Coatings

16 pages, 3662 KiB

Open AccessArticle

Synthesis and Characterization of SiO₂ Nanoparticles for Application as Nanoadsorbent to Clean Wastewater

by Nora Elizondo-Villarreal, Eleazar Gandara-Martínez, Manuel García-Méndez, Miguel Gracia-Pinilla, Ana María Guzmán-Hernández, Víctor M. Castaño and Cristian Gómez-Rodríguez

Coatings 2024, 14(7), 919; https://doi.org/10.3390/coatings14070919 - 22 Jul 2024

Viewed by 782

Abstract

By way of the sol–gel chemical synthesis method, it is possible to synthesize SiO₂ nanoparticles with a defined specific particle size, a surface area, and a defined crystal structure that can be effectively used as a nanoadsorbent to remove various organic dyes. [...] Read more.

By way of the sol–gel chemical synthesis method, it is possible to synthesize SiO₂ nanoparticles with a defined specific particle size, a surface area, and a defined crystal structure that can be effectively used as a nanoadsorbent to remove various organic dyes. SiO₂ nanoparticles were synthesized by the sol–gel method using sodium silicate (Na₂SiO₃) by a green method without using a tetraethyl orthosilicate (TEOS) precursor, which is very expensive and highly toxic. This sol–gel process involves the formation of a colloidal suspension (sol) and solid gelation to form a network in a continuous liquid phase (gel). In addition, it requires controlled atmospheres. XRD indicates the presence of an amorphous phase with a diffraction angle of 2θ = 23°, associated with SiO₂. UV-Vis spectroscopy reveals an absorbance value in the region of 200 nm to 300 nm, associated with SiO₂ nanoparticles. The application as a nanoadsorbent to remove dyes was measured, and it was found that the nanoparticles with the best performance were those that were synthesized with pH 7, showing a 97% removal with 20 mg of SiO₂ nanoparticles in 60 min. Therefore, SiO₂ nanoparticles can be used as a nanoadsorbent, using a low-cost and scalable method for application to remove methylene blue in an aqueous medium. Full article

(This article belongs to the Special Issue Advanced Technology in Environmental Remediation and Resource Utilization, 2nd Edition)

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11 pages, 3988 KiB

Open AccessArticle

Preparation of Highly Efficient and Stable All-Inorganic CsPbBr₃ Perovskite Solar Cells Using Pre-Crystallization Multi-Step Spin-Coating Method

by Yulong Zhang, Zhaoyi Jiang, Jincheng Li, Guanxiong Meng, Jiajun Guo and Weijia Zhang

Coatings 2024, 14(7), 918; https://doi.org/10.3390/coatings14070918 - 22 Jul 2024

Cited by 1 | Viewed by 723

Abstract

All-inorganic CsPbBr₃ perovskite solar cells have garnered extensive attention in the photovoltaic domain due to their remarkable environmental stability. Nevertheless, CsPbBr₃ prepared using the conventional sequential deposition method suffers from issues such as inferior crystallinity, low phase purity, and poor film [...] Read more.

All-inorganic CsPbBr₃ perovskite solar cells have garnered extensive attention in the photovoltaic domain due to their remarkable environmental stability. Nevertheless, CsPbBr₃ prepared using the conventional sequential deposition method suffers from issues such as inferior crystallinity, low phase purity, and poor film morphology. Herein, we propose a pre-crystallization methodology by introducing a minute quantity of CsBr into the PbBr₂ precursor solution to generate a small amount of CsPb₂Br₅ crystals within the PbBr₂ film, leading to a porous PbBr₂ film with enhanced crystallinity. Under the influence of more pores and CsPb₂Br₅ crystals as nucleation sites for inducing growth, a CsPbBr₃ film with a larger crystal size, lower grain boundary density, stronger crystallinity, and higher phase purity is formed. Compared with untreated devices, photovoltaic devices prepared using the pre-crystallization method achieved a champion photovoltaic conversion efficiency (PCE) of 8.62%. Furthermore, pre-crystallized devices demonstrate higher stability than untreated ones and can still retain 94% of the original PCE after being exposed to air for 1000 h without encapsulating. Full article

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

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17 pages, 5984 KiB

Open AccessArticle

Self-Healing Performance of Cellulose-Based Gel Coating with Highly Loaded Hybrid Inhibitor

by Xiong Zhao, Jixing Wang, Haibing Zhang, Hailong Zhang, Lu Ma, Xianfeng Zhang, Wenhua Cheng, Huiyu Zhang, Ali Hussein Khalaf, Bing Lin and Junlei Tang

Coatings 2024, 14(7), 917; https://doi.org/10.3390/coatings14070917 - 22 Jul 2024

Viewed by 572

Abstract

The self-healing performance of an ethyl-cellulose-based gel coating with different corrosion inhibitors was investigated in this work. Various contents of 11 alkyl imidazoline (IMO-11) were pre-loaded into the gel coating. The EIS results of scratched coatings with inhibitors confirmed the self-healing performance of [...] Read more.

The self-healing performance of an ethyl-cellulose-based gel coating with different corrosion inhibitors was investigated in this work. Various contents of 11 alkyl imidazoline (IMO-11) were pre-loaded into the gel coating. The EIS results of scratched coatings with inhibitors confirmed the self-healing performance of the coating. As the inhibitor contents increased, the improved self-healing effect was attributed to inhibitor release, while the increased inhibitor content would also affect the film-forming ability and mechanical properties of the composite coating, and lead to the accelerated failure of the coating. Different contents of thiourea and sodium oleate were added to the gel coating with 25% IMO-11. It was hoped that the hybrid inhibitor in the coating would obtain the synergistic effect of different inhibitors during the self-healing progress. The SEM and FT-IR results indicate the hybrid inhibitor was successfully loaded into the gel coating. The EIS and morphology results of scratched coatings confirmed the enhance effect of the synergistic inhibitor on the self-healing performance of the coating. The high content of the hybrid inhibitor could enhance the corrosion protection effect of the intact gel coating. Once the coating is damaged, the fast released inhibitor could extend the corrosion protection time. The synergistic effect difference of thiourea and sodium oleate with IMO-11 did not show much difference in the coating self-healing effect in this work. Full article

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

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13 pages, 6471 KiB

Open AccessArticle

Fabrication and Tribological Properties of Diamond-like Carbon Film with Cr Doping by High-Power Impulse Magnetron Sputtering

by Shuai Liu, Wenjian Zhuang, Jicheng Ding, Yuan Liu, Weibo Yu, Ying Yang, Xingguang Liu, Jing Yuan and Jun Zheng

Coatings 2024, 14(7), 916; https://doi.org/10.3390/coatings14070916 - 22 Jul 2024

Viewed by 583

Abstract

The present study aims to investigate the advantages of diamond-like carbon (DLC) films in reducing friction and lubrication to address issues such as the low surface hardness, high friction coefficients, and poor wear resistance of titanium alloys. Cr-doped DLC films were deposited by [...] Read more.

The present study aims to investigate the advantages of diamond-like carbon (DLC) films in reducing friction and lubrication to address issues such as the low surface hardness, high friction coefficients, and poor wear resistance of titanium alloys. Cr-doped DLC films were deposited by high-power impulse magnetron sputtering (HiPIMS) in an atmosphere of a gas mixture of Ar and C₂H₂. The energy of the deposited particles was controlled by adjusting the target powers, and four sets of film samples with different powers (4 kW, 8 kW, 12 kW, and 16 kW) were fabricated. The results showed that with an increase in target power, the Cr content increased from 3.73 at. % to 22.65 at. %; meanwhile, the microstructure of the film evolved from an amorphous feature to a nanocomposite structure, with carbide embedded in an amorphous carbon matrix. The sp²-C bond content was also increased in films, suggesting an intensification of the film’s graphitization. The hardness of films exhibited a trend of initially increasing and then decreasing, reaching the maximum value at 12 kW. The friction coefficient and wear rate of films showed a reverse trend compared to hardness variation, namely initially decreasing and then increasing. The friction coefficient reached a minimum value of 0.14, and the wear rate was 2.50 × 10⁻⁷ (mm³)/(N·m), at 8 kW. The abrasive wear was the primary wear mechanism for films deposited at a higher target power. Therefore, by adjusting the target power parameter, it is possible to control the content of the metal and sp²/sp³ bonds in metal-doped DLC films, thereby regulating the mechanical and tribological properties of the films and providing an effective approach for addressing surface issues in titanium alloys. Full article

(This article belongs to the Special Issue Advanced Nano-Structured Hard Coatings: Design, Synthesis, and Applications)

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18 pages, 4576 KiB

Open AccessArticle

Evaluation of Slurry-Eroded Rubber Surface Using Gloss Measurement

by Wichain Chailad and Liu Yang

Coatings 2024, 14(7), 915; https://doi.org/10.3390/coatings14070915 - 22 Jul 2024

Viewed by 675

Abstract

Slurry erosion testing is essential for evaluating the durability of materials under erosive conditions. This study examines the slurry erosion behaviours of chloroprene rubber (CR) under varying impact conditions to assess its durability. Traditional mass loss methods and qualitative techniques, including microscopy, SEM, [...] Read more.

Slurry erosion testing is essential for evaluating the durability of materials under erosive conditions. This study examines the slurry erosion behaviours of chloroprene rubber (CR) under varying impact conditions to assess its durability. Traditional mass loss methods and qualitative techniques, including microscopy, SEM, and AFM, were employed to analyse eroded CR samples. Results indicate that cumulative material loss in CR increases linearly with sand impingement after approximately 60 kg of sand and correlates with an impact energy of about 30 kJ. The highest erosion rate was found at an impact angle of 15°. Erosion mechanisms vary with impact angle, affecting surface topography from cutting and ploughing at lower angles to deformation and crater formation at higher angles. Despite their efficacy, these methods are time-intensive and costly. This paper presents a novel approach utilising gloss measurement for continuous, non-destructive monitoring of eroded rubber surfaces. Gloss measurements are 24 times faster than traditional mass loss methods. Correlating gloss values with cumulative material loss, steady-state erosion, and impact energy offers significant time savings and an enhanced understanding of the erosion process. Experimental results demonstrate the effectiveness of gloss measurement as a reliable tool in slurry erosion testing of rubbers. The quantitative output from gloss measurements could support proactive maintenance strategies to extend service life and optimise operational efficiency in industrial applications, particularly in the mining industry. Full article

(This article belongs to the Special Issue Advances in Protective Coatings: Materials, Fabrication, Corrosion and Applications)

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21 pages, 14325 KiB

Open AccessArticle

Fatigue-Healing Performance Analysis of Warm-Mix Rubber Asphalt Mastic Using the Simplified Viscoelastic Continuum Damage Theory

by Ping Li, Xiao Li, Shangjun Yu, Linhao Sun, Jinchao Yue and Ruixia Li

Coatings 2024, 14(7), 914; https://doi.org/10.3390/coatings14070914 - 21 Jul 2024

Viewed by 844

Abstract

As a green and low-carbon road material, warm-mix rubber asphalt (WMRA) has received extensive attention from scholars for its road performance. In the in-depth study of its properties, the fatigue characteristics of WMRA are particularly critical. However, in current studies on asphalt fatigue [...] Read more.

As a green and low-carbon road material, warm-mix rubber asphalt (WMRA) has received extensive attention from scholars for its road performance. In the in-depth study of its properties, the fatigue characteristics of WMRA are particularly critical. However, in current studies on asphalt fatigue performance, its self-healing ability is often underestimated or neglected. Furthermore, the simplified viscoelastic continuum damage theory (S-VECD), with its accuracy, speed, and convenience, provides a powerful tool for analyzing asphalt fatigue performance. Therefore, to analyze the fatigue and self-healing performances of WMRA in practical applications, four sample materials were selected in this study: virgin asphalt mastic (VAM), rubber asphalt mastic (RAM), Sasobit rubber asphalt mastic (SRAM), and Evotherm rubber asphalt mastic (ERAM). Subsequently, the samples were subjected to a comprehensive experimental design with frequency sweep tests, linear amplitude sweep tests, and multiple intermittent loading time sweep tests under different aging conditions. The fatigue and self-healing performances of different aging degrees and different types of WMRA were evaluated based on the S-VECD theory. The results show that aging reduces the fatigue and self-healing performances of asphalt mastic to a certain extent, and at a 7% strain, the fatigue life of SRAM after long-term aging is only 30.7% of the life of the unaged sample. The greater the aging degree, the more pronounced the effect. Under different aging levels, the warm-mix agent can significantly improve the fatigue and self-healing performances of rubber asphalt mastic. After undergoing ten fatigue intermittent loading tests, the recovery rate of the complex shear modulus for the long-term aged VAM was 0.65, which is lower than that of SRAM under the same conditions, and the warm mix can further extend the fatigue life of rubber asphalt by improving the self-healing properties of the asphalt. The role of Sasobit in enhancing the fatigue and self-healing performances of rubber asphalt mastic is more significant. This study can provide a theoretical basis for the promotion and application of WMRA pavements and contribute to the sustainable development of road construction. Full article

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

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36 pages, 24456 KiB

Open AccessReview

Research Progress on Numerical Simulation of the Deposition and Deformation Behavior of Cold Spray Particles

by Zhihao Liu, Jianwu Liu, Haifeng Li, Zizhao Wu, Yuan Zhong, Chidambaram Seshadri Ramachandran, Yingliang Cheng and Qun Wang

Coatings 2024, 14(7), 913; https://doi.org/10.3390/coatings14070913 - 21 Jul 2024

Cited by 1 | Viewed by 799

Abstract

It is of significant theoretical and practical value to study the deposition process and deformation behavior of cold-sprayed particles to find the deposition mechanism of cold-sprayed coatings, further improve the coating performance, and expand its application scope. However, observing the deposition process and [...] Read more.

It is of significant theoretical and practical value to study the deposition process and deformation behavior of cold-sprayed particles to find the deposition mechanism of cold-sprayed coatings, further improve the coating performance, and expand its application scope. However, observing the deposition process and particle behavior through experiments is difficult due to the brief deposition duration of cold spray particles. Numerical simulation offers a means to slow the deposition process and predict the critical velocity, deformation behavior, bonding mechanism, and residual stress of cold-sprayed particles. This paper uses finite element analysis software, including ANSYS LS Dynamic-2022 R1 and ABAQUS-6.14, alongside various prevalent finite element methods for numerically simulating cold spray particle deposition. These methods involve the Lagrange, Euler, arbitrary Lagrange-Euler (ALE), and Smoothed Particle Hydrodynamics (SPH) to investigate the cold spray particle deposition process. The recent literature primarily summarizes the simulation outcomes achieved by applying these methodologies for simulating the deposition process and deformation characteristics of different particles under varying cold spraying conditions. In addition, the reliability of these simulation results is analyzed by comparing the consistency between the simulation results of single-particle and multi-particle and the actual experimental results. On this basis, these methods’ advantages, disadvantages, and applicability are comprehensively analyzed, and the future simulation research work of particle deposition process and deformation behavior of cold spraying prospects is discussed. Future research is expected to provide a more in-depth study of the micro-mechanisms, such as the evolution of the inter-particle and internal organization of the particles, near the actual situation. Full article

(This article belongs to the Special Issue Cold-Sprayed Coatings: Microstructure, Mechanical Properties, and Wear Behaviour)

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10 pages, 13225 KiB

Open AccessArticle

Experimental Study on Microalloyed Steel with Layers Subjected to Diesel

by Noé López Perrusquia, Tomas de la Mora Ramírez, Gerardo Julián Pérez Mendoza, Víctor Hugo Olmos Domínguez, David Sánchez Huitron and Marco Antonio Doñu Ruiz

Coatings 2024, 14(7), 912; https://doi.org/10.3390/coatings14070912 - 21 Jul 2024

Viewed by 676

Abstract

This work studies the mechanical behavior of microalloyed steels (API X60 and API X70) with boride layers using a boriding process and immersion in diesel. First, the microalloyed steels were borided using dehydrated boron paste at a temperature of 1273 K for 6 [...] Read more.

This work studies the mechanical behavior of microalloyed steels (API X60 and API X70) with boride layers using a boriding process and immersion in diesel. First, the microalloyed steels were borided using dehydrated boron paste at a temperature of 1273 K for 6 h, and then the borided microalloyed steels were immersed in diesel for one year. The characterization of the layers on the specimens subjected to diesel used scanning electron microscopy (SEM), energy dispersive spectroscopy, and X-ray diffraction (XRD). The evaluation of the mechanical properties was performed with tensile tests according to ASTM E8, and then the fracture surface was observed by SEM. This work contributes to the understanding of the changes in the mechanical properties of borided microalloyed steel immersed in diesel for possible potential applications in the storage of fuels, oils, hydrogen, and biofuels. Full article

(This article belongs to the Special Issue Surface Engineering, Coatings and Tribology)

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11 pages, 3986 KiB

Open AccessArticle

High-Quality 4H-SiC Homogeneous Epitaxy via Homemade Horizontal Hot-Wall Reactor

by Xiaoliang Gong, Tianle Xie, Fan Hu, Ping Li, Sai Ba, Liancheng Wang and Wenhui Zhu

Coatings 2024, 14(7), 911; https://doi.org/10.3390/coatings14070911 - 20 Jul 2024

Viewed by 956

Abstract

In this paper, using a self-developed silicon carbide epitaxial reactor, we obtained high-quality 6-inch epitaxial wafers with doping concentration uniformity less than 2%, thickness uniformity less than 1% and roughness less than 0.2 nm on domestic substrates, which meets the application requirements of [...] Read more.

In this paper, using a self-developed silicon carbide epitaxial reactor, we obtained high-quality 6-inch epitaxial wafers with doping concentration uniformity less than 2%, thickness uniformity less than 1% and roughness less than 0.2 nm on domestic substrates, which meets the application requirements of high-quality Schottky Barrier Diode (SBD) and Metal–Oxide–Semiconductor Field-Effect Transistor (MOSFET) devices. We found that increasing the carrier gas flow rate can minimize source gas depletion and optimize the doping uniformity of the 6-inch epitaxial wafer from over 5% to less than 2%. Moreover, reducing the C/Si ratio significantly can suppress the “two-dimensional nucleation growth mode” and improve the wafer surface roughness Ra from 1.82 nm to 0.16 nm. Full article

(This article belongs to the Special Issue Advanced Surface Technology and Application)

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19 pages, 11064 KiB

Open AccessArticle

Multi-Objective Optimization of Surface Integrity in the Grind-Hardening Process

by Chunyan Wang, Guicheng Wang, Chungen Shen and Xinyu Dai

Coatings 2024, 14(7), 910; https://doi.org/10.3390/coatings14070910 - 20 Jul 2024

Viewed by 628

Abstract

Grind-hardening machining is a new integrated manufacturing technology that integrates the theory of material surface quenching and grinding machining. The surface integrity of grind-hardening directly affects the performance and reliability of the parts. Improving the grind-hardening quality has always been the focus and [...] Read more.

Grind-hardening machining is a new integrated manufacturing technology that integrates the theory of material surface quenching and grinding machining. The surface integrity of grind-hardening directly affects the performance and reliability of the parts. Improving the grind-hardening quality has always been the focus and difficulty in this field. Based on the surface integrity theory and the characteristics of the grind-hardening process, this paper proposed four optimization criteria for grinding parameters according to the engineering application requirements of materials. Using the expectation function, the burr cross-sectional area, depth of the effective hardened layer, and surface roughness were comprehensively analyzed under each optimization criterion to obtain an optimal combination of grinding parameters. The results revealed a significant inconsistency in the optimized grinding parameters under each optimization criterion. When considering the depth of the effective hardened layer as the primary optimization parameter and ignoring the surface roughness and burr cross-sectional area, the highest overall desirability was 0.926395. In practical application, the optimization criteria should be reasonably selected according to the actual engineering requirements. Full article

(This article belongs to the Section Ceramic Coatings and Engineering Technology)

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15 pages, 12864 KiB

Open AccessArticle

The Influence of Aging Temperatures on the Microstructure and Stress Relaxation Resistance of Cu-Cr-Ag-Si Alloy

by Haitao Liu, Longlong Lu, Guojie Wang and Yong Liu

Coatings 2024, 14(7), 909; https://doi.org/10.3390/coatings14070909 - 20 Jul 2024

Viewed by 526

Abstract

Copper alloys used in connectors rely significantly on stress relaxation resistance as a key property. In this study, a heavily deformed Cu-Cr-Ag-Si alloy underwent aging at varying temperatures, with a subsequent analysis of its mechanical properties and microstructure, with a particular emphasis on [...] Read more.

Copper alloys used in connectors rely significantly on stress relaxation resistance as a key property. In this study, a heavily deformed Cu-Cr-Ag-Si alloy underwent aging at varying temperatures, with a subsequent analysis of its mechanical properties and microstructure, with a particular emphasis on understanding the mechanism of improving stress relaxation resistance. As the aging temperature rose, the Cr precipitated into a Cr-Si composite element precipitated phase. Both work hardening and precipitation strengthening played vital roles in enhancing the stress relaxation resistance of the Cu-Cr-Ag-Si alloy, with the latter exerting a more pronounced impact. The notable performance enhancement observed after aging at 450 °C can be attributed to the synergistic effects of work hardening and precipitation strengthening. Following aging at 450 °C, the alloy demonstrated optimal performance, boasting a tensile strength of 495.25 MPa, an electrical conductivity of 84.2% IACS, and a level of 91.12%. These exceptional properties position the alloy as a highly suitable material for connector contacts. Full article

(This article belongs to the Special Issue Surface Modification of Advanced Transition Metal-Based Materials for Electrochemical Energy Storage)

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14 pages, 5504 KiB

Open AccessFeature PaperArticle

Durable Superhydrophobic Aluminum Surfaces against Immersion and Hot Steam Impact: A Comparative Evaluation of Different Hydrophobization Methods and Coatings

by Panagiotis Sarkiris, Kosmas Ellinas and Evangelos Gogolides

Coatings 2024, 14(7), 908; https://doi.org/10.3390/coatings14070908 - 20 Jul 2024

Viewed by 937

Abstract

Controlling the wettability properties of metallic materials and surfaces can enhance their applicability and improve their performance and durability in several fields, such as corrosion protection, heat transfer applications, self-cleaning, and friction reduction. Here, we present and compare some versatile fabrication methods that [...] Read more.

Controlling the wettability properties of metallic materials and surfaces can enhance their applicability and improve their performance and durability in several fields, such as corrosion protection, heat transfer applications, self-cleaning, and friction reduction. Here, we present and compare some versatile fabrication methods that can provide aluminum surfaces with durable superhydrophobic performance which are suitable for heat transfer applications. To probe their stability in heat transfer applications, two evaluation protocols are designed, one which suggests immersion in hot water for several hours, and a second testing against the harsh conditions of hot steam impact. The superhydrophobic aluminum surfaces are fabricated by first creating micro or micro-nano roughness on an initially flat surface, followed by the minimization of its surface energy through two hydrophobization methods, one wet and one dry, thus creating a series of different coating materials. Surfaces are then evaluated by immersing them in hot water and exposing them to steam impact. It is demonstrated that despite the fact that all hydrophobization methods tested resulted in surfaces exhibiting superhydrophobic properties, only the ultra-thin Teflon-like coating, obtained after plasma deposition using C₄F₈ plasma, exhibited robust superhydrophobicity with hysteresis lower than 8° when immersed in water at 90 °C for 10 h. This surface also showed minimal wettability changes and was the only one to retain its hysteresis below 6° after 4 h of exposure to hot steam. Full article

(This article belongs to the Special Issue Advances in Hydrophobic Surfaces, Texturing, and Coatings: Unveiling the Future of Surface Engineering)

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18 pages, 12149 KiB

Open AccessArticle

Microstructures and Corrosion Behaviors of Non-Equiatomic Al_0.32CrFeTi_0.73(Ni_1.50−xMo_x)(x = 0, 0.23) High-Entropy Alloy Coatings Prepared by the High-Velocity Oxygen Fuel Method

by Xiaoyong Shu, Hao Wang and Jianping Zhao

Coatings 2024, 14(7), 907; https://doi.org/10.3390/coatings14070907 - 20 Jul 2024

Viewed by 668

Abstract

The non-equiatomic Al_0.32CrFeTi_0.73(Ni_1.50−xMo_x) (x = 0, 0.23) high-entropy alloy (HEA) coatings were prepared by the high-velocity oxygen fuel (HVOF) method. The microstructures and corrosion behaviors of the HVOF-prepared coatings were investigated. The corrosion behaviors were [...] Read more.

The non-equiatomic Al_0.32CrFeTi_0.73(Ni_1.50−xMo_x) (x = 0, 0.23) high-entropy alloy (HEA) coatings were prepared by the high-velocity oxygen fuel (HVOF) method. The microstructures and corrosion behaviors of the HVOF-prepared coatings were investigated. The corrosion behaviors were characterized by polarization, EIS and Mott-Schottky tests under a 3.5 wt.% sodium chloride aqueous solution open to air at room temperature. The Al_0.32CrFeTi_0.73Ni_1.50 coating is a simple BCC single-phase solid solution structure compared with the corresponding poly-phase composite bulk. The structure of the Al_0.32CrFeTi_0.73Ni_1.27Mo_0.23 coating, combined with the introduction of the Mo element, means that the (Cr,Mo)-rich sigma phase precipitates out of the BCC solid solution matrix phase, thus forming Cr-depleted regions around the sigma phases. The solid solution of large atomic-size Mo element causes the lattice expansion of the BCC solid solution matrix phase. Micro-hole and micro-crack defects are formed on the surface of both coatings. The growth of both coatings’ passivation films is spontaneous. Both passivation films are stable and Cr₂O₃-rich, P-type, single-layer structures. The Al_0.32CrFeTi_0.73Ni_1.50 coating has better corrosion resistance and much less pitting susceptibility than the corresponding bulk. The corrosion type of the Mo-free coating is mainly pitting, occurring in the coating’s surface defects. The Al_0.32CrFeTi_0.73Ni_1.27Mo_0.23 coating with the introduction of Mo element increases pitting susceptibility and deteriorates corrosion resistance compared with the Mo-free Al_0.32CrFeTi_0.73Ni_1.50 coating. The corrosion type of the Mo-bearing coating is mainly pitting, occurring in the coating’s surface defects and Cr-depleted regions. Full article

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

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16 pages, 6467 KiB

Open AccessArticle

Preparation of CrCoFeNiMn High-Entropy Alloy Coatings Using Gas Atomization and Laser Cladding: An Investigation of Microstructure, Mechanical Properties, and Wear Resistance

by Haodong Tian, Yuzhen Yu, Xi Wang, Fan Chen and He Liu

Coatings 2024, 14(7), 906; https://doi.org/10.3390/coatings14070906 - 19 Jul 2024

Viewed by 695

Abstract

In this study, a spherical CrCoFeNiMn high-entropy alloy (HEA) powder with uniform size was prepared using gas atomization. High-quality CrCoFeNiMn HEA coatings were then applied to a 316L stainless steel substrate using prepowdered laser cladding. The main focus of the study is on [...] Read more.

In this study, a spherical CrCoFeNiMn high-entropy alloy (HEA) powder with uniform size was prepared using gas atomization. High-quality CrCoFeNiMn HEA coatings were then applied to a 316L stainless steel substrate using prepowdered laser cladding. The main focus of the study is on the phase structure composition and stability, microstructure evolution mechanism, mechanical properties, and wear resistance of CrCoFeNiMn HEA coatings. The results show that the CrCoFeNiMn HEA coatings prepared using gas atomization and laser melting techniques have a single FCC phase structure with a stable phase composition. The coatings had significantly higher diffraction peak intensities than the prepared HEA powders. The coating showed an evolution of columnar and equiaxed crystals, as well as twinned dislocation structures. Simultaneously, the microstructure transitions from large-angle grain boundaries to small-angle grain boundaries, resulting in a significant refinement of the grain structure. The CrCoFeNiMn HEA coating exhibits excellent mechanical properties. The microhardness of the coating increased by 66.06% when compared to the substrate, the maximum wear depth was reduced by 65.59%, and the average coefficient of friction decreased by 9.71%. These improvements are mainly attributed to the synergistic effects of grain boundary strengthening, fine grain strengthening, and twinning and dislocation strengthening within the coating. Full article

(This article belongs to the Special Issue Laser Surface Modifications and Additive Manufacturing)

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28 pages, 9038 KiB

Open AccessArticle

Analysis of the Interfacial Interaction between Wood Tar-Rejuvenated Asphalt and Aggregate Based on Molecular Dynamics Simulation

by Le Xu, Guoqing Gong, Deliang Zeng, Yongwei Li, Xing Chen, Kefei Liu and Quan Li

Coatings 2024, 14(7), 905; https://doi.org/10.3390/coatings14070905 - 19 Jul 2024

Viewed by 492

Abstract

This study utilized molecular dynamics simulation to investigate the adhesion process between wood tar-rejuvenated asphalt and acid/alkaline aggregate. Initially, various indicators including the contact area, cohesion coefficient, and interaction energy were employed to assess the adhesion effect under dry conditions. This revealed the [...] Read more.

This study utilized molecular dynamics simulation to investigate the adhesion process between wood tar-rejuvenated asphalt and acid/alkaline aggregate. Initially, various indicators including the contact area, cohesion coefficient, and interaction energy were employed to assess the adhesion effect under dry conditions. This revealed the action mechanism of the wood tar-rejuvenator in enhancing the adhesion performance between aged asphalt and aggregate. Subsequently, an asphalt–water–aggregate interface model was developed to simulate the water damage process of the asphalt mixture. This aimed to unveil the damage mechanism of water intrusion on the adhesion performance of the asphalt–aggregate interface and evaluate the water damage resistance of wood tar-rejuvenated asphalt through adhesion energy, stripping work, and the energy ratio. The findings indicate that wood tar-rejuvenated asphalt exhibits favorable adhesion properties with both acid and alkaline aggregates. The addition of wood tar-rejuvenated asphalt increased the interaction energy between aged asphalt and acid and alkali aggregates by 67.75 kJ/mol and 97.3 kJ/mol, respectively. The addition of a wood tar rejuvenator enhances the interaction energy between aged asphalt and aggregate, thereby increasing mutual attraction and enlarging the contact area. The adhesion between asphalt and aggregates hinges on the interaction between asphaltene and aggregates, and the wood tar rejuvenator reduces the diffusion ability of asphaltene in the attractive state of the aggregate, resulting in stable aggregation. Moisture intrusion increased the aggregation distance between asphaltene and aggregate by 14.1% and decreased the degree of aggregation by 24.0%, thereby reducing the interaction energy. The extent of damage caused by water intrusion is linked to the aggregation distance, with greater distances leading to deeper damage. Under wet conditions, the interaction energy of wood tar-rejuvenated asphalt increased by 78.2% in the acidic aggregate system and 98.1% in the basic aggregate system compared with aged asphalt. Meanwhile, wood tar-based rejuvenated asphalt improves the adhesion between aged asphalt and aggregate and reduces the stripping function of asphalt affected by water replacement, which results in the ER value of wood tar-rejuvenated asphalt being higher than that of the original asphalt by 0.12 and 0.22 in the acidic and alkaline environments, respectively, thus showing excellent resistance to water damage. This study provides new criteria for the selection of rejuvenators for waste asphalt, which will help in the future selection of superior rejuvenators for aged asphalt and reduce the possibility of choosing the wrong rejuvenator. Full article

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

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11 pages, 6595 KiB

Open AccessArticle

Study on the Degradation Performance of AlGaN-Based Deep Ultraviolet LEDs under Thermal and Electrical Stress

by Mingfeng Gong, Xuejiao Sun, Cheng Lei, Ting Liang, Fengchao Li, Yu Xie, Jinmin Li and Naixin Liu

Coatings 2024, 14(7), 904; https://doi.org/10.3390/coatings14070904 - 19 Jul 2024

Cited by 1 | Viewed by 689

Abstract

AlGaN-based deep-ultraviolet (DUV) LEDs could realize higher optical power output when adopting a p-AlGaN contact layer instead of a p-GaN contact layer. However, this new type DUV LEDs exhibit poor reliability. Thus, this study thoroughly investigates the degradation behaviors of AlGaN-based DUV LEDs [...] Read more.

AlGaN-based deep-ultraviolet (DUV) LEDs could realize higher optical power output when adopting a p-AlGaN contact layer instead of a p-GaN contact layer. However, this new type DUV LEDs exhibit poor reliability. Thus, this study thoroughly investigates the degradation behaviors of AlGaN-based DUV LEDs with a p-AlGaN contact layer through different aging tests, including single thermal stress, single electrical stress with air-cooling, single electrical stress, and thermoelectric complex stress. It can be found that both high temperature and large working current play crucial roles in accelerating the degradation of optoelectronic properties of the DUV LEDs, and the single high thermal stress without electrical stress can also bring obvious performance degradation to the DUV LEDs, which is a significantly different finding from previous studies. This is because thermal stress on DUV LED could bring some metal electrode elements entering the p-AlGaN layer. Thus, the degradation of optical and electrical properties under the thermal and electrical stress could be not only attributed to the degradation of the device’s ohmic contacts, but also due to the metal electrode elements entering the p-AlGaN layer through thermal diffusion, leading to the generation of tunneling current and the generation of defects within or around the active region. Despite that the peak wavelengths of the DUV LEDs remained stable, the turn-on voltage and series resistance increased. Particularly worth mentioning is that the value of the optical power degradation under thermoelectric conditions is larger than the sum of the single thermal and single electrical optical power degradation, which is a result of the mutual reinforcement of thermal and electrical stresses to exacerbate the defect generation and ohmic contact degradation. Based on the study above, preparing p-AlGaN layers with hyperfine gradient aluminum fractions and reducing the junction temperature may help to improve the reliability of AlGaN-based DUV LEDs with the p-AlGaN contact layer. Full article

(This article belongs to the Special Issue Optical Thin Films: Preparation, Application and Development)

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9 pages, 3107 KiB

Open AccessCommunication

Atomic-Scale Structural and Magnetic Coupling Properties of Twin Boundaries in Lithium Ferrite (Li_0.5Fe_2.5O₄) Film

by Kun Liu, Jiankang Li and Songyou Zhang

Coatings 2024, 14(7), 903; https://doi.org/10.3390/coatings14070903 - 19 Jul 2024

Viewed by 581

Abstract

It is of great academic significance to understand the influence that the atomic-scale structure of interfaces and boundaries within materials has on magnetic coupling characteristics and promote the innovation of advanced magnetic devices. Here, we carried out a systematic investigation of the atomic [...] Read more.

It is of great academic significance to understand the influence that the atomic-scale structure of interfaces and boundaries within materials has on magnetic coupling characteristics and promote the innovation of advanced magnetic devices. Here, we carried out a systematic investigation of the atomic and electronic structures of twin boundaries (TBs) in Li_0.5Fe_2.5O₄ (LFO) thin films and determined their concurrent magnetic couplings using atomic-resolution transmission electron microscopy and first-principle calculations at the atomic scale. The results show that ferromagnetic or antiferromagnetic coupling can exist across the different TBs in LFO thin films, and electrical structures within a few atomic layers directly rely on the atom arrangement across the TB. Uncovering one-to-one relationships between the magnetic coupling properties of individual TBs and atomic-scale structures can clarify a thorough comprehension of numerous fascinating magnetic properties of commonly utilized magnetic materials, which will undoubtedly encourage the progress of sophisticated magnetic materials and devices. Full article

(This article belongs to the Section Thin Films)

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15 pages, 7613 KiB

Open AccessArticle

Failure of Electron Beam Physical Vapor Deposited Thermal Barrier Coatings System under Cyclic Thermo-Mechanical Loading with a Thermal Gradient

by Liyu Liu, Delin Liu, Huangyue Cai, Rende Mu, Wenhui Yang and Limin He

Coatings 2024, 14(7), 902; https://doi.org/10.3390/coatings14070902 - 18 Jul 2024

Viewed by 1942

Abstract

The failure mechanism of a thermal barrier coatings (TBCs) system is investigated using cyclic thermo-mechanical loading with a thermal gradient. Hollow circular cylindrical specimens are employed, consisting of a nickel-based single-crystal alloy DD6 coated with a NiCoCrAlYHf bond coat via arc-ion plating and [...] Read more.

The failure mechanism of a thermal barrier coatings (TBCs) system is investigated using cyclic thermo-mechanical loading with a thermal gradient. Hollow circular cylindrical specimens are employed, consisting of a nickel-based single-crystal alloy DD6 coated with a NiCoCrAlYHf bond coat via arc-ion plating and a surface electron beam physical vapor deposited (EB-PVD) yttria-stabilized zirconia topcoat. The experimental setup allows for a surface temperature of 1130 °C and a substrate temperature of 1070 °C, while a tensile mechanical load of 200 MPa is employed to simulate the centrifugal stress in the middle of the high-pressure turbine blade. The comparison between TBCs with and without mechanical loading implies that the coupled thermo-mechanical load significantly promotes coating spallation since the superposition of mechanical strain enhances the local tensile stress at the peak region of the topcoat/thermally grown oxides (TGOs) interface. A subsequent interfacial morphology analysis demonstrates that the topcoat/TGO interface exhibited a degradation in the direction parallel to the mechanical loading axis. For all the specimens, TGO comprises a duplex structure, consisting of outer spinel and inner α-Al₂O₃. Full article

(This article belongs to the Special Issue Recent Advances in the Materials, Preparations, and Properties of Thermal Barrier Coatings)

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12 pages, 3243 KiB

Open AccessArticle

Effects of Precursors Ratio and Curing Treatment on the Icephobicity of Polydimethylsiloxane

by Marcella Balordi, Alessandro Casali, Paolo Gadia, Paolo Pelagatti, Francesco Pini and Giorgio Santucci de Magistris

Coatings 2024, 14(7), 901; https://doi.org/10.3390/coatings14070901 - 18 Jul 2024

Viewed by 664

Abstract

Elastomers are intriguing materials for many applications, one of these being icephobic coatings. Elastic modulus and work of adhesion are the key parameters coming into play in ice detachment mechanisms, and can be related to hardness and wettability. Polydimethylsiloxane (PDMS) is widely used [...] Read more.

Elastomers are intriguing materials for many applications, one of these being icephobic coatings. Elastic modulus and work of adhesion are the key parameters coming into play in ice detachment mechanisms, and can be related to hardness and wettability. Polydimethylsiloxane (PDMS) is widely used for anti-ice applications; however, not many works deal with the correlation between cross-linking grade, curing treatments, and icephobicity. This study focuses on PDMS (Sylgard184^®) coatings, encompassing four different pre-polymer to cross-linking agent (A:B) ratios ranging from 5:1 to 30:1, and nine curing treatments. The results indicate that increasing the A:B ratio enhances hydrophobicity, softness, and icephobicity, assessed through shear stress measurements. Curing treatments primarily affect hardness and icephobicity, with longer heat treatments resulting in higher hardness and ice adhesion. All samples exhibit promising performances in lowering shear stress values, up to seven times in respect to the uncoated reference for 30:1 ratio. Additionally, a durability assessment is conducted on samples exposed to stress tests in the climatic chamber. A slight deterioration in hydrophobicity across all samples is observed and, notably, a significant hardness increase, around 13%, is experienced for the 5:1 ratio only. The samples also demonstrate an overall robust icephobicity after stress tests, and, for the 30:1 ratio, an average shear stress value four times lower than the reference is maintained. In this work, we highlight the importance of the fine-tuning of the precursors ratio and thermal treatments on the PDMS properties and durability. Full article

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

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20 pages, 7035 KiB

Open AccessArticle

Biochemical and Microbiological Properties of the Cotton–Copper Composite Material Obtained via Sputter Deposition

by Małgorzata Świerczyńska, Zdzisława Mrozińska, Michał Juszczak, Katarzyna Woźniak and Marcin H. Kudzin

Coatings 2024, 14(7), 900; https://doi.org/10.3390/coatings14070900 - 18 Jul 2024

Viewed by 988

Abstract

This study investigated the biochemical and microbiological properties of Cotton–Copper composite materials obtained using magnetron sputtering technology. Copper particles were precisely distributed on the fabric surface, ensuring free airflow without the need to create additional layers. The Cotton–Copper composite materials were subjected to [...] Read more.

This study investigated the biochemical and microbiological properties of Cotton–Copper composite materials obtained using magnetron sputtering technology. Copper particles were precisely distributed on the fabric surface, ensuring free airflow without the need to create additional layers. The Cotton–Copper composite materials were subjected to physiochemical and biological investigations. The physiochemical analysis included the elemental analysis of composites (C, N, O, S, Cu) and analyses of their microscopic and surface properties (specific surface area and total pore volume). The biological investigations consisted of microbiological and biochemical–hematological tests, including evaluation of the activated partial thromboplastin time and prothrombin time. Experiments showed significant effectiveness of the antibacterial material against representative strains of fungi and bacterial species. We also demonstrated the ability of the cotton–copper material to interact directly with the plasmid DNA. Full article

(This article belongs to the Special Issue Advances in Functional Bio-Coatings)

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14 pages, 7718 KiB

Open AccessArticle

Development of Method for Applying Multilayer Gradient Thermal Protective Coatings Using Detonation Spraying

by Dastan Buitkenov, Aiym Nabioldina and Nurmakhanbet Raisov

Coatings 2024, 14(7), 899; https://doi.org/10.3390/coatings14070899 - 18 Jul 2024

Viewed by 602

Abstract

In this work, multilayer gradient coatings obtained by detonation spraying were studied. To obtain a multilayer gradient coating by detonation spraying, two modes with different numbers of shots of NiCrAlY and YSZ were developed. The presented results demonstrate the effectiveness of creating a [...] Read more.

In this work, multilayer gradient coatings obtained by detonation spraying were studied. To obtain a multilayer gradient coating by detonation spraying, two modes with different numbers of shots of NiCrAlY and YSZ were developed. The presented results demonstrate the effectiveness of creating a gradient structure in coatings, ensuring a smooth transition from metal to ceramic materials. Morphological analysis of the coatings confirmed a layered gradient structure, consisting of a lower metallic (NiCrAlY) layer and an upper ceramic (YSZ) layer. The variation in the contents of elements along the thickness of the coatings indicates the formation of a gradient structure. X-ray analysis shows that all peaks in the X-ray diffraction patterns correspond to a single ZrO₂ phase, indicating the formation of a non-transformable tetragonal primary (t′) phase characteristic of the thermal protective coatings. This phase is known for its stability and resistance to phase transformation under changing operating temperature conditions. As the thickness of the coatings increased, an improvement in their mechanical characteristics was found, such as a decrease in the coefficient of friction, an increase in hardness, and an increase in surface roughness. These properties make such coatings more resistant to mechanical wear, especially under sliding conditions, which confirms their prospects for use in a variety of engineering applications, including aerospace and power generation. Full article

(This article belongs to the Special Issue Applications of Ceramic and Cermet Coatings)

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17 pages, 1194 KiB

Open AccessArticle

On the Representativeness of Proton Radiation Resistance Tests on Optical Coatings for Interplanetary Missions

by Anna Sytchkova, Maria Lucia Protopapa, Paolo Olivero, Zicai Shen and Yanzhi Wang

Coatings 2024, 14(7), 898; https://doi.org/10.3390/coatings14070898 - 18 Jul 2024

Viewed by 474

Abstract

Optical instrumentation used in space normally employs optical coatings. Future interplanetary space missions will be characterized by ever longer stays in environmental conditions where low energy protons represent one of the main types of radiation impacting the coating longevity and performance. To ensure [...] Read more.

Optical instrumentation used in space normally employs optical coatings. Future interplanetary space missions will be characterized by ever longer stays in environmental conditions where low energy protons represent one of the main types of radiation impacting the coating longevity and performance. To ensure the reliability of coated optics, environmental resistance tests should be accurately planned to be representative for a mission. To this end, the existing standards for coating tests and the test results interpretation have been constantly improved. In this study, we analyze the relevant standards of the European Space Agency (ESA) and of the Chinese Space Agency (CSA) for testing coated optics for interplanetary missions, and in particular for the missions at the Lagrange points. We focus in particular on the applicability of these standards and hence on their possible refinement when specifically implemented to the optical thin films and coatings. We proceed with the development of a methodology for reliable interpretation of the proton irradiation tests for the optical coatings for interplanetary missions, first briefly overviewing the existing tools which allow for space environment simulation and hence deriving the test conditions for the Lagrange points. Furthermore, we apply the approach to testing of aluminum oxide optical coatings for applications in the visible spectral range, concluding on the representativeness of the proposed approach and on possible refinement of the existing standards for coating tests when they are specifically developed for optical applications. Full article

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15 pages, 5913 KiB

Open AccessArticle

In Situ Fabrication of Ti-xNb Alloys by Conventional Powder Metallurgy

by Rogelio Macias, Jr., Pedro Garnica González, Luis Olmos, Ivon Alanis-Fuerte, Omar Jimenez, Francisco Alvarado-Hernández, Melina Velasco-Plascencia and Jorge Alejandro Ávila-Olivera

Coatings 2024, 14(7), 897; https://doi.org/10.3390/coatings14070897 - 18 Jul 2024

Viewed by 725

Abstract

The present study shows the effect of Nb on a Ti matrix to fabricate composites via the conventional powder metallurgy for medical applications. Ti powder mixture compacts with different Nb contents were obtained from the conventional pressing and sintering technique. The sintering behavior [...] Read more.

The present study shows the effect of Nb on a Ti matrix to fabricate composites via the conventional powder metallurgy for medical applications. Ti powder mixture compacts with different Nb contents were obtained from the conventional pressing and sintering technique. The sintering behavior was evaluated using the dilatometry technique, and the microstructure was studied using scanning electron microscopy (SEM) and X-ray diffraction (XDR). The mechanical properties were obtained from simple compression tests, and the corrosion resistance was determined from a standard three-electrode arrangement in Hank’s solution. The results showed that the Nb in the Ti matrix limits the evolution of sintering depending on the Nb content. Nb slightly accelerates the phase transition temperature. The microstructure and X-rays revealed that biphasic α + β-Ti structures can be obtained, in addition to retaining the β-Ti phase and forming the martensitic phases α′ and α″ of Ti. Likewise, the mechanical behavior showed a Young’s modulus of 10–45 GPa, which is close to that reported for human bones. Furthermore, the circuit analysis revealed that the Ti-Nb sintered systems were conditioned by the surface oxide layer and that the oxide layer formed within the residual pores of the sintering process. Finally, it was demonstrated that adding Nb to the Ti matrix increases the corrosion resistance and that contents close to 15 wt.% of this element have the best results. Full article

(This article belongs to the Special Issue Trends in Spark Plasma Sintering of Advanced Materials)

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10 pages, 1653 KiB

Open AccessArticle

Effect of Gas Flow Ratio on the Chemical and Electrochemical Properties of Bismuth-Oxygen Films Deposited in Reactive Phase Sputtering

by Giovany Orozco-Hernandez, Jhon Jairo Olaya-Flórez, Jose Edgar Alfonso-Orjuela, Daniel Alejandro Pineda-Hernandez and Elisabeth Restrepo-Parra

Coatings 2024, 14(7), 896; https://doi.org/10.3390/coatings14070896 - 17 Jul 2024

Viewed by 628

Abstract

In this work, the study of chemical, physical, and electrochemical behavior of bismuth and oxygen-based thin films, produced through an unbalanced magnetron sputtering (UMS) technique in reactive phase, is presented. The main aim of this investigation is to analyze the influence of Ar/O [...] Read more.

In this work, the study of chemical, physical, and electrochemical behavior of bismuth and oxygen-based thin films, produced through an unbalanced magnetron sputtering (UMS) technique in reactive phase, is presented. The main aim of this investigation is to analyze the influence of Ar/O₂ gas flow on the microstructure, chemical composition, and corrosion properties of bismuth and oxygen-based thin films. Coatings were grown keeping the power at 50 W with a mixture of Ar:O₂ (80/20) as constants, while the gas flow rate was varied taking values of 12, 15, 20, 25, and 30 sccm. X-ray diffraction (XRD) analyses were carried out showing that films exhibited a polycrystalline Bi phase and no crystalline bismuth oxide phases. For elemental composition analysis, the Rutherford backscattering spectroscopy (RBS) technique was used. The results suggested that film compositions were a mixture of metallic bismuth and amorphous bismuth oxide; moreover, chemical elemental distribution was studied using proton-induced X-ray emission (PIXE) measurements determining that before the corrosion analysis, samples exhibited a uniform distribution of Bi and O. Finally, the influence of the gas flow on the films anticorrosive properties was discussed. Potentiodynamic polarization technique results revealed that the corrosive behavior highly depends on the sample production parameters; samples grown at 20 and 30 sccm showed the best corrosion resistance represented in lower corrosion current density. This behavior is probably due to the thickness of these films. Full article

(This article belongs to the Section Thin Films)

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22 pages, 4157 KiB

Open AccessArticle

Characterization of Indium Tin Oxide (ITO) Thin Films towards Terahertz (THz) Functional Device Applications

by Anup Kumar Sahoo, Wei-Chen Au and Ci-Ling Pan

Coatings 2024, 14(7), 895; https://doi.org/10.3390/coatings14070895 - 17 Jul 2024

Viewed by 736

Abstract

In this study, we explored the manipulation of optical properties in the terahertz (THz) frequency band of radio-frequency (RF) sputtered indium tin oxide (ITO) thin films on highly resistive silicon substrate by rapid thermal annealing (RTA). The optical constants of as-deposited and RTA-processed [...] Read more.

In this study, we explored the manipulation of optical properties in the terahertz (THz) frequency band of radio-frequency (RF) sputtered indium tin oxide (ITO) thin films on highly resistive silicon substrate by rapid thermal annealing (RTA). The optical constants of as-deposited and RTA-processed ITO films annealed at 400 °C, 600 °C and 800 °C are determined in the frequency range of 0.2 to 1.0 THz. The transmittance can be changed from ~27% for as-deposited to ~10% and ~39% for ITO films heat-treated at different annealing temperatures (T_a’s). Such variations of optical properties in the far infrared for the samples under study are correlated with their mobility and carrier concentration, which are extracted from Drude–Smith modeling of THz conductivity with plasma frequency, scattering time and the c-parameters as fitting parameters. Resistivities of the films are in the range of 10⁻³ to 10⁻⁴ Ω-cm, confirming that annealed ITO films can potentially be used as transparent conducting electrodes for photonic devices operating at THz frequencies. The highest mobility, μ = 47 cm²/V∙s, with carrier concentration, N_c = 1.31 × 10²¹ cm⁻³, was observed for ITO films annealed at T_a = 600 °C. The scattering times of the samples were in the range of 8–21 fs, with c-values of −0.63 to −0.87, indicating strong backscattering of the carriers, mainly by grain boundaries in the polycrystalline film. To better understand the nature of these films, we have also characterized the surface morphology, microscopic structural properties and chemical composition of as-deposited and RTA-processed ITO thin films. For comparison, we have summarized the optical properties of ITO films sputtered onto fused silica substrates, as-deposited and RTA-annealed, in the visible transparency window of 400–800 nm. The optical bandgaps of the ITO thin films were evaluated with a Tauc plot from the absorption spectra. Full article

(This article belongs to the Special Issue Thermoelectric Thin Films for Thermal Energy Harvesting)

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15 pages, 8012 KiB

Open AccessArticle

Bamboo-like MnO₂/TiO₂ Nanotube Arrays with Enhanced Photocatalytic Degradation

by Feng Liang, Yanxiong Xiang, Yunjiang Yu and Changwei Zou

Coatings 2024, 14(7), 894; https://doi.org/10.3390/coatings14070894 - 17 Jul 2024

Viewed by 548

Abstract

In this paper, the photocatalytic degradation of methyl orange solution by MnO₂/TiO₂ nanotube arrays (NTAs) with different structure was studied. Initially, bamboo-like TiO₂ NTAs with folded tube walls were synthesized using the anodic oxidation method. Subsequently, MnO₂ nanowires/TiO [...] Read more.

In this paper, the photocatalytic degradation of methyl orange solution by MnO₂/TiO₂ nanotube arrays (NTAs) with different structure was studied. Initially, bamboo-like TiO₂ NTAs with folded tube walls were synthesized using the anodic oxidation method. Subsequently, MnO₂ nanowires/TiO₂ NTAs and MnO₂ nanoparticles/TiO₂ NTAs were prepared via high-temperature and low-temperature hydrothermal methods, respectively. Photocurrent-time transient tests revealed that MnO₂ nanoparticles/TiO₂ NTAs produced by the low-temperature hydrothermal method exhibited a relatively good photocurrent response. All the deposited MnO₂/TiO₂ bamboo-like nanotube nanocomposites were tested for photocatalytic decomposition under different pH and light conditions. The results showed that MnO₂ could adsorb and degrade methyl orange in the absence of light and acidity, and the degradation degree was proportional to the concentrations of Mn. MnO₂ was stimulated to produce photogenic electrons, which migrated to the surface of the TiO₂ and extended the life of photogenic charge carriers. Full article

(This article belongs to the Collection Advanced Surface Coating of Nanoparticles)

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15 pages, 7208 KiB

Open AccessArticle

Chemical Bonding of Nanorod Hydroxyapatite to the Surface of Calciumfluoroaluminosilicate Particles for Improving the Histocompatibility of Glass Ionomer Cement

by Sohee Kang, So Jung Park, Sukyoung Kim and Inn-Kyu Kang

Coatings 2024, 14(7), 893; https://doi.org/10.3390/coatings14070893 - 17 Jul 2024

Viewed by 602

Abstract

Glass ionomer cement (GIC) is composed of anionic polyacrylic acid and a silica-based inorganic powder. GIC is used as a filling material in the decayed cavity of the tooth; therefore, compatibility with the tooth tissue is essential. In the present study, we aimed [...] Read more.

Glass ionomer cement (GIC) is composed of anionic polyacrylic acid and a silica-based inorganic powder. GIC is used as a filling material in the decayed cavity of the tooth; therefore, compatibility with the tooth tissue is essential. In the present study, we aimed to improve the histocompatibility of GIC by introducing nano-hydroxyapatite (nHA), a component of teeth, into a silica-based inorganic powder. CFAS-nHA was prepared by chemically bonding nanorod hydroxyapatite (nHA) to the surface of calciumfluoroaluminosilicate (CFAS). The synthesis of CFAS-nHA was confirmed using Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The prepared CFAS-nHA was mixed with polyacrylic acid and cured to prepare GIC containing nHA (GIC-nHA). Cytocompatibility tests of GIC-nHA and GIC were performed using osteoblasts. Osteoblast activity and bone formation ability were superior after GIC-nHA treatment than after control GIC treatment. This enhanced histocompatibility is believed to be due to the improvement of the biological activity of osteoblasts induced by the HA introduced into the GIC. Therefore, to enhance its compatibility with dental tissues, GIC could be manufactured by chemically bonding nHA to the surface of GI inorganic powder. Full article

(This article belongs to the Special Issue Advanced Biomaterials and Coatings)

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16 pages, 11755 KiB

Open AccessArticle

Microstructure and High-Temperature Mechanical Properties of a Superalloy Joint Deposited with CoCrMo and CoCrW Welding Wires

by Shuai Huang, Tianyuan Wang, Jian Miao, Xing Chen, Guohui Zhang, Bingqing Chen and Biao Zhou

Coatings 2024, 14(7), 892; https://doi.org/10.3390/coatings14070892 - 17 Jul 2024

Viewed by 421

Abstract

The preparation of a single crystal superalloy surface overlay welding coating to improve its high-temperature mechanical properties is of great significance for prolonging the service life of blades. This work selected two types of welding wire alloys, CoCrMo and CoCrW, to prepare coatings [...] Read more.

The preparation of a single crystal superalloy surface overlay welding coating to improve its high-temperature mechanical properties is of great significance for prolonging the service life of blades. This work selected two types of welding wire alloys, CoCrMo and CoCrW, to prepare coatings on the surface of a single crystal superalloy. A comparative study was conducted on their mechanical properties, such as tension, compression, fatigue, durability, and wear at a high temperature of 900 ℃, aiming to reveal the high-temperature mechanical properties of the two types of welding coatings. Results showed that the average high-temperature tensile strength of the CoCrMo welded specimen was smaller than that of the CoCrW welded specimen; the average high-temperature duration of CoCrMo welded specimens at 150 MPa was lower than the average duration of CoCrW welded specimens; the high-temperature fatigue life of CoCrMo welded specimens at 220 MPa was 7.186 × 10⁵; and the average high-temperature wear rate of CoCrMo sample was 3.64 × 10⁻⁶ mm³·N⁻¹·m⁻¹. The CoCrW alloy was more wear resistant than CoCrMo. The hardness of CoCrMo welded joints gradually increased from the substrate to the heat-affected zone and then to the fusion zone, and was much higher in the fusion zone than in the CoCrW alloy. Full article

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

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19 pages, 4965 KiB

Open AccessArticle

Adsorption Capability and Mechanism of Pb(II) Using MgO Nanomaterials Synthesized by Ultrasonic Electrodeposition

by Dan Tang, Quanqing Zhang, Guanglei Tan, Lijie He and Fafeng Xia

Coatings 2024, 14(7), 891; https://doi.org/10.3390/coatings14070891 - 17 Jul 2024

Viewed by 639

Abstract

This work describes the process of synthesizing magnesia (MgO) nanomaterials through ultrasonic electrodeposition, followed by an examination of their ability and mechanism to remove Pb(II) from industrial soil at 100, 150, and 200 W ultrasonic powers. Nanomaterials were examined for their surface shape [...] Read more.

This work describes the process of synthesizing magnesia (MgO) nanomaterials through ultrasonic electrodeposition, followed by an examination of their ability and mechanism to remove Pb(II) from industrial soil at 100, 150, and 200 W ultrasonic powers. Nanomaterials were examined for their surface shape and phase composition using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffractometry (XRD). The capability of magnesia nanomaterials to adsorb Pb(II) improved greatly when operated at 150 W, attaining a maximal 68.94 mg/g value. Adsorption of Pb(II) onto magnesia nanomaterial surfaces was examined by utilizing the pseudo-second-order kinetic and Langmuir models. The nanomaterials exhibited significant features of both chemical and monolayer adsorptions for Pb(II) as a result of the intense chemical interactions between the atoms of the magnesia nanomaterials’ surface and Pb(II), as shown by Fourier transform infrared (FTIR) analysis. At 30 °C, the magnesia nanomaterial exhibited the highest adsorption capacity for Pb(II), suggesting that temperature played a significant role in this capacity. Furthermore, the Langmuir model produced a correlation coefficient greater than 0.99, indicating an excellent fit for the adsorption behavior of magnesia towards Pb(II). The findings suggest that ultrasonic power significantly impacts the adsorption characteristics of magnesia nanoparticles synthesized via ultrasonic electrodeposition. Specifically, ultrasonic power of 150 W yields the most efficient adsorption characteristics. Moreover, the 150 W-fabricated magnesia materials demonstrated exceptional pH compatibility. Full article

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17 pages, 16914 KiB

Open AccessArticle

Experimental Investigation of Corrosion Behavior of Zinc–Aluminum Alloy-Coated High-Strength Steel Wires under Stress Condition

by Kun Fang, Xiaoyong Liu, Pei Chen, Xianfu Luo, Zhenliang Liu, Xiaoqin Zha, Xinyao Zhang and Jianfei Zhai

Coatings 2024, 14(7), 890; https://doi.org/10.3390/coatings14070890 - 17 Jul 2024

Viewed by 546

Abstract

To cope with harsh working conditions, new corrosion-resistant coated steel wires with higher tensile strength have been developed. This study investigates the corrosion characteristics of a new zinc–aluminum alloy-coated steel wire under stress conditions. The particulate corrosion products generated by the oxidation of [...] Read more.

To cope with harsh working conditions, new corrosion-resistant coated steel wires with higher tensile strength have been developed. This study investigates the corrosion characteristics of a new zinc–aluminum alloy-coated steel wire under stress conditions. The particulate corrosion products generated by the oxidation of the coating in the initial stage of corrosion are converted into layer-structured corrosion products at the early stage of corrosion. Moreover, high-stress conditions have a significant influence on the critical conversion time from the coating corrosion stage to the iron matrix corrosion stage. Thus, the uniform corrosion depth (i.e., the mass loss rate) could be fitted with a continuous power function model rather than the previously used two-stage model owing to an ambiguous moment of conversion under stress conditions. The pitting corrosion depth could be fitted with a lognormal distribution in this study. The probability distributions for the aspect ratios of corrosion pits under different stress conditions tended to be consistent. Finally, the block’s maximum pitting factor followed a Gumbel distribution with a scale parameter that changed linearly with the stress level and a location parameter related to the square of the stress level. Full article

(This article belongs to the Special Issue Micro- and Nano- Mechanical Testing of Coatings and Surfaces)

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