with the highest additive ratios in terms of specific wear rate. NbC coatings generally showed lower performance values compared to other coating types under the examined experimental conditions.

Coatings doi: 10.3390/coatings16091003

Authors: Qinhao Deng Xinkui Yang Wei Liu Xintao Wang Shibo Zhang Shaopeng Wu

Capsaicin is an amphiphilic organic molecule containing both a hydrophobic hydrocarbon chain and polar functional groups, giving it the potential to regulate the surface wettability and interfacial interactions of organic materials. To evaluate capsaicin as an interfacial modifier for improving the anti-icing performance of asphalt binder, capsaicin-modified binders with different dosages were prepared and systematically characterized in terms of conventional properties, high- and low-temperature rheological performance, chemical structure, surface wettability, and water-droplet freezing and melting-induced shedding behavior. Capsaicin was incorporated into the asphalt matrix mainly through physical blending and moderately increased the high-temperature stiffness. At an appropriate dosage, the low-temperature creep and stress-relaxation properties were also improved. The addition of capsaicin increased the water contact angle and reduced the total surface free energy, thereby weakening water spreading and water-asphalt interfacial interactions. At temperatures from −5 to −20 °C, all modified binders exhibited delayed complete freezing and facilitated the gravity-driven shedding of frozen droplets during melting at room temperature. Pearson correlation analysis further showed that longer freezing times and shorter ice-shedding times were closely associated with a larger water contact angle and lower surface free energy. Additional validation after long-term aging confirmed that the surface-regulation and freezing-shedding effects of capsaicin remained effective after aging. Considering both binder performance and freezing-shedding behavior, a capsaicin dosage of 12% provided the best overall balance. These findings identify capsaicin as a promising interfacial modifier for the design of anti-icing asphalt materials.

Coatings doi: 10.3390/coatings16091002

Authors: Xingnan Hu Dongze Li Liang Li Shiren La

SBS-modified asphalt is widely used in high-grade pavements for its excellent rutting and fatigue resistance; however, how its friction behavior evolves under submerged conditions with surface distress remains poorly understood. To address this gap, we developed a rubber–asphalt friction tester to characterize quasi-static rubber–asphalt friction under submerged conditions with three typical distresses: pothole, crack, and surface void. Our results show that friction increases with roughness, load, and water temperature, but degrades progressively under cyclic loading. Among the three distresses, surface void offers the most stable friction performance, whereas pothole exhibits the largest friction loss under repeated loading, identifying them as high-priority repair targets. The positive temperature–friction correlation further implies that wet-skid risks are higher at lower temperatures, providing a basis for seasonal maintenance scheduling. Three-dimensional wear analysis reveals distinct mechanisms: pothole causes localized deep-pit wear, while surface void generates uniform roughening, explaining their contrasting durability. These findings directly support distress prioritization, friction-performance evaluation, and maintenance planning for SBS-modified pavements in rainy environments.

Coatings doi: 10.3390/coatings16091001

Authors: Haohui Dong Yubo Shao Baisheng Liu Juan Ding Yingwei Zhang Wenfeng Guo Guoan Hou

In cold and humid environments in high-latitude, high-altitude, and offshore regions, ice accretion sometimes occurs on airfoil blade surfaces, such as those of wind turbines. Therefore, a potential hazard exists for the equipment. For this reason, the aerodynamic characteristics of the airfoil blade degrade and power generation decreases. In the present study, the icing characteristics of airfoils in cold and foggy environments were investigated. A novel icing wind tunnel with a low LWC of 0.3 g/m3 and a small MVD of 10 μm was designed and built. An airfoil sample with the aerodynamic profile of NACA 0018 was selected, and the effects of the airfoil material and the temperature on the icing area, the thickness of ice, and the coverage scope of ice were tested and analyzed. The experimental results showed that the temperature had a more significant effect on the icing characteristics in comparison with the airfoil material. At the medium temperature, −7 °C in the present study, the icing area, the thickness of ice, and coverage scope all reached their maximum value. Specifically, the maximum cross-sectional icing areas (CIAs) on the aluminum airfoil at −4 °C, −7 °C, and −10 °C for 60 min were 35.088 mm2, 66.357 mm2, and 51.538 mm2, respectively, and those on the FRP airfoil were 36.204 mm2, 70.352 mm2, and 47.814 mm2, respectively. The FRP airfoil had a larger icing area and thickness of ice. In contrast, the aluminum airfoil had a larger coverage scope of ice, which was −0.10~0.15. In addition, the aerodynamic performance of the iced airfoil, including Cd and Cm, was also obtained through CFD. The research findings provided a foundation for further exploring the atmospheric icing of wind turbines and other structures with airfoil profiles.

Coatings doi: 10.3390/coatings16091000

Authors: Harrison de la Rosa-Ramírez Caterina Valentino Federica Giuliano Melania Elettra Vaccari María Dolores Samper Federico Barrino

The development of bioactive hybrid coatings for biomedical implants requires materials exhibiting suitable thermal stability, bioactivity, and biocompatibility. In this study, hybrid organic–inorganic sol–gel coatings based on silica (SiO2) and polyethylene glycol (PEG, 24 wt%) were functionalized with different concentrations of caffeic acid (CafA 5, 10, and 15 wt%) and deposited onto AISI 304 and AISI 316 stainless steel substrates by dip-coating without surface pre-treatment. The proposed approach enabled the formation of homogeneous hybrid coatings on untreated stainless steel substrates through a simple and scalable deposition process. A thermal analysis demonstrated the stability of the hybrid network and the effective integration of the organic and inorganic phases. Bioactivity was evaluated by in vitro immersion in simulated body fluid (SBF), while SEM observations revealed the formation of mineral deposits on the coating surface, and an EDX analysis confirmed the presence of calcium and phosphorus within the deposited layer. The formation of crystalline hydroxyapatite (HA) was subsequently confirmed by X-ray diffraction (XRD), confirming that all investigated formulations retained their ability to induce apatite formation after SBF immersion. In addition, in vitro biocompatibility assays confirmed that the developed materials exhibited concentration-dependent cytocompatibility, with the cellular response being influenced by the amount of incorporated CafA. Overall, the results demonstrate that the proposed hybrid materials combine thermal stability, bioactivity, and cytocompatibility, highlighting their potential as bioactive coatings for biomedical applications.

Coatings doi: 10.3390/coatings16090999

Authors: Haibo Wu Yixiang Liu Yi Cai Ning Guo

Fe-Al intermetallic coatings were fabricated on 0Cr21Al6Nb stainless steel by pack cementation to systematically investigate the effects of temperature (650–800 °C) and holding time (2–16 h) on the coating microstructure, phase constitution, and hardness. The coatings primarily consisted of Fe2Al5, with a minor amount of FeAl3 confined to the outermost surface. The coating/substrate interface exhibited a characteristic serrated or tongue-like morphology, which became increasingly pronounced with increasing temperature and holding time, indicating enhanced interdiffusion across the interface. Both increasing temperature and prolonging holding time markedly promoted coating growth and increased the coating thickness, while simultaneously facilitating the enrichment of FeAl3 in the near-surface region. Despite these microstructural variations, the coating hardness remained relatively stable at approximately 960 HV, which was substantially higher than that of the substrate; meanwhile, the substrate exhibited a slight reduction in hardness after aluminizing. Thermodynamic analysis revealed that Fe2Al5 was preferentially formed owing to its relatively lower Gibbs free energy, and its formation remained thermodynamically favored during subsequent coating growth, whereas FeAl3 was restricted to the coating surface. Kinetic analysis demonstrated that coating growth followed a parabolic law, indicating a diffusion-controlled growth mechanism, with an apparent activation energy of 107.5 kJ·mol−1 for Al diffusion. Furthermore, temperature exerted a more pronounced influence on coating growth than holding time, highlighting temperature as the dominant kinetic parameter governing the formation and thickening of the Fe-Al intermetallic coating.

Coatings doi: 10.3390/coatings16090998

Authors: Piergiulio Cappelletti Francesco Izzo Concetta Rispoli Antonino Pollio Antonino De Natale Mariagioia Petraretti Andrea Carpentieri Leila Birolo Chiara Melchiorre Valeria Di Fratta Giarita Ferraro Anna Manzone Alessandro Vergara

This study presents an integrated surface diagnostic investigation and a diagnostic-driven restoration of the marble sculpture Real Infante Carlo Tito di Borbone (1775), attributed to Giuseppe Sanmartino and preserved at the Royal Palace of Caserta (Italy). Despite the artistic relevance of the sculptor, scientific investigations of his works remain limited. The aim of this work is to characterize surface coatings, identify alteration processes, and support conservation strategies through a multi-analytical approach. The results reveal that the sculpture is composed of calcitic marble covered by an altered organic surface film. Spectroscopic and chromatographic data indicate the presence of lipidic compounds consistent with natural wax, likely associated with previous conservation treatments. An epoxy-based adhesive was also identified, suggesting past restoration interventions. Microbiological analyses detected fungal and bacterial species potentially involved in surface alteration processes. The integration of analytical data enabled the development of a targeted restoration strategy. Cleaning procedures were defined based on the chemical nature of the surface coatings, while structurally stable previous restorations were preserved. A biocide treatment was applied to mitigate biological colonization. This study highlights the importance of surface-oriented diagnostics in understanding coating materials and guiding conservation interventions, providing a methodological framework applicable to marble artworks.

Coatings doi: 10.3390/coatings16080997

Authors: Jingwei Liang Qingnian Deng Yile Chen Liang Zheng

Lianxi Academy in Zhuhai, Guangdong, is a rare surviving rammed-earth academy ruin representative of Lingnan architectural tradition, yet its rammed-earth walls suffer persistent weathering under the subtropical marine monsoon climate, with no site-specific material baseline available. This study aims to characterize the microstructural, mineralogical and particle-size features of wall surfaces, clarify internal compositional differentiation, and provide quantitative baseline data for earthen heritage conservation. Four surface crust specimens from wall facades were analyzed via multiscale scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM–EDS), X-ray diffraction (XRD), and laser diffraction granulometry. Results show all samples share an O–Si-rich background with notable local contrasts. Local EDS analyses record 12.93 wt% Ca in Sample 2 (accompanied by a unique intersecting rod-shaped network), 6.92 wt% Al and 4.97 wt% K in Sample 3, and 11.33 wt% Fe in Sample 4. Quartz dominates all XRD patterns with strongest reflections at 26.70–26.78° 2θ, accompanied by features consistent with subordinate carbonate-, aluminosilicate-, and Fe-bearing components. Particle-size distributions are highly heterogeneous: Sample 1 is the coarsest (D50 = 34.97 μm; 41.69% ≥ 63 μm), while Samples 3 and 4 are fine-fraction-dominated (D50 = 8.93 and 8.52 μm). These findings define three distinct surface material subgroups within a universal quartz-rich matrix, and are consistent with a heterogeneous wetting and selective particulate detachment weathering model. This work fills the data gap for Lingnan rammed-earth academy heritage, and the quantitative parameters serve as preliminary benchmarks for wall condition mapping, rainwater erosion regulation, and compatible repair material trial formulation.

Coatings doi: 10.3390/coatings16080996

Authors: Tianwei Yan Hongzhou Zhu Qianrong Luo Jianhong Chen Peiqiu Wu

The application of two-dimensional molybdenum disulfide (MoS2) in asphalt binder modification is limited by its inherent chemical inertness and severe agglomeration. In this study, four surface-functionalization strategies, including (3-aminopropyl)triethoxysilane (APTES) silanization, polydopamine (PDA) coating, tannic acid (TA)–APTES co-deposition, and PDA–APTES hybrid modification, were used to improve the dispersion and compatibility of MoS2 nanosheets in styrene–butadiene–styrene (SBS)-modified asphalt binders. Scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD) results indicated that surface functionalization introduced organic functional groups, reduced nanosheet restacking, and preserved the intrinsic 2H-MoS2 crystal structure. Binder-level rheological tests and thermogravimetry–differential scanning calorimetry (TG–DSC) analysis showed that surface-functionalized MoS2 improved the high-temperature deformation resistance, creep recovery, fatigue resistance, low-temperature relaxation capacity, and thermal stability of SBS-modified asphalt. Among the investigated binders, PDA–APTES-functionalized MoS2/SBS-modified asphalt exhibited the most balanced performance. At 3.2 kPa, its recovery rate reached 79.5%, while its non-recoverable creep compliance decreased to 0.105 kPa−1. Its fatigue life at 15% strain increased by 76.8% compared with SBS-modified asphalt, and its creep stiffness at −24 °C decreased to 222 MPa. Mechanistic interpretation suggests that the PDA–APTES hybrid layer may act as an organic–inorganic interfacial transition region, improving MoS2 dispersion and compatibility with the SBS–asphalt phase and facilitating more effective integration of the nanosheets into the composite structure. These results indicate that PDA–APTES-functionalized MoS2 nanosheets are promising interfacial modifiers for improving the rheological and thermal performance of SBS-modified asphalt binders.

Coatings doi: 10.3390/coatings16080995

Authors: Chengcheng Zhang Hongmei Han Hongyi Ye Bao Chen Huangjian Xie Zhongxian Chen Donghui Zheng Mingjie Wang

Ag-Ti3SiC2 composites are promising electrical contact materials, yet the atomic-scale interfacial behaviour between Ti3SiC2 and Ag remains poorly understood. Here, first-principles calculations were performed to investigate the interfacial stability, electronic structure, and alloying effects at the Ti3SiC2(0001)/Ag(111) interface. Surface-energy calculations for six terminations of Ti3SiC2(0001) show that the TiC(TiC) termination is preferred at low carbon chemical potential, whereas the TiC(TiSi) termination becomes the most stable once ΔμC exceeds −1.50 eV. Eighteen interface models combining the six terminations with three stacking sequences (OT, MT, and HCP) were constructed, and their work of adhesion (Wad) and equilibrium spacing (d0) were determined by the Universal Binding Energy Relation and full structural relaxation. The HCP stacking is preferred for all terminations, and the C(TiC)-terminated HCP interface exhibits the highest work of adhesion among all configurations, with Wad = 9.25 J/m2 at d0 = 1.2 Å; relaxation enhances Wad by 10%–75%. Charge density, charge density difference, and partial density of states analyses reveal that the interfacial bonding is dominated by C 2p-Ag 4d hybridization accompanied by electron transfer from Ag and Ti atoms to the interfacial C atoms, which accounts for the adhesion hierarchy. Substitutional alloying with Cu, Ni, Zn, and Cr preferentially segregates into the interfacial Ag layer, where the defect formation energies, although positive, are the lowest, and Wad increases in the order Cu < Zn < Ni < Cr, reaching 11.0 J/m2 for interfacial Cr, an enhancement of 19% over the pristine interface. The strengthening correlates directly with the filling of the dopant 3d band. These results provide theoretical guidance for the interfacial design of high-performance Ag-Ti3SiC2 electrical contact composites.

Coatings doi: 10.3390/coatings16080994

Authors: Shuaimou Zhang Liangliang Bao Tao Fu Yongdong Wang

Corrosion-resistant coatings with a double-layer structure are deposited on the surface of S30408 stainless steel at welding currents of 170 A, 200 A, and 230 A using metal active gas (MAG) arc welding technology. The influence of welding current on the microstructure, microhardness, wear resistance, and electrochemical corrosion behavior of the coating is systematically studied. The results show that the coating produced at 200 A exhibited the finest martensitic structure, the highest microhardness (~450 HV), and the lowest mass loss (139.9 mg), indicating its superior wear resistance. In contrast, the coating fabricated at 230 A displayed the most positive corrosion potential (−0.302 V vs. saturated calomel electrode (SCE)) in 3.5 wt.% NaCl solution, which is attributed to enhanced elemental homogenization arising from the higher heat input. This paper clarifies the critical role of welding current in balancing wear and corrosion performance and provides a practical guideline for the cost-effective surface enhancement of S30408 steel components.

Coatings doi: 10.3390/coatings16080993

Authors: Jian Liu Shijun Chen Manxiang Li Baojun Zheng Chaoming Wang Juantao Zhang Ning Liu Xiaofei Cao

The corrosion behavior of N80 steel in a simulated coalbed–methane environment was investigated in a high-temperature, high-pressure autoclave. Uniform corrosion and maximum pit depth were quantified by weight-loss measurements and ultra-depth-of-field three-dimensional microscopy, respectively, while SEM, EDS, and XRD were used to characterize the morphology, elemental composition, and crystalline phases of the surface corrosion products. A one-factor-at-a-time design was applied at a constant total pressure of 10 MPa to evaluate the effects of nominal CO2 partial pressure (0.10–1.00 MPa), nominal O2 partial pressure (0–0.40 MPa), Cl− concentration (3–187 g/L), and temperature (40–75 °C). Increasing the nominal CO2 partial pressure raised the uniform corrosion rate from 0.712 to 0.930 mm/a but reduced the maximum pitting corrosion rate from 1.691 to 0.280 mm/a, while FeCO3-containing surface coverage increased. Increasing the nominal O2 partial pressure intensified both corrosion modes; at 0.40 MPa, the uniform and maximum pitting corrosion rates reached 1.446 and 2.202 mm/a, respectively, and the corrosion-product layer exhibited extensive cracking and spallation. Increasing the Cl− concentration reduced the uniform corrosion rate from 1.078 to 0.839 mm/a but increased the maximum pitting corrosion rate from 0.474 to 1.807 mm/a, indicating a shift in the principal damage risk from average metal loss to localized penetration. The uniform corrosion rate reached a maximum of 1.516 mm/a at 60 °C, whereas the maximum pitting corrosion rate increased continuously to 2.202 mm/a at 75 °C. XRD identified Fe, FeCO3, Fe2O3, Fe3O4, and FeOOH. The persistent Fe substrate reflections, interpreted together with the SEM observations, revealed spatially heterogeneous corrosion-product coverage. These results show that the protective contribution of FeCO3-containing products depends on their surface coverage and visible integrity rather than on phase presence alone. The findings support stringent oxygen-ingress control, targeted pitting protection in high-salinity environments, and enhanced corrosion surveillance of intermediate- and high-temperature well sections.

Coatings doi: 10.3390/coatings16080992

Authors: Ming Sun Shuyan Wang Yihe Dong Dongao Yu

To further enhance the application effectiveness and energy efficiency of dielectric barrier discharge plasma coupled with catalytic technology, this study investigates the synergistic effect between coated catalysts and dielectric barrier discharge. A two-dimensional fluid model was established, and numerical simulations were conducted using the finite element method to evaluate NO removal from automobile exhaust gases. Results show that, compared to dielectric barrier discharge alone, the degradation efficiency of low-concentration NO increases by 6%–29% when a coated catalyst is introduced. Three coated catalysts, including Mn/TiO2/γ-Al2O3, Mn/γ-Al2O3 and TiO2, are compared for 1% NO treatment, whose degradation efficiencies are 63.1%, 53.7% and 40.2%, respectively. As the NO concentration increased from 1% to 3%, the degradation efficiency of all three catalysts decreased. In terms of NO2 by-product generation, the synergistic system with Mn/TiO2/γ-Al2O3 produces the least NO2. This coupling technology effectively removes low-concentration nitrogen oxides from vehicle exhaust, enriches plasma-catalysis theory, and supports global efforts in controlling motor vehicle emissions pollution.

Coatings doi: 10.3390/coatings16080991

Authors: Zheng Sun Jin Yue Jixiang Xie Jie Chen Bing Du Yong Ye Yong Wang

The surface of nodular cast iron is susceptible to wear failure under high-load conditions. In this study, Fe-Cr-Ni wear-resistant coatings were developed on the surface of nodular cast iron using laser cladding technology. The influence of laser power (P), powder feeding rate (F), scanning speed (V), and overlapping rate (φ) on the microhardness and dilution rate of the coatings was analyzed by response surface methodology, while the model’s accuracy was evaluated through analysis of variance. Subsequently, the multi-objective particle swarm optimization algorithm was utilized to identify the optimal process parameters (P = 1350 W, V = 12.5 mm/s, F = 9 g/min, and φ = 45%) based on non-destructive testing results. The predictive model values closely matched the experimental results. The average microhardness of the Fe-Cr-Ni cladding layer was 620.3 HV, which was 2.8 times that of the nodular cast iron substrate. Importantly, the laser cladding layer demonstrated a significant improvement in wear resistance compared to the substrate. The wear mechanisms for the coating predominantly involved mild abrasive wear and adhesive wear, while the substrate primarily experienced severe adhesive wear. This study offers valuable insights for optimizing laser cladding process parameters for nodular cast iron.

Coatings doi: 10.3390/coatings16080990

Authors: Qibo Wang Sung-Ki Lyu Yu-Ting Wu Haiqin Gu Zhen Qin

Viscous fingering is a canonical nonlinear interfacial instability that arises when a less viscous fluid displaces a more viscous one under an adverse viscosity contrast. Despite extensive investigations into the effects of fluid properties, operating conditions, and rheology, systems involving a shear-thickening displaced phase remain largely unexplored. Here, three-dimensional numerical simulations of immiscible air–fluid displacement in a Hele–Shaw cell are performed to elucidate how interfacial tension, air-inlet velocity, and gap-depth gradient regulate instability evolution. Increasing interfacial tension strengthens the Laplace-pressure barrier, suppresses shear-induced necking and pinch-off, and preserves finger topology; however, it intensifies flow diversion and delays the advancement of the central finger. Increasing the inlet velocity markedly amplifies the local interfacial shear rate and triggers pronounced shear thickening. The resulting viscous-resistance barrier redistributes momentum toward paths of least hydraulic resistance, directly promoting tip splitting and severe topological breakup. Even a small gap-depth gradient reorganizes the local hydraulic resistance and pressure field. Positive and negative gradients induce resistance-reduction and throttling effects, respectively, generating pronounced pressure shielding that governs asymmetric momentum transfer and preferential flow-path selection. These findings identify the capillary, rheological, and geometric mechanisms controlling viscous fingering during the air-driven displacement of shear-thickening fluids. Because such instabilities compromise the integrity of geological-fracture seals and the operating efficiency of semi-solid flow batteries, this study provides a mechanistic basis for stabilizing immiscible displacement and optimizing industrial fluid-transport systems.

Coatings doi: 10.3390/coatings16080989

Authors: Chunying Ji Yaxuan Yi Binhui Wang Baicheng Liu Hongliang Zhang Teng Liu Zhisheng Nong

Titanium alloys are widely used for implants, yet corrosion, bacterial colonization and incomplete osseointegration remain important causes of interfacial failure. This review critically analyzes major biomedical functional coating fabrication techniques employed to enhance the surface properties of titanium alloys, including micro-arc oxidation, anodic oxidation, magnetron sputtering, electrochemical deposition, electrophoretic deposition, plasma spraying, physical vapor deposition, plasma immersion ion implantation, laser surface treatment, and hybrid (composite) approaches. For each method, key operational principles, structural and functional characteristics, performance advantages and limitations, and representative application domains are critically analyzed. Across these routes, biological performance depends on coating continuity, pore or nanotube geometry, interfacial bonding, phase composition and ion release. Calcium- and phosphorus-rich oxides and hydroxyapatite deposits generally promote cell adhesion, proliferation, alkaline phosphatase activity, mineralization and osteogenic differentiation. Dense oxide, nitride, tantalum and carbon-based films strengthen corrosion barriers, whereas Mn, Zn, Cu and Ag containing surfaces can inhibit bacterial adhesion and biofilm formation. Excessive ion release, however, may compromise cytocompatibility. Reported outcomes also vary with test medium, exposure time, bacterial strain and cell model. Standardized quantitative endpoints and longer-term corrosion, biofilm and osseointegration studies are required to guide clinically reliable multifunctional coatings.

Coatings doi: 10.3390/coatings16080987

Authors: Serguei P. Murzin

Ultrafast laser processing enables the creation of functional surfaces in metals, semiconductors, ceramics, polymers and other materials through spatially controlled nonequilibrium energy deposition. However, the resulting surface functionality cannot be explained solely by laser parameters or geometric features. Femtosecond irradiation induces a sequence of coupled processes, including nanoscale structuring, phase transformation, chemical modification, defect formation, and relaxation, which define the final surface state. This review introduces the Surface-by-Design concept, where functional surfaces are considered as engineered material states formed through controlled laser–matter interaction rather than as predefined patterns. Representative examples including laser-induced periodic surface structures, hierarchical micro/nanotextures, modified oxide layers, and laser-generated functional interfaces are analyzed in relation to wettability, tribological behavior, corrosion resistance, optical response, and other properties. The review further examines how advanced characterization, digital engineering, beam shaping, in situ diagnostics, and data-driven methods contribute to controlling surface evolution. Remaining challenges include reproducibility, scalability, and reliable prediction of functional behavior during service conditions. Future progress in femtosecond laser surface engineering will depend on the ability to control not only the generated morphology but also the evolving structural and physicochemical state of functional interfaces.

Coatings doi: 10.3390/coatings16080988

Authors: Ishmaeel Ghouri Richard Barker Suman Shrestha David Charles Barton

The new Euro 7 standard will be the first legislation to limit the emissions produced by an automotive brake system. This has caused brake manufacturers to seek radical solutions to reduce the emissions generated from conventional grey cast iron (GCI) friction brakes. The regenerative braking system of electric vehicles (EVs) will require the friction brakes to be used less frequently than for an internal combustion engine vehicle. This may lead to a build-up of corrosion products on the friction surfaces that may not only affect the performance and service life of the GCI friction brake but also increase wear particle emissions when braking. Plasma electrolytic oxidation (PEO) ceramic-coated aluminium alloy rotors could be an alternative solution to reduce the effects of corrosion, produce lower brake emissions and also improve the energy efficiency of the EV by reducing its unsprung mass. To understand the interrelation between brake rotor corrosion and particulate emissions, this study concentrates on quantifying wear particles from a PEO-coated Al6082 brake rotor, both before and after exposure to salt fog corrosion. The results are compared to those for a standard uncoated GCI rotor and for an aluminium metal matrix composite (MMC) rotor subject to the same braking and corrosion test cycles. It was found that the PEO brake rotor produced a higher steady-state coefficient of friction in both the uncorroded and corroded conditions than either the GCI or MMC rotor, but emitted fewer wear particles in the uncorroded state, apart from at the highest brake line pressure. In the corroded state, the PEO rotor produced far lower emissions than either the corroded GCI or MMC rotors across all brake line pressures.

Coatings doi: 10.3390/coatings16080986

Authors: Yang Chen Heping Hou

To reveal how meniscus dynamics affect wet film uniformity during slot-die coating for perovskite solar cell manufacturing, a 2D numerical model employing the VOF method is established for perovskite precursor fluids. A photoresist is used as a qualitative substitute liquid for auxiliary experimental validation, and dry film thickness is measured to characterize the relative uniformity of wet coating. The results show that the capillary number governs the upstream meniscus shape. Inlet velocity, slot gap, and coating gap influence film thickness by altering the downstream meniscus climbing height. Optimal film thickness uniformity is achieved when the pre-coating liquid volume accounts for about 31% of the total coating volume; this empirical optimal ratio is only valid within the tested inlet flow rate range under the fixed experimental conditions adopted in this work, and further multi-parameter verification under diverse process windows will be carried out in follow-up research.

Coatings doi: 10.3390/coatings16080985

Authors: Gewei Wang Li Shi Rongli Deng Yue Luo Chenwei Zheng Jinghao Wu Xiao Tan Changce Wang Haoyu Zhang Jiasheng Song

The cooling performance of turbine vanes with thermal barrier coatings (TBCs) is significantly affected by the flow distribution of internal cooling channels. To investigate the influence of channel flow distribution on the vane cooling characteristics, this study adopts the Latin hypercube sampling method to realize differentiated flow distribution of each cooling channel under a nearly constant total cooling flow rate. Numerical simulations are performed to obtain vane cooling characteristic data under various flow distribution schemes, followed by multi-condition quantitative comparison and mechanism analysis. The results show that the trailing edge channel serves as the dominant factor controlling the overall vane temperature, while the middle channels exhibit obvious cooling redundancy. Specifically, the flow rates of the leading edge arc and trailing edge dominate the peak temperature and average temperature of the suction surface, respectively. Unlike geometric optimization that alters vane internal structures, this study focuses on flow redistribution under the strict constraint of fixed total cooling air consumption. This strategy offers a zero-cost approach to cooling enhancement for in-service turbines with no structural modifications required. The cooling benefit is enhanced without additional cooling air consumption. The overall surface peak temperature is reduced by 0.4%. By region, the peak temperatures of the pressure surface and the suction surface reduced by 0.40% and 0.435% respectively, and the leading edge arc reduced by 0.20%. The overall average surface temperature has reduced by 0.117%. The research conclusions can provide a theoretical reference for the flow optimization of turbine vane cooling channels and the improvement of overall cooling uniformity, which is qualitatively beneficial to reducing the thermal failure risk of coatings.

Coatings doi: 10.3390/coatings16080983

Authors: Ming Zhang Jiujiang Wu Linzi Yu

Local scour reduces the lateral restraint provided by surrounding soil and may amplify the impact-induced response of bridge foundations. This study investigates the response of a lattice-shaped diaphragm wall (LSDW) foundation–soil system under predefined local-scour conditions using a three-dimensional explicit finite element model and a nominally rigid steel impactor. A 1:30 reduced-scale configuration was analyzed at impact velocities of 2, 3, and 4 m/s and scour depths of 0, 200, 300, and 400 mm. Increasing impact velocity generally increased wall displacement, velocity, and elastic principal-stress demand, whereas deeper scour reduced the remaining embedment and the restraint provided by the surrounding soil. Relative to the corresponding unscoured conditions, the normalized peak wall-top displacement ratios were 1.28–1.38, 2.01–3.66, and 3.28–5.45 for scour depths of 200, 300, and 400 mm, respectively. The velocity distribution showed an increasingly pronounced rotational contribution as the remaining embedment decreased. Case 9 produced the largest overall response, with a peak wall-top displacement of 398.7 mm and a peak wall-top velocity of 5.2 m/s. Because direct physical validation was unavailable, the results should be interpreted as comparative model-scale trends rather than validated prototype predictions.

Coatings doi: 10.3390/coatings16080984

Authors: Joern Kohlscheen

CrAlN PVD coatings are frequently used to protect cutting tools because of their superior hardness and wear resistance. However, the influence of carbon addition to such coatings remains largely unexplored. Therefore, Cr-Al-C-N coatings were deposited by HiPIMS using a commercial PVD unit equipped with a segmented sputter target. The target consisted of an upper half of Cr and a lower half of Al. Carbon was added under reactive sputtering conditions with the aim of reducing internal stress and introducing a friction-reducing component. A range of different Al-Cr-C compositions could be efficiently explored by varying the acetylene reactive gas flow. Depending on the positioning of the samples, Cr/Al ratios could be varied between about 4/1 and 1/2 while three different levels of carbon concentration (0, 11, and 25 atomic % of total coating composition) were investigated. It was found that an intermediate carbon concentration effectively increased the hardness of Cr-rich coatings, achieving maximum plastic hardness values over 40 GPa. With increasing Al content, hardness drops to below 30 GPa. The cubic CrN phase with mostly 200-oriented grains was detected for most variants. With increasing Al and C contents, a rapid decrease in crystallite size is observed, accompanied by a reduced intensity of the (200) XRD reflection. A turning test on stainless steel showed decreasing flank wear with higher Al contents. However, no improvement associated with carbon addition could be confirmed within the investigated concentration range.

Coatings doi: 10.3390/coatings16080982

Authors: Maria-Anthoniette Oghenetejiro Onoriode-Afunezie Arminas Gloveckas Brigita Abakevičienė Agnė Šulčiūtė

The persistence of antibiotics like ciprofloxacin (CIP) in aquatic environments necessitates the development of efficient, low-cost wastewater treatment technologies. This study investigates a low-temperature fabrication strategy for mixed-phase copper oxide (CuO/Cu2O) coatings synthesized via co-precipitation and immobilized using electrophoretic deposition (EPD). A critical finding was that a 25 min precursor aging time (T25) preserved a metastable mixture of CuO and Cu2O phases, which is highly advantageous for creating heterojunction interfaces that enhance charge separation. In contrast, extended aging (T35) promoted phase consolidation toward bulk CuO, reducing catalytic surface area. During the EPD process, applied voltage acted as an influence to the relative phase composition and deposition behavior of the deposited coatings; 1.0 V was identified as the optimal condition, balancing high phase fidelity with enhanced crystallinity (average crystallite size of 30.6 nm) and mechanical stability. Photocatalytic experiments demonstrated significant CIP degradation, with the 0.9 V and 1.0 V films outperforming the 1.2 V film, possibly due to more favorable surface chemistry and phase diversity. While the 0.9 V film achieved the highest mineralization efficiency (18% TOC removal), the 1.0 V film offered the best balance between photocatalytic activity, structural stability, and phase selectivity for practical applications. High-Performance Liquid Chromatography-Mass Spectrometry HPLC-MS analysis suggested that degradation proceeds through oxidative pathways involving piperazine ring cleavage and defluorination.

Coatings doi: 10.3390/coatings16080981

Authors: Huayu Yang Shiquan Liu Xinyun Wang Heping Li

Hydrogen permeation barriers (HPBs) are essential to the development of both hydrogen and nuclear fusion energy. However, their structural stability and barrier efficiency under extreme conditions are scarcely reported, despite their significant importance to practical applications. Here, we experimentally investigated the effect of Li4SiO4 corrosion and deuterium aging on the structure and performance of an α-Al2O3 composite hydrogen permeation barrier coating under simulated fusion conditions. The results demonstrate that this coating could retain its dense and defect-free structure after corrosion with Li4SiO4 powders at 550 °C for 2 days, exhibiting good tritium breeder compatibility. Moreover, after the deuterium aging test for 6 months, its phase composition and microstructure show no significant changes, maintaining a compact and crack-free matrix strongly bonded to the substrate. After 6-month aging, the hydrogen permeation resistance of the α-Al2O3 composite coating at 500 °C is still 1450 times higher than that of the steel substrate without any aging. This work provides critical insights into designing highly reliable hydrogen permeation barrier coatings and understanding their performance evolution under harsh fusion environments.

Coatings doi: 10.3390/coatings16080980

Authors: Dávid Čuchor Jozef Bronček Mário Drbúl Viera Zatkalíková Mirosław Bonek Jozef Holubják

The corrosion behavior of AISI 316Ti stainless steel was examined in NaCl solutions (0.9%, 3.5%, and 5%), whereas tribocorrosion tests were performed in both chloride-containing solutions and distilled water as a reference environment. Potentiodynamic polarization tests were performed to evaluate passive film stability, while tribocorrosion experiments were conducted under a 10 N normal load using a ball-on-flat configuration with continuous monitoring of open circuit potential (OCP) and coefficient of friction (COF). Surface degradation was quantified using optical 3D profilometry and scanning electron microscopy. Electrochemical results confirmed passive behavior in all environments; however, increasing chloride concentration shifted corrosion and pitting potentials toward more negative values and reduced passive stability. During sliding, a pronounced cathodic OCP shift indicated mechanical depassivation, with the magnitude of the shift increasing in chloride-rich solutions. Repassivation after sliding was progressively hindered as NaCl concentration increased. Wear analysis revealed a clear dependence on chloride content, with the wear area in 5% NaCl (0.0020 mm2) exceeding that in distilled water (0.0009 mm2) by approximately 122%. Abrasive wear was identified as the dominant mechanism, accompanied by delamination wear in highly aggressive environments. The results demonstrate a strong synergistic interaction between wear and corrosion, with chloride concentration significantly intensifying tribocorrosion-induced material degradation.

Coatings doi: 10.3390/coatings16080979

Authors: Jiahang Zhang Hai Liu Zhuang Liu

To improve the antifouling and self-cleaning performance of 3003 aluminum alloy, a fluorine-free water-repellent surface was fabricated by combining nanosecond laser texturing with subsequent heat treatment. The effects of scanning speed, laser power, pulse frequency, and scanning interval on surface wettability were systematically investigated. Under the optimal conditions of 2700 mm/s, 6 W, 35 kHz, and 20 μm, the surface achieved a maximum static water contact angle of 154.3 ± 0.8°. Surface characterization showed that laser processing generated hierarchical micro-/nano-scale structures, while heat treatment promoted surface chemical evolution associated with enhanced hydrophobicity. The highly water-repellent behavior resulted from the synergistic effect of hierarchical roughness and heat-treatment-induced surface chemical changes. The fabricated surface exhibited effective self-cleaning performance, achieving a SiO2 removal efficiency of 98.8% under the specified test conditions. In addition, relatively high water repellency was retained after repeated water-impact and tape-peeling tests. These results demonstrate that nanosecond laser texturing combined with heat treatment provides a simple and environmentally friendly strategy for fabricating water-repellent AA3003 surfaces for antifouling and surface-protection applications.

Coatings doi: 10.3390/coatings16080978

Authors: Alexandra Musza Dávid Ugi Nguyen Quang Chinh Ádám Vida

The cross-sectional microstructure, local chemical composition, and mechanical behavior of anodic oxide layers produced by oxalic acid anodizing of cast A356 aluminum alloy were investigated using digital optical microscopy, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and in situ nanoindentation inside the SEM chamber. The anodized specimens contained a compact oxide-side interfacial region adjacent to the substrate–oxide interface and an outer porous oxide layer. The oxide layers formed at the higher nominal charge density were generally thicker than those formed at the lower charge density. Cross-sectional nanoindentation revealed two characteristic interface-related features: localized, unusually high apparent hardness values on the oxide side of the interface and a gradual hardness increase within the adjacent substrate-side region. The highest apparent values exceeded the expected hardness range of anodic oxide layers on A356 alloy and were therefore interpreted as interface-affected responses rather than intrinsic oxide hardness values. Their repeated occurrence at a well-defined position nevertheless supported their association with the oxide-side interfacial region. The substrate-side hardness increase was characterized by the estimated width of an anodizing-affected substrate zone. EDS line scans showed that the oxide-side interfacial region retained a significant oxygen concentration, whereas the substrate-side hardness increase was not accompanied by a systematic elemental concentration gradient. The results demonstrate that the cross-sectional mechanical response of oxalic-acid-anodized A356 alloy is governed not only by the conventional barrier-layer–porous-layer structure, oxide thickness, and porosity, but also by local chemical composition, microstructural heterogeneity, and substrate/interface-related effects.

Coatings doi: 10.3390/coatings16080977

Authors: Yanhe Liu Zhaolong Zhu Jianbo Zhou Bin Zhang

In the manufacturing industry, cutting force is the primary factor affecting bamboo milling. Excessive cutting force can increase tool wear and affect processing quality, processing energy consumption, and processing stability. Cutting parameters have significant impacts on cutting forces. The cutting force is also one of the important indexes for evaluating machining performance. This article uses response surface methodology to study the influence of different cutting parameters on the cutting force during the bamboo milling process. Moreover, the importance of cutting parameters to cutting forces was determined by variance analysis, corresponding mathematical models were established, and the interaction between cutting parameters and cutting forces was analyzed to optimize the bamboo milling process. On this basis, the cutting parameter combination corresponding to the optimal milling process under experimental conditions was determined and experimentally verified. The prediction accuracy was high and the test optimization was good. Therefore, the proposed method can be used to predict and optimize the actual cutting force, providing a scientific basis for high-quality processing of bamboo milling.

Coatings doi: 10.3390/coatings16080976

Authors: George-Daniel Dima Nataliia Rudenko Mircea Laurențiu Dan Nicolae Vaszilcsin

This study investigates the efficacy of Reserpine (RZ), a natural indole alkaloid, that serves as a sustainable inhibitor of corrosion for OLC52 and aluminum in a 0.5/0.25 mol L−1 acetic acid/potassium acetate solution, relevant to de-icing applications. The electrochemical methods used in this study included cyclic (CV) and linear sweep voltammetry (LSV), chronoamperometry (CA) and electrochemical impedance spectroscopy analysis (EIS), and allowed for the determination of the necessary parameters for the evaluation of the adsorption behavior. In addition to electrochemical studies, theoretical molecular modeling calculations were also carried out. The results indicate that RZ reduces the corrosion rate at the highest tested concentration of 10−3 M RZ, reaching inhibitory efficiencies of 90% for OLC52 and 94% for Al. The adsorption aspects have been described by the Langmuir and Freundlich isotherms, whose ∆Gadso resulting values suggest a physicochemical adsorption by forming a compact and protective layer. Molecular modeling demonstrates RZ’s ability to interact with metal surfaces taken into action through both donor–acceptor and electrostatic interactions, highlighting the potential of RZ as a green corrosion inhibitor in similar environments, usable in de-icing solution formulations.

Coatings doi: 10.3390/coatings16080975

Authors: Yongsheng Li Jiahao Yan Min Wen Guanglei Liu Dingding Xiang

Metal additive manufacturing (MAM) enables the fabrication of geometrically complex and high-performance components but is accompanied by steep thermal gradients, repeated thermal cycling, phase transformation, residual stress, and deformation. These effects can reduce dimensional accuracy, manufacturing stability, fatigue resistance, and service reliability. This review systematically examines residual-stress and deformation behavior in MAM from the perspectives of formation mechanisms, influencing factors, measurement and prediction methods, mitigation strategies, and service-related consequences. The temperature gradient, mechanical constraint, and phase transition mechanisms are discussed as quantitatively coupled rather than independent processes. Comparative attention is given to process-specific differences, alloy-dependent thermophysical and metallurgical behavior, multi-track and multi-material interactions, and complex geometries. Destructive and non-destructive measurement techniques are compared in terms of penetration depth, spatial resolution, uncertainty, and cross-validation. Thermo-mechanical finite element, inherent strain, analytical, reduced-order, machine-learning, physics-informed, and digital-twin approaches are evaluated according to accuracy, efficiency, transferability, and applicability. Mitigation strategies are further compared considering residual-stress reduction, deformation control, manufacturing cost, and mechanical-property retention. Finally, challenges associated with uncertainty quantification, service environments, post-machining stress redistribution, and closed-loop control are identified. This review provides an integrated framework for selecting measurement, prediction, and mitigation approaches for reliable and high-precision MAM.

Coatings doi: 10.3390/coatings16080974

Authors: Ivana Ilievska Fatme Padikova Georgi Kotlarski Edmon Lazarov Borislav Stoyanov Lyubomira Veleva Angel Anchev Maria Ormanova Stefan Valkov

Ti–Nb alloys are widely recognized as highly promising materials for orthodontic applications due to their excellent functional properties, including superior biocompatibility and a relatively low Young’s modulus that better matches that of human bone. The formation of Ti–Nb surface alloys or surface-modified layers is particularly attractive, as the surface properties of biomedical materials strongly influence their mechanical and biological interactions during service. In the present study, Ti-Nb coatings were fabricated on commercially pure titanium substrates using an electron beam surface treatment (EBST) technique. Initially, a 1 μm thick Nb layer was deposited onto the Ti substrates by direct current (DC) magnetron sputtering. Subsequently, the samples were modified through scanning electron beam irradiation, with beam power varied between 1000 and 2000 W to promote Ti-Nb alloyed layers. The phase composition of the resulting structures was analyzed by X-ray diffraction (XRD). Microstructural characteristics and chemical composition were examined using scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectroscopy (EDS). Mechanical properties were evaluated in terms of hardness and Young’s modulus. The findings of this study demonstrate the feasibility of tailoring the structural and mechanical properties of Ti–Nb surface alloys through controlled electron-beam processing and support their further investigation for potential orthodontic and dental applications.

Coatings doi: 10.3390/coatings16080973

Authors: Jincheng Wang Carlos Valentin Kayde Bowers Lingxuan Hao Bei Fan Hui Hu

Freezing rain poses a substantial hazard to the operation and safety of unmanned aerial vehicles (UAVs) in cold-weather environments. In the present study, a comprehensive experimental campaign was conducted to investigate the effect of surface icephobicity on ice accretion and shedding from rotating UAV propellers under freezing-rain conditions. A novel, durable, slippery liquid-like surface (SLLS) coating, characterized by low contact-angle hysteresis and low ice adhesion, is utilized as a passive strategy for UAV icing mitigation. The coating was assessed through wettability and ice-adhesion measurements, phase-locked high-speed imaging of supercooled large-droplet impingements, rotating-propeller ice accretion experiments, accelerated rain erosion testing, and surface-topography characterization. The measurement results revealed distinct normal and oblique droplet impingement regimes and demonstrated that the evolving leading-edge ice geometry substantially altered droplet deformation, liquid redistribution, and subsequent ice growth. Compared with the uncoated, baseline propeller, the SLLS-coated propeller was found to promote earlier ice shedding and reduce the ice-induced power consumption by approximately 36%. These findings highlight the potential of SLLS coatings as a promising strategy for UAV propeller icing protection to ensure safer and more efficient UAV operations under adverse weather conditions.

Coatings doi: 10.3390/coatings16080972

Authors: Jinlong Zhang Zhenyin Lu Dianhao Dong Shuai Jiao Dongyue Yan Dongdong Li Shenghuan Fang

Surface nanoparticle defects are among the key factors that reduce the laser-induced damage threshold (LIDT) of high-power laser coatings. In this study, the effects of nanosecond laser conditioning and continuous-wave laser conditioning on the removal of surface nanoparticle defects with different sizes and material compositions, as well as on the LIDT of SiO2 coatings, were systematically investigated. The results show that laser conditioning can reduce the number density of surface particles and improve the LIDT of the coatings under appropriate conditions. Under nanosecond laser conditioning, particle detachment is mainly attributed to the inertial effect induced by rapid transient thermal expansion. In contrast, under continuous-wave laser conditioning, particle detachment is primarily governed by interfacial instability induced by thermal expansion mismatch between the particles and the coating. This study provides experimental evidence and clarifies the dominant surface particle-detachment mechanisms under nanosecond and continuous-wave laser conditioning in optical materials, and offers a useful reference for the fabrication of optical coatings with high laser damage thresholds.

Coatings doi: 10.3390/coatings16080971

Authors: Wei Zhang Shi Hu Shuai Zhang Qin Liu Yihan Shi Jian Ouyang

As a road repair material, emulsified asphalt offers advantages such as convenient construction, good fluidity, and environmental safety. However, its relatively low strength limits its application range, making performance enhancement a key research focus. In this study, waterborne epoxy resin (WER) was used to modify emulsified asphalt, and the preparation process and performance were systematically investigated. Three types of waterborne epoxy systems were selected, and through compatibility, film-forming performance, and bonding strength tests, the JT waterborne epoxy system was identified as having the best overall performance, with an optimal epoxy-to-curing-agent ratio of 1:0.6. Modified emulsified asphalts with different proportions of WER and styrene–butadiene rubber were prepared. Using fluorescence microscopy, image recognition techniques, and multiple experimental evaluations, the distribution of epoxy resin in the emulsified asphalt was quantitatively analyzed. The results show that the addition of WER significantly improves the bonding strength of emulsified asphalt, with the fastest rate of increase observed in the 5−10% range. However, a comprehensive evaluation considering microstructure uniformity, rheological performance, and water resistance indicates that the optimal overall performance is achieved in the 10−12% range, and the WER content should strictly be controlled below 15% to avoid severe local agglomeration. Meanwhile, the modified water-boiling test reveals that the adhesion between WERAE and aggregates is significantly enhanced, implying a potentially improved resistance to moisture-induced damage under practical service conditions. The standard deviation of area results indicate that when the WER content exceeds 15%, local agglomeration occurs, which is unfavorable for strength development of the modified system; the distribution uniformity results further show that when the WER content is greater than 12%, it negatively affects the uniform dispersion of WER within the emulsified asphalt.

Coatings doi: 10.3390/coatings16080970

Authors: Yang Liu Jing Li Kaibao Wang Huirong Le

Ultra-high molecular weight polyethylene (UHMWPE) is the preferred bearing material for total knee arthroplasty, yet its limited service life (15–20 years) remains a clinical challenge. This study investigates graphene oxide (GO) nanoplatelets as reinforcing fillers to enhance the mechanical and tribological performance of UHMWPE for longer-lasting implants. GO/UHMWPE composites with 0–1 wt% GO were fabricated via solution blending and hot compression molding. Direct SEM imaging combined with oxygen elemental mapping confirmed uniform GO dispersion up to 0.5 wt%, whereas higher loadings induced agglomeration. Dynamic mechanical analysis showed that the storage modulus at 37 °C increased with GO content, peaking at 0.5 wt% (improved by ~28% over neat UHMWPE), then decreased due to aggregation. Tribological tests under dry reciprocating sliding revealed that GO progressively reduced the wear rate (up to ~45% at 1.0 wt%), but also raised the steady-state friction coefficient from 0.13 to 0.19, attributed to molecular chain anchoring. The optimal balance of enhanced stiffness and wear resistance, with only a marginal friction increase, was achieved at 0.5 wt% GO. The reinforcement mechanism involves efficient stress transfer to rigid GO sheets and reduced surface peeling. This work provides a robust processing route and direct dispersion evidence, offering practical guidance for designing high-performance UHMWPE composites for orthopedic applications.

Coatings doi: 10.3390/coatings16080969

Authors: He Tian Limin He Rende Mu

Yttria-stabilized zirconia (YSZ) thermal barrier coatings suffer from t′ phase destabilization and insufficient thermal insulation above 1200 °C. In this work, YbO1.5-stabilized ZrO2 powders (xYbSZ, x = 4–12 mol% YbO1.5 on a cation basis, equivalent to 2–6 mol% Yb2O3) were synthesized by chemical co-precipitation, consolidated by spark plasma sintering, and evaluated at 1300 °C in terms of phase stability, sintering behavior, thermal conductivity, and fracture toughness. A common compositional boundary near 8 mol% YbO1.5 was identified across all four responses. 8YbSZ retained the metastable t′ phase with a monoclinic content below 10 mol% after 300 h at 1300 °C, whereas grain coarsening accelerated markedly and the thermal conductivity reduction efficiency per unit doping at 1000 °C was approximately halved beyond this composition, with κ decreasing from 2.41 to 1.96 W·m−1·K−1 across the series. The toughness gain produced by thermal treatment fell from 34% (4YbSZ) to about 10% (10–12YbSZ) as the dominant toughening mechanism shifted from transformation and microcrack toughening (4–6 mol%) to ferroelastic domain switching (8 mol%), with both being lost in the compositions in which the cubic phase predominated. These results identify 8 mol% YbO1.5 as the optimal composition balancing phase stability, sintering resistance, thermal insulation, and mechanical integrity for TBC applications at 1300 °C.

Coatings doi: 10.3390/coatings16080968

Authors: Jasna V. Džunuzović Ivan S. Stefanović Enis S. Džunuzović

Polyurethanes have attracted significant and constant attention since their initial introduction by Otto Bayer in 1937, primarily due to their inherent versatility. To expand their application potential and overcome limitations under extreme industrial conditions, the performance of pure polyurethanes is frequently enhanced through the incorporation of adequate fillers. This review provides a comprehensive analysis of recent advancements in the field of polyurethane composites, focusing on the role of functional fillers in improving the properties of the polyurethane matrix. Special attention is given to the classification and effects of various types and sizes of the most commonly applied and promising fillers, including both individual and hybridized systems.

Coatings doi: 10.3390/coatings16080967

Authors: Yuhan Liang Lijie Chen Mingyue Feng Tong Zhang Rongbang Sun Yang Liu Yifu Fu Yunxiang Chen Lan Chen

Aiming at the rapid corrosion of degradable magnesium alloys in physiological environments and the insufficient long-term protection of single plasma electrolytic oxidation (PEO) coatings, Mg-Mn-Fe layered double hydroxide (LDH) and baicalin (BA)-loaded LDH/BA composite coatings were prepared in situ on PEO-pretreated ZE21C magnesium alloy substrates. BA was stably anchored on the LDH surface via coordination bonds between its oxygen-containing functional groups and laminate metal sites. Benefiting from the physical barrier of the LDH lamellar structure and the corrosion inhibition effect of baicalin, the LDH/BA coating significantly improved the corrosion resistance of the magnesium alloy matrix. The composite coating exhibited peroxidase-like catalytic activity for reactive oxygen species generation, which could be enhanced by near-infrared irradiation. It also possessed stable photothermal conversion performance and pH-responsive drug release behavior under acidic conditions. Biological characterization demonstrated that BA-loaded LDH composite coatings exert potent inhibitory effects on 143B cell proliferation. This work integrates long-term corrosion resistance, controlled drug release, and photoresponsive catalytic functions onto magnesium alloy surfaces, providing an effective strategy for developing high-performance biodegradable magnesium alloys.

Coatings doi: 10.3390/coatings16080966

Authors: Chenyao Huang Jie Chen Yikun Yang Yuying Feng Yixian Xie Xi Cao Zhengjie Guo Fuyueyang Tan Yuxuan Duan Zaijin Li Yi Qu Lin Li

Tunable external cavity diode lasers (ECDLs) are core light sources for portable quantum precision measurement, offering narrow linewidth, wide tuning range, and high spectral purity. This review systematically summarizes the research progress of ECDLs for portable quantum applications, classifying mainstream configurations into Littrow, Littman, fiber grating, and filter types. The structural principles, performance characteristics, and recent breakthroughs of each type are elaborated, with in-depth analysis of the trade-offs among tuning range, linewidth, side-mode suppression ratio (SMSR), and output power. Key progress in miniaturization and integration is highlighted, focusing on MEMS-driven tuning and silicon waveguide hybrid integration technologies, which address the conflict between performance and portability. Current challenges including mode hopping, thermal stability, and packaging loss are discussed, and future directions such as multi-band extension, isolator-free frequency stabilization, and AI-assisted control are prospected. This work provides a systematic reference for the development of compact, high-performance ECDLs toward field-deployable quantum sensors.

Coatings doi: 10.3390/coatings16080965

Authors: Hongwu Zhang Huafeng Wei Heng Yue

The stable crosslinked structure of glass-fiber-reinforced epoxy composites in end-of-life wind turbine blades complicates their recycling and reuse. Mechanically ground blade powder can be incorporated into new epoxy systems, but its heterogeneous surface composition and limited compatibility with the matrix restrict its reinforcing efficiency. In this study, sequential NaOH activation and KH560 treatment were used to regulate the surface characteristics of recycled wind-turbine-blade powder. FTIR and direct powder XPS measurements revealed changes in the hydroxylated silicate environment and the introduction of KH560-associated organic and organosilicon surface species. Representative SEM observations showed greater resin attachment and a more integrated local powder-matrix morphology after sequential treatment. At a fixed recycled-powder loading of 40 phr, corresponding to approximately 28.4 wt% of the total uncured mixture, EP-KH560 achieved mean flexural and tensile strengths of 67.00 and 38.81 MPa, respectively. These values were 47.8% and 57.1% higher than those of the composite containing untreated powder. Under the fixed formulation and processing conditions investigated, the results demonstrate that sequential NaOH/KH560 treatment improves the interfacial compatibility and comparative mechanical performance of recycled wind-turbine-blade powder/epoxy composites.

Coatings doi: 10.3390/coatings16080964

Authors: Hany M. Abd El-Lateef Ibrahim M. A. Mohamed

Recently, gel coatings have been studied as a promising method that can provide electrochemical corrosion protection. This review presents a comprehensive analysis of advanced gels such as sol–gel coatings, hybrid organic–inorganic, self-healing, and crack repair gels. These gels employ different mechanisms for corrosion protection, from passive barrier formation to active self-healing and corrosion inhibition. Their performance can be influenced by gel chemistry, microstructure, and the incorporation of functional additives. Recent studies have shown that gel coatings can achieve promising corrosion resistance. This high efficiency can be attributed to the formation of dense barrier layers that restrict the mobility of attacking ions. The incorporation of functional additives such as silica nanoparticles can enhance mechanical characteristics for gels. In the field of crack-repair, bio-gels based on microbially induced calcium carbonate precipitation show acceptable sealing capability. Additionally, the evolution of polarization resistance and corrosion current suggests the sustained protective performance of these gels. Multifunctional gels extend this concept by combining crack sealing, alkalinity restoration, and steel re-passivation. Gel coatings are transitioning from simple barrier coatings to multifunctional smart inhibition capable of self-healing, corrosion sensing, and long-term durability. This review highlights the relationship between gel chemistry, microstructure, and corrosion resistance for the development of next-generation gel coatings.

Coatings doi: 10.3390/coatings16080963

Authors: Pu Zhang Wei Xiong

Photocatalytic antibacterial coatings have emerged as a promising antibiotic-free strategy for combating healthcare-associated infections, biofilm formation, marine biofouling, and environmental microbial contamination. Unlike conventional antimicrobial approaches, photocatalytic systems continuously generate reactive oxygen species (ROS) under light irradiation, enabling broad-spectrum antimicrobial activity while minimizing the risk of antimicrobial resistance. This review systematically summarizes the fundamental mechanisms underlying photocatalytic antibacterial activity, including photogenerated charge-carrier dynamics, ROS generation pathways, and microbial inactivation processes. We further highlight recent advances in photocatalyst design, spanning conventional semiconductor photocatalysts, heterojunction engineering, cocatalyst modification, and two-dimensional material-assisted strategies for enhanced photocatalytic performance. Crucially, particular emphasis is placed on coating architectures and interfacial regulation, including encompassing fabrication methodologies, coating–substrate adhesion, internal heterointerface design, and coating–microorganism interactions, which dictate long-term durability and antibacterial efficacy. Finally, we explore the diverse applications of these coatings in medical devices, environmental remediation, and marine antifouling, while identifying current bottlenecks and future research trajectories toward developing durable, highly efficient, and clinically translatable antimicrobial surface technologies.

Coatings doi: 10.3390/coatings16080962

Authors: Najma Saleem Tahreem Ashraf Ibtisam Daqqa Sufian Munawar Nazeran Idrees Farkhanda Afzal Deeba Afzal

This reply presents a point-by-point response to the comments received from Pantokratoras in our previously published research article. The comments highlighted that the values of electrical conductivity assigned to alumina (Al2O3), silicon dioxide (SiO2), and titanium dioxide (TiO2) nanoparticles were not appropriate and the experimental value of the Prandtl number for blood should remain within the range of 29–32. In response the electrical conductivity values for each nanoparticle were corrected and revised the Prandtl number values accordingly. The recomputed findings revealed that only small changes appeared in quantitative results while the overall trends and insights remained same.

Coatings doi: 10.3390/coatings16080961

Authors: Asterios Pantokratoras

The base fluid in [...]

Coatings doi: 10.3390/coatings16080960

Authors: Xiaotong Yin Xiaojuan Yin Ruixi Liu Tiance Zhang

The oxide interface on silicon carbide is a critical microstructural feature that enhances the mechanical properties of its reinforced composites; therefore, investigating the oxidation behavior and oxide layer morphology of silicon carbide is of great significance. This work systematically elucidates the oxidation behavior and oxide layer morphology evolution of silicon carbide particles within the temperature range of 1100 to 1400 °C through quantitative analysis and visual characterization. Meanwhile, based on the measurement results of mass, particle size, and atomic ratio, three semi-quantitative estimation formulas for oxide layer thickness are derived (1.214rk, 2.226Δh, and 193pH/(213-126p), respectively), providing a reference for rapid assessment of oxide layer thickness when direct and macroscopic observation means are lacking. This work provides a reference for understanding the oxidation behavior of silicon carbide particles and for related composite material research.

Coatings doi: 10.3390/coatings16080959

Authors: Bryan Jesús Albino Arbieto Christian Serafin Ferrer Chavesta Sleyther Arturo De La Cruz Vega

Traditional structural strengthening methods involve high costs, increased self-weight of the structure, and complex construction procedures. In this context, there is a need for alternative materials that improve the mechanical performance of concrete without compromising its functionality. The objective of this study was to evaluate the effect of applying fiberglass layers to concrete with a design compressive strength of f’c = 20.59 MPa (210 kg/cm2). An applied research approach was used, with a quantitative methodology and a quasi-experimental design. Cylindrical concrete specimens measuring 12 cm × 6 cm were cured for 28 days and then coated with 1, 2, and 3 layers of fiberglass. The results showed that fiberglass has a chemical composition dominated by sodium (54.28%), silicon (25.64%), magnesium (9.98%), and aluminum (7.19%), which contributes to its stiffness and stability. Regarding compressive strength, the control specimens achieved an average strength of 20.69 MPa, while specimens coated with 1, 2, and 3 layers of fiberglass reached average strengths of 21.72 MPa, 23.49 MPa, and 25.71 MPa, respectively. These values represent increases of 4.98%, 13.53%, and 24.26% compared to conventional concrete. In terms of flexural strength, the control beams reached an average value of 3.50 MPa, whereas beams reinforced with 1, 2, and 3 fiberglass layers achieved average strengths of 3.66 MPa, 3.89 MPa, and 4.10 MPa, respectively. The results demonstrate that fiberglass improves both the compressive and flexural performance of concrete by providing external confinement, delaying crack propagation, and increasing the load-bearing capacity of the structural elements. It is concluded that fiberglass constitutes an effective and technically viable alternative for strengthening concrete structures.

Coatings doi: 10.3390/coatings16080958

Authors: Chenkai Zhu Yong Wang Zhenzong Shao Libin Lu

Rapid corrosion and poor coating adhesion continue to limit the use of magnesium alloys as temporary orthopedic implants. The two-stage laser process was developed to separate the high-temperature melting of 45S5 bioactive glass (BG) from the low-melting-point AZ31 substrate. Femtosecond-laser grids with spacings of 100, 200, and 300 μm were first produced on AZ31 to provide anchoring sites. Then, the target 45S5 BG was suspended above the substrate, locally melted with CO2 laser, and transported onto the textured surface by gas jet. The 200 μm grid texture for Mg substrate with lowest water contact angle could give the highest tape-test adhesion rating (4B). At the selected deposition conditions of 20 W and 20 L·min−1, two coating cycles produced a continuous layer approximately 50.5 μm thick. Relative to bare Mg alloy, this double-layer coating increased polarization resistance from 1.20 × 103 to 1.39 × 105 Ω·cm2 and decreased corrosion current density from 8.70 × 10−4 to 5.33 × 10−6 A·cm−2. It also limited alkalization and mass loss during 28 days in simulated body fluid. As such, the double-layer surface coating supported apatite formation and improved MC3T3-E1 proliferation and alkaline phosphatase activity. These findings indicated that suspended-target deposition was able to form adherent, bioactive glass coatings on magnesium while limiting direct thermal damage to the substrate.

Coatings doi: 10.3390/coatings16080957

Authors: Huixiang Wang Guoyuan Huang Byungchan Lee

This review paper systematically investigates the surface modification technology of wooden table tennis blades, with a particular focus on the inherent conflict between coating-induced protection and the preservation of acoustic performance—a critical yet underexplored aspect of blade design. While protective coatings are essential for enhancing durability against moisture, wear, and impact, they inevitably alter the blade’s vibrational characteristics and acoustic feedback, compromising the tactile–auditory perception that elite players rely upon. The current literature predominantly treats protection and acoustics as separate design objectives, lacking an integrated framework to resolve their inherent trade-off. To address this gap, this review establishes a material–structure–function integrated design paradigm that elucidates the synergistic optimization of coating protection and acoustic response. We systematically analyze the regulatory mechanisms of key coating parameters—specifically elastic modulus, density, and damping coefficient—on blade vibration modes and impact sound characteristics, demonstrating that conventional singular optimization inevitably leads to undesirable frequency shifts and diminished tactile feedback. Our synthesis of materials science, acoustic analysis, and biomechanics reveals that the key to synergy lies in constructing a mechanical impedance-matching transition system through material selection and thickness gradient design. Notably, we show that a multi-layer gradient coating architecture, guided by finite element simulation, can enhance protective performance by 40% while restricting acoustic deviation to within 5%, validating a rational “design–simulation–verification” closed-loop methodology. Furthermore, this review identifies critical research frontiers, including smart adaptive coatings and sustainable bio-based materials, and proposes a multi-objective optimization framework to bridge the gap between laboratory innovation and manufacturable, high-performance sporting equipment. This work provides a foundational theoretical roadmap for the next-generation design of competition-grade table tennis blades, balancing durability with the nuanced sensory demands of elite athletes.

Coatings doi: 10.3390/coatings16080956

Authors: Yinglong Hu Chenghai Sun Lizhou Zhao Zhengwei Zhang Jian Miao Jinggang Yin Xiang Liu

To alleviate the shortage of high-quality natural aggregates and promote the sustainable utilization of mining waste rock, this study employed lead–zinc mine waste rock-derived aggregate to replace 50% of the coarse aggregate by mass in cement-stabilized crushed stone. A series of tests, including drying shrinkage, thermal shrinkage, freeze–thaw cycling, scouring, and sulfate attack, were conducted to investigate the cracking resistance and durability of the resulting mixtures. The effects of basalt fiber, low-alkali cement, and a sulfate-resistant agent were further evaluated. Although the waste rock aggregates exhibited relatively inferior particle morphology, they could be incorporated into cement-stabilized crushed stone through rational gradation design. Among the investigated fiber contents, the mixture containing 4‰ basalt fiber exhibited relatively favorable shrinkage, freeze–thaw, and scouring resistance. The sulfate-resistant agent reduced mass loss and strength degradation under the investigated sulfate wet–dry cycling conditions. In contrast, low-alkali cement showed limited effectiveness in improving shrinkage resistance and freeze–thaw durability. These results provide experimental evidence for the feasibility of using lead–zinc mine waste rock as a partial coarse aggregate replacement in road base materials under the investigated laboratory conditions.

Coatings doi: 10.3390/coatings16080955

Authors: Rui Hao Lianbo Wang Rui Wang Nianhua Chen

This study investigates the effect of hot-rolling speed on the microstructure and mechanical properties of STS304/1050Al/STS304 (304 stainless steel/1050 aluminum alloy/304 stainless steel) three-layer composite plates. The results show that as rolling speed increases, the tensile strength increases from 300.3 MPa to 366.2 MPa and the elongation after fracture increases from 42.96% to 50.56%, achieving simultaneous improvement in strength and ductility. At high rolling speeds, the strengthening of the STS304 layer is attributed to deformation-induced martensitic transformation and dislocation multiplication (17.2% increase in tensile strength), while the softening of the Al1050 layer is predominantly attributed to dynamic recovery (37.3% increase in elongation after fracture), which contributes to a synergistic “steel strengthening and aluminum softening” effect. The rightward shift in the intersection point on the work-hardening rate curves indicates enhanced uniform deformation capacity, and the coarsening of dimples on fracture surfaces is consistent with ductile fracture mechanisms. Appropriately increasing the hot-rolling speed represents an effective process route for optimizing the strength–ductility synergy of such steel/aluminum composite plates.

Coatings doi: 10.3390/coatings16080954

Authors: Yu Ru Yuzhe Li Ruixin Wang Yikun Wang Li Zhong Maolong Zhang Jingchun Huang Yifan Bao Yu Qiao

To explore the high-value utilization of liquid recovery products from waste wind turbine blades in road binders, a liquid-rich fraction obtained from subcritical acetic acid degradation and subsequent vacuum distillation of waste wind turbine blade epoxy composites was introduced into styrene–butadiene–styrene (SBS)-modified asphalt to prepare composite-modified asphalt. Conventional property tests, dynamic shear rheological tests, bending beam rheological tests, steady shear tests, master curve analysis, Fourier transform infrared spectroscopy (FTIR), and gel permeation chromatography (GPC) were conducted to systematically evaluate the influence of the liquid-rich fraction on the properties and structural characteristics of the composite-modified asphalt. The results showed that, with increasing liquid-rich fraction content, the softening point increased, while penetration and ductility decreased, and the rotational viscosity at 135 °C increased, indicating enhanced overall stiffness and high-temperature flow resistance. High-temperature rheological results showed that the liquid-rich fraction increased the storage modulus, loss modulus, and rutting factor, while decreasing the phase angle improved the high-temperature deformation resistance of the composite-modified asphalt. Low-temperature rheological results indicated that the creep stiffness S increased, the m-value decreased, and the S/m ratio increased, suggesting weakened stress relaxation capacity and reduced cracking resistance at low temperature. Fatigue factor and steady shear results revealed that the liquid-rich fraction enhanced structural stability and flow resistance but also increased fatigue damage sensitivity at intermediate temperature. Master curves, Black diagram, and Cole–Cole plots further demonstrated that the liquid-rich fraction increased the modulus level over a wide frequency domain and strengthened the structural stability of the asphalt system. FTIR and GPC results indicated that the introduction of the liquid-rich fraction increased the relative contents of aromatic structures and polar oxygen-containing groups and promoted molecular association and increased the apparent molecular weight level of the system. Overall, the liquid-rich fraction acted as a structure-enhancing modifier in SBS-modified asphalt, improving its high-temperature performance while causing a certain trade-off in low-temperature and fatigue properties. Therefore, the dosage should be selected by balancing high-temperature stability, low-temperature cracking resistance, and fatigue durability, and the practical sustainability of this recycling route still requires dedicated economic and environmental evaluation.

Coatings doi: 10.3390/coatings16080953

Authors: Jie Shen Binhui Lei Yuchen Du Xiaoyan Guan Yujie Fan Kang Zhao

Cemented carbide is extensively applied in cutting tools. Surface laser micro-texturing alleviates tool surface wear and boosts cutting performance. This work adopts response surface methodology to investigate circular micro-texture parameters (diameter, spacing, offset) of YG8 carbide tools with average friction coefficient as the response, constructing a quadratic regression model to acquire optimal texture parameters: diameter 0.46 mm, spacing 0.93 mm, offset 0.31 mm. Friction tests reveal texture parameters greatly affect tribological properties, and the wear mitigation mechanism of optimized textures is analyzed. Turning experiments compare plain tools, air-ablation and liquid-phase laser textured tools. Cutting force and temperature models for smooth and liquid-phase textured cutters are built and validated. Results show air-textured tools reduce cutting force by 26.35% and average temperature by 13.42%, while liquid-phase counterparts achieve 30.07% force drop and 20.73% temperature reduction. Genetic algorithm optimization yields liquid-texture force attenuation coefficient 0.3646 and temperature coefficient 0.2961, offering theoretical support for high-performance textured cutter design.