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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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21 pages, 1088 KB  
Review
Present and Future of ZrO2 Nanostructure as Reservoir for Drug Loading and Release
by Ramona-Daniela Radu (Dușman) and Doina Drăgănescu
Coatings 2023, 13(7), 1273; https://doi.org/10.3390/coatings13071273 - 20 Jul 2023
Cited by 19 | Viewed by 4183
Abstract
Extensive research has been conducted on ZrO2 nanostructures due to their favorable biocompatibility, low toxicity, and promising prospects in various biomedical applications. They can be used as drug carriers, facilitating the administration of therapeutic substances into the body while enhancing their effectiveness [...] Read more.
Extensive research has been conducted on ZrO2 nanostructures due to their favorable biocompatibility, low toxicity, and promising prospects in various biomedical applications. They can be used as drug carriers, facilitating the administration of therapeutic substances into the body while enhancing their effectiveness and safety. This is achieved by regulating the timing, location, and rate at which drugs are released within the body. Several factors can influence the effectiveness of drug loading onto ZrO2 nanostructures, such as the physicochemical characteristics of the drugs, the surface properties of the ZrO2 nanostructures, and the specific methods used for drug loading. A wide range of drugs may be loaded onto ZrO2 nanostructures including anti-cancer drugs, antibiotics, anti-inflammatory drugs, antifungal drugs, anti-osteoporotic drugs, etc. The release kinetics of drugs can be influenced by different factors, such as the size and shape of ZrO2 nanostructures, the pH and temperature of the release medium, and the characteristics and molecular weight of the specific drug being released. While ZrO2 nanostructures have demonstrated significant potential as drug delivery systems, further research on these structures is essential to optimize drug loading and release strategies. Full article
(This article belongs to the Special Issue New Strategies and Recent Advances in Investigations of Micro- and Nano-Coatings for Technological and Biomedical Applications)
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21 pages, 10324 KB  
Article
Effect of Zn on Phase Evolution and Shear Resistance of Stainless Steel and Aluminum Alloy Interface by Laser Cladding
by Keyan Wang, Xianqing Yin, Chengxin Li and Kaiping Du
Coatings 2023, 13(7), 1267; https://doi.org/10.3390/coatings13071267 - 19 Jul 2023
Cited by 1 | Viewed by 1814
Abstract
The connection between aluminum and iron alloys is of immense significance in the pursuit of lightweight industrial products. However, the Fe-Al interface’s inherent weakness restricts its widespread application. This study investigates the impact of Zn at the interface of Al-Fe laser cladding on [...] Read more.
The connection between aluminum and iron alloys is of immense significance in the pursuit of lightweight industrial products. However, the Fe-Al interface’s inherent weakness restricts its widespread application. This study investigates the impact of Zn at the interface of Al-Fe laser cladding on the phase and mechanical properties of the interface. Specifically, we examine the influence of the applied Zn powder layer and alloying Zn layer on the morphology of the Fe-based cladding layer. The inclusion of Zn enhances the spreadability of the Fe-based cladding layer. Additionally, we elucidate the effect of Zn on the composition and phase of the Fe-Al laser cladding interface. Notably, the affinity between Zn and the η phase surpasses that of the θ phase, and an increased Zn content significantly thickens the η phase. Shear tests reveal that the failure mode of shear fracture encompasses both brittle and ductile fractures. Density functional theory (DFT) calculations indicate that Zn has a limited effect on the strength of the η phase but reduces the enthalpy of formation of the η phase. Our findings demonstrate that the alloyed Zn layer initially facilitates the formation of a continuous and uniform η layer, while an increased Zn content enhances and stabilizes the shear strength of the interface. Full article
(This article belongs to the Special Issue Laser Cladding Coatings: Microstructure, Properties, and Applications)
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11 pages, 12980 KB  
Article
Quasi Non-Destructive Quality Assessment of Thermally Sprayed AISI 316L Coatings Using Polarization Measurements in 3.5% NaCl Gel Electrolyte
by Maximilian Grimm, Pia Kutschmann, Christian Pluta, Olga Schwabe, Thomas Lindner and Thomas Lampke
Coatings 2023, 13(7), 1256; https://doi.org/10.3390/coatings13071256 - 16 Jul 2023
Cited by 1 | Viewed by 1787
Abstract
There is currently a lack of suitable methods of non-destructive quality assessment of thermally sprayed coatings. Therefore, this study investigates the suitability of polarization measurements that are adapted to the special needs of thermally sprayed coatings for non-destructive quality testing. For this purpose, [...] Read more.
There is currently a lack of suitable methods of non-destructive quality assessment of thermally sprayed coatings. Therefore, this study investigates the suitability of polarization measurements that are adapted to the special needs of thermally sprayed coatings for non-destructive quality testing. For this purpose, a gel electrolyte containing 3.5% NaCl and a measuring cell based on the three-electrode arrangement were developed to prevent the corrosion medium from infiltrating the typical microstructure of thermally sprayed coatings (pores and microcracks). The newly developed method was evaluated on AISI 316L coatings deposited by high velocity air fuel (HVAF) and atmospheric plasma spraying (APS). The polarization curves showed significant differences as a result of spraying process-related changes in the coating microstructure. Even slight differences in oxide content within the AISI 316L coating produced by APS can be detected by the new method. In order to verify the new findings, the coatings were analyzed regarding their microstructure by optical microscope, scanning electron microscope and energy dispersive X-ray spectroscopy. The measuring cell and gel electrolyte developed offer a promising opportunity to evaluate the quality of thermally sprayed coatings in a largely non-destructive manner using polarization curves. Full article
(This article belongs to the Special Issue Advances in Novel Coatings)
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9 pages, 5005 KB  
Article
Optoelectronic Properties of Ferroelectric Composites of Bi3.25La0.75Ti3O12 (BLT) and Co-Doped BLT Thin Films Modified by FeCo-Doped BLT
by Rui Tang, Rui He, Sangmo Kim and Chung Wung Bark
Coatings 2023, 13(7), 1223; https://doi.org/10.3390/coatings13071223 - 8 Jul 2023
Viewed by 1628
Abstract
Driven by the growing demand for renewable and clean energy, the photovoltaic effect of various solar cells and materials was investigated for the conversion of light energy into electricity. We modified the Bi3.25La0.75Ti3O12 (BLT) and Co-doped [...] Read more.
Driven by the growing demand for renewable and clean energy, the photovoltaic effect of various solar cells and materials was investigated for the conversion of light energy into electricity. We modified the Bi3.25La0.75Ti3O12 (BLT) and Co-doped BLT (Co–BLT) composites with Fe and Co-doped BLT (FeCo–BLT) films to narrow the bandgap and increase visible light absorption, thereby improving the efficiency of the photovoltaic reaction. In this study, BLT and Co–BLT thin films were fabricated by off-axis sputtering and then modified with FeCo–BLT thin films to produce dual-ferroelectric, thin-film composite materials that improved the photovoltaic power generation performance. Photoelectric test results showed that the modified double-ferroelectric, thin-film composites had superior optoelectronic properties. The current density was significantly enhanced by modifying the BLT films with doped Fe and Co. Therefore, this modification improved the efficiency of ferroelectric thin-film photovoltaic reactions. Full article
(This article belongs to the Special Issue Optical Thin Film and Photovoltaic (PV) Related Technologies, Volume II)
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14 pages, 5148 KB  
Article
High-Entropy Composite Coating Based on AlCrFeCoNi as an Anode Material for Li-Ion Batteries
by Dávid Csík, Gabriela Baranová, Róbert Džunda, Dóra Zalka, Ben Breitung, Mária Hagarová and Karel Saksl
Coatings 2023, 13(7), 1219; https://doi.org/10.3390/coatings13071219 - 7 Jul 2023
Cited by 12 | Viewed by 5112
Abstract
In this study, a high entropy composite coating was synthesized by oxidizing a high entropy alloy, AlCrFeCoNi, at elevated temperatures in a pure oxygen atmosphere. X-Ray diffraction (XRD) analysis revealed that the prepared material was a dual-phase composite material consisting of a spinel-structured [...] Read more.
In this study, a high entropy composite coating was synthesized by oxidizing a high entropy alloy, AlCrFeCoNi, at elevated temperatures in a pure oxygen atmosphere. X-Ray diffraction (XRD) analysis revealed that the prepared material was a dual-phase composite material consisting of a spinel-structured high entropy oxide and a metallic phase with a face-centered cubic structure. The metallic phase can improve the electrical conductivity of the oxide phase, resulting in improved electrochemical performance. Scanning electron microscopy with energy dispersive spectroscopy (SEM/EDS) analysis unveiled the compositional homogeneity of the composite material. The prepared material was utilized as an anode active material in lithium-ion batteries. Cyclic voltammetry (CV) revealed the oxidation and reduction regions, while the electrochemical impedance spectroscopy (EIS) measurements showed a decrease in the charge transfer resistance during the cycling process. A long-term rate capability test was conducted at various current densities: 100, 200, 500, 1000, and 2000 mA g−1. During this test, a notable phenomenon was observed in the regeneration process, where the capacity approached the initial discharge capacity. Remarkably, a high regeneration efficiency of 98% was achieved compared with the initial discharge capacity. This phenomenon is typically observed in composite nanomaterials. At a medium current density of 500 mA g−1, an incredible discharge capacity of 543 mAh g−1 was obtained after 1000 cycles. Based on the results, the prepared material shows great potential for use as an anode active material in lithium-ion batteries. Full article
(This article belongs to the Section Ceramic Coatings and Engineering Technology)
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16 pages, 20266 KB  
Article
Thin 1,2,4-Triazole Films for the Inhibition of Carbon Steel Corrosion in Sulfuric Acid Solution
by Yaroslav G. Avdeev, Tatyana A. Nenasheva, Andrey Yu. Luchkin, Andrey I. Marshakov and Yurii I. Kuznetsov
Coatings 2023, 13(7), 1221; https://doi.org/10.3390/coatings13071221 - 7 Jul 2023
Cited by 11 | Viewed by 1993
Abstract
Etching of steel items in sulfuric acid solution is used in various human activities (oil and gas industry, metal production, utilities, transport, etc.). This operation is associated with significant material costs due to corrosion losses of the metal. It has been found that [...] Read more.
Etching of steel items in sulfuric acid solution is used in various human activities (oil and gas industry, metal production, utilities, transport, etc.). This operation is associated with significant material costs due to corrosion losses of the metal. It has been found that an efficient way to prevent corrosion of steel in sulfuric acid solution involves the formation of thin protective films consisting of corrosion inhibitor molecules of triazole class on its surface. It has been shown that the protection of steels with a 3-substituted 1,2,4-triazole (3ST) in H2SO4 solution is accompanied by the formation of a polymolecular layer up to 4 nm thick. The 3ST layer immediately adjacent to the steel surface is chemisorbed on it. The efficiency of this compound as an inhibitor of corrosion and hydrogen absorption by steel is determined by its ability to form a protective organic layer, as experimentally confirmed by XPS and AFM data. The kinetic constants of the main stages of hydrogen evolution and permeation into steel in the H2SO4 solution were determined. A significant decrease in both the reaction rate of cathodic hydrogen evolution and the rate of hydrogen permeation into steel by the triazole in question was noted. It has been shown that the preservation of the metal plasticity in the acid medium containing the triazole under study is due to a decrease in the hydrogen concentration in the metal bulk. Full article
(This article belongs to the Section Corrosion, Wear and Erosion)
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12 pages, 5771 KB  
Article
Stoichiometric and Nonstoichiometric Surface Structures of Pyrochlore Y2Zr2O7 and Their Relative Stabilities: A First-Principles Investigation
by Huajian Wu, Jianning Zhang, Yiren Wang, Jiacheng Shang and Yong Jiang
Coatings 2023, 13(7), 1203; https://doi.org/10.3390/coatings13071203 - 5 Jul 2023
Cited by 2 | Viewed by 1812
Abstract
First-principle total energy calculations were performed to investigate the atomic structures and relative stabilities of two low miller-index surfaces of pyrochlore Y2Zr2O7. The stoichiometric Y2Zr2O7 (110) and (100) surfaces were predicted, with [...] Read more.
First-principle total energy calculations were performed to investigate the atomic structures and relative stabilities of two low miller-index surfaces of pyrochlore Y2Zr2O7. The stoichiometric Y2Zr2O7 (110) and (100) surfaces were predicted, with lowest formation energies of 1.20 and 1.47 J/m2, respectively. Based on a thermodynamic defect model, non-stoichiometric Y2Zr2O7 surface energies were further evaluated as a function of environmental oxygen partial pressure (pO2) and temperature (T). With all of the results, we were able to construct the surface phase diagrams for T = 300 and 1400 K. The strong correlation between the structural stabilities and the surface stoichiometry was revealed as varying T and pO2. At a given T, the most stable termination of the (110) surfaces would change from a (Y,Zr)−rich (ns−2Y2Zr6O) to O−rich ones (ns−4O_2 and ns−4O_1) as increasing pO2, while that of the (100) surfaces would change from the stoichiometric (stoi−1Y1Zr_1) to the O−rich one (ns−5O). The critical pO2 value for termination transition moves to its higher end as increasing T. Full article
(This article belongs to the Special Issue Nanostructured Materials and Interfaces: Energy and Environmental Applications)
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15 pages, 3658 KB  
Article
Epoxy Coating Modification with Metal Nanoparticles to Improve the Anticorrosion, Migration, and Antibacterial Properties
by Marina Samardžija, Ivan Stojanović, Marija Vuković Domanovac and Vesna Alar
Coatings 2023, 13(7), 1201; https://doi.org/10.3390/coatings13071201 - 4 Jul 2023
Cited by 7 | Viewed by 5443
Abstract
Nanoparticles are capable of making more durable and stronger materials with better chemical resistance. They are used for a wide range of applications. Likewise, the potential of metal nanoparticles as antimicrobial agents has been widely studied. In this work, we investigate various nanoparticles [...] Read more.
Nanoparticles are capable of making more durable and stronger materials with better chemical resistance. They are used for a wide range of applications. Likewise, the potential of metal nanoparticles as antimicrobial agents has been widely studied. In this work, we investigate various nanoparticles (Al, Ni, Ag) incorporated into epoxy coating. The anticorrosion and antibacterial properties of the unmodified and modified coatings were evaluated. According to the SEM and EDS analyses, the coating did not contain agglomerates, which confirms the quality of the dispersion of inorganic nanoparticles in the coating. After 24 h and 10days immersions in a 3.5 wt.% NaCl solution, the corrosion behaviour for all nanocomposite was studied by means of EIS investigations. The study included the evaluation of the inhibition zone of the nanoparticles and the antimicrobial properties of the nanocomposite. It was found that the nanoparticles of Al and Ag provide excellent antibacterial properties. The epoxy nanocomposite with Al NP showed the migration of ions in the range from 0.75 to 1 mg/L in a wastewater solution for 30 days, indicating a potential for antimicrobe activity. The 1% Al NP epoxy nanocomposite showed good anticorrosion and antibacterial properties and demonstrated great potential for applications in pipelines. Full article
(This article belongs to the Special Issue Investigation on Corrosion Behaviour of Metallic Materials)
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23 pages, 5911 KB  
Article
Hybrid Materials Based on ZnO Nanoparticles and Organo-Modified Silica Coatings as Eco-Friendly Anticorrosive Protection for Metallic Historic Artifacts
by Mihaela Ioan, Dan Florin Anghel, Mihai Anastasescu, Ioana Catalina Gifu, Elvira Alexandrescu, Roxana Ioana Matei, Cristian Petcu, Ioana Stanculescu, Georgiana Alexandra Sanda, Daniela Bala and Ludmila Otilia Cinteza
Coatings 2023, 13(7), 1193; https://doi.org/10.3390/coatings13071193 - 3 Jul 2023
Cited by 6 | Viewed by 4114
Abstract
Cultural heritage metallic artifacts are often subjected to environmental factors that promote degradation through corrosion processes. Anticorrosion protection is needed both for the long-term preservation of outdoor monuments and the short-term conservation of archaeological artifacts. In this work, functional nanocoatings based on ZnO [...] Read more.
Cultural heritage metallic artifacts are often subjected to environmental factors that promote degradation through corrosion processes. Anticorrosion protection is needed both for the long-term preservation of outdoor monuments and the short-term conservation of archaeological artifacts. In this work, functional nanocoatings based on ZnO nanoparticles (NPs) in a silica matrix are prepared as a replacement for a commercial Incralac lacquer. Facile sol–gel synthesis is employed for obtaining silica filmogenic materials, using tetraethoxysilane (TEOS) and 3-glycidyloxypropyl trimethoxysilane (GPTMS). Silica-based nanocomposite coatings, with and without ZnO NPs and benzotriazole (BTA) as anticorrosion agents, applied on copper coupons by brushing are characterized by using VIS and FTIR spectroscopy, SEM and AFM and compared to Incralac lacquer as reference materials. The optical and morphological properties of the proposed silica coatings are similar to the Incralac specimens. The protective effect against corrosion is investigated on the copper coupons as model metallic objects subjected to a corrosion test by using potentiodynamic polarization in a 3.5% NaCl solution at ambient temperature. The influence of the presence of BTA and ZnO NPs in both silica and Incralac coatings is studied, and the variations in the anticorrosive, morphological and optical properties with the concentration of ZnO NPs are evidenced. The presence of moderate concentrations of ZnO in both nanomaterials leads to changes in the color parameters slightly above the limit accepted in the field of cultural heritage (ΔE* 5.09 and 6.13), while a high ZnO concentration of 3% leads to higher values (ΔE* > 10). Regarding the anticorrosive effect, the silica-based coatings with ZnO and BTA present similar efficiencies to that of the Incralac reference material (corrosion rates in the range of 0.044–0.067 mm/year for silica coatings compared to 0.055 mm/year for Incralac). Full article
(This article belongs to the Special Issue New Strategies and Recent Advances in Investigations of Micro- and Nano-Coatings for Technological and Biomedical Applications)
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29 pages, 15287 KB  
Review
Research Progress on the Wear and Corrosion Resistant Plasma Electrolytic Oxidation Composite Coatings on Magnesium and Its Alloys
by Chen Zhao, Xingwei Wang, Bo Yu, Meirong Cai, Qiangliang Yu and Feng Zhou
Coatings 2023, 13(7), 1189; https://doi.org/10.3390/coatings13071189 - 1 Jul 2023
Cited by 26 | Viewed by 6490
Abstract
Plasma electrolytic oxidation (PEO), as a cost effective and environmentally friendly technology, has been applied on magnesium and its alloys to improve wear and corrosion resistance. Additionally, combining with particles addition in the electrolyte and/or various post-treatments could diminish the intrinsic structural defects [...] Read more.
Plasma electrolytic oxidation (PEO), as a cost effective and environmentally friendly technology, has been applied on magnesium and its alloys to improve wear and corrosion resistance. Additionally, combining with particles addition in the electrolyte and/or various post-treatments could diminish the intrinsic structural defects of the PEO coatings and provide multifunctionalities, including wear resistance, corrosion resistance, self-lubrication, and self-healing. This paper reviews recent progress on PEO composite coatings prepared by in situ incorporation of functional particles and/or post-treatments on magnesium and its alloys. The focus is given to the microstructural and functional changes of the PEO coatings, particularly on the wear and corrosion behaviors. Full article
(This article belongs to the Section Plasma Coatings, Surfaces & Interfaces)
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12 pages, 3861 KB  
Article
Lignin and Starch Derivatives with Selenium Nanoparticles for the Efficient Reduction of Dyes and as Polymer Fillers
by Anna Modrzejewska-Sikorska, Mariola Robakowska, Emilia Konował, Hubert Gojzewski, Łukasz Gierz, Bartosz Wieczorek, Łukasz Warguła and Wiktor Łykowski
Coatings 2023, 13(7), 1185; https://doi.org/10.3390/coatings13071185 - 30 Jun 2023
Cited by 2 | Viewed by 3315
Abstract
Selenium nanoparticles (SeNPs) were synthesized and stabilized by biopolymers, namely, sodium lignosulfonate (LS) and starch sodium octenyl succinate (OSA). The obtained selenium nanoparticles were studied for their catalytic activity in the reduction of a dye (C.I. Basic Blue 9, methylene blue) by sodium [...] Read more.
Selenium nanoparticles (SeNPs) were synthesized and stabilized by biopolymers, namely, sodium lignosulfonate (LS) and starch sodium octenyl succinate (OSA). The obtained selenium nanoparticles were studied for their catalytic activity in the reduction of a dye (C.I. Basic Blue 9, methylene blue) by sodium borohydride. The SeNPs-OSA and SeNPs-LS nanoparticles were also dispersed in a photosensitive matrix and studied as polymer composites. The research confirmed the catalytic abilities of the prepared SeNPs in the reduction of the organic dye. Mechanical tests on the polymers and their composites showed an improvement in the composites’ strength in all tested cases. An increase in hardness and Young’s modulus values of the filled materials compared to the pure matrix was found as well. Full article
(This article belongs to the Special Issue Advanced Technology in Environmental Remediation and Resource Utilization)
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13 pages, 12441 KB  
Communication
The Microstructure, Hardness, Phase Transformation and Mechanical Properties of a NiTi Coating Applied to Graphite Substrate via a Plasma Spraying Process
by Sneha Samal, Jakub Zeman, Jaromír Kopeček and Petr Šittner
Coatings 2023, 13(7), 1174; https://doi.org/10.3390/coatings13071174 - 29 Jun 2023
Cited by 5 | Viewed by 2420
Abstract
In this study, Ni50Ti50 powder was coated on the surface of graphite substrate (C) via a plasma spraying process using a radio frequency inductively coupled plasma reactor. The coating was carried out using 12- and 9-kW power under Ar atmosphere. [...] Read more.
In this study, Ni50Ti50 powder was coated on the surface of graphite substrate (C) via a plasma spraying process using a radio frequency inductively coupled plasma reactor. The coating was carried out using 12- and 9-kW power under Ar atmosphere. The cross-section of coating layers and the surface were examined with Scanning Electron Microscope (SEM), Energy Dispersive X-ray Spectrum (EDX), and X-ray Diffractometer (XRD) analyses and microhardness test. The thickness and quality of the coating increased with the input power. Many pores were detected in the cross-sectional surface areas. Higher input power caused a better coating layer of NiTi alloy. The hardness of the coating layer decreases with higher input power. Full article
(This article belongs to the Section Plasma Coatings, Surfaces & Interfaces)
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19 pages, 630 KB  
Review
Biodegradable Packaging Materials for Foods Preservation: Sources, Advantages, Limitations, and Future Perspectives
by Andreas Panou and Ioannis Konstantinos Karabagias
Coatings 2023, 13(7), 1176; https://doi.org/10.3390/coatings13071176 - 29 Jun 2023
Cited by 64 | Viewed by 24471
Abstract
Biodegradable packaging materials generally comprise a solution to the environmental problem caused by the consecutive use of conventional packaging materials (petroleum-based materials) even though these have a high cost. The monomers resulting from the slow degradation of petroleum-based materials contribute to the pollution [...] Read more.
Biodegradable packaging materials generally comprise a solution to the environmental problem caused by the consecutive use of conventional packaging materials (petroleum-based materials) even though these have a high cost. The monomers resulting from the slow degradation of petroleum-based materials contribute to the pollution of the environment. Biodegradable packaging materials distinguished by high biodegradability and biocompatibility can successfully replace the aforementioned packaging materials and thus solve the environmental problems caused by their use or deposition. Although several of the biodegradable packaging materials present defective properties, mainly mechanical and barrier properties, these are reduced or even eliminated by the addition of various improving additives and by blending them with other biopolymers. Various natural preservatives such as essential oils or other phytochemical extracts can also be incorporated into the biopolymer network to increase its efficacy. This treatment is particularly beneficial since it contributes to the increasing of the shelf life and storability of packaged foods such as fruits, vegetables, dairy products, meat and its products, poultry, and fish. For all the above reasons, the preferences of consumers and the critical thinking/decisions of the food product manufacturing industries in favor of the potential use of biodegradable packaging materials in foods are increasing more and more. In this context, the present review article addresses the most recently used biodegradable packaging materials for foods preservation by presenting their sources, advantages, limitations, and future perspectives. Full article
(This article belongs to the Special Issue Bio-Based Packaging Films: Development, Characterization, and Application)
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11 pages, 7764 KB  
Article
Optimization of Crystalline Diamond Coating Structure Architecture for Improving Adhesion and Cutting Performance in Milling with Cemented Carbide Inserts
by Georgios Skordaris, Konstantinos-Dionysios Bouzakis, Antonios Bouzakis, Dimitrios Tsakalidis, Apostolos Boumpakis, Spyridon Kompogiannis, Emmanouil Bouzakis, Oliver Lemmer, Werner Kölker and Michael Woda
Coatings 2023, 13(7), 1170; https://doi.org/10.3390/coatings13071170 - 28 Jun 2023
Cited by 2 | Viewed by 3339
Abstract
The adhesion, structure architecture, and residual stresses of crystalline diamond coatings (CDCs) on cemented carbide inserts are the factors that significantly affect tool life. The influence of these factors on cutting performance cannot be investigated separately since interactions among them exist. The paper [...] Read more.
The adhesion, structure architecture, and residual stresses of crystalline diamond coatings (CDCs) on cemented carbide inserts are the factors that significantly affect tool life. The influence of these factors on cutting performance cannot be investigated separately since interactions among them exist. The paper elucidates such dependencies to optimize the CDC architecture and improve cutting performance. In this context, diamond coatings possessing different architectures were deposited on cemented carbide tools. The fatigue endurance and the milling performance of the coated tools were investigated using impact and milling tests, respectively. The residual stresses in the film structures were determined through impact tests and appropriate (Finite Element Analysis) FEA evaluation of the corresponding results. According to the obtained results, the application of a bottom micro-structured CDC prior to the deposition of an upper nanolayered one with inferior thickness improves the coated tools’ cutting performance. An optimum coating architecture is associated with a thickness ratio between the micro-structured bonding to the upper nanolayered CDCs of 2/1. Hereupon, the augmentation of coated tool life via the application of an optimum diamond coating architecture compensates for the high tool cost and improves milling productivity. The latter is further enhanced as the number of tool replacements decreases. Full article
(This article belongs to the Special Issue New Cutting Techniques for Improved Machining)
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59 pages, 9745 KB  
Article
Principles of Machine Learning and Its Application to Thermal Barrier Coatings
by Yuan Liu, Kuiying Chen, Amarnath Kumar and Prakash Patnaik
Coatings 2023, 13(7), 1140; https://doi.org/10.3390/coatings13071140 - 23 Jun 2023
Cited by 13 | Viewed by 6471
Abstract
Artificial intelligence (AI), machine learning (ML) and deep learning (DL) along with big data (BD) management are currently viable approaches that can significantly help gas turbine components’ design and development. Optimizing microstructures of hot section components such as thermal barrier coatings (TBCs) to [...] Read more.
Artificial intelligence (AI), machine learning (ML) and deep learning (DL) along with big data (BD) management are currently viable approaches that can significantly help gas turbine components’ design and development. Optimizing microstructures of hot section components such as thermal barrier coatings (TBCs) to improve their durability has long been a challenging task in the gas turbine industry. In this paper, a literature review on ML principles and its various associated algorithms was presented first and then followed by its application to investigate thermal conductivity of TBCs. This combined approach can help better understand the physics behind thermal conductivity, and on the other hand, can also boost the design of low thermal conductivity of the TBCs system in terms of microstructure–property relationships. Several ML models and algorithms such as support vector regression (SVR), Gaussian process regression (GPR) and convolution neural network and regression algorithms were used via Python. A large volume of thermal conductivity data was compiled and extracted from the literature for TBCs using PlotDigitizer software and then used to test and validate ML models. It was found that the test data were strongly associated with five key factors as identifiers. The prediction of thermal conductivity was performed using three approaches: polynomial regression, neural network (NN) and gradient boosting regression (GBR). The results suggest that NN using the BR model and GBR have better prediction capability. Full article
(This article belongs to the Special Issue Advances in Thermal Barrier Coatings (TBCs): Materials, Fabrication, Corrosion and Applications)
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10 pages, 13583 KB  
Article
Seeking the Oxidation Mechanism of Debris in the Fretting Wear of Titanium Functionalized by Surface Laser Treatments
by María del Carmen Marco de Lucas, Franck Torrent, Gianni-Paolo Pillon, Pascal Berger and Luc Lavisse
Coatings 2023, 13(6), 1110; https://doi.org/10.3390/coatings13061110 - 16 Jun 2023
Cited by 1 | Viewed by 2376
Abstract
Surface laser treatment (SLT) using nanosecond IR lasers has been shown to improve the tribological behaviour of titanium. Here, we studied the fretting wear of SLT-functionalized pure titanium in a mixture of reactive gases O2 (20 vol.%) + N2 (80 vol.%). [...] Read more.
Surface laser treatment (SLT) using nanosecond IR lasers has been shown to improve the tribological behaviour of titanium. Here, we studied the fretting wear of SLT-functionalized pure titanium in a mixture of reactive gases O2 (20 vol.%) + N2 (80 vol.%). The contact geometry was a ball on a plane and the ball was made of bearing steel. The very small amplitude of relative displacement between reciprocating parts in fretting wear makes the evacuation of wear particles difficult. Moreover, the oxidation mechanism of the debris depends on the accessibility of the surrounding atmosphere to the tribological contact. This work focused in the analysis of debris generation and oxidation mechanisms, and sought to differentiate the role of oxygen forming part of the ambient O2 + N2 gas mixture from oxygen present in the surface layer of the SL-treated titanium. Before the fretting test, the surface of the commercially pure titanium plates was treated with a laser under a mixture of O2 + N2 gases with oxygen enriched in the 18O isotope. Then, the fretting tests were performed in regular air containing natural oxygen. Micro-Raman spectroscopy and ion beam analysis (IBA) techniques were used to analyse the TiO2 surface layers and fretting scars. Iron oxide particles were identified by Raman spectroscopy and IBA as the third body in the tribological contact. The spatial distribution of 18O, Ti, 16O and Fe in the fretting scars was studied by IBA. The analysis showed that the areas containing high concentrations of Fe displayed also high concentrations of 16O, but smaller concentrations of 18O and Ti. Therefore, it was concluded that tribological contact allows the oxidation of iron debris by its reaction with ambient air. Full article
(This article belongs to the Section Laser Coatings)
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19 pages, 3299 KB  
Article
Bimetallic 3D Nickel-Manganese/Titanium Bifunctional Electrocatalysts for Efficient Hydrogen and Oxygen Evolution Reaction in Alkaline and Acidic Media
by Sukomol Barua, Aldona Balčiūnaitė, Jūrate Vaičiūnienė, Loreta Tamašauskaitė-Tamašiūnaitė and Eugenijus Norkus
Coatings 2023, 13(6), 1102; https://doi.org/10.3390/coatings13061102 - 15 Jun 2023
Cited by 7 | Viewed by 3251
Abstract
In this work, 3D nickel-manganese (NiMn) bimetallic coatings have been studied as electrocatalysts for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline (1.0 M KOH) media and the HER in acidic (0.5 M H2SO4) media. [...] Read more.
In this work, 3D nickel-manganese (NiMn) bimetallic coatings have been studied as electrocatalysts for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline (1.0 M KOH) media and the HER in acidic (0.5 M H2SO4) media. The catalysts have been deposited on a titanium substrate (1 × 1 cm2) using low-cost and facile electrochemical deposition method through a dynamic hydrogen bubble template technique. The electrocatalytic performance of these fabricated catalysts was investigated by using Linear Sweep Voltammetry (LSV) for HER and OER at different temperatures ranging from 25 up to 75 °C and also was characterized by scanning electron microscopy (SEM) and inductively coupled plasma optical emission spectroscopy (ICP-OES). It was found that fabricated NiMn/Ti-5 electrocatalyst with Ni2+/Mn2+ molar ratio of 1:5 exhibits excellent HER activity in alkaline media with overpotential of 127.1 mV to reach current density of 10 mA cm−2. On the contrary, NiMn/Ti-1 electrocatalyst that fabricated with Ni2+/Mn2+ molar proportion of 1:1 and lowest Mn-loading of 13.43 µgcm−2 demonstrates exceptional OER activity with minimum overpotential of 356.3 mV to reach current density of 10 mA cm−2. The current densities increase ca. 1.8–2.2 times with an increase in temperature from 25 °C to 75 °C for both HER and OER investigation. Both catalysts also have exhibited excellent long-term stability for 10 h at constant potentials as well as constant current density of 10 mA cm−2 that assure their robustness and higher durability regarding alkaline water splitting. Full article
(This article belongs to the Special Issue New Advance in Nanoparticles, Fiber, and Coatings)
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14 pages, 4667 KB  
Article
Characterization of Two Types of Polylactic Acid Coating Loaded with Gentamicin Sulphate Deposed on AZ31 Alloy
by Manuela Elena Voicu, Daniela Ionita, George-Octavian Buica, Doina Draganescu, Valentina Anuta, Florentina Monica Raduly and Ioana Demetrescu
Coatings 2023, 13(6), 1105; https://doi.org/10.3390/coatings13061105 - 15 Jun 2023
Cited by 3 | Viewed by 2018
Abstract
This paper compares two types of polylactic acid (PLA) coating on AZ31 alloy obtained by dip coating and electrospinning. Both types of coating were loaded with gentamicin sulphate (GS) and the drug-loading efficiency and release were assessed. A higher encapsulation and release efficiency [...] Read more.
This paper compares two types of polylactic acid (PLA) coating on AZ31 alloy obtained by dip coating and electrospinning. Both types of coating were loaded with gentamicin sulphate (GS) and the drug-loading efficiency and release were assessed. A higher encapsulation and release efficiency of GS was seen for dip coating (73% and 49.53%, respectively) compared to nanofiber coating (65% and 12.37%, respectively). Furthermore, the antibacterial effect of the samples with and without GS was assessed using Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) bacteria, showing that the samples with the drug encapsulated are more resistant to bacteria than the other samples. The electrochemical data reveal a higher stability in the SBF of the surface obtained by dipping than that obtained by electrospinning. The PLA coating shows a porosity of 46% for the sample obtained through dip coating and 32% for nanofibers, which is in accordance with the BET analysis results. Moreover, a higher adhesion strength was obtained for AZ31-PLA-dip (4.99 MPa) than for the AZ31-PLA-nanofibers (1.66 MPa). All samples were structurally, morphologically, and topographically characterized. Full article
(This article belongs to the Special Issue New Strategies and Recent Advances in Investigations of Micro- and Nano-Coatings for Technological and Biomedical Applications)
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27 pages, 6140 KB  
Review
Bioactive Calcium Phosphate Coatings for Bone Implant Applications: A Review
by Richard Drevet, Joël Fauré and Hicham Benhayoune
Coatings 2023, 13(6), 1091; https://doi.org/10.3390/coatings13061091 - 13 Jun 2023
Cited by 42 | Viewed by 14498
Abstract
This review deals with the design of bioactive calcium phosphate coatings deposited on metallic substrates to produce bone implants. The bioceramic coating properties are used to create a strong bonding between the bone implants and the surrounding bone tissue. They provide a fast [...] Read more.
This review deals with the design of bioactive calcium phosphate coatings deposited on metallic substrates to produce bone implants. The bioceramic coating properties are used to create a strong bonding between the bone implants and the surrounding bone tissue. They provide a fast response after implantation and increase the lifespan of the implant in the body environment. The first part of the article describes the different compounds belonging to the calcium phosphate family and their main properties for applications in biomaterials science. The calcium-to-phosphorus atomic ratio (Ca/P)at. and the solubility (Ks) of these compounds define their behavior in a physiological environment. Hydroxyapatite is the gold standard among calcium phosphate materials, but other chemical compositions/stoichiometries have also been studied for their interesting properties. The second part reviews the most common deposition processes to produce bioactive calcium phosphate coatings for bone implant applications. The last part describes key physicochemical properties of calcium phosphate coatings and their impact on the bioactivity and performance of bone implants in a physiological environment. Full article
(This article belongs to the Special Issue Calcium Phosphate and Bioglass Materials for Bone Implant Applications)
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17 pages, 3867 KB  
Article
Copper Nitride: A Versatile Semiconductor with Great Potential for Next-Generation Photovoltaics
by M. I. Rodríguez-Tapiador, J. M. Asensi, M. Roldán, J. Merino, J. Bertomeu and S. Fernández
Coatings 2023, 13(6), 1094; https://doi.org/10.3390/coatings13061094 - 13 Jun 2023
Cited by 14 | Viewed by 8767
Abstract
Copper nitride (Cu3N) has gained significant attention recently due to its potential in several scientific and technological applications. This study focuses on using Cu3N as a solar absorber in photovoltaic technology. Cu3N thin films were deposited on [...] Read more.
Copper nitride (Cu3N) has gained significant attention recently due to its potential in several scientific and technological applications. This study focuses on using Cu3N as a solar absorber in photovoltaic technology. Cu3N thin films were deposited on glass substrates and silicon wafers via radio-frequency magnetron sputtering at different nitrogen flow ratios with total pressures ranging from 1.0 to 5.0 Pa. The thin films’ structural, morphology, and chemical properties were determined using XRD, Raman, AFM, and SEM/EDS techniques. The results revealed that the Cu3N films exhibited a polycrystalline structure, with the preferred orientation varying from 100 to 111 depending on the working pressure employed. Raman spectroscopy confirmed the presence of Cu-N bonds in characteristic peaks observed in the 618–627 cm−1 range, while SEM and AFM images confirmed the presence of uniform and smooth surface morphologies. The optical properties of the films were investigated using UV-VIS-NIR spectroscopy and photothermal deflection spectroscopy (PDS). The obtained band gap, refractive index, and Urbach energy values demonstrated promising optical properties for Cu3N films, indicating their potential as solar absorbers in photovoltaic technology. This study highlights the favourable properties of Cu3N films deposited using the RF sputtering method, paving the way for their implementation in thin-film photovoltaic technologies. These findings contribute to the progress and optimisation of Cu3N-based materials for efficient solar energy conversion. Full article
(This article belongs to the Special Issue Advanced Materials for Energy Storage and Conversion)
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13 pages, 5802 KB  
Article
Electrophoretic Deposition of Rochelle Salt Nanocrystals on Aluminum Plate
by Rostislav Rusev, Boriana Tzaneva and George Angelov
Coatings 2023, 13(6), 1074; https://doi.org/10.3390/coatings13061074 - 10 Jun 2023
Cited by 1 | Viewed by 4389
Abstract
A straightforward and inexpensive electrophoretic method for obtaining environment-friendly nanocrystalline piezo layers from Rochelle salt (RS) is presented here. The electrophoretic deposition process includes the formation of nanocrystals by precipitation of Rochelle salt/water solutions in ethanol (anti-solvent method) under the influence of a [...] Read more.
A straightforward and inexpensive electrophoretic method for obtaining environment-friendly nanocrystalline piezo layers from Rochelle salt (RS) is presented here. The electrophoretic deposition process includes the formation of nanocrystals by precipitation of Rochelle salt/water solutions in ethanol (anti-solvent method) under the influence of a high electric field. A nanoporous anodic aluminum oxide membrane is used to separate the electrochemical cell into two chambers. The composition of the RS:H2O:EtOH mixture and the spatial separation of the process of precipitation from electrophoretic deposition allow control of the nanocrystal size and the uniformity of the layer. The reaction kinetics, the morphology, and the piezo response to the resulting layers are all investigated. The best samples were obtained at RS:H2O:EtOH ratio 1:22.5:37.5. Under these conditions, the nanocrystals are preferentially oriented on the aluminum substrate and form a dense and homogeneous layer. Although the obtained structure is polycrystalline, the resulting piezo effect is 1120 pC/N, which is comparable to inorganic monocrystals and piezoceramics. This allows the use of electrophoretically deposited polycrystalline piezo layers in applications such as energy harvesting. Full article
(This article belongs to the Section Surface Engineering for Energy Harvesting, Conversion, and Storage)
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33 pages, 8498 KB  
Review
Recent Advances in the Plasma-Assisted Synthesis of Silicon-Based Thin Films and Nanostructures
by Pietro Mandracci and Paola Rivolo
Coatings 2023, 13(6), 1075; https://doi.org/10.3390/coatings13061075 - 10 Jun 2023
Cited by 11 | Viewed by 5836
Abstract
Silicon-based thin films and nanostructures are of paramount importance in a wide range of applications, including microelectronics, photovoltaics, large area sensors, and biomedicine. The wide accessibility of silicon and its relatively low cost have driven a continuous improvement of technology based on this [...] Read more.
Silicon-based thin films and nanostructures are of paramount importance in a wide range of applications, including microelectronics, photovoltaics, large area sensors, and biomedicine. The wide accessibility of silicon and its relatively low cost have driven a continuous improvement of technology based on this element. Plasma technology has been widely used for the synthesis of coatings and nanostructures based on silicon. Moreover, it has made a fundamental contribution to continuous improvement of the physicochemical properties of silicon-based materials and allows the synthesis of nanometric structures with well-defined shapes and morphologies. In this work, we have reviewed the most interesting developments in plasma-assisted processes for the synthesis of Si-based materials, both inorganic and organic, in the last five years. Special attention has been paid to new techniques, or modifications of already-existing ones, that open up new possibilities for the synthesis of materials with new properties, as well as nanostructures with novel characteristics. Full article
(This article belongs to the Special Issue Recent Advances in Silicon-Based Amorphous and Nanostructured Coatings)
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16 pages, 3643 KB  
Article
Evaluation of the Mechanical and Corrosion Behavior of Twin Wire Arc Sprayed Ni-Al Coatings with Different Al and Mo Content
by Jaehui Bang and Eunkyung Lee
Coatings 2023, 13(6), 1069; https://doi.org/10.3390/coatings13061069 - 9 Jun 2023
Cited by 6 | Viewed by 2259
Abstract
In this study, the surface properties of marine structures were improved by applying a twin wire arc spray process to high-strength low alloys. The effect of Al and Mo contents in Ni-Al coatings on their mechanical and corrosion behaviors was analyzed using hardness [...] Read more.
In this study, the surface properties of marine structures were improved by applying a twin wire arc spray process to high-strength low alloys. The effect of Al and Mo contents in Ni-Al coatings on their mechanical and corrosion behaviors was analyzed using hardness tests, electrochemical experiments, and immersion tests. The increase in Al content resulted in the formation of oxides and intermetallic compounds, leading to a significant improvement in the mechanical properties by approximately 222 HV. Despite a fine galvanic phenomenon causing a decrease in corrosion resistance by up to 8.91%, a higher Al content demonstrated the highest corrosion resistance after high-temperature exposure, with an enhancement of approximately 20.9%, attributed to the formation of an oxide film generated by intermetallic phase transformation. However, the mechanical properties experienced a reduction of 134.3 HV. This study demonstrated a correlation between the microstructure of the coating layers that form passivation films and their respective mechanical and corrosion properties. It also revealed that the content of Al and Mo significantly affects the mechanical and corrosion behavior of Ni-Al coatings. Full article
(This article belongs to the Special Issue Corrosion Resistance, Mechanical Properties and Characterization of Metallic Materials and Coatings)
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10 pages, 4936 KB  
Article
Effect of the Working Pressure and Oxygen Gas Flow Rate on the Fabrication of Single-Phase Ag2O Thin Films
by Jiyoon Choi, Jiha Seong, Sangbin Park, Hyungmin Kim, Sangmo Kim, Kyung Hwan Kim and Jeongsoo Hong
Coatings 2023, 13(6), 1061; https://doi.org/10.3390/coatings13061061 - 7 Jun 2023
Viewed by 2384
Abstract
Ag2O thin films have been applied in various devices, such as photodetectors, photocatalysts, and gas sensors, because of their excellent thermal stability, strong electrical properties, and stable structures. However, because various phases of silver oxide exist, the fabrication of single-phase Ag [...] Read more.
Ag2O thin films have been applied in various devices, such as photodetectors, photocatalysts, and gas sensors, because of their excellent thermal stability, strong electrical properties, and stable structures. However, because various phases of silver oxide exist, the fabrication of single-phase Ag2O thin films using a general deposition system is difficult. In this study, Ag2O thin films were deposited on glass substrates at different working pressures and O2 gas flow rates using a facing-target sputtering (FTS) system. After optimizing the working pressure and O2 gas flow rate, the Ag2O thin films were post-annealed at different temperatures ranging from 100 to 400 °C to improve their crystallographic properties. The X-ray diffraction patterns of the as-fabricated Ag2O thin films indicated the presence of a single phase of Ag2O, and the ultraviolet–visible (UV–vis) spectral analysis indicated transmittance of 65% in the visible light region. The optimum working pressure and O2 gas flow rate were determined to be 4 mTorr and 3.4 sccm, respectively. Finally, the effect of the post-annealing temperature on the thin film was investigated; the Ag2O peak had high intensity at 300 °C, suggesting this as the optimum post-annealing temperature. Full article
(This article belongs to the Special Issue Optical Thin Film and Photovoltaic (PV) Related Technologies, Volume II)
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18 pages, 5917 KB  
Article
Effects of Wet and Dry Treatments on Surface Functional Groups and Mechanical Properties of Flax Fiber Composites
by Ghane Moradkhani, Jacopo Profili, Mathieu Robert, Gaétan Laroche and Saïd Elkoun
Coatings 2023, 13(6), 1036; https://doi.org/10.3390/coatings13061036 - 2 Jun 2023
Cited by 18 | Viewed by 5441
Abstract
Flax fibers have found widespread use in eco-composite materials because of their remarkable mechanical properties compared to glass fibers. However, their low stability limits their use on a larger scale when employed in hot or humid environments. Therefore, the surfaces should be modified [...] Read more.
Flax fibers have found widespread use in eco-composite materials because of their remarkable mechanical properties compared to glass fibers. However, their low stability limits their use on a larger scale when employed in hot or humid environments. Therefore, the surfaces should be modified before the composite process to provide the best interfacial interactions and increase the dispersion of natural fibers. To tackle this problem, two kinds of modifications can be considered: wet and dry modifications. This research explores different methods to improve the adhesion between flax fibers and the poly lactic acid (PLA) polymer. Morphological and chemical modifications in the presence of acetone, alkali (as a wet modification), and with air atmospheric pressure plasma (as a dry modification) are compared in this research. The results revealed that altering the chemical characteristics on the surface significantly changed the mechanical properties of the final composite. More specifically, the Fourier transform infrared spectroscopy (FTIR) data indicate that wax-related peaks (2850 and 2920 cm−1) were eliminated by both wet and dry treatments. Dynamic mechanical analysis (DMA) results also highlighted that a better bond between the flax fibers and the PLA matrix is obtained with the plasma modification. Full article
(This article belongs to the Special Issue Sustainable Coatings for Functional Textile and Packaging Materials)
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12 pages, 7543 KB  
Article
Refined Grain Enhancing Lithium-Ion Diffusion of LiFePO4 via Air Oxidation
by Xinjie Shen, Zijun Qin, Peipei He, Xugang Ren, Yunjiao Li, Feixiang Wu, Yi Cheng and Zhenjiang He
Coatings 2023, 13(6), 1038; https://doi.org/10.3390/coatings13061038 - 2 Jun 2023
Cited by 5 | Viewed by 2923
Abstract
LiFePO4 is a type of cathode material with good safety and long service life. However, the problems of the low Li ion diffusion rate and low electron conductivity limit the application of LiFePO4 in the field of electric vehicles. In this [...] Read more.
LiFePO4 is a type of cathode material with good safety and long service life. However, the problems of the low Li ion diffusion rate and low electron conductivity limit the application of LiFePO4 in the field of electric vehicles. In this paper, FePO4 with different grain sizes was prepared via the air oxidation precipitation method and then sintered to prepare LiFePO4. The refined grain can shorten the diffusion distance of Li+, accelerate the diffusion of Li+, and improve the diffusion coefficient of Li+. The results show that LiFePO4 with a smaller grain size has better electrochemical performance. The discharge capacity of the first cycle is 151.3 mAh g−1 at 1 C, and the capacity retention rate is 95.04% after 230 cycles. Its rate performance is more outstanding, not only at 0.2 C, where the discharge capacity is as high as 155 mAh g−1, but also at 10 C, the capacity fade is less, and it can still reach 131 mAh g−1. The air oxidation precipitation method reduces the production cost, shortens the production process, and prepares FePO4 with small grains, which provides a reference for further improving the properties of precursors and LiFePO4. Full article
(This article belongs to the Section Surface Engineering for Energy Harvesting, Conversion, and Storage)
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12 pages, 6196 KB  
Article
Permeability of Skin-Mimicking Cell Coatings by Polymers of Complex Architecture Based on Polyoxazolines
by Gia Storti, Giulia Romano, Kristen Gilmore, Nicholas Sadowski, Andrii Tiiara, Igor Luzinov and Alexander Sidorenko
Coatings 2023, 13(6), 1007; https://doi.org/10.3390/coatings13061007 - 29 May 2023
Cited by 2 | Viewed by 2795
Abstract
In the scope of drug delivery, the transdermal route is desirable because it provides attainable therapeutic concentrations and has minimal systemic side effects. To make the skin a feasible route for the delivery of therapeutic agents, the biggest challenge is overcoming its natural [...] Read more.
In the scope of drug delivery, the transdermal route is desirable because it provides attainable therapeutic concentrations and has minimal systemic side effects. To make the skin a feasible route for the delivery of therapeutic agents, the biggest challenge is overcoming its natural coating. In this paper, we investigate the effect of the architectures (homopolymer vs. block copolymer vs. hybrid block–graft copolymer) of several amphiphilic polymeric derivatives of poly(2-oxazoline) on skin permeability. The block copolymers are composed of a hydrophobic poly(2-oxazoline) block and a hydrophilic PEG block. The hybrid block–graft copolymers are obtained by grafting hydrophobic side chains of polycaprolactone to a poly(2-oxazoline) backbone. We used the commercially available EpiDerm™ by MatTek, composed of human epidermal cells, as a model of human skin. Two parameters of skin permeation are reported: penetration rate and lag time. We hypothesize that the skin permeation characteristics correlate with the critical micelle concentration and particle size of the studied polymers, while both parameters are a function of the complex architectures of the presented macromolecular constructs. While homopolymer poly(2-oxazolines) show the least permeation, the block copolymers demonstrate partial permeation. The hybrid block–graft copolymers exhibited full penetration through the model skin samples. Full article
(This article belongs to the Special Issue Toward Sustainability through Bio-Based Materials at the Interfaces with Living Systems)
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13 pages, 3344 KB  
Article
Complex Bioactive Chitosan–Bioglass Coatings on a New Advanced TiTaZrAg Medium–High-Entropy Alloy
by Andrei Bogdan Stoian, Radu Nartita, Georgeta Totea, Daniela Ionita and Cristian Burnei
Coatings 2023, 13(5), 971; https://doi.org/10.3390/coatings13050971 - 22 May 2023
Cited by 8 | Viewed by 2311
Abstract
High-entropy alloys (HEAs), also known as multicomponent or multi-principal element alloys (MPEAs), differ from traditional alloys, which are usually based only on one principal element, in that they are usually fabricated from five or more elements in large percentages related to each other, [...] Read more.
High-entropy alloys (HEAs), also known as multicomponent or multi-principal element alloys (MPEAs), differ from traditional alloys, which are usually based only on one principal element, in that they are usually fabricated from five or more elements in large percentages related to each other, in the range of 5%–35%. Despite the usually outstanding characteristics of HEAs, based on a properly selected design, many such alloys are coated with advanced composites after their elaboration to further improve their qualities. In this study, 73Ti-20Zr-5Ta-2Ag samples were covered with chitosan and a mixture of chitosan, bioglass, and ZnO particles to improve the materials’ antibacterial properties. A variety of methods, including scanning electron microscopy, atomic force microscopy, and mechanical and electrochemical determinations, has permitted a quantified comparison between the coated and uncoated surfaces of this medium–high-entropy alloy. The materials’ properties were enhanced by the complex coating, giving the alloys not only high antibacterial activity, but also good corrosion protection. Full article
(This article belongs to the Special Issue New Strategies and Recent Advances in Investigations of Micro- and Nano-Coatings for Technological and Biomedical Applications)
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18 pages, 13890 KB  
Article
Aluminium-Based Dissimilar Alloys Surface Composites Reinforced with Functional Microparticles Produced by Upward Friction Stir Processing
by Filipe Moreira, Pedro M. Ferreira, Rui J. C. Silva, Telmo G. Santos and Catarina Vidal
Coatings 2023, 13(5), 962; https://doi.org/10.3390/coatings13050962 - 21 May 2023
Cited by 12 | Viewed by 3575
Abstract
Surface metal matrix composites offer an excellent solution for applications where surface properties play a crucial role in components’ performance and durability, such as greater corrosion resistance, better wear resistance, and high formability. Solid-state processing techniques, such as friction surfacing and friction stir [...] Read more.
Surface metal matrix composites offer an excellent solution for applications where surface properties play a crucial role in components’ performance and durability, such as greater corrosion resistance, better wear resistance, and high formability. Solid-state processing techniques, such as friction surfacing and friction stir welding/processing, offer several advantages over conventional liquid-phase processing methods. This research investigated the feasibility of producing surface composites of aluminium-based dissimilar alloys reinforced with functional microparticles through experimental validation, determined the process parameters that resulted in a more homogeneous distribution of the particles in the surface composites, and enhanced the understanding of Upward Friction Stir Processing (UFSP) technology. The production of aluminium-based dissimilar alloys (AA 7075-T651 and AA 6082-T651) surface composites reinforced with SiC particles was studied, and it was concluded that the macrography and micrography analyses, scanning electron microscopy (SEM) analysis, microhardness measurements, and eddy currents technique reveal an extensive and homogeneous incorporation of SiC particles. In the stirred zone, a decrease of approximately 20 HV 0.5 in hardness was observed compared to the base material. This reduction is attributed to the weakening effect caused by low-temperature annealing during UFSP, which reduces the strengthening effect of the T651 heat treatment. Additionally, the presence of particles did not affect the surface composite hardness in the stirred zone. Furthermore, despite the presence of significant internal defects, SEM analyses revealed evidence of the lower alloy merging with the upper zone, indicating that the lower plate had a role beyond being merely sacrificial. Therefore, the production of bimetallic composites through UFSP may offer advantages over composites produced from a monometallic matrix. The results of the eddy currents testing and microhardness measurements support this finding and are consistent with the SEM/EDS analyses. Full article
(This article belongs to the Special Issue Surface Engineering Treatments and Innovative Coatings for Additive Manufacturing Materials)
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13 pages, 5486 KB  
Article
Fabrication and Characterization of Ti/TiC Composite Layers by an Electron-Beam Surface Modification
by Stefan Valkov, Daniela Nedeva, Vladimir Dunchev, Fatme Padikova, Maria Ormanova, Borislav Stoyanov and Nikolay Nedyalkov
Coatings 2023, 13(5), 951; https://doi.org/10.3390/coatings13050951 - 19 May 2023
Cited by 3 | Viewed by 3379
Abstract
In this study, the possibilities for modification and improvement of the surface structure and properties of titanium substrates by a formation of composite Ti/TiC layers are presented. The layers were fabricated by a two-step electron-beam surface modification technique. The first step consists of [...] Read more.
In this study, the possibilities for modification and improvement of the surface structure and properties of titanium substrates by a formation of composite Ti/TiC layers are presented. The layers were fabricated by a two-step electron-beam surface modification technique. The first step consists of injection of C powder within the pure Ti substrates by electron-beam alloying technology. The second step is the refinement and homogenization of the microstructure by the electron-beam remelting procedure. During the remelting, the speed of the motion of the samples was varied, and two (most representative) velocities were chosen: 5 and 15 mm/s. Considering both speeds of the motion of the specimens, a composite structure in the form of fine TiC particles distributed within the base titanium matrix was formed. The remelting speed of 5 mm/s led to the formation of a much thicker composite layer, where the TiC particles were significantly more homogeneously distributed. The results obtained for the Vickers microhardness exhibit a significant increase in the value in the mentioned mechanical characteristic in comparison with the base Ti substrate. In the case of the lower speed of the motion of the specimen during the remelting procedure, the microhardness is 510 HV, or about 2.5 times higher than that of the titanium substrate. The application of a higher speed of the specimen motion leads to a decrease in the microhardness in comparison with the case of lower velocity. However, it is still much higher than that of the base Ti material. The mean microhardness of the sample obtained by the remelting speed of motion of 15 mm/s is 360 HV, or it is 1.8 times higher than that of the base material. Full article
(This article belongs to the Special Issue Surface Modification for Improving the Performance of Engineering Components)
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15 pages, 8013 KB  
Article
Facile Fabrication of Robust and Fluorine-Free Superhydrophobic PDMS/STA-Coated Cotton Fabric for Highly Efficient Oil-Water Separation
by Daibin Tang and Enzhou Liu
Coatings 2023, 13(5), 954; https://doi.org/10.3390/coatings13050954 - 19 May 2023
Cited by 13 | Viewed by 3464
Abstract
Oil–water separation using special wettability materials has received much attention due to its low energy consumption and high separation efficiency. Herein, a fluorine-free superhydrophobic cotton fabric (PDMS/STA-coated cotton fabric) was successfully prepared by a simple impregnation method using hydroxyl-capped polydimethylsiloxane (PDMS-OH), tetraethoxysilane (TEOS), [...] Read more.
Oil–water separation using special wettability materials has received much attention due to its low energy consumption and high separation efficiency. Herein, a fluorine-free superhydrophobic cotton fabric (PDMS/STA-coated cotton fabric) was successfully prepared by a simple impregnation method using hydroxyl-capped polydimethylsiloxane (PDMS-OH), tetraethoxysilane (TEOS), and stearic acid (STA) as precursors. The investigation found that the cross-linking reactions between the hydroxyl groups of PDMS-OH and hydrolyzed TEOS enabled a strong interaction between PDMS-OH and cotton fabric. Furthermore, a suitable roughness surface of coated cotton fabric was established by introducing STA due to its long chain structure. The contact angle of this composite can reach 158.7° under optimal conditions due to its low surface energy and desired roughness. The oil/water separation efficiency of PDMS/STA-coated cotton fabric is higher than 90% even after 10 cycles of oil–water separation, and the oil flux can reach 11862.42 L m−2 h−1. In addition, PDMS/STA-coated cotton fabric exhibits excellent chemical stability and durability under extreme conditions such as strong acid (HCl, pH = 1~2) and alkali (NaOH, pH = 13~14), and the hydrophobicity of PDMS/STA-coated cotton fabric was decreased to 147° after 300 cycles of abrasion testing. Full article
(This article belongs to the Special Issue Sustainable Coatings for Functional Textile and Packaging Materials)
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26 pages, 11891 KB  
Article
The Electrodeposition of Derivatives of Pyrrole and Thiophene on Brass Alloy in the Presence of Dodecane-1-Sulfonic Acid Sodium Salt in Acidic Medium and Its Anti-Corrosive Properties
by Florina Branzoi and Simona Petrescu
Coatings 2023, 13(5), 953; https://doi.org/10.3390/coatings13050953 - 19 May 2023
Cited by 4 | Viewed by 2133
Abstract
In this paper, potentiostatic and galvanostatic deposition (electrochemical deposition) processes have been used for the obtained of a new composite polymer: N-methylpyrrole-sodium 1-dodecanesulfonate/poly 2-methylthiophene (PNMPY-1SSD/P2MT) coatings over brass electrode for corrosion protection. The sodium 1-dodecanesulfonate as a dopant ion employed in the electropolymerization [...] Read more.
In this paper, potentiostatic and galvanostatic deposition (electrochemical deposition) processes have been used for the obtained of a new composite polymer: N-methylpyrrole-sodium 1-dodecanesulfonate/poly 2-methylthiophene (PNMPY-1SSD/P2MT) coatings over brass electrode for corrosion protection. The sodium 1-dodecanesulfonate as a dopant ion employed in the electropolymerization procedure can have a meaningful effect on the anti-corrosion protection of the composite polymeric film by stopping the penetration of corrosive ions. The composite coatings have been characterized by cyclic voltammetry, Fourier transform infrared (FT-IR) spectroscopy, and scanning electron microscopy (SEM) procedures. The anti-corrosion performance of PNMPY-1SSD/P2MT coated brass has been investigated by potentiostatic and potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) practices in 0.5 M H2SO4 medium. The corrosion assessment of PNMPY-1SSD/P2MT coated brass was noticed to be ~9 times diminished than of uncoated brass, and the efficiency of these protective coatings of this coating is above 90%. The highest effectiveness is realized by the electrochemical deposition of PNMPY-1SSD/P2MT obtained at 1.1 V and 1.4 V potential applied and at 0.5 mA/cm2 and 1 mA/cm2 current densities applied in molar ratio 5:3. The outcomes of the corrosion tests denoted that PNMPY-1SSD/P2MT coatings assure good anti-corrosion protection of brass in corrosive media. Full article
(This article belongs to the Special Issue New Developments of Protective Coatings, Organic Polymers, and Surface Analysis)
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17 pages, 2552 KB  
Article
Plasma-Deposited Organosilicon Hydrophobic Coatings on Cellulosic Materials for Wet Packaging Applications
by Jacopo Profili, Sara Babaei, Mariam Al Rashidi, Annie Dorris, Siavash Asadollahi, Andranik Sarkissian and Luc Stafford
Coatings 2023, 13(5), 924; https://doi.org/10.3390/coatings13050924 - 15 May 2023
Cited by 9 | Viewed by 3276
Abstract
Non-toxic organosilicon coatings with hydrophobic properties were deposited on Kraft paper films using atmospheric-pressure dielectric barrier discharge. In order to assess the applicability of the plasma-deposited coating in the food packaging industry, its stability in different liquids (i.e., food simulants) was studied. Chemical [...] Read more.
Non-toxic organosilicon coatings with hydrophobic properties were deposited on Kraft paper films using atmospheric-pressure dielectric barrier discharge. In order to assess the applicability of the plasma-deposited coating in the food packaging industry, its stability in different liquids (i.e., food simulants) was studied. Chemical analyses reveal that the food simulants, namely, de-ionized water, acetic acid, ethanol, and heptane, do not significantly alter the chemical composition or the hydrophobicity of the coatings. Based on inductively coupled plasma-optical emission spectroscopy analyses, the amount of Si released from the plasma-deposited coating is less than that typically detected in tap water. Overall, the results obtained suggest that hydrophobic plasma-deposited organosilicon coatings have great potential for use in food and wet packaging applications, especially considering their environmentally friendly character. Full article
(This article belongs to the Special Issue Recent Advances in Functional Biopolymers for Food Packaging and Biomedical Applications)
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16 pages, 5107 KB  
Article
Efficacy Evaluation of Cu- and Ag-Based Antibacterial Treatments on Polypropylene Fabric and Comparison with Commercial Products
by Nunzia Gallo, Giorgia Natalia Iaconisi, Mauro Pollini, Federica Paladini, Sudipto Pal, Concetta Nobile, Loredana Capobianco, Antonio Licciulli, Giovanna Giuliana Buonocore, Antonella Mansi, Luca Salvatore and Alessandro Sannino
Coatings 2023, 13(5), 919; https://doi.org/10.3390/coatings13050919 - 14 May 2023
Cited by 6 | Viewed by 3152
Abstract
Filter masks are disposable devices intended to be worn in order to reduce exposure to potentially harmful foreign agents of 0.1–10.0 microns. However, to perform their function correctly, these devices should be replaced after a few hours of use. Because of this, billions [...] Read more.
Filter masks are disposable devices intended to be worn in order to reduce exposure to potentially harmful foreign agents of 0.1–10.0 microns. However, to perform their function correctly, these devices should be replaced after a few hours of use. Because of this, billions of non-biodegradable face masks are globally discarded every month (3 million/minute). The frequent renewal of masks, together with the strong environmental impact of non-biodegradable plastic-based mask materials, highlights the need to find a solution to this emerging ecological problem. One way to reduce the environmental impact of masks, decrease their turnover, and, at the same time, increase their safety level is to make them able to inhibit pathogen proliferation and vitality by adding antibacterial materials such as silver, copper, zinc, and graphene. Among these, silver and copper are the most widely used. In this study, with the aim of improving commercial devices’ efficacy and eco-sustainability, Ag-based and Cu-based antibacterial treatments were performed and characterized from morphological, compositional, chemical–physical, and microbiological points of view over time and compared with the antibacterial treatments of selected commercial products. The results demonstrated the good distribution of silver and copper particles onto the surface of the masks, along with almost 100% antibacterial capabilities of the coatings against both Gram-positive and Gram-negative bacteria, which were still confirmed even after several washing cycles, thus indicating the good potential of the developed prototypes for mask application. Full article
(This article belongs to the Special Issue Advances in Antibacterial Coatings: From Materials to Applications)
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16 pages, 4588 KB  
Article
Al2O3 Ceramic/Nanocellulose-Coated Non-Woven Separator for Lithium-Metal Batteries
by Dong-Min Shin, Hyunsu Son, Ko Un Park, Junyoung Choi, Jungdon Suk, Eun Seck Kang, Dong-Won Kim and Do Youb Kim
Coatings 2023, 13(5), 916; https://doi.org/10.3390/coatings13050916 - 13 May 2023
Cited by 8 | Viewed by 5796
Abstract
Separators play an essential role in lithium (Li)-based secondary batteries by preventing direct contact between the two electrodes and providing conduction pathways for Li-ions in the battery cells. However, conventional polyolefin separators exhibit insufficient electrolyte wettability and thermal stability, and in particular, they [...] Read more.
Separators play an essential role in lithium (Li)-based secondary batteries by preventing direct contact between the two electrodes and providing conduction pathways for Li-ions in the battery cells. However, conventional polyolefin separators exhibit insufficient electrolyte wettability and thermal stability, and in particular, they are vulnerable to Li dendritic growth, which is a significant weakness in Li-metal batteries (LMBs). To improve the safety and electrochemical performance of LMBs, Al2O3 nanoparticles and nanocellulose (NC)-coated non-woven poly(vinylidene fluoride)/polyacrylonitrile separators were fabricated using a simple, water-based blade coating method. The Al2O3/NC-coated separator possessed a reasonably porous structure and a significant number of hydroxyl groups (-OH), which enhanced electrolyte uptake (394.8%) and ionic conductivity (1.493 mS/cm). The coated separator also exhibited reduced thermal shrinkage and alleviated uncontrollable Li dendritic growth compared with a bare separator. Consequently, Li-metal battery cells with a LiNi0.8Co0.1Mn0.1O2 cathode and an Al2O3/NC-coated separator using either liquid or solid polymer electrolytes exhibited improved rate capability, cycle stability, and safety compared with a cell with a bare separator. The present study demonstrates that combining appropriate materials in coatings on separator surfaces can enhance the safety and electrochemical performance of LMBs. Full article
(This article belongs to the Special Issue Advanced Materials for Energy Storage and Conversion)
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17 pages, 9111 KB  
Article
Atmospheric Pressure Plasma Treatment of Magnesium Alloy for Enhanced Coating Adhesion and Corrosion Resistance
by Gyoung Gug Jang, Jiheon Jun, Sinchul Yeom, Mina Yoon, Yi Feng Su, John Wade, Michael S. Stephens and Jong K. Keum
Coatings 2023, 13(5), 897; https://doi.org/10.3390/coatings13050897 - 10 May 2023
Cited by 11 | Viewed by 4068
Abstract
Atmospheric pressure plasma (AP) treatment, using an open-air jet of ionized CO2, N2, or air, was applied to AZ91D Mg alloy surfaces to investigate its effects on primer coating adhesion and corrosion resistance. The CO2 and air AP treatments [...] Read more.
Atmospheric pressure plasma (AP) treatment, using an open-air jet of ionized CO2, N2, or air, was applied to AZ91D Mg alloy surfaces to investigate its effects on primer coating adhesion and corrosion resistance. The CO2 and air AP treatments formed an O- and C-rich surface layer (Mg-O-C) consisting of agglomerated nanoparticles and pits with a depth of a few microns and increasing the surface roughness by 6–8 times compared with the reference 600 grit-finished surface. Then, three commercial primers, zinc phosphate (ZnP), chromate-containing epoxy, and MIL23377, were applied on the treated surfaces to evaluate the corrosion resistance associated with the coating adhesion. Microscopic analysis demonstrated stronger interlocking between the primer layer and the nano-/microrough Mg-O-C surface compared to the untreated (600 grit-finished) surfaces, indicating improved coating adhesion and corrosion resistance. Crosscut tests of the MIL23377 primer on the CO2 and air AP-treated surfaces showed the highest level of adhesion, ASTM class 5B. Salt spray corrosion tests showed that after 8 days of exposure, the primer coatings on air AP-treated surfaces had corrosion areas that were more than four times smaller than that of the 600 grit-finished surface. The N2 AP treatment showed similar adhesion enhancement. The preliminary operation expenses for AP treatment using CO2, N2, and air were estimated at USD 30.62, USD 35.45, and USD 29.75 (from an air cylinder)/USD 0.66 (from an air compressor) per m2, respectively. Full article
(This article belongs to the Section Plasma Coatings, Surfaces & Interfaces)
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18 pages, 4956 KB  
Article
Migration of TiO2 from PET/TiO2 Composite Films Used for Polymer-Laminated Steel Cans in Acidic Solution
by Jingying Cui, Jinyang Chen, Jie Gu, Xiaomin Hong, Menghan Hong, Zheying Wu and Yu Hu
Coatings 2023, 13(5), 887; https://doi.org/10.3390/coatings13050887 - 8 May 2023
Cited by 4 | Viewed by 2984
Abstract
Nano-TiO2 is widely used as a commercial food contact material (FCM), which poses potential risks to food. Therefore, the migration of TiO2 is crucial for the safety of FCM. Since PET/TiO2 composite films are food contact layers used for producing [...] Read more.
Nano-TiO2 is widely used as a commercial food contact material (FCM), which poses potential risks to food. Therefore, the migration of TiO2 is crucial for the safety of FCM. Since PET/TiO2 composite films are food contact layers used for producing polymer-laminated steel cans and the majority of beverages contained in cans are acidic, it is necessary to study the migration of TiO2 from PET/TiO2 composite films in acidic solutions. The migration of TiO2 in 4% (v/v) acetic acid was studied through the ICP-OES method. The corrosion process that occurred during the migration process was studied using electrochemical impedance spectroscopy (EIS). The morphology of Ti nanoparticles and films was measured by SEM, TEM, and dynamic light scattering (DLS) techniques. The results indicate that, at a temperature of 60 °C, the maximum migration concentration of TiO2 is 0.32 mg/kg. The TiO2 particles released during the migration process are unstable and tend to aggregate in the simulated material, with most of the Ti being present in the form of particles. Therefore, the migration of TiO2 does not follow the Fick law of diffusion but rather conforms to the Weibull model based on the non-Fick law of diffusion. Full article
(This article belongs to the Special Issue New Developments of Protective Coatings, Organic Polymers, and Surface Analysis)
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16 pages, 5640 KB  
Article
Comparison of Tribological Characteristics of AA2024 Coated by Plasma Electrolytic Oxidation (PEO) Sealed by Different sol–gel Layers
by Hafiza Ayesha Khalid, Sajjad Akbarzadeh, Yoann Paint, Véronique Vitry and Marie-Georges Olivier
Coatings 2023, 13(5), 871; https://doi.org/10.3390/coatings13050871 - 5 May 2023
Cited by 5 | Viewed by 3172
Abstract
The application of sol–gel on plasma electrolytic oxidation (PEO) coatings can increase wear resistance by sealing the surface defects such as pores and cracks in the outer layer of the PEO layer and strengthen the coating. Four different sol–gel formulations based on precursors—(3-glycidyloxypropyl)trimethoxysilane [...] Read more.
The application of sol–gel on plasma electrolytic oxidation (PEO) coatings can increase wear resistance by sealing the surface defects such as pores and cracks in the outer layer of the PEO layer and strengthen the coating. Four different sol–gel formulations based on precursors—(3-glycidyloxypropyl)trimethoxysilane (GPTMS), methyltriethoxysilane (MTES), methacryloxypropyltrimethoxysilane (MAPTMS), (3-aminopropyl)triethoxysilane (APTES), and zirconium(IV) propoxide (ZTP) along with tetraethoxysilane (TEOS)—were used to seal PEO pores, and the samples were tested tribologically. A sliding reciprocating tribometer was used to carry out a wear test with an alumina ball as the counter body in two different conditions: (a) 2.5 N load for 20 min, and (b) 3 N load for 40 min. The coefficient of friction and wear rate as volume loss per unit sliding length were obtained for all sol–gel-sealed specimens and unsealed PEO-coated and bare AA2024 substrate. 3D mechanical profilometer surface scans were used to compare the depth of wear traces. The elemental color mapping using SEM and EDS revealed that silicon remains present in the wear tracks of PEO coatings sealed with sol–gel layers containing GPTMS (PSG) and ZTP (PSG-ZT). GPTMS (PSG) was able to fill the pores of the PEO layer efficiently due to its cross-linked network. Moreover, sol–gel containing ZTP (PSG-ZT) was deposited as a thick layer on top of the PEO layer which provided good lubrication and resistance to wear. However, other sol–gel formulations (PSG-MT and PSG-AP) were worn out during tests at a higher load (3 N). The most stable friction coefficient (COF) and specific wear rates were observed with sol–gels with GPTMS and ZTP. Full article
(This article belongs to the Special Issue Plasma Electrolytic Oxidation (PEO) Coatings, 2nd Edition)
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16 pages, 749 KB  
Article
Optical Characterization of Inhomogeneous Thin Films Deposited onto Non-Absorbing Substrates
by Jan Dvořák, Jiří Vohánka, Vilma Buršíková, Daniel Franta and Ivan Ohlídal
Coatings 2023, 13(5), 873; https://doi.org/10.3390/coatings13050873 - 5 May 2023
Cited by 2 | Viewed by 3239
Abstract
In this study, a novel approach for characterizing the optical properties of inhomogeneous thin films is presented, with a particular focus on samples exhibiting absorption in some part of the measured spectral range. Conventional methods of measuring the samples only from the film [...] Read more.
In this study, a novel approach for characterizing the optical properties of inhomogeneous thin films is presented, with a particular focus on samples exhibiting absorption in some part of the measured spectral range. Conventional methods of measuring the samples only from the film side can be limited by incomplete information at the lower boundary of the film, leading to potentially unreliable results. To address this issue, depositing the thin films onto non-absorbing substrates to enable measurements from both sides of the sample is proposed. To demonstrate the efficacy of this approach, a combination of variable-angle spectroscopic ellipsometry and spectrophotometry at near-normal incidence was employed to optically characterize three inhomogeneous polymer-like thin films. The spectral dependencies of the optical constants were modeled using the Kramers–Kronig consistent model. It was found that it is necessary to consider thin, weakly absorbing transition layers between the films and the substrates. The obtained results show excellent agreement between the fits and the measured data, providing validation of the structural and dispersion models, as well as the overall characterization procedure. The proposed approach offers a method for optically characterizing a diverse range of inhomogeneous thin films, providing more reliable results when compared to traditional one-sided measurements. Full article
(This article belongs to the Special Issue Recent Advancement in Thin Film Deposition, Characterization, and Surface Engineering (Second Volume))
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19 pages, 17846 KB  
Article
Effect of Scanning Strategies on Anisotropy of YCF104 Alloy Mechanical Properties by Laser Cladding
by Yu Zhao, Wenkai Shi, Liaoyuan Chen, Wenzheng Wu and Tianbiao Yu
Coatings 2023, 13(5), 842; https://doi.org/10.3390/coatings13050842 - 28 Apr 2023
Cited by 3 | Viewed by 2358
Abstract
YCF104 alloy specimens were fabricated by laser cladding on #45 steel following three different scanning strategies. The microstructure, phase composition, friction coefficient, microhardness, tensile strength, and compressive strength of the specimens formed by different scanning strategies were investigated. The results show that the [...] Read more.
YCF104 alloy specimens were fabricated by laser cladding on #45 steel following three different scanning strategies. The microstructure, phase composition, friction coefficient, microhardness, tensile strength, and compressive strength of the specimens formed by different scanning strategies were investigated. The results show that the uniformity of laser remelting of solidified layers improved the uniformity of microstructure and refined the grains. The strengthening effect of the Fe–Cr/Mo solid solution was primarily responsible for the high strength. YCF104 cladding specimens exhibit brittle failure, and with the change of metallurgical bonding form in the overlap area, the compressive strength (the maximum value is 3235 MPa) and the tensile strength (specimen via strategy 3 is 527.44 MPa), there appears significant anisotropy. With the improvement of the uniformity of temperature distribution, the friction coefficient as well as the microhardness decreased when the GCr15 was used as the friction pair. The mechanical anisotropy of the coating is related to both the microstructure and metallurgical bonding strength in the overlap area. Full article
(This article belongs to the Special Issue Laser Cladding Coatings: Microstructure, Properties, and Applications)
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10 pages, 6646 KB  
Article
3D Multilayered Metamaterials with High Plasmonic Hotspot Density for Surface—Enhanced Raman Spectroscopy
by Jun Chen, Chai Zhang, Feng Tang, Xin Ye, Yubin Zhang, Jingjun Wu, Kaixuan Wang, Ning Zhang and Liming Yang
Coatings 2023, 13(5), 844; https://doi.org/10.3390/coatings13050844 - 28 Apr 2023
Viewed by 2027
Abstract
Three-dimensional (3D) plasmonic metamaterials have become a trend in the application of nanophotonic devices. In this paper, a convenient and inexpensive method for the design of 3D multilayer plasmonic metamaterials is constructed using a one-step self-shielded reactive-ion-etching process (OSRP) and a thermal evaporation [...] Read more.
Three-dimensional (3D) plasmonic metamaterials have become a trend in the application of nanophotonic devices. In this paper, a convenient and inexpensive method for the design of 3D multilayer plasmonic metamaterials is constructed using a one-step self-shielded reactive-ion-etching process (OSRP) and a thermal evaporation system, which provides an efficient and low-cost method for the preparation of surface-enhanced Raman spectroscopy (SERS) substrates. The near-field enhancement of the 3D plasmonic metamaterials provides highly efficient electromagnetic resonance, and highly sensitive and uniform SERS sensing capabilities. The SERS detection results of rhodamine B (Rh. B) and rhodamine 6G (R6G) on this substrate show that the detection limit could reach 10–13 mol/L, and the signal could give expression to excellent uniform stability. The results show that high sensitivity and high robustness SERS substrates can be prepared with high efficiency and low cost. Full article
(This article belongs to the Special Issue Micro-Nano Optics and Its Applications)
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17 pages, 8974 KB  
Article
Corrosion Evolution of Nickel Aluminum Bronze in Clean and Sulfide-Polluted Solutions
by Liu Yang and Yinghua Wei
Coatings 2023, 13(5), 846; https://doi.org/10.3390/coatings13050846 - 28 Apr 2023
Cited by 3 | Viewed by 3152
Abstract
Nickel aluminum bronze (NAB) alloys are reported to suffer accelerated local corrosion in sulfide-polluted seawater. In this work, the real-time in situ scanning vibrating electrode technique (SVET) was employed to monitor the evolution of the corrosion product film of a typical NAB alloy [...] Read more.
Nickel aluminum bronze (NAB) alloys are reported to suffer accelerated local corrosion in sulfide-polluted seawater. In this work, the real-time in situ scanning vibrating electrode technique (SVET) was employed to monitor the evolution of the corrosion product film of a typical NAB alloy immersed in the clean and sulfide-polluted 3.5% NaCl solutions. In the sulfide-free condition, the corrosion current peak surged at the individual point of the NAB surface and receded to calm in 2 h. In the presence of the sulfide, however, multiple active points on the measured metal surface released high corrosion current for a long time, indicating that intense corrosion had occurred. The corrosion mass loss was more than four times the former. Global electrochemical techniques, scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) were adopted to perform a comprehensive analysis of the composition of the corrosion product films. The results show that a dense layer of aluminum and cuprous oxide forms on the NAB surface in the sulfide-free solution, while a loose mixture of cuprous sulfide and cuprous oxide is detected in the sulfide-contaminated solution. This finding is believed to account for the observed distinction between the corrosion behavior of NAB in the two solutions. Full article
(This article belongs to the Section Corrosion, Wear and Erosion)
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17 pages, 11521 KB  
Article
Microstructure and Properties of Direct Laser-Deposited CeO2-Modified Cobalt-Based Composite Coatings
by Yan Liu, Hui Han, Tao Ding, Dengwen Hu, Zhenlin Zhang, Hang Lv and Hui Chen
Coatings 2023, 13(5), 834; https://doi.org/10.3390/coatings13050834 - 26 Apr 2023
Cited by 2 | Viewed by 2083
Abstract
The seawater circulation pump is a significant piece of equipment in coastal nuclear power plants that is susceptible to erosion and corrosion in the seawater. In this work, CeO2-modified cobalt-based composite coatings were prepared on the surface of martensitic stainless steel [...] Read more.
The seawater circulation pump is a significant piece of equipment in coastal nuclear power plants that is susceptible to erosion and corrosion in the seawater. In this work, CeO2-modified cobalt-based composite coatings were prepared on the surface of martensitic stainless steel by direct laser deposition. The effect of CeO2 on the phase composition, microstructure, microhardness, corrosion resistance, and erosion properties of the cobalt-based composite coatings was systematically investigated. While the addition of CeO2 did not affect the phase composition of the coatings that comprised γ-Co, γ-Ni, M7C3, and M23C6 (M = Cr, W, Fe) metallic carbides, the eutectic organization showed an obvious phenomenon of contiguous aggregation. Microscopic pores were found in the coatings with 2 wt.% CeO2, and the number of pores increased with the increase in CeO2 content. Despite the higher self-corrosion potential (−0.27668 V) of cobalt-based alloy coating compared to the substrate (−0.37019 V), indicating enhanced corrosion resistance, the difference in self-corrosion potential among coatings with varying CeO2 addition amounts is small (0.027 V), and the corrosion current densities are within one order of magnitude (10−8 A/cm2). These findings suggest that the addition of CeO2 has no significant impact on the coating’s corrosion resistance. Full article
(This article belongs to the Section Laser Coatings)
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24 pages, 3314 KB  
Article
Influence of Drop Viscosity and Surface Wettability on Impact Outcomes
by Ghokulla Haran Krishnan, Kevin Fletcher and Eric Loth
Coatings 2023, 13(5), 817; https://doi.org/10.3390/coatings13050817 - 23 Apr 2023
Cited by 10 | Viewed by 4968
Abstract
To understand the effects of liquid viscosity and surface wettability on the outcomes for a drop impacting perpendicularly on a dry, clean surface at a normal temperature and pressure, experiments were conducted for a wide variety of droplets and substrate surfaces. These experiments [...] Read more.
To understand the effects of liquid viscosity and surface wettability on the outcomes for a drop impacting perpendicularly on a dry, clean surface at a normal temperature and pressure, experiments were conducted for a wide variety of droplets and substrate surfaces. These experiments included a range of receding contact angles (from ~18° to ~150°) and liquid viscosities (from 1 cp to 45 cp); the broadest such combination is yet published. The surface wettabilities were quantitatively characterized using a new set of definitions: superphillic (θrec < 30°), phillic (30° < θrec < 90°), phobic (90° < θrec < 150°), and superphobic (θrec > 150°). Six different outcome regimes were found (including a new beaded deposition outcome) as a function of Ohnesorge number, Weber number, and the cosine of the receding contact angle. The beaded deposition is a hybrid of the well-known splash and deposition outcomes. The critical Weber number that separates the outcome boundaries was found to be significantly influenced by both the Ohnesorge numbers and the receding contact angle. In particular, there is a consistent reduction in the critical Weber number from superphilic to philic to neutral wettability conditions. Interestingly, this same decreasing trend line continues from neutral to phobic to superphobic conditions, but instead, it separates the regimes of deposition and bouncing. At higher Weber numbers, an additional boundary regime was found between splashing and bounce, which also decreased as the surface wettability decreased. This same type of trend was seen for several Ohnesorge numbers, indicating that wetting characterization should be based on the contact angles for the combination of the droplet liquid and the surface. In addition, a new regime map for droplet rebound on superphobic surfaces was obtained from the present and previous results indicating (for the first time) that the total rebound generally occurs for Weber numbers between 2.2 and 32 with Ohnesorge numbers less than 0.17. Additional studies are recommended to explore an even broader range of test conditions (especially intermediate wettability conditions), the separate influence of advancing and/or hysteresis contact angles, and to include the effects of the inclination angle, gas pressure, and heat transfer. Full article
(This article belongs to the Special Issue Liquid–Fluid Interfaces and Dynamics)
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18 pages, 8616 KB  
Article
Synthesis of CaCO3-Based Hyperdispersants and Their Application in Aqueous Coatings
by Jue Bai and Yu Li
Coatings 2023, 13(5), 819; https://doi.org/10.3390/coatings13050819 - 23 Apr 2023
Cited by 4 | Viewed by 3548
Abstract
As an essential pigment particle in white water-based coatings, light calcium carbonate (CaCO3) is difficult to disperse in water-based systems. The hard-to-disperse particles agglomerate, causing the viscosity of the coating to rise, which in turn affects the quality of the coating. [...] Read more.
As an essential pigment particle in white water-based coatings, light calcium carbonate (CaCO3) is difficult to disperse in water-based systems. The hard-to-disperse particles agglomerate, causing the viscosity of the coating to rise, which in turn affects the quality of the coating. Therefore, in order to obtain efficient dispersion, the hyperdispersant SSS–MPEGA–DMAEA (SMD) has been prepared in this study using sodium styrene sulfonate (SSS), polyethylene glycol monomethyl ether acrylate (MPEGA), and dimethylaminoethyl acrylate (DMAEA) as monomers through aqueous solution polymerization. Firstly, we utilized the central composite design method to conduct mathematical modeling of the monomer ratios so as to optimize the dispersion performance of the hyperdispersants. Secondly, the structural characteristics and molecular weight distribution of SMD were characterized by 1H NMR spectroscopy and GPC. Then, the effect of SMD on the dispersion of the CaCO3 slurry was investigated through particle size distribution and TEM measurements. Finally, we applied the SMD in aqueous white coatings and tested the surface properties of the paint film by SEM as well as the stability of the paint film. The results showed that SMD can significantly reduce the viscosity and particle size of the CaCO3 slurry. The waterborne coatings prepared by SMD had good storage stability and corrosion resistance, so the materials owned broad application prospects. Full article
(This article belongs to the Section Functional Polymer Coatings and Films)
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14 pages, 2288 KB  
Article
Linear and Nonlinear Optical Properties of Iridium Nanoparticles Grown via Atomic Layer Deposition
by Paul Schmitt, Pallabi Paul, Weiwei Li, Zilong Wang, Christin David, Navid Daryakar, Kevin Hanemann, Nadja Felde, Anne-Sophie Munser, Matthias F. Kling, Sven Schröder, Andreas Tünnermann and Adriana Szeghalmi
Coatings 2023, 13(4), 787; https://doi.org/10.3390/coatings13040787 - 18 Apr 2023
Cited by 9 | Viewed by 3959
Abstract
Nonlinear optical phenomena enable novel photonic and optoelectronic applications. Especially, metallic nanoparticles and thin films with nonlinear optical properties offer the potential for micro-optical system integration. For this purpose, new nonlinear materials need to be continuously identified, investigated, and utilized for nonlinear optical [...] Read more.
Nonlinear optical phenomena enable novel photonic and optoelectronic applications. Especially, metallic nanoparticles and thin films with nonlinear optical properties offer the potential for micro-optical system integration. For this purpose, new nonlinear materials need to be continuously identified, investigated, and utilized for nonlinear optical applications. While noble-metal nanoparticles, nanostructures, and thin films of silver and gold have been widely studied, iridium (Ir) nanoparticles and ultrathin films have not been investigated for nonlinear optical applications yet. Here, we present a combined theoretical and experimental study on the linear and nonlinear optical properties of iridium nanoparticles deposited via atomic layer deposition (ALD). Linear optical constants, such as the effective refractive index and extinction coefficient, were evaluated at different growth stages of nanoparticle formation. Both linear and nonlinear optical properties of these Ir ALD coatings were calculated theoretically using the Maxwell Garnett theory. The third-order susceptibility of iridium nanoparticle samples was experimentally investigated using the z-scan technique. According to the experiment, for an Ir ALD coating with 45 cycles resulting in iridium nanoparticles, the experimentally determined nonlinear third-order susceptibility is about χIr(3) = (2.4 − i2.1) × 10−17 m2/V2 at the fundamental wavelength of 700 nm. The theory fitted to the experimental results predicts a 5 × 106-fold increase around 230 nm. This strong increase is due to the proximity to the Mie resonance of iridium nanoparticles. Full article
(This article belongs to the Special Issue Optical Properties of Crystals and Thin Films)
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13 pages, 3371 KB  
Article
Bacterial Detection and Differentiation of Staphylococcus aureus and Escherichia coli Utilizing Long-Period Fiber Gratings Functionalized with Nanoporous Coated Structures
by Shuyue He, Jue Wang, Fan Yang, Tzu-Lan Chang, Ziyu Tang, Kai Liu, Shuli Liu, Fei Tian, Jun-Feng Liang, Henry Du and Yi Liu
Coatings 2023, 13(4), 778; https://doi.org/10.3390/coatings13040778 - 17 Apr 2023
Cited by 13 | Viewed by 3330
Abstract
A biosensor utilizing long-period fiber gratings (LPFG) functionalized with nanoporous coated structures was developed for the rapid detection of Staphylococcus aureus (S. aureus) bacteria. The nanoporous structure coatings on the LPFG surface facilitated specific adhesion and interaction with S. aureus, [...] Read more.
A biosensor utilizing long-period fiber gratings (LPFG) functionalized with nanoporous coated structures was developed for the rapid detection of Staphylococcus aureus (S. aureus) bacteria. The nanoporous structure coatings on the LPFG surface facilitated specific adhesion and interaction with S. aureus, resulting in an instantaneous shift in the resonance wavelength (RW) in the transmission spectrum of the LPFG. The LPFG with nanoporous polyelectrolyte coatings exhibited an approximately seven-fold RW shift compared to the bare LPFG under the optimal experiment conditions. By tracking the RW shifts, we were able to monitor the real-time S. aureus adhesion to study the interaction process in detail. The bacterial differentiation and S. aureus specificity of the method was confirmed through a series of studies using Escherichia coli (E. coli). This nanoporous structure-enabled LPFG-based biosensor scheme holds significant promise for rapid, reliable, and low-cost detection of S. aureus for biomedical applications. Full article
(This article belongs to the Special Issue New Advance in Nanoparticles, Fiber, and Coatings)
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21 pages, 2587 KB  
Review
Thermal Barrier Coatings for High-Temperature Performance of Nickel-Based Superalloys: A Synthetic Review
by Izabela Barwinska, Mateusz Kopec, Dominik Kukla, Cezary Senderowski and Zbigniew L. Kowalewski
Coatings 2023, 13(4), 769; https://doi.org/10.3390/coatings13040769 - 14 Apr 2023
Cited by 55 | Viewed by 13757
Abstract
With the rising demands of industry to increase the working temperature of gas turbine blades and internal combustion engines, thermal barrier coatings (TBC) were found to be an effective way to further enhance the lifetime of aero components through the improvement of mechanical [...] Read more.
With the rising demands of industry to increase the working temperature of gas turbine blades and internal combustion engines, thermal barrier coatings (TBC) were found to be an effective way to further enhance the lifetime of aero components through the improvement of mechanical properties and oxidation-resistance. Thus, this paper aims to review coating technologies with special emphasis on plasma-sprayed thermal barrier coatings (PS), and those produced by physical vapor deposition (PVD) and chemical vapor deposition (CVD) methods. Each technology was assessed in terms of its effectiveness to enhance the mechanical response and oxidation resistance of nickel-based parts working at high temperature. The effect of coating technology on mechanical strength, hardness, fatigue and creep of nickel alloys was discussed to reveal the potential candidates for future applications in aggressive environments. Full article
(This article belongs to the Section Ceramic Coatings and Engineering Technology)
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22 pages, 6668 KB  
Review
Biobased Anti-Adhesive Marine Coatings from Polyhydroxyalkanoates and Polysaccharides
by Fabienne Faÿ, Marie Champion, Alexandra Guennec, Xavier Moppert, Christelle Simon-Colin and Mathieu Elie
Coatings 2023, 13(4), 766; https://doi.org/10.3390/coatings13040766 - 13 Apr 2023
Cited by 13 | Viewed by 5549
Abstract
Due to environmental regulations, antifouling marine coatings must be gradually replaced by biocide-free coatings. Marine organisms weakly adhere to fouling release coatings, presenting a low surface free energy and a high elasticity, so they can be readily removed by the sheer force of [...] Read more.
Due to environmental regulations, antifouling marine coatings must be gradually replaced by biocide-free coatings. Marine organisms weakly adhere to fouling release coatings, presenting a low surface free energy and a high elasticity, so they can be readily removed by the sheer force of water. Currently, these materials are mainly composed of petrochemical polymers, such as silicone or fluoropolymers, with hydrophilic polymers as additives. However, following the ever-increasing environmental concerns, the research on new, alternative, eco-friendly coatings is oriented towards the use of biobased polymers from renewable resources. Two main families have been studied: polyhydroxyalkanoates (PHAs) and polysaccharides. PHAs are produced by bacteria in stressful conditions, while polysaccharides are extracted from plants, animals, or micro-organisms such as bacteria, in which case they are called exopolysaccharides (EPS). Since the use of these polymers is a non-toxic approach to controlling fouling colonization, this review provides an overview of these biobased polymers for their applications in new anti-adhesive marine coatings. Full article
(This article belongs to the Special Issue Environmentally-Friendly Coatings towards Biofouling Control and Microbiologically Influenced Corrosion (MIC) Inhibition)
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17 pages, 4240 KB  
Article
Novel Hybrid Organic–Inorganic Polymeric Coatings Containing Phosphonium or Acidic Groups for Improving Flame Retardancy of Wood
by Vasilis Koukoumtzis, Georgia C. Lainioti, George A. Voyiatzis and Joannis K. Kallitsis
Coatings 2023, 13(4), 754; https://doi.org/10.3390/coatings13040754 - 9 Apr 2023
Cited by 3 | Viewed by 2399
Abstract
Flame-retardant polymeric coatings with high limiting oxygen index (LOI) were prepared by combining inorganic mineral huntite (H5) and polymeric additives synthesized in the present work into a polymeric formulation. In order to improve the dispersion of the Mg- (and Ca)-based H5 particles, additives [...] Read more.
Flame-retardant polymeric coatings with high limiting oxygen index (LOI) were prepared by combining inorganic mineral huntite (H5) and polymeric additives synthesized in the present work into a polymeric formulation. In order to improve the dispersion of the Mg- (and Ca)-based H5 particles, additives containing phosphonium and acidic groups were employed to homogenize the inorganic fillers into the polymer matrix. Specific blend combinations of the commercial matrix Ecrovin® LV 340 eco with huntite and the additives poly(benzyltriphenylphosphonium-co-4-styrene sulfonic acid) P(SSH-co-SSBTPB60) and poly(hexadecyltributylphosphonium-co-4-styrene sulfonic acid) P(SSH-co-SSTBHDPB80), combining acidic and phosphonium groups, led to LOI values of 34.5% and 33.5%, respectively. The novel flame-retardant polymeric coatings inhibited the combustion of the coated wood substrates, which is attributed to the combination of acidic groups that promote the dispersion of inorganic filler in the polymer matrix and phosphonium groups that support the increase in LOI values. Full article
(This article belongs to the Section Functional Polymer Coatings and Films)
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