Coatings

10 pages, 2646 KB

Open AccessArticle

Synergistic Strategy of Oxidation and Coordination for Removing Post-Service Silicon-Modified Diffusion Aluminum Coating on Turbine Blades

by Dongling Yang, Shusuo Li, Xingpu Wang, Yidong Sun, Yanling Pei, Ruoying Cui, Kuilin Luo, Tinghong Hou and Taili Chen

Coatings 2026, 16(8), 941; https://doi.org/10.3390/coatings16080941 (registering DOI) - 8 Aug 2026

Abstract

Engine blade maintenance can extend engine service life, with coating removal being the initial step in the regeneration process. Silicon-modified diffusion aluminum-silicon coating (AlSi coating) is well-established as a protective coating for nickel-based superalloys due to its excellent oxidation and corrosion resistance, and [...] Read more.

Engine blade maintenance can extend engine service life, with coating removal being the initial step in the regeneration process. Silicon-modified diffusion aluminum-silicon coating (AlSi coating) is well-established as a protective coating for nickel-based superalloys due to its excellent oxidation and corrosion resistance, and is widely used in applications such as aero-engines and gas turbines. This study proposes a synergistic strategy combining oxidation and coordination to remove AlSi coating from nickel-based superalloy surfaces. The results demonstrate that this formulation effectively removes the coating while controlling substrate corrosion, avoiding detrimental effects such as intergranular corrosion and over-etching that compromise product quality. Mechanism analysis based on Density Functional Theory Simulations indicates that oxidizing elements such as Ni and Al into nickel oxide and aluminum oxide, followed by electronic structure modulation via a chelating agent, promotes efficient and uniform removal of the post-service AlSi coating by the acid solution. Full article

(This article belongs to the Section High-Energy Beam Surface Engineering and Coatings)

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32 pages, 9393 KB

Open AccessReview

Modification of Steel Slag Aggregate in Road Engineering: Key Technologies, Performance Enhancements, and Sustainable Prospects

by Juncheng Ma, Jue Li and Yongdong Lu

Coatings 2026, 16(8), 940; https://doi.org/10.3390/coatings16080940 - 7 Aug 2026

Abstract

The growing demand for natural aggregates and continued stockpiling of steel slag have increased interest in using steel slag aggregate (SSA) in road engineering. However, delayed hydration of free calcium oxide (f-CaO) and free magnesium oxide (f-MgO), porous and rough surfaces, and the [...] Read more.

The growing demand for natural aggregates and continued stockpiling of steel slag have increased interest in using steel slag aggregate (SSA) in road engineering. However, delayed hydration of free calcium oxide (f-CaO) and free magnesium oxide (f-MgO), porous and rough surfaces, and the potential release of hazardous elements constrain its long-term application. This review compares aging treatment, surface modification, direct carbonation, microbially induced calcium carbonate precipitation (MICP), and combined treatments from a raw-material heterogeneity and defect-oriented perspective. Their effectiveness is strongly condition-dependent. Aging treatment can control volume expansion, but reaction depth and treatment uniformity remain limited. Surface modification can reduce water absorption and improve interfacial performance but cannot eliminate internal expansive phases. Direct carbonation and MICP can stabilize reactive phases, refine pore structures, and reduce the mobility of some elements, but are limited by mass transfer and equipment requirements, and by mineralization uniformity and ammonium by-product management, respectively. Combined treatments can address multiple defects but increase process complexity, resource consumption, and quality-control requirements. Because material properties and evaluation methods vary among studies, reported performance gains should not be directly used for technology ranking. Instead, technology selection should follow the framework of “raw-material characteristics–dominant defects–preferred technology–engineering boundaries”. From a life-cycle perspective, sustainability depends on balancing resource and environmental benefits against additional treatment burdens. Near-term implementation should integrate raw-material classification, process monitoring, long-term durability and dynamic leaching verification, and the progressive incorporation of key performance and environmental indicators into road-material specifications and engineering acceptance criteria. Full article

(This article belongs to the Special Issue Novel Cleaner Materials for Pavements)

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28 pages, 18561 KB

Open AccessArticle

Assessment of Low-Temperature Fracture Behavior in Bituminous Mixtures Incorporating Sustainable Waste Additives: SCB Testing and Finite Element Analysis

by Ömer Faruk Keleş, Muhammed Ali Çolak, Ahmet Oğuz Demiriz and Fatih İrfan Baş

Coatings 2026, 16(8), 939; https://doi.org/10.3390/coatings16080939 - 7 Aug 2026

Abstract

In this study, the combined effect of waste lubricating oil (WLO) and waste pine branch ash (WPBA) was investigated to improve the low-temperature fracture behavior of asphalt mixtures. To investigate the low-temperature fracture behavior of the mixtures containing 2%–6% WLO and 3%–12% WPBA, [...] Read more.

In this study, the combined effect of waste lubricating oil (WLO) and waste pine branch ash (WPBA) was investigated to improve the low-temperature fracture behavior of asphalt mixtures. To investigate the low-temperature fracture behavior of the mixtures containing 2%–6% WLO and 3%–12% WPBA, the semi-circular bending (SCB) test was conducted at −15 °C, and the experimental results were analyzed using a statistical approach. Fracture toughness (K_(IC)), total fracture energy (G_F) and its pre-peak and post-peak components, crack resistance index (CRI), flexibility index (FI), and toughness index (TI) were determined. The findings indicate that the optimal combination depends on the fracture parameter under consideration. The best fracture toughness results, K_(IC) = 24.96 MPa·mm^0.5, indicating increased resistance to crack initiation, was obtained at 4% WLO and 12% WPBA content. On the other hand, the best fracture energy results, G_F = 1.202 N/mm, reflecting an increase in energy dissipation during crack propagation, was obtained at 4% WLO and 9% WPBA content. The highest FI, CRI, and TI values were obtained with 6% WLO and 9% WPBA, corresponding to increases of approximately 66%, 69%, and 16%, respectively, compared with the reference mixture. This resulted in greater crack-initiation resistance, improved post-peak deformation capacity, and higher energy-dissipation capacity, although the greater WLO content led to a decrease in structural integrity. When the results are evaluated overall, it is understood that the use of WLO in the mixtures increases deformation capacity, while the use of WPBA controls crack propagation through its hardening and filling effects. In mixtures containing 4% WLO and 9%–12% WPBA, a balanced behavior was achieved in terms of crack initiation, crack propagation, and stiffness under low-temperature conditions. Full article

(This article belongs to the Special Issue Functional Load-Bearing Coatings)

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31 pages, 14915 KB

Open AccessArticle

Influence of Tris-Buffering on the Integrity and Degradation of PEO and Duplex PEO/Sol-Gel Coatings on AZ31 for Biodegradable Implant Applications

by Lara Moreno, Yoann Paint and Marie-Georges Olivier

Coatings 2026, 16(8), 938; https://doi.org/10.3390/coatings16080938 - 7 Aug 2026

Abstract

Magnesium alloys are promising candidates for biomedical implants, but their rapid corrosion limits clinical use. Simulated body fluid (SBF) is commonly used to evaluate corrosion behaviour; however, Ca-P and carbonate deposits can mask the intrinsic performance of protective coatings. Tris(hydroxymethyl)aminomethane (Tris) has been [...] Read more.

Magnesium alloys are promising candidates for biomedical implants, but their rapid corrosion limits clinical use. Simulated body fluid (SBF) is commonly used to evaluate corrosion behaviour; however, Ca-P and carbonate deposits can mask the intrinsic performance of protective coatings. Tris(hydroxymethyl)aminomethane (Tris) has been proposed as an SBF modifier, although its effect on coated magnesium remains poorly understood. While Tris modifies the buffering characteristics of the solution, it also alters the stability of Mg(OH)₂ and the precipitation equilibria of corrosion products, resulting in more aggressive corrosion conditions than standard SBF. Here, the corrosion behaviour of AZ31 alloy, a plasma electrolytic oxidation (PEO) coating, and a sol-gel sealed PEO coating was investigated in SBF with and without Tris. Electrochemical impedance spectroscopy, immersion tests, pH monitoring, and post-immersion SEM/EDS analyses were used to evaluate coating performance under physiological and aggressive conditions. The results show that AZ31 and PEO coatings exhibit higher apparent corrosion resistance in SBF without Tris due to corrosion-product stabilization and Ca-P-rich deposits that partially block electrolyte access. In contrast, SBF with Tris accelerates degradation, causing uniform corrosion of AZ31 and premature PEO failure through electrolyte penetration and coating cracking. The PEO-AR/ZTP system maintains the highest electrochemical resistance and the best protective performance in both media. Full article

(This article belongs to the Special Issue Advances in Surface Engineering and Biocompatible Coatings for Biomedical Applications, 3rd Edition)

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13 pages, 29333 KB

Open AccessArticle

CTAB-Assisted Surface Immobilization of Silver Nanoparticles onto Porous Ceramic: Effects of Reducing Agents and Soaking Time

by Chanin Khomlaem, Parichat Somsong, Pimlada Jindasamut, Praewa Phasuk and Natthanon Phonchai

Coatings 2026, 16(8), 937; https://doi.org/10.3390/coatings16080937 - 7 Aug 2026

Abstract

Porous ceramic pellets (PCPs) coated with silver nanoparticles (Ag NPs) have attracted considerable attention as surface-modified ceramic materials because they combine the structural stability of porous ceramics with the unique physicochemical properties of Ag NPs. In this work, the PCPs were prepared from [...] Read more.

Porous ceramic pellets (PCPs) coated with silver nanoparticles (Ag NPs) have attracted considerable attention as surface-modified ceramic materials because they combine the structural stability of porous ceramics with the unique physicochemical properties of Ag NPs. In this work, the PCPs were prepared from local Thai clay, and Ag NPs were immobilized onto the PCP surface using cetyltrimethylammonium bromide (CTAB) as the surface immobilization. The effects of ceramic composition, reducing agents, and soaking time on the surface immobilization of Ag NPs were systematically investigated. The optimal ceramic composition consisting of 65 wt% red clay, 25 wt% ceramic powder, and 10 wt% rice husk exhibited good structural stability after soaking and a porosity of approximately 35%. Ag NPs were synthesized in situ using ascorbic acid (AA) and sodium borohydride (NaBH₄) as reducing agents, and coating performance was examined at soaking times of 6, 12, 24, and 48 h. FE-SEM observations revealed that Ag NPs synthesized using AA tended to form relatively large agglomerates, whereas NaBH₄ produced a more homogeneous nanoparticle distribution on the PCP surface. Among the investigated conditions, NaBH₄ with a soaking time of 12 h exhibited the most homogeneous nanoparticle distribution. These results suggest that CTAB-assisted surface immobilization is an effective strategy for immobilizing Ag NPs on porous ceramic substrates. The present study primarily focuses on surface immobilization behavior rather than biological performance. Full article

(This article belongs to the Section Surface Characterization, Deposition and Modification)

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22 pages, 17473 KB

Open AccessArticle

Trace Phosphorus-Modified Hot-Dip Sn Coatings on Cu Substrates: Surface Film Formation and Corrosion Resistance in NaCl Solution

by Yupeng Wang, Zhuangchao Zhan, Yuheng Han, Hongbo Qin, Jiaqiang Huang, Wangyun Li, Caihang Liang, Lili Wang, Chengxu Lin, Mingzhen Hu and Tianhan Liu

Coatings 2026, 16(8), 936; https://doi.org/10.3390/coatings16080936 - 6 Aug 2026

Abstract

To improve the corrosion resistance of Sn coatings on Cu substrates in chloride-containing environments, pure Sn and Sn–P coatings containing 0.02, 0.05, and 0.08 wt.% P were prepared by hot-dip coating. Their surface morphology, surface-film chemistry, and corrosion behavior were characterized using electrochemical [...] Read more.

To improve the corrosion resistance of Sn coatings on Cu substrates in chloride-containing environments, pure Sn and Sn–P coatings containing 0.02, 0.05, and 0.08 wt.% P were prepared by hot-dip coating. Their surface morphology, surface-film chemistry, and corrosion behavior were characterized using electrochemical measurements, atomic force microscopy (AFM), scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM/EDS), and X-ray photoelectron spectroscopy (XPS). The results demonstrate that trace phosphorus addition enhances the electrochemical stability of Sn coatings prepared via the hot-dip method. The corrosion current density decreased from 1.55 × 10⁻⁶ A·cm⁻² for pure Sn to 3.28 × 10⁻⁷ A·cm⁻² for SnP0.02, corresponding to a reduction of approximately 79%. Meanwhile, the total resistance increased from 10.46 to 19.03 kΩ·cm², confirming the enhanced barrier effect of the surface film. AFM results showed that the surface roughness Ra decreased from 13.41 nm for pure Sn to 8.72–12.69 nm for the Sn–P coatings. XPS identified Sn–O, P–O, and Sn–P species, suggesting the formation of a Sn–O/P–O-containing protective film. SnP0.02 exhibited the best overall corrosion resistance, whereas excessive P promoted local P-rich regions and non-uniform film formation, limiting further improvement. Full article

(This article belongs to the Special Issue Anti-Corrosion Coatings: New Ideas to Make Them More Effective)

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30 pages, 10588 KB

Open AccessArticle

Short- and Long-Term Electrochemical Response Prediction of Ni-Al-Powder-Coated Steel with Machine Learning

by Ayla Ocak, Ümit Işıkdağ, Sinan Melih Nigdeli and Gebrail Bekdaş

Coatings 2026, 16(8), 935; https://doi.org/10.3390/coatings16080935 - 6 Aug 2026

Abstract

Steel is the most fundamental material used in structural system elements in the construction industry. It needs to be coated with materials that provide resistance to high temperatures, wear, and corrosion. Ni-Al powder is preferred in coatings because nickel increases corrosion resistance and [...] Read more.

Steel is the most fundamental material used in structural system elements in the construction industry. It needs to be coated with materials that provide resistance to high temperatures, wear, and corrosion. Ni-Al powder is preferred in coatings because nickel increases corrosion resistance and aluminium forms an oxide layer to reduce oxidation. In the long term, the protective effect of coatings decreases, and corrosion resistance declines. In this study, a random forest model was evaluated using experimental data on the corrosion performance of A36 steel coated with Ni-Al powder for corrosion prevention, after exposure to a 3.5% NaCl solution for 1 h and 30 days for short- and long-term electrochemical response prediction. The impedance and phase angle characteristics, which represent the electrochemical response of coated and uncoated steel, have been predicted. In addition, the model’s reproducibility was investigated using the multi-seed (30 seeds) method to analyse the stability and consistency of the random forest model. The aim of this study was to develop a machine learning model that learns the frequency-dependent electrochemical impedance (Bode) response of graphene oxide-enriched Ni–Al coatings on steel, which reflects the corrosion-related electrochemical behaviour of the coating system, and to evaluate the model for predicting the impedance magnitude and phase angle of reference coatings over the investigated frequency range. The developed artificial intelligence model predicted the Bode response (impedance magnitude and phase angle) of coated and uncoated steel to NaCl solution after 1 h and 30 days as a function of frequency and coating type. The predicted impedance spectra reflected the deterioration of the corrosion protection performance of the Ni–Al coatings with increasing exposure time. The predicted EIS responses were subsequently used to assess changes in the corrosion-related electrochemical behaviour of the coatings over short- and long-term exposure. According to the findings, the random forest models can predict the frequency-dependent electrochemical response (impedance magnitude and phase angle) with high accuracy. Full article

(This article belongs to the Section Surface Characterization, Deposition and Modification)

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18 pages, 7126 KB

Open AccessArticle

Predictive Evaluation of Aluminum Profile Corrosion Using Electrochemical Impedance Spectroscopy

by Eleni Lamprou, Aikaterini Baxevani, Fani Stergioudi, Georgios Skordaris, Azarias Mavropoulos, Nikolaos Michailidis and Antonios Bouzakis

Coatings 2026, 16(8), 934; https://doi.org/10.3390/coatings16080934 - 5 Aug 2026

Abstract

This study investigates the time-dependent corrosion behavior of 6060 aluminum profiles subjected to three industrially relevant surface treatments: clear anodizing, black anodizing, and pre-anodizing followed by polyester powder coating during 30 days of immersion in NaCl solution. Electrochemical Impedance Spectroscopy combined with equivalent [...] Read more.

This study investigates the time-dependent corrosion behavior of 6060 aluminum profiles subjected to three industrially relevant surface treatments: clear anodizing, black anodizing, and pre-anodizing followed by polyester powder coating during 30 days of immersion in NaCl solution. Electrochemical Impedance Spectroscopy combined with equivalent electrical circuit modeling was used to monitor corrosion evolution and identify the governing degradation mechanisms. Black-anodized specimens exhibited the highest initial corrosion resistance during the first 4 days of immersion, while clear-anodized specimens provided superior protection between 7 and 15 days due to the formation of a more protective inner oxide layer. Both anodized systems showed evidence of repassivation during prolonged exposure through corrosion product accumulation within the porous oxide structure. The pre-anodized/powder-coated system delayed corrosion initiation beyond 15 days, demonstrating the highest long-term barrier performance. Dynamic perpendicular impact loading after corrosion exposure revealed significant differences in mechanical durability: clear-anodized specimens maintained coating integrity up to 15 days, whereas black-anodized specimens experienced complete coating removal, associated with corrosion-induced microcracks and void formation observed by SEM. Overall, clear anodizing provided the best balance between corrosion resistance and post-corrosion mechanical durability, while the pre-anodized/powder-coated system offered the greatest long-term corrosion protection, demonstrating that the optimum surface treatment depends on the intended service conditions. Full article

(This article belongs to the Collection Feature Papers Collection in 'Surface Characterization, Deposition and Modification')

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18 pages, 16856 KB

Open AccessArticle

Deterioration Mechanism and Constitutive Model of BFRC Corroded by Acid Rain

by Xinzhong Wang, Linshu Li, Mei Wei, Yi Xiang, Zhengyi He and Eguo Xiao

Coatings 2026, 16(8), 933; https://doi.org/10.3390/coatings16080933 - 5 Aug 2026

Abstract

To elucidate the long-term degradation mechanism of basalt-fiber-reinforced concrete (BFRC) subjected to acid rain corrosion, this study conducted mechanical tests on BFRC specimens with a fiber content of 0.15% under simulated acid rain (pH = 3.0) over 0–120 corrosion cycles. Results reveal a [...] Read more.

To elucidate the long-term degradation mechanism of basalt-fiber-reinforced concrete (BFRC) subjected to acid rain corrosion, this study conducted mechanical tests on BFRC specimens with a fiber content of 0.15% under simulated acid rain (pH = 3.0) over 0–120 corrosion cycles. Results reveal a nonlinear evolution in both compressive and splitting tensile strengths—an initial decrease, subsequent increase, and final gradual decline—with peak values attained at 60 and 30 cycles, respectively, corresponding to maximum enhancements of 20% and 45% relative to the initial strength. Microstructural analyses (SEM-EDS) identify a three-phase deterioration process: chemical dissolution (surface decalcification), competitive pore filling coupled with C-S-H decalcification, and expansive cracking induced by ettringite formation. Integrating the experimental data and degradation mechanisms with maturity theory, a dynamic constitutive model incorporating corrosion cycles is developed. The model accurately predicts the time-dependent mechanical degradation of BFRC under acid rain exposure, providing a theoretical foundation for durability design and assessment of fiber-reinforced concrete in corrosive environments. Full article

(This article belongs to the Section Architectural and Infrastructure Coatings)

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21 pages, 3413 KB

Open AccessArticle

Formation of Single-Phase Ti–Au Intermetallic Coatings via Au Deposition and Annealing-Induced Diffusion: Microstructure and Electrochemical Performance

by Baoshuai Du, Zhicheng Yan, Wenjing Li, Guoqing Zhao, Haiyun Xu, Min Zhang, Wei Feng and Xubin Li

Coatings 2026, 16(8), 932; https://doi.org/10.3390/coatings16080932 - 4 Aug 2026

Abstract

Ti–Au intermetallic compound (IMC) coatings have attracted considerable interest for biomedical devices and corrosion-protective surfaces owing to their excellent corrosion resistance, hardness, and biocompatibility. Although magnetron sputtering is widely used for high-performance functional coatings, conventional co-sputtering strategies tend to induce undesired secondary-phase formation [...] Read more.

Ti–Au intermetallic compound (IMC) coatings have attracted considerable interest for biomedical devices and corrosion-protective surfaces owing to their excellent corrosion resistance, hardness, and biocompatibility. Although magnetron sputtering is widely used for high-performance functional coatings, conventional co-sputtering strategies tend to induce undesired secondary-phase formation in Ti–Au coatings, impairing phase stability and coating performance. In this work, Ti–Au IMC coatings were fabricated through a sequential Au-deposition/diffusion-annealing route, and the effects of annealing temperature and holding time on phase formation, phase selection, and microstructural evolution were systematically examined. Diffusion annealing produced a bilayered coating, with Ti₃Au preferentially formed in the inner layer, while the outer layer evolved successively from TiAu₂ to TiAu and then to Ti₃Au as diffusion proceeded. Under sufficient diffusion conditions, the coating was converted into a single-phase Ti₃Au intermetallic layer. Despite the limited durability of Ti–Au IMC coatings under the harsh PEMFC environment, electrochemical measurements in corrosive human body environments confirmed the corrosion resistance of the Ti–Au IMC coatings. The diffusion-mediated route via magnetron sputtering with annealing offers a practical means of tailoring Ti–Au IMC coatings for corrosion-stable biomedical and protective applications. Full article

(This article belongs to the Section High-Energy Beam Surface Engineering and Coatings)

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15 pages, 4549 KB

Open AccessArticle

A Comparative Study of Machine Learning Algorithms for Measuring Thin-Film Thickness Using Terahertz Time-Domain Waves Simulated by the Finite Difference Time Domain Method

by Pingan Liu, Xiangjun Li, Yibing Liu and Liguo Zhu

Coatings 2026, 16(8), 931; https://doi.org/10.3390/coatings16080931 - 4 Aug 2026

Abstract

Terahertz (THz) waves offer unique advantages, including non-contact operation, high penetration capability, and high resolution, making them particularly well-suited for the non-destructive thickness measurement of film-structured materials. In reflective terahertz time-domain spectroscopy (THz-TDS), thickness measurement approaches are generally classified into three categories: optimization-based [...] Read more.

Terahertz (THz) waves offer unique advantages, including non-contact operation, high penetration capability, and high resolution, making them particularly well-suited for the non-destructive thickness measurement of film-structured materials. In reflective terahertz time-domain spectroscopy (THz-TDS), thickness measurement approaches are generally classified into three categories: optimization-based methods that rely on theoretical models, time-of-flight (ToF), and machine learning. Model-based optimization techniques require precise knowledge of the optical parameters and structural configuration of each layer; however, they often suffer from slow convergence and are prone to becoming trapped in local optima. In contrast, ToF-based methods determine thickness by calculating the time delay between echo pulses reflected from different interfaces, yet their applicability is limited when the film thickness is extremely small. Machine learning, especially deep learning, enables the establishment of a direct, data-driven mapping between THz waveforms (or their extracted features) and the target thickness. Such approaches offer rapid inference, strong robustness to noise, and good adaptability to thin or structurally complex films, although their accuracy remains dependent on the quality of training data and the generalization capability of the model. In this study, high-fidelity THz waveform data generated via finite-difference time-domain (FDTD) simulations are utilized to conduct a comparative investigation into the film thickness prediction performance of several representative machine learning algorithms, including Back Propagation (BP) neural networks, Support Vector Machines (SVM), Random Forests (RF), Extreme Learning Machines (ELM), K-Nearest Neighbors (KNN), and Partial Least Squares (PLS) regression. The results indicate that, in terms of prediction error, the overall ranking of algorithmic performance from best to worst is: PLS > RF > SVM > BP > ELM > KNN. These findings provide valuable guidance for the future application of machine learning-assisted THz-TDS in precise film thickness measurement. Full article

(This article belongs to the Section Thin Films)

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47 pages, 6541 KB

Open AccessArticle

Electrochemical Impedance Spectroscopy and Equivalent Circuit Modeling of Low-Impedance Lithium-Ion Battery Cells for Electric Vehicles

by Siyuan Wang, Masoud Rostami Angas, Vidyu Challa, Cing-Dao Kan and Leyu Wang

Coatings 2026, 16(8), 930; https://doi.org/10.3390/coatings16080930 - 4 Aug 2026

Abstract

Accurate electrochemical impedance spectroscopy (EIS) characterization of low-impedance (<1 mΩ) lithium-ion battery cells used in electric vehicles is challenging because resistance and inductance in the measurement pathway can be comparable to the intrinsic cell impedance. This study investigates an EV-grade, large-format commercial lithium-ion [...] Read more.

Accurate electrochemical impedance spectroscopy (EIS) characterization of low-impedance (<1 mΩ) lithium-ion battery cells used in electric vehicles is challenging because resistance and inductance in the measurement pathway can be comparable to the intrinsic cell impedance. This study investigates an EV-grade, large-format commercial lithium-ion pouch cell using a four-terminal EIS configuration and a custom connection fixture designed to maintain low and consistent contact resistance and reduce measurement-pathway effects. The EIS measurements shows good repeatability, and their linearity was confirmed using the Kramers–Kronig validity test. Impedance spectra acquired under selected state-of-charge (SOC) and temperature conditions were interpreted using an equivalent circuit model comprising an effective series inductance, an ohmic resistance, a constant phase element, a charge-transfer resistance, and a generalized Warburg element. Bayesian optimization followed by Nelder–Mead refinement was applied for parameter identification. The selected model represents the measured inductive, interfacial, and diffusion-related features as effective lumped responses rather than as a unique mechanistic decomposition. Across the SOC conditions investigated, the fitted ohmic resistance and charge-transfer resistance generally decreased as the temperature increased from 25 °C to 40 °C. By reducing the measurement errors related to the connection method rather than relying solely on instrument-side accuracy improvements, this work provides a practical approach for EIS measurements of milliohm-scale battery cells. These results establish a foundation for future temperature-compensated impedance diagnostics and further investigation of interfacial and transport behavior in EV battery cells. Full article

(This article belongs to the Special Issue Emerging Materials and Surface Chemistry for High-Efficiency Energy Storage and Conversion)

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16 pages, 14594 KB

Open AccessArticle

Pitting Corrosion Resistance of LDED-Manufactured IN625-YSZ Coatings Exposed to Sulfide-Containing NaCl Solution

by Yonghua Yu, Yujing Gan, Xiangdong Ma, Li Yi, Jian Zhang, Jian Zhang and Ruifeng Li

Coatings 2026, 16(8), 929; https://doi.org/10.3390/coatings16080929 - 4 Aug 2026

Abstract

Pitting corrosion is a more insidious and dangerous failure mode than uniform corrosion for protective coatings in marine environments, especially when sulfide ions (S²⁻) are present. In this work, Inconel 625 (IN625) and IN625-5 wt.% yttria-stabilized zirconia (YSZ) composite coatings were [...] Read more.

Pitting corrosion is a more insidious and dangerous failure mode than uniform corrosion for protective coatings in marine environments, especially when sulfide ions (S²⁻) are present. In this work, Inconel 625 (IN625) and IN625-5 wt.% yttria-stabilized zirconia (YSZ) composite coatings were fabricated on 20G steel by laser-directed energy deposition (LDED) using optimized parameters. The coatings exhibit dense microstructures, with porosities of 1.87% ± 0.10% and 1.67% ± 0.10%, respectively. The pitting resistance was systematically evaluated by cyclic potentiodynamic polarization (CPP) and electrochemical impedance spectroscopy (EIS) in 3.5 wt.% NaCl solution without and with 20 ppm Na₂S. The CPP results show that the addition of YSZ decreases the pitting potential (E_pit) and protection potential (E_prot), indicating reduced resistance to pit initiation, while the smaller hysteresis loop suggests an improved tendency for repassivation. S²⁻ induces a notable drop in E_prot and impairs repassivation for both coatings, yet the IN625-YSZ coating retains a slightly higher E_prot than IN625. EIS analysis reveals that the IN625-YSZ coating in S²⁻-containing solution shows an increased R_ct of 2.738 × 10⁵ Ω·cm² compared with its counterpart in 3.5 wt.% NaCl solution, while the corresponding R_L decreases to 2.513 Ω·cm², suggesting a weakened outer barrier layer despite partial interfacial blocking. Post-corrosion morphology shows that YSZ particles act as preferential pitting nucleation sites; in sulfide-free solution they produce numerous shallow pits, whereas in S²⁻-containing solution they lead to larger and deeper pits. The results may provide a reference for the future design and evaluation of LDED-manufactured composite coatings under sulfide-containing marine environments. Full article

(This article belongs to the Special Issue Coating Innovations in Energy-Assisted Deposition)

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25 pages, 7206 KB

Open AccessArticle

Optimization of Back Surface Field Layers for High-Performance CZTSe Ultrathin-Film Solar Cells Using SCAPS-1D Simulations

by Serap Yiğit Gezgin, Zeynep Kişnişci and Hamdi Şükür Kiliç

Coatings 2026, 16(8), 928; https://doi.org/10.3390/coatings16080928 - 3 Aug 2026

Abstract

This study explores the performance of an ultrathin Cu₂ZnSnSe₄ (CZTSe) absorber-based solar cell using numerical simulations carried out with SCAPS-1D software (version 3.8). Ultrathin absorber layers, generally thinner than 500 nm, are attractive because they require less material, reduce manufacturing [...] Read more.

This study explores the performance of an ultrathin Cu₂ZnSnSe₄ (CZTSe) absorber-based solar cell using numerical simulations carried out with SCAPS-1D software (version 3.8). Ultrathin absorber layers, generally thinner than 500 nm, are attractive because they require less material, reduce manufacturing costs, and can improve carrier collection due to the shorter distance that charge carriers must travel. However, when the absorber layer becomes very thin, it cannot absorb enough photons, which may limit the overall device performance. To overcome this challenge, the use of back surface field (BSF) layers is examined as a practical approach to improve photovoltaic efficiency. In this work, a solar cell structure composed of Carbon/BSF/CZTSe/CdS/i-ZnO/ITO was designed and simulated, with the thickness of the CZTSe absorber layer kept constant at 85 nm. Three different p⁺-type BSF materials, V₂O₅, Sb₂S₃, and CuSCN, were studied to understand how they influence device behavior. Important parameters such as electron affinity, interface defect density, acceptor defect density in the absorber layer, recombination processes, back contact properties, and operating temperature were systematically investigated. The addition of BSF layers forms a strong electric field at the p⁺–p interface, which helps push minority carriers toward the depletion region and reduces recombination losses at the back contact. The simulation results show that selecting a suitable BSF material can significantly enhance charge carrier collection and improve the efficiency of ultrathin CZTSe solar cells, offering useful guidance for designing more efficient thin-film photovoltaic devices. Full article

(This article belongs to the Special Issue Multilayer Thin Films: Fabrication and Interface Engineering)

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17 pages, 2150 KB

Open AccessArticle

Study on Microstructure and Wear Resistance Service Characteristics of AlCrN-Coated Relay Injection Mold

by Rongchuan Lin, Rongyi Fu, Yipin Wang, Zhihao Chen, Ke Li, Pengcheng Wang, Sheng Lin, Qingmin Huang and Shasha Wei

Coatings 2026, 16(8), 927; https://doi.org/10.3390/coatings16080927 - 3 Aug 2026

Abstract

To address the problem of the short service life of relay injection molds caused by erosion of high-temperature glass fibers, AlCrN coatings were deposited on the surface of ELMAX mold steel using multi-arc ion plating technology. The surface morphology, cross-sectional morphology, and elemental [...] Read more.

To address the problem of the short service life of relay injection molds caused by erosion of high-temperature glass fibers, AlCrN coatings were deposited on the surface of ELMAX mold steel using multi-arc ion plating technology. The surface morphology, cross-sectional morphology, and elemental composition of the coatings were analyzed using scanning electron microscopy (SEM) and the attached energy-dispersive X-ray spectroscopy (EDS). The phase structure was characterized by X-ray diffraction (XRD). The surface hardness, film–substrate adhesion strength, and friction and wear performance were tested using a nanoindenter, a scratch tester, and a friction and wear tester, respectively. The effects of duty cycle, arc current, and negative bias voltage on the coating microstructure, hardness, adhesion strength, and friction and wear performance were systematically investigated. Increasing the duty cycle increases surface particles and pits but improves coating density; increasing the arc current increases coating thickness but coarsens particles; increasing the negative bias voltage refines particles but increases pits. Through a three-factor, three-level orthogonal experiment and a multi-index equal-weight weighting method, with hardness, adhesion strength, and friction coefficient as comprehensive evaluation objectives, the optimal process parameters were determined as a duty cycle of 70%, an arc current of 60 A, and a negative bias voltage of 110 V. The optimized coating achieved a hardness of 36.04 GPa (399% higher than that of the uncoated substrate), an adhesion strength of 143.87 N, and a friction coefficient of 0.422. In production cycle tests, the coated mold exhibited an average service life of 128,070 cycles, which is 277% higher than that of the uncoated mold (33,985 cycles). The surface of the coated mold showed only slight scratches, while the uncoated mold exhibited severe glass-fiber plowing grooves. This study provides a process optimization and verification solution for extending the service life of injection molds. Full article

(This article belongs to the Section Corrosion, Wear and Erosion)

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20 pages, 5621 KB

Open AccessArticle

Pulse-Reverse Electrodeposition of Thin Au Coatings on Ni-Coated Brass: Effects of Pulse Parameters on Microstructure and Corrosion Behavior

by Xinyu Ouyang, Fangxiang Song, Yuejun Shen and Huajiang Luo

Coatings 2026, 16(8), 926; https://doi.org/10.3390/coatings16080926 - 3 Aug 2026

Abstract

Pulse-reverse electrodeposition was investigated as a route to reduce Au consumption while maintaining coating continuity and corrosion performance in thin Ni/Au finishes. A pulse-plated Ni barrier layer with an average thickness of approximately 4.45 μm was first prepared on brass, followed by Au [...] Read more.

Pulse-reverse electrodeposition was investigated as a route to reduce Au consumption while maintaining coating continuity and corrosion performance in thin Ni/Au finishes. A pulse-plated Ni barrier layer with an average thickness of approximately 4.45 μm was first prepared on brass, followed by Au deposition from a potassium dicyanoaurate-based electrolyte containing a cobalt additive. Pulse frequency, duty cycle, forward current density, and reverse current density were evaluated with respect to Au thickness, surface morphology, corrosion potential, roughness, and electrochemical impedance. The processing window was selected hierarchically by requiring an Au thickness of 0.3–0.6 μm, a relatively noble corrosion potential, a compact surface with few visible defects, low roughness, and a consistent impedance response; charge-transfer resistance was not treated as the sole criterion. Within the present bath, substrate, electrode geometry, and power-supply configuration, 800 Hz, 22% duty cycle, 0.11 A·dm⁻² forward current density, and −0.004 A·dm⁻² reverse current density provided the most balanced overall response. Full article

(This article belongs to the Special Issue Advanced Surface Modification and Protective Coatings for Durable Structural Materials and Engineering Structures)

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19 pages, 3557 KB

Open AccessArticle

The Effect of Electrolyte Composition on the Corrosion Protection Performance of PANI and PANI/CeO₂ Composite Coatings

by Lin Zhang, Haoyao Zhou, Yu Chen, Zhongnian Yang and Lu Zhang

Coatings 2026, 16(8), 925; https://doi.org/10.3390/coatings16080925 - 3 Aug 2026

Abstract

The electrolytic composition plays an important role in the structure and corrosion protection performance of electro-polymerized coating. In the present work, oxalic acid, hydrochloric acid, sulfuric acid, phosphoric acid and benzoic acid were utilized as electrodeposition electrolytes to prepare a PANI coating. The [...] Read more.

The electrolytic composition plays an important role in the structure and corrosion protection performance of electro-polymerized coating. In the present work, oxalic acid, hydrochloric acid, sulfuric acid, phosphoric acid and benzoic acid were utilized as electrodeposition electrolytes to prepare a PANI coating. The PANI coating deposited in benzoic acid showed a compact and uniform structure with an adhesion grade of 0. Electrochemical tests revealed that the benzoic acid-doped PANI coating exhibited the smallest value of corrosion current density of 2.571 μA·cm⁻² and the largest inhibition efficiency of 92.6% among the investigated acidic electrolytes. Moreover, the influence of co-electrodeposition conditions, including cerium nitrate concentration, ammonium acetate concentration and electrolyte pH value on the corrosion protection performance of co-electrodeposited PANI/CeO₂ was investigated and the optimal co-electrodeposition condition was found to be 0.3 mol/L aniline, 0.04 mol/L benzoic acid, 0.10 mol/L cerium nitrate, 0.10 mol/L ammonium acetate and pH of 5.5, under which condition the corrosion current density was decreased to 0.199 μA·cm⁻² and the inhibition efficiency reached 99.4%. Full article

(This article belongs to the Special Issue Tribological Behavior and Corrosion Resistance Characterization of Advanced Materials and Coatings)

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1 pages, 126 KB

Open AccessCorrection

Correction: Tao et al. Simulated Performance of a Broadband Solar Absorber Composed of Sectioned Au Disk Structures and ZnS/Au Thin Layers. Coatings 2022, 12, 1863

by Gang Tao, Yingting Yi, Mengxuan Zang, Zhipeng Zheng and Yougen Yi

Coatings 2026, 16(8), 924; https://doi.org/10.3390/coatings16080924 - 3 Aug 2026

Abstract

In the original publication [...] Full article

26 pages, 17893 KB

Open AccessArticle

Study on the Surface Enhancement Enrichment Mechanism of Fe₃O₄-PDA-Au-GO Substrate for Phenanthrene Detection

by Junyu Liu, Pengshuai Li, Wencan Cui, Keyu Lin, Hao Yan, Shihua Sang, Liang Guan and Kecheng Gu

Coatings 2026, 16(8), 923; https://doi.org/10.3390/coatings16080923 - 3 Aug 2026

Abstract

In our prior research (2022), a Fe₃O₄@PDA@Au@GO composite was reported as a surface-enhanced Raman scattering (SERS) substrate for phenanthrene detection, with a detection limit of 10⁻⁷ g/L. The current study is a mechanistic follow-up investigation, which aims to [...] Read more.

In our prior research (2022), a Fe₃O₄@PDA@Au@GO composite was reported as a surface-enhanced Raman scattering (SERS) substrate for phenanthrene detection, with a detection limit of 10⁻⁷ g/L. The current study is a mechanistic follow-up investigation, which aims to explore the enhancement and enrichment mechanisms of the same substrate. By integrating density functional theory (DFT) calculations, adsorption experiments, and spectroscopic analyses (Raman, FTIR, XPS) before and after adsorption, the surface enhancement mechanism of the Fe₃O₄-PDA-Au-GO composite substrate is investigated. Our findings suggest that Fe₃O₄ enables efficient magnetic separation. The polydopamine (PDA) modification layer appears to enhance the uniformity and stability of the substrate surface, which is beneficial for uniform loading of Au nanoparticles (Au NPs). Graphene oxide (GO) and PDA are found to contribute to the effective enrichment of phenanthrene. Au NPs (mostly in the metallic Au⁰ state) may provide electromagnetic enhancement through localized surface plasmon resonance, and may also contribute to chemical enhancement through possible interactions with phenanthrene. Overall, the stepwise comparison presented in this study is consistent with the proposed roles of Au and GO in enhancing the SERS performance, which collectively improve the detection sensitivity. Full article

(This article belongs to the Section Surface Characterization, Deposition and Modification)

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