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Editor’s Choice Articles

Editor’s Choice articles are based on recommendations by the scientific editors of MDPI journals from around the world. Editors select a small number of articles recently published in the journal that they believe will be particularly interesting to readers, or important in the respective research area. The aim is to provide a snapshot of some of the most exciting work published in the various research areas of the journal.

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17 pages, 7764 KB  
Article
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 4 | Viewed by 2097
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  
Article
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 5 | Viewed by 2074
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  
Article
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 2207
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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12 pages, 27979 KB  
Article
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 3044
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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12 pages, 5330 KB  
Article
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 2700
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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25 pages, 11956 KB  
Article
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 8 | Viewed by 3736
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 (Sa ~ 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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9 pages, 1993 KB  
Article
Ultra-Structural Surface Characteristics of Dental Silane Monolayers
by Xiaotian Liu, Winnie Wing-Yee Shum and James Kit-Hon Tsoi
Coatings 2024, 14(8), 1005; https://doi.org/10.3390/coatings14081005 - 8 Aug 2024
Cited by 4 | Viewed by 1895
Abstract
This study aims to study the formation quality of the film of dental silanes. Two dental silanes, 3-methacryloxyproyltrimethoxysilane (MPS) and 3-acryloyloxypropyltrimethoxysilane (ACPS), were deposited on the silica glass-equivalent model surface (i.e., n-type silicon(100) wafer) by varying the deposition time (5 h and 22 [...] Read more.
This study aims to study the formation quality of the film of dental silanes. Two dental silanes, 3-methacryloxyproyltrimethoxysilane (MPS) and 3-acryloyloxypropyltrimethoxysilane (ACPS), were deposited on the silica glass-equivalent model surface (i.e., n-type silicon(100) wafer) by varying the deposition time (5 h and 22 h). The film quality was then evaluated by ellipsometry, surface contact angle (CA) and surface free energy (SFE), atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) in survey and high-resolution modes on Si2p, O1s and C1s. Ellipsometry confirmed that both silanes at the two different deposition times would produce 0.85–1.22 nm thick self-assembled monolayer on the silicon wafer surface. While the water CA of silanized surfaces (60.7–71.5°) was larger than the surface without silane (29.6°), the SFE values of all silanes (40.0–44.5 mN/m) were slightly less than that of the wafer surface (46.3 mN/m). AFM revealed that the MPS with 22 h silanization yielded a significantly higher roughness (0.597 μm) than other groups (0.254–0.297 μm). High-resolution XPS on C1s identified a prominent peak at 288.5 eV, which corresponds to methacrylate O-C*=O, i.e., the silane monolayer is extended fully in the vertical direction, while others are in defect states. This study proves that different dental silanes under various dipping times yield different chemical qualities of the film even if they look thin physically. Full article
(This article belongs to the Special Issue Surface Properties of Dental Materials and Instruments, 2nd Edition)
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10 pages, 5124 KB  
Article
Thick Columnar-Structured Thermal Barrier Coatings Using the Suspension Plasma Spray Process
by Dianying Chen and Christopher Dambra
Coatings 2024, 14(8), 996; https://doi.org/10.3390/coatings14080996 - 7 Aug 2024
Cited by 9 | Viewed by 2745
Abstract
Higher operating temperatures for gas turbine engines require highly durable thermal barrier coatings (TBCs) with improved insulation properties. A suspension plasma spray process (SPS) had been developed for the deposition of columnar-structured TBCs. SPS columnar TBCs are normally achieved at a short standoff [...] Read more.
Higher operating temperatures for gas turbine engines require highly durable thermal barrier coatings (TBCs) with improved insulation properties. A suspension plasma spray process (SPS) had been developed for the deposition of columnar-structured TBCs. SPS columnar TBCs are normally achieved at a short standoff distance (50.0 mm–75.0 mm), which is not practical when coating complex-shaped engine hardware since the plasma torch may collide with the components being sprayed. Therefore, it is critical to develop SPS columnar TBCs at longer standoff distances. In this work, a commercially available pressure-based suspension delivery system was used to deliver the suspension to the plasma jet, and a high-enthalpy TriplexPro-210 plasma torch was used for the SPS coating deposition. Suspension injection pressure was optimized to maximize the number of droplets injected into the hot plasma core and achieving the best particle-melting states and deposition efficiency. The highest deposition efficiency of 51% was achieved at 0.34 MPa injection pressure with a suspension flow rate of 31.0 g/min. With the optimized process parameters, 1000 μm thick columnar-structured SPS 8 wt% Y2O3-stabilized ZrO2 (8YSZ) TBCs were successfully developed at a standoff distance of 100.0 mm. The SPS TBCs have a columnar width between 100 μm and 300 μm with a porosity of ~22%. Furnace cycling tests at 1125 °C showed the SPS columnar TBCs had an average life of 1012 cycles, which is ~2.5 times that of reference air-plasma-sprayed dense vertically cracked TBCs with the same coating thickness. The superior durability of the SPS columnar TBCs can be attributed to the high-strain-tolerant microstructure. SEM cross-section characterization indicated the failure of the SPS TBCs occurred at the ceramic top coat and thermally grown oxide (TGO) interface. Full article
(This article belongs to the Special Issue Functional Coatings and Surface Science for Precision Engineering)
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17 pages, 2702 KB  
Review
Microorganisms in Red Ceramic Building Materials—A Review
by Elżbieta Stanaszek-Tomal
Coatings 2024, 14(8), 985; https://doi.org/10.3390/coatings14080985 - 5 Aug 2024
Cited by 2 | Viewed by 2872
Abstract
Ceramic materials have a very long tradition of use in construction. Their durability is related to the surface of the material and the action of the corrosive environment. One of the corrosive factors acting on ceramic materials is microorganisms. They can contribute to [...] Read more.
Ceramic materials have a very long tradition of use in construction. Their durability is related to the surface of the material and the action of the corrosive environment. One of the corrosive factors acting on ceramic materials is microorganisms. They can contribute to the deterioration of the technical and performance properties of building materials. Aesthetic, physical, and chemical deterioration are considered to be the main destructive processes in ceramic materials. This work shows how the different types of the most commonly used ceramic materials, i.e., brick and tiles, are damaged. Each of these types is susceptible to microbial growth. Most microorganisms that occur on ceramic materials produce staining substances and thus form coloured biofilms. The direct action of metabolic products secreted by organisms on inorganic substrates is the main cause of chemical biodeterioration. Therefore, this work presents the impact of microorganisms on ceramic building materials. Full article
(This article belongs to the Collection Review Papers Collection for Bioactive Coatings)
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12 pages, 2175 KB  
Article
Protection against Atmospheric Corrosion of Zinc in Marine Environment Rich in H2S Using Self-Assembled Monolayers Based on Sargassum fluitans III Extract
by Prescilla Lambert, Mahado Said-Ahmed, Benoit Lescop, Stéphane Rioual and Mounim Lebrini
Coatings 2024, 14(8), 988; https://doi.org/10.3390/coatings14080988 - 5 Aug 2024
Cited by 1 | Viewed by 1574
Abstract
The self-assembled monolayers (SAMs) process is one of the techniques used for the production of ultra-thin layers. The present work is therefore devoted to the study of the inhibition of zinc corrosion in a marine environment rich in H2S by SAMs [...] Read more.
The self-assembled monolayers (SAMs) process is one of the techniques used for the production of ultra-thin layers. The present work is therefore devoted to the study of the inhibition of zinc corrosion in a marine environment rich in H2S by SAMs based on Sargassum fluitans III. The protective effect of crude extracts of Sargassum fluitans on the surface of zinc using the SAMs process was evaluated by gravimetry and impedance on two different sites after three months of exposure. The formation of SAMs was characterized by FTIR, and the corrosion products formed on the surfaces were analyzed by XRD. The results obtained show that SAMs based on Sargassum fluitans III effectively inhibit zinc corrosion. Full article
(This article belongs to the Section Corrosion, Wear and Erosion)
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16 pages, 3022 KB  
Article
Data-Driven Optimization of Plasma Electrolytic Oxidation (PEO) Coatings with Explainable Artificial Intelligence Insights
by Patricia Fernández-López, Sofia A. Alves, Aleksey Rogov, Aleksey Yerokhin, Iban Quintana, Aitor Duo and Aitor Aguirre-Ortuzar
Coatings 2024, 14(8), 979; https://doi.org/10.3390/coatings14080979 - 3 Aug 2024
Cited by 3 | Viewed by 2895
Abstract
PEO constitutes a promising surface technology for the development of protective and functional ceramic coatings on lightweight alloys. Despite its interesting advantages, including enhanced wear and corrosion resistances and eco-friendliness, the industrial implementation of PEO technology is limited by its relatively high energy [...] Read more.
PEO constitutes a promising surface technology for the development of protective and functional ceramic coatings on lightweight alloys. Despite its interesting advantages, including enhanced wear and corrosion resistances and eco-friendliness, the industrial implementation of PEO technology is limited by its relatively high energy consumption. This study explores the development and optimization of novel PEO processes by means of machine learning (ML) to improve the coating thickness. For this purpose, ML models random forest and XGBoost were employed to predict the thickness of the developed PEO coatings based on the key process variables (frequency, current density, and electrolyte composition). The predictive performance was significantly improved by including the composition of the used electrolyte in the models. Furthermore, Shapley values identified the pulse frequency and the TiO2 concentration in the electrolyte as the most influential variables, with higher values leading to increased coating thickness. The residual analysis revealed a certain heteroscedasticity, which suggests the need for additional samples with high thickness to improve the accuracy of the model. This study reveals the potential of artificial intelligence (AI)-driven optimization in PEO processes, which could pave the way for more efficient and cost-effective industrial applications. The findings achieved further emphasize the significance of integrating interactions between variables, such as frequency and TiO2 concentration, into the design of processing operations. Full article
(This article belongs to the Special Issue Functional Films/Coatings Processing Technologies: Deposition and Process)
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13 pages, 8603 KB  
Article
Natural Tannin Layers for the Corrosion Protection of Steel in Contact with Water-Based Media
by Rossella Sesia, Silvia Spriano, Marco Sangermano, Massimo Calovi, Stefano Rossi and Sara Ferraris
Coatings 2024, 14(8), 965; https://doi.org/10.3390/coatings14080965 - 2 Aug 2024
Cited by 4 | Viewed by 3609
Abstract
Numerous strategies have been developed for the corrosion protection of steel; however, most of them have a significant environmental impact and employ toxic compounds. Tannins are a green and promising solution for sustainable corrosion protection strategies. In this context, this work was focused [...] Read more.
Numerous strategies have been developed for the corrosion protection of steel; however, most of them have a significant environmental impact and employ toxic compounds. Tannins are a green and promising solution for sustainable corrosion protection strategies. In this context, this work was focused on natural (condensed and hydrolysable) tannin layers as a possible corrosion protection strategy for carbon steel. The impact of the tannins’ dissolution medium (ultrapure water or Phosphate-Buffered Saline), surface pre-treatment (acid pickling or plasma), and deposition technology (dipping or spin coating) on layer homogeneity and adhesion has been evaluated. The effects of these parameters on coating formation, homogeneity, and adhesion have been investigated by means of visual inspections, swabbing, Fourier Transformed Infrared spectroscopy (FTIR), Scanning Electron Microscopy equipped with Energy Dispersive Spectroscopy (SEM-EDS) and tape adhesion tests. Preliminary electrochemical corrosion tests have been performed on the most promising material (carbon steel acid pickled and coated with a hydrolysable tannin solved in water by spin coating) to estimate the protective ability of the developed layers and highlight the main criticisms to be overcome. Full article
(This article belongs to the Special Issue Advanced Anticorrosion Coatings and Coating Testing)
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18 pages, 12340 KB  
Article
High-Temperature Mechanical and Tribological Performance of W-DLC Coating with Cr interlayer on X40CrMoV5-1 Hot Work Tool Steel
by Mária Hagarová, Gabriela Baranová, Mária Heželová, Martin Truchlý, Marek Vojtko, Ondrej Petruš and Dávid Csík
Coatings 2024, 14(8), 971; https://doi.org/10.3390/coatings14080971 - 2 Aug 2024
Cited by 5 | Viewed by 2323
Abstract
Diamond-like carbon (DLC) coatings enhance tool wear resistance across various temperatures. The sp3/sp2 bond ratio within DLC significantly impacts its properties and thermal stability. Elevated temperatures can alter DLC’s structure, while metallic elements and interlayers like chromium can modify its [...] Read more.
Diamond-like carbon (DLC) coatings enhance tool wear resistance across various temperatures. The sp3/sp2 bond ratio within DLC significantly impacts its properties and thermal stability. Elevated temperatures can alter DLC’s structure, while metallic elements and interlayers like chromium can modify its microstructure and performance. To evaluate the potential of W-DLC coatings with a chromium interlayer on 40CrMoV5-1 hot work tool steel under elevated temperatures, mechanical and tribological properties were assessed at room temperature and at temperatures of 100, 200, 300, 400, and 500 °C. Nanoindentation revealed a maximum hardness of 14.1 ± 1.3 GPa for the coating deposited at room temperature, attributed to a high sp3 content confirmed by Raman spectroscopy. Hardness decreased to 9.3 ± 1.0 GPa at 400 °C due to graphitization. The elastic modulus remained relatively constant across all temperatures. Tribological tests indicated a low coefficient of friction (CoF) of 0.15 at room temperature, increasing to 0.35 at 100 °C. The CoF further rose to 0.5 at 200 °C, coinciding with increased graphitization. However, the CoF reduced to 0.45 and 0.35 at 400 °C and 500 °C, respectively, likely due to the formation of a WO3 tribo-film and the protective effect of the chromium interlayer. 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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14 pages, 11328 KB  
Article
High-Temperature Zn-5Al Hot Dip Galvanizing of Reinforcement Steel
by Anżelina Marek, Veronika Steinerová, Petr Pokorný, Henryk Kania and Franciszek Berger
Coatings 2024, 14(8), 959; https://doi.org/10.3390/coatings14080959 - 1 Aug 2024
Cited by 2 | Viewed by 2431
Abstract
This article presents the results of research on the growth kinetics, microstructure (SEM/EDS/XRD), and corrosion behavior of Zn-5Al coatings obtained using a high-temperature hot dip process on B500B reinforcing steel. The corrosion resistance of the coatings was determined using the neutral salt spray [...] Read more.
This article presents the results of research on the growth kinetics, microstructure (SEM/EDS/XRD), and corrosion behavior of Zn-5Al coatings obtained using a high-temperature hot dip process on B500B reinforcing steel. The corrosion resistance of the coatings was determined using the neutral salt spray (NSS) test (EN ISO 9227). Based on chemical composition tests in micro-areas (EDS) and phase composition tests (XRD), corrosion products formed on the coating surface after exposure to a corrosive environment containing chlorides were identified. In the outer layer of the coating, areas rich in Zn and Al were found, which were solid solutions of Al in Zn (α), while the diffusion layer was formed by a layer of Fe(Al,Zn)3 intermetallics. The growth kinetics of the coatings indicate the sequential growth of the diffusion layer, controlled by diffusion in the initial phase of growth, and the formation of a periodic layered structure with a longer immersion time. The NSS test showed an improved corrosion resistance of reinforcing bars with Zn-5Al coatings compared to a conventional hot-dip-galvanized zinc coating. The increase in corrosion resistance was caused by the formation of beneficial corrosion products: layered double hydroxides (LDH) based on Zn2+ and Al3+ cations and Cl− anions and simonkolleite—Zn5(OH)8Cl2·H2O. Full article
(This article belongs to the Special Issue High-Temperature Corrosion and Oxidation of Metals and Alloys)
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22 pages, 78862 KB  
Article
Fatigue Behaviour and Life Prediction of YSZ Thermal Barrier Coatings at Elevated Temperature under Cyclic Loads
by Qiannan Tao, Yanrong Wang and Yu Zheng
Coatings 2024, 14(8), 960; https://doi.org/10.3390/coatings14080960 - 1 Aug 2024
Cited by 6 | Viewed by 2321
Abstract
The concentration of interfacial normal stress at the free edges of thermal barrier coatings (TBCs) can result in coating spallation. Fatigue cracking is one of the main reasons for creating free edges under complex loads. It is crucial to investigate the fatigue cracking [...] Read more.
The concentration of interfacial normal stress at the free edges of thermal barrier coatings (TBCs) can result in coating spallation. Fatigue cracking is one of the main reasons for creating free edges under complex loads. It is crucial to investigate the fatigue cracking of coatings under cyclic loads to assess potential coating failure. To address this issue, a novel model was proposed to predict the fatigue life of the YSZ topcoat under stress parallel to the interface. Firstly, this study conducted uniaxial and tensile-torsional fatigue tests at elevated temperatures on specimens with atmospheric plasma-sprayed TBCs. The test results revealed that fatigue cracks appeared in the topcoat under cyclic loads, but these cracks did not propagate into the bondcoat or substrate immediately. The number of cycles before the topcoat cracked was found to be associated with the magnitude of the cyclic load. Secondly, this study analyzed the test conditions using the finite element method. Simulations indicated that the crack direction in the topcoat under complex loading conditions was aligned with the first principal stress direction. Finally, the fatigue life prediction model of the topcoat was established based on experiments and simulations. The predicted results fell within a fourfold scatter band. Full article
(This article belongs to the Section Surface Characterization, Deposition and Modification)
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14 pages, 9409 KB  
Article
The Effects of Nitrogen Content on the Mechanical and Tribological Properties of CrTaWNx Thin Films
by Li-Chun Chang, Li-Zhu Wang and Yung-I Chen
Coatings 2024, 14(8), 939; https://doi.org/10.3390/coatings14080939 - 26 Jul 2024
Cited by 2 | Viewed by 1328
Abstract
In the study described herein, CrTaWNx thin films were deposited on Si and 304 stainless-steel (SUS304) substrates through magnetron co-sputtering using CrW and Ta targets. The nitrogen flow ratio (fN2 = [N2/(N2 + Ar)]) was adjusted to [...] Read more.
In the study described herein, CrTaWNx thin films were deposited on Si and 304 stainless-steel (SUS304) substrates through magnetron co-sputtering using CrW and Ta targets. The nitrogen flow ratio (fN2 = [N2/(N2 + Ar)]) was adjusted to 0.05, 0.2, 0.4, and 0.5 to fabricate CrTaWNx films with various N contents. The CrTaWNx films prepared at a low fN2 of 0.05 exhibited a low stoichiometric ratio x of 0.16 and a nanocrystalline structure. In contrast, the CrTaWNx films fabricated at an fN2 of 0.2–0.5 exhibited x values of 0.42–0.62 and formed a face-centered cubic phase. The nanocrystalline (Cr0.34Ta0.20W0.46)N0.16 film exhibited mechanical properties and wear resistances that were inferior to those of the crystalline CrTaWNx thin films. A (Cr0.38Ta0.15W0.47)N0.55 film exhibited a hardness of 25.2 GPa, an elastic modulus of 289 GPa, and a low wear rate of 0.51 × 10−5 mm3/Nm. Full article
(This article belongs to the Special Issue Thin-Film Synthesis, Characterization and Properties)
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10 pages, 9460 KB  
Article
Influence of Oxygen Flow Rate on the Phase Structures and Properties for Copper Oxide Thin Films Deposited by RF Magnetron Sputtering
by Junghwan Park, Young-Guk Son, Chang-Sik Son and Donghyun Hwang
Coatings 2024, 14(8), 930; https://doi.org/10.3390/coatings14080930 - 25 Jul 2024
Cited by 4 | Viewed by 2395
Abstract
This study examines the impact of varying oxygen flow rates on the properties of Cu2O thin films deposited via radio frequency (RF) magnetron sputtering. X-ray diffraction (XRD) analysis showed a phase transition from cubic Cu2O to a mixed Cu [...] Read more.
This study examines the impact of varying oxygen flow rates on the properties of Cu2O thin films deposited via radio frequency (RF) magnetron sputtering. X-ray diffraction (XRD) analysis showed a phase transition from cubic Cu2O to a mixed Cu2O and CuO phase, eventually forming a Cu4O3 tetragonal structure as oxygen content increased. The surface morphology and cross-sectional structure of Cu2O thin films observed through field emission scanning electron microscopy (FE-SEM) were found to vary significantly depending on the oxygen flow rate. X-ray photoelectron spectroscopy (XPS) indicated notable variations in the chemical states of copper and oxygen. The Cu 2p spectra revealed peaks around 933 eV and 953 eV for all samples, with the S01 sample (deposited with only argon gas) exhibiting the lowest intensity. The S02 sample showed the highest peak intensity, which then gradually decreased from S03 to S06. The O 1s spectra followed a trend with peak intensity being highest in S02 and decreasing with further oxygen flow rates, indicating the formation of complex oxides such as Cu4O3. UV-Vis-NIR spectroscopy results demonstrated a decrease in transmittance and optical band gap energy with increasing oxygen content, suggesting a decline in crystallinity and an increase in defects and impurities. These findings underscore the critical role of precise oxygen flow rate control in tailoring the structural, morphological, compositional, and optical properties of Cu2O thin films for specific electronic and optical applications. Full article
(This article belongs to the Special Issue Magnetron Sputtering Coatings: From Materials to Applications)
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19 pages, 15991 KB  
Article
Amorphous Alumina ALD Coatings for the Protection of Limestone Cultural Heritage Objects
by Gillian P. Boyce, Suveena Sreenilayam, Eleonora Balliana, Elisabetta Zendri and Raymond J. Phaneuf
Coatings 2024, 14(8), 931; https://doi.org/10.3390/coatings14080931 - 25 Jul 2024
Cited by 1 | Viewed by 2258
Abstract
From natural erosion to pollution-accelerated decay, stone cultural heritage deteriorates constantly through interactions with the environment. Common protective treatments such as acrylic polymers are generally prone to degradation and loss of performance, and they are often limited in their ability to achieve uniform [...] Read more.
From natural erosion to pollution-accelerated decay, stone cultural heritage deteriorates constantly through interactions with the environment. Common protective treatments such as acrylic polymers are generally prone to degradation and loss of performance, and they are often limited in their ability to achieve uniform and conformal coverage across a stone’s topographical features. In this work, atomic layer deposition (ALD) was explored to address these issues by growing protective amorphous alumina coatings on compact carbonate (Istria) stone. ALD protective coatings, unlike coatings produced by traditional methods, do not significantly alter morphology by filling open pores or accumulating on the surface in more compact areas. Our morphological and spectroscopic investigations revealed that the ALD alumina films deposited uniformly over the surfaces of Istria stone, without significantly altering the topography or appearance. The protective effects of the ALD coatings were investigated by aqueous acid immersion. The solution pH, along with the Ca2+ concentration, was tracked over time for a constant volume of acetic acid solution with an initial pH of 4 with the stone samples immersed. We found that the protective effects of ALD alumina coatings were extremely promising, slowing the average rate of pH evolution significantly. The eventual failure of the ALD coatings during immersion was also investigated, with interesting morphological findings that point to the role of defects in the coatings, suggesting new directions for improving the use of ALD coatings in future research and applications. Full article
(This article belongs to the Special Issue Recent Advances in Chemical Vapor Deposition)
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18 pages, 6306 KB  
Article
Self-Assembled Pd Nanocomposites into a Monolayer for Enhanced Sensing Performance
by Mohammad Navvabpour, Pierre-Michel Adam, Safi Jradi and Suzanna Akil
Coatings 2024, 14(8), 934; https://doi.org/10.3390/coatings14080934 - 25 Jul 2024
Cited by 4 | Viewed by 1411
Abstract
To date, the advanced synthetic approaches for palladium nanoparticle-based catalysts involve multistep, toxic, and high-cost fabrication routes with low catalytic and sensing performance. In this work, we introduce a new one-shot approach to produce highly sensitive Pd nanocomposites using a large-area polymer self-assembly [...] Read more.
To date, the advanced synthetic approaches for palladium nanoparticle-based catalysts involve multistep, toxic, and high-cost fabrication routes with low catalytic and sensing performance. In this work, we introduce a new one-shot approach to produce highly sensitive Pd nanocomposites using a large-area polymer self-assembly strategy. This synthesis method allowed us to control the Pd nanoparticle shape and to tailor their plasmonic band positions in a wide light spectral range from ~350 to ~800 nm. We thus determined the critical synthesis conditions that give rise to a ringlike morphology in a reproducible manner. No need for a reducing agent and preliminary functionalization of the surface supporting the nanoparticles upon synthesis. To the best of our knowledge, few works have demonstrated the good performance of PdNPs in sensing. Here, we have demonstrated a robust SERS response for 4-mercaptopyridine with an enhancement factor of 4.2 × 105. We were able to exceed this high value, which matches the current maximum found in the literature, by decreasing the gap distances between Pd nanorings due to the high density of hotspots and the exacerbation of the coupling effect between PdNPs. These tailored products provide new insights for the use of Pd nanomaterials in photocatalysis applications, according to the well-established catalytic performance of Pd materials obtained in this work. Full article
(This article belongs to the Section Surface Engineering for Energy Harvesting, Conversion, and Storage)
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15 pages, 4340 KB  
Article
Enhancing the Antibacterial Properties of Chitosan Coatings: Ag@Chitosan and Chitosan from Insects
by Michela Marsico, Rezvan Azari, Mariangela Curcio, Roberto Teghil, Micaela Triunfo, Patrizia Falabella, Aldo Roberto Boccaccini and Angela De Bonis
Coatings 2024, 14(8), 925; https://doi.org/10.3390/coatings14080925 - 24 Jul 2024
Cited by 8 | Viewed by 4903
Abstract
In this study, the electrophoretic deposition (EPD) technique was used to prepare chitosan-based coatings with enhanced antibacterial activity suitable for bone implant applications. We designed, prepared, and compared the physico-chemical and biological properties of coatings obtained with commercial chitosan, chitosan enriched with silver [...] Read more.
In this study, the electrophoretic deposition (EPD) technique was used to prepare chitosan-based coatings with enhanced antibacterial activity suitable for bone implant applications. We designed, prepared, and compared the physico-chemical and biological properties of coatings obtained with commercial chitosan, chitosan enriched with silver nanoparticles, and chitosan obtained from insects. With the aim to consider the issue of sustainability, silver nanoparticles were directly prepared in the chitosan solution by laser ablation via a liquid technique, avoiding the use of chemicals and limiting the production of wastes. Moreover, a sustainable source of chitosan, such as Hermetia Illucens exuviae, was considered. The EPD process was optimized by adjusting parameters like voltage and deposition time to achieve ideal coating thickness and adhesion. The prepared films were characterized by spectroscopic and microscopic techniques such as SEM, XRD, and FTIR. Antimicrobial tests against E. coli and S. aureus revealed that silver nanoparticles enhanced the antibacterial properties of the polymer, whereas the biological evaluation using the WST8 test on MG63 human osteoblast-like cells showed that all coatings were non-toxic. Finally, chitosan obtained from insect showed comparable properties with respect to the commercial polymer, suggesting it could replace seafood-derived chitosan in biomedical applications, whereas the Ag@chitosan composite demonstrated superior antibacterial activity without compromising its biocompatibility. Full article
(This article belongs to the Section Bioactive Coatings and Biointerfaces)
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24 pages, 5687 KB  
Article
CMAS Corrosion Resistance of Plasma-Sprayed YSZ and Yb2O3-Y2O3-Co-Stabilized ZrO2 Coatings under 39–40 KW Spraying Power
by Wenkang Zhang, Wei Liu, Yangguang Liu, Weize Wang, Ting Yang, Kaibin Li, Junhao Wang, Xiaoqin Zhang, Shilong Yang, Pengpeng Liu and Chengcheng Zhang
Coatings 2024, 14(8), 928; https://doi.org/10.3390/coatings14080928 - 24 Jul 2024
Cited by 1 | Viewed by 1885
Abstract
This study uses atmospheric plasma spraying (APS) technology to prepare thermal barrier coatings (TBCs) with yttrium-stabilized zirconia (YSZ) and Yb2O3-Y2O3-co-stabilized ZrO2 (YbYSZ) materials at different spraying powers. It analyzes the differences and changes in [...] Read more.
This study uses atmospheric plasma spraying (APS) technology to prepare thermal barrier coatings (TBCs) with yttrium-stabilized zirconia (YSZ) and Yb2O3-Y2O3-co-stabilized ZrO2 (YbYSZ) materials at different spraying powers. It analyzes the differences and changes in the microstructure, thermodynamic properties, and mechanical properties of the TBCs. The CaO-MgO-Al2O3-SiO2 (CMAS) resistance of coatings was tested using thermal cycling-CMAS experiments and isothermal corrosion experiments. Compared to YSZ coatings, YbYSZ coatings have lower thermal conductivity, a higher hardness and elastic modulus, a longer lifetime under thermal cycling-CMAS conditions, and lower penetration and degradation depths. Under thermal cycling-CMAS coupling conditions, the optimal power range for the longest thermal cycling lifetime for both coatings is 39–40 kW. Overall, compared to the YSZ material, the YbYSZ material exhibits superior properties. Full article
(This article belongs to the Section Corrosion, Wear and Erosion)
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21 pages, 8106 KB  
Article
Synthesis and Characterization of Titania-Coated Hollow Mesoporous Hydroxyapatite Composites for Photocatalytic Degradation of Methyl Red Dye in Water
by Farishta Shafiq, Simiao Yu, Yongxin Pan and Weihong Qiao
Coatings 2024, 14(8), 921; https://doi.org/10.3390/coatings14080921 - 23 Jul 2024
Cited by 6 | Viewed by 1848
Abstract
Hollow mesoporous hydroxyapatite (HM-HAP) composites coated with titania are prepared to increase the stability and catalytic performance of titania for azo dyes present in the wastewater system. In this work, HM-HAP particles were first synthesized by a hydrothermal method utilizing the CaCO3 [...] Read more.
Hollow mesoporous hydroxyapatite (HM-HAP) composites coated with titania are prepared to increase the stability and catalytic performance of titania for azo dyes present in the wastewater system. In this work, HM-HAP particles were first synthesized by a hydrothermal method utilizing the CaCO3 core as a template and then coated with titania to form TiO2/HM-HAP composites. Utilizing SEM, XRD, XPS, BET, FTIR, EDS, UV–vis DRS spectroscopy, and point of zero charge (PZC) analysis, the coating morphological and physicochemical parameters of the produced samples were analyzed. The photocatalytic efficiency of the synthesized coated composites was assessed by the degradation of methyl red (MR) dye in water. The results indicated that TiO2/HM-HAP particles could efficiently photodegrade MR dye in water under UV irradiation. The 20% TiO2/HM-HAP coating exhibited high catalytic performance, and the degradation process was followed by the pseudo-first-order (PFO) kinetic model with a rate constant of 0.033. The effect of pH on the degradation process was also evaluated, and the maximum degradation was observed at pH 6. The analysis of degraded MR dye products was investigated using LC-MS and FTIR analysis. Finally, a good support material, HM-HAP for TiO2 coatings, which provides a large number of active adsorption sites and has catalytic degradation performance for MR dye, was revealed. Full article
(This article belongs to the Special Issue Synthesis, Characterization and Performance Enhancement of Electrode and Biomaterial Coatings)
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22 pages, 6636 KB  
Article
Chemical and UV Durability of Hydrophobic and Icephobic Surface Layers on Femtosecond Laser Structured Stainless Steel
by Roland Fürbacher, Gabriel Grünsteidl, Andreas Otto and Gerhard Liedl
Coatings 2024, 14(8), 924; https://doi.org/10.3390/coatings14080924 - 23 Jul 2024
Cited by 2 | Viewed by 1952
Abstract
Femtosecond laser processing significantly alters the surface structure and chemical composition, impacting its wetting properties. Post-treatments such as immersion in a hydrocarbon liquid (petrol) or storage in a vacuum can significantly reduce ice adhesion, making the surfaces interesting for anti-ice applications. This study [...] Read more.
Femtosecond laser processing significantly alters the surface structure and chemical composition, impacting its wetting properties. Post-treatments such as immersion in a hydrocarbon liquid (petrol) or storage in a vacuum can significantly reduce ice adhesion, making the surfaces interesting for anti-ice applications. This study investigates their durability against acetone, ethylene glycol, and UV radiation. The laser-structured surfaces were immersed in the respective liquids for up to 48 h. The results indicate limited durability of the superhydrophobic and icephobic layers when submerged in acetone and ethylene glycol, with more favorable results for petrol treatment than vacuum treatment. Similar results were obtained after 100 h of UV exposure, showing a decrease in superhydrophobic properties and an increase in ice adhesion. However, repeated vacuum treatments conducted after the chemical durability tests revealed the potential for partial recovery of the hydrophobic and icephobic properties. XPS analysis was performed throughout the experiments to evaluate changes in surface chemistry resulting from the post-laser treatments and the durability tests. Full article
(This article belongs to the Special Issue Recent Advances in Hydrophobic Surface and Materials)
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12 pages, 3243 KB  
Article
Effects of Precursors Ratio and Curing Treatment on the Icephobicity of Polydimethylsiloxane
by Marcella Balordi, Alessandro Casali, Paolo Gadia, Paolo Pelagatti, Francesco Pini and Giorgio Santucci de Magistris
Coatings 2024, 14(7), 901; https://doi.org/10.3390/coatings14070901 - 18 Jul 2024
Viewed by 1719
Abstract
Elastomers are intriguing materials for many applications, one of these being icephobic coatings. Elastic modulus and work of adhesion are the key parameters coming into play in ice detachment mechanisms, and can be related to hardness and wettability. Polydimethylsiloxane (PDMS) is widely used [...] Read more.
Elastomers are intriguing materials for many applications, one of these being icephobic coatings. Elastic modulus and work of adhesion are the key parameters coming into play in ice detachment mechanisms, and can be related to hardness and wettability. Polydimethylsiloxane (PDMS) is widely used for anti-ice applications; however, not many works deal with the correlation between cross-linking grade, curing treatments, and icephobicity. This study focuses on PDMS (Sylgard184®) coatings, encompassing four different pre-polymer to cross-linking agent (A:B) ratios ranging from 5:1 to 30:1, and nine curing treatments. The results indicate that increasing the A:B ratio enhances hydrophobicity, softness, and icephobicity, assessed through shear stress measurements. Curing treatments primarily affect hardness and icephobicity, with longer heat treatments resulting in higher hardness and ice adhesion. All samples exhibit promising performances in lowering shear stress values, up to seven times in respect to the uncoated reference for 30:1 ratio. Additionally, a durability assessment is conducted on samples exposed to stress tests in the climatic chamber. A slight deterioration in hydrophobicity across all samples is observed and, notably, a significant hardness increase, around 13%, is experienced for the 5:1 ratio only. The samples also demonstrate an overall robust icephobicity after stress tests, and, for the 30:1 ratio, an average shear stress value four times lower than the reference is maintained. In this work, we highlight the importance of the fine-tuning of the precursors ratio and thermal treatments on the PDMS properties and durability. Full article
(This article belongs to the Section Surface Characterization, Deposition and Modification)
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15 pages, 7208 KB  
Article
Chemical Bonding of Nanorod Hydroxyapatite to the Surface of Calciumfluoroaluminosilicate Particles for Improving the Histocompatibility of Glass Ionomer Cement
by Sohee Kang, So Jung Park, Sukyoung Kim and Inn-Kyu Kang
Coatings 2024, 14(7), 893; https://doi.org/10.3390/coatings14070893 - 17 Jul 2024
Cited by 3 | Viewed by 1464
Abstract
Glass ionomer cement (GIC) is composed of anionic polyacrylic acid and a silica-based inorganic powder. GIC is used as a filling material in the decayed cavity of the tooth; therefore, compatibility with the tooth tissue is essential. In the present study, we aimed [...] Read more.
Glass ionomer cement (GIC) is composed of anionic polyacrylic acid and a silica-based inorganic powder. GIC is used as a filling material in the decayed cavity of the tooth; therefore, compatibility with the tooth tissue is essential. In the present study, we aimed to improve the histocompatibility of GIC by introducing nano-hydroxyapatite (nHA), a component of teeth, into a silica-based inorganic powder. CFAS-nHA was prepared by chemically bonding nanorod hydroxyapatite (nHA) to the surface of calciumfluoroaluminosilicate (CFAS). The synthesis of CFAS-nHA was confirmed using Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The prepared CFAS-nHA was mixed with polyacrylic acid and cured to prepare GIC containing nHA (GIC-nHA). Cytocompatibility tests of GIC-nHA and GIC were performed using osteoblasts. Osteoblast activity and bone formation ability were superior after GIC-nHA treatment than after control GIC treatment. This enhanced histocompatibility is believed to be due to the improvement of the biological activity of osteoblasts induced by the HA introduced into the GIC. Therefore, to enhance its compatibility with dental tissues, GIC could be manufactured by chemically bonding nHA to the surface of GI inorganic powder. Full article
(This article belongs to the Special Issue Advanced Biomaterials and Coatings)
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22 pages, 4157 KB  
Article
Characterization of Indium Tin Oxide (ITO) Thin Films towards Terahertz (THz) Functional Device Applications
by Anup Kumar Sahoo, Wei-Chen Au and Ci-Ling Pan
Coatings 2024, 14(7), 895; https://doi.org/10.3390/coatings14070895 - 17 Jul 2024
Cited by 7 | Viewed by 5187
Abstract
In this study, we explored the manipulation of optical properties in the terahertz (THz) frequency band of radio-frequency (RF) sputtered indium tin oxide (ITO) thin films on highly resistive silicon substrate by rapid thermal annealing (RTA). The optical constants of as-deposited and RTA-processed [...] Read more.
In this study, we explored the manipulation of optical properties in the terahertz (THz) frequency band of radio-frequency (RF) sputtered indium tin oxide (ITO) thin films on highly resistive silicon substrate by rapid thermal annealing (RTA). The optical constants of as-deposited and RTA-processed ITO films annealed at 400 °C, 600 °C and 800 °C are determined in the frequency range of 0.2 to 1.0 THz. The transmittance can be changed from ~27% for as-deposited to ~10% and ~39% for ITO films heat-treated at different annealing temperatures (Ta’s). Such variations of optical properties in the far infrared for the samples under study are correlated with their mobility and carrier concentration, which are extracted from Drude–Smith modeling of THz conductivity with plasma frequency, scattering time and the c-parameters as fitting parameters. Resistivities of the films are in the range of 10−3 to 10−4 Ω-cm, confirming that annealed ITO films can potentially be used as transparent conducting electrodes for photonic devices operating at THz frequencies. The highest mobility, μ = 47 cm2/V∙s, with carrier concentration, Nc = 1.31 × 1021 cm−3, was observed for ITO films annealed at Ta = 600 °C. The scattering times of the samples were in the range of 8–21 fs, with c-values of −0.63 to −0.87, indicating strong backscattering of the carriers, mainly by grain boundaries in the polycrystalline film. To better understand the nature of these films, we have also characterized the surface morphology, microscopic structural properties and chemical composition of as-deposited and RTA-processed ITO thin films. For comparison, we have summarized the optical properties of ITO films sputtered onto fused silica substrates, as-deposited and RTA-annealed, in the visible transparency window of 400–800 nm. The optical bandgaps of the ITO thin films were evaluated with a Tauc plot from the absorption spectra. Full article
(This article belongs to the Special Issue Thermoelectric Thin Films for Thermal Energy Harvesting)
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21 pages, 6113 KB  
Article
Exploring Heterointerface Characteristics and Charge-Storage Dynamics in ALD-Developed Ultra-Thin TiO2-In2O3/Au Heterojunctions
by Mohammad Karbalaei Akbari, Nasrin Siraj Lopa and Serge Zhuiykov
Coatings 2024, 14(7), 880; https://doi.org/10.3390/coatings14070880 - 14 Jul 2024
Viewed by 1416
Abstract
Directional ionic migration in ultra-thin metal-oxide semiconductors under applied electric fields is a key mechanism for developing various electronic nanodevices. However, understanding charge transfer dynamics is challenging due to rapid ionic migration and uncontrolled charge transfer, which can reduce the functionality of microelectronic [...] Read more.
Directional ionic migration in ultra-thin metal-oxide semiconductors under applied electric fields is a key mechanism for developing various electronic nanodevices. However, understanding charge transfer dynamics is challenging due to rapid ionic migration and uncontrolled charge transfer, which can reduce the functionality of microelectronic devices. This research investigates the supercapacitive-coupled memristive characteristics of ultra-thin heterostructured metal-oxide semiconductor films at TiO2-In2O3/Au Schottky junctions. Using atomic layer deposition (ALD), we nano-engineered In2O3/Au-based metal/semiconductor heterointerfaces. TEM studies followed by XPS elemental analysis revealed the chemical and structural characteristics of the heterointerfaces. Subsequent AFM studies of the hybrid heterointerfaces demonstrated supercapacitor-like behavior in nanometer-thick TiO2-In2O3/Au junctions, resembling ultra-thin supercapacitors, pseudocapacitors, and nanobatteries. The highest specific capacitance of 2.6 × 104 F.g−1 was measured in the TiO2-In2O3/Au junctions with an amorphous In2O3 electron gate. Additionally, we examined the impact of crystallization, finding that thermal annealing led to the formation of crystalline In2O3 films with higher oxygen vacancy content at TiO2-In2O3 heterointerfaces. This crystallization process resulted in the evolution of non-zero I-V hysteresis loops into zero I-V hysteresis loops with supercapacitive-coupled memristive characteristics. This research provides a platform for understanding and designing adjustable ultra-thin Schottky junctions with versatile electronic properties. Full article
(This article belongs to the Special Issue Advanced Films and Coatings Based on Atomic Layer Deposition)
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13 pages, 4598 KB  
Article
Magnetron Sputtered Low-Platinum Loading Electrode as HER Catalyst for PEM Electrolysis
by Antía Villamayor, Alonso Alba, Laura V. Barrio, Sergio Rojas and Eva Gutierrez-Berasategui
Coatings 2024, 14(7), 868; https://doi.org/10.3390/coatings14070868 - 11 Jul 2024
Cited by 2 | Viewed by 3020
Abstract
The development of cost-effective components for Proton Exchange Membrane (PEM) electrolyzers plays a crucial role in the transformation of renewable energy into hydrogen. To achieve this goal, two main issues should be addressed: reducing the Platinum Group Metal (PGM) content present on the [...] Read more.
The development of cost-effective components for Proton Exchange Membrane (PEM) electrolyzers plays a crucial role in the transformation of renewable energy into hydrogen. To achieve this goal, two main issues should be addressed: reducing the Platinum Group Metal (PGM) content present on the electrodes and finding a large-scale electrode manufacturing method. Magnetron sputtering could solve these hurdles since it allows the production of highly pure thin films in a single-step process and is a well-established industrial and automated technique for thin film deposition. In this work, we have developed an ultra-low 0.1 mg cm−2 Pt loading electrode using magnetron sputtering gas aggregation method (MSGA), directly depositing the Pt nanoparticles on top of the carbon substrate, followed by a complete evaluation of the electrochemical properties of the sputtered electrode. These ultra-low Pt content electrodes have been thoroughly characterized and tested in a real electrolyzer cell. They demonstrate similar efficiency to commercial electrodes with a Pt content of 0.3 mg/cm2, achieving a 67% reduction in Pt loading. Additionally, durability tests indicate that these electrodes offer greater stability compared to their commercial counterparts. Thus, magnetron sputtering has been proven as a promising technology for manufacturing optimum high-performance electrodes at an industrial scale. Full article
(This article belongs to the Special Issue Synthesis, Characterization and Performance Enhancement of Electrode Coatings for Energy Sustainability)
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9 pages, 4872 KB  
Article
Enhancing Wear Resistance of A390 Aluminum Alloy: A Comprehensive Evaluation of Thermal Sprayed WC, CrC, and Al2O3 Coatings
by Jaehui Bang and Eunkyung Lee
Coatings 2024, 14(7), 853; https://doi.org/10.3390/coatings14070853 - 8 Jul 2024
Cited by 7 | Viewed by 2004
Abstract
This study comparatively analyzed the wear characteristics and adhesion properties of 86WC–10Co–4Cr (WC) coatings deposited using the high velocity oxygen fuel process and 75Cr3C2–25NiCr (CrC) and Al2O3–3TiO2 (Al2O3) coatings deposited [...] Read more.
This study comparatively analyzed the wear characteristics and adhesion properties of 86WC–10Co–4Cr (WC) coatings deposited using the high velocity oxygen fuel process and 75Cr3C2–25NiCr (CrC) and Al2O3–3TiO2 (Al2O3) coatings deposited using the atmospheric plasma spray process on an A390 aluminum alloy substrate. The adhesion strength and wear test results demonstrated that the WC coating exhibited superior wear resistance. In contrast, the CrC and Al2O3 coatings showed lower adhesion properties and unstable frictional variations due to a higher number of defects compared to the WC coating. The WC coating layer, protected by WC particles, exhibited minimal damage and a low wear rate, followed by CrC and Al2O3. Ultimately, WC coating is highlighted as the optimal choice to enhance the wear resistance of A390 aluminum alloy. Full article
(This article belongs to the Special Issue Additive Manufacturing of Metallic Components for Hard Coatings)
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16 pages, 13325 KB  
Article
Effect of NOX and SOX Contaminants on Corrosion Behaviors of 304L and 316L Stainless Steels in Monoethanolamine Aqueous Amine Solutions
by Eleni Lamprou, Fani Stergioudi, Georgios Skordaris, Nikolaos Michailidis, Evie Nessi, Athanasios I. Papadopoulos and Panagiotis Seferlis
Coatings 2024, 14(7), 842; https://doi.org/10.3390/coatings14070842 - 5 Jul 2024
Cited by 2 | Viewed by 2715
Abstract
This work is devoted to evaluating the corrosion behaviors of SS 304L and SS 316L in monoethanolamine solutions (MEA) containing SOX and NOX pollutants, examining both lean and CO2-loaded conditions at 25 °C and 40 °C. Electrochemical techniques (potentiodynamic [...] Read more.
This work is devoted to evaluating the corrosion behaviors of SS 304L and SS 316L in monoethanolamine solutions (MEA) containing SOX and NOX pollutants, examining both lean and CO2-loaded conditions at 25 °C and 40 °C. Electrochemical techniques (potentiodynamic and cyclic polarization) were used along with Scanning Electron Microscopy, Confocal Microscopy and weight loss measurements. The results reveal that the introduction of SOX and NOX pollutants increased the corrosion rate, whereas CO2 loading primarily reduced the corrosion resistance in the lean MEA solution, while its impact on solutions with SOX and NOX was less pronounced. This suggests that SOX and NOX play primary roles in the metal’s dissolution. Also, SS 316L demonstrated superior corrosion resistance compared to 304L in nearly all of the cases examined. Elevated temperatures were also found to intensify the corrosion rate, indicating a correlation between the corrosion rate and temperature. A microscopic observation and EDX analysis revealed that corrosion products are characterized by high concentrations of iron (Fe) and oxygen (O) as well as carbon (C). There is also an indication of the possible formation of amine complexes, suggesting a potential for amine degradation. No pitting corrosion was observed in SS 304L and SS 316L across any tested solution. Finally, the immersion results expose a tendency for passivity in all amine solutions and at both temperatures after several days of exposure. Moreover, they confirm the very low corrosion rate calculated from potentiodynamic curves due to minimal weight loss after 24 days of immersion. Full article
(This article belongs to the Collection Feature Papers Collection in 'Surface Characterization, Deposition and Modification')
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19 pages, 29254 KB  
Article
Biochemical Evaluation and Structural Characteristics of Copper Coating Cellulose Nonwovens Prepared by Magnetron Sputtering Technology
by Małgorzata Świerczyńska, Zdzisława Mrozińska, Agnieszka Lisiak-Kucińska, Anetta Walawska and Marcin H. Kudzin
Coatings 2024, 14(7), 843; https://doi.org/10.3390/coatings14070843 - 5 Jul 2024
Cited by 2 | Viewed by 1456
Abstract
The research aimed to enhance the aqua-jet/spunlace cellulose nonwoven fabric by deposition of copper coating by magnetron sputtering technology. Plasma technology facilitated the efficient distribution of copper particles on the surface of the cellulose nonwoven fabric, while maintaining free airflow and eliminating the [...] Read more.
The research aimed to enhance the aqua-jet/spunlace cellulose nonwoven fabric by deposition of copper coating by magnetron sputtering technology. Plasma technology facilitated the efficient distribution of copper particles on the surface of the cellulose nonwoven fabric, while maintaining free airflow and eliminating the need for additional layers. New cellulose-copper composites exhibit potential in biomedical applications, while minimizing their impact on biological processes such as blood plasma coagulation. Consequently, they can be utilized in the production of dressings, bandages, and other medical products requiring effective protection against bacterial infections. The cellulose-copper composite material was subjected to the physiochemical and biological investigations. The physiochemical analysis included the elemental analysis of composites, their microscopic analysis and the surface properties analysis (specific surface area and total pore volume). The biological investigations consisted of biochemical-hematological tests including the evaluation of the activated partial thromboplastin time and pro-thrombin time. Biodegradable materials based on cellulose nonwoven fabrics with the addition of copper offer a promising alternative to conventional materials. Their innovative properties, coupled with environmental friendliness and minimal impact on biological processes, offer vast application possibilities in healthcare and the production of hygiene products. Full article
(This article belongs to the Special Issue Advances in Functional Bio-Coatings)
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12 pages, 3290 KB  
Article
Anti-Corrosion SiOx-Doped DLC Coating for Raster Steel Linear Scales
by Algirdas Lazauskas, Viktoras Grigaliūnas, Dalius Jucius, Šarūnas Meškinis, Mindaugas Andrulevičius, Asta Guobienė, Andrius Vasiliauskas and Albinas Kasparaitis
Coatings 2024, 14(7), 818; https://doi.org/10.3390/coatings14070818 - 1 Jul 2024
Cited by 2 | Viewed by 1864
Abstract
In this study, we investigated the efficacy of SiOx-doped diamond-like carbon (DLC) films for enhancing the corrosion resistance of raster steel linear scales. The research work highlights the significant role of DLC film materials in enhancing corrosion resistance, making them a [...] Read more.
In this study, we investigated the efficacy of SiOx-doped diamond-like carbon (DLC) films for enhancing the corrosion resistance of raster steel linear scales. The research work highlights the significant role of DLC film materials in enhancing corrosion resistance, making them a promising solution for various industrial applications. The Raman spectroscopy analysis of SiOx-doped DLC films, synthesized via a direct ion beam technique with HMDSO vapor, revealed prominent D and G bands characteristic of amorphous carbon materials, with a high degree of disorder indicated by an ID/IG ratio of 1.85. X-ray diffraction patterns confirmed the amorphous nature of the SiOx-doped DLC films and the minimal impact of the DLC deposition process on the underlying crystalline structure of steel. UV–Vis-NIR reflectance spectra of SiOx-doped DLC on stainless steel demonstrated improvements in the blue wavelength region compared to stainless steel with ripples alone, which is beneficial for applications utilizing blue light. Corrosion tests, including immersion in a 5% salt solution and salt spray testing, showed that SiOx-doped DLC-coated stainless steel exhibited superior corrosion resistance compared to uncoated steel, with no significant signs of corrosion observed after extended exposure. These findings underscore the potential of SiOx-doped DLC coatings to provide long-term corrosion protection and maintain the structural integrity and surface quality of steel components in harsh environments. Full article
(This article belongs to the Special Issue Recent Developments on Functional Coatings for Industrial Applications, Volume II)
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11 pages, 5061 KB  
Article
Interface Engineering Induced N, P-Doped Carbon-Shell-Encapsulated FeP/NiP2/Ni5P4/NiP Nanoparticles for Highly Efficient Hydrogen Evolution Reaction
by Ting Zhang, Jianguo Zhong, Wei Gao and Yuxin Wang
Coatings 2024, 14(7), 817; https://doi.org/10.3390/coatings14070817 - 1 Jul 2024
Cited by 3 | Viewed by 1948
Abstract
Modifying the electronic structure of a catalyst through interface engineering is an effective strategy to enhance its activity in the hydrogen evolution reaction (HER). Interface engineering is a viable strategy to enhance the catalytic activity of transition metal phosphides (TMPs) in the HER [...] Read more.
Modifying the electronic structure of a catalyst through interface engineering is an effective strategy to enhance its activity in the hydrogen evolution reaction (HER). Interface engineering is a viable strategy to enhance the catalytic activity of transition metal phosphides (TMPs) in the HER process. The interface-engineered FeP/NiP2/Ni5P4/NiP multi-metallic phosphide nanoparticles confined in a N, P-doped carbon matrix was developed by a simple one-step low-temperature phosphorization treatment, which only requires 72 and 155 mV to receive the current density of 10 mA/cm2 in acid and alkaline electrolyte, respectively. This enhanced performance can be primarily attributed to the heterointerface of FeP/NiP2/Ni5P4/NiP multi-metallic phosphides, which promotes electron redistribution and optimizes the adsorption/desorption strength of H* on the active sites. Furthermore, the N, P-doped carbon framework that encapsulates the nanoparticles inhibits their aggregation, leading to an increased availability of active sites throughout the reaction. The results of this study open up a straightforward and innovative approach to developing high-performance catalysts for hydrogen production. Full article
(This article belongs to the Section Surface Engineering for Energy Harvesting, Conversion, and Storage)
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12 pages, 4831 KB  
Article
Lifetime Extension of Atmospheric and Suspension Plasma-Sprayed Thermal Barrier Coatings in Burner Rig Tests by Pre-Oxidizing the CoNiCrAlY Bond Coats
by Jens Igel, Walter Sebastian Scheld, Daniel Emil Mack, Olivier Guillon and Robert Vaßen
Coatings 2024, 14(7), 793; https://doi.org/10.3390/coatings14070793 - 26 Jun 2024
Cited by 2 | Viewed by 2204
Abstract
Oxidation of the bond coat during turbine operation leads to additional stresses in the thermal barrier coating (TBC) system that promotes spalling of the thermal insulation. Therefore, the oxidation behavior of a TBC system plays an important role in the thermal cycling of [...] Read more.
Oxidation of the bond coat during turbine operation leads to additional stresses in the thermal barrier coating (TBC) system that promotes spalling of the thermal insulation. Therefore, the oxidation behavior of a TBC system plays an important role in the thermal cycling of a TBC system. To delay the loss of thermal insulation, research has typically focused for a long time on the composition and microstructure of the ceramic topcoats and metallic bond coats. More recently, heat treatment for the diffusion annealing of the bond coat has also become a focus of research. Several studies have shown that pre-oxidation of the bond coat prior to the application of the ceramic topcoat slows down the subsequent oxidation of the bond coat in service. The improved thermal cyclability has been demonstrated in studies for systems with atmospheric plasma-sprayed (APS), suspension plasma-sprayed (SPS) or electron beam physical vapor deposition (EB-PVD) top coatings. However, no study has directly compared the effects of pre-oxidation on different topcoats. Therefore, this study compared the effect of pre-oxidation on APS and SPS coatings with the same bond coat. For both topcoats, pre-oxidation slowed the subsequent TGO growth and thus increased the lifetime of the coatings. The improvement in lifetime was particularly pronounced for the systems with an SPS topcoat. Overall, the lifetime of the coatings with an APS topcoat was higher as the critical energy release rate within the coating was not exceeded in these coatings. Full article
(This article belongs to the Section Plasma Coatings, Surfaces & Interfaces)
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17 pages, 8596 KB  
Article
Corrosion Efficiency of Zn-Ni/ZrO2 and Zn-Co/ZrO2 Bi-Layer Systems: Impact of Zn-Alloy Sublayer Thickness
by Nelly Boshkova, Daniela Stoyanova, Irina Stambolova, Ognian Dimitrov, Sylviya Simeonova, Georgi Avdeev, Miglena Peshova, Vasil Bachvarov, Sonya Smrichkova and Nikolai Boshkov
Coatings 2024, 14(7), 792; https://doi.org/10.3390/coatings14070792 - 25 Jun 2024
Cited by 2 | Viewed by 1963
Abstract
The presented manuscript demonstrates the effect of the thickness of a zinc alloy sublayer on the corrosion resistance and stability of three types of bi-layer systems composed of Co- or Ni-modified zinc coatings (both as sublayers) and a top sol–gel ZrO2 film [...] Read more.
The presented manuscript demonstrates the effect of the thickness of a zinc alloy sublayer on the corrosion resistance and stability of three types of bi-layer systems composed of Co- or Ni-modified zinc coatings (both as sublayers) and a top sol–gel ZrO2 film in a 5% NaCl solution. In order to obtain more detailed information, the alloy sublayers were electrodeposited with three different thicknesses (1, 5 and 10 µm, respectively) on a low-carbon steel substrate. Three consecutive dip-coated ZrO2 sol–gel layers were deposited thereafter on the individual zinc alloy sublayers. For comparison, an ordinary electrodeposited zinc coating was obtained and investigated. The aim of this study was to evaluate the effect of the thickness of the zinc-based sublayer on the protective characteristics of the bi-layer systems. The surface morphology features and the phase composition of the latter systems were examined using scanning electron microscopy (SEM), atomic force microscopy (AFM), water contact angle (WCA) measurements and X-ray diffraction (XRD) analyses. The corrosion stability was evaluated by means of potentiodynamic polarization (PDP) curves and polarization resistance (Rp) measurements. The zirconia finish layers possessed an amorphous, dense and hydrophobic nature, while the sublayers were multicrystalline. The results confirmed the increased corrosion resistance of the protective system, which contains electrodeposited sublayer of Zn-Co alloy with a 10 µm thickness in a corrosive test medium. Full article
(This article belongs to the Special Issue Effects of Surface Layer Modification on Fatigue, Corrosion and Wear Behavior of Metallic Materials)
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18 pages, 7606 KB  
Article
Symbiosis of Sulfate-Reducing Bacteria and Total General Bacteria Affects Microbiologically Influenced Corrosion of Carbon Steel
by Juxing Jin, Yingchao Li, Huaiwei Huang, Yong Xiang and Wei Yan
Coatings 2024, 14(7), 788; https://doi.org/10.3390/coatings14070788 - 24 Jun 2024
Cited by 4 | Viewed by 1958
Abstract
The effects of the symbiosis of sulfate-reducing bacteria (SRB) and total general bacteria (TGB) on the microbiologically influenced corrosion (MIC) of carbon steel were investigated in this research. The SRB was the main corrosive bacterium, and TGB induced slightly general MIC. The symbiosis [...] Read more.
The effects of the symbiosis of sulfate-reducing bacteria (SRB) and total general bacteria (TGB) on the microbiologically influenced corrosion (MIC) of carbon steel were investigated in this research. The SRB was the main corrosive bacterium, and TGB induced slightly general MIC. The symbiosis of SRB and TGB induced more severe MIC and pitting corrosion than SRB. The main corrosion products were FeS, Fe2O3, and FeOOH. The presence of TGB facilitates MIC and pitting corrosion by providing a locally anaerobic shelter for SRB. An MIC mechanism of the symbiosis of SRB and TGB was proposed. Full article
(This article belongs to the Special Issue Investigation on Structure and Corrosion Resistance of Steels/Alloys)
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19 pages, 11634 KB  
Article
Tribological Properties and Surface Wettability of Coatings Produced on the Mg-AZ31B Alloy by Plasma Electrolytic Oxidation
by Mateusz Niedźwiedź, Marek Bara, Joanna Korzekwa, Sławomir Kaptacz, Maciej Sowa, Aleksander Olesiński and Wojciech Simka
Coatings 2024, 14(7), 780; https://doi.org/10.3390/coatings14070780 - 21 Jun 2024
Cited by 5 | Viewed by 2188
Abstract
This paper presents the influence of plasma electrolytic oxidation parameters (peak current density, process time, pulse frequency) on the tribological properties and surface wettability of the produced coatings. The process parameters were selected in accordance with Hartley’s research plan for three input variables [...] Read more.
This paper presents the influence of plasma electrolytic oxidation parameters (peak current density, process time, pulse frequency) on the tribological properties and surface wettability of the produced coatings. The process parameters were selected in accordance with Hartley’s research plan for three input variables with three variable values. Oxide coatings were made on the AZ31B magnesium alloy using a trapezoidal voltage waveform and a two-component alkaline electrolyte. The tribological properties of the coatings were determined as a result of tribological tests carried out on the T-17 tester in reciprocating motion. The tribological partner for the coatings was a PEEK/HPV pin. As a result of tribological tests, the friction coefficient µ, the mass wear of the pin and the average change in sample mass were determined. The tests showed changes in both the friction coefficient and pin wear. Before and after tribological tests, profilographometric measurements of the coatings were performed. The tests allowed for the determination of roughness parameters and the load–bearing curve of the sample surfaces. Surface wettability tests were carried out by determining the contact angles. Full article
(This article belongs to the Special Issue Surface Engineering, Coatings and Tribology)
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13 pages, 3564 KB  
Article
Characterisation of TiCN Coatings for Biomedical Applications
by Monika Madej and Katarzyna Piotrowska
Coatings 2024, 14(6), 775; https://doi.org/10.3390/coatings14060775 - 20 Jun 2024
Cited by 2 | Viewed by 1975
Abstract
This study aims to characterise TiCN coatings deposited on Ti6Al4V by physical vapour deposition. Findings on surface morphology, geometric structure, adhesion, instrumental hardness, and tribology are presented. Microscopic examination revealed a uniform coating with a thickness of about 1.5 µm and roughness (Sq) [...] Read more.
This study aims to characterise TiCN coatings deposited on Ti6Al4V by physical vapour deposition. Findings on surface morphology, geometric structure, adhesion, instrumental hardness, and tribology are presented. Microscopic examination revealed a uniform coating with a thickness of about 1.5 µm and roughness (Sq) equal to 0.13 µm. Mechanical tests showed that the coating deposition increased the hardness of the Ti6Al4V alloy by about 75%. The artificial saliva solution used in the tribological tests reduced the coefficient of friction and the volumetric wear of the tested friction pairs. Microscopic observations of wear tracks after tribological tests allowed for the identification of wear mechanisms: micro-cutting/ploughing wear dominated in both the Ti6Al4V alloy and TiCN coating samples, but wear was much less pronounced overall with the TiCN coating. The study results demonstrate that the deposition of a TiCN coating simultaneously imparts low-friction and anti-wear properties to the surface of titanium alloys. Full article
(This article belongs to the Special Issue Bioactive Coatings on Elements Used in the Oral Cavity Environment)
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13 pages, 8128 KB  
Article
Enhancing Tribological Performance of Micro-Arc Oxidation Coatings on 6061 Aluminum Alloy with h-BN Incorporation
by Xia Zhao, Jingfu Song, Jingyi Lin, Guoqing Wang and Gai Zhao
Coatings 2024, 14(6), 771; https://doi.org/10.3390/coatings14060771 - 19 Jun 2024
Cited by 6 | Viewed by 1819
Abstract
Micro-arc oxidation (MAO) coatings of aluminum alloy have great potential applications due to their high hardness and wear resistance. However, the micro-pores and defects formed in the discharge channels during the MAO process limit its application in the corrosion field. This study delves [...] Read more.
Micro-arc oxidation (MAO) coatings of aluminum alloy have great potential applications due to their high hardness and wear resistance. However, the micro-pores and defects formed in the discharge channels during the MAO process limit its application in the corrosion field. This study delves into the impact of h-BN nanoparticles into MAO coatings on their structure, corrosion resistance, phase composition, and tribological properties. The results show that the incorporation of h-BN particles reduces the porosity and surface roughness of the coating while enhancing its hardness and wear resistance. The best corrosion resistance is obtained at a concentration of 2 g/L h-BN. An analysis of worn surface morphology, corrosion resistance, and friction coefficient change was conducted to evaluate the performance of this coating. This method provides a new approach to enhance the surface hardness and wear resistance of aluminum alloys, which is significant for expanding the application of aluminum alloys in corrosion environments. Full article
(This article belongs to the Special Issue Tribological Behavior and Mechanical Performance of Coatings and Materials)
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21 pages, 21058 KB  
Article
Tribocatalytic Reaction Enabled by TiO2 Nanoparticle for MoDTC-Derived Tribofilm Formation at ta-C/Steel Contact
by Daiki Matsukawa, Jae-Hyeok Park, Woo-Young Lee, Takayuki Tokoroyama, Jae-Il Kim, Ryoichi Ichino and Noritsugu Umehara
Coatings 2024, 14(6), 773; https://doi.org/10.3390/coatings14060773 - 19 Jun 2024
Cited by 4 | Viewed by 2481
Abstract
Tribochemically produced triboproducts are becoming increasingly important in tribosystems and serve to improve system performance by preventing friction or wear. Diamond-like carbon (DLC) is chemically stable, which features a trade-off with tribological pros and cons. Chemically stable DLC is thermally stable and suppresses [...] Read more.
Tribochemically produced triboproducts are becoming increasingly important in tribosystems and serve to improve system performance by preventing friction or wear. Diamond-like carbon (DLC) is chemically stable, which features a trade-off with tribological pros and cons. Chemically stable DLC is thermally stable and suppresses surface damage in a high-temperature operating environment; however, it causes a detrimental effect that hinders the formation of a competent tribofilm. In this study, we dispersed highly reactive TiO2 nanoparticles (TDONPs) in molybdenum dithiocarbamate (MoDTC)-containing lubricant for adhering triboproducts on the DLC surface. In addition, TDONPs contributed to the decomposition of triboproducts by promoting the decomposition of MoDTC through its catalytic role. Rutile TDONPs were more helpful in reducing friction than anatase TDONPs and improved the friction performance by up to ~100%. Full article
(This article belongs to the Special Issue Advanced Tribological Coatings: Fabrication and Application)
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16 pages, 19888 KB  
Article
A Deep Learning Image Corrosion Classification Method for Marine Vessels Using an Eigen Tree Hierarchy Module
by Georgios Chliveros, Iason Tzanetatos and Stylianos V. Kontomaris
Coatings 2024, 14(6), 768; https://doi.org/10.3390/coatings14060768 - 18 Jun 2024
Cited by 5 | Viewed by 2969
Abstract
This paper involves the automation of a visual characterisation technique for corrosion in marine vessels, as it appears in the hull preventive coatings of marine vessels and their surfaces. We propose a module that maximizes the utilisation of features learned by a deep [...] Read more.
This paper involves the automation of a visual characterisation technique for corrosion in marine vessels, as it appears in the hull preventive coatings of marine vessels and their surfaces. We propose a module that maximizes the utilisation of features learned by a deep convolutional neural network to identify areas of corrosion and segment pixels in regions of inspection interest for corrosion detection. Our segmentation module is based on Eigen tree decomposition and information-based decision criteria in order to produce specific corroded spots—regions of interest. To assess performance and compare it with our method, we utilize several state-of-the-art deep learning architectures.The results indicate that our method achieves higher accuracy and precision while maintaining the significance score across the entire dataset. To the best of our knowledge, this is the first Eigen tree-based module in the literature in the context of trained neural network predictors for classifying corrosion in marine vessel images. Full article
(This article belongs to the Special Issue Effects of Surface Layer Modification on Fatigue, Corrosion and Wear Behavior of Metallic Materials)
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19 pages, 21066 KB  
Article
The Influence of Bias Voltage and Gas Pressure on Edge Covering during the Arc-PVD Deposition of Hard Coatings
by Otmar Zimmer, Tim Krülle and Thomas Litterst
Coatings 2024, 14(6), 732; https://doi.org/10.3390/coatings14060732 - 7 Jun 2024
Cited by 1 | Viewed by 2025
Abstract
The edge area is especially essential for cutting tools, since this is the contact zone between the work piece and the tool. Hard coatings (PVD or CVD coatings) can protect the edge against wear and they are commonly used. The geometries of the [...] Read more.
The edge area is especially essential for cutting tools, since this is the contact zone between the work piece and the tool. Hard coatings (PVD or CVD coatings) can protect the edge against wear and they are commonly used. The geometries of the cutting edges change during the coating process, with the edge radius increasing. Therefore, the film thickness is limited and the initial radius of the uncoated tool must be smaller than the target radius of the coated edge. A new coating process based on vacuum arc PVD was developed to overcome this limitation. The film growth at the edges can be properly controlled by means of selected coating materials and process conditions. Thus, it is possible to grow edges sharper than the initial edge geometry. Different substrates were coated with different coating systems. Parameters such as the bias voltage, coating pressure, and initial radius were varied within this work. It was found that the application of a bias voltage is crucial for the generation of sharp edges. It was also found that the edge sharpening caused by coatings works best on samples with an initial radius of around 15 µm. Full article
(This article belongs to the Special Issue Advanced Coating Technology by Physical Vapor Deposition and Applications)
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18 pages, 6375 KB  
Article
Automated Crack Detection in 2D Hexagonal Boron Nitride Coatings Using Machine Learning
by Md Hasan-Ur Rahman, Bichar Dip Shrestha Gurung, Bharat K. Jasthi, Etienne Z. Gnimpieba and Venkataramana Gadhamshetty
Coatings 2024, 14(6), 726; https://doi.org/10.3390/coatings14060726 - 6 Jun 2024
Cited by 3 | Viewed by 3169
Abstract
Characterizing defects in 2D materials, such as cracks in chemical vapor deposited (CVD)-grown hexagonal boron nitride (hBN), is essential for evaluating material quality and reliability. Traditional characterization methods are often time-consuming and subjective and can be hindered by the limited optical contrast of [...] Read more.
Characterizing defects in 2D materials, such as cracks in chemical vapor deposited (CVD)-grown hexagonal boron nitride (hBN), is essential for evaluating material quality and reliability. Traditional characterization methods are often time-consuming and subjective and can be hindered by the limited optical contrast of hBN. To address this, we utilized a YOLOv8n deep learning model for automated crack detection in transferred CVD-grown hBN films, using MATLAB’s Image Labeler and Supervisely for meticulous annotation and training. The model demonstrates promising crack-detection capabilities, accurately identifying cracks of varying sizes and complexities, with loss curve analysis revealing progressive learning. However, a trade-off between precision and recall highlights the need for further refinement, particularly in distinguishing fine cracks from multilayer hBN regions. This study demonstrates the potential of ML-based approaches to streamline 2D material characterization and accelerate their integration into advanced devices. Full article
(This article belongs to the Special Issue Advances in Nanostructured Thin Films and Coatings, 2nd Edition)
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20 pages, 13497 KB  
Article
Effects of Dynamic Flow Rates on the In Vitro Bio-Corrosion Behavior of Zn-Cu Alloy
by Xin Zhang, Lu Zhang, Linyuan Han, Jing Bai, Zhihai Huang, Chao Guo, Feng Xue, Paul K. Chu and Chenglin Chu
Coatings 2024, 14(6), 711; https://doi.org/10.3390/coatings14060711 - 5 Jun 2024
Cited by 4 | Viewed by 1434
Abstract
In the complicated real physiological environment in vivo, body fluids and blood are constantly replenished and move dynamically, and therefore, the dynamic impacts of bodily fluids and blood need to be considered in the evaluation of biodegradable materials. However, little research has [...] Read more.
In the complicated real physiological environment in vivo, body fluids and blood are constantly replenished and move dynamically, and therefore, the dynamic impacts of bodily fluids and blood need to be considered in the evaluation of biodegradable materials. However, little research has been conducted on the impact of dynamic flowing circumstances on the corrosion characteristics of zinc-based alloys, particularly at high flow rates. The effects of various flow rates on the bio-corrosion behavior of the Zn-Cu alloy are thoroughly explored in this study. A model is developed using finite element analysis to investigate the impacts of flow rates and fluid-induced shear stress. The results reveal that the corrosion process of the Zn-Cu alloy is significantly accelerated by a higher flow rate, and a large fluid-induced shear stress caused by the boundary effect is found to promote corrosion. Furthermore, the empirical power function between the average flare rates in Hank’s solution and the corrosion rates of the Zn-Cu alloy is established by numerical simulation. The results provide insightful theoretical and experimental guidance to improve and evaluate the efficacy and lifespan of biomedical zinc-based alloy implants. Full article
(This article belongs to the Section Corrosion, Wear and Erosion)
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17 pages, 10024 KB  
Article
Exploring the Impact of Spray Process Parameters on Graphite Coatings: Morphology, Thickness, and Tribological Properties
by Adedoyin Abe, Josue A. Goss and Min Zou
Coatings 2024, 14(6), 714; https://doi.org/10.3390/coatings14060714 - 5 Jun 2024
Cited by 5 | Viewed by 2788
Abstract
This study explores, through a full factorial experimental design, the effects of graphite concentration and spray flow rate on the morphology, thickness, and tribological performance of graphite coatings for potential tribological applications. Coatings were applied to rough substrates using varying concentrations and flow [...] Read more.
This study explores, through a full factorial experimental design, the effects of graphite concentration and spray flow rate on the morphology, thickness, and tribological performance of graphite coatings for potential tribological applications. Coatings were applied to rough substrates using varying concentrations and flow rates, followed by analysis of their morphological characteristics, roughness, thickness, coefficient of friction (COF), and wear behavior. The results revealed distinct differences in the coating morphology based on flow rate, with low-flow-rate coatings exhibiting a porous structure and higher roughness, while high-flow-rate coatings displayed denser structures with lower roughness. A COF as low as 0.09 was achieved, which represented an 86% reduction compared to uncoated steel. COF and wear track measurements showed that thickness was influential in determining friction and the extent of wear. Flow rate dictated the coating structure, quantity of transfer film on the ball, and the extent of graphite compaction in the wear track to provide a protective layer. SEM and elemental analysis further revealed that graphite coatings provided effective protection against wear, with graphite remaining embedded in the innermost crevices of the wear track. Low flow rates may be preferable for applications requiring higher roughness and porosity, while high flow rates offer advantages in achieving denser coatings and better wear resistance. Overall, this study highlights the importance of optimizing graphite concentration and spray flow rate to tailor coating morphology, thickness, and tribological performance for practical applications. Full article
(This article belongs to the Special Issue Friction, Wear, Lubrication and Mechanics of Surfaces and Interfaces)
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13 pages, 3006 KB  
Article
Optimum Design of Coaxial Hydraulic Sealing Systems Made from Polytetrafluoroethylene and Its Compounds
by Andrea Deaconescu and Tudor Deaconescu
Coatings 2024, 14(6), 723; https://doi.org/10.3390/coatings14060723 - 5 Jun 2024
Cited by 1 | Viewed by 1526
Abstract
Fluidic actuation systems are optimizable as to energy consumption by reducing the friction in the hydraulic cylinders. Polymeric materials with special antifriction properties and good resistance to hydraulic fluids can be deployed to enhance the performance of hydraulic cylinders. Small friction forces can [...] Read more.
Fluidic actuation systems are optimizable as to energy consumption by reducing the friction in the hydraulic cylinders. Polymeric materials with special antifriction properties and good resistance to hydraulic fluids can be deployed to enhance the performance of hydraulic cylinders. Small friction forces can also be ensured by facilitating the hydrodynamic separation of the elements of the friction tribosystem, namely the seal and sealed-off surface, respectively. The study presented in this paper analyzed the hydrodynamic separation phenomenon in hydraulic cylinders with coaxial sealing systems of the pistons. The process underlying the forming of the fluid film between the seal and its contact surface was considered and the formula for calculating film thickness was deduced. This paper presents graphs that describe the variation of the fluid film thickness versus the dimensional and material characteristics of the sealing systems. The study yielded recommendations as to the most adequate polymeric material to be used and the optimum dimensional characteristics of the seal. Full article
(This article belongs to the Special Issue Friction, Wear, Lubrication and Mechanics of Surfaces and Interfaces)
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18 pages, 7265 KB  
Article
Use of Organic Acids as Additives for Plasma Electrolytic Oxidation (PEO) of Titanium
by Federica Ceriani, Luca Casanova and Marco Ormellese
Coatings 2024, 14(6), 703; https://doi.org/10.3390/coatings14060703 - 3 Jun 2024
Cited by 6 | Viewed by 1164
Abstract
The present study investigates the influence of organic acids, added to the electrolytic solution, on the structure, morphology, and corrosion behaviour of plasma electrolytic oxidation (PEO) coatings produced on titanium grade 2. Particular attention is paid to the role of functional groups in [...] Read more.
The present study investigates the influence of organic acids, added to the electrolytic solution, on the structure, morphology, and corrosion behaviour of plasma electrolytic oxidation (PEO) coatings produced on titanium grade 2. Particular attention is paid to the role of functional groups in the modification of the oxide’s properties. For this reason, all three selected acids, namely glutaric, glutamic, and tartaric acid, display two carboxylic groups, thus they interact with the substrate material mainly through –COO− adsorption. However, glutamic acid also has an amine group, while tartaric acid has two hydroxyl groups. The presence of such additional functional groups is found to impact the formation of the PEO coatings. According to scanning electron microscopy (SEM) analyses, the number of defects and their dimension increase with an increasing number of active groups present in the organic molecules. Then, when glutaric acid with only two carboxyl groups, is employed as an additive, smaller pores are produced. The dimension of defects increases when glutamic and tartaric acid are used. X-ray diffraction (XRD) testing demonstrates that rutile and anatase are present in all the coatings and that when using tartaric acid, a relatively high level of amorphism is reached. The electrochemical and corrosion behaviours are evaluated by potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) performed in a heated sulphuric acid solution. It is found that all types of coatings provide protection against corrosion, with oxides produced using glutamic acid showing the lowest corrosion current density (0.58 mA·m−2) and low corrosion rate (1.02 μm·y−1). Full article
(This article belongs to the Section Corrosion, Wear and Erosion)
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12 pages, 6042 KB  
Article
Influence of Flow Rates and Flow Times of Plasma-Enhanced Atomic Layer Deposition Purge Gas on TiN Thin Film Properties
by Ju Eun Kang, Surin An and Sang Jeen Hong
Coatings 2024, 14(6), 673; https://doi.org/10.3390/coatings14060673 - 27 May 2024
Viewed by 2930
Abstract
This study investigated the effect of purge gas flow rate and purge gas flow time on the properties of TiN thin films via chemical reaction simulation and the plasma-enhanced atomic layer deposition (PEALD) process along purge gas flow rates and time settings. Chemical [...] Read more.
This study investigated the effect of purge gas flow rate and purge gas flow time on the properties of TiN thin films via chemical reaction simulation and the plasma-enhanced atomic layer deposition (PEALD) process along purge gas flow rates and time settings. Chemical reaction simulation unveiled an incremental increase in generating volatile products along purge gas flow rates. In contrast, increased purge gas flow times enhanced the desorption of physically adsorbed species flow time in the film surface. Subsequent thin film analysis showed that the increased Ar purge gas flow rate caused a shift of 44% in wafer non-uniformity, 46% in carbon composition, and 11% in oxygen composition in the deposited film. Modulations in the Ar purge gas flow time yielded variations of 50% in wafer non-uniformity, 46% in carbon composition, and 15% in oxygen content. Notably, 38% of the resistivity and 35% of the film thickness occurred due to experimental variations in the Ar purge step condition. Increased purge gas flow rates had a negligible impact on the film composition, thickness, and resistivity, but the film’s non-uniformity on a 6-inch wafer was notable. Extended purge gas flow times with inadequate flow rates resulted in undesired impurities in the thin film. This study employed a method that utilized reaction simulation to investigate the impact of purge gas flow and verified these results through film properties analysis. These findings can help in determining optimal purge conditions to achieve the desired film properties of PEALD-deposited TiN thin films. Full article
(This article belongs to the Special Issue Application of Advanced Plasma Technology in Coatings, Films and Etching)
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16 pages, 6415 KB  
Article
Comparative Study of Multilayer Hard Coatings Deposited on WC-Co Hardmetals
by Mateja Šnajdar, Danko Ćorić and Matija Sakoman
Coatings 2024, 14(6), 674; https://doi.org/10.3390/coatings14060674 - 27 May 2024
Cited by 2 | Viewed by 2238
Abstract
This paper examines the impact of a multilayered gradient coating, applied via plasma-activated chemical vapor deposition (PACVD), on the structural and mechanical attributes of nanostructured WC-Co cemented carbides. WC-Co samples containing 5 and 15 wt.% Co were synthesized through a hot isostatic pressing [...] Read more.
This paper examines the impact of a multilayered gradient coating, applied via plasma-activated chemical vapor deposition (PACVD), on the structural and mechanical attributes of nanostructured WC-Co cemented carbides. WC-Co samples containing 5 and 15 wt.% Co were synthesized through a hot isostatic pressing (HIP) process using nanoparticle powders and coated with two distinct multilayer coatings: titanium nitride (TiN) and titanium carbonitride (TiCN). Nanosized grain formation without microstructural defects of the substrates, prior to coating, was confirmed by magnetic saturation and coercivity testing, microstructural analysis, and field emission scanning electron microscope (FESEM). Nanoindentation, fracture toughness and hardness testing were conducted for uncoated samples. After coatings deposition, characterizations including microscopy, surface roughness determination, adhesion testing, coating thickness measurement, and microhardness examination were conducted. The impact of deposited coatings on wear resistance of produced hardmetals was analyzed via scratch test and dry sliding wear test. Samples with higher Co content exhibited improved adhesion, facilitating surface cleaning and activation before coating. TiN and TiCN coatings demonstrated similar roughness on substrates of identical composition, suggesting Co content’s minimal influence on layer growth. Results of the mechanical tests showed higher microhardness, higher elastic modulus, better adhesion, and overall superior tribological properties of the TiCN coating. Full article
(This article belongs to the Special Issue Advances in Deposition and Characterization of Hard Coatings)
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17 pages, 3740 KB  
Article
Magnetron-Sputtered Long-Term Superhydrophilic Thin Films for Use in Solid-State Cooling Devices
by Maria Barrera, Olaf Zywitzki, Thomas Modes and Fred Fietzke
Coatings 2024, 14(5), 622; https://doi.org/10.3390/coatings14050622 - 14 May 2024
Cited by 2 | Viewed by 1942
Abstract
Pulse-magnetron-sputtered long-term superhydrophilic coatings have been synthesized to functionalize the surfaces of solid-state cooling devices, e.g., electrocaloric heat pumps, where not only a complete wetting of the surface by a fluid is intended, but also fast wetting and dewetting processes are required. The [...] Read more.
Pulse-magnetron-sputtered long-term superhydrophilic coatings have been synthesized to functionalize the surfaces of solid-state cooling devices, e.g., electrocaloric heat pumps, where not only a complete wetting of the surface by a fluid is intended, but also fast wetting and dewetting processes are required. The coatings consist of a (Ti,Si)O2 outer layer that provides lasting hydrophilicity thanks to the mesoporous structure, followed by an intermediate WO3 film that enables the reactivation of the wettability through visible light irradiation, and a W underlayer which can work as a top electrode of the electrocaloric components thanks to its suitable electrical and thermal conductivity properties. Process parameter optimization for each layer of the stack as well as the influence of the microstructure and composition on the wetting properties are presented. Finally, water contact angle measurements, surface energy evaluations, and a contact line dynamics assessment of evaporating drops on the coatings demonstrate that their enhanced wetting performance is attributed not only to their intrinsic hydrophilic nature but also to their porous microstructure, which promotes wicking and spreading at the nanometric scale. Full article
(This article belongs to the Section Thin Films)
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