Coatings

9 pages, 956 KB

Open AccessEditor’s ChoiceArticle

Atomic Layer Deposition of Y₂O₃ Thin Films Using Y(MeCp)₂(iPr-nPrAMD) Precursor and H₂O, and Their Erosion Resistance in CF₄-Based Plasma

by Seong Lee, Hyunchang Kim and Sehun Kwon

Coatings 2025, 15(1), 22; https://doi.org/10.3390/coatings15010022 - 30 Dec 2024

Cited by 2 | Viewed by 1604

Abstract

Atomic layer deposition (ALD) of Y₂O₃ thin films was investigated using Y(MeCp)₂(iPr-nPrAMD) precursor and H₂O reactant. The self-limiting reaction mechanism of ALD-Y₂O₃ thin films was confirmed at a growth temperature of 260 °C. [...] Read more.

Atomic layer deposition (ALD) of Y₂O₃ thin films was investigated using Y(MeCp)₂(iPr-nPrAMD) precursor and H₂O reactant. The self-limiting reaction mechanism of ALD-Y₂O₃ thin films was confirmed at a growth temperature of 260 °C. And, the saturated growth rate was confirmed to be ~0.11 nm/cycle. Also, it was demonstrated that a wide ALD temperature window from 150 °C to 290 °C maintains a consistent growth rate. ALD-Y₂O₃ thin films were found to have a typical cubic polycrystalline structure, independent of growth temperature, which can be attributed to their stoichiometric composition of Y₂O₃, negligible carbon impurity, and high film density, analogous to the Y₂O₃ bulk. Even at a low growth temperature of 150 °C, ALD-Y₂O₃ exhibited a markedly lower plasma etching rate (~0.77 nm/min) than that (~4.6 nm/min) of ALD-Al₂O₃ when using RIE at a plasma power of 400 W with a mixed gas of Ar/CF₄/O₂. Furthermore, the growth temperature of Y₂O₃ thin films had minimal impact on the etching rate. Full article

(This article belongs to the Special Issue Anti-Corrosion and Anti-Wear Coatings: Fundamentals, Technologies, and Applications)

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20 pages, 17374 KB

Open AccessEditor’s ChoiceArticle

Tribological Behavior of Gas-Nitrided 42CrMo4 Steel at Elevated Temperatures

by Dominika Panfil-Pryka, Michal Kulka, Mateusz Kotkowiak, Jerzy Michalski and Karol Grochalski

Coatings 2025, 15(1), 18; https://doi.org/10.3390/coatings15010018 - 28 Dec 2024

Cited by 1 | Viewed by 1258

Abstract

Nitriding is a well-known thermochemical treatment improving the surface hardness and the wear resistance of steel. The phase composition and growth kinetics of the nitrided layer can be controlled using a gas nitriding with changeable nitriding potential. In this work, such a gas [...] Read more.

Nitriding is a well-known thermochemical treatment improving the surface hardness and the wear resistance of steel. The phase composition and growth kinetics of the nitrided layer can be controlled using a gas nitriding with changeable nitriding potential. In this work, such a gas nitriding was used to produce, on 42CrMo4 steel, the two nitrided layers differing in the thickness of compound zone and diffusion zone. The microstructure and nanohardness of these layers were studied. For the first time, the tribological behavior of gas nitrided layers at elevated temperatures (from 23 to 400 °C) was investigated. The compound zone consisted of ε + (ε + γ’) iron nitrides and, in the diffusion zone, the nitric sorbite with γ’ precipitates was observed. The highest nanohardness was measured in the ε + γ’ zone. The lowest values of friction coefficients were obtained if the contact surface of the friction pair entered the ε + γ’ zone. After the wear process, at a final temperature of 400 °C, worn surfaces showed only intensive abrasive wear, evidenced by shallow grooves. The increased oxygen content at the edges of wear tracks indicated possible oxidative wear. Full article

(This article belongs to the Special Issue Wear-Resistance and Corrosion-Resistance Coatings)

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24 pages, 6981 KB

Open AccessEditor’s ChoiceArticle

Machine-Learning-Driven Optimization of Cold Spray Process Parameters: Robust Inverse Analysis for Higher Deposition Efficiency

by Abderrachid Hamrani, Aditya Medarametla, Denny John and Arvind Agarwal

Coatings 2025, 15(1), 12; https://doi.org/10.3390/coatings15010012 - 26 Dec 2024

Cited by 4 | Viewed by 2221

Abstract

Cold spray technology has become essential for industries requiring efficient material deposition, yet achieving optimal deposition efficiency (DE) presents challenges due to complex interactions among process parameters. This study developed a two-stage machine learning (ML) framework incorporating Bayesian optimization to address these challenges. [...] Read more.

Cold spray technology has become essential for industries requiring efficient material deposition, yet achieving optimal deposition efficiency (DE) presents challenges due to complex interactions among process parameters. This study developed a two-stage machine learning (ML) framework incorporating Bayesian optimization to address these challenges. In the first stage, a classification model predicted the occurrence of deposition, while the second stage used a regression model to forecast DE values given deposition presence. The approach was validated on Aluminum 6061 data, demonstrating its capability to accurately predict DE and identify optimal process parameters for target efficiencies. Model interpretability was enhanced with SHAP analysis, which identified gas temperature and gas type as primary factors affecting DE. Scenario-based inverse analysis further validated the framework by comparing model-predicted parameters to literature data, revealing high accuracy in replicating real-world conditions. Notably, substituting hydrogen as the gas carrier reduced the required gas temperature and pressure for high DE values, suggesting economic and operational benefits over helium and nitrogen. This study demonstrates the effectiveness of AI-driven solutions in optimizing cold spray processes, contributing to more efficient and practical approaches in material deposition. Full article

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

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19 pages, 14017 KB

Open AccessEditor’s ChoiceArticle

Multi-Step Simulations of Ionized Metal Physical Vapor Deposition to Enhance the Plasma Formation Uniformity

by Cheongbin Cheon, Min Young Hur, Ho Jun Kim and Hae June Lee

Coatings 2025, 15(1), 11; https://doi.org/10.3390/coatings15010011 - 25 Dec 2024

Viewed by 1248

Abstract

Ionized metal physical vapor deposition (IMPVD), which is operated at a very low pressure to take advantage of the metal sputtering effect on the target surface, has unique properties compared with conventional DC magnetron sputtering. In this study, we investigated the effect of [...] Read more.

Ionized metal physical vapor deposition (IMPVD), which is operated at a very low pressure to take advantage of the metal sputtering effect on the target surface, has unique properties compared with conventional DC magnetron sputtering. In this study, we investigated the effect of the rotating magnetic field on the plasma formation of IMPVD to enhance the deposition uniformity. This was accomplished through a multi-step simulation, which enabled plasma analysis, sputtered particle and chemical reaction analysis, and deposition profile analysis. A two-dimensional particle-in-cell Monte Carlo simulation utilizes the exact cross-section data of the Cu ion collisions and calculates the particle trajectories under specific magnetic field profiles. This new methodology gives guidance for the design of the magnetic field profiles of IMPVD and an understanding of the physical mechanism. Full article

(This article belongs to the Special Issue Advanced Coating Technology by Physical Vapor Deposition and Applications)

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18 pages, 1365 KB

Open AccessEditor’s ChoiceArticle

Increasing the Resistance of Steel and Austenitic Stainless Steels Against Pitting Corrosion by a γ-Irradiated Self-Assembled Amphiphilic Molecular Layer

by Éva Kocsisné Pfeifer, Zoltán May, Miklós Péter Mohai, János Mink, István Gábor Gyurika and Judit Telegdi

Coatings 2024, 14(12), 1601; https://doi.org/10.3390/coatings14121601 - 21 Dec 2024

Viewed by 973

Abstract

This study, based on our previous research, aims to quantitatively determine the enhanced protection of austenitic stainless steels against pitting corrosion in NaCl solution by self-assembled molecular (SAM) layers, in their original form and after γ-irradiation. This study focuses on four stainless steels [...] Read more.

This study, based on our previous research, aims to quantitatively determine the enhanced protection of austenitic stainless steels against pitting corrosion in NaCl solution by self-assembled molecular (SAM) layers, in their original form and after γ-irradiation. This study focuses on four stainless steels of varying compositions, covered by self-assembled undecenyl phosphonic acid layers. The metal dissolution in corrosion experiments was measured by a special, highly sensitive analytical technique using the inductively coupled plasma–optical emission spectrometry (ICP-OES). The comparison of the dissolved metal ion concentrations measured in the presence of different metals with and without nanocoatings allowed the evaluation of the anticorrosion effectiveness of nanofilms as well as the importance of the alloying elements. The ICP-OES results demonstrated that the quality of layers have a significant impact on anticorrosion efficacy. The γ-irradiated self-assembled layers were the most effective in controlling the dissolution of stainless steels. The mechanisms of the inhibition in the presence of these nanolayers were elucidated by infrared spectroscopy. First of all, it revealed the differences in the adsorption of the undecenyl phosphonic acid self-assembled layer, both with and without γ-irradiation. The other important observation that confirmed the increased anticorrosion efficiency after γ-irradiation proved the formation of a more compact, polymer-like layer over the metal surface. The increased anticorrosion efficacy, defined as the enhancement in Pitting Resistance Equivalent Numbers (PRENs) in the presence of self-assembled layers (either pre- or post-γ-irradiation), can be documented. Full article

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

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17 pages, 13353 KB

Open AccessEditor’s ChoiceArticle

Microstructural, Nanomechanical, and Tribological Properties of Thin Dense Chromium Coatings

by E. Broitman, A. Jahagirdar, E. Rahimi, R. Meeuwenoord and J. M. C. Mol

Coatings 2024, 14(12), 1597; https://doi.org/10.3390/coatings14121597 - 20 Dec 2024

Cited by 2 | Viewed by 1299

Abstract

Nowadays, Thin Dense Chromium (TDC) coatings are being industrially used in rolling bearings applications due to their claimed advantages such as high hardness, low wear, and good corrosion resistance. However, despite their broad commercial use, very little has been published in the open [...] Read more.

Nowadays, Thin Dense Chromium (TDC) coatings are being industrially used in rolling bearings applications due to their claimed advantages such as high hardness, low wear, and good corrosion resistance. However, despite their broad commercial use, very little has been published in the open scientific literature regarding their microstructure, nanomechanical, and tribological properties. In this paper, TDC coatings with a thickness of about 5 µm were deposited by a customized electrochemical process on ASTM 52100 bearing steel substrates. Surface microstructure and chemical composition analysis of the TDC coatings was carried out by scanning electron microscopy and atomic force microscopy. The results revealed a coating with a dense, nodular, and polycrystalline microstructure. Unlike standard electrodeposited “Hard Chromium” coatings, TDC coatings show no presence of micro/nano-cracks, likely contributing to their superior corrosion resistance. The nanomechanical behavior, studied by nanoindentation as a function of penetration depths, exhibits a pronounced size effect near the coating surface that can be linked to the nodular microstructure. A hard surface with hardness H_IT 14.9 ± 0.5 GPa and reduced elastic modulus E_r = 216.8 ± 3.9 GPa was observed. Tribological characterization under the presence of lubricants was performed by two single-contact tribometers using coated and uncoated steel balls against flat steel substrates. An in-house fretting wear rig was used to measure the lubricated friction coefficient in pure sliding conditions, whilst the friction performance in rolling/sliding lubricated conditions was evaluated using a WAM test rig. In pure sliding, TDC/TDC contacts show ~13% lower friction than for steel. Under rolling/sliding conditions with 5% sliding, the traction coefficient of TDC/TDC coating contact was at least 20% lower than that for steel/steel contact. The tribological results obtained in various contact conditions demonstrate the benefits of applying TDC coatings to reduce bearing friction. Full article

(This article belongs to the Special Issue Advanced Tribological Coatings: Fabrication and Application)

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11 pages, 3079 KB

Open AccessEditor’s ChoiceArticle

Controlled Aggregation of Cobalt and Platinum Atoms via Plasma Treatment for Exceptional Hydrogen Evolution Reaction Activity

by Guoqing Zhang, Jiankun Li, Yixing Wang, Linfeng Lei and Linzhou Zhuang

Coatings 2024, 14(12), 1569; https://doi.org/10.3390/coatings14121569 - 15 Dec 2024

Cited by 1 | Viewed by 1024

Abstract

Designing and developing highly active, stable, and cost-effective hydrogen evolution reaction (HER) catalysts is crucial in the field of water electrolysis. In this study, we utilize N-doped porous carbon (CoNC) derived from zeolite imidazole metal–organic frameworks (ZIF-67) as support and prepare CoNC-Pt-IM-P via [...] Read more.

Designing and developing highly active, stable, and cost-effective hydrogen evolution reaction (HER) catalysts is crucial in the field of water electrolysis. In this study, we utilize N-doped porous carbon (CoNC) derived from zeolite imidazole metal–organic frameworks (ZIF-67) as support and prepare CoNC-Pt-IM-P via chemical impregnation (CoNC-Pt-IM) and plasma treatment. Systematic analyses reveal that calcined CoNC with pyridinic nitrogen could serve as a robust support to strongly anchor PtCo nanoclusters, while argon plasma treatment could lead to a noticeable aggregation of Co and Pt atoms so as to alter the electronic environment and enhance intrinsic HER catalytic activity. CoNC-Pt-IM-P could exhibit outstanding catalytic activity toward HER, achieving an exceptionally low overpotential of 31 mV at the current density of −10 mA cm⁻² and a Tafel slope of 36 mV dec⁻¹. At an overpotential of 50 mV, its mass activity reaches 4.90 A mg_Pt⁻¹, representing enhancements of 1.5 times compared to CoNC-Pt-IM and 12.3 times compared to commercial 20 wt% Pt/C. Furthermore, it could operate stably for over 110 h at a current density of −10 mA cm⁻², demonstrating its exceptional durability. This work uses plasma treatment to achieve the controllable aggregation of Co and Pt atoms to enhance their catalytic activity, which has the advantage of avoiding excessive particle aggregation compared to the commonly used method of high-temperature calcination. Full article

(This article belongs to the Special Issue Coatings as Key Materials in Catalytic Applications)

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15 pages, 2546 KB

Open AccessEditor’s ChoiceArticle

Essential Oils and Essential Oil-Based Products Compared to Chemical Biocides Against Microbial Patinas on Stone Cultural Heritage

by Federica Antonelli, Sara Iovine, Carlotta Sacco Perasso, Natalia Macro, Eleonora Gioventù, Filippo Edoardo Capasso and Marco Bartolini

Coatings 2024, 14(12), 1546; https://doi.org/10.3390/coatings14121546 - 11 Dec 2024

Cited by 2 | Viewed by 1173

Abstract

In recent years, attention has been paid to finding eco-friendly products that could represent an alternative for the chemicals usually used during conservation procedures. In the field of the devitalization of biological patinas, the most studied products are essential oils (EOs). Several works [...] Read more.

In recent years, attention has been paid to finding eco-friendly products that could represent an alternative for the chemicals usually used during conservation procedures. In the field of the devitalization of biological patinas, the most studied products are essential oils (EOs). Several works tested EOs in vitro on microorganisms isolated from stone artifacts but few applied these products on real artworks colonized by a complex patina. In the present work, the biocidal effect of two EOs (cinnamon bark and oregano) and two EO-based products (Biotersus and Essenzio) was compared to that of three chemical biocides commonly used in the conservation of stone artifacts (Biotin R1+R2, NewDes50, and Preventol RI50). The products were applied by brush in situ on a marble slab characterized by a green patina. The biocidal activity was evaluated by analyzing the chlorophyll fluorescence and quantifying ATP through biochemical tests. Furthermore, the products’ interference with stone was evaluated by colorimetric measures on sedimentary rock samples. The results indicate that chemical biocides exhibited biocidal activity of greater than 99.5% with a single application, while cinnamon oil (at a 1% concentration) and Essenzio required two applications to achieve the same level of efficacy. Conversely, oregano oil and Biotersus were not able to effectively reduce microorganism vitality, even with repeated applications. Full article

(This article belongs to the Special Issue Coatings for Cultural Heritage: Cleaning, Protection and Restoration)

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19 pages, 4428 KB

Open AccessEditor’s ChoiceArticle

Machine Learning-Driven Optimization of Micro-Textured Surfaces for Enhanced Tribological Performance: A Comparative Analysis of Predictive Models

by Zhenghui Ge, Qifan Hu, Rui Wang, Haolin Fei, Yongwei Zhu and Ziwei Wang

Coatings 2024, 14(12), 1539; https://doi.org/10.3390/coatings14121539 - 8 Dec 2024

Cited by 1 | Viewed by 1371

Abstract

Micro-textured surfaces show promise in improving tribological properties, but predicting their performance remains challenging due to complex relationships between surface features and frictional behavior. This study evaluates five algorithms—linear regression, decision tree, gradient boosting, support vector machine, and neural network—for their ability to [...] Read more.

Micro-textured surfaces show promise in improving tribological properties, but predicting their performance remains challenging due to complex relationships between surface features and frictional behavior. This study evaluates five algorithms—linear regression, decision tree, gradient boosting, support vector machine, and neural network—for their ability to predict load-carrying capacity and friction force based on texture parameters including depth, side length, surface ratio, and shape. The neural network model demonstrated superior performance, achieving the lowest MAE (24.01) and highest R-squared value (0.99) for friction force prediction. The results highlight the potential of machine learning techniques to enhance the understanding and prediction of friction-reducing micro-textures, contributing to the development of more efficient and durable tribological systems in industrial applications. Full article

(This article belongs to the Special Issue Advances in Measurement and Data Analysis of Surfaces with Functionalized Coatings)

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12 pages, 1561 KB

Open AccessEditor’s ChoiceArticle

Silver Linings: Electrochemical Characterization of TiO₂ Sol-Gel Coating on Ti6Al4V with AgNO₃ for Antibacterial Excellence

by Julia Both, Gabriella Stefania Szabó, Alexandra Ciorîță and Liana Maria Mureșan

Coatings 2024, 14(12), 1532; https://doi.org/10.3390/coatings14121532 - 4 Dec 2024

Viewed by 1226

Abstract

This study aimed to synthesize TiO₂ and silver-containing TiO₂ layers on Ti6Al4V titanium alloy substrates, also known as titanium grade 5 (TiGr5), to provide corrosion resistance and antibacterial activity. The TiO₂ layers were prepared through the sol-gel method and dip-coating [...] Read more.

This study aimed to synthesize TiO₂ and silver-containing TiO₂ layers on Ti6Al4V titanium alloy substrates, also known as titanium grade 5 (TiGr5), to provide corrosion resistance and antibacterial activity. The TiO₂ layers were prepared through the sol-gel method and dip-coating technique. Silver introduction into the layers was performed in two different ways. One was the impregnation method by dipping the TiO₂ layer-covered metal in aqueous AgNO₃ solutions of various concentrations (TiO₂/AgNO₃), and the other was by direct introduction of AgNO₃ into the precursor sol (Ag-TiO₂). The two methods for incorporating AgNO₃ into the coating matrix are novel, as they preserve silver in its ionic form rather than reducing it to metallic silver. The samples were put through electrochemical characterization, namely potentiodynamic polarization and electrochemical impedance spectroscopy (EIS), and were tested in Hank’s solution, simulating a physiological environment. The behavior of the layers was monitored over time. Also, the thin layers’ thickness and adhesion to the substrate were determined. Microbiological evaluation of the Ag-doped coatings on glass substrates confirmed their significant bactericidal activity against Gram-negative Escherichia coli. Among the two types of coatings, the impregnated coatings demonstrated the most promising electrochemical performance, as evidenced by both EIS and potentiodynamic polarization analyses. Full article

(This article belongs to the Special Issue Advances in Nanostructured Thin Films and Coatings, 2nd Edition)

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20 pages, 20891 KB

Open AccessEditor’s ChoiceArticle

Efficient Photocatalytic Reduction of Hexavalent Chromium by NiCo₂S₄/BiOBr Heterogeneous Photocatalysts

by Shumeng Qin, Ruofan Xu, Qiu Jin, Sen Wang, Yi Ren, Yulin Huang, Ziye Zheng, Lihui Xiao, Dong Zhai, Shuguang Wang and Zuoli He

Coatings 2024, 14(12), 1492; https://doi.org/10.3390/coatings14121492 - 27 Nov 2024

Cited by 4 | Viewed by 1163

Abstract

For typical Cr(VI)-containing industrial wastewater, more efficient water treatment technologies need to be used to ensure that Cr(VI) concentrations are reduced to safe levels before discharge. Photocatalytic technology is highly efficient, environmentally friendly, and has been extensively used to address this demand. Herein, [...] Read more.

For typical Cr(VI)-containing industrial wastewater, more efficient water treatment technologies need to be used to ensure that Cr(VI) concentrations are reduced to safe levels before discharge. Photocatalytic technology is highly efficient, environmentally friendly, and has been extensively used to address this demand. Herein, heterogeneous NiCo₂S₄/BiOBr photocatalysts with different ratios were prepared using a solvothermal method. When compared with pure NiCo₂S₄ and BiOBr, the NiCo₂S₄/BiOBr-30 had significantly increased adsorption capacity and visible-light-driven photocatalytic reduction activity for Cr(VI) removal. The improved adsorption performance of the NiCo₂S₄/BiOBr-30 was mainly due to its increased specific surface area, and the enhanced photocatalytic performance of the NiCo₂S₄/BiOBr-30 could be attributed to the improved separation and transfer of photogenerated carriers at the interface. Lastly, a possible enhanced photocatalytic Cr(VI) reduction mechanism of the NiCo₂S₄/BiOBr heterostructure was developed. Full article

(This article belongs to the Special Issue Advanced Materials and Coatings for Photocatalytic Applications)

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19 pages, 6285 KB

Open AccessEditor’s ChoiceArticle

Improving Prediction Model for Colorimetric Changes Due to Coating Processes with Oil-Based and UV Coatings

by Igor Zjakić, Eduard Galić, Ivana Ljevak and Mile Matijević

Coatings 2024, 14(12), 1488; https://doi.org/10.3390/coatings14121488 - 26 Nov 2024

Cited by 1 | Viewed by 1017

Abstract

The measurability and predictability of the printing process are influenced by the impact of various coating methods. Besides enhancing and protecting the printed product, these methods can alter the colorimetric properties of spot colors across different wavelengths. Prediction models based on ink trapping [...] Read more.

The measurability and predictability of the printing process are influenced by the impact of various coating methods. Besides enhancing and protecting the printed product, these methods can alter the colorimetric properties of spot colors across different wavelengths. Prediction models based on ink trapping formulas were analyzed, particularly those from Deshpande, Green, and Hoffstadt, designed to forecast colorimetric values in overprinted spot color scenarios. This study examined the influence of coating methods on the colorimetric properties of spot colors and evaluated the applicability of the prediction model for these conditions. Spectrophotometric and densitometric methods, combined with mathematical analysis, were used to quantify the degree of color change induced by different coatings. The findings clearly indicate the extent of colorimetric changes in spot colors resulting from various coating applications. They also highlight the potential, albeit limited, application of this model in predicting color changes for improved process repeatability and predictability. While the prediction method analyzed in this study proved inadequate for coating-over-spot-color scenarios, it remains useful for predicting colorimetric shifts in spot-on-spot-color overprinting. The model demonstrated that it is not entirely accurate, as some coatings show ∆E₀₀ deviations of up to 10. To improve the model’s applicability, a varnishing coefficient, V, should be introduced, which can reduce ∆E₀₀ variation for each color and substrate. The research showed that a coefficient range from 0.8 to 1.2 yields acceptable results, bringing ∆E₀₀ below 2, thus making the model suitable for coating processes with oil-based and UV coatings. Full article

(This article belongs to the Section Coatings for Food Technology and System)

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16 pages, 5245 KB

Open AccessEditor’s ChoiceArticle

Ball-on-Disk Wear Maps for Bearing Steel–Hard Anodized EN AW-6082 Aluminum Alloy Tribocouple in Dry Sliding Conditions

by Enrico Baroni, Annalisa Fortini, Lorenzo Meo, Chiara Soffritti, Mattia Merlin and Gian Luca Garagnani

Coatings 2024, 14(11), 1469; https://doi.org/10.3390/coatings14111469 - 19 Nov 2024

Cited by 2 | Viewed by 1400

Abstract

In recent years, Golden Hard Anodizing (G.H.A.^®) has been developed as a variant of the traditional hard anodizing process with the addition of Ag⁺ ions in the nanoporous structure. The tribological properties of this innovative surface treatment are still not [...] Read more.

In recent years, Golden Hard Anodizing (G.H.A.^®) has been developed as a variant of the traditional hard anodizing process with the addition of Ag⁺ ions in the nanoporous structure. The tribological properties of this innovative surface treatment are still not well understood. In this study, ball-on-disk tests were conducted in dry sliding conditions using 100Cr6 (AISI 52100) bearing steel balls as a counterbody and GHA^®-anodized EN AW-6082 aluminum alloy disks. The novelty of this work lies in the mapping of the wear properties of the tribocouple under different test conditions for a better comparison of the results. Three different normal loads (equal to 5, 10, and 15 N) and three different reciprocating frequencies (equal to 2, 3, and 4 Hz) were selected to investigate a spectrum of operating conditions for polished and unpolished G.H.A.^®-anodized EN AW-6082 aluminum alloy. Quantitative wear maps were built based on the resulting wear rate values to define the critical operating limits of the considered tribocouple. The results suggest that the coefficient of friction (COF) was independent of test conditions, while different wear maps were found for polished and non-polished surfaces. Polishing before anodizing permitted the acquisition of lower wear for the anodized disks and the steel balls. Full article

(This article belongs to the Special Issue Mechanical Properties and Tribological Behavior of Alloy/Coatings, 2nd Edition)

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13 pages, 7529 KB

Open AccessEditor’s ChoiceArticle

Ammonia Plasma Surface Treatment for Enhanced Cu–Cu Bonding Reliability for Advanced Packaging Interconnection

by Ho Jeong Jeon and Sang Jeen Hong

Coatings 2024, 14(11), 1449; https://doi.org/10.3390/coatings14111449 - 14 Nov 2024

Cited by 3 | Viewed by 2171

Abstract

With the emergence of 3D stacked semiconductor products, such as high-bandwidth memory, bonding-interface reliability cannot be overemphasized. The condition of the surface interface before bonding is important and can substantially affect product reliability. Plasma technology can be used to control the state of [...] Read more.

With the emergence of 3D stacked semiconductor products, such as high-bandwidth memory, bonding-interface reliability cannot be overemphasized. The condition of the surface interface before bonding is important and can substantially affect product reliability. Plasma technology can be used to control the state of a bonding interface, but various factors of interest, such as surface roughness, chemical bonding state, and surface cleanliness, may depend on the type of gaseous plasma. These factors may increase voids at the interface, which can jeopardize the product reliability. In this study, NH₃ plasma surface treatment is investigated and compared with the conventionally preferred surface treatment under Ar plasma. Under the latter method, specific anomalies occurred and led to void formation at the interface during bonding. By contrast, NH₃ plasma treatment maintained higher uniformity, higher overall surface conditions, and a smooth reduction process. Furthermore, the formation of a nitride passivation layer effectively inhibited the oxidation of the metal surface, and the flat surface resulted in the decrease in voids compared with the Ar plasma treatment after the copper–copper bonding. From the experimental analysis, we achieved a 12% reduction in resistance in the samples treated with NH₃ plasma treatment due to the suppression of surface oxidation. However, it is unfortunate that the shear strength in the experimental samples treated with NH₃ plasma treatment needs to be further improved. Full article

(This article belongs to the Special Issue Application of Advanced Plasma Technology in Coatings, Films and Etching)

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13 pages, 6719 KB

Open AccessEditor’s ChoiceArticle

Fatigue Crack Growth Behavior of Additively Manufactured Ti Metal Matrix Composite with TiB Particles

by Thevika Balakumar, Afsaneh Edrisy and Reza A. Riahi

Coatings 2024, 14(11), 1447; https://doi.org/10.3390/coatings14111447 - 13 Nov 2024

Viewed by 1267

Abstract

Fatigue crack growth behavior of additively manufactured Ti metal matrix composite with TiB particles at room temperature was studied using a compact tension specimen and at the stress ratio of 0.1 (R = 0.1). The composite studied in this work was manufactured with [...] Read more.

Fatigue crack growth behavior of additively manufactured Ti metal matrix composite with TiB particles at room temperature was studied using a compact tension specimen and at the stress ratio of 0.1 (R = 0.1). The composite studied in this work was manufactured with a unique additive technique called plasma transferred arc solid free-form fabrication, which was designed to manufacture low-cost near-net-shaped components for aerospace and automotive industries. The fatigue crack growth rate experiments were carried perpendicular and parallel to the additive material build, aiming to find any fatigue anisotropies at room temperature. The findings reveal that additively manufactured Ti-TiB composite shows isotropic fatigue properties with respect to fatigue crack growth. Furthermore, the fatigue crack growth mechanisms in this additive composite material were identified as void nucleation/coalescence and the bypassing of particles and matrix, depending on the interparticle distance. Full article

(This article belongs to the Special Issue Latest Insights in Metal Fatigue, Failure, and Fracture)

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17 pages, 4223 KB

Open AccessEditor’s ChoiceArticle

Stainless Steel Deposits on an Aluminum Support Used in the Construction of Packaging and Food Transport Containers

by Steluța Radu and Stefan Lucian Toma

Coatings 2024, 14(11), 1431; https://doi.org/10.3390/coatings14111431 - 11 Nov 2024

Cited by 1 | Viewed by 1527

Abstract

A series of chemical elements from the chemical composition of the packs of liquid food products migrate inside them or they combine with other chemical elements existing in the food, resulting in chemical compounds that worsen the quality of the food. In the [...] Read more.

A series of chemical elements from the chemical composition of the packs of liquid food products migrate inside them or they combine with other chemical elements existing in the food, resulting in chemical compounds that worsen the quality of the food. In the present paper, layers of food stainless steel were deposited using thermal arc spraying on an aluminum alloy substrate to stop the migration of aluminum ions inside liquid food products. The physical-chemical and mechanical properties of the protection system: stainless steel layer used in the food industry (suggestively called: food-grade stainless steel)—aluminum substrate were investigated, and then the organoleptic properties of the food liquids that came into contact with the deposit were evaluated. It was found that food-gradestainless steel deposits have low porosity (3.8%) and relatively high adhesion and hardness, which allows complete isolation of the substrate material. The investigations carried out on the properties of food liquids that come into contact with the stainless steel deposit revealed the fact that it perfectly seals the aluminum start. The food-grade stainless steel coating (80T) was much better and safer for preserving dairy products maintaining a constant acidity up to 17 degrees Thorner, wines (with an average acidity of 3.5–4 degrees), juices (with natural pigments), and oils (with a good absorbance level correlated with clarity). This aspect suggests that the created system can be successfully used to manufacture containers for the transport of liquid products. Full article

(This article belongs to the Special Issue Advances in Novel Coatings)

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17 pages, 7142 KB

Open AccessEditor’s ChoiceArticle

Wear and Corrosion Resistance of ZrN Coatings Deposited on Ti6Al4V Alloy for Biomedical Applications

by Stanislava Rabadzhiyska, Dimitar Dechev, Nikolay Ivanov, Tatyana Ivanova, Velichka Strijkova, Vesela Katrova, Velko Rupetsov, Nina Dimcheva and Stefan Valkov

Coatings 2024, 14(11), 1434; https://doi.org/10.3390/coatings14111434 - 11 Nov 2024

Cited by 8 | Viewed by 1779

Abstract

Zirconium nitrides films were synthesized on Ti6Al4V substrates at a bias voltage of −50 V, −80 V, −110 V and −150 V by the direct current (DC) reactive magnetron sputtering technique. The as-deposited coatings were characterized by X-ray diffraction (XRD), Fourier-transform infrared (FTIR) [...] Read more.

Zirconium nitrides films were synthesized on Ti6Al4V substrates at a bias voltage of −50 V, −80 V, −110 V and −150 V by the direct current (DC) reactive magnetron sputtering technique. The as-deposited coatings were characterized by X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM) and atomic force microscopy (AFM). The wear and corrosion resistance of the obtained ZrN coatings were evaluated to determine the possibility for their implementation in modern biomedical applications. It was found that the intensity of the diffraction peak of the Zr-N phase corresponding to the (1 1 1) crystallographic plane rose as the bias voltage increased, while the ZrN coatings’ thickness reduced from 1.21 µm to 250 nm. The ZrN films’ surface roughness rose up to 75 nm at −150 V. Wear tests showed an increase in the wear rate and wear intensity as the bias voltage increased. Corrosion studies of the ZrN coatings were carried out by three electrochemical methods: open circuit potential (OCP), cyclic voltammetry (polarization measurements) and electrochemical impedance spectroscopy (EIS). All electrochemical measurements confirmed that the highest protection to corrosion is the ZrN coating, which was deposited on the Ti6Al4V substrate at a bias voltage of −150 V. Full article

(This article belongs to the Special Issue Anti-corrosion Coatings of Metals and Alloys—New Perspectives)

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23 pages, 16310 KB

Open AccessEditor’s ChoiceArticle

Coupling APS/SPS Techniques for Cu-TiO₂ Antibacterial Coating Deposition: Application to Water Treatment

by Laurène Youssef, Audrey Prorot, Laurène Gnodé, Pierre Th’Madiou Verdieu, Armelle Vardelle, Vincent Rat and Alain Denoirjean

Coatings 2024, 14(11), 1426; https://doi.org/10.3390/coatings14111426 - 9 Nov 2024

Viewed by 1782

Abstract

Since the COVID-19 pandemic, efforts in the field of surface decontamination have been redoubled. Finding innovative self-cleaning devices has become a challenge, and several solutions have been proposed in the market in recent years. In this work, an optimized powder/suspension plasma spray process [...] Read more.

Since the COVID-19 pandemic, efforts in the field of surface decontamination have been redoubled. Finding innovative self-cleaning devices has become a challenge, and several solutions have been proposed in the market in recent years. In this work, an optimized powder/suspension plasma spray process at atmospheric pressure, using a Triplex Pro 210^TM torch, is implemented to produce Cu-TiO₂ surface coatings on stainless steel. The purpose is to investigate the potential improvement of antibacterial efficacy by the reactive surface species generated from TiO₂ photoactivity under irradiation. A water-based suspension, prepared with AnalaR NORMAPUR^TM TiO₂, is used as a precursor to incorporate the photocatalyst into an antibacterial copper matrix. Surface antibacterial tests according to ASTM 2180 standards were performed, and experiments were performed in treated contaminated water. Sub-stoichiometric blue TiO₂ coatings showed complete bacterial elimination after 90 min of visible light irradiation, and Cu-TiO₂ surface coatings were even able to disinfect the surfaces under white light, making the application interesting for bacterial destruction under natural illumination. These materials are also intended for application in water treatment, including both pathogens and chemical micropollutants, which is a pressing issue facing many countries today. Full article

(This article belongs to the Special Issue Advances in Thermal Spray Coatings: Technologies and Applications)

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13 pages, 4685 KB

Open AccessEditor’s ChoiceArticle

High-Performance SAW-Based Microfluidic Actuators Composed of Sputtered Al–Cu IDT Electrodes

by Hwansun Kim, Youngjin Lee, Peddathimula Puneetha, Sung Jin An, Jae-Cheol Park and Siva Pratap Reddy Mallem

Coatings 2024, 14(11), 1420; https://doi.org/10.3390/coatings14111420 - 8 Nov 2024

Viewed by 2267

Abstract

To realize highly sensitive SAW devices, novel Al–Cu thin films were developed using a combinatorial sputtering system. The Al–Cu sample library exhibited a wide range of chemical compositions and electrical resistivities, providing valuable insights for selecting optimal materials for SAW devices. Considering the [...] Read more.

To realize highly sensitive SAW devices, novel Al–Cu thin films were developed using a combinatorial sputtering system. The Al–Cu sample library exhibited a wide range of chemical compositions and electrical resistivities, providing valuable insights for selecting optimal materials for SAW devices. Considering the significant influence of electrode resistivity and density on acoustic wave propagation, an Al–Cu film with 65 at% Al was selected as the IDT electrode material. The selected Al–Cu film demonstrated a resistivity of 6.0 × 10⁻⁵ Ω-cm and a density of 4.4 g/cm³, making it suitable for SAW-based microfluidic actuator applications. XRD analysis revealed that the Al–Cu film consisted of a physical mixture of Al and Cu without the formation of Al–Cu alloy phases. The film exhibited a fine-grained microstructure with an average crystallite size of 7.5 nm and surface roughness of approximately 6 nm. The SAW device fabricated with Al–Cu IDT electrodes exhibited excellent acoustic performance, resonating at 143 MHz without frequency shift and achieving an insertion loss of −13.68 dB and a FWHM of 0.41 dB. In contrast, the Au electrode-based SAW device showed significantly degraded acoustic characteristics. Moreover, the SAW-based microfluidic module equipped with optimized Al–Cu IDT electrodes successfully separated 5 μm polystyrene (PS) particles even at high flow rates, outperforming devices with Au IDT electrodes. This enhanced performance can be attributed to the improved resonance characteristics of the SAW device, which resulted in a stronger acoustic radiation force exerted on the PS particles. Full article

(This article belongs to the Special Issue Thin Films and Nanostructures for Electronics)

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5 pages, 178 KB

Open AccessEditor’s ChoiceEditorial

Innovations in Active Food Packaging During the Pandemic and into the ‘New Normal’

by Maria-Ioana Socaciu, Dan Cristian Vodnar and Cristina Anamaria Semeniuc

Coatings 2024, 14(11), 1419; https://doi.org/10.3390/coatings14111419 - 8 Nov 2024

Viewed by 1387

Abstract

COVID-19 significantly impacted global socioeconomic conditions and food security [...] Full article

(This article belongs to the Special Issue Innovations in Active Food Packaging during the Pandemic and into the 'New Normal')

18 pages, 8817 KB

Open AccessEditor’s ChoiceArticle

Shrouding Gas Plasma Deposition Technique for Developing Low-Friction, Wear-Resistant WS₂-Zn Thin Films on Unfilled PEEK: The Relationship Between Process and Coating Properties

by Dietmar Kopp, Christine Bandl, Reinhard Kaindl, Thomas Prethaler, Anna Maria Coclite and Wolfgang Waldhauser

Coatings 2024, 14(11), 1365; https://doi.org/10.3390/coatings14111365 - 27 Oct 2024

Cited by 3 | Viewed by 3883

Abstract

In this study, tungsten disulfide–zinc (WS₂-Zn) composite films were generated on polyether ether ketone (PEEK) disks by an atmospheric pressure plasma jet (APPJ) equipped with a shrouding attachment. The friction and wear properties of the WS₂-Zn coatings were intensively [...] Read more.

In this study, tungsten disulfide–zinc (WS₂-Zn) composite films were generated on polyether ether ketone (PEEK) disks by an atmospheric pressure plasma jet (APPJ) equipped with a shrouding attachment. The friction and wear properties of the WS₂-Zn coatings were intensively investigated by using a rotational ball-on-disk setup under dry sliding and ambient room conditions. In order to gain more information about the lubrication mechanism, the coating areas as deposited and the worn areas (i.e., in the wear track) were analyzed with a scanning electron microscope (SEM) with regard to their chemical composition in depth by energy-dispersive X-ray spectroscopy (EDS). X-ray photoelectron spectroscopy (XPS) was conducted to obtain precise chemical information from the surface. The results indicated that WS₂-Zn coatings significantly improved the tribological properties, exhibiting a coefficient of friction (COF) of <0.2. However, the tribological performance of the coatings is strongly dependent on the plasma process settings (i.e., plasma current, dwell time of the powder particles in the plasma jet), which were tuned to reduce the oxidation by-products of WS₂ to a minimum. The COF values achieved of the dry lubricant films were significantly reduced in contrast to the uncoated PEEK by a factor of four. Full article

(This article belongs to the Special Issue Advances in Thermal Spray Coatings: Technologies and Applications)

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18 pages, 9372 KB

Open AccessEditor’s ChoiceArticle

Effect of Coating Treatment on the Properties of Extruded Mg-1.0Zn-0.3Zr-1.0Y-2.0Sn Alloys

by Junguang He, Qinglei Gao, Jiuba Wen, Yuan Gong, Wuyun Feng, Zhenfei Cheng and Xuyang Li

Coatings 2024, 14(11), 1350; https://doi.org/10.3390/coatings14111350 - 24 Oct 2024

Viewed by 1001

Abstract

The impact of fluoride-based coatings on the microstructure and mechanical integrity of extruded Mg-1.0Zn-0.3Zr-1.0Y-2.0Sn alloys was assessed utilizing optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), immersion testing, electrochemical analysis, and tensile testing. It was observed that the magnesium alloys could [...] Read more.

The impact of fluoride-based coatings on the microstructure and mechanical integrity of extruded Mg-1.0Zn-0.3Zr-1.0Y-2.0Sn alloys was assessed utilizing optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), immersion testing, electrochemical analysis, and tensile testing. It was observed that the magnesium alloys could be immersed in hydrofluoric acid (HF) for varying durations to achieve coatings of distinct thicknesses, with the coating thickness stabilizing at approximately 8 μm after a 48 h immersion period. The application of the fluoride coating significantly enhanced the corrosion resistance of the alloys, with a corrosion rate (CR_H) of 0.13 ± 0.012 mm/y. Upon a 20-day immersion in simulated body fluid (SBF), the degradation rates of the yield strength (YS), tensile strength (UTS), and elongation (EL) for the cast alloys were recorded as 62%, 59%, and 64%, respectively. For the extruded alloys, these rates escalated to 77%, 76%, and 95%. In contrast, the fluorine-coated alloys exhibited significantly lower degradation rates of 28%, 23%, and 39% after a 25-day immersion in SBF. Upon extrusion, the specimens exhibit a diminished corrosion resistance and a more substantial decline in mechanical properties compared to their as-cast state. Upon the application of the coating, there is a discernible reduction in the rate of mechanical property degradation observed in the specimens. This indicates that the fluorinated coating can mitigate the corrosion rate and enhance the corrosion resistance of magnesium alloys. Full article

(This article belongs to the Special Issue Enhanced Mechanical Properties of Metals by Surface Treatments)

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16 pages, 5483 KB

Open AccessEditor’s ChoiceArticle

Periodically Sinusoidal Magnetic Stray Field and Improved Film Quality of CoMnP Micro-Magnet Arrays for Magnetic Encoders by Electrodeposition with the Assistance of Ultrasound

by Geng-Hua Xu, Jung-Yen Chang, Hsiang-Chun Hsueh and Chiao-Chi Lin

Coatings 2024, 14(10), 1340; https://doi.org/10.3390/coatings14101340 - 21 Oct 2024

Viewed by 3340

Abstract

Magnetic encoders are composed of a magnetic sensor, a hard magnetic recording medium and a signal processing circuit. Electrodeposited micro-magnet arrays produced by micro-fabrication are promising recording media for enhancing encoder performance. However, two major engineering issues have yet to be resolved. One [...] Read more.

Magnetic encoders are composed of a magnetic sensor, a hard magnetic recording medium and a signal processing circuit. Electrodeposited micro-magnet arrays produced by micro-fabrication are promising recording media for enhancing encoder performance. However, two major engineering issues have yet to be resolved. One issue is an unknown relationship between the feature sizes of micro-magnet arrays and their stray field shapes, and another issue is the formation of micro-cracks due to the built-up residual stresses of thick films. In this study, we investigated the effect of feature sizes on the emanating stray field shape at various observation heights. Feature sizes include two height (i.e., film thickness) values of 78 μm and 176 μm, and both width and spacing with three values of 360 μm, 520 μm and 680 μm. Ultrasound-assisted agitation was adopted for investigating the effects of electrodepositing current densities on the film crystalline microstructures and magnetic properties. Narrowing the width of micro-magnets helps the stray field to become a sinusoidal profile. Thinner film, i.e., thickness 78 μm in this study, supports the stray field taking on a sinusoidal profile. Moreover, the spacing between the micro-magnets plays a key factor in determining the shape of the stray field. Under 37 kHz/156 W ultrasound agitation, the optimal hard magnetic properties of electrodeposited CoMnP films are residual magnetization 2329 G and coercivity 968 Oe by a current density of 10.0 mA/cm². Ultrasound-assisted electrodeposition, along with duly designed feature size, facilitates the micro-magnet arrays having a sinusoidal stray field shape using high quality films. Furthermore, for the first time, a systematic understanding of feature-size-dependent stray field evolution and improved polarities quality has been realized for the recording media of sinusoidal magnetic encoders. Full article

(This article belongs to the Special Issue Functional Coatings and Surface Science for Precision Engineering)

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15 pages, 2719 KB

Open AccessEditor’s ChoiceArticle

Physical-Vapor-Deposition-Coated Natural Rocks as Sustainable Cutting Material: First Insights into the Effect of Substrate Integrity on Properties of TiN Thin Film

by Hilke Petersen, Dominic Graf, Nelson Filipe Lopes Dias, Wolfgang Tillmann, Philipp Dan Hendrik Wolters, Benjamin Bergmann and Bernd Breidenstein

Coatings 2024, 14(10), 1333; https://doi.org/10.3390/coatings14101333 - 17 Oct 2024

Viewed by 1194

Abstract

The most important cutting materials for machining are carbides. Their production requires both tungsten and cobalt; however, these materials are becoming increasingly difficult to obtain and are sometimes mined under ethically questionable conditions. As a result, increasing efforts are being made to expand [...] Read more.

The most important cutting materials for machining are carbides. Their production requires both tungsten and cobalt; however, these materials are becoming increasingly difficult to obtain and are sometimes mined under ethically questionable conditions. As a result, increasing efforts are being made to expand the range of cutting materials. The basic suitability of natural rocks for cutting tools in less demanding processes has already been demonstrated. PVD coating of the natural rocks could improve their performance. The adhesion mechanisms in TiN-coated natural rock samples are discussed below. The TiN thin film is characterized in depth. Full article

(This article belongs to the Special Issue Modern Methods of Shaping the Structure and Properties of Coatings)

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18 pages, 4583 KB

Open AccessEditor’s ChoiceReview

Ni Catalysts for Thermochemical CO₂ Methanation: A Review

by Jungpil Kim

Coatings 2024, 14(10), 1322; https://doi.org/10.3390/coatings14101322 - 16 Oct 2024

Cited by 12 | Viewed by 5160

Abstract

This review underscores the pivotal role that nickel-based catalysts play in advancing CO₂ methanation technologies, which are integral to achieving carbon neutrality. This study meticulously examines various aspects of catalyst design, including the significance of support materials and co-catalysts in enhancing catalytic [...] Read more.

This review underscores the pivotal role that nickel-based catalysts play in advancing CO₂ methanation technologies, which are integral to achieving carbon neutrality. This study meticulously examines various aspects of catalyst design, including the significance of support materials and co-catalysts in enhancing catalytic activity and selectivity. This discussion reveals that while nickel catalysts offer a cost-effective solution due to their availability and high performance, challenges such as sintering and carbon deposition at high temperatures remain. These issues necessitate the development of catalysts with superior thermal stability or those capable of maintaining high activity at lower temperatures. This review also highlights the innovative use of three-dimensional fiber deposition technology in fabricating catalysts, which has shown promising results in improving reaction efficiency and stability over prolonged operation. Moving forward, this research emphasizes the importance of optimizing catalyst structure and fabrication techniques to overcome existing limitations. The ongoing development in this field holds great promise for the industrial application of CO₂ methanation, contributing significantly to global efforts in reducing greenhouse gas emissions and promoting sustainable energy use. Full article

(This article belongs to the Special Issue Advanced Research on Energy Storage Materials and Devices)

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17 pages, 9928 KB

Open AccessEditor’s ChoiceArticle

Anti-Corrosion and Wave-Absorbing Properties of Epoxy-Based Coatings on Q235 Steel

by Rehan Zhang, Kai Yang, Bo Dang, Mengling Zhan, Pingze Zhang and Shuqin Li

Coatings 2024, 14(10), 1315; https://doi.org/10.3390/coatings14101315 - 15 Oct 2024

Cited by 3 | Viewed by 1921

Abstract

Carbon nanotube/epoxy resin (CNE) coatings and carbon nanotube/carboxy iron powder/epoxy resin (CIE) coatings were applied on the surface of Q235 steel, and their corrosion, absorption properties and other characteristics were measured in this work. The results indicate that the average thickness of a [...] Read more.

Carbon nanotube/epoxy resin (CNE) coatings and carbon nanotube/carboxy iron powder/epoxy resin (CIE) coatings were applied on the surface of Q235 steel, and their corrosion, absorption properties and other characteristics were measured in this work. The results indicate that the average thickness of a single application was approximately 400 μm, and the surface of the CNE coating was still smooth and intact after a 3000 h copper ion accelerated salt spray test without bubbles, falling off or other corrosion phenomena. The same was true for 28 days of full immersion in solutions of 10% hydrochloric acid (HCl) and 10% sodium hydroxide (NaOH) of the coating. The electrochemical testing exhibited the corrosion current of the CNE coating as being markedly lower than that of Q235 steel, with a protection efficiency of 81.68% for the Q235 steel. The CNE-0.6 coating had the maximum corrosion voltage (−0.390 V), and the CNE-0.3 coating had the minimum corrosion current of 2.07 × 10⁻⁶ A·cm². The adhesion between the coating and Q235 could reach level 0, and the tensile strength of the coating was up to 18.75 MPa. The coating was observed to remain intact and free from detachment upon undergoing a drop test from a height of 50 cm. In addition, the CIE-0.6 coating exhibited an effective absorption band of 9.1 GHz, covering the range from 8.2 to 13.7 GHz, and it achieved a maximum reflection loss of −15.1 dB at a frequency of 8.6 GHz. Full article

(This article belongs to the Special Issue Oxidation, Wear, Corrosion Behaviors and Activated Bonding Properties of Coatings Deposited on Metals)

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15 pages, 2271 KB

Open AccessEditor’s ChoiceArticle

Preparation and Characterization of PLA-Based Films Fabricated with Different Citrus Species Peel Powder

by Antonios S. Koutoulis, Andreas E. Giannakas, Dimitrios G. Lazaridis, Apostolos-Panagiotis Kitsios, Vassilios K. Karabagias, Aris E. Giannakas, Athanasios Ladavos and Ioannis K. Karabagias

Coatings 2024, 14(10), 1311; https://doi.org/10.3390/coatings14101311 - 14 Oct 2024

Cited by 6 | Viewed by 2201

Abstract

The present study aimed to investigate whether different citrus peel powders (orange, mandarin, and lemon) could be incorporated into polylactic acid (PLA), for the preparation and characterization of biodegradable films made of this fruit waste. In particular, films were prepared by the solvent [...] Read more.

The present study aimed to investigate whether different citrus peel powders (orange, mandarin, and lemon) could be incorporated into polylactic acid (PLA), for the preparation and characterization of biodegradable films made of this fruit waste. In particular, films were prepared by the solvent casting method and tested in terms of physicochemical and biochemical parameters, along with mechanical properties. Furthermore, the citrus peel powders were tested for their physicochemical and biochemical properties after ethanolic extraction. The results showed that the addition of citrus powders into PLA proved to be efficient compared to the control films (PLA). The citrus peel-based films showed high antioxidant capacity (38.37%–32.54%), a considerable total phenolic content (17.2–12.58 mg GAE/L), good lightness (L*: 42.83–41.93), elastic Young’s modulus (257.95–175.38 MPa), oxygen transmission rate (976.5 mL m⁻² day⁻¹–1218 mL m⁻² day⁻¹), elongation at break (183.06%–135.95%), and tensile strength (6.15–4.56 MPa), which were affected significantly (p < 0.05) by the botanical origin of citrus peel. Concerning the citrus peel extracts, the highest values in antioxidant capacity (52.56%), total phenolic content (724.8 mg GAE/L), and titratable acidity (714.67 mg of citric acid/L) were recorded in the extract of lemon peel powders. The corresponding values for orange peel powder extracts were 39.43%, 563.8 mg GAE/L, and 576 mg of citric acid/L, while those for mandarin were 33.01%, 558.46 mg GAE/L, and 54.67 mg of citric acid/L. The application of multivariate analysis of variance and linear discriminant analysis on the mechanical properties, physicochemical, and biochemical data resulted in the differentiation of pure PLA and PLA-based films fabricated with citrus peel powder. From the above findings, it is concluded that citrus peel powders are sources of phytochemicals and can be used for the preparation of PLA-based films for potential applications in food preservation. Full article

(This article belongs to the Special Issue Trends in Sustainable Food Packaging and Coatings)

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14 pages, 7559 KB

Open AccessEditor’s ChoiceArticle

First-Principles Study on the Influence of Crystal Structures on the Interface Properties of Graphene/Titanium Composites

by Xiuli Han, Rui Wang, Pengchao Kang, Wanying Li and Gaohui Wu

Coatings 2024, 14(10), 1293; https://doi.org/10.3390/coatings14101293 - 10 Oct 2024

Viewed by 1654

Abstract

In recent years, significant advancements have been made in the fabrication and application of graphene-reinforced metal matrix composites. The remarkable mechanical properties of graphene have led to a substantial enhancement in the strength of titanium-based composites reinforced with graphene nanosheets. However, the occurrence [...] Read more.

In recent years, significant advancements have been made in the fabrication and application of graphene-reinforced metal matrix composites. The remarkable mechanical properties of graphene have led to a substantial enhancement in the strength of titanium-based composites reinforced with graphene nanosheets. However, the occurrence of severe interfacial reactions remains one of the most challenging issues in graphene-reinforced titanium matrix composites. This study, grounded in first principles, investigates the interfacial bonding between pure titanium and graphene across two distinct crystal structures, as well as the impact of vacancy defects on the composite’s interfacial structure. The bond strength between beta titanium and graphene is found to be relatively weaker, which may facilitate a reduction in the reactivity between graphene and titanium. Furthermore, the presence of vacancy defects is identified as a crucial factor influencing the formation of titanium carbide. This study presents a novel approach to enhance the interfacial adhesion between graphene and titanium. Full article

(This article belongs to the Special Issue Heat Treatment and Surface Engineering of Tools and Dies)

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15 pages, 7321 KB

Open AccessEditor’s ChoiceArticle

Hybrid Activity of P–Si–N Moieties for Improved Fire Retardancy of Cotton Fabric Coated Using Sol-Gel Process

by Zeeshan Ur Rehman, Hamid Hassan, Laila Khan, Lee Hwain, Yun Chiho and Bon Heun Koo

Coatings 2024, 14(10), 1283; https://doi.org/10.3390/coatings14101283 - 8 Oct 2024

Cited by 2 | Viewed by 1071

Abstract

A sol-gel matrix was generated from S– and P-based acids to prepare a fire-retardant solution system for coating natural cotton fibers. The physical properties, surface morphology, and elemental composition of the coated samples were assessed using optical scanning electron microscopy. The thermal behavior [...] Read more.

A sol-gel matrix was generated from S– and P-based acids to prepare a fire-retardant solution system for coating natural cotton fibers. The physical properties, surface morphology, and elemental composition of the coated samples were assessed using optical scanning electron microscopy. The thermal behavior of the coated samples was documented using TGA and VFT tests, which confirmed higher thermal stability of the phosphate-based coatings. High char residue formation (~44.5%) and self-extinguishing properties were observed for the phosphate-based coating under non-curing conditions. The superior properties of phosphate-based coatings P5-4h could be ascribed to the collaborative effect of P–Si–N—i.e., the combined activity during the combustion process and pyrolysis of the coated sample. Full article

(This article belongs to the Special Issue Science and Technology of Fabric Coatings)

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12 pages, 4234 KB

Open AccessEditor’s ChoiceArticle

Characterization of Mechanical Properties and Surface Wettability of Epoxy Resin/Benzoxazine Composites in a Simulated Acid Rain Environment

by Poom Narongdej, Riley Gomez, Daniel Tseng, Ehsan Barjasteh and Sara Moghtadernejad

Coatings 2024, 14(10), 1279; https://doi.org/10.3390/coatings14101279 - 7 Oct 2024

Cited by 6 | Viewed by 2103

Abstract

Despite the robustness of thermosetting coatings in various applications, prolonged exposure to acidic environments can cause gradual deterioration, leading to structural or functional damage. This study investigates composite materials comprised of cycloaliphatic epoxy resin (CER) and benzoxazine (BZ) at three different weight ratios: [...] Read more.

Despite the robustness of thermosetting coatings in various applications, prolonged exposure to acidic environments can cause gradual deterioration, leading to structural or functional damage. This study investigates composite materials comprised of cycloaliphatic epoxy resin (CER) and benzoxazine (BZ) at three different weight ratios: 50:50, 25:75, and 0:100. These composites were exposed to nitric acid, simulating acid rain, for durations ranging from 1 to 5 h. The specimens were characterized for weight change, mechanical properties (flexural strength and short beam strength), and surface properties (contact angle and contact angle hysteresis). Although minimal changes in the physical and mechanical properties of both homopolymer and copolymer composites were detected after short acid exposure (up to 5 h), surface wettability analysis via static contact angle and contact angle hysteresis revealed more pronounced deterioration. The static contact angle decreased by 24.96% and 28.32% for homopolymer BZ and copolymer BZ-CER composites, respectively. Contact angle hysteresis increased by 19.39% and 27.80% for 5 h acid-exposed homopolymer BZ and copolymer CER, respectively. This study underscores the utility of surface wettability analysis as a valuable tool for monitoring deterioration from acidic aging in polymers, particularly in BZ-CER systems used in structural and high-performance applications. Full article

(This article belongs to the Special Issue Coatings and Surface Modification for Tribological Applications)

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14 pages, 4155 KB

Open AccessEditor’s ChoiceArticle

Flexible Piezoelectric 0–3 PZT@C/PDMS Composite Films for Pressure Sensor and Limb Motion Monitoring

by Chungang Li, Chao Li, Yingzi Wang, Yaoting Zhao, Fengzhen Yang, Gensheng Dong, Xiujuan Lin, Shifeng Huang and Changhong Yang

Coatings 2024, 14(10), 1269; https://doi.org/10.3390/coatings14101269 - 3 Oct 2024

Cited by 3 | Viewed by 2291

Abstract

The flexible piezoelectric pressure sensor is essential in areas such as machine sensing and human activity monitoring. Here, 0-dimensional PZT piezoelectric ceramic nanoparticles with carbon coating were synthesized by a surface-modified technique. The excellent electrical conductivity of the carbon shell causes redistribution and [...] Read more.

The flexible piezoelectric pressure sensor is essential in areas such as machine sensing and human activity monitoring. Here, 0-dimensional PZT piezoelectric ceramic nanoparticles with carbon coating were synthesized by a surface-modified technique. The excellent electrical conductivity of the carbon shell causes redistribution and accumulation of mobile charges in the carbon layer, resulting in a greatly increased piezoelectric effect by inducing an enhanced electric field. A series of organic–inorganic composite films were prepared by the spin-coating method using polydimethylsiloxane (PDMS) as the matrix. The as-fabricated flexible PZT@C/PDMS composite film with 40 wt% PZT@C powder exhibits an excellent output voltage of ~74 V, a peak of output current ~295 nA, as well as a big sensitivity of 5.26 V N⁻¹. Moreover, the composite film can be used as a pressure sensor to detect changes in force as well as for monitoring limb movements such as finger flexion, wrist flexion, and pedaling. This study reveals the promising applications of flexible 40%PZT@C/PDMS composite film for limb motion monitoring and pressure sensing. Full article

(This article belongs to the Special Issue Advances in Deposition and Surface Modification of Oxide Thin Films and Nanocoatings)

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24 pages, 1442 KB

Open AccessEditor’s ChoiceReview

Thermochromic Polymers in Food Packaging: A Comprehensive Systematic Review and Patent Landscape Analysis

by Colette Breheny, Kieran Donlon, Alan Harrington, Declan Mary Colbert, Gilberto S. N. Bezerra and Luke M. Geever

Coatings 2024, 14(10), 1252; https://doi.org/10.3390/coatings14101252 - 1 Oct 2024

Cited by 6 | Viewed by 4530

Abstract

This study addresses the gap in research on the application of thermochromic polymers (TPs) in food packaging and their potential for real-time temperature monitoring, aiding in the assessment of food quality and shelf-life. TPs exhibit a visible color change in response to temperature [...] Read more.

This study addresses the gap in research on the application of thermochromic polymers (TPs) in food packaging and their potential for real-time temperature monitoring, aiding in the assessment of food quality and shelf-life. TPs exhibit a visible color change in response to temperature variations. A comprehensive systematic review (SR) across multiple engineering peer-review databases using predefined terms was conducted. Additionally, international patent databases were investigated using the same predefined terms. Independent experts reviewed the methodology to identify and address potential biases. A total of 288 eligible articles and 922 patents were identified. After a duplicate selection and extraction process according to the inclusion criteria, four related full-text publications were selected from the initial 288 articles, and five relevant patents were selected from the 922 patents. The qualitative review suggests that TPs hold significant promise as food packaging materials due to their unique physical properties. The study concludes that TPs offer valuable properties for the food packaging industry, meriting further investigation to exploit their benefits fully. Full article

(This article belongs to the Section Coatings for Food Technology and System)

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13 pages, 8918 KB

Open AccessEditor’s ChoiceArticle

Effect of SiC Contents on Wear Resistance Performance of Electro-Codeposited Ni-SiC Composite Coatings

by Shaoqing Wang, Faqin Xie and Xiangqing Wu

Coatings 2024, 14(9), 1224; https://doi.org/10.3390/coatings14091224 - 23 Sep 2024

Cited by 4 | Viewed by 1301

Abstract

This paper focuses on the wear resistance performance of Ni-SiC composite coatings with various contents of SiC particles. The coatings were characterized via a scanning electron microscope (SEM), X-ray diffractometer (XRD), and transmission electron microscopy (TEM), and the wear behaviors of different coatings [...] Read more.

This paper focuses on the wear resistance performance of Ni-SiC composite coatings with various contents of SiC particles. The coatings were characterized via a scanning electron microscope (SEM), X-ray diffractometer (XRD), and transmission electron microscopy (TEM), and the wear behaviors of different coatings were tested. The results show that SiC particle incorporation results in a nanocrystalline metal matrix and nanotwins in nickel nanograins. The microhardness and wear resistance Ni-SiC composite coatings increased with the increasing SiC content. Microhardness was improved due to the grain-refinement strengthening effect and the presence of a nanotwin structure. The dominant wear mechanism was described in two stages: the first stage involves the interaction of SiC particles/the counter ball, and the second stage involves the formation of the oxide film its breaking up into wear debris. A higher SiC content increased the duration of the first stage and slowed down the rate of breaking up into debris, thereby decreasing the wear rate. Full article

(This article belongs to the Section Tribology)

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15 pages, 4976 KB

Open AccessEditor’s ChoicePerspective

Low-Carbon Embodied, Self-Cleaning, and Air-Purifying Building Envelope Components Using TiO₂ Photocatalysis, 3D Printing, and Recycling

by Aníbal Maury-Ramírez, Mario Rinke and Johan Blom

Coatings 2024, 14(9), 1228; https://doi.org/10.3390/coatings14091228 - 23 Sep 2024

Cited by 3 | Viewed by 4493

Abstract

This perspective article describes the past, present, and future directions on TiO₂ photocatalysis, 3D concrete printing, and recycling for developing innovative building envelope components from façade skins. Using a methodology consisting of three phases, first the historical evolution of TiO₂ photocatalysis, [...] Read more.

This perspective article describes the past, present, and future directions on TiO₂ photocatalysis, 3D concrete printing, and recycling for developing innovative building envelope components from façade skins. Using a methodology consisting of three phases, first the historical evolution of TiO₂ photocatalysis, 3D concrete printing, and recycling policies was investigated. Second, the rationale and positioning with regard to the state of the art were developed. Third, the cementitious mix design assessment for 3D printing of the building envelope components, evaluation of the photocatalytic activity, evaluation of the self-cleaning and air-purifying properties, and environmental and health assessment of the building envelope components were identified and discussed as major issues in developing innovative building envelope components that have the potential to mitigate urban air pollution, reduce building maintenance activities, and reduce building embedded carbon while, for example, recycling significant amounts of construction and demolition waste. Full article

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

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37 pages, 2592 KB

Open AccessEditor’s ChoiceReview

Recent Applications and Future Trends of Nanostructured Thin Films-Based Gas Sensors Produced by Magnetron Sputtering

by Pedro Catalão Moura and Susana Sério

Coatings 2024, 14(9), 1214; https://doi.org/10.3390/coatings14091214 - 20 Sep 2024

Cited by 2 | Viewed by 3208

Abstract

The field of gas sensors has been developing for the last year due to the necessity of characterizing compounds and, in particular, volatile organic compounds whose detection can be of special interest in a vast range of applications that extend from clinical evaluation [...] Read more.

The field of gas sensors has been developing for the last year due to the necessity of characterizing compounds and, in particular, volatile organic compounds whose detection can be of special interest in a vast range of applications that extend from clinical evaluation to environmental monitoring. Among all the potential techniques to develop sensors, magnetron sputtering has emerged as one of the most suitable methodologies for the production of large-scale uniform coatings, with high packing density and strong adhesion to the substrate at relatively low substrate temperatures. Furthermore, it presents elevated deposition rates, allows the growth of thin films with high purity, permits a precise control of film thickness, enables the simple manufacturing of sensors with low power consumption and, consequently, low costs involved in the production. This work reviewed all the current applications of gas sensors developed through magnetron sputtering in the field of VOCs assessment by gathering the most relevant scientific works published. A total of 10 compounds were considered for this work. Additionally, 13 other compounds were identified as promising targets and classified as future trends in this field. Overall, this work summarizes the state-of-the-art in the field of gas sensors developed by magnetron sputtering technology, allowing the scientific community to take a step forward in this field and explore new research areas. Full article

(This article belongs to the Special Issue Advanced Nanostructured Coatings Deposited by Magnetron Sputtering)

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15 pages, 3961 KB

Open AccessEditor’s ChoiceArticle

Forming Epoxy Coatings on Laser-Engraved Surface of Aluminum Alloy to Reinforce the Bonding Joint with a Carbon Fiber Composite

by Hongping Zhu, Jinheng Zhang, Fei Cheng, Jiangzhou Li, Bo Wu and Zhijie Zhao

Coatings 2024, 14(9), 1201; https://doi.org/10.3390/coatings14091201 - 18 Sep 2024

Cited by 3 | Viewed by 1548

Abstract

This study designed laser engraving and resin pre-coating (RPC) treatments on an aluminum alloy (AA) surface to construct through-the-thickness “epoxy pins” for improving the bonding strength with carbon fiber reinforced polymer (CFRP). A laser engraving treatment was used to create a pitted structure [...] Read more.

This study designed laser engraving and resin pre-coating (RPC) treatments on an aluminum alloy (AA) surface to construct through-the-thickness “epoxy pins” for improving the bonding strength with carbon fiber reinforced polymer (CFRP). A laser engraving treatment was used to create a pitted structure on the AA surface; higher wettability was acquired and greater vertical spaces were formed to impregnate epoxy resin, resulting in stronger mechanical interlocking. The RPC technique was further used to guide high-viscosity epoxy resin into pits to form the epoxy coatings and to minimize defects between the resin and the substrate. The bonding strength of the specimen treated with both laser engraving with a unit dimension of 0.3 mm and RPC increased up to 227.1% in comparison with that of the base. The failure modes of the hybrid composites changed from the debonding failure of the AA surface to the delamination-dominated failure of the laminated CFRP composites. It was confirmed that laser engraving is a feasible and effective method when combined with RPC for treating AAs to improve the bonding strength of AA-CFRP composites, which provides a reference for preparing high-performance hybrid composites with metals. Full article

(This article belongs to the Special Issue Advanced Additive Manufacturing and Surface Modifications of Metallic Materials)

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23 pages, 6574 KB

Open AccessEditor’s ChoiceReview

Polymer Capacitor Films with Nanoscale Coatings for Dielectric Energy Storage: A Review

by Liang Cao, Rui Xi, Chen Zhou, Gaohui He, Feng Yang, Lingna Xu and He Li

Coatings 2024, 14(9), 1193; https://doi.org/10.3390/coatings14091193 - 15 Sep 2024

Cited by 2 | Viewed by 3478

Abstract

Enhancing the energy storage properties of dielectric polymer capacitor films through composite materials has gained widespread recognition. Among the various strategies for improving dielectric materials, nanoscale coatings that create structurally controlled multiphase polymeric films have shown great promise. This approach has garnered considerable [...] Read more.

Enhancing the energy storage properties of dielectric polymer capacitor films through composite materials has gained widespread recognition. Among the various strategies for improving dielectric materials, nanoscale coatings that create structurally controlled multiphase polymeric films have shown great promise. This approach has garnered considerable attention in recent years due to its effectiveness. This review examines surface-coated polymer composites used for dielectric energy storage, discussing their dielectric properties, behaviors, and the underlying physical mechanisms involved in energy storage. The review thoroughly examines the fabrication methods for nanoscale coatings and the selection of coating materials. It also explores the latest advancements in the rational design and control of interfaces in organic–inorganic, organic–organic, and heterogeneous multiphase structures. Additionally, the review delves into the structure–property relationships between different interfacial phases and various interface structures, analyzing how nanoscale coatings the impact dielectric constant, breakdown strength, conduction and charge transport mechanisms, energy density and efficiency, thermal stability, and electrothermal durability of polymeric capacitor films. Moreover, the review summarizes relevant simulation methods and offers computational insights. The potential practical applications and characteristics of such nanoscale coating techniques are discussed, along with the existing challenges and practical limitations. Finally, the review concludes with a summary and outlook, highlighting potential research directions in this rapidly evolving field. Full article

(This article belongs to the Special Issue Trends and Advances in Thin Films and Coatings for High-Efficiency Organic Solar Cells)

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16 pages, 13078 KB

Open AccessEditor’s ChoiceArticle

Metallization of Carbon Fiber-Reinforced Plastics (CFRP): Influence of Plasma Pretreatment on Mechanical Properties and Splat Formation of Atmospheric Plasma-Sprayed Aluminum Coatings

by Christian Semmler, Willi Schwan and Andreas Killinger

Coatings 2024, 14(9), 1169; https://doi.org/10.3390/coatings14091169 - 11 Sep 2024

Cited by 1 | Viewed by 1863

Abstract

Carbon fiber-reinforced plastics (CFRPs) have broad applications as lightweight structural materials due to their remarkable strength-to-weight ratio. Aluminum is often used as a bond coating to ensure adhesion between CFRPs and further coatings with a higher melting temperature. However, challenges persist in optimizing [...] Read more.

Carbon fiber-reinforced plastics (CFRPs) have broad applications as lightweight structural materials due to their remarkable strength-to-weight ratio. Aluminum is often used as a bond coating to ensure adhesion between CFRPs and further coatings with a higher melting temperature. However, challenges persist in optimizing their surface properties and adhesion attributes for diverse applications. This investigation explores the impact of sandblasting and plasma pretreatment on CFRP surfaces and their influence on plasma-sprayed aluminum coatings. Two distinct CFRP substrates, distinguished by their cyanate ester and epoxy resin matrices, and two different aluminum powder feedstocks were employed. Plasma pretreatment induced micro-surface roughening in the range of 0.5 µm and significantly reduced the contact angles on polished specimens. Notably, on sandblasted specimens, plasma-activated surfaces displayed improved wetting behavior, which is attributed to the removal of polymeric fragments and augmented fiber exposure. Aluminum splats show a better interaction with carbon fibers compared to a polymeric matrix material. The impact of plasma activation on the coating adhesion proved relatively limited. All samples with plasma activation had deposition efficiencies that increased by 12.5% to 34.4%. These findings were supported by SEM single-splat analysis and contribute to a deeper comprehension of surface modification strategies tailored to CFRPs. Full article

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

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27 pages, 11026 KB

Open AccessEditor’s ChoiceArticle

Niobium Oxide Thin Films Grown on Flexible ITO-Coated PET Substrates

by Alice Marciel, Alexandre Bastos, Luiz Pereira, Suresh Kumar Jakka, Joel Borges, Filipe Vaz, Marco Peres, Katharina Lorenz, Arijeta Bafti, Luka Pavić, Rui Silva and Manuel Graça

Coatings 2024, 14(9), 1127; https://doi.org/10.3390/coatings14091127 - 2 Sep 2024

Cited by 4 | Viewed by 2089

Abstract

Niobium oxide thin films were grown on both rigid and flexible substrates using DC magnetron sputtering for electrochromic applications. Three experimental series were conducted, varying the oxygen to argon flow rate ratio and deposition time. In the first series, the oxygen to argon [...] Read more.

Niobium oxide thin films were grown on both rigid and flexible substrates using DC magnetron sputtering for electrochromic applications. Three experimental series were conducted, varying the oxygen to argon flow rate ratio and deposition time. In the first series, the oxygen to argon ratio was adjusted from 0 to 0.32 while maintaining a constant growth time of 30 min. For the second and third series, the oxygen to argon ratios were fixed at 0.40 and 0.56, respectively, with deposition times ranging from 15 to 60 min. A structural transition from crystalline to amorphous was observed at an oxygen to argon flow rate ratio of 0.32. This transition coincided with a change in appearance, from non-transparent with metallic-like electrical conductivity to transparent with dielectric behavior. The transparent niobium oxide films exhibited thicknesses between 51 nm and 198 nm, with a compact, dense, and featureless morphology, as evidenced by both top-view and cross-sectional images. Films deposited on flexible indium tin oxide (ITO)-coated polyethylene terephthalate (PET) substrates displayed a maximum surface roughness (Sq) of 9 nm and a maximum optical transmission of 83% in the visible range. The electrochromic response of niobium oxide thin films on ITO-coated PET substrates demonstrated a maximum coloration efficiency of 30 cm² C⁻¹ and a reversibility of 96%. Mechanical performance was assessed through bending tests. The ITO-coated PET substrate exhibited a critical bending radius of 6.5 mm. Upon the addition of the niobium oxide layer, this decreased to 5 mm. Electrical resistance measurements indicated that the niobium oxide film mitigated rapid mechanical degradation of the underlying ITO electrode beyond the critical bending radius. Full article

(This article belongs to the Special Issue Advances in Deposition and Surface Modification of Oxide Thin Films and Nanocoatings)

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17 pages, 5858 KB

Open AccessEditor’s ChoiceArticle

Effect of Two Types of Chitosan Thermochromic Microcapsules Prepared with Syringaldehyde and Sodium Tripolyphosphate Crosslinking Agents on the Surface Coating Performance of Basswood Board

by Jingyi Hang, Bo Zhang, Hongwei Fan, Xiaoxing Yan and Jun Li

Coatings 2024, 14(9), 1118; https://doi.org/10.3390/coatings14091118 - 2 Sep 2024

Cited by 3 | Viewed by 1545

Abstract

In order to investigate the effect of thermochromic microcapsules on the surface coating performance of basswood board, two types of microcapsules prepared with syringaldehyde and sodium tripolyphosphate crosslinking agents were added to a UV primer and coated on the surface of basswood board. [...] Read more.

In order to investigate the effect of thermochromic microcapsules on the surface coating performance of basswood board, two types of microcapsules prepared with syringaldehyde and sodium tripolyphosphate crosslinking agents were added to a UV primer and coated on the surface of basswood board. The color-change effect of the surface coating on basswood board with microcapsules added with syringaldehyde as the crosslinking agent was better than that with microcapsules added with sodium tripolyphosphate as the crosslinking agent, and the color difference varied more significantly with temperature. The effect of the two types of microcapsules on the glossiness of the surface coating on basswood board was relatively weak. The glossiness of the surface coating on basswood board with microcapsules containing syringaldehyde as the crosslinking agent showed an overall increasing trend with the increase in microcapsules, and the change trend was relatively gentle. The glossiness of the surface coating on basswood board with microcapsules containing sodium tripolyphosphate as the crosslinking agent increased first and then decreased as the amount of microcapsules added increased. The addition of microcapsules with syringaldehyde as the crosslinking agent had no significant effect on the reflectance in the visible light band of the surface coating on basswood board. Among the two groups of samples, the hardness increase in the surface coating on basswood board with syringaldehyde as the crosslinking agent was more significant. The adhesion level of the coating on the surface of the basswood board with the two microcapsules did not change. Neither of the microcapsules had a significant effect on the impact resistance of the surface on basswood board. In the comprehensive analysis, the surface coating on basswood board with microcapsules added with syringaldehyde as the crosslinking agent at a content of 4.0% had better comprehensive performance, better surface morphology, better color-change effect, and moderate mechanical properties. The color difference was found to be 21.0 at 25 °C, the reflectivity was found to be 57.06%, the hardness was found to be 3H, the adhesion was found to be five, and the impact resistance was found to be three. Full article

(This article belongs to the Special Issue Surface Properties and Surface Treatments of Wood and Wood-Based Composites)

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25 pages, 3225 KB

Open AccessEditor’s ChoiceReview

Electrophoretic Deposition of Bioactive Glass Coatings for Bone Implant Applications: A Review

by Richard Drevet, Joël Fauré and Hicham Benhayoune

Coatings 2024, 14(9), 1084; https://doi.org/10.3390/coatings14091084 - 23 Aug 2024

Cited by 9 | Viewed by 4065

Abstract

This literature review deals with the electrophoretic deposition of bioactive glass coatings on metallic substrates to produce bone implants. Biocompatible metallic materials, such as titanium alloys or stainless steels, are commonly used to replace hard tissue functions because their mechanical properties are appropriate [...] Read more.

This literature review deals with the electrophoretic deposition of bioactive glass coatings on metallic substrates to produce bone implants. Biocompatible metallic materials, such as titanium alloys or stainless steels, are commonly used to replace hard tissue functions because their mechanical properties are appropriate for load-bearing applications. However, metallic materials barely react in the body. They need a bioactive surface coating to trigger beneficial biological and chemical reactions in the physiological environment. Bioactive coatings aim to improve bone bonding, shorten the healing process after implantation, and extend the lifespan of the implant. Bioactive glasses, such as 45S5, 58S, S53P4, 13-93, or 70S30C, are amorphous materials made of a mixture of oxides that are accepted by the human body. They are used as coatings to improve the surface reactivity of metallic bone implants. Their high bioactivity in the physiological environment induces the formation of strong chemical bonding at the interface between the metallic implant and the surrounding bone tissue. Electrophoretic deposition is one of the most effective solutions to deposit uniform bioactive glass coatings at low temperatures. This article begins with a review of the different compositions of bioactive glasses described in the scientific literature for their ability to support hard tissue repair. The second part details the different stages of the bioactivity process occurring at the surface of bioactive glasses immersed in a physiological environment. Then, the mechanisms involved in the electrophoretic deposition of bioactive glass coatings on metallic bone implants are described. The last part of the article details the current developments in the process of improving the properties of bioactive glass coatings by adding biocompatible elements to the glassy structure. Full article

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

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14 pages, 4991 KB

Open AccessEditor’s ChoiceArticle

The Evolution of Surfaces on Medium-Carbon Steel for Fatigue Life Estimations

by Phanuphak Seensattayawong and Eberhard Kerscher

Coatings 2024, 14(8), 1077; https://doi.org/10.3390/coatings14081077 - 22 Aug 2024

Cited by 2 | Viewed by 1450

Abstract

Early in fatigue life, fatigue cracks are often initiated at persistent slip bands (PSBs), which play the main role in surface evolution when the components are subjected to cyclic loading. Therefore, this paper aims to study the behavior of the surface development of [...] Read more.

Early in fatigue life, fatigue cracks are often initiated at persistent slip bands (PSBs), which play the main role in surface evolution when the components are subjected to cyclic loading. Therefore, this paper aims to study the behavior of the surface development of medium-carbon steel, specifically 42CrMo4 (SAE 4140). Tests were conducted using tension–compression fatigue testing with stress amplitudes set at 30%, 40%, and 50% of the ultimate tensile strength (UTS); a load ratio of R = −1; and a frequency of f = 10 Hz. The ultimate number of test cycles was 2 × 10⁵. The fatigue test specimens with as-machined surface quality (Ra < 100 nm) were tested on a servo-hydraulic push–pull testing machine, and the tests were interrupted a few times to bring the specimens out for surface measuring with a confocal microscope. The linear roughness values of the arithmetic mean deviation (Ra), maximum height (Rz), maximum profile peak height (Rp), and maximum profile valley depth (Rv) were investigated and further used to determine the roughness evolution during cyclic loading (REC) by analyzing the inclinations of the fitting curves of roughness and number-of-cycles diagrams. REC could then be used to estimate and classify the fatigue lifetime. Full article

(This article belongs to the Special Issue Microstructure, Fatigue and Wear Properties of Steels, 2nd Edition)

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15 pages, 5469 KB

Open AccessEditor’s ChoiceArticle

High-Temperature Hot Corrosion Resistance of CrAl/NiCoCrAlY/AlSiY Gradient Composite Coating on TiAl Alloy

by Yuanyuan Sun, Qiang Miao, Shijie Sun, Wenping Liang, Zheng Ding, Jiangqi Niu, Feilong Jia, Jianyan Xu and Jiumei Gao

Coatings 2024, 14(8), 1067; https://doi.org/10.3390/coatings14081067 - 20 Aug 2024

Cited by 6 | Viewed by 1737

Abstract

TiAl alloys are used in high-temperature components such as the turbine blades of aeroengines because of their excellent properties. However, TiAl alloys are prone to thermal corrosion when in near-ocean service. In order to solve this problem, a hot-corrosion-resistant CrAl/NiCoCrAlY/AlSiY gradient composite coating [...] Read more.

TiAl alloys are used in high-temperature components such as the turbine blades of aeroengines because of their excellent properties. However, TiAl alloys are prone to thermal corrosion when in near-ocean service. In order to solve this problem, a hot-corrosion-resistant CrAl/NiCoCrAlY/AlSiY gradient composite coating was prepared on the surface of the TiAl alloy. The phase composition and morphology of the coating were analyzed. Hot corrosion tests of the traditional NiCoCrAlY coating and CrAl/NiCoCrAlY/AlSiY gradient composite coating on a TiAl substrate were performed. The samples were coated with 75%Na₂SO₄ + 25%NaCl salt film and treated at 950 °C for 100 h, and the corrosion products were analyzed. The results indicate that compared with the TiAl substrate and traditional NiCoCrAlY-coated samples, the composite coating showed better hot corrosion resistance, only slightly cracking, and no corrosion loss occurred. This is mainly because the continuous Al₂O₃ layer can effectively resist the damage caused by the melting reaction in salt, and the Cr-rich layer can not only slow the mutual diffusion of elements but also generate a good corrosion resistance chromium oxide protective layer under serious corrosion. Moreover, the corrosion mechanism of the TiAl substrate, traditional NiCoCrAlY coating, and experimental composite coating was analyzed in detail. Full article

(This article belongs to the Special Issue High-Temperature Corrosion and Oxidation of Metals and Alloys)

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14 pages, 4242 KB

Open AccessEditor’s ChoiceArticle

Fabrication of Vanadate-Exchanged Electrodeposited Zn-Al Layered Double Hydroxide (LDH) Coating on a ZX21 Mg Alloy to Improve the Corrosion Resistance

by Wei-Lun Hsiao and Peng-Wei Chu

Coatings 2024, 14(8), 1047; https://doi.org/10.3390/coatings14081047 - 16 Aug 2024

Cited by 2 | Viewed by 1815

Abstract

This study presents a vanadate-exchanged Zn-Al layered double hydroxide (LDH) coating on a ZX21 Mg alloy (Mg-2.15 wt%Zn-0.97 wt%Ca) by electrodeposition and immersion anion-exchange post-treatment. With the prepared vanadate-exchanged electrodeposited Zn-Al LDH coating, the corrosion resistance of the ZX21 Mg alloy improves with [...] Read more.

This study presents a vanadate-exchanged Zn-Al layered double hydroxide (LDH) coating on a ZX21 Mg alloy (Mg-2.15 wt%Zn-0.97 wt%Ca) by electrodeposition and immersion anion-exchange post-treatment. With the prepared vanadate-exchanged electrodeposited Zn-Al LDH coating, the corrosion resistance of the ZX21 Mg alloy improves with a decrease in the corrosion current density from 62.4 μA/cm² to 3.32 μA/cm². The fabricated vanadate-exchanged electrodeposited Zn-Al LDH coating contains complex anions in the interlayers, including mainly nitrate (NO₃⁻), carbonate (CO₃²⁻), and different vanadates. The coating not only serves as a physical barrier on the ZX21 Mg alloy but also absorbs chloride ions in the environment through anion exchange and inhibits corrosion with the reduction of the interlayer vanadates. Furthermore, the vanadates can also be released into the damaged area of the coating. Full article

(This article belongs to the Special Issue Advances in Corrosion-Resistant Coatings, 2nd Edition)

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17 pages, 7764 KB

Open AccessEditor’s ChoiceArticle

An Innovative Wood Fire-Retardant Coating Based on Biocompatible Nanocellulose Surfactant and Expandable Graphite

by Tereza Jurczyková, Elena Kmeťová, František Kačík, Martin Lexa and Jakub Ťoupal

Coatings 2024, 14(8), 1036; https://doi.org/10.3390/coatings14081036 - 15 Aug 2024

Cited by 3 | Viewed by 1946

Abstract

Nanocellulose (CNC) seems to be a promising surfactant, which, together with expandable graphite (EG), forms the essence of an effective natural-based fire-retardant wood coating. In our research, the most suitable composition of the mixture was tested concerning good solubility, dispersion, and consistency. Favorable [...] Read more.

Nanocellulose (CNC) seems to be a promising surfactant, which, together with expandable graphite (EG), forms the essence of an effective natural-based fire-retardant wood coating. In our research, the most suitable composition of the mixture was tested concerning good solubility, dispersion, and consistency. Favorable results were achieved with the formulation composed of a 4% CNC alkaline solution with 80 wt.% of the selected EG. Subsequently, six different types of EG were used to prepare these wood fire-retardant coatings. The effectiveness of treatments was verified using a test with a radiant heat source, where the test samples’ relative weight loss, relative burning rate, and surface temperature during 600 s were evaluated. All prepared formulations can be characterized as more or less equally effective. However, the best results were obtained with the EG of GG 200–100 N, where the mass loss of the sample was 8.10 ± 1.24%. Very good results were also achieved by graphite 25 E + 180 HPH (8.70 ± 0.89%), which is similar to the previous one, even according to the microscopic assessment of the coating as well as the expanded layer. The graphite type 25 K + 180 (8.86 ± 0.65%) shows the expanded layer’s best adhesion, coating uniformity, and ease of application. The results of this work confirmed that the CNC coating itself has significant retardation effects. Full article

(This article belongs to the Special Issue New Challenges in Wood Adhesives and Coatings, 2nd Edition)

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15 pages, 4336 KB

Open AccessEditor’s ChoiceArticle

Microstructure and Wear Performance of TaC and Ta/TaC Coatings on 30CrNi2MoVA Steel

by Kai Yang, Xuming Lv, Bo Dang, Zhuoyan Lai, Xiaohu Chen, Dongbo Wei, Shuqin Li and Pingze Zhang

Coatings 2024, 14(8), 1039; https://doi.org/10.3390/coatings14081039 - 15 Aug 2024

Cited by 2 | Viewed by 1826

Abstract

To enhance the wear resistance of artillery barrels in harsh environments, TaC and Ta/TaC coatings were prepared on 30CrNi2MoVA steel using double-glow plasma surface metallurgy technology. These coatings, of which their surfaces consisted of almost pure TaC phases, showed defect-free interfaces with the [...] Read more.

To enhance the wear resistance of artillery barrels in harsh environments, TaC and Ta/TaC coatings were prepared on 30CrNi2MoVA steel using double-glow plasma surface metallurgy technology. These coatings, of which their surfaces consisted of almost pure TaC phases, showed defect-free interfaces with the substrate. The Ta/TaC coating demonstrated excellent integration, forming a nearly homogeneous structure. The coatings exhibited a gradient cross-sectional hardness, affecting a depth of approximately 20 μm. The Ta transition layer significantly enhanced the microhardness and adhesive strength of the TaC coating, with about 16.7% and 68.5% increases in the Ta/TaC coating, respectively. Both coatings markedly improved the wear resistance, showing slight wear at room temperature and minor oxidative wear at high temperatures. The Ta/TaC coating had more stable friction coefficient curves and a lower specific wear rate, with an 11.4% wear rate of the substrate at 500 °C. Thermal mismatch and stress concentration under wear loads caused extensive cracks and edge chipping in the TaC coating. In contrast, the good compatibility between the Ta transition layer and the TaC layer allowed for cooperative deformation with the substrate, creating a plastic deformation zone that reduced internal stresses and stress concentration, maintaining the intact structure. This study provides insights into applying Ta/TaC coatings for artillery barrel protection and broadens the possible application scenarios of the preparation technology. Full article

(This article belongs to the Special Issue Oxidation, Wear, Corrosion Behaviors and Activated Bonding Properties of Coatings Deposited on Metals)

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17 pages, 21836 KB

Open AccessEditor’s ChoiceArticle

Effect of Two Types of Pomelo Peel Flavonoid Microcapsules on the Performance of Water-Based Coatings on the Surface of Fiberboard

by Jinzhe Deng, Tingting Ding and Xiaoxing Yan

Coatings 2024, 14(8), 1032; https://doi.org/10.3390/coatings14081032 - 14 Aug 2024

Cited by 3 | Viewed by 1921

Abstract

In order to achieve antibacterial properties in water-based coatings, two types of antibacterial pomelo peel flavonoid microcapsules were added to water-based coatings and decorated on the surface of fiberboard. The surface coatings of the substrates were tested and analyzed. The antibacterial rate of [...] Read more.

In order to achieve antibacterial properties in water-based coatings, two types of antibacterial pomelo peel flavonoid microcapsules were added to water-based coatings and decorated on the surface of fiberboard. The surface coatings of the substrates were tested and analyzed. The antibacterial rate of the surface coatings of the two groups of fiberboards gradually increased with the increase in the content of the microcapsules. The color difference of the surface coatings of both groups increased slightly, the glossiness decreased, the gloss loss rate increased greatly, and the reflectivity increased slightly. The adhesion of the surface coatings of the two groups of fiberboards did not change significantly, the roughness gradually increased, the hardness of the melamine-resin-coated pomelo peel flavonoid microcapsules gradually increased, and the impact resistance slightly improved. Compared with the antibacterial results of the coating without substrate at the same content, the antibacterial effect of the fiberboard surface coating was slightly decreased. Overall, the surface coating on the fiberboard with 9.0% chitosan-coated pomelo peel flavonoid microcapsules demonstrated superior performance, superior coating morphology, and enhanced antibacterial properties. The antibacterial rate was 73.7% against Escherichia coli, and the antibacterial rate was 77.4% against Staphylococcus aureus. The color difference was 3.85, the gloss loss rate was 90.0%, and the reflectivity was 20.19%. The hardness was HB, the adhesion was level 1, the impact resistance level was 3, and the roughness was 1.94 μm. This study explored the effect of antibacterial microcapsules on coating performance, providing a technical basis for the application of the antibacterial microcapsules. Full article

(This article belongs to the Special Issue Surface Properties and Surface Treatments of Wood and Wood-Based Composites)

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25 pages, 11956 KB

Open AccessEditor’s ChoiceArticle

Innovative Paper Coatings: Regenerative Superhydrophobicity through Self-Structuring Aqueous Wax-Polymer Dispersions

by Cynthia Cordt, Jennifer Daeg, Oliver Elle, Andreas Geissler and Markus Biesalski

Coatings 2024, 14(8), 1028; https://doi.org/10.3390/coatings14081028 - 13 Aug 2024

Cited by 7 | Viewed by 3342

Abstract

For a wide range of applications, paper materials require effective protection against the destructive effect of water, which is most effectively realized by superhydrophobic coatings. In recent years, a considerable amount of scientific research has been carried out in this area, focusing particularly [...] Read more.

For a wide range of applications, paper materials require effective protection against the destructive effect of water, which is most effectively realized by superhydrophobic coatings. In recent years, a considerable amount of scientific research has been carried out in this area, focusing particularly on biogenic resources. With this contribution, we go one step further and examine how biogenic materials can be transferred into aqueous dispersions and coated onto paper via existing technologies. With this paper coating, based on a hydrophobic cellulose derivative in combination with a structurally similar wax, thermally regenerable flower-like surface morphologies are obtained via self-assembly, where the hydrophobic cellulose polymer acts as a structural template for the co-crystallization of the wax component. Such hydrophobic structures in the low micrometer range ensure perfectly water-repellent paper surfaces with contact angles > 150° starting from coating weights of 5 g/m². The dispersion can be successfully applied to a variety of commercially available paper substrates, whereby the effects of different roughness, porosity, and hydrophobicity were investigated. In this context, a certain roughness of the base paper (S_a ~ 1.5–3 µm) was found to be beneficial for achieving the highest possible contact angles. Furthermore, the approach proved to be paper process-compatible, recyclable, and regenerable, whereby the processing temperatures allow the coating properties to be thermally generated in situ. With this work, we demonstrate how biogenic waxes are very well suited for superhydrophobic, regenerative coatings and, importantly, how they can be applied from aqueous coatings, enabling simple transfer into the paper industry. Full article

(This article belongs to the Special Issue Trends in Coatings and Surface Technology, 2nd Edition)

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12 pages, 5330 KB

Open AccessEditor’s ChoiceArticle

Friction and Wear Behavior of 3D-Printed Inconel 718 Alloy under Dry Sliding Conditions

by Ioannis Karagiannidis, Athanasios Tzanis, Dirk Drees, Lais Lopes, Georgios Chondrakis, Maria Myrto Dardavila, Emmanuel Georgiou and Angelos Koutsomichalis

Coatings 2024, 14(8), 1029; https://doi.org/10.3390/coatings14081029 - 13 Aug 2024

Cited by 1 | Viewed by 2359

Abstract

Tailor-made materials used for advanced applications are nowadays of great research interest in various industrial and technological fields, ranging from aerospace and automotive applications to consumer goods and biomedical components. In the present research, Inconel 718 superalloy specimens were fabricated by the selective [...] Read more.

Tailor-made materials used for advanced applications are nowadays of great research interest in various industrial and technological fields, ranging from aerospace and automotive applications to consumer goods and biomedical components. In the present research, Inconel 718 superalloy specimens were fabricated by the selective laser melting (SLM) technique. Structural characterization of the 3D-printed samples showed that they consisted of γ solid solution along with spherical carbide particles. To explore the applicability of these materials in abrasive tribological applications, reciprocating sliding tests were performed under dry conditions versus an Al₂O₃ counter-body. A 3D representation (triboscopy) of the tangential force during each sliding cycle was carried out in order to obtain better insight on the evolution of friction and to visualize localized tribological phenomena. Quantification of wear was performed with confocal microscopy and the wear mechanisms were analyzed with SEM and EDS techniques. Furthermore, the effect of surface finishing (as-printed and polished) on friction and wear were also investigated, and a comparison with other industrial materials is also included to evaluate the applicability of these alloys. The results indicated that surface finishing had an effect on friction during the run-in stage, whereas in steady-state conditions, no significant differences were observed between the as-printed and polished specimens. In all cases, the main wear mechanisms observed were a mixture of two-body and three-body abrasion, along with oxidative wear (indicated by the formation of an oxide-based tribo-layer). Full article

(This article belongs to the Special Issue Surface Engineering Processes for Reducing Friction and Wear)

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12 pages, 27979 KB

Open AccessEditor’s ChoiceArticle

Extraction of Anthocyanin Dye from Staghorn Sumac Fruit in Various Solvents and Use for Pigment Printing

by Maja Klančnik and Elena Koradin

Coatings 2024, 14(8), 1025; https://doi.org/10.3390/coatings14081025 - 13 Aug 2024

Cited by 3 | Viewed by 2572

Abstract

This study investigates the potential of the dye extracted from the fruits of the alien invasive plant staghorn sumac (lat. Rhus typhina) as a sustainable and environmentally friendly colorant. By using a range of solvents, including distilled water, methanol, ethanol, propanol, acetonitrile, [...] Read more.

This study investigates the potential of the dye extracted from the fruits of the alien invasive plant staghorn sumac (lat. Rhus typhina) as a sustainable and environmentally friendly colorant. By using a range of solvents, including distilled water, methanol, ethanol, propanol, acetonitrile, acetone, and dichloromethane, this study aims to determine the optimum solvent for the extraction of anthocyanin dyes from the fruit of staghorn sumac for the formulation of printing inks and for screen printing on paper and cotton fabric. The colors of the prints made with different dye extracts varied between more or less intense brownish-yellow hues, with the exception of the dye extracts in methanol and ethanol, which gave more brownish-orange hues. All prints showed excellent resistance to rubbing on cotton fabrics as well as to wet ironing. The light fastness of prints made with inks containing dyes extracted from all organic solvents was very good. Good wash fastness of prints on cotton fabrics was only achieved with inks made with dyes extracted in propanol and dichloromethane. The ink made from the dye extracted in propanol proved to be the best choice for printing on cotton fabric due to its uniform, intense, and resilient prints, while the inks made from the dyes extracted in distilled water and ethanol were also a good choice for printing on paper. Full article

(This article belongs to the Section Environmental Aspects in Colloid and Interface Science)

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