Coatings

15 pages, 12185 KiB

Open AccessArticle

The Thickness Dependence of the Superconducting Properties of MgB₂ Spherical Shells Deposited on 1 mm Diameter Si₃N₄ Spheres

by Ruining Sun, Tiequan Xu, Yue Wang, Furen Wang and Zizhao Gan

Coatings 2025, 15(4), 377; https://doi.org/10.3390/coatings15040377 (registering DOI) - 23 Mar 2025

Abstract

Superconducting spherical shells have important application value or potential in various fields, such as inertial navigation, gravity measurement, and nuclear fusion. Depending on the needs of the applications, the thickness of the superconducting shell may vary from micrometers to nanometers. We report an [...] Read more.

Superconducting spherical shells have important application value or potential in various fields, such as inertial navigation, gravity measurement, and nuclear fusion. Depending on the needs of the applications, the thickness of the superconducting shell may vary from micrometers to nanometers. We report an investigation into the superconducting properties of MgB

_{2}

spherical shells deposited on 1 mm diameter Si

_{3}

N

_{4}

spheres, with the shell thickness varying from approximately 200 nm to 720 nm. The upper critical field

H_{c 2}

, the lower critical field

H_{c 1}

, and the superconducting critical current density

J_{c}

were determined from electrical resistance, initial magnetization, and magnetization hysteresis loop measurements, respectively. As the shell thickness decreased, it was observed that

H_{c 2}

was enhanced,

H_{c 1}

declined, and

J_{c}

rose. This systematic evolution of the superconducting properties is suggested to have arisen from a reduction in the grain size with a decrease in the shell thickness, as shown by surface morphology images of the shells. A reduction in the grain size leads to increased grain boundaries and scattering strength, which decrease the electron diffusivities, thereby enhancing

H_{c 2}

and suppressing

H_{c 1}

as the shell thickness diminishes. The proliferation of grain boundaries would also provide more effective flux pinning in the shell, giving rise to an improvement in

J_{c}

. Our study demonstrated a close correlation between the microstructure, specifically, the grain size, and the superconducting properties in MgB

_{2}

spherical shells and the effectiveness of tuning them by varying the thickness of the shell. Moreover, it also revealed that the superconducting properties of the fabricated spherical shells, particularly their evolutions with the shell thickness, were critically influenced by the multiband superconductivity of MgB

_{2}

. These findings would provide a helpful reference for fabricating MgB

_{2}

superconducting shells with desired thicknesses and properties, enabling them to better meet the requirements of applications in various fields. Full article

19 pages, 1803 KiB

Open AccessArticle

Enhanced Flame Retardancy of Unsaturated Polyester Resin via Simultaneously Using a Novel DOPO-Based Organic Flame Retardant and Modified Silicon Carbide

by Piye Wu, Jingjie Hu, Chanyu Liu, Ping He, Feng You, Hao Yang and Man Xu

Coatings 2025, 15(4), 376; https://doi.org/10.3390/coatings15040376 (registering DOI) - 23 Mar 2025

Abstract

Unsaturated polyester (UP) resin is widely utilized in the construction and automotive industries. The flammable nature of UP must be constrained when its products are manufactured. A novel organic flame retardant has been synthesized from 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and triallyl isocyanate (TAIC). This DOPO-TAIC [...] Read more.

Unsaturated polyester (UP) resin is widely utilized in the construction and automotive industries. The flammable nature of UP must be constrained when its products are manufactured. A novel organic flame retardant has been synthesized from 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and triallyl isocyanate (TAIC). This DOPO-TAIC additive has been used to reduce the flammability of a matrix. Additionally, this flame retardant was then combined with dopamine-modified silicon carbide (M-SiC) to further diminish the flammability of UP. The limiting oxygen index (LOI) value combustion of a UP/DOPO-TAIC/M-SiC blend was 30.8% when the filler contents of DOPO-TAIC and M-SiC was 15 wt.% and 30 wt.%, respectively. These materials exhibited a UL 94 V-0 rating for combustion. Compared to the values for combustion of the neat UP, the peak heat release rate (Pk-HRR) and total heat release rate (THR) for this blend were reduced by 51% and 35%, respectively. The mode of action for flame retardant of UP blends containing DOPO-TAIC and M-SiC has been composed. The presence of a flame retardant containing P-Si elements can significantly reduce flammability compared to that of unmodified resin. Full article

19 pages, 59654 KiB

Open AccessArticle

Study on Adhesion Characteristics of Rubber–Soil Interface Based on Electric Double-Layer and Water Film Theories

by Mingyang Yuan, Ze Zhang, Hang Li, Zhiyuan Wang and Doudou Jin

Coatings 2025, 15(4), 375; https://doi.org/10.3390/coatings15040375 (registering DOI) - 23 Mar 2025

Abstract

Soil adhesion is one of the basic physical properties of soil. The existence of soil adhesion will cause additional energy consumption of transport vehicles, which is an urgent scientific problem to be solved. In this paper, rubber tires are used as test materials, [...] Read more.

Soil adhesion is one of the basic physical properties of soil. The existence of soil adhesion will cause additional energy consumption of transport vehicles, which is an urgent scientific problem to be solved. In this paper, rubber tires are used as test materials, and the adhesion between rubber tires and different soils is measured by the improved adhesion test device. The rubber surface after the test is processed and analyzed by image analysis software. The results showed that the soil adhesion increased with the increase in soil moisture content and reached the maximum when it was close to the liquid limit. The maximum adhesion increased with the increase in soil clay content. The image processing analysis showed that the watermark area on the rubber surface will gradually increase with the increase in soil moisture content. According to the test results and the characteristics of soil colloid, the electric double-layer theory was introduced to establish the contact, adhesion, and separation model of the rubber–soil interface, and the adhesion mechanism of the rubber–soil interface was expounded. This study will promote the study of soil adhesion and provide a reference for estimating the additional energy consumption caused by adhesion during transportation. Full article

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9 pages, 3314 KiB

Open AccessCommunication

Flexibility-Engineered Nb₂O₅ Carbon Nanofiber Film Anodes: Concentration-Dependent Optimization for Mechanically Robust and Stable Sodium Storage

by Xuhui Zhu, Duiming Lin, Siying Liu, Jufang Li, Yi Tang, Yancheng Pan, Qinglin Deng and Lingmin Yao

Coatings 2025, 15(4), 374; https://doi.org/10.3390/coatings15040374 (registering DOI) - 22 Mar 2025

Abstract

This study systematically investigates the correlation between the concentration of niobium oxide (Nb₂O₅) in carbon nanofibers (CNFs) and the microstructural characteristics and electrochemical performance of the composites. Through rational optimization of Nb₂O₅-to-CNFs mass ratios, we [...] Read more.

This study systematically investigates the correlation between the concentration of niobium oxide (Nb₂O₅) in carbon nanofibers (CNFs) and the microstructural characteristics and electrochemical performance of the composites. Through rational optimization of Nb₂O₅-to-CNFs mass ratios, we demonstrate that 50% Nb₂O₅ CNFs composite achieves an optimal balance between enhanced rate capability and structural stability. The composites transition from brittle to flexible with increasing Nb₂O₅ content, achieving unprecedented bending durability at 50% loading. This mechanical–electrochemical synergy positions Nb₂O₅ CNFs as viable candidates for flexible energy storage devices. Comprehensive characterization reveals that appropriate Nb₂O₅ incorporation significantly improves specific capacity (181 mA h g⁻¹ at 0.1 A g⁻¹) and rate performance compared to pristine CNFs. However, excessive Nb₂O₅ doping (>50%) induces detrimental hydrolysis reactions during synthesis, compromising both material processability and electrochemical reversibility. This work contributes to the development of flexible self-supporting frameworks that are superior to hard carbon for constructing high-performance flexible sodium-ion batteries. Full article

(This article belongs to the Special Issue New Functional Coatings and Thin Films for Sensor and Green Energy Technologies)

19 pages, 4484 KiB

Open AccessArticle

Investigation into the Preparation and Electrochemical Energy Storage Performance of Nickel Cobalt Oxide-Based Composite Anode Materials

by Yuyang Wang, Xiangquan Kong, Zhijie Wang, Dongming Zhang, Yu Song, Su Ma, Ying Duan, Andrii Vyshnikin, Vitalii Palchykov and Jinlong Zuo

Coatings 2025, 15(4), 373; https://doi.org/10.3390/coatings15040373 (registering DOI) - 22 Mar 2025

Abstract

Microbial fuel cells (MFCs) are a novel bioenergy technology that utilizes microorganisms to catalyze the conversion of fuels into electricity. However, traditional MFCs are constrained by the low electricity generation capacity of microorganisms, resulting in relatively low power output. Additionally, the inability of [...] Read more.

Microbial fuel cells (MFCs) are a novel bioenergy technology that utilizes microorganisms to catalyze the conversion of fuels into electricity. However, traditional MFCs are constrained by the low electricity generation capacity of microorganisms, resulting in relatively low power output. Additionally, the inability of traditional MFCs to store electricity significantly limits their practical applications. In this study, we fabricate a novel oxide graphite/nickel cobalt oxide (GO/NiCo₂O₄) capacitive composite bioanode material supported on stainless-steel fiber felt (SSFF). This composite material combines the excellent biocompatibility of graphite oxide and the energy storage capacity of nickel cobalt oxide. Consequently, the prepared anode exhibits significant advantages, including high specific capacitance, efficient electron transport, and enhanced biocompatibility. The MFC with the SSFF/GO/NiCo₂O₄ anode demonstrated a significantly enhanced power density, achieving a maximum of 1267.5 mW/m²—1.38-fold and 2.23-fold higher than those of the SSFF/GO and SSFF anodes, respectively. Moreover, the modified anode (SSFF/GO/NiCo₂O₄) exhibited a stored charge (Q_s) of 1405.35 C/m², representing 2.61-fold and 35.79-fold increases compared to the SSFF/GO and SSFF anodes, respectively. High-throughput analysis revealed that SSFF/GO/NiCo₂O₄-modified anode achieved an electrogenic bacterial efficiency exceeding 81%, which was significantly higher than that of the SSFF/GO and SSFF anodes. The results of this study not only provide valuable insights and theoretical guidance for the development of MFCs using capacitive composite anode materials, they also present sustainable power solutions for low-power electronic systems, such as miniaturized sensors and IoT devices. Full article

11 pages, 2921 KiB

Open AccessArticle

Optical Coating Deposition on Submicron-Patterned Surfaces

by Lina Grineviciute, Simas Melnikas, Julianija Nikitina, Mantas Drazdys, Algirdas Selskis and Darija Astrauskytė

Coatings 2025, 15(4), 372; https://doi.org/10.3390/coatings15040372 (registering DOI) - 22 Mar 2025

Abstract

Periodically modulated optical coatings, fabricated by depositing conformal films on modulated substrates, offer unique capabilities for spectral and spatial filtering of light. However, conventional deposition methods often do not achieve required replication and conformality on submicron-size structured surfaces. In this paper, we compare [...] Read more.

Periodically modulated optical coatings, fabricated by depositing conformal films on modulated substrates, offer unique capabilities for spectral and spatial filtering of light. However, conventional deposition methods often do not achieve required replication and conformality on submicron-size structured surfaces. In this paper, we compare various thin film deposition techniques, including electron beam evaporation, atomic layer deposition, and ion beam sputtering, to evaluate their ability to control multilayer coating growth on periodically modulated substrates. Our study demonstrates that both single-layer and multilayer coatings produced by ion beam sputtering effectively replicate the initial geometry of structured surfaces, thereby enhancing optical performance. Full article

(This article belongs to the Special Issue Optical Coatings: From Materials to Applications)

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15 pages, 3069 KiB

Open AccessArticle

A Comparative Study on the Impact of Different Antifreeze Agents on Composite Cement at −10 °C

by Bitao Zhang, Yongkang Du, Dong Liu and Yanyan Hu

Coatings 2025, 15(4), 371; https://doi.org/10.3390/coatings15040371 (registering DOI) - 22 Mar 2025

Abstract

Construction in cold regions faces significant challenges due to delayed cement hydration and frost damage caused by sub-zero temperatures. This study investigated the effects of three antifreeze agents on the performance of composite cement under sub-zero temperatures. The setting time, compressive strength, freezing [...] Read more.

Construction in cold regions faces significant challenges due to delayed cement hydration and frost damage caused by sub-zero temperatures. This study investigated the effects of three antifreeze agents on the performance of composite cement under sub-zero temperatures. The setting time, compressive strength, freezing point, and hydration mechanisms were evaluated. The results revealed that CaCl₂ optimally accelerated hydration, while achieving the continuous development of compressive strengths through freezing-point depression and dense microstructure formation. NaNO₂ exhibited the lowest freezing point but delayed setting at high dosages, while Li₂CO₃ showed limited impact due to insufficient freezing point depression. Li₂CO₃ showed limited efficacy under continuous low temperatures but enabled strength recovery after the temperature transition from sub-zero to ambient conditions. This research provides a basis for the application of antifreeze agents in the composite cement system for construction in cold environments. Full article

(This article belongs to the Special Issue Surface Treatment and Mechanical Properties of Sustainable Pavement Materials)

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27 pages, 5212 KiB

Open AccessArticle

Bio-Based Alkyd–Polyesteramide–Polyurethane Coatings from Castor, Neem, and Karanja Oils with Inherent Antimicrobial Properties for Enhanced Hygiene

by Abhinav Sati, Omkar Nandiwdekar, Aditya Ratnaparkhi, Ranjeet B. Doke, Dipak V. Pinjari, Suraj N. Mali and Amit P. Pratap

Coatings 2025, 15(4), 370; https://doi.org/10.3390/coatings15040370 (registering DOI) - 21 Mar 2025

Abstract

Background: One of the foremost causes of microbial infections and propagation is improper sanitation and hygiene maintained in public places. Accumulation of stains and microbes results in the spread of infections. Also, due to the extensive use of non-renewable materials like petrochemicals, etc., [...] Read more.

Background: One of the foremost causes of microbial infections and propagation is improper sanitation and hygiene maintained in public places. Accumulation of stains and microbes results in the spread of infections. Also, due to the extensive use of non-renewable materials like petrochemicals, etc., there is an increasing demand for sustainable growth in the coating industries. Currently, there is no such technology that tackles this problem. Methods: Our present work aims to find a prolonged solution for these problems for the first time by synthesizing and formulating bio-based coatings with inherent antimicrobial properties and durable surface properties with a fast air-curing system. A formulation of alkyd and polyesteramide resins from castor, neem, and karanja oils was crosslinked with isocyanates to form the surface coatings. An esterification reaction of castor oil monoglyceride and phthalic anhydride synthesized the castor oil alkyd resin. The corresponding neem and karanja oil polyesteramides were synthesized by amidation with diethanolamine, followed by an esterification reaction. Results: The coatings exhibit an antimicrobial efficacy of 74%–84% against both Gram-positive and Gram-negative bacteria and contain 76.5% bio-based content. Factors such as thermal stability, physicochemical properties, and chemical and solvent stability were studied. After 24 h of inoculation with 40% polyesteramide resin (AMRESN-4), E. coli and S. aureus CFU values decreased from 6 × 10⁵ to 0.28 × 10⁵ CFU/g and from 5.7 × 10⁵ to 0.26 × 10⁵ CFU/g, respectively. These bio-based coatings are particularly suited for environments requiring high durability and antimicrobial protection, such as food-processing facilities, healthcare settings, and public restrooms. Full article

(This article belongs to the Section Bioactive Coatings and Biointerfaces)

25 pages, 7713 KiB

Open AccessArticle

Study on Fatigue Characteristics of Cement-Emulsified Asphalt Mortar Under Coupled Effects of Humidity and Freeze–Thaw

by Shanshan Jin, Pengfei Liu, Zhen Wang, Daxing Zhou, Xiang Li, Zengmiao Xu, Yang Zhang, Yuling Yan and Yaodong Zhao

Coatings 2025, 15(4), 369; https://doi.org/10.3390/coatings15040369 - 21 Mar 2025

Abstract

Cement-emulsified asphalt mortar (CA mortar) is an organic–inorganic composite material composed of cement, emulsified asphalt, fine sand, water, and various admixtures. It is mainly used as the cushion layer for high-speed railway ballastless tracks. CA mortar cushion layers in North China often have [...] Read more.

Cement-emulsified asphalt mortar (CA mortar) is an organic–inorganic composite material composed of cement, emulsified asphalt, fine sand, water, and various admixtures. It is mainly used as the cushion layer for high-speed railway ballastless tracks. CA mortar cushion layers in North China often have to withstand the coupling effects of humidity and freeze–thaw, which has a very important impact on the fatigue performance of CA mortar. Based on the big data statistical results, the temperature conditions and cycle times of the CA mortar layer Freeze–Thaw cycle in North China were determined. Also, a fatigue performance test under humidity–freeze–thaw coupling conditions was designed and carried out. The fitting curve equations of fatigue stress and fatigue life under different humidity conditions and freeze–thaw coupling were established. The relationship between fatigue performance parameters K and n and humidity conditions was analyzed. This study shows that with the increase in humidity, the fatigue life of CA mortar under different humidity conditions shows an overall downward trend. The fatigue performance and fatigue life stress level sensitivity of CA mortar decrease with increasing humidity. The proportion of water damage and freeze–thaw damage to total damage increases with increasing humidity, which means that the humidity and freeze–thaw have a more significant impact on the fatigue properties of CA mortar. When the humidity is low, the fatigue cracks of CA mortar are mostly generated across the cement paste, and the macroscopic damage presents as longitudinal cracking. When the humidity is high, the fatigue cracks of CA mortar are mostly generated at the interface between aggregate and paste, and the macroscopic damage presents as oblique cracking. Based on the analysis of the damage mechanism, it is suggested that the humidity of CA mortar should be controlled below 25% in the actual project to ensure its durability. Full article

20 pages, 11840 KiB

Open AccessArticle

Effect of Trace Er Addition on the Microstructural Evolution and Heat Resistance Properties of an Al-Zn-Mg-Cu Alloy During High Temperature Tensile and Thermal Exposure

by Juangang Zhao, Ruizhi Zhang, Ruiting Li, Yu Liu, Song Bai, Xuetong Zhao, Jianquan Sang, Jianping Huang, Chunquan Liu, Xinbin Liu and Fuming Du

Coatings 2025, 15(4), 368; https://doi.org/10.3390/coatings15040368 - 21 Mar 2025

Abstract

High temperature tensile properties and long-term thermal stability play an important role in practical applications of Al-Zn-Mg-Cu alloys. In order to evaluate the effect of Er addition on the properties of an Al-Zn-Mg-Cu alloy as potential high temperature structural materials, the heat resistance [...] Read more.

High temperature tensile properties and long-term thermal stability play an important role in practical applications of Al-Zn-Mg-Cu alloys. In order to evaluate the effect of Er addition on the properties of an Al-Zn-Mg-Cu alloy as potential high temperature structural materials, the heat resistance properties of an Al-Zn-Mg-Cu alloy were investigated at various temperatures. After high temperature tensile testing and long periods of heat exposure testing, the microstructures of Al-Zn-Cu-Mg alloys with and without small Er addition is intentionally investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), and quantitative transmission electron microscopy (TEM) characterization to explore the potential effect of Er on the tensile properties. The experimental results reveal that the heat resistance of T76-tempered Al-Zn-Cu-Mg alloy is obviously improved by adding trace Er. The Al₈Cu₄Er phase is found to segregate at the localized regions along grain boundaries and strengthens the grain boundaries at elevated temperatures. The η′ and η precipitation is obviously promoted by adding trace Er, and dispersed nano-sized Al₃(Er, Zr) precipitates were formed in the Er-containing alloys after homogenization, thereby enhancing the strength of Al-Zn-Mg-Cu. In addition, precipitates in both alloys gradually coarsen with the increase in thermal exposure temperature and the extension of thermal exposure time. The influence of precipitates on mechanical properties of the investigatived alloy after thermal exposure is also discussed. Full article

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24 pages, 35112 KiB

Open AccessArticle

Heat Transfer Characteristics of Electrical Heating Deicing and Snow-Melting Asphalt Pavement Under Different Operating Conditions

by Kai Xu, Zhi Chen, Henglin Xiao, Mengjun Zhu and Zhiyong Wang

Coatings 2025, 15(4), 367; https://doi.org/10.3390/coatings15040367 - 21 Mar 2025

Abstract

To further investigate the heat transfer characteristics of electric heating snow-melting pavement, this study developed two finite element models of such systems and conducted small-scale field experiments. An analysis was performed on the snow-melting pavement systems’ temperature field, temperature change rate, and gradient [...] Read more.

To further investigate the heat transfer characteristics of electric heating snow-melting pavement, this study developed two finite element models of such systems and conducted small-scale field experiments. An analysis was performed on the snow-melting pavement systems’ temperature field, temperature change rate, and gradient distribution during summer and winter, with entransy dissipation introduced to further analyze the heat transfer characteristics of asphalt snow-melting pavement. The results indicate that during system shutdown in summer and winter, the pavement structure exhibits reduced heat transfer capacity, leading to progressive decreases in the temperature variation rate and gradient with depth. The primary heat transfer loss occurs in the asphalt layer, with entransy dissipation predominantly concentrated during summer daylight and winter nighttime. During winter operation, the cable heat source modifies the temperature field distribution and gradient, which alters entransy dissipation. Installing an insulation layer improves snow-melting efficiency, and operating the system from 00:00 to 05:00 effectively prevents pavement icing. Full article

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15 pages, 8841 KiB

Open AccessArticle

Preparation of Superhydrophobic Flame-Retardant UHMWPE Fabrics with Excellent Mechanical Stability by Simple Coating Method

by Xiakeer Saitaer, Jianing Wang, Qiang Gao, Ying Li, Jiahao Sun, Jiqiang Cao, Ying Wang, Zengying Liu and Xiang Liu

Coatings 2025, 15(4), 366; https://doi.org/10.3390/coatings15040366 - 21 Mar 2025

Abstract

Ultra-high-molecular-weight polyethylene (UHMWPE) fabric is widely used in many fields due to its excellent properties such as high modulus, high strength, and impact resistance. However, its high flammability prevents its application in high-temperature environments. Therefore, it is important to develop multifunctional UHMWPE fabric [...] Read more.

Ultra-high-molecular-weight polyethylene (UHMWPE) fabric is widely used in many fields due to its excellent properties such as high modulus, high strength, and impact resistance. However, its high flammability prevents its application in high-temperature environments. Therefore, it is important to develop multifunctional UHMWPE fabric to meet its different requirements in firefighting, military, and other scenarios. Here, we have prepared a durable flame-retardant superhydrophobic UHMWPE fabric by a simple coating method. A polyurethane solution mixed with decabromodiphenylethane and antimony trioxide is scraped on the surface of the fabric to form a coating, which endows the fabric with flame retardancy. The sprayed fluorinated hydrophobic agent provides superhydrophobic properties to the fabric. It is worth mentioning that plasma pretreatment greatly improves the adhesion properties of the coating by stimulating the active groups on the surface of the fabric. Tests have shown that the adhesion between the coating and the surface of the plasma-treated UHMWPE fabric has been greatly improved. The limiting oxygen index value of the coating UHMWPE fabric has increased by 90%, and it immediately extinguishes after leaving the flame, demonstrating excellent flame retardancy. The contact angle between its surface and water reaches 156°, exhibiting excellent superhydrophobicity and self-cleaning properties. This study provides a simple, convenient, and effective method for the development of multifunctional UHMWPE fabric, greatly expanding its application scenarios and providing ideas for future development. Full article

(This article belongs to the Special Issue Functional Coatings for Flexible Materials)

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18 pages, 1388 KiB

Open AccessReview

Ni-P Coatings as Hydrogen Permeation Barriers—A Review

by Deborah Biggio, Bernhard Elsener and Antonella Rossi

Coatings 2025, 15(4), 365; https://doi.org/10.3390/coatings15040365 - 21 Mar 2025

Abstract

Hydrogen became one of the most studied energy carriers after the global energy crisis and can replace gas and oil as clean fuels. The main challenge is its safe storage and long-distance transportation: steel is among the materials most used for hydrogen storage [...] Read more.

Hydrogen became one of the most studied energy carriers after the global energy crisis and can replace gas and oil as clean fuels. The main challenge is its safe storage and long-distance transportation: steel is among the materials most used for hydrogen storage and transportation. However, steel is susceptible to hydrogen embrittlement (HE). HE can be prevented by depositing hydrogen barrier coatings on the steel surface. This review provides an overview of the hydrogen permeation mechanism and the analytical methods employed to evaluate the performance of the hydrogen permeation barriers. The focus is on Ni and electroless Ni-P coatings deposited on steel as hydrogen barriers. These coatings have been used so far for their anti-corrosion and wear properties; they are currently of interest due to their low hydrogen permeability. The simplicity of production and the possibility of achieving a homogeneous coating, regardless of the geometry of the substrate, make the electroless deposition process of the Ni-P alloy a candidate for ‘in situ’ applications in existing pipelines. This process can be implemented by using and adapting the established pig batch technology. Full article

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

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18 pages, 1972 KiB

Open AccessArticle

A Physics-Guided Parameter Estimation Framework for Cold Spray Additive Manufacturing Simulation

by Md Munim Rayhan, Abderrachid Hamrani, Md Sharif Ahmed Sarker, Arvind Agarwal and Dwayne McDaniel

Coatings 2025, 15(4), 364; https://doi.org/10.3390/coatings15040364 - 21 Mar 2025

Abstract

This work presents a physics-guided parameter estimation framework for cold spray additive manufacturing (CSAM), focusing on simulating and validating deposit profiles across diverse process conditions. The proposed model employs a two-zone flow representation: quasi-constant velocity near the nozzle exit followed by an exponentially [...] Read more.

This work presents a physics-guided parameter estimation framework for cold spray additive manufacturing (CSAM), focusing on simulating and validating deposit profiles across diverse process conditions. The proposed model employs a two-zone flow representation: quasi-constant velocity near the nozzle exit followed by an exponentially decaying free jet to capture particle acceleration and impact dynamics. The framework employs a comprehensive approach by numerically integrating drag-dominated particle trajectories to predict deposit formation with high accuracy. This physics-based framework incorporates both operational and geometric parameters to ensure robust prediction capabilities. Operational parameters include spray angle, standoff distance, traverse speed, and powder feed rate, while geometric factors encompass nozzle design characteristics such as exit diameter and divergence angle. Validation is performed using 36 experimentally measured profiles of commercially pure titanium powder. The simulator shows excellent agreement with the experimental data, achieving a global root mean square error (RMSE) of 0.048 mm and a coefficient of determination

R^{2} = 0.991

, improving the mean absolute error by more than 40% relative to a neural network-based approach. Sensitivity analyses reveal that nozzle geometry, feed rate, and critical velocity strongly modulate the amplitude and shape of the deposit. Notably, decreasing the nozzle exit diameter or divergence angle significantly increases local deposition rates, while increasing the standoff distance dampens particle velocities, thereby reducing deposit height. Although the partial differential equation (PDE)-based framework entails a moderate increase in computational time—about 50 s per run, roughly 2.5 times longer than simpler empirical models—this remains practical for most process design and optimization tasks. Beyond its accuracy, the PDE-based simulation framework’s principal advantage lies in its minimal reliance on sampling data. It can readily be adapted to new materials or untested process parameters, making it a powerful predictive tool in cold spray process design. This study underscores the simulator’s potential for guiding parameter selection, improving process reliability and offering deeper physical insights into cold spray deposit formation. Full article

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17 pages, 3279 KiB

Open AccessArticle

Dual Modulation Polarization-Independent Terahertz BIC Metasurface for Multi-Wavelength Sensing

by Yanru Ren, Jingwei Lv, Chao Liu, Debao Wang, Renfeng Li, Liangliang Li, Xili Lu, Qiang Liu, Jianxin Wang, Wei Liu and Paul K. Chu

Coatings 2025, 15(3), 363; https://doi.org/10.3390/coatings15030363 - 20 Mar 2025

Abstract

The use of bound states in the continuum (BICs) has emerged as an effective tool to trap light at the nanoscale and has many potential applications in photonics. Breaking the structural symmetry is regarded as an effective way to excite quasi-BICs (QBICs) and [...] Read more.

The use of bound states in the continuum (BICs) has emerged as an effective tool to trap light at the nanoscale and has many potential applications in photonics. Breaking the structural symmetry is regarded as an effective way to excite quasi-BICs (QBICs) and generate high-Q resonances. However, this approach may impact the resonance polarization sensitivity, consequently limiting its practicality in multi-wavelength polarization-dependent applications. Furthermore, the introduction of different types of structural perturbations into the design to form BICs has yet to be explored in depth. In this study, we present an optical sensor consisting of an L-shaped metasurface that supports three quasi-BIC modes in the terahertz band, where specific displacements, collective perturbations, or both occur. Furthermore, we analyze the field distributions in detail and combine them with multipolar decomposition to reveal the underlying mechanisms of the different resonant modes. Multiple asymmetric perturbations are found to affect the sensitivity of the metasurface in refractive index sensing, thus allowing for a comparison of different resonant modes. The quasi-BIC mode can attain a Q-factor of 1067.6, a sensitivity (S) of 300 GHz/RIU, and a figure of merit (FOM) of 5367.8 RIU⁻¹ for vertical light incidence. These three quasi-BIC modes are polarization-independent, and their properties are maintained even for circularly polarized light. The results reveal a novel design strategy for metasurface-based sensors with promising application potential in biosensing, filtering, and lasers. Full article

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29 pages, 10331 KiB

Open AccessArticle

Using Preexisting Surface Cracks to Prevent Thermal Fatigue Failure and Crack Delamination in FGM Thermal Barrier Coatings

by Kai-Chien Lo, Jenn-Kun Kuo, Pei-Hsing Huang and Chang-Yu Hsiao

Coatings 2025, 15(3), 362; https://doi.org/10.3390/coatings15030362 - 20 Mar 2025

Abstract

Thermal shock testing has long been employed to assess thermal barrier coatings (TBCs), with crack formation and propagation on TBC surfaces serving as important indicators of fracture toughness. In this study, the influence of preexisting cracks within TBC coatings was investigated. These cracks [...] Read more.

Thermal shock testing has long been employed to assess thermal barrier coatings (TBCs), with crack formation and propagation on TBC surfaces serving as important indicators of fracture toughness. In this study, the influence of preexisting cracks within TBC coatings was investigated. These cracks can help alleviate stress concentrations at the interface and within the thermally grown oxide (TGO) layers of the TBC model. In other words, surface crack propagation may eventually intersect the interface, leading to delamination and spallation. This research focused on modifying the volume fraction of functionally graded materials (FGMs) and optimizing preexisting surface cracks in TBCs to extend their lifespan before delamination occurs. The accuracy of the J-integral and displacement correlation technique (DCT) methods was evaluated for use in thermal shock testing simulations. The results showed that both the stress intensity factor (SIF) and interface tensile stress of preexisting cracks were significantly reduced when the volume fraction was set at N = 3. Furthermore, the SIF values demonstrated strong agreement with calculations using the J-integral and DCT methods. The SIF for preexisting cracks dropped to below 62.42% of the fracture toughness when the crack length was approximately 50% of the TBC coating thickness in FGM structures, with a crack density of 10 cracks per inch (CPI). Full article

(This article belongs to the Special Issue Microstructure, Friction and Wear, Hardness Properties and Numerical Simulation of Coatings)

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32 pages, 2445 KiB

Open AccessReview

Toxicity, Irritation, and Allergy of Metal Implants: Historical Perspective and Modern Solutions

by Grzegorz Szczęsny, Mateusz Kopec and Zbigniew L. Kowalewski

Coatings 2025, 15(3), 361; https://doi.org/10.3390/coatings15030361 - 20 Mar 2025

Abstract

The widespread adoption of metal implants in orthopaedics and dentistry has revolutionized medical treatments, but concerns remain regarding their biocompatibility, toxicity, and immunogenicity. This study conducts a comprehensive literature review of traditional biomaterials used in orthopaedic surgery and traumatology, with a particular focus [...] Read more.

The widespread adoption of metal implants in orthopaedics and dentistry has revolutionized medical treatments, but concerns remain regarding their biocompatibility, toxicity, and immunogenicity. This study conducts a comprehensive literature review of traditional biomaterials used in orthopaedic surgery and traumatology, with a particular focus on their historical development and biological interactions. Research articles were gathered from PubMed and Web of Science databases using keyword combinations such as “toxicity, irritation, allergy, biomaterials, corrosion, implants, orthopaedic surgery, biocompatible materials, steel, alloys, material properties, applications, implantology, and surface modification”. An initial pool of 400 articles was screened by independent reviewers based on predefined inclusion and exclusion criteria, resulting in 160 relevant articles covering research from 1950 to 2025. This paper explores the electrochemical processes of metals like iron, titanium, aluminium, cobalt, molybdenum, nickel, and chromium post-implantation, which cause ion release and wear debris formation. These metal ions interact with biological molecules, triggering localized irritation, inflammatory responses, and immune-mediated hypersensitivity. Unlike existing reviews, this paper highlights how metal–protein interactions can form antigenic complexes, contributing to delayed hypersensitivity and complications such as peri-implant osteolysis and implant failure. While titanium is traditionally considered bioinert, emerging evidence suggests that under certain conditions, even inert metals can induce adverse biological effects. Furthermore, this review emphasizes the role of oxidative stress, illustrating how metal ion release and systemic toxicity contribute to long-term health risks. It also uncovers the underappreciated genotoxic and cytotoxic effects of metal ions on cellular metabolism, shedding light on potential long-term repercussions. By integrating a rigorous methodological approach with an in-depth exploration of metal-induced biological responses, this paper offers a more nuanced perspective on the complex interplay between metal implants and human biology, advancing the discourse on implant safety and material innovation. Full article

(This article belongs to the Collection Review Papers Collection for Bioactive Coatings)

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20 pages, 16430 KiB

Open AccessArticle

Study on the Properties of Plastic Fillers in Carbon Dioxide Capture System Under High Temperature and High Pressure

by Kun Fang, Xuehua Fan, Jie Chen, Lei Dong, Jiahui Hu, Yiying Liu, Shengyuan Liu, Jianbo Sun, Xiangyu Zheng and Guojian Liu

Coatings 2025, 15(3), 360; https://doi.org/10.3390/coatings15030360 - 20 Mar 2025

Abstract

In the CO₂-amine solution system, metal packings in purification devices face corrosion risks, while plastic packings have garnered attention due to their lightweight nature, ease of processing, and excellent corrosion resistance. Since different plastic packings have varying applicable temperature ranges, exceeding [...] Read more.

In the CO₂-amine solution system, metal packings in purification devices face corrosion risks, while plastic packings have garnered attention due to their lightweight nature, ease of processing, and excellent corrosion resistance. Since different plastic packings have varying applicable temperature ranges, exceeding their tolerance limits can significantly reduce their corrosion resistance. Therefore, selecting suitable plastic packings at different temperatures is crucial for ensuring safety. This study selected four plastic materials–PVC-C, PP, FEP, and PEEK–and systematically tested their performance indicators, such as volume, mass, strength, elongation, and thermal stability, in a CO₂-amine solution system at experimental temperatures ranging from 60 to 130 °C. The experimental results show that PEEK outperformed the other three materials within the 60–130 °C range, making it suitable as a packing material for purification devices in high-temperature environments. Although FEP demonstrated good performance under the same conditions, its tendency to deform may limit its applicability. PP and PVC-C exhibited poor performance at high temperatures, with PVC-C particularly failing above 100 °C, rendering it unsuitable for high-temperature applications. This research provides important insights for the future selection of packing materials in CO₂-amine solution systems for purification devices. Full article

(This article belongs to the Special Issue Investigation on Structure and Corrosion Resistance of Steels/Alloys, 2nd Edition)

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30 pages, 8153 KiB

Open AccessArticle

Anticorrosive Effect of New Polymer Composite Coatings on Carbon Steel in Aggressive Environments by Electrochemical Procedures

by Florina Branzoi, Adriana Băran, Marius Alexandru Mihai and Alexandru Praschiv

Coatings 2025, 15(3), 359; https://doi.org/10.3390/coatings15030359 - 20 Mar 2025

Abstract

In this investigation, electrochemical deposition procedures were reported to synthesize a novel composite polymer, 3-methylpyrrole-dodecyl sulfate sodium/3,4-ethylenedioxythiophene (3MPY-SDS/EDOT) coatings, on OL 37 samples for anticorrosion protection. The anionic surfactant dodecyl sulfate sodium used in deposition can have a relevant action on the protective [...] Read more.

In this investigation, electrochemical deposition procedures were reported to synthesize a novel composite polymer, 3-methylpyrrole-dodecyl sulfate sodium/3,4-ethylenedioxythiophene (3MPY-SDS/EDOT) coatings, on OL 37 samples for anticorrosion protection. The anionic surfactant dodecyl sulfate sodium used in deposition can have a relevant action on the protective capacity. These coatings were considered by cyclic voltammetry (CV), Fourier transform infrared (FT-IR) spectroscopy, and scanning electron microscopy (SEM) methods. The protective attributes of OL 37 coated with P3MPY-SDS/PEDOT have been examined by potentiostatic and potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) procedures in 0.5 M H₂SO₄. The corrosion rate of the P3MPY-SDS/PEDOT-coated OL 37 sample was found to be approximately nine times lower than that of the uncoated sample. The protective layers of these composites demonstrate an effectiveness of over 90%. The optimal efficiency is obtained by electrochemical deposition of P3MPY-SDS/PEDOT, performed at applied potentials of 1.0 V, 1.2 V, and 1.4 V, with current densities of 3 mA/cm² and 5 mA/cm² and a molar ratio of 5:3 at 20 min. The influence of electrochemical polymerization parameters—applied potential, current density, scan rate, cycle number, and monomer ratio—on the protective behavior of P3MPY-SDS/PEDOT layers was analyzed, identifying optimal synthesis conditions. Corrosion examinations confirmed that P3MPY-SDS/PEDOT coatings provide effective protection for OL 37 in a corrosive environment. Full article

(This article belongs to the Special Issue New Developments of Protective Coatings, Organic Polymers, and Surface Analysis: 2nd Edition)

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