Coatings

29 pages, 2249 KB

Open AccessReview

TiO₂-Based Photocatalytic Self-Cleaning Coatings for Building Materials: Surface Mechanisms, Performance Metrics, and Outdoor Durability

by Yunzhang Li, Simeng Li, Zhenglin Han and Tao Ding

Coatings 2026, 16(9), 1061; https://doi.org/10.3390/coatings16091061 (registering DOI) - 6 Sep 2026

Abstract

Building facades and construction materials are continuously exposed to airborne particulate matter, organic pollutants, and microbial colonization, which cause progressive soiling, aesthetic degradation, and structural deterioration while imposing high maintenance and energy burdens. Photocatalytic titanium dioxide (TiO₂) has emerged as the [...] Read more.

Building facades and construction materials are continuously exposed to airborne particulate matter, organic pollutants, and microbial colonization, which cause progressive soiling, aesthetic degradation, and structural deterioration while imposing high maintenance and energy burdens. Photocatalytic titanium dioxide (TiO₂) has emerged as the most widely studied material for imparting self-cleaning functionality to building surfaces, owing to its ability to mineralize adsorbed contaminants under solar irradiation and to modulate surface wettability. This narrative review provides a structured account of TiO₂-based self-cleaning coatings for building materials, organized around three complementary themes: surface mechanisms, performance metrics, and outdoor durability. We first rationalize the two intertwined self-cleaning mechanisms—photocatalytic oxidative degradation and photoinduced superhydrophilicity—and their combination with physically repellent (superhydrophobic/superamphiphobic) wetting states. We then survey the principal coating-design strategies, including morphology and facet engineering, SiO₂-TiO₂ composites, metal/non-metal doping and heterojunction construction for visible-light activation, and dual-functional photocatalytic–superhydrophobic systems, and their integration into cementitious substrates, natural stone and cultural heritage, and transparent glass/photovoltaic surfaces. The quantitative metrics used to benchmark self-cleaning performance—water contact angle, dye photodegradation, NO_x and VOC abatement, and antimicrobial activity—are critically discussed together with the limitations of standardized laboratory tests. Finally, we analyze the weathering-induced deactivation pathways (photocatalyst leaching, surface contamination by soluble salts, and UV aging of organic matrices) and the emerging strategies for durable coatings, including inorganic binders, light-driven hydration, and defect- and heterojunction-engineered photocatalysts. The review concludes with an outlook on the open challenges that must be addressed to translate these coatings from laboratory demonstrations to long-lived, large-scale building applications. Full article

(This article belongs to the Section Thin Films)

19 pages, 9547 KB

Open AccessArticle

Microstructure and Properties of Piezoelectric Hydrophilic Bioactive Ceramic Coatings for Biomimetic Biomineralization

by Yukang Chang, Zixin Deng, Jian Xiao, Haotian Wu, Tao Chen, Defu Liu and Yi Xiong

Coatings 2026, 16(9), 1060; https://doi.org/10.3390/coatings16091060 (registering DOI) - 6 Sep 2026

Abstract

By introducing BaTiO₃ into conventional hydroxyapatite (HA) bioactive ceramic coatings, a novel HA/BaTiO₃ piezoelectric-hydrophilic bioactive ceramic coating was developed. In this research, four groups of composite coatings with BaTiO₃ contents of 0, 10, 20, and 30 wt.% were comparatively fabricated [...] Read more.

By introducing BaTiO₃ into conventional hydroxyapatite (HA) bioactive ceramic coatings, a novel HA/BaTiO₃ piezoelectric-hydrophilic bioactive ceramic coating was developed. In this research, four groups of composite coatings with BaTiO₃ contents of 0, 10, 20, and 30 wt.% were comparatively fabricated and investigated, which in situ constructs a bioelectric microenvironment on the titanium surface. This strategy achieves the effective integration of electrical stimulation with bioactive ceramic coatings, resulting in a piezoelectric-hydrophilic bioactive ceramic layer that mimics biomineralization-driven osteogenesis. Experimental results demonstrate that, through laser cladding, BaTiO₃ particles can be embedded within the piezoelectric-hydrophilic bioactive ceramic coating, endowing the coating with mechano-electrical conversion functionality. Microdomain piezoelectric responses were successfully generated on the coating surface, and based on the maximum local piezoelectric response, the optimal BaTiO₃ content was determined to be 20 wt.%, yielding a microdomain piezoelectric coefficient of 712.6 pm/V. Furthermore, the piezoelectric-hydrophilic bioactive ceramic coating exhibits excellent bioactivity. Electrostatic interactions between piezoelectric charges and inorganic ions in physiological fluids facilitate the adsorption of calcium and phosphorus salts onto the coating surface, thereby enhancing surface hydrophilicity. This promotes the infiltration of inorganic ions and water molecules at the material interface, which in turn strengthens bioactivity, accelerates bone integration, and expedites the establishment of a robust osseointegration interface between joint prostheses and host bone. Full article

(This article belongs to the Special Issue Advances in Functional Bio-Coatings: Emerging Materials and Advanced Deposition Technologies, 2nd Edition)

54 pages, 3334 KB

Open AccessReview

Mechanisms and Diagnostic Indicators of Biodeterioration in Mineral Coating–Substrate Systems: A Critical Review

by Elżbieta Stanaszek-Tomal

Coatings 2026, 16(9), 1059; https://doi.org/10.3390/coatings16091059 (registering DOI) - 6 Sep 2026

Abstract

Biodeterioration of mineral coating–substrate systems develops through interactions among microbial colonization, environmental exposure and the physicochemical properties of the coating, interface and substrate. Microbial presence, however, is still often taken as evidence of deterioration even when a causal link with material transformation or [...] Read more.

Biodeterioration of mineral coating–substrate systems develops through interactions among microbial colonization, environmental exposure and the physicochemical properties of the coating, interface and substrate. Microbial presence, however, is still often taken as evidence of deterioration even when a causal link with material transformation or loss of performance has not been demonstrated. This critical review examines mechanisms and diagnostic indicators relevant to cement-, lime-, gypsum-, silicate- and polymer-modified mineral coatings. It distinguishes between susceptibility, microbial colonization, biological activity, chemical and mineralogical transformation, microstructural and moisture-transport alteration, and mechanical or functional deterioration. Reported mechanisms include acidification, mineral dissolution, ion redistribution, secondary mineral precipitation, pore opening or filling, moisture redistribution, cracking, cohesion loss and interfacial deterioration. These responses can be non-monotonic and depend strongly on material composition and exposure conditions. Most material-response indicators have limited biological specificity, since similar changes may result from carbonation, salts, moisture, pollutants or aging. Reliable attribution depends on convergence between microbial activity and spatially corresponding material transformation, with plausible abiotic mechanisms considered at the same time. Five evidentiary categories are distinguished: susceptibility, microbial colonization, active microbial process, probable biodeterioration and confirmed biodeterioration. On the basis of current evidence, universal numerical severity thresholds are not justified. Full article

(This article belongs to the Special Issue Advanced Protective Coatings and Surface Modification for Civil Engineering Structures: Corrosion, Fire and Thermal Protection)

22 pages, 8446 KB

Open AccessArticle

Interpretable Machine Learning for Corrosion Fatigue Life Prediction of Q345C Steel with Scarce Experimental Data

by Yuan Xiong, Guiming Zhang, Qi Zhang, Zegang Song, Shuang Gong, Jin Xie and Guodong Wang

Coatings 2026, 16(9), 1058; https://doi.org/10.3390/coatings16091058 (registering DOI) - 6 Sep 2026

Abstract

Reliable fatigue life prediction for corroded bridge steel remains challenging. Severe surface damage, sparse tests, and heterogeneous literature data obscure the link between corrosion morphology, stress state, and fatigue resistance. In this study, electrochemical accelerated corrosion, three-dimensional laser scanning, tensile testing, axial fatigue [...] Read more.

Reliable fatigue life prediction for corroded bridge steel remains challenging. Severe surface damage, sparse tests, and heterogeneous literature data obscure the link between corrosion morphology, stress state, and fatigue resistance. In this study, electrochemical accelerated corrosion, three-dimensional laser scanning, tensile testing, axial fatigue testing, and scanning electron microscopy were combined with an interpretable machine learning framework for pre-corroded Q345C steel. A dimensionless feature-aligned support vector regression model was developed by normalizing stress amplitude with material strength, adding Gaussian noise regularization, and integrating multi-source corrosion fatigue data. For 27 experimental validation samples, the model achieved a coefficient of determination of 0.795 and a root mean square error of 0.146, with 26 samples falling within the predefined twofold error band. Shapley additive explanations identified mass loss ratio as the dominant predictor and showed a physically consistent negative effect of normalized stress amplitude on fatigue life. These results suggest that physically informed dimensionless feature alignment can improve small-sample corrosion fatigue prediction while retaining interpretable links to damage mechanisms. Full article

(This article belongs to the Special Issue Advances in Corrosion Protection and Corrosion Mechanisms of Steel)

14 pages, 23525 KB

Open AccessArticle

Influence of FDM-3D Printing Parameters on the Tensile Property and ILSS of CCF/PA and CF/PEEK Composites

by Peng Wang, Weimin Huang, Guijie Wang, Yulong Zhang, Ziyu Huang and Bin Zou

Coatings 2026, 16(9), 1057; https://doi.org/10.3390/coatings16091057 (registering DOI) - 6 Sep 2026

Abstract

The mechanical properties of continuous-fiber-reinforced composites in FDM-3D printing are significantly influenced by process parameters. However, research in this area is constrained by printing equipment, control software, and material preparation. This study examines how the tensile and interlaminar shear properties of CCF/PA and [...] Read more.

The mechanical properties of continuous-fiber-reinforced composites in FDM-3D printing are significantly influenced by process parameters. However, research in this area is constrained by printing equipment, control software, and material preparation. This study examines how the tensile and interlaminar shear properties of CCF/PA and CF/PEEK are affected by continuous-fiber nozzle temperature, platform temperature, and printing speed. Studies indicate that enhancing the nozzle temperature can notably improve mechanical properties by enhancing material flowability, ensuring consistent fiber encapsulation and reducing pore defects. Increasing the platform temperature initially boosts both tensile strength and ILSS, but, beyond a certain point, these properties decline. Inadequate platform temperature can result in uneven infiltration and diffusion among deposited CCF/PA paths, leading to void defects. Conversely, excessive platform temperature can cause semi-molten CCF/PA layers to be vulnerable to nozzle pressure and scraping, resulting in continuous-fiber debonding and interlayer tearing. Furthermore, lower printing speeds extend the melt wetting time between adjacent paths, promoting diffusion and adhesion for enhanced performance. Following an experimental investigation, the optimal parameters are identified as a nozzle temperature of 295 °C, a platform temperature of 240 °C, and a printing speed of 3 mm/s. This research provides valuable guidance for the practical production of continuous-fiber-reinforced composites using FDM-3D printing. Full article

(This article belongs to the Special Issue Exploring Wear and Friction Mechanisms in Tribological Coatings and Surface Textures)

► Show Figures

Figure 1

48 pages, 24154 KB

Open AccessReview

The Role and Impact of Coated Bearings in Wind Turbines: A Review

by Esteban Broitman

Coatings 2026, 16(9), 1056; https://doi.org/10.3390/coatings16091056 (registering DOI) - 5 Sep 2026

Abstract

Rolling bearings in modern wind turbines operate under demanding tribological conditions that include high contact stresses, mixed lubrication, transient loads, electrical discharge, corrosion, and hydrogen-assisted damage. These factors contribute to premature failures such as micropitting, scuffing, white etching cracks (WECs), and electrical fluting, [...] Read more.

Rolling bearings in modern wind turbines operate under demanding tribological conditions that include high contact stresses, mixed lubrication, transient loads, electrical discharge, corrosion, and hydrogen-assisted damage. These factors contribute to premature failures such as micropitting, scuffing, white etching cracks (WECs), and electrical fluting, which remain major reliability challenges in both onshore and offshore turbines. Surface-engineering technologies have emerged as effective tools to mitigate these failure modes. Carbon-based coatings improve sliding performance and reduce wear under boundary-lubricated conditions; black oxide conversion layers enhance the corrosion resistance, lubricant retention, and early-life running-in behavior; and insulating ceramic coatings protect generator bearings from electrical discharge damage. Additional solutions, including polymer overlays, composite films, and hybrid ceramic architectures, offer further improvements in friction, surface fatigue resistance, and environmental robustness. This manuscript reviews the current state of coated bearing technologies relevant to wind turbine applications, synthesizing findings from tribological research, industrial practice, and emerging material developments. While only a limited number of coating suppliers provide documented evidence of coating use in wind turbine drivetrain bearings, the collective progress in surface engineering demonstrates clear potential for improving reliability and extending service life across the installed turbine base. The analysis highlights the mechanisms by which coatings enhance performance, the conditions under which they are most effective, and the gaps that remain in field validation and large-scale deployment. Coated bearings represent a promising pathway toward higher turbine availability, reduced maintenance costs, and improved drivetrain durability. Continued advances in carbon-based films, multilayer architectures, and insulating coatings, combined with better integration of lubrication strategies and condition-monitoring technologies, will play an increasingly important role in enabling the next generation of high-power wind energy systems. Full article

(This article belongs to the Section Tribology)

► Show Figures

Figure 1

33 pages, 4189 KB

Open AccessArticle

Structural Stability and Hydration-Induced Failure Mechanisms of Borax-Modified PVA-Coated PAA-SAP Beads for Mine Pipeline Transport

by Bin Shen, Yu Guan, Qinglan Zhang, Xuanxuan Wang and Xinlei Liu

Coatings 2026, 16(9), 1055; https://doi.org/10.3390/coatings16091055 (registering DOI) - 5 Sep 2026

Abstract

Poly(acrylic acid)-based superabsorbent polymer (PAA-SAP) rapidly absorbs water and swells during pipeline transport in mine water-based inhibitor fluids, increasing flow resistance and potentially causing blockage. To improve aqueous structural stability, PAA-SAP beads were coated with poly(vinyl alcohol) (PVA) by rotary spraying and hot-air [...] Read more.

Poly(acrylic acid)-based superabsorbent polymer (PAA-SAP) rapidly absorbs water and swells during pipeline transport in mine water-based inhibitor fluids, increasing flow resistance and potentially causing blockage. To improve aqueous structural stability, PAA-SAP beads were coated with poly(vinyl alcohol) (PVA) by rotary spraying and hot-air curing, with borax introduced to regulate the coating structure. The effects of PVA concentration, coating thickness, temperature, and hydrodynamic disturbance were evaluated using stability tests, scanning electron microscope (SEM), energy-dispersive X-ray spectrometer (EDS), fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), dry-film swelling, and mass-loss analyses. A 10% PVA formulation showed favorable film-forming and processing performance. Increasing coating thickness prolonged structural retention, whereas higher temperature and stronger disturbance accelerated hydration and failure. At 0.30 mm coating thickness and 2.5 m·s⁻¹ laboratory hydrodynamic disturbance parameter, the borax-modified PVA coating failed after approximately 16 min, compared with 10 and 12 min for PVA and PVA/poly(vinylpyrrolidone) (PVP) coatings, respectively. Boron incorporation and possible boron–oxygen interactions restricted chain mobility and improved coating compactness and stability. A power-law model based on 46 datasets showed good interpolation performance (Coefficient of determination (R²) = 0.9421; Mean Absolute Percentage Error (MAPE) = 5.44%). Failure involved swelling, gelation, network weakening, cracking, and chain dissolution, with core swelling potentially promoting crack propagation. These findings support coating-parameter selection and subsequent mine-scale pipeline validation. Full article

(This article belongs to the Special Issue Advanced Polymer Coatings: Materials, Methods, and Applications)

19 pages, 14003 KB

Open AccessArticle

CeO₂-Doped Laser-Clad 17-4PH/WC/TiC Composite Coatings for Agricultural Reversible Plowshares

by Hai Yang, Yongyan Zhang and Weiwei Sun

Coatings 2026, 16(9), 1054; https://doi.org/10.3390/coatings16091054 (registering DOI) - 5 Sep 2026

Abstract

This study investigates the application of 17-4PH/WC/TiC composite coatings doped with varying CeO₂ concentrations in agricultural reversible plows. Coatings with CeO₂ contents of 0 wt.%, 0.5 wt.%, 1.0 wt.%, 1.5 wt.%, and 2.0 wt.% were fabricated using laser cladding technology, and [...] Read more.

This study investigates the application of 17-4PH/WC/TiC composite coatings doped with varying CeO₂ concentrations in agricultural reversible plows. Coatings with CeO₂ contents of 0 wt.%, 0.5 wt.%, 1.0 wt.%, 1.5 wt.%, and 2.0 wt.% were fabricated using laser cladding technology, and their microstructures, mechanical properties, and wear resistance were systematically characterized. The results demonstrate that appropriate CeO₂ doping significantly enhanced the overall performance of the coatings. The 1.0 wt.% CeO₂-doped sample exhibited the optimal performance profile, achieving a hardness of 628 HV_0.5, a mean friction coefficient of 0.38, and a wear rate of 1.22 × 10⁻⁴ mm³ N⁻¹ m⁻¹, representing a 52.3% reduction in wear rate compared with the undoped coating. Microstructural analysis revealed that CeO₂ refined the grain size and promoted a more uniform distribution of second-phase particles. This study provides a theoretical foundation and technical support for developing high-performance materials for agricultural tool contact components. Full article

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

19 pages, 55437 KB

Open AccessArticle

Influence of Nano-CeO₂ on the Corrosion Resistance of PTFE/PEEK Coatings Prepared by Electrostatic Powder Spraying Technique

by Mingkun Han, Junxin Song, Jiahao Tian, Keqi Wu, Xuewei Zhu and Xiaofeng Wei

Coatings 2026, 16(9), 1053; https://doi.org/10.3390/coatings16091053 (registering DOI) - 5 Sep 2026

Abstract

Polytetrafluoroethylene/Polyetheretherketone (PTFE/PEEK) corrosion-resistant coatings were prepared on the surface of 7075 aluminum alloy by the electrostatic powder spraying technique (EPST). To achieve a denser microstructure and improved hydrophobic properties, we introduced nano-CeO₂ to fill the coatings and analyzed the mechanism of its [...] Read more.

Polytetrafluoroethylene/Polyetheretherketone (PTFE/PEEK) corrosion-resistant coatings were prepared on the surface of 7075 aluminum alloy by the electrostatic powder spraying technique (EPST). To achieve a denser microstructure and improved hydrophobic properties, we introduced nano-CeO₂ to fill the coatings and analyzed the mechanism of its effect on the different coating structures. The corrosion resistance of the coatings was evaluated using NaCl immersion. The results indicate that nano-CeO₂ enhances the coatings by filling local defects and forming a denser microstructural barrier, thereby improving the hydrophobicity and corrosion resistance of the composite coatings. Additionally, the addition of nano-CeO₂ to the 20 µm PTFE/PEEK composite coating increases structural heterogeneity and pore defects, reduces coating densification, and facilitates the penetration of corrosive media, thereby weakening the barrier capability of the coating. However, in the 50 µm PTFE/PEEK/CeO₂ composite coating, nano-CeO₂ particles fill part of the pre-existing defects and improve coating densification, thereby increasing the resistance to the penetration of corrosive media through the coating. This enhanced barrier effect delays the contact of corrosive media with the substrate and improves the corrosion resistance of the coating. In this study, the 50 μm PTFE/PEEK/CeO₂ composite coating with a nano-CeO₂ content of 0.5 wt.% exhibited the best corrosion resistance, with a corrosion current density of 8.02 × 10⁻⁴ μA·cm⁻², while |Z|_0.01Hz remained above 10⁶ Ω·cm² after 720 h of immersion in NaCl solution. Full article

(This article belongs to the Special Issue Anti-Corrosion Coatings: From Materials to Applications)

► Show Figures

Figure 1

22 pages, 2459 KB

Open AccessArticle

Effect of Green-Synthesized CaO-Based Nanoparticle Coatings on Postharvest Quality and Bioactive Compounds of Strawberry Fruits During Cold Storage

by Emircan Dinçer, Nesrin Korkmaz, Osman Nuri Öcalan and Onur Saraçoğlu

Coatings 2026, 16(9), 1052; https://doi.org/10.3390/coatings16091052 - 4 Sep 2026

Abstract

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), [...] Read more.

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. Full article

(This article belongs to the Special Issue Sustainable and Biodegradable Coatings for Food Packaging and Agricultural Applications)

31 pages, 3221 KB

Open AccessArticle

Damage Failure Behavior and Thermo-Mechanical Coupled Damage Prediction of TiAlSiN-Coated Tools in High-Speed Milling of GH4169

by Zhihao Geng, Jingjie Zhang, Hui Ma, Xiaolan Bai and Haiying Mao

Coatings 2026, 16(9), 1051; https://doi.org/10.3390/coatings16091051 - 4 Sep 2026

Abstract

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 [...] Read more.

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. Full article

(This article belongs to the Topic Advances in Processing, Microstructure and Mechanical Properties of Lightweight Alloys)

22 pages, 4089 KB

Open AccessArticle

Phosphorylated Nanocellulose-Templated AgNPs in Waterborne Polyurethane Composite Films: Antibacterial, Mechanical, and Antistatic Properties

by Liangsong Cheng, Fang Liu and Nicolas Brosse

Coatings 2026, 16(9), 1050; https://doi.org/10.3390/coatings16091050 - 4 Sep 2026

Abstract

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 [...] Read more.

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. Full article

(This article belongs to the Special Issue Functional Polymer Materials and Coatings for Next-Generation Biomedical Applications)

► Show Figures

Figure 1

14 pages, 2550 KB

Open AccessArticle

Optimization of Process Parameters for Electrostatic Rotary Bell Spraying Based on Response Surface Methodology

by Nian Zhang, Shuzhen Zhang, Shijie Wu, Yi Wang, Yang Liu and Zhendong Mao

Coatings 2026, 16(9), 1049; https://doi.org/10.3390/coatings16091049 - 4 Sep 2026

Abstract

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 [...] Read more.

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. Full article

(This article belongs to the Section Metal Surface Process)

► Show Figures

Figure 1

13 pages, 2176 KB

Open AccessArticle

Effect of Ni/Co Molar Ratio on the CO Oxidation Activity of Ni_xCo_3−xO₄ Catalysts

by Xia Wang, Yufan Wang, Hongliang Liu, Xiaofeng Yuan, Xiangang Cui and Jiefeng Wang

Coatings 2026, 16(9), 1048; https://doi.org/10.3390/coatings16091048 - 3 Sep 2026

Abstract

A series of Ni_xCo_3−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, [...] Read more.

A series of Ni_xCo_3−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. Full article

(This article belongs to the Section Surface Engineering for Energy Harvesting, Conversion, and Storage)

► Show Figures

Graphical abstract

20 pages, 10113 KB

Open AccessArticle

Structure–Property Relationships of Tungsten Nitride Coatings on Copper Substrates Prepared by Reactive Direct Current Magnetron Sputtering

by Daniela Stoeva, Georgi Kotlarski, Dimitar Dechev, Edmon Lazarov, Nikolay Ivanov, Stefan Valkov, Valentin Mateev, Iliana Marinova and Maria Ormanova

Coatings 2026, 16(9), 1047; https://doi.org/10.3390/coatings16091047 - 3 Sep 2026

Abstract

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. [...] Read more.

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. Full article

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

► Show Figures

Figure 1

28 pages, 4642 KB

Open AccessArticle

Multi-Feature Characterization and Numerical Simulation of Interfacial Damage in Thermal Barrier Coatings Using Immersion Ultrasonics

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

Coatings 2026, 16(9), 1046; https://doi.org/10.3390/coatings16091046 - 3 Sep 2026

Abstract

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 [...] Read more.

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. Full article

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

► Show Figures

Graphical abstract

24 pages, 3832 KB

Open AccessArticle

The Performance, Mechanism, and Sustainability of a Mechanochemically Activated Copper Tailings–Slag–Metakaolin Solid-Waste-Based Grouting Material

by Jie Yao, Zhongming He and Tangxin Xie

Coatings 2026, 16(9), 1045; https://doi.org/10.3390/coatings16091045 - 3 Sep 2026

Abstract

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 [...] Read more.

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. Full article

(This article belongs to the Special Issue Transportation Solid Waste in Pavement Maintenance: Materials Recycling, Surface Modification and Management)

15 pages, 1387 KB

Open AccessArticle

Experimental Study on Prestressed Forming of Carbon-Fiber-Reinforced Polymer Composites

by Xuelei Li, Mingli Xiang, Peng Wu and Haobin Tian

Coatings 2026, 16(9), 1044; https://doi.org/10.3390/coatings16091044 - 3 Sep 2026

Abstract

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 [...] Read more.

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. Full article

(This article belongs to the Section Composite Coatings)

16 pages, 4192 KB

Open AccessArticle

Co-O-Al Interfacial Bonding in Sol–Gel-Derived Co₃O₄-Coated Ceramic Membranes: Correlative FIB-HRTEM and First-Principles Analysis

by Jia Xu, Wei Qiu and Jingjing Yao

Coatings 2026, 16(9), 1043; https://doi.org/10.3390/coatings16091043 - 3 Sep 2026

Abstract

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 [...] Read more.

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. Full article

(This article belongs to the Topic Production, Processing, Microstructure and Functional Properties in Materials Engineering)

Journal Description

Coatings

Latest Articles

Journal Menu

Journal Browser

Highly Accessed Articles

Latest Books

E-Mail Alert

News

Topics

Conferences

Special Issues

Topical Collections

Further Information

Guidelines

MDPI Initiatives

Follow MDPI