Search Results (192)

This study provides an investigation into the influence of surface roughness, porosity, and chemistry on the wettability and infiltration behavior of calcia-magnesia-alumino-silicates (CMASs) in thermal and environmental barrier coatings (T/EBCs) used in high-temperature gas turbine engines. High-temperature contact angle measurements were performed at 1260 °C on 7 wt.% yttria-stabilized zirconia (7YSZ) and yttrium ytterbium disilicate (YYbDS, (Y_1/2Yb_1/2)₂Si₂O₇) to evaluate the interaction of CMASs with different surface finishes and coating microstructures. The findings demonstrate that porosity plays a dominant role in determining CMAS infiltration dynamics. In YYbDS, increasing porosity from 6.3% to 22.7% facilitated the formation of an apatite layer that limited CMAS penetration to approximately 2 µm. Surface roughness exhibited a subtler influence in that reducing Sa from 0.61 µm to 0.05 µm increased the change in the contact angle by ~2°, although its impact was found to be less significant compared to porosity and reactive chemistry. These results indicate that an integrated approach that optimizes porosity, chemistry, and surface morphology can significantly enhance CMAS resistance. The study emphasizes that leveraging both microstructural and chemical properties is critical to developing coatings capable of withstanding the harsh conditions encountered in aerospace environments. Full article

Hybrid silane-based coatings were developed via the sol–gel process using two precursors, vinyltrimethoxysilane (VTMS) and tetraethoxysilane (TEOS), and subsequently deposited onto three titanium-based substrates: commercially pure titanium Grade 2, Ti6Al4V, and Ti13Nb13Zr. Comprehensive physicochemical characterization was performed, including microstructural (optical and SEM), topographical (3D roughness), spectroscopic (FTIR), and electrochemical (potentiodynamic) analyses. The coatings were continuous, transparent, smooth, and exhibited high gloss with no visible cracks or surface defects. Surface roughness (Sa ≈ 0.3 μm) was consistent across all samples and remained unaffected by both the VTMS to TEOS ratio and the substrate type. Coating thickness ranged from 8 to 15 μm, as confirmed by both digital microscopy and thickness gauge measurements. All coatings demonstrated strong adhesion to the substrates. FTIR analysis confirmed the presence of key functional groups, such as CH₂, C=C, C–H, Si–O–Si, Si–OH, Si–O–Ti, CH=CH₂, and O–Si–O, regardless of the substrate type. Electrochemical tests in Ringer’s solution showed excellent corrosion resistance, particularly for coatings with a VTMS to TEOS ratio of 1:1. Post-corrosion imaging confirmed the integrity of the coatings and their effectiveness as protective barriers in simulated physiological environments. These findings support the potential of VTMS/TEOS sol–gel coating as a surface modification strategy for biomedical titanium implants. Full article

Modern industrial systems and biomass-fired furnaces require surface treatments that can withstand aggressive chemical, thermal, and corrosive environments. This study investigates the corrosion and thermal resistance of plasma-sprayed Al₂O₃-TiO₂ coatings produced using a DC air–hydrogen plasma spray process. Coatings of compositions of Al₂O₃, Al₂O₃-3 wt.% TiO₂, Al₂O₃-13 wt.% TiO₂, and Al₂O₃-40 wt.% TiO₂ were deposited on steel substrates with a Ni/Cr bond layer by plasma spraying. The coatings were characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD) to evaluate their morphology, elemental composition, and crystalline phases. Electrochemical tests were performed in a naturally aerated 0.5 mol/L NaCl solution and cyclic thermal–chemical exposure tests (500 °C using 35% KCl) to assess their corrosion kinetics and thermal stability. The results indicate that pure Al₂O₃ and low TiO₂ (3 wt.%) coatings exhibit fine barrier properties, while coatings with a higher TiO₂ content develop additional phases (e.g., Ti₃O₅, Al₂TiO₅) that improve thermal resistance but reduce chemical durability. Full article

Thermally grown oxide (TGO) layers—primarily alumina (Al₂O₃)—provide oxidation resistance and high-temperature protection for thermal barrier coatings. However, during their service in humid and hot environments, water vapor accelerates TGO degradation by stabilizing metastable alumina phases (e.g., θ-Al₂O₃) and inhibiting their transformation to the thermodynamically stable α-Al₂O₃, a phenomenon which has been shown in numerous experimental studies. However, the microscopic mechanisms by which water vapor affects the phase stability and transformation of alumina remain unresolved. This study employs first-principles calculations to investigate hydrogen’s role in altering vacancy formation, aggregation, and atomic migration in θ- and α-Al₂O₃. The results reveal that hydrogen incorporation reduces the formation energies for aluminum and oxygen vacancies by up to 40%, promoting defect generation and clustering; increases aluminum migration barriers by 25–30% while lowering oxygen migration barriers by 15–20%, creating asymmetric diffusion kinetics; and stabilizes oxygen-deficient sublattices, disrupting the structural reorganization required for θ- to α-Al₂O₃ transitions. These effects collectively sustain metastable θ-Al₂O₃ growth and delay phase stabilization. By linking hydrogen-induced defect dynamics to macroscopic coating degradation, this work provides atomic-scale insights for designing moisture-resistant thermal barrier coatings through the targeted inhibition of vacancy-mediated pathways. Full article

The development of self-healing coatings represents a promising approach to enhance the durability of metal substrates exposed to corrosive environments, demanding thorough in situ investigations. In this study, poly(urea–formaldehyde–melamine) (PUF) microcapsules containing linseed oil (LO) were synthesized via in situ polymerization to act as healing agents in protective coatings. The microcapsules were characterized using scanning electron microscopy (SEM), optical microscopy (OM), Fourier-transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA). The capsules exhibited a regular spherical morphology with an average diameter of 96 µm and an LO encapsulation efficiency of 81 wt%. TGA confirmed their thermal stability up to 200 °C, while FTIR verified the successful encapsulation of LO. For performance evaluation, 10 wt% of the microcapsules was incorporated into an epoxy matrix and applied to carbon steel. Corrosion resistance was evaluated using electrochemical impedance spectroscopy (EIS) in 0.1 mol/L of NaCl solution over 500 h. The coating with microcapsules exhibited a |Z|_0.01 of 10⁶ Ω·cm², higher than the 10⁴ Ω·cm² observed for the coating without microcapsules, indicating improved barrier properties. Raman spectroscopy confirmed the auto-oxidation of LO at damaged areas, evidencing the self-healing mechanism. Although full barrier recovery was not achieved, the system effectively delayed corrosion progression. Full article

Concrete coating technology is a key measure that enhances the durability of concrete structures. This paper systematically studies the performance, applicability, and impact of different types of anti-corrosion coatings on concrete durability, focusing on their resistance to chloride ion penetration, freeze–thaw cycles, carbonation, and sulfate corrosion. The applicability of existing testing methods and standard systems is also evaluated. This study shows that surface-film-forming coatings can create a dense barrier, reducing chloride ion diffusion coefficients by more than 50%, making them suitable for humid and high-chloride environments. Pore-sealing coatings fill capillary pores, improving the concrete’s impermeability and making them ideal for highly corrosive environments. Penetrating hydrophobic coatings form a water-repellent layer, reducing water absorption by over 75%, which is particularly beneficial for coastal and underwater concrete structures. Additionally, composite coating technology is becoming a key approach to addressing multi-environment adaptability challenges. Experimental results have indicated that combining penetrating hydrophobic coatings with surface-film-forming coatings can enhance concrete’s resistance to chloride ion penetration while ensuring weather resistance and wear resistance. However, this study also reveals that there are several challenges in the standardization, engineering application, and long-term performance assessment of coating technology. The lack of globally unified testing standards leads to difficulties in comparing the results obtained from different test methods, affecting the practical application of these coatings in engineering. Moreover, construction quality control and long-term service performance monitoring remain weak points in their use in engineering applications. Some engineering case studies indicate that coating failures are often related to an insufficient coating thickness, improper interface treatment, or lack of maintenance. To further improve the effectiveness and long-term durability of coatings, future research should focus on the following aspects: (1) developing intelligent coating materials with self-healing, high-temperature resistance, and chemical corrosion resistance capabilities; (2) optimizing multilayer composite coating system designs to enhance the synergistic protective capabilities of different coatings; and (3) promoting the creation of global concrete coating testing standards and establishing adaptability testing methods for various environments. This study provides theoretical support for the optimization and standardization of concrete coating technology, contributing to the durability and long-term service safety of infrastructure. Full article

Rare-earth tantalates (RETaO₄) are considered as a type of emerging thermal barrier coating materials applied to the hot components of gas turbines and aerospace engines due to their excellent thermal stability, high-temperature fracture toughness, corrosion resistance and extremely low thermal conductivity. However, the relatively low hardness and thermal expansion coefficients may limit their service lifetime in a harsh engine environment. To address the current limitation of rare-earth tantalates and further optimize the mechanical and thermal properties, the defective fluorite-structured Y₂Zr₂O₇ (YZ) was introduced as a second phase into the YTaO₄ (YT) matrix to form YT_1−x–YZ_x (x = 0, 0.25, 0.5, 0.75, 1) composite ceramics in this work. The mechanical and thermal properties of YT_1−x–YZ_x composite ceramics are significantly improved compared to pure-phase YTaO₄ ceramics. The Vickers hardness of YT_1−x–YZ_x (x = 0.25, 0.5, 0.75) composite ceramics is 9.1~11.3 GPa, which are 2~2.5 times higher than that of YTaO₄ (4.5 GPa). Among them, YT_0.75–YZ_0.25 exhibits a maximum fracture toughness (3.7 ± 0.5 MPa·m^1/2), achieving a 23% improvement compared to YTaO₄ (3.0 ± 0.23 MPa·m^1/2) and a 118% improvement compared to Y₂Zr₂O₇ (1.73 ± 0.28 MPa·m^1/2). The enhancement is attributed to the combined effect of the intrinsic strengthening of the second phase, as well as the residual stress and grain refinement caused by the introduction of a second phase. Additionally, the thermal expansion coefficients of YT_1−x–YZ_x composite ceramics at 1673 K range from 10.3 × 10⁻⁶ K⁻¹ to 11.0 × 10⁻⁶ K⁻¹, which is also higher than that of YTaO₄ (10.0 × 10⁻⁶ K⁻¹). Consequently, the superior mechanical and thermal properties indicate that YT–YZ composite ceramics possess promising application prospects for thermal barrier coatings. Full article

Thermal barrier coatings (TBCs) can be applied on the inner surface of the combustion chamber of internal combustion engines to reduce fuel consumption and pollution and also improve the fatigue life of their components. The purpose of the present work was to evaluate the corrosion resistance in an environment equivalent to the one generated by combustion gases for three types of TBCs—P1 from Cr₃C2-25(Ni20Cr), P2 from MgZrO₃-35NiCr and P3 from ZrO₂-5CaO—with all of them having a base coat from Al₂O₃-30(Ni20Al) powder. The coatings were deposited via atmospheric plasma spray (APS) on the intake/exhaust valves of a gasoline internal combustion engine, both before and after their use in operation (Dacia 1400 model, gasoline fuel, Dacia Company, Mioveni, Romania). The samples were studied from the electrochemical corrosion resistance point of view, and their morphology and structure were analyzed using SEM, EDS and XRD methods. After analyzing the results of the samples before and after testing them in operation, it was observed that the presence of the coatings improved the corrosion resistance of the material used for the production of the valves. Full article

Introduction. The rise of multidrug resistance in Gram-negative ESKAPE pathogens is a critical challenge for modern healthcare. Colistin (CT), a peptide antibiotic, remains a last-resort treatment for infections caused by these superbugs due to its potent activity against Gram-negative bacteria and the rarity of resistance. However, its clinical use is severely limited by high nephro- and neurotoxicity, low oral bioavailability, and other adverse effects. A promising strategy to improve the biopharmaceutical properties and safety profile of antibiotics is the development of biopolymer-based delivery systems, also known as nanoantibiotics. Objective. The aim of this study was to develop polyelectrolyte complexes (PECs) for the oral delivery of CT to overcome its major limitations, such as poor bioavailability and toxicity. Methods. PECs were formulated using chondroitin sulfate (CHS) and a cyanocobalamin–chitosan conjugate (CSB12). Vitamin B12 was incorporated as a targeting ligand to enhance intestinal permeability through receptor-mediated transport. The resulting complexes (CHS-CT-CSB12) were characterized for particle size, ζ-potential, encapsulation efficiency, and drug release profile under simulated gastrointestinal conditions (pH 1.6, 6.5, and 7.4). The antimicrobial activity of the encapsulated CT was evaluated in vitro against Pseudomonas aeruginosa. Results. The CHS-CT-CSB12 PECs exhibited a hydrodynamic diameter of 446 nm and a ζ-potential of +28.2 mV. The encapsulation efficiency of CT reached 100% at a drug loading of 200 µg/mg. In vitro release studies showed that approximately 70% of the drug was released within 1 h at pH 1.6 (simulating gastric conditions), while a cumulative CT release of 80% over 6 h was observed at pH 6.5 and 7.4 (simulating intestinal conditions). This release profile suggests the potential use of enteric-coated capsules or specific administration guidelines, such as taking the drug on an empty stomach with plenty of water. The antimicrobial activity of encapsulated CT against P. aeruginosa was comparable to that of the free drug, with a minimum inhibitory concentration of 1 µg/mL for both. The inclusion of vitamin B12 in the PECs significantly improved intestinal permeability, as evidenced by an apparent permeability coefficient (P_app) of 1.1 × 10⁻⁶ cm/s for CT. Discussion. The developed PECs offer several advantages over conventional CT formulations. The use of vitamin B12 as a targeting ligand enhances drug absorption across the intestinal barrier, potentially increasing oral bioavailability. In addition, the controlled release of CT in the intestinal environment reduces the risk of systemic toxicity, particularly nephro- and neurotoxicity. These findings highlight the potential of CHS-CT-CSB12 PECs as a nanotechnology-based platform for improving the delivery of CT and other challenging antibiotics. Conclusions. This study demonstrates the promising potential of CHS-CT-CSB12 PECs as an innovative oral delivery system for CT that addresses its major limitations and improves its therapeutic efficacy. Future work will focus on in vivo evaluation of the safety and efficacy of the system, as well as exploring its applicability for delivery of other antibiotics with similar challenges. Full article

Under high fluence and a high repetition rate, femtosecond laser drilling still produces defects due to heat accumulation. In order to suppress these defects, this study conducted research on water-assisted femtosecond laser drilling. This study focused on the impact of two different water-assisted methods, static-water-based and flowing-water-based approaches, on the quality of microholes made using layer-by-layer helical drilling with a femtosecond laser in thermal-barrier-coated superalloys. Furthermore, the effects of single-pulse laser energy on the hole entrance/exit diameter, taper angle, sidewall morphology, sidewall roughness, and sidewall oxygen content in the two water environments were compared and analyzed. Water-based-assisted laser drilling is an auxiliary method where the lower surface of the workpiece is placed in water while the upper surface remains in the air. On the other hand, the water flows horizontally in the flowing-water-based method. The experimental results demonstrate that both static- and flowing-water-based methods can significantly improve the quality of femtosecond laser drilling. Notably, the improvement effect was more pronounced with the flowing-water-based method. At a laser pulse energy of 50 μJ, the hole taper angle in the flowing-water environment was reduced by 38.80% compared with that in the air. With flowing-water-based assistance, the hole sidewall roughness was lower and the melt was less. Flowing water was better at carrying away the debris and heat generated by processing. The oxygen content of the hole sidewalls decreased significantly in both kinds of water-assisted environments. The experimental results provide a valuable reference for optimizing water-assisted femtosecond laser drilling. Full article

The Ni-Au coating with its inherent chemical stability is recognized as an effective method for boosting corrosion resistance in humid environments while preserving exceptional electrical conductivity. However, its anti-corrosion performance is affected by the structure characteristics of the coating due to the high corrosion potentials of Au and Ni. To enhance its protection properties, the deposition process parameters, including deposition time, deposition current density, and zincating times, were investigated. The morphology and structure of the coatings were characterized, while its anti-corrosion performance was assessed through electrochemical and accelerated salt-spray tests. Eventually, the elevated current density in the Ni-Au coating resulted in reduced grain size and improved surface morphology, ensuring superior anti-corrosion performance. Additionally, extending the Ni deposition time provided a second physical barrier for the dense and thick Ni layer to resist the invasion of corrosive media. Furthermore, grey theory was applied to predict the service life of the Ni-Au coating. This research provides valuable insights and constructive guidance for optimizing Ni-Au coating in various engineering applications. Full article

Healthcare-associated infections pose a significant global health challenge, negatively impacting patient outcomes and burdening healthcare systems. A major contributing factor to healthcare-associated infections is the formation of biofilms, structured microbial communities encased in a self-produced extracellular polymeric substance matrix. Biofilms are critical in disease etiology and antibiotic resistance, complicating treatment and infection control efforts. Their inherent resistance mechanisms enable them to withstand antibiotic therapies, leading to recurrent infections and increased morbidity. This review explores the development of biofilms and their dual roles in health and disease. It highlights the structural and protective functions of the EPS matrix, which shields microbial populations from immune responses and antimicrobial agents. Key molecular mechanisms of biofilm resistance, including restricted antibiotic penetration, persister cell dormancy, and genetic adaptations, are identified as significant barriers to effective management. Biofilms are implicated in various clinical contexts, including chronic wounds, medical device-associated infections, oral health complications, and surgical site infections. Their prevalence in hospital environments exacerbates infection control challenges and underscores the urgent need for innovative preventive and therapeutic strategies. This review evaluates cutting-edge approaches such as DNase-mediated biofilm disruption, RNAIII-inhibiting peptides, DNABII proteins, bacteriophage therapies, antimicrobial peptides, nanoparticle-based solutions, antimicrobial coatings, and antimicrobial lock therapies. It also examines critical challenges associated with biofilm-related healthcare-associated infections, including diagnostic difficulties, disinfectant resistance, and economic implications. This review emphasizes the need for a multidisciplinary approach and underscores the importance of understanding biofilm dynamics, their role in disease pathogenesis, and the advancements in therapeutic strategies to combat biofilm-associated infections effectively in clinical settings. These insights aim to enhance treatment outcomes and reduce the burden of biofilm-related diseases. Full article

The development of environmentally friendly materials is a subject of increasing interest in corrosion protection research. The objective of the present investigation is to propose the preparation procedure of chitosan–alginate (CHI/ALG) nanocontainers loaded with zinc oxide (ZnO) nanoparticles or combining ZnO nanoparticles with corrosion inhibitor caffeine (CAF), both suitable for incorporation into the matrix of ordinary zinc coatings on mild steel substrates. The nanocontainers were synthesized through spontaneous polysaccharide complexation in the presence of ZnO nanoparticles and CAF using a cross-linking agent, namely tripolyphosphate (TPP). Dynamic light scattering and laser Doppler velocimetry measurements are used for evaluation of the size distribution and zeta potentials of the nanocontainers, both loaded or unloaded with CAF. Using UV-spectroscopy, entrapment efficiency and release amounts of CAF are quantitatively evaluated. The nanocontainers thus obtained were incorporated into the matrices of ordinary zinc coatings via co-electrodeposition with zinc from zinc sulfate solution, aiming to improve the corrosion protection of steel in corrosive environments containing chloride ions. The surface morphology and elemental composition of the electrodeposited hybrid coatings before and after treating in the model corrosive medium of 3.5% NaCl is studied by scanning electron microscopy (SEM). The cyclic voltammetry method (CVA) is applied to characterize the cathodic (electrodeposition) and anodic (dissolution) processes. The protective characteristics of the hybrid coatings are investigated by application of potentiodynamic polarization (PDP) curves and polarization resistance (Rp) measurements after a time interval of 40 days. The obtained results indicate that both hybrid coating types could prolong the life time of mild steel in aggressive Cl⁻ ion-containing solution, combining the protection effect of sacrificial zinc with barrier (ZnO) and active (CAF) protective effects. Full article

In this paper, the ceramic coating of thermal barrier coatings (TBCs) was prepared on the surface of the tube specimens by Electron Beam Physical Vapor Deposition (EB-PVD) process. Subsequently, a service simulation was conducted using a simulation device to analyze the failure behavior of the TBCs. The effects of high-temperature sintering and CaO-MgO-Al₂O₃-SiO₂ (CMAS) corrosion on the microstructural evolution, phase structural changes, and insulation performance of the thermal barrier coatings were investigated. The results indicated that with increasing high-temperature sintering time, the “feather” structures at the boundaries of the columnar grains evolve into the “tentacle” structure that facilitates the fusion of adjacent columnar grains, resulting in increased grain diameter and wider gaps. No transformation from t’-ZrO₂ to the monoclinic phase m-ZrO₂ occurred during the high-temperature sintering process. Over time, CMAS wets the coating surface and infiltrates the interior of the coating, causing corrosion to the Yttria-stabilised zirconia (YSZ) and accelerating sintering. A new phase, ZrSiO₄, was formed after corrosion without inducing the transition. Full article

The development of corrosion mechanisms is a major issue that industrial experts are faced with while dealing with all phases of metal exploitation. Damage caused by corrosion affects the increase in both direct and indirect costs of manufacture. With adequate surface protection technology, it is possible to lessen the intensity of corrosion mechanisms’ development. In order for the selected surface protection technology to provide its full protective action, it is necessary to be familiar with its process parameters. This paper deals with a surface protection system that creates a barrier between the aggressive environment and the base material. The tested barrier was created on a base material surface by electrostatic powder spraying. In this experiment, three types of base material (carbon steel, aluminum and galvanized steel) were coated by applying different combinations of operating parameters. Operating parameters, i.e., the voltage and strength of the electric current, were taken as numerical input variables in the experiment. Each experiment design was focused on measuring the thickness of the protective layer. Analysis of the obtained results and statistical data processing confirmed that appropriate parameters (input variables) provided the target thickness of the protective coating on each of the tested materials. Optimization of parameters contributes to the efficiency of production, shortens the processing time and ensures that coating thickness stays within the limits defined either by the manufacturer or the end user. Full article