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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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11 pages, 3789 KB  
Article
Single-Layer MoS2: A Two-Dimensional Material with Negative Poisson’s Ratio
by Yucheng Zhu, Xiaofei Cao, Yuan Tan, Yao Wang, Jun Hu, Baotong Li and Zhong Chen
Coatings 2023, 13(2), 283; https://doi.org/10.3390/coatings13020283 - 26 Jan 2023
Cited by 13 | Viewed by 3835
Abstract
Negative Poisson’s ratio (NPR) materials have broad applications such as heat dissipation, vibration damping, and energy absorption because of their designability, lightweight quality, and high strength ratio. Here, we use first-principles calculations to find a two-dimensional (2D) auxetic material (space group R [...] Read more.
Negative Poisson’s ratio (NPR) materials have broad applications such as heat dissipation, vibration damping, and energy absorption because of their designability, lightweight quality, and high strength ratio. Here, we use first-principles calculations to find a two-dimensional (2D) auxetic material (space group R3¯m), which exhibits a maximum in-plane NPR of −0.0846 and a relatively low Young’s modulus in the planar directions. Calculations show that the NPR is mainly related to its unique zigzag structure and the strong interaction between the 4d orbital of Mo and the 3p orbital of S. In addition, molecular dynamics (MD) simulations show that the structure of this material is thermodynamically stable. Our study reveals that this layered MoS2 can be a promising 2D NPR material for nanodevice applications. Full article
(This article belongs to the Special Issue Synthesis, Characterization and Performance Enhancement of Electrode and Biomaterial Coatings)
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10 pages, 8986 KB  
Article
Room Temperature Synthesis of Branched ZnO Nanowires Array with Tunable Morphology
by Wei Zhao, Hsiang-Shun Chang, Kefu Yao and Yang Shao
Coatings 2023, 13(2), 275; https://doi.org/10.3390/coatings13020275 - 25 Jan 2023
Cited by 1 | Viewed by 1793
Abstract
Herein, a novel method is proposed to synthesize B-ZnO NWA by simply immersing the Zn NWA in NaOH solution at room temperature (25 °C). Based on the systematic investigation of various factors that affect the growth of B-ZnO NWA, the growth mechanism of [...] Read more.
Herein, a novel method is proposed to synthesize B-ZnO NWA by simply immersing the Zn NWA in NaOH solution at room temperature (25 °C). Based on the systematic investigation of various factors that affect the growth of B-ZnO NWA, the growth mechanism of B-ZnO NWA is clarified. Guided by the growth mechanism, the control of the morphology of B-ZnO NWA is achieved by adjusting the pore structure of anodized aluminum oxide templates, hot-pressing parameters, NaOH concentration, solution temperature, and immersion time. In contrast to previous reports, the prepared B-ZnO NWA has hollow trunks, which can further increase the specific area of B-ZnO NWA. Considering the facile, environmental, and low-cost synthesis, the prepared B-ZnO NWA with tunable morphology has great prospects in a wide range of applications, especially those related to the conversion and utilization of solar energy, which are gaining increasing interest nowadays. Full article
(This article belongs to the Special Issue Feature Papers of Coatings for Energy Applications)
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44 pages, 10027 KB  
Review
A Review of Advances in Cold Spray Additive Manufacturing
by Rodolpho Fernando Vaz, Andrea Garfias, Vicente Albaladejo, Javier Sanchez and Irene Garcia Cano
Coatings 2023, 13(2), 267; https://doi.org/10.3390/coatings13020267 - 23 Jan 2023
Cited by 65 | Viewed by 17049
Abstract
Cold Spray Additive Manufacturing (CSAM) produces freeform parts by accelerating powder particles at supersonic speed which, impacting against a substrate material, trigger a process to consolidate the CSAM part by bonding mechanisms. The literature has presented scholars’ efforts to improve CSAM materials’ quality, [...] Read more.
Cold Spray Additive Manufacturing (CSAM) produces freeform parts by accelerating powder particles at supersonic speed which, impacting against a substrate material, trigger a process to consolidate the CSAM part by bonding mechanisms. The literature has presented scholars’ efforts to improve CSAM materials’ quality, properties, and possibilities of use. This work is a review of the CSAM advances in the last decade, considering new materials, process parameters optimization, post-treatments, and hybrid processing. The literature considered includes articles, books, standards, and patents, which were selected by their relevance to the CSAM theme. In addition, this work contributes to compiling important information from the literature and presents how CSAM has advanced quickly in diverse sectors and applications. Another approach presented is the academic contributions by a bibliometric review, showing the most relevant contributors, authors, institutions, and countries during the last decade for CSAM research. Finally, this work presents a trend for the future of CSAM, its challenges, and barriers to be overcome. Full article
(This article belongs to the Special Issue Advanced Cold Spraying Technology)
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13 pages, 782 KB  
Review
Changes in Strength Parameters of Composite Cements as Affected by Storage Temperature—A Review of the Literature
by Joanna Giełzak, Beata Dejak, Jerzy Sokołowski and Kinga Bociong
Coatings 2023, 13(2), 244; https://doi.org/10.3390/coatings13020244 - 20 Jan 2023
Cited by 3 | Viewed by 2736
Abstract
Fixed restorations are now among the most common restorations in modern dental prosthodontics. The current view in prosthodontics of maximum preparation economy is causing an increased interest in the mechanical properties of cements. Among the most important properties of materials used for indirect [...] Read more.
Fixed restorations are now among the most common restorations in modern dental prosthodontics. The current view in prosthodontics of maximum preparation economy is causing an increased interest in the mechanical properties of cements. Among the most important properties of materials used for indirect cementation are mechanical properties, i.e., hardness and compressive strength. These properties can change as a result of changes in physical factors. The purpose of this study was to analyze the available literature on the effect of conditioning temperature of cements used for cementation of indirect fixed restorations on the durability of their bonding to dental tissues and their mechanical and physical properties. The following databases were used: Mendeley, PubMed, ResearchGate, National Library of Medicine, and Google Scholar. Analysis of the available literature was carried out according to the Prisma diagram program. Forty-eight articles were selected, which were the following types of studies: clinical reports, research article, and review articles. Some studies indicated that mechanical properties, such as flexural strength, polymerization shrinkage, and conversion factor, did not change after heating the composite material. According to some researchers, preheating the composite material increased its conversion degree, which consequently led to an increase in hardness and fracture toughness, an increase in flexural strength and an increase in elastic modulus, and an increase in abrasion resistance. Studies on changes in the mechanical and physical properties of composite materials, as well as composite cements, have not always provided clear answers, as there are still no laboratory and clinical studies that fully confirm the benefits of heating composite cements. Conducting studies evaluating the effect of elevated storage temperature on the strength parameters of cements, in conjunction with the type of material and its composition, could provide answers to many clinical questions that are still unresolved. If the benefits of heating cements were unequivocally confirmed in laboratory studies, this could open up many possibilities for improving the retention of fixed prosthetic restorations. Full article
(This article belongs to the Special Issue Surface Properties of Dental Materials and Instruments, 2nd Edition)
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9 pages, 4258 KB  
Article
Tunnel Magnetoresistance-Based Sensor for Biomedical Application: Proof-of-Concept
by Crina Ghemes, Oana-Georgiana Dragos-Pinzaru, Mihai Tibu, Mihaela Lostun, Nicoleta Lupu and Horia Chiriac
Coatings 2023, 13(2), 227; https://doi.org/10.3390/coatings13020227 - 18 Jan 2023
Cited by 8 | Viewed by 3585
Abstract
The aim of this work was to investigate and prove the possibility of the real-time detection of magnetic nanoparticles (MNPs) distributed in solid material by using a tunnel magnetoresistance-based (TMR) sensor. Following the detection tests of FeCrNbB magnetic nanoparticles distributed in transparent epoxy [...] Read more.
The aim of this work was to investigate and prove the possibility of the real-time detection of magnetic nanoparticles (MNPs) distributed in solid material by using a tunnel magnetoresistance-based (TMR) sensor. Following the detection tests of FeCrNbB magnetic nanoparticles distributed in transparent epoxy resin (EPON 812) and measuring the sensor output voltage changes at different particle concentrations, the detection ability of the sensor was demonstrated. For the proposed TMR sensor, we measured a maximum magnetoresistance ratio of about 53% and a sensitivity of 1.24%/Oe. This type of sensor could facilitate a new path of research in the field of magnetic hyperthermia by locating cancer cells. Full article
(This article belongs to the Special Issue Ceramic and Metallic Biomaterials. Application in Medical Sciences)
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12 pages, 8469 KB  
Article
Characterization of Hydroxyapatite/Chitosan Composite Coating Obtained from Crab Shells on Low-Modulus Ti–25Nb–8Sn Alloy through Hydrothermal Treatment
by Hsueh-Chuan Hsu, Shih-Ching Wu, Chien-Yu Lin and Wen-Fu Ho
Coatings 2023, 13(2), 228; https://doi.org/10.3390/coatings13020228 - 18 Jan 2023
Cited by 12 | Viewed by 3391
Abstract
In this study, hydroxyapatite/chitosan (HA/CS) composite coatings were prepared by hydrothermal treatment on the surface of low-modulus Ti–25Nb–8Sn alloy to improve the surface bioactivity of the alloy. HA, the main mineral composition of the human skeleton, has excellent bioactivity and is often used [...] Read more.
In this study, hydroxyapatite/chitosan (HA/CS) composite coatings were prepared by hydrothermal treatment on the surface of low-modulus Ti–25Nb–8Sn alloy to improve the surface bioactivity of the alloy. HA, the main mineral composition of the human skeleton, has excellent bioactivity and is often used as a surface coating on biometal implants. CS, a natural polymer with good antibacterial, hydrophilic and non-toxic characteristics, is often used as dermal regeneration templates, hemostatic agents and drug delivery systems. In this experiment, a natural crab shell was used as a raw material to prepare the HA/CS composite coating by alkali treatment and hydrothermal reaction at various temperatures. The microstructure, morphology and phase composition of the coating surfaces were analyzed by XRD, SEM, and FTIR, and the sample coated with HA/CS was soaked in simulated body fluid (SBF) to evaluate its bioactivity. The experimental results showed that the HA/CS composite coatings through hydrothermal treatment at various temperatures can be successfully fabricated on the surface of the Ti alloy. HA on the coating surface exhibited mainly spherical particles and contained A- and B-type carbonate. When the hydrothermal temperature was up to 200 °C, the spherical particles were approximately 20–40 nm. An ultrasonic vibration test was used to evaluate the adhesion of the coatings, showing that the CS exhibited significantly improved adhesion capacity to the substrate. After being soaked in SBF for 7 days, apatite was deposited on the entire surfaces of the HA/CS coatings, indicating that the coating possesses excellent bioactivity. Full article
(This article belongs to the Special Issue Synthetic and Biological-Derived Hydroxyapatite Implant Coatings)
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10 pages, 8999 KB  
Article
Hydrothermal Preparation of TiO2/Graphite Nanosheets Composites and Its Effect on Electrothermal Behavior
by Chunyu Wang, Weiyao Tian, Sibo Kang, Bo Zhong, Chunlin Qin and Hongyang Wang
Coatings 2023, 13(2), 226; https://doi.org/10.3390/coatings13020226 - 18 Jan 2023
Cited by 4 | Viewed by 2273
Abstract
Nowadays, carbon materials are supposed to replace the resistance wire made of metal alloy to be the next generation of heat-generating materials due to their excellent electrical conductivity and corrosion resistance. In this study, TiO2/graphite nanosheets (GNs) composite was prepared by [...] Read more.
Nowadays, carbon materials are supposed to replace the resistance wire made of metal alloy to be the next generation of heat-generating materials due to their excellent electrical conductivity and corrosion resistance. In this study, TiO2/graphite nanosheets (GNs) composite was prepared by chemical exfoliation and hydrothermal methods. XRD, FTIR, and Raman spectra confirm TiO2 particles are on the surface of GNs. SEM photographs show TiO2 nanoparticles covering the surface of the GNs uniformly. We used TiO2/GNs and sodium silicate to produce the electrothermal film coated on the glass. As compared to raw GNs, the heating rate and maximum temperature have greatly improved. In order to find the reasons for the improvement, the BET and zeta potential of TiO2/GNs were tested, and we found that the enhancement of the surface area and the dispersion to the composite by TiO2 particles and sodium silicate make the distribution of GNs more uniform. Full article
(This article belongs to the Special Issue Thermal and Mechanical Properties of Polymer Based Materials and Adhesives)
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14 pages, 4111 KB  
Article
All-Inkjet-Printed Ti3C2 MXene Capacitor for Textile Energy Storage
by Eugenio Gibertini, Federico Lissandrello, Luca Bertoli, Prisca Viviani and Luca Magagnin
Coatings 2023, 13(2), 230; https://doi.org/10.3390/coatings13020230 - 18 Jan 2023
Cited by 12 | Viewed by 3264
Abstract
The emerging wearable electronics integrated into textiles are posing new challenges both in materials and micro-fabrication strategies to produce textile-based energy storage and power source micro-devices. In this regard, inkjet printing (IJP) offers unique features for rapid prototyping for various thin-film (2D) devices. [...] Read more.
The emerging wearable electronics integrated into textiles are posing new challenges both in materials and micro-fabrication strategies to produce textile-based energy storage and power source micro-devices. In this regard, inkjet printing (IJP) offers unique features for rapid prototyping for various thin-film (2D) devices. However, all-inkjet-printed capacitors were very rarely reported in the literature. In this work, we formulated a stable Ti3C2 MXene aqueous ink for inkjet printing current-collector-free electrodes on TPU-coated cotton fabric, together with an innovative inkjet-printable and UV-curable solvent-based electrolyte precursor. The electrolyte was inkjet-printed on the electrode’s surface, and after UV polymerization, a thin and soft gel polymer electrolyte (GPE) was obtained, resulting in an all-inkjet-printed symmetrical capacitor (a-IJPSC). The highest ionic conductivity (0.60 mS/cm) was achieved with 10 wt.% of acrylamide content, and the capacitance retention was investigated both at rest (flat) and under bending conditions. The flat a-IJPSC textile-based device showed the areal capacitance of 0.89 mF/cm2 averaged on 2k cycles. Finally, an array of a-IJPSCs were demonstrated to be feasible as both a textile-based energy storage and micro-power source unit able to power a blue LED for several seconds. Full article
(This article belongs to the Section Surface Engineering for Energy Harvesting, Conversion, and Storage)
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9 pages, 2250 KB  
Article
Dual-Type Flexible-Film Thermoelectric Generators Using All-Carbon Nanotube Films
by Ryota Konagaya and Masayuki Takashiri
Coatings 2023, 13(1), 209; https://doi.org/10.3390/coatings13010209 - 16 Jan 2023
Cited by 12 | Viewed by 3580
Abstract
The long-term stability of n-type single-walled carbon nanotubes (SWCNTs) in air makes all-carbon thermoelectric generators (TEGs) viable. To increase the performance of TEGs, we developed a dual-type flexible-film thermoelectric generator (DFTEG). The vacuum filtering was used to form p- and n-type SWCNT films [...] Read more.
The long-term stability of n-type single-walled carbon nanotubes (SWCNTs) in air makes all-carbon thermoelectric generators (TEGs) viable. To increase the performance of TEGs, we developed a dual-type flexible-film thermoelectric generator (DFTEG). The vacuum filtering was used to form p- and n-type SWCNT films from ethanol-based dispersion and water-based solutions with cationic surfactant, respectively. DFTEGs were fabricated as follows: strip-shaped p- and n-type SWCNT films were attached on the top and back sides of a polyimide substrate, respectively, and were connected alternately in series by bending copper tapes on the edge of the polyimide substrate. The thermoelectric performance was measured after attaching the DFTEG outside a beaker full of water, where the water surface reached the center of the DFTEG. For a 10 mm long film and 15 p-n pairs, the DFTEG had an output voltage of 40 mV and a maximum power of 891 nW at a temperature difference of 25 K. The measured thermoelectric performance was significantly higher than that of the single-type TEG for almost the same SWCNT films. This result demonstrates that thermoelectric performance can be improved by using DFTEGs that are fabricated with optimum structural designs. Full article
(This article belongs to the Collection Feature Paper Collection in Thin Films)
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15 pages, 3415 KB  
Article
Abrasive and Erosive Wear of TI6Al4V Alloy with Electrospark Deposited Coatings of Multicomponent Hard Alloys Materials Based of WC and TiB2
by Todor Penyashki, Georgi Kostadinov, Mara Kandeva, Valentin Kamburov, Antonio Nikolov and Rayna Dimitrova
Coatings 2023, 13(1), 215; https://doi.org/10.3390/coatings13010215 - 16 Jan 2023
Cited by 10 | Viewed by 2508
Abstract
In the present work, abrasive and erosive wear of wear-resistant composite coatings with a complex structure and different phase compositions deposited on titanium surfaces was studied. The coatings were obtained by electrospark deposition (ESD) using two types of hard-alloy compositions: WC–TiB2–B [...] Read more.
In the present work, abrasive and erosive wear of wear-resistant composite coatings with a complex structure and different phase compositions deposited on titanium surfaces was studied. The coatings were obtained by electrospark deposition (ESD) using two types of hard-alloy compositions: WC–TiB2–B4C–Co–Ni–Cr–Si–B and TiB2–TiAl reinforced with dispersed nanoparticles of ZrO2 and NbC. The influence of the ESD process parameters on the roughness, thickness, composition, structure and coefficient of friction of the coated surfaces was investigated, and their role in protecting the titanium surfaces from wear was clarified. Dense coatings with the presence of newly formed wear-resistant phases and crystalline-amorphous structures were obtained, with roughness, thickness and microhardness that can be varied by the ESD modes in the range Ra = 2.5 ÷ 4.5 µm, δ = 8 ÷ 30 µm and HV 8.5 ÷ 14.0 GPa. The new coatings were found to reduce the abrasive and erosive wear of the coated surfaces by up to four times. The influence of the geometric characteristics, composition and structure of coatings on the wear intensity and wear resistance of coatings was studied. Full article
(This article belongs to the Special Issue Coatings and Surface Modification for Tribological Applications)
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19 pages, 2632 KB  
Review
Laser Obtained Superhydrophobic State for Stainless Steel Corrosion Protection, a Review
by Kirill A. Emelyanenko, Alexandre M. Emelyanenko and Ludmila B. Boinovich
Coatings 2023, 13(1), 194; https://doi.org/10.3390/coatings13010194 - 15 Jan 2023
Cited by 48 | Viewed by 6326
Abstract
Stainless steel has become an integral part of modern engineering materials and daily life due to its mechanical efficiency, strength, recyclability, high resistance to oxidation and corrosive attack, which make it the ideal material for many kinds of applications. At the same time, [...] Read more.
Stainless steel has become an integral part of modern engineering materials and daily life due to its mechanical efficiency, strength, recyclability, high resistance to oxidation and corrosive attack, which make it the ideal material for many kinds of applications. At the same time, steel suffers from certain types of corrosion, such as intergranular corrosion, or contact corrosion that develops when stainless steel comes into contact with carbon steel or another metal with a different electrochemical potential. Finally, pitting corrosion is a serious problem often occurring when stainless steel parts work in sea water. This paper provides a brief overview of methods for protecting stainless steel from corrosion using a new approach based on superhydrophobization of the surface of stainless steel using laser processing followed by the deposition of a layer of a substance with a low surface energy. The review discusses the mechanisms of corrosion protection by such coatings and the properties of superhydrophobic coatings presented in the literature. Superhydrophobic protective coatings on stainless steel have been shown to significantly reduce corrosion, with some demonstrating a decrease in corrosion current of up to 156 times. However, a more comprehensive analysis of the mechanisms contributing to this effect, as well as a comparison with anti-corrosion coatings on other metals, suggests that the combination of these mechanisms has the potential to create even more durable and effective surfaces for corrosion protection of stainless steel. Full article
(This article belongs to the Collection Feature Paper Collection in Corrosion, Wear and Erosion)
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16 pages, 6883 KB  
Article
High Temperature Oxidation and Oxyacetylene Ablation Properties of ZrB2-ZrC-SiC Ultra-High Temperature Composite Ceramic Coatings Deposited on C/C Composites by Laser Cladding
by Kaijin Huang, Yahao Xia and Aihua Wang
Coatings 2023, 13(1), 173; https://doi.org/10.3390/coatings13010173 - 12 Jan 2023
Cited by 9 | Viewed by 3068
Abstract
In order to improve the high temperature oxidation and ablation resistance of C/C composites, ZrB2-ZrC-SiC ultra-high temperature composite ceramic coatings were prepared on C/C composites by laser cladding using Zr, B4C, and Si as raw materials. The microstructure of [...] Read more.
In order to improve the high temperature oxidation and ablation resistance of C/C composites, ZrB2-ZrC-SiC ultra-high temperature composite ceramic coatings were prepared on C/C composites by laser cladding using Zr, B4C, and Si as raw materials. The microstructure of the coating was characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Air isothermal oxidation (1600 °C, 80 min) and oxyacetylene flame ablation (2400 kW/m2, 300 s) were used to evaluate the high-temperature oxidation and ablation properties of the coating, respectively. The results show that the microstructure of laser cladding coating is a totem of black and white. The white part is mainly the first solidified high melting point ZrB2 phase, and the black part is the latter solidified eutectic structure, which is mainly composed of ZrB2(ZrB12)-ZrC or ZrB2(ZrB12)-SiC two phases. After oxidation at 1600 °C and 80 min, the coating is mainly composed of ZrO2 and ZrSiO4 phases, and ZrSiO4 is basically distributed among ZrO2 particles. The high temperature oxidation and ablation properties of the coating are better than the C/C composite matrix, and the mass ablation rate of the coating is about 1/4 of the latter. Full article
(This article belongs to the Special Issue Laser Cladding Coatings: Microstructure, Properties, and Applications)
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11 pages, 2170 KB  
Article
In Situ and Ex Situ Raman Studies of Cysteine’s Behavior on a Titanium Surface in Buffer Solution
by Dominika Święch, Natalia Piergies, Gaetano Palumbo and Czesława Paluszkiewicz
Coatings 2023, 13(1), 175; https://doi.org/10.3390/coatings13010175 - 12 Jan 2023
Cited by 6 | Viewed by 3385
Abstract
In this paper, surface-enhanced Raman spectroscopy (SERS) was used to investigate the adsorption process of cysteine (Cys). Studies were carried out in the presence of phosphate-buffered saline solution (PBS), at pH 7.4, and acidified to pH 5, 3, and 1, on the surface [...] Read more.
In this paper, surface-enhanced Raman spectroscopy (SERS) was used to investigate the adsorption process of cysteine (Cys). Studies were carried out in the presence of phosphate-buffered saline solution (PBS), at pH 7.4, and acidified to pH 5, 3, and 1, on the surface of Ti for implant application. In situ SERS spectra obtained for the Cys/Ti solution system, after 24 h of immersion time, indicated that the buffer solution strongly influences the adsorption behavior of Cys on the Ti surface. This results in a decrease in Cys adsorption on the Ti surface, in the range of pH 7.4 to 3. The strong interaction between a sulfur atom of Cys and a Ti surface was observed only at pH = 1, under strongly acidic conditions. In contrast, ex situ SERS spectra recorded for the same samples but in a dried Cys/Ti system show a completely different behavior of Cys on the Ti surface. Formation of a disulfide (S-S) bond has occurred as a result of the dimerization or aggregation of Cys molecules on the Ti surface. Detailed analysis of the adsorption behavior of Cys on the Ti surface can be very important in the preparation of bioactive materials (i.e., coated by organic layers). Full article
(This article belongs to the Special Issue Novel Approaches on the Coatings Materials: Biomedical and Industrial Applications)
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11 pages, 3059 KB  
Article
Antifrictional Effects of Group IVB Elements Deposited as Nanolayers on Anodic Coatings
by Tadas Matijošius, Giedrius Stalnionis, Gedvidas Bikulčius, Sigitas Jankauskas, Laurynas Staišiūnas and Svajus Joseph Asadauskas
Coatings 2023, 13(1), 132; https://doi.org/10.3390/coatings13010132 - 10 Jan 2023
Cited by 2 | Viewed by 1790
Abstract
The utilization of anodized aluminum (Al) components would contribute greatly to combat against dry friction if good tribological properties could be attained. Despite its hardness, the wear rate of anodic coatings presents a major problem in many applications, including automotive, aerospace and high-tech [...] Read more.
The utilization of anodized aluminum (Al) components would contribute greatly to combat against dry friction if good tribological properties could be attained. Despite its hardness, the wear rate of anodic coatings presents a major problem in many applications, including automotive, aerospace and high-tech industries. Recently, nanolayers of Ti demonstrated high tribological effectiveness and unusually low dry friction on anodic coatings. However, few researchers focus on the tribological characterization of nanolayers of other elements. In this study, nanolayers of Ti, Zr, Hf, Cu, Cr, Nb and Sn were deposited on anodized 1050 and 6082 alloys by magnetron sputtering and Atomic Layer Deposition. Major attention was devoted to surface roughness and hardness measurements, because of their importance for static friction. The results showed that structural, chemical and other intrinsic properties of nanolayers of Group IVB elements in many cases led to significant friction reduction, when compared to those of Cu, Cr and Hf. Nanolayers of 15 nm to 75 nm thicknesses appeared most effective tribologically, while 180 nm or thicker layers progressively lost their ability to sustain low dynamic friction. Deposition of nanoscale structures could provide advantages for the anodized Al industry in protection against incidental friction and wear. Full article
(This article belongs to the Special Issue Coatings and Surface Modification for Tribological Applications)
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10 pages, 3179 KB  
Article
Functionally Gradient Material Fabrication Based on Cr, Ti, Fe, Ni, Co, Cu Metal Layers via Spark Plasma Sintering
by Oleg O. Shichalin, Evgeniy K. Papynov, Igor Yu. Buravlev, Anastasiya A. Buravleva, Sergey V. Chuklinov, Ekaterina A. Gridasova, Anton V. Pogodaev, Valreiia A. Nepomnyushchaya, Zlata E. Kornakova, Alexey O. Lembikov, Danila V. Gritsuk, Olesya V. Kapustina, Sofia S. Gribanova and Yun Shi
Coatings 2023, 13(1), 138; https://doi.org/10.3390/coatings13010138 - 10 Jan 2023
Cited by 7 | Viewed by 3332
Abstract
The paper presents a method of obtaining functionally graded material (FGM) of heterogeneous (layered) type based on joined metals Cr-Ti-Fe-Co-Ni-Cu using spark plasma sintering (SPS) technology. The structure, elemental and phase composition of FGM obtained on the basis of joined metals with different [...] Read more.
The paper presents a method of obtaining functionally graded material (FGM) of heterogeneous (layered) type based on joined metals Cr-Ti-Fe-Co-Ni-Cu using spark plasma sintering (SPS) technology. The structure, elemental and phase composition of FGM obtained on the basis of joined metals with different values of the temperature coefficient of linear expansion (CTLE) were studied by SEM, EDS and XRD methods with regard to the phase states of the alloy system. Based on the Vickers microhardness data, the evaluation of the mechanical characteristics of FGM in the whole sample body and locally at the contact boundaries of the joined metals was carried out. The results of the study are new and represent a potential for FGM, as well as functionally graded coatings (FGC), which have special physical, chemical and mechanical properties and are highly demanded for the manufacture of structures and products for industrial applications. Full article
(This article belongs to the Special Issue Trends in Spark Plasma Sintering of Advanced Materials)
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15 pages, 1914 KB  
Article
Development of Catalyst-Free Self-Healing Biobased UV-Curable Coatings via Maleate Monoester Transesterification
by Xixi Yu, Yun Hu, Wen Lei, Chengguo Liu and Yonghong Zhou
Coatings 2023, 13(1), 110; https://doi.org/10.3390/coatings13010110 - 7 Jan 2023
Cited by 12 | Viewed by 2643
Abstract
Developing environmentally friendly UV-curable polymers with multi-functionality is very significant for sustainable development and environmental protection. In this work, a novel tung-oil-based UV-curable oligomer (TOMAH) was synthesized by Diels–Alder and ring-opening reactions via microwave technology. Subsequently, catalyst-free self-healing UV-curable materials based on a [...] Read more.
Developing environmentally friendly UV-curable polymers with multi-functionality is very significant for sustainable development and environmental protection. In this work, a novel tung-oil-based UV-curable oligomer (TOMAH) was synthesized by Diels–Alder and ring-opening reactions via microwave technology. Subsequently, catalyst-free self-healing UV-curable materials based on a maleate monoester transesterification (MMETER) were developed by co-photopolymerization of TOMAH and hydroxyethyl methacrylate (HEMA). The obtained UV-cured materials possessed a high glass transition temperature (Tg > 81 °C), excellent adhesion (grade 1), and flexibility (2 mm). Particularly, the outstanding photopolymerization activity of the UV-curable resins was proved by UV-curing kinetics. In addition, dynamic transesterifications occurred without an external catalyst at a moderate temperature, resulting in good self-healing properties (with a scratch-repair efficiency of 78.6–93.3%) and shape-memory properties for the obtained UV-cured materials. This work combines the multiple advantages of biomass raw material, microwave synthesis technology, UV-curing method, and multifunctional polymers, thus providing an innovative strategy to fabricate sustainable and intelligent coatings. Full article
(This article belongs to the Section Bioactive Coatings and Biointerfaces)
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16 pages, 5415 KB  
Article
In Vitro Investigation of Corrosion Control of Magnesium with Degradable Polycaprolactone Coatings for Cardiovascular Grafts
by Sara Knigge, Marc Mueller, Lara Fricke, Tobias Schilling and Birgit Glasmacher
Coatings 2023, 13(1), 94; https://doi.org/10.3390/coatings13010094 - 4 Jan 2023
Cited by 10 | Viewed by 3468
Abstract
Magnesium is a promising metal for resorbable cardiovascular implants due to its high biocompatibility, high corrosion tendency, and mechanical properties. However, adapting its corrosion rate to the physiological healing processes is required to ascertain a safe graft function. A protective polymeric layer is [...] Read more.
Magnesium is a promising metal for resorbable cardiovascular implants due to its high biocompatibility, high corrosion tendency, and mechanical properties. However, adapting its corrosion rate to the physiological healing processes is required to ascertain a safe graft function. A protective polymeric layer is supposed to slow down the corrosion rate of magnesium. Additionally, coatings can improve the host’s tissue interaction with the implant by implementing the local delivery of antibiotic drugs and growth or cell adhesion factors. However, little is known about the interaction of polymer-based coatings, their degradation, and magnesium corrosion. This study examines the corrosion mechanism of magnesium protected by spin coatings and electrospun fiber coatings under physiological conditions. Pure magnesium specimens were coated with polycaprolactone (PCL). The corrosion of the coated magnesium was evaluated using an immersion test in simulated body fluid. Spin coatings provided efficient protection against corrosive attacks and a significantly lower corrosion rate by 75% compared to uncoated magnesium. In contrast, fiber coatings did not provide relevant corrosion protection. On the other hand, magnesium corrosion caused the accelerated degradation of the PCL layer. A reliable and safe implant function is vital, especially in cardiovascular applications. Magnesium coating, therefore, should be carried out with spin coatings. Full article
(This article belongs to the Special Issue Multifunctional Coatings on Medical Devices)
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14 pages, 1613 KB  
Article
The Application of Rubber Aggregate-Combined Permeable Concrete Mixture in Sponge City Construction
by Bowen Qi, Shouwu Gao and Peilong Xu
Coatings 2023, 13(1), 87; https://doi.org/10.3390/coatings13010087 - 3 Jan 2023
Cited by 34 | Viewed by 4496
Abstract
Permeable concrete is a new type of pavement material, which can effectively improve the urban flood discharge system, and is of great significance to the construction of sponge city. In order to optimize the use effect of permeable concrete and improve the application [...] Read more.
Permeable concrete is a new type of pavement material, which can effectively improve the urban flood discharge system, and is of great significance to the construction of sponge city. In order to optimize the use effect of permeable concrete and improve the application value of permeable concrete in permeable road engineering, the combination of rubber aggregate and permeable concrete is proposed, and the mix ratio of rubber permeable concrete mixture material is designed, which is applied to the engineering of pavement in Hunan Province, and its comprehensive pavement performance is analyzed and evaluated. The results show that the rubber permeable concrete has the best performance when the water cement ratio is 0.3, the designed porosity is 15%, the rubber particle size is 16 mesh, the rubber content is 15% and the coarse aggregate ratio is 4:6. The removal rates of suspended solids and metal pollutants are 0.65 and 0.72, respectively, which are increased by 0.23 and 0.19, respectively, compared with ordinary permeable concrete. This shows that rubber permeable concrete improves the ecological benefits of permeable concrete pavement, gives full play to the economic benefits of waste rubber products, reduces the construction cost of permeable concrete pavement, and provides assistance for promoting the construction of sponge city. Full article
(This article belongs to the Topic Properties of the Corroding Interface)
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20 pages, 10512 KB  
Article
Effect of Al2O3, ZnO and TiO2 Atomic Layer Deposition Grown Thin Films on the Electrochemical and Mechanical Properties of Sputtered Al-Zr Coating
by Elias Kaady, Roland Habchi, Mikhael Bechelany, Elia Zgheib and Akram Alhussein
Coatings 2023, 13(1), 65; https://doi.org/10.3390/coatings13010065 - 30 Dec 2022
Cited by 6 | Viewed by 6522
Abstract
The 316L stainless steels, often used in turbine blades for naval and marine applications, usually suffer from localized pitting corrosion after long exposure to chlorinated environments. The aluminum-zirconium coatings deposited by magnetron sputtering technique can be used to ensure cathodic protection for steels. [...] Read more.
The 316L stainless steels, often used in turbine blades for naval and marine applications, usually suffer from localized pitting corrosion after long exposure to chlorinated environments. The aluminum-zirconium coatings deposited by magnetron sputtering technique can be used to ensure cathodic protection for steels. In this work, we study the influence of atomic layer deposited (ALD) Al2O3, ZnO, and TiO2 thin films on the structural, mechanical, and electrochemical properties of Al-Zr (4 at.% Zr) magnetron sputtered coatings. The morphology, preferred orientation growth, mechanical properties, wettability, and corrosion resistance were investigated. The change in the sputtered Al-Zr morphology is mainly due to the insertion of the ALD layer. The Al-Zr layer deposited on ZnO and TiO2 layers presented a distinctive morphology. The agglomerate particles of AlZr/Al2O3/AlZr, AlZr/ZnO/AlZr and AlZr/TiO2/AlZr coatings exhibited a cauliflower shape. For ALD/PVD coatings, the insertion of an ALD oxide layer promoted the intensity of the peaks corresponding to the (111) crystallographic orientation. The nanoindentation measurements confirmed the enhancement in the mechanical properties, where the hardness increased by about 75%. The ALD oxide layers promoted the hydrophobicity of the coatings. The electrochemical characterization in a 3.5 wt.% NaCl solution also confirmed the role of the ALD oxides layers in delaying the pitting corrosion of the Al-Zr coating by widening the passive region and enhancing the protective efficiency of the passive film. Full article
(This article belongs to the Special Issue Chemical/Physical Vapor Deposition Coatings on Metallic Substrates)
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30 pages, 2701 KB  
Review
Steel Surface Defect Recognition: A Survey
by Xin Wen, Jvran Shan, Yu He and Kechen Song
Coatings 2023, 13(1), 17; https://doi.org/10.3390/coatings13010017 - 22 Dec 2022
Cited by 121 | Viewed by 11245
Abstract
Steel surface defect recognition is an important part of industrial product surface defect detection, which has attracted more and more attention in recent years. In the development of steel surface defect recognition technology, there has been a development process from manual detection to [...] Read more.
Steel surface defect recognition is an important part of industrial product surface defect detection, which has attracted more and more attention in recent years. In the development of steel surface defect recognition technology, there has been a development process from manual detection to automatic detection based on the traditional machine learning algorithm, and subsequently to automatic detection based on the deep learning algorithm. In this paper, we discuss the key hardware of steel surface defect detection systems and offer suggestions for related options; second, we present a literature review of the algorithms related to steel surface defect recognition, which includes traditional machine learning algorithms based on texture features and shape features as well as supervised, unsupervised, and weakly supervised deep learning algorithms (Incomplete supervision, inexact supervision, imprecise supervision). In addition, some common datasets and algorithm performance evaluation metrics in the field of steel surface defect recognition are summarized. Finally, we discuss the challenges of the current steel surface defect recognition algorithms and the corresponding solutions, and our future work focus is explained. Full article
(This article belongs to the Special Issue Solid Surfaces, Defects and Detection)
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11 pages, 3667 KB  
Article
A Two-Dimensional Guidance Strategy to Fabricate Perovskite Gadolinium Aluminate Ceramic Film
by Tao Zhang, Lu Chen, Jing Yao and Qi Zhu
Coatings 2022, 12(12), 1927; https://doi.org/10.3390/coatings12121927 - 8 Dec 2022
Cited by 1 | Viewed by 2118
Abstract
Gadolinium aluminate is an effective host for doping with various ions, and it can emit various colors. However, it is not easy to prepare transparent ceramics of gadolinium aluminate using traditional methods, although transparent ceramics are very suitable for solid lighting. In this [...] Read more.
Gadolinium aluminate is an effective host for doping with various ions, and it can emit various colors. However, it is not easy to prepare transparent ceramics of gadolinium aluminate using traditional methods, although transparent ceramics are very suitable for solid lighting. In this work, a two-dimensional guidance strategy has been successfully carried out for perovskite-structured aluminate ceramic film. Through the two-dimensional interfacial reaction, GdAlO3:Eu3+ (GAP:Eu3+) transparent ceramic films were successfully fabricated using nanosheets exfoliated from layered gadolinium hydroxide, a rare earth source. The final films were tested by characterization techniques, including XRD, SEM, TEM, FT-IR, PLE/PL spectroscopy, temperature-dependent PL spectroscopy, and luminescence decay analysis. The perovskite film of transparent ceramics can be obtained by calcining LRH nanosheets on the substrate of amorphous alumina at 1550 °C in air with a reaction time of 2 h. During the interface reaction, temperature-dependent element diffusion takes the dominant role, and increased reactants take in the reaction with increasing calcination temperature. The grain for ceramic film is only 2–5 μm, which is much smaller than that for bulk ceramic. This is mainly due to the lower temperature and the interface diffusion. Ceramic film has a high transmittance larger than 90% at the visible range. Upon UV excitation at 254 nm, the film exhibits intense emission at the red wavelength range. The outcomes described in this work may have wide implications for transparent ceramics and layered rare-earth hydroxides. Full article
(This article belongs to the Special Issue Ceramic Films and Coatings: Properties and Applications)
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19 pages, 8925 KB  
Article
Microsurfacing Pavement Solutions with Alternative Aggregates and Binders: A Full Surface Texture Characterization
by Sergio Copetti Callai, Manuel De Rose, Piergiorgio Tataranni, Christina Makoundou, Cesare Sangiorgi and Rosolino Vaiana
Coatings 2022, 12(12), 1905; https://doi.org/10.3390/coatings12121905 - 6 Dec 2022
Cited by 9 | Viewed by 2127
Abstract
The road surface texture is responsible for controlling several quality/safety road indicators, such as friction, noise, and fuel consumption. Road texture can be classified into different wavelengths, and it is dependent on the material used in the paving solution. With the aim of [...] Read more.
The road surface texture is responsible for controlling several quality/safety road indicators, such as friction, noise, and fuel consumption. Road texture can be classified into different wavelengths, and it is dependent on the material used in the paving solution. With the aim of evaluating and characterizing the surface texture of a microsurfacing road pavement, six microsurfacing samples were made in the laboratory with both traditional materials (basaltic aggregates and bituminous emulsion) and with innovative materials from recycling procedures (crumb rubber (CR) and artificial engineered aggregate (AEA)). The characterization was performed through the use of a conoscopic holography profilometer with high precision and post-processing of the profiles detected through consolidated algorithms (ISO standards). We found that the aggregate type plays a very important role in the pavement texture. The binder agent seems to be highly important, but more studies regarding this are necessary. The use of crumb rubber as an aggregate proved to be feasible, and the texture parameters that were obtained were in accordance with the benchmark ones. In addition, the study shows that the use of artificial engineered aggregates does not impair the surface texture. Finally, the use of the texture parameters defined by the ISO standards, together with a statistical analysis, could be useful for defining the surface texture characteristics of microsurfacing. Full article
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25 pages, 4317 KB  
Article
Influence of Post-Deposition Thermal Treatments on the Morpho-Structural, and Bonding Strength Characteristics of Lithium-Doped Biological-Derived Hydroxyapatite Coatings
by L. Duta, G. E. Stan, G. Popescu-Pelin, I. Zgura, M. Anastasescu and F. N. Oktar
Coatings 2022, 12(12), 1883; https://doi.org/10.3390/coatings12121883 - 4 Dec 2022
Cited by 10 | Viewed by 3091
Abstract
We report on hydroxyapatite (HA) of biological-origin doped with lithium carbonate (LiC) and lithium phosphate (LiP) coatings synthesized by Pulsed laser deposition onto Ti6Al4V substrates fabricated by the Additive manufacturing technique. A detailed comparison from the structural, morphological, chemical composition, wetting behavior and [...] Read more.
We report on hydroxyapatite (HA) of biological-origin doped with lithium carbonate (LiC) and lithium phosphate (LiP) coatings synthesized by Pulsed laser deposition onto Ti6Al4V substrates fabricated by the Additive manufacturing technique. A detailed comparison from the structural, morphological, chemical composition, wetting behavior and bonding strength standpoints of as-deposited (NTT) and post-deposition thermal-treated (TT) coatings at temperatures ranging from 400 to 700 °C (i.e., TT400–TT700), was performed. Structural investigations indicated a complete crystallization of the initially amorphous HA-based layers at temperatures in excess of 500 °C. The morphological analyses emphasized the rough appearance of the film surfaces, consisting of particulates whose dimensions increased at higher temperatures, with an emphasis on LiC coatings. AFM investigations evidenced rough surfaces, with a clear tendency to increase in corrugation with the applied temperature, in the case of LiC coatings. A hydrophobic behavior was observed for control, NTT and TT400 samples, whilst a radical shift towards hydrophilicity was demonstrated for both types of structures at higher temperatures. In the case of TT500–TT700 coatings, the pull-out adherence values increased considerably compared to control ones. Taking into consideration the obtained results, the positive influence of post-deposition thermal treatments (performed at higher temperatures) on the physical–chemical and mechanical properties of LiC and LiP coatings was indicated. Alongside these improved characteristics observed at elevated temperatures, the sustainable nature of the used BioHA materials should recommend them as viable alternatives to synthetic HA ones for bone implant applications. Full article
(This article belongs to the Special Issue Synthetic and Biological-Derived Hydroxyapatite Implant Coatings)
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13 pages, 4747 KB  
Article
Effect of Annealing on the Microstructure, Opto-Electronic and Hydrogen Sensing Properties of V2O5 Thin Films Deposited by Magnetron Sputtering
by Michał Mazur, Szymon Kiełczawa and Jarosław Domaradzki
Coatings 2022, 12(12), 1885; https://doi.org/10.3390/coatings12121885 - 4 Dec 2022
Cited by 5 | Viewed by 2740
Abstract
This paper reports results of investigations on selected properties of vanadium oxide thin films deposited using gas impulse magnetron sputtering and annealed at temperatures in the range of 423 K to 673 K. Post-process annealing was shown to allow phase transition of as-deposited [...] Read more.
This paper reports results of investigations on selected properties of vanadium oxide thin films deposited using gas impulse magnetron sputtering and annealed at temperatures in the range of 423 K to 673 K. Post-process annealing was shown to allow phase transition of as-deposited films from amorphous to nanocrystalline V2O5 with crystallite sizes in the range of 23 to 27 nm. Simultaneously, annealing resulted in an increase in surface roughness and grain size. Moreover, a decrease in transparency was observed in the visible wavelength range of approximately 50% to 30%, while the resistivity of formed vanadium pentoxide thin films was almost unchanged and was in the order of 102 Ω·cm. Simultaneously, the best optoelectronic performance, testified by evaluated figure of merit parameter, indicated the as-deposited amorphous films. Performed Seebeck coefficient measurements indicated the electron type of electrical conduction of each prepared thin film. Furthermore, gas sensing properties towards diluted hydrogen were investigated for annealed V2O5 thin films, and it was found that the highest senor response was obtained for a thin film annealed at 673 K and measured at operating temperature of 623 K. Full article
(This article belongs to the Special Issue Optical Properties of Crystals and Thin Films)
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12 pages, 2490 KB  
Article
Electrodeposition of Copper Oxides as Cost-Effective Heterojunction Photoelectrode Materials for Solar Water Splitting
by Tai-Hsin Yin, Bu-Jine Liu, Yu-Wei Lin, Yi-Syuan Li, Chih-Wei Lai, Yu-Pin Lan, Changsik Choi, Han-Chen Chang and YongMan Choi
Coatings 2022, 12(12), 1839; https://doi.org/10.3390/coatings12121839 - 28 Nov 2022
Cited by 21 | Viewed by 5727
Abstract
Photoelectrocatalytic hydrogen production is crucial to reducing greenhouse gas emissions for carbon neutrality and meeting energy demands. Pivotal advances in photoelectrochemical (PEC) water splitting have been achieved by increasing solar light absorption. P-type Cu-based metal oxide materials have a wide range of energy [...] Read more.
Photoelectrocatalytic hydrogen production is crucial to reducing greenhouse gas emissions for carbon neutrality and meeting energy demands. Pivotal advances in photoelectrochemical (PEC) water splitting have been achieved by increasing solar light absorption. P-type Cu-based metal oxide materials have a wide range of energy band gaps and outstanding band edges for PEC water splitting. In this study, we first prepared Cu2O thin films using electrodeposition and fabricated a heterojunction structure of CuO/Cu2O by controlling annealing temperatures. The surface morphological, optical, and electrochemical properties were characterized using various analytical tools. X-ray and Raman spectroscopic approaches were used to verify the heterojunction of CuO/Cu2O, while surface analyses revealed surface roughness changes in thin films as the annealing temperatures increased. Electrochemical impedance spectroscopic measurements in conjunction with the Mott–Schottky analysis confirm that the CuO/Cu2O heterojunction thin film can boost photocurrent generation (1.03 mA/cm2 at 0 V vs. RHE) via enhanced light absorption, a higher carrier density, and a higher flat band potential than CuO and Cu2O thin films (0.92 and 0.08 mA/cm2, respectively). Full article
(This article belongs to the Special Issue Advanced Electrochemical Surface Properties)
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17 pages, 6463 KB  
Article
Photocatalytic Performance of ZnO/Ag(NPs) Nanocomposite Thin Films under Natural Conditions
by Mouna Khiari, Michaël Lejeune, Mickaël Gilliot, Florica Lazar and Aomar Hadjadj
Coatings 2022, 12(11), 1782; https://doi.org/10.3390/coatings12111782 - 21 Nov 2022
Cited by 2 | Viewed by 2405
Abstract
The original technique developed for the direct incorporation and efficient dispersion of silver metal NPs into ZnO precursor solution allowed us to elaborate nanocomposite thin films with a large effective surface area for interaction with the external environment as well as a large [...] Read more.
The original technique developed for the direct incorporation and efficient dispersion of silver metal NPs into ZnO precursor solution allowed us to elaborate nanocomposite thin films with a large effective surface area for interaction with the external environment as well as a large surface area for metal–semiconductor interaction suitable for surface photocatalysis reactions. Such photocatalysts have the advantage of being in solid form, combining the benefits of the semiconductor material and the metallic nanoparticles embedded in it, while being eco-friendly. Their photocatalytic performance was analyzed under different operating conditions. The improved photocatalytic performance, stability, and reusability of the nanocomposite were demonstrated under both laboratory and natural conditions of use. The results of the present study provide interesting perspectives for the application of these photocatalysts in water treatment. Full article
(This article belongs to the Special Issue Recent Advances in Functional Transparent Semiconductor Films and Coatings)
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17 pages, 4281 KB  
Article
Insights into the Electrical Characterization of Graphene-like Materials from Carbon Black
by Raffaella Ferraiuolo, Michela Alfe, Valentina Gargiulo, Giovanni Piero Pepe, Francesco Tafuri, Alessandro Pezzella, Giovanni Ausanio and Domenico Montemurro
Coatings 2022, 12(11), 1788; https://doi.org/10.3390/coatings12111788 - 21 Nov 2022
Cited by 2 | Viewed by 2878
Abstract
A new class of graphene-related materials (GRMs) obtained as water suspensions through a two-step oxidation/reduction of a nanostructured carbon black, namely graphene-like (GL) materials, has recently emerged. GL materials undergo self-assembly in thin amorphous films after drying upon drop-casting deposition on different surfaces. [...] Read more.
A new class of graphene-related materials (GRMs) obtained as water suspensions through a two-step oxidation/reduction of a nanostructured carbon black, namely graphene-like (GL) materials, has recently emerged. GL materials undergo self-assembly in thin amorphous films after drying upon drop-casting deposition on different surfaces. The GL films, with thicknesses of less than a micron, were composed of clusters of nanoparticles each around 40 nm in size. The exploitation of the GL films for different options (e.g., bioelectronic, sensoristic, functional filler in composite) requires a deep characterization of the material in terms of their electric transport properties and their possible interaction with the surface on which they are deposited. In this work, a careful electrical characterization of GL films was performed at room temperature and the results were compared with those achieved on films of benchmark graphenic materials, namely graphene oxide (GO) materials, obtained by the exfoliation of graphite oxide, which differ both in morphology and in oxidation degree. The results indicate a non-linear current–voltage relationship for all the investigated films. The extrapolated dielectric constant (ε) values of the investigated GRMs (GL and GO materials) agree with the experimental and theoretically predicted values reported in the literature (ε~2–15). Because similar conductance values were obtained for the GL materials deposited on glass and silicon oxide substrates, no significant interactions of GL materials with the two different substrates were highlighted. These results are the starting point for boosting a feasible use of GL materials in a wide spectrum of applications, ranging from electronics to optics, sensors, membranes, functional coatings, and biodevices. Full article
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16 pages, 10896 KB  
Article
High Temperature Low Friction Behavior of h-BN Coatings against ZrO2
by Qunfeng Zeng
Coatings 2022, 12(11), 1772; https://doi.org/10.3390/coatings12111772 - 19 Nov 2022
Cited by 11 | Viewed by 3514
Abstract
This paper presents high temperature low friction behaviors of the h-BN coatings, which were deposited on high-speed tool steel by radio frequency magnetron sputtering. A tribometer was used to investigate high temperature tribological properties of h-BN coatings against ZrO2 from 500 °C [...] Read more.
This paper presents high temperature low friction behaviors of the h-BN coatings, which were deposited on high-speed tool steel by radio frequency magnetron sputtering. A tribometer was used to investigate high temperature tribological properties of h-BN coatings against ZrO2 from 500 °C to 800 °C. The surface morphology, mechanical properties and chemical states of the worn surface of the friction pair were characterized and investigated systemically. The experimental results show that h-BN coatings are of significant importance to improve high temperature tribological properties of steel. Moreover, it is found that high temperature super low friction of the friction pairs is successfully achieved due to tribochemistry, which plays a key role in forming the in-situ generated Fe2O3/h-BN composites on the worn surface of h-BN coatings. CoFs of the friction pair are as super low as about 0.02 at 800 °C and around 0.03 at 600 °C at the stable stage. The high temperature super low friction mechanism of the friction pair is discussed in detail. The present study opens a new strategy to achieve high temperature super low friction of the friction system during sliding. Full article
(This article belongs to the Special Issue Technologies of Coatings and Surface Hardening for Tool Industry II)
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17 pages, 3663 KB  
Article
Chemical Structure, Optical and Dielectric Properties of PECVD SiCN Films Obtained from Novel Precursor
by Evgeniya Ermakova, Konstantin Mogilnikov, Igor Asanov, Anastasiya Fedorenko, Irina Yushina, Vadim Kichay, Eugene Maksimovskiy and Marina Kosinova
Coatings 2022, 12(11), 1767; https://doi.org/10.3390/coatings12111767 - 18 Nov 2022
Cited by 7 | Viewed by 5095
Abstract
A phenyl derivative of hexamethyldisilazane—bis(trimethylsilyl)phenylamine—was first examined as a single-source precursor for SiCN film preparation by plasma enhanced chemical vapor deposition. The use of mild plasma (20 W) conditions allowed the preparation of highly hydrogenated polymeric-like films. The synthesis was carried out under [...] Read more.
A phenyl derivative of hexamethyldisilazane—bis(trimethylsilyl)phenylamine—was first examined as a single-source precursor for SiCN film preparation by plasma enhanced chemical vapor deposition. The use of mild plasma (20 W) conditions allowed the preparation of highly hydrogenated polymeric-like films. The synthesis was carried out under an inert He atmosphere or under that of NH3 with the deposition temperature range from 100 to 400 °C. The chemical bonding structure and elemental composition were characterized by Fourier-transform infrared spectroscopy, energy-dispersive X-ray analysis and X-ray photoelectron spectroscopy. The surface morphology was investigated by scanning electron microscopy. Ellipsometric porosimetry, a unique high-precision technique to investigate the porosity of thin films, was applied to examine the porosity of SiCN samples. The films were found to possess a morphologically homogenous dense defect-free structure with a porosity of 2–3 vol.%. SiCN films were studied in terms of their optical and dielectric properties. Depending on the deposition conditions the refractive index ranged from 1.53 to 1.78. The optical bandgap obtained using UV-Vis spectroscopy data varied from 2.7 eV for highly hydrogenated polymeric-like film to 4.7 eV for cross-linked nitrogen-rich film. The dielectric constant was found to decrease from 3.51 to 2.99 with the rise of hydrocarbon groups’ content. The results obtained in this study were compared to the literature data to understand the influence of precursor design to the optical and electrical properties of the films. Full article
(This article belongs to the Special Issue Coatings and Thin Film for Chemical Vapor Deposition (CVD) Application)
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29 pages, 4262 KB  
Review
Magnetron Sputtering of Transition Metal Nitride Thin Films for Environmental Remediation
by Linda Aissani, Akram Alhussein, Abdul Wasy Zia, Gcina Mamba and Sami Rtimi
Coatings 2022, 12(11), 1746; https://doi.org/10.3390/coatings12111746 - 14 Nov 2022
Cited by 35 | Viewed by 8470
Abstract
The current economic and ecological situation encourages the use of steel to push the technological limits and offer more cost-effective products. The enhancement of steel properties like wear, corrosion, and oxidation resistance is achieved by the addition of small amounts of chemical elements [...] Read more.
The current economic and ecological situation encourages the use of steel to push the technological limits and offer more cost-effective products. The enhancement of steel properties like wear, corrosion, and oxidation resistance is achieved by the addition of small amounts of chemical elements such as Cr, Ni, Si, N, etc. The steel surface can be protected by different treatments such as heating and coating, among others. For many decades, coatings have been an effective solution to protect materials using thin hard films. Several technologies for thin film deposition have been developed. However, some of them are restricted to certain fields because of their complex operating conditions. In addition, some deposition techniques cannot be applied to a large substrate surface type. The magnetron sputtering deposition process is a good option to overcome these challenges and can be used with different substrates of varying sizes with specific growth modes and for a wide range of applications. In this review article, we present the sputtering mechanism and film growth modes and focus on the mechanical and tribological behavior of nitride thin films deposited by the magnetron sputtering technique as a function of process conditions, particularly bias voltage and nitrogen percentage. The biomedical properties of transition metal nitride coatings are also presented. Full article
(This article belongs to the Special Issue Bio-Based Packaging Films: Development, Characterization, and Application)
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14 pages, 7654 KB  
Article
Water-Repellent Coatings on Corrosion Resistance by Femtosecond Laser Processing
by Zexu Zhao, Guoyun Luo, Manping Cheng and Lijun Song
Coatings 2022, 12(11), 1736; https://doi.org/10.3390/coatings12111736 - 13 Nov 2022
Cited by 11 | Viewed by 3095
Abstract
Metal corrosion causes huge economic losses and major disasters every year. Inspired by the lotus leaf and nepenthes pitcher, the superhydrophobic surfaces (SHS) and the slippery liquid-infused porous surfaces (SLIPS) were produced as a potential strategy to prevent metal corrosion. However, how to [...] Read more.
Metal corrosion causes huge economic losses and major disasters every year. Inspired by the lotus leaf and nepenthes pitcher, the superhydrophobic surfaces (SHS) and the slippery liquid-infused porous surfaces (SLIPS) were produced as a potential strategy to prevent metal corrosion. However, how to prepare stable water-repellent coatings that can prevent the intrusion of corrosive ions remains to investigate. In this work, we first fabricated a micro/nano hierarchical structure on the aluminum surface by femtosecond laser processing. Then, the SHS was prepared on the above structure by fluorosilane modification. Finally, the SLIPS was fabricated on the SHS by coating lubricant. The morphology and wettability of the fabricated samples were evaluated by scanning electron microscopy and contact angle measurements. Furthermore, the corrosion resistance properties of SHS and SLIPS in simulated seawater were characterized by electrochemical measurements. From the comparison of the electrochemical parameters of different immersion times, both water-repellent coatings are effective in protecting the aluminum alloy from corrosion in simulated seawater due to reduced contact area between the metal substrate and corrosive solution. In comparison with the SHS, the SLIPS has a corrosion inhibition efficiency of up to 99.95% and it maintains long-term stability in the corrosive solution. This work also provides a promising method for the water-repellent coatings by femtosecond laser processing for metal corrosion prevention in practical industrial applications. Full article
(This article belongs to the Special Issue Novel Coatings for Preventing Marine Biofouling and Corrosion)
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17 pages, 1908 KB  
Review
Corrosion of Laser Cladding High-Entropy Alloy Coatings: A Review
by Yusheng Liu, Dingding Xiang, Kaiming Wang and Tianbiao Yu
Coatings 2022, 12(11), 1669; https://doi.org/10.3390/coatings12111669 - 3 Nov 2022
Cited by 30 | Viewed by 4660
Abstract
Material corrosion is a common phenomenon. Severe corrosion not only causes material failure, but may also lead to unexpected catastrophic accidents. Therefore, reducing the loss caused by corrosion has become a problem faced by countries around the world. As a surface modification technology, [...] Read more.
Material corrosion is a common phenomenon. Severe corrosion not only causes material failure, but may also lead to unexpected catastrophic accidents. Therefore, reducing the loss caused by corrosion has become a problem faced by countries around the world. As a surface modification technology, laser cladding (LC) can be used to prepare coatings that can achieve metallurgical bonding with the substrate. High-entropy alloys (HEAs) are a new material with superior anti-corrosion ability. Therefore, HEA coatings prepared by LC have become a research hotspot to improve the anti-corrosive ability of material surfaces. In this work, the effects of LC process parameters, post-processing, and the HEA material system on the anti-corrosion ability of HEA coatings and their mechanisms are reviewed. Among them, the LC process parameters influence the anti-corrosion ability by affecting the macroscopic quality, dilution rate, and uniformity of the coatings. The post-processing enhances the anti-corrosion ability of the coatings by improving the internal defects and refining the grain structure. The anti-corrosion ability of the coatings can be improved by appropriately adding transition metal elements such as Ni, Cr, Co, and rare earth elements such as Ce and Y. However, the lattice distortion, diversification of phase composition, and uneven distribution caused by excess elements will weaken the corrosion protection of the coatings. We reviewed the impact of corrosion medium on the anti-corrosion ability of coatings, in which the temperature and pH value of the corrosion medium affect the quality of the passive film on the surface of the coatings, thereby affecting the anti-corrosion ability of the coatings. Finally, to provide references for future research, the development trend of preparing HEA coatings by LC technology is prospected. Full article
(This article belongs to the Special Issue Laser Cladding Coatings: Microstructure, Properties, and Applications)
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10 pages, 2899 KB  
Article
Oxidation and Mechanical Behavior of Cr-Coated Laser Beam Welds Made from E110 Zirconium Alloy
by E. B. Kashkarov, K. S. Gusev, D. A. Ashikhmin, A. V. Abdulmenova and D. V. Sidelev
Coatings 2022, 12(11), 1623; https://doi.org/10.3390/coatings12111623 - 26 Oct 2022
Cited by 2 | Viewed by 2317
Abstract
This article describes the oxidation resistance of laser beam welds made from E110 zirconium alloy with a chromium coating obtained using multi-cathode magnetron sputtering. Oxidation tests of the welded Zr alloy without and with Cr coating were performed in an air atmosphere at [...] Read more.
This article describes the oxidation resistance of laser beam welds made from E110 zirconium alloy with a chromium coating obtained using multi-cathode magnetron sputtering. Oxidation tests of the welded Zr alloy without and with Cr coating were performed in an air atmosphere at 1100 °C for 2–90 min. Then, analysis of their cross-section microstructure in different regions (weld, heat-affected, and bulk zones) was done using optical microscopy. Hardness measurements and three-point bending tests demonstrated the hardening of the Cr-coated welded Zr alloy after the oxidation that is discussed in the article. Brittle fracture behavior was observed for uncoated Zr weld even after a short period of high-temperature oxidation. Full article
(This article belongs to the Special Issue Advanced Coatings for Accident Tolerant Fuel Claddings)
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16 pages, 9104 KB  
Article
Solidification Microstructure Prediction of Ti-6Al-4V Alloy Produced by Laser Melting Deposition
by Jin Liu, Hang Lv, Shao Xie, Ruipeng Han, Zhenlin Zhang, Yan Liu, Hui Chen, Yong Chen, Jian She and Dupeng He
Coatings 2022, 12(11), 1610; https://doi.org/10.3390/coatings12111610 - 22 Oct 2022
Cited by 7 | Viewed by 2828
Abstract
The ability to achieve a predictable solidification microstructure would greatly accelerate the qualification of the additive manufacturing process. Solidification microstructure control is a challenging issue for the additive manufacturing of metallic components using the laser melting deposition (LMD) method. To obtain desirable microstructure [...] Read more.
The ability to achieve a predictable solidification microstructure would greatly accelerate the qualification of the additive manufacturing process. Solidification microstructure control is a challenging issue for the additive manufacturing of metallic components using the laser melting deposition (LMD) method. To obtain desirable microstructure characteristics and mechanical properties, it is essential to research the solidification mechanism of microstructures initiated during the LMD process. In this study, the grain morphology and size of an LMD-fabricated Ti-6Al-4V alloy were predicted using a three-dimensional cellular automaton (CA) model coupled with a finite element (FE) model (CA–FE). First, the temperature distribution and solidification microstructure were established with the multi-scale CA–FE model, and the simulated results were shown to be in qualitative agreement with the experimental results. Moreover, the effects of the process parameters on both the thermal characteristics and the solidification microstructure were identified, and the morphologies and sizes of prior β grains under different laser power levels and scanning speeds were compared. The average grain size of the molten pool was shown to decrease with decreasing incident energy (lower laser power/higher scanning speed), and columnar-to-equiaxed transformation could be achieved under the proper processing parameters. This work will serve as a guide for the optimization and regulation of microstructures in the LMD process. Full article
(This article belongs to the Section Laser Coatings)
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11 pages, 3786 KB  
Article
Finite Element Analysis of Nanoindentation Responses in Bi2Se3 Thin Films
by Shu-Wei Cheng, Bo-Syun Chen, Sheng-Rui Jian, Yu-Min Hu, Phuoc Huu Le, Le Thi Cam Tuyen, Jyh-Wei Lee and Jenh-Yih Juang
Coatings 2022, 12(10), 1554; https://doi.org/10.3390/coatings12101554 - 15 Oct 2022
Cited by 5 | Viewed by 3497
Abstract
In this study, the nanoindentation responses of Bi2Se3 thin film were quantitatively analyzed and simulated by using the finite element method (FEM). The hardness and Young’s modulus of Bi2Se3 thin films were experimentally determined using the continuous [...] Read more.
In this study, the nanoindentation responses of Bi2Se3 thin film were quantitatively analyzed and simulated by using the finite element method (FEM). The hardness and Young’s modulus of Bi2Se3 thin films were experimentally determined using the continuous contact stiffness measurements option built into a Berkovich nanoindenter. Concurrently, FEM was conducted to establish a model describing the contact mechanics at the film/substrate interface, which was then used to reproduce the nanoindentation load-depth and hardness-depth curves. As such, the appropriate material parameters were obtained by correlating the FEM results with the corresponding experimental load-displacement curves. Moreover, the detailed nanoindentation-induced stress distribution in the vicinity around the interface of Bi2Se3 thin film and c-plane sapphires was mapped by FEM simulation for three different indenters, namely, the Berkovich, spherical and flat punch indenters. The results indicated that the nanoindentation-induced stress distribution at the film/substrate interface is indeed strongly dependent on the indenter’s geometric shape. Full article
(This article belongs to the Special Issue Recent Advances in the Growth and Characterizations of Thin Films)
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20 pages, 5424 KB  
Article
Application of the Holomorphic Tauc-Lorentz-Urbach Function to Extract the Optical Constants of Amorphous Semiconductor Thin Films
by Manuel Ballester, Marcos García, Almudena P. Márquez, Eduardo Blanco, Susana M. Fernández, Dorian Minkov, Aggelos K. Katsaggelos, Oliver Cossairt, Florian Willomitzer and Emilio Márquez
Coatings 2022, 12(10), 1549; https://doi.org/10.3390/coatings12101549 - 14 Oct 2022
Cited by 13 | Viewed by 3863
Abstract
The Tauc–Lorentz–Urbach (TLU) dispersion model allows us to build a dielectric function from only a few parameters. However, this dielectric function is non-analytic and presents some mathematical drawbacks. As a consequence of this issue, the model becomes inaccurate. In the present work, we [...] Read more.
The Tauc–Lorentz–Urbach (TLU) dispersion model allows us to build a dielectric function from only a few parameters. However, this dielectric function is non-analytic and presents some mathematical drawbacks. As a consequence of this issue, the model becomes inaccurate. In the present work, we will adopt a procedure to conveniently transform the TLU model into a self-consistent dispersion model. The transformation involves the integration of the original TLU imaginary dielectric function ϵ2 by using a Lorentzian-type function of semi-width, Γ. This novel model is analytic and obeys the other necessary mathematical requirements of the optical constants of solid-state materials. The main difference with the non-analytic TLU model occurs at values of the photon energy near or lower than that of the bandgap energy (within the Urbach absorption region). In particular, this new model allows us to reliably extend the optical characterization of amorphous-semiconductor thin films within the limit to zero photon energy. To the best of our knowledge, this is the first time that the analytic TLU model has been successfully used to accurately determine the optical constants of unhydrogenated a-Si films using only their normal-incidence transmission spectra. Full article
(This article belongs to the Special Issue New Advances in Novel Optical Materials and Devices)
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16 pages, 3537 KB  
Article
Characterization and Tribological Behavior of Electroless-Deposited Ni-P-PTFE Films on NBR Substrates for Dynamic Contact Applications
by Beatriz Vasconcelos, Ricardo Serra, João Oliveira and Carlos Fonseca
Coatings 2022, 12(10), 1410; https://doi.org/10.3390/coatings12101410 - 27 Sep 2022
Cited by 10 | Viewed by 3767
Abstract
The use of rubber in dynamic contacts often results in severe degradation and wear of the rubber surface, which is why dynamic rubber seal contacts are usually oil lubricated to ensure their functionality. However, the increasing demand for more convenient and environmentally friendly [...] Read more.
The use of rubber in dynamic contacts often results in severe degradation and wear of the rubber surface, which is why dynamic rubber seal contacts are usually oil lubricated to ensure their functionality. However, the increasing demand for more convenient and environmentally friendly sealing solutions has prompted the development of dry low-friction rubber coatings. In this work, and for the first time, Ni-P and polytetrafluoroethylene (PTFE) particles were co-deposited by electroless plating on Nitrile Butadiene Rubber (NBR), as a low-cost solution to improve the NBR tribological behavior. A cationic surfactant, cetyltrimethylammonium bromide (CTAB), was added to the plating bath to ensure a homogeneous and efficient incorporation of PTFE into the Ni-P. The optimized PTFE incorporation reached 6.8%, and the composite coating adhesion to NBR was 20% higher than that of nickel-phosphorous (Ni-P) films. The tribological properties of the coatings evaluated by pin-on-disk tests showed a marginal decrease in the coefficient of friction (CoF) (10%, 1 N load), compared to that of Ni-P. However, the tested PTFE-based coatings displayed significantly smoother surfaces with less debris and cracks, clearly demonstrating the benefits of the PTFE in terms of wear resistance for loads up to 5 N. Full article
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10 pages, 1384 KB  
Article
Gold Nanoparticles Decorated Titanium Oxide Nanotubes with Enhanced Antibacterial Activity Driven by Photocatalytic Memory Effect
by Hongqin Zhu, Ji Tan, Jiajun Qiu, Donghui Wang, Zhe Zhao, Zihan Lu, Gaoshan Huang, Xuanyong Liu and Yongfeng Mei
Coatings 2022, 12(9), 1351; https://doi.org/10.3390/coatings12091351 - 16 Sep 2022
Cited by 13 | Viewed by 2936
Abstract
Titanium and its alloys have been widely used for orthopedic and dental implants. However, implant failures often occur due to the implant-related bacterial infections. Herein, titanium oxide nanotubes (TNTs) with an average diameter of 75 nm were formed by anodizing on the surface [...] Read more.
Titanium and its alloys have been widely used for orthopedic and dental implants. However, implant failures often occur due to the implant-related bacterial infections. Herein, titanium oxide nanotubes (TNTs) with an average diameter of 75 nm were formed by anodizing on the surface of titanium, and subsequently gold (Au) nanoparticles were deposited on TNTs by magnetron sputtering (Au@TNTs). The antibacterial study shows that TNTs surface decorated with Au nanoparticles exhibits the preferable effect in restricting the growth of Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) even under dark conditions, and the antibacterial rates reached 84% and 75%, respectively. In addition, the constructed film showed no cytotoxicity. Such a selective bactericidal effect of Au@TNTs samples might be attributed to the photocatalytic memory effect, which provides a new insight in the designing of antibacterial surfaces for biomedical application. Full article
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11 pages, 2532 KB  
Article
Ferroelectric B-Site Modified Bismuth Lanthanum Titanate Thin Films for High-Efficiency PV Systems
by Rui Tang, Rui He, Sangmo Kim and Chung Wung Bark
Coatings 2022, 12(9), 1315; https://doi.org/10.3390/coatings12091315 - 9 Sep 2022
Cited by 2 | Viewed by 2093
Abstract
Over the past decades, ferroelectric photovoltaic (FE-PV) systems, which use a homogenous ferroelectric material as a light-absorbing layer, have been studied using ferroelectric oxides. The PV activity of materials can be enhanced by adjusting the bandgap of materials, and it would have a [...] Read more.
Over the past decades, ferroelectric photovoltaic (FE-PV) systems, which use a homogenous ferroelectric material as a light-absorbing layer, have been studied using ferroelectric oxides. The PV activity of materials can be enhanced by adjusting the bandgap of materials, and it would have a large effect on the ferroelectric complex oxides. This phenomenon in epitaxial thin films of ferroelectric complex oxide, Bi3.25La0.75Ti3O12 (BLT), Fe- and Co-doped films were observed. Compared with undoped BLT, Co-(BLCT) doping and Fe and Co combined (BLFCT) doping resulted in the gradual reduction in the bandgap and efficient visible light absorption. The reduction in the bandgap to 11.4% and 18.1% smaller than the experimentally measured Eg of the bismuth titanate-based film using a simple Fe- and Co-doping method was performed, while maintaining ferroelectricity by analyzing the BLCT and BLFCT films based on polarization loops, and the temperature range of the out-of-plane lattice parameters and the photocurrent density of the BLFCT film was 32.2 times higher than that of the BLT film, which was caused by the decrease in the bandgap. This simple doping technique can be used to tune additional wide-bandgap complex oxides so that they can be used in photovoltaic energy conversion or optoelectronic devices. Full article
(This article belongs to the Special Issue Optical Thin Film and Photovoltaic (PV) Related Technologies)
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11 pages, 2650 KB  
Article
Comparison of K340 Steel Microstructure and Mechanical Properties Using Shallow and Deep Cryogenic Treatment
by Patricia Jovičević-Klug, László Tóth and Bojan Podgornik
Coatings 2022, 12(9), 1296; https://doi.org/10.3390/coatings12091296 - 2 Sep 2022
Cited by 17 | Viewed by 3816
Abstract
In this research, Böhler K340 cold work tool steel was subjected to three different heat treatment protocols, conventional heat treatment (CHT), shallow cryogenic treatment (SCT), and deep cryogenic treatment (DCT). The study compares the effect of SCT and DCT on the microstructure and [...] Read more.
In this research, Böhler K340 cold work tool steel was subjected to three different heat treatment protocols, conventional heat treatment (CHT), shallow cryogenic treatment (SCT), and deep cryogenic treatment (DCT). The study compares the effect of SCT and DCT on the microstructure and consequently on the selected mechanical properties (micro- and macroscale hardness and impact toughness). The study shows no significant difference in macroscale hardness after the different heat treatments. However, the microhardness values indicate a slightly lower hardness in the case of SCT and DCT. Microstructure analysis with light (LM) and scanning electron microscopy (SEM) indicated a finer and more homogenous microstructure with smaller lath size and preferential orientation of the martensitic matrix in SCT and DCT samples compared to CHT. In addition, the uniform precipitation of more spherical and finer carbides is determined for both cryogenic treatments. Moreover, the precipitation of small dispersed secondary carbides is observed in SCT and DCT, whereas in the CHT counterparts, these carbide types were not detected. X-ray diffraction (XRD) and electron backscatter diffraction (EBSD) confirms that SCT and DCT are very effective in minimizing the amount of retained austenite down to 1.8 vol.% for SCT and even below 1 vol.% for the DCT variant. Full article
(This article belongs to the Special Issue Mechanical, Corrosive and Tribological Degradation of Metal Coatings and Modified Metallic Surfaces)
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17 pages, 3020 KB  
Article
Spectrophotometric Characterization of Thin Semi-Transparent Aluminum Films Prepared by Electron Beam Evaporation and Magnetron Sputtering
by Steffen Wilbrandt, Olaf Stenzel, Abrar Liaf, Peter Munzert, Stefan Schwinde, Sven Stempfhuber, Nadja Felde, Marcus Trost, Tina Seifert and Sven Schröder
Coatings 2022, 12(9), 1278; https://doi.org/10.3390/coatings12091278 - 1 Sep 2022
Cited by 3 | Viewed by 3986
Abstract
Aluminum thin films with thicknesses between approximately 10 and 60 nm have been deposited by evaporation and sputtering techniques. Layer characterization focused on reflectance, optical constants, and surface quality. Reflectance fits have been performed using a merger of three standard dispersion models, namely [...] Read more.
Aluminum thin films with thicknesses between approximately 10 and 60 nm have been deposited by evaporation and sputtering techniques. Layer characterization focused on reflectance, optical constants, and surface quality. Reflectance fits have been performed using a merger of three standard dispersion models, namely the Drude model, the Lorentzian oscillator model, and the beta-distributed oscillator model. A thickness dependence of the optical constants could be established in the investigated thickness range. Full article
(This article belongs to the Special Issue Metal or Metal-Containing Films: From Preparation to Optical Applications)
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12 pages, 6385 KB  
Article
Characteristics of Thin High Entropy Alloy Films Grown by Pulsed Laser Deposition
by Edwin Alexandru Laszlo, Doina Crăciun, Gabriela Dorcioman, Gabriel Crăciun, Victor Geantă, Ionelia Voiculescu, Daniel Cristea and Valentin Crăciun
Coatings 2022, 12(8), 1211; https://doi.org/10.3390/coatings12081211 - 18 Aug 2022
Cited by 11 | Viewed by 2986
Abstract
Starting from solid-solutions (SS) of AlCoCrFeNix high-entropy alloys (HEAs) that have been produced with high purity constituent elements by vacuum arc remelting (VAR) method varying the nickel molar ratio x from 0.2 to 2.0, we investigated the synthesis of protective thin films [...] Read more.
Starting from solid-solutions (SS) of AlCoCrFeNix high-entropy alloys (HEAs) that have been produced with high purity constituent elements by vacuum arc remelting (VAR) method varying the nickel molar ratio x from 0.2 to 2.0, we investigated the synthesis of protective thin films of HEAs and high-entropy nitrides (HENs) with the aid of the pulsed laser deposition (PLD) system. The structure of all ten available bulk targets have been examined by means of X-Ray Diffraction (XRD), as well as their elemental composition by means of energy dispersion X-ray spectroscopy (EDS). Three targets with nickel molar composition x = 0.4, 1.2 and 2.0 corresponding to BCC, mixed BCC and FCC, and finally FCC structures were used for thin film depositions using a KrF excimer laser. The depositions were performed in residual low vacuum (10−7 mbar) and under N2 (10−4 mbar) at room temperature (RT~25 °C) on Si and glass substrates. The deposited films’ structure was investigated using grazing incidence XRD, their surface morphology, thickness and elemental composition by scanning electron microscopy (SEM), EDS and X-ray photoelectron spectroscopy (XPS), respectively. A homemade four-point probe (4PP) set-up was applied to determine layers electrical resistance. Besides, a Nanoindentation (NI) was employed to test films’ mechanical properties. XRD results showed that all deposited films, regardless of the initial structure of targets, were a mixture of FCC and BCC structures. Additionally, the quantitative and qualitative EDS and XPS results showed that the elemental composition of films was rather close to that of the targets. The depositions under an N2 atmosphere resulted in the inclusion of several percentage nitrogen atoms in a metallic nitride type compound into films, which may explain their higher electrical resistivity. The Young’s modulus, nanohardness and friction coefficient values showed that the deposited films present good mechanical properties and could be used as protective coatings to prevent damage in harsh environments. Full article
(This article belongs to the Special Issue 2D Materials-Based Thin Films and Coatings)
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17 pages, 8446 KB  
Article
Effect of the Cooling Rate of Thermal Simulation on the Microstructure and Mechanical Properties of Low-Carbon Bainite Steel by Laser-Arc Hybrid Welding
by Jintao Chen, Zhenlin Zhang, Zhiyi Zhang, Yingzong Liu, Xu Zhao, Jingqing Chen and Hui Chen
Coatings 2022, 12(8), 1045; https://doi.org/10.3390/coatings12081045 - 24 Jul 2022
Cited by 11 | Viewed by 3118
Abstract
A new kind of low-carbon bainite steel with excellent strength and toughness was developed, serving as the bogie of the next-generation high-speed train. However, the softening of the heat-affected zone (HAZ) in laser-arc hybrid welding (LAHW) needs to be overcome. In this study, [...] Read more.
A new kind of low-carbon bainite steel with excellent strength and toughness was developed, serving as the bogie of the next-generation high-speed train. However, the softening of the heat-affected zone (HAZ) in laser-arc hybrid welding (LAHW) needs to be overcome. In this study, the effect of the cooling rate of the LAHW process on the microstructure and mechanical properties in the HAZ was explored via thermal simulation. The results showed that with increased cooling rate, the grain size increased, the content of lath martensite decreased, and the lath bainite gradually changed to a granular shape in the thermal simulation specimen. With the decrease in the cooling rate, i.e., with the increase of t8/5, the strength–toughness matching of the material showed a downward trend. The thermal simulation specimen with a t8/5 of 6~8 s had higher strength and good toughness, which can be considered a potential welding parameter reference. The content of martensitic austenite (M-A) constituents was the main factor that determined the strength and toughness of the joint. During the tensile test, the axial force caused the material to tighten, and the transverse stress as obvious in the part of the M-A constituents that are prone to microcracks and many defects, resulting in cracks, paths, and multi-component layers in the center. As a result, the thermal cycle specimens had mixed fracture characteristics. Full article
(This article belongs to the Section Laser Coatings)
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17 pages, 2026 KB  
Article
Gravure Printing for PVDF Thin-Film Pyroelectric Device Manufacture
by Giuliano Sico, Maria Montanino, Fausta Loffredo, Carmela Borriello and Riccardo Miscioscia
Coatings 2022, 12(7), 1020; https://doi.org/10.3390/coatings12071020 - 19 Jul 2022
Cited by 13 | Viewed by 4442
Abstract
Pyroelectric energy harvesting is one of the more recent and promising solid-state approaches for directly converting time-dependent temperature fluctuations into electric energy. Conventional printing technologies can offer many advantages for the production of pyroelectric thin-film-based devices, such as low cost, low temperature, the [...] Read more.
Pyroelectric energy harvesting is one of the more recent and promising solid-state approaches for directly converting time-dependent temperature fluctuations into electric energy. Conventional printing technologies can offer many advantages for the production of pyroelectric thin-film-based devices, such as low cost, low temperature, the use of flexible substrates and shaping at the same time as deposition. Nevertheless, some issues related to low printed thickness and film-forming microstructure control need to be addressed. In this exploratory study, the possibility of exploiting the highly attractive gravure printing process for the potential industrial manufacture of flexible polyvinylidene fluoride (PVDF) thin-film pyroelectric devices was investigated. By the use of corona pre-treatment of the printing substrate and low-temperature polar solvent evaporation, multilayer gravure-printed PVDF pyroelectric devices were successfully manufactured for the first time, achieving a maximum generated current of 0.1 nA at 2.5 K/s from a device with an active area of 1 cm2. Considering the very low thermal inertia and performance scaling by the area expected for pyroelectric thin-film-based devices, combined with the upscaling potential of roll-to-roll gravure printing, our results provide new opportunities for on-demand, low-cost pyroelectric device manufacture and their integration in hybrid harvesters. Full article
(This article belongs to the Special Issue Printed Functional Thin Films for Electronic, Optoelectronic and Sensing Applications)
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9 pages, 15217 KB  
Article
Mechanical Properties and Thermal Stability of CrZrN/CrZrSiN Multilayer Coatings with Different Bilayer Periods
by Hoe-Kun Kim, Sung-Min Kim and Sang-Yul Lee
Coatings 2022, 12(7), 1025; https://doi.org/10.3390/coatings12071025 - 19 Jul 2022
Cited by 11 | Viewed by 2731
Abstract
The CrZrN/CrZrSiN multilayer coatings at a bilayer period range decreasing from 1.35 μm to 0.45 μm were synthesized on a Si (100) wafer and WC-6 wt.% Co substrate using a closed-field unbalanced magnetron sputter, and the thickness effects on the mechanical properties and [...] Read more.
The CrZrN/CrZrSiN multilayer coatings at a bilayer period range decreasing from 1.35 μm to 0.45 μm were synthesized on a Si (100) wafer and WC-6 wt.% Co substrate using a closed-field unbalanced magnetron sputter, and the thickness effects on the mechanical properties and thermal stability were investigated. The CrZrN/CrZrSiN multilayer coatings showed high hardness and elastic modulus in the ranges of 28 to 33 GPa and 255 to 265 GPa, respectively, and the friction coefficient showed the lowest value of 0.24 on the multilayer coating with a bilayer period of 0.54 μm. The bilayer periods affected the adhesion strength of the multilayer coatings. From the scratch test, the critical load (Lc2) steadily increased with the decreasing of the bilayer period, and the CrZrN/CrZrSiN multilayer coating with a bilayer period of 0.45 μm showed the highest critical load (Lc2) of 79 N. In the case of the annealing test, the bilayer periods affected the thermal stability of the multilayer coatings, and the CrZrN/CrZrSiN multilayer coatings with 0.54 μm showed a maximum hardness value of approximately 30 GPa up to 800 °C. Full article
(This article belongs to the Special Issue Technologies of Coatings and Surface Hardening for Tool Industry II)
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18 pages, 6899 KB  
Article
Implementing Supervised and Unsupervised Deep-Learning Methods to Predict Sputtering Plasma Features, a Step toward Digitizing Sputter Deposition of Thin Films
by Ali Salimian, Evan Haine, Cova Pardo-Sanchez, Abul Hasnath and Hari Upadhyaya
Coatings 2022, 12(7), 953; https://doi.org/10.3390/coatings12070953 - 5 Jul 2022
Cited by 3 | Viewed by 3643
Abstract
The spectral emission data from the plasma glow of various sputtering targets containing indium oxide, zinc oxide, and tin oxide were obtained. The plasma was generated at various power and chamber pressures. These spectral data were then converted into two-dimensional arrays by implementing [...] Read more.
The spectral emission data from the plasma glow of various sputtering targets containing indium oxide, zinc oxide, and tin oxide were obtained. The plasma was generated at various power and chamber pressures. These spectral data were then converted into two-dimensional arrays by implementing a basic array-reshaping technique and a more complex procedure utilizing an unsupervised deep-learning technique, known as the self-organizing-maps method. The two-dimensional images obtained from each single-emission spectrum of the plasma mimic an image that can then be used to train a convolutional neural network model capable of predicting certain plasma features, such as impurity levels in the sputtering target, working gas composition, plasma power, and chamber pressure during the machine operation. We show that our single-array-to-2D-array conversion technique, coupled with deep-learning techniques and computer vision, can achieve high predictive accuracy and can, therefore, be fundamental to the construction of a sputtering system’s digital twin. Full article
(This article belongs to the Special Issue New Advances in Plasma Deposition and Its Applications)
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23 pages, 12925 KB  
Article
The Role of Anodising Parameters in the Performance of Bare and Coated Aerospace Anodic Oxide Films
by Mariana Paz Martinez-Viademonte, Shoshan T. Abrahami, Meisam D. Havigh, Kristof Marcoen, Theodor Hack, Malte Burchardt and Herman Terryn
Coatings 2022, 12(7), 908; https://doi.org/10.3390/coatings12070908 - 27 Jun 2022
Cited by 5 | Viewed by 3999
Abstract
The anodising process parameters (voltage, temperature, and electrolyte) control the morphology and the chemical composition of the resulting anodic oxide film by altering the balance between oxide growth and oxide dissolution reactions. The porosity of the oxide film is reduced by the addition [...] Read more.
The anodising process parameters (voltage, temperature, and electrolyte) control the morphology and the chemical composition of the resulting anodic oxide film by altering the balance between oxide growth and oxide dissolution reactions. The porosity of the oxide film is reduced by the addition of tartaric acid to a sulfuric acid electrolyte, while anodising at elevated temperatures enhances oxide dissolution, leading to wider pores and rougher surfaces. No significant changes in the oxide chemical composition as a function of anodising parameters was found; in particular, no tartrate incorporation took place. The resistance of uncoated anodic oxide films against aggressive media and galvanic stress as a function of anodising parameters has been studied by electrochemical methods. Anodising in a mixed tartaric and sulfuric acid electrolyte improves the resistance of the anodic oxide against galvanic stress and aggressive media in comparison to sulfuric acid anodising processes. However, the corrosion protection performance of the anodic oxide films in combination with a corrosion-inhibitor loaded organic coating is not governed by the blank oxide properties but by the adhesion-enhancing morphological features formed during anodising at elevated temperatures at the oxide/coating interface. Full article
(This article belongs to the Special Issue Surface Modification/Engineering for Electrochemical Applications)
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11 pages, 3088 KB  
Article
Effects of Substrate Temperature on Nanomechanical Properties of Pulsed Laser Deposited Bi2Te3 Films
by Hui-Ping Cheng, Phuoc Huu Le, Le Thi Cam Tuyen, Sheng-Rui Jian, Yu-Chen Chung, I-Ju Teng, Chih-Ming Lin and Jenh-Yih Juang
Coatings 2022, 12(6), 871; https://doi.org/10.3390/coatings12060871 - 20 Jun 2022
Cited by 8 | Viewed by 2785
Abstract
The correlations among microstructure, surface morphology, hardness, and elastic modulus of Bi2Te3 thin films deposited on c-plane sapphire substrates by pulsed laser deposition are investigated. X-ray diffraction (XRD) and transmission electron microscopy are used to characterize the microstructures of [...] Read more.
The correlations among microstructure, surface morphology, hardness, and elastic modulus of Bi2Te3 thin films deposited on c-plane sapphire substrates by pulsed laser deposition are investigated. X-ray diffraction (XRD) and transmission electron microscopy are used to characterize the microstructures of the Bi2Te3 thin films. The XRD analyses revealed that the Bi2Te3 thin films were highly (00l)-oriented and exhibited progressively improved crystallinity when the substrate temperature (TS) increased. The hardness and elastic modulus of the Bi2Te3 thin films determined by nanoindentation operated with the continuous contact stiffness measurement (CSM) mode are both substantially larger than those reported for bulk samples, albeit both decrease monotonically with increasing crystallite size and follow the Hall—Petch relation closely. Moreover, the Berkovich nanoindentation-induced crack exhibited trans-granular cracking behaviors for all films investigated. The fracture toughness was significantly higher for films deposited at the lower TS; meanwhile, the fracture energy was almost the same when the crystallite size was suppressed, which indicated a prominent role of grain boundary in governing the deformation characteristics of the present Bi2Te3 films. Full article
(This article belongs to the Special Issue Recent Advances in the Growth and Characterizations of Thin Films)
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11 pages, 2785 KB  
Article
Diffusion Barrier Characteristics of WSiN Films
by Yung-I Chen, Kuo-Hong Yeh, Tzu-Yu Ou and Li-Chun Chang
Coatings 2022, 12(6), 811; https://doi.org/10.3390/coatings12060811 - 10 Jun 2022
Cited by 4 | Viewed by 3150
Abstract
WSiN films were produced through hybrid pulse direct current/radio frequency magnetron co-sputtering and evaluated as diffusion barriers for Cu metallization. The Cu/WSiN/Si assemblies were annealed for 1 h in a vacuum at 500–900 °C. The structural stability and diffusion barrier performance of the [...] Read more.
WSiN films were produced through hybrid pulse direct current/radio frequency magnetron co-sputtering and evaluated as diffusion barriers for Cu metallization. The Cu/WSiN/Si assemblies were annealed for 1 h in a vacuum at 500–900 °C. The structural stability and diffusion barrier performance of the WSiN films were explored through X-ray diffraction, Auger electron spectroscopy, and sheet resistance measurement. The results indicated that the Si content of WSiN films increased from 0 to 9 at.% as the power applied to the Si target was increased from 0 to 150 W. The as-deposited W76N24, W68Si0N32, and W63Si4N33 films formed a face-centered cubic W2N phase, whereas the as-deposited W59Si9N32 film was near-amorphous. The lattice constants of crystalline WSiN films decreased after annealing. The sheet resistance of crystalline WSiN films exhibited a sharp increase as they were annealed at 800 °C, accompanied by the formation of a Cu3Si compound. The failure of the near-amorphous W59Si9N32 barrier against Cu diffusion was observed when annealed at 900 °C. Full article
(This article belongs to the Collection Feature Paper Collection in Thin Films)
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28 pages, 2814 KB  
Review
Nano- and Micro-Scale Impact Testing of Hard Coatings: A Review
by Ben D. Beake
Coatings 2022, 12(6), 793; https://doi.org/10.3390/coatings12060793 - 8 Jun 2022
Cited by 27 | Viewed by 4743
Abstract
In this review, the operating principles of the nano-impact test technique are described, compared and contrasted to micro- and macro-scale impact tests. Impact fatigue mechanisms are discussed, and the impact behaviour of three different industrially relevant coating systems has been investigated in detail. [...] Read more.
In this review, the operating principles of the nano-impact test technique are described, compared and contrasted to micro- and macro-scale impact tests. Impact fatigue mechanisms are discussed, and the impact behaviour of three different industrially relevant coating systems has been investigated in detail. The coating systems are (i) ultra-thin hard carbon films on silicon, (ii) DLC on hardened tool steel and (iii) nitrides on WC-Co. The influence of the mechanical properties of the substrate and the load-carrying capacity (H3/E2) of the coating, the use of the test to simulate erosion, studies modelling the nano- and micro-impact test and performing nano- and micro-impact tests at elevated temperature are also discussed. Full article
(This article belongs to the Special Issue 10th Anniversary of Coatings: Invited Papers in "Surface Characterization, Deposition and Modification" Section)
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