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Coatings, Volume 10, Issue 5 (May 2020) – 77 articles

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Open AccessArticle
Study on the Chloride Threshold and Risk Assessment of Rebar Corrosion in Simulated Concrete Pore Solutions under Applied Potential
Coatings 2020, 10(5), 505; https://doi.org/10.3390/coatings10050505 (registering DOI) - 24 May 2020
Abstract
The pitting corrosion behavior of HRB400 steel in various simulated concrete environments was investigated by the combination of polarization curves and statistical method. The results indicated that the chloride concentration threshold ([Cl]th) for pitting of the steel was greatly [...] Read more.
The pitting corrosion behavior of HRB400 steel in various simulated concrete environments was investigated by the combination of polarization curves and statistical method. The results indicated that the chloride concentration threshold ([Cl]th) for pitting of the steel was greatly affected by pH when the applied potential exists, which is always caused by random stray current. The interaction of applied potential and chloride concentration on the pitting behavior was discussed. Finally, pitting-risk-evaluation diagrams were built up, which could be easily used to assess the pitting risk of reinforcing bars under the chloride-containing environment with stray current. Full article
(This article belongs to the Special Issue Modern Trends in Corrosion Protection of Steels)
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Open AccessArticle
Investigation of Conductive Mechanism of Amorphous IGO Resistive Random-Access Memory with Different Top Electrode Metal
Coatings 2020, 10(5), 504; https://doi.org/10.3390/coatings10050504 (registering DOI) - 24 May 2020
Abstract
In this paper, resistive random-access memory (RRAM) with InGaO (IGO) as an active layer was fabricated by radio-frequency (RF) sputtering system and the resistive switching mechanism with the different top electrode (TE) of Pt, Ti, and Al were investigated. The Pt/IGO/Pt/Ti RRAM exhibits [...] Read more.
In this paper, resistive random-access memory (RRAM) with InGaO (IGO) as an active layer was fabricated by radio-frequency (RF) sputtering system and the resistive switching mechanism with the different top electrode (TE) of Pt, Ti, and Al were investigated. The Pt/IGO/Pt/Ti RRAM exhibits typical bipolar resistive switching features with an average set voltage of 1.73 V, average reset voltage of −0.60 V, average high resistance state (HRS) of 54,954.09 Ω, and the average low resistance state (LRS) of 64.97 Ω, respectively. Ti and Al were substituted for Pt as TE, and the conductive mechanism was different from TE of Pt. When Ti and Al were deposited onto the switching layer, both TE of Ti and Al will form oxidation of TiOx and AlOx because of their high activity to oxygen. The oxidation will have different effects on the forming of filaments, which may further affect the RRAM performance. The details of different mechanisms caused by different TE will be discussed. In brief, IGO is an excellent candidate for the RRAM device and with the aids of TiOx, the set voltage, and reset voltage, HRS and LRS become much more stable. Full article
(This article belongs to the Special Issue Advances in Thin Film Transistors: Properties and Applications)
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Open AccessArticle
Experimental Investigation to Improve the Energy Efficiency of Solar PV Panels Using Hydrophobic SiO2 Nanomaterial
Coatings 2020, 10(5), 503; https://doi.org/10.3390/coatings10050503 (registering DOI) - 24 May 2020
Abstract
This research aims to experimentally improve the overall efficiency of solar photovoltaic (PV) panels by coating them with hydrophobic SiO2 nanomaterial. Also, an accurate mathematical model was used to estimate the parameters of the PV panel, which is a non-linear optimization problem. [...] Read more.
This research aims to experimentally improve the overall efficiency of solar photovoltaic (PV) panels by coating them with hydrophobic SiO2 nanomaterial. Also, an accurate mathematical model was used to estimate the parameters of the PV panel, which is a non-linear optimization problem. Based on the experimental data and using the particle swarm optimization (PSO) algorithm, the optimal five parameters of a single diode model of a PV panel were determined in this study. This experimental work was conducted and carried out in the Renewable Energy Laboratory of Assiut University, Egypt. A comparative analysis was completed for three identical solar PV panels; the first panel was coated with hydrophobic SiO2 nanomaterial, so it was considered to be a self-cleaning panel; the second panel was uncoated and cleaned manually on a daily basis; and the third panel was kept dusty all the time through the experimental investigation, and was used as a reference. Experimentally, the output power of the PV panels was monitored for each panel in this study. Also, the anti-static and anti-reflection effects of coating solar PV panels with hydrophobic SiO2 nanomaterial were investigated experimentally. According to the obtained experimental results, it was found that the use of SiO2 coating for PV panels results in the better performance of the PV panels. The overall efficiency of the coated panel increased by 15% and 5%, compared to the dusty panel and the uncoated panel which was manually cleaned daily, respectively. Full article
(This article belongs to the Special Issue Coatings for Solar Cell Applications)
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Open AccessArticle
Fabrication, Wear, and Corrosion Resistance of HVOF Sprayed WC-12Co on ZE41 Magnesium Alloy
Coatings 2020, 10(5), 502; https://doi.org/10.3390/coatings10050502 (registering DOI) - 24 May 2020
Abstract
This study shows that WC-12Co coatings with low porosity and high wear and corrosion resistance can be applied by high velocity oxygen-fuel (HVOF) on a low melting and highly flammable ZE41 magnesium alloy. This provides a novel and promising use of the high-energy [...] Read more.
This study shows that WC-12Co coatings with low porosity and high wear and corrosion resistance can be applied by high velocity oxygen-fuel (HVOF) on a low melting and highly flammable ZE41 magnesium alloy. This provides a novel and promising use of the high-energy thermal spraying technique on low temperature melting substrates. The spraying distance used was 300 mm, which is between two and three times the recommended distanced for HVOF coating with WC-12Co on steels. Despite this, the WC-12Co coatings obtained were homogeneous, crack-free, and dense. The coatings were very well adhered to the substrates and the spraying distance allowed avoiding any thermal affectation of the substrate. The thickness of the coatings was limited to 45 μm to avoid a big mass increase in the samples. The effect of the number of layers, the O2/H2 ratio and the gas transport flow in the coating was studied. The coatings reduced the wear rate of the substrate by 104 times, making them wear resistant. Electrochemical corrosion tests were conducted to study the corrosion protection of the coatings, showing that it is possible to protect the magnesium substrate for 96 h in contact with 3.5 wt.% NaCl aqueous solution. Full article
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Open AccessReview
Ultra-Short Pulsed Laser Deposition of Oxides, Borides and Carbides of Transition Elements
Coatings 2020, 10(5), 501; https://doi.org/10.3390/coatings10050501 (registering DOI) - 23 May 2020
Viewed by 153
Abstract
Oxides, borides and carbides of the transition elements are materials of great interest from a technologic point of view. Many of these materials are used in the form of thin films, so several techniques are commonly used to deposit them. Among these techniques, [...] Read more.
Oxides, borides and carbides of the transition elements are materials of great interest from a technologic point of view. Many of these materials are used in the form of thin films, so several techniques are commonly used to deposit them. Among these techniques, Pulsed Laser Deposition (PLD) performed using ultra-short pulse lasers, mainly fs lasers, presents unique characteristics in respect to PLD performed using conventional short pulse lasers. Indeed, the films deposited using fs PLD are often nanostructured, and this technique often allows the target stoichiometry to be transferred to the films. In this work, we will review the use of ultra-short PLD in the production of films obtained from transition metal oxides, borides and carbides, evidencing the advantages offered by this technique, together with the problems arising with some of the studied systems. We conclude that even if ultra-short PLD is surely one of the most important and useful deposition techniques, it also presents limits that cannot be ignored. Full article
(This article belongs to the Special Issue Advances in Pulsed Laser Ablation Techniques)
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Open AccessArticle
Synthesis and Characterization of Efficient ZnO/g-C3N4 Nanocomposites Photocatalyst for Photocatalytic Degradation of Methylene Blue
Coatings 2020, 10(5), 500; https://doi.org/10.3390/coatings10050500 (registering DOI) - 23 May 2020
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Abstract
We examine the photocatalytic activity (PCA) of ZnO/graphitic carbon nitride g-C3N4 (g-CN) composite material for methylene blue (MB) degradation under visible-light irradiation (VLI). The polymeric g-CN materials were fabricated by the pyrolysis of urea and thiourea. More importantly, ZnO/g-CN nanostructured [...] Read more.
We examine the photocatalytic activity (PCA) of ZnO/graphitic carbon nitride g-C3N4 (g-CN) composite material for methylene blue (MB) degradation under visible-light irradiation (VLI). The polymeric g-CN materials were fabricated by the pyrolysis of urea and thiourea. More importantly, ZnO/g-CN nanostructured composites were fabricated by adding the different mounts (60, 65, 70, and 75 wt.%) of g-CN into ZnO via the simple hydrothermal process. Among fabricated composites, the 75% ZnO/g-CN nanocomposites displayed a superior PCA for MB degradation, which were ~three-fold an enhancement over the pure ZnO nanoparticles. The fabricated materials have been evaluated by X-ray diffraction (XRD), UV-Vis, Fourier transform infrared (FT-IR) spectroscopy, and electron microscopy. More importantly, the photodegradation of MB could get 98% in ZnO/g-CN could be credited to efficient separation of photo-induced charge carriers between ZnO and g-CN. Also, the recycling efficiency of the as-prepared composites was studied for multiple cycles, which shows that the photocatalysts are stable and suitable to carry out photocatalytic degradation in the logistic mode. Additionally, the probable photocatalytic mechanism has also discussed. The synthetic procedure of ZnO/g-CN based materials can be used in numerous fields such as environmental and in energy storage applications. Full article
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Open AccessArticle
Facile Fabrication of Methylcellulose/PLA Membrane with Improved Properties
Coatings 2020, 10(5), 499; https://doi.org/10.3390/coatings10050499 - 22 May 2020
Viewed by 155
Abstract
With the rapid exhaustion of fossil resources, and environmental pollution relative to the use of fossil-based products, developing eco-friendly products using biomass and/or biodegradable resources is becoming increasingly conspicuous. In this study, ecofriendly and biodegradable composite membranes containing varying MC/PLA (methylcellulose/polylactic acid) mass [...] Read more.
With the rapid exhaustion of fossil resources, and environmental pollution relative to the use of fossil-based products, developing eco-friendly products using biomass and/or biodegradable resources is becoming increasingly conspicuous. In this study, ecofriendly and biodegradable composite membranes containing varying MC/PLA (methylcellulose/polylactic acid) mass ratios were prepared. The properties and structures of the MC/PLA membranes were studied by mechanical testing, 13C NMR techniques, X-ray diffraction (XRD), thermogravimetric analysis (TGA), and hot compression. The MC/PLA membranes displayed markedly improved tensile strength and elongation at the MC/PLA mass ratio range of 99:1 to 9:1. The tensile strength and elongation of the MC/PLA (97:3) membrane was found to be the optimum, at 30% and 35% higher than the neat MC, respectively. It was also found that hot compression could improve the tensile strength and elongation of the membranes. At the same time, the membranes showed enough good thermal stability. In addition, the effect of MC/PLA mass ratio on morphologies of the membranes were studied by microscopy technique. Full article
Open AccessArticle
The Effects of the Addition of Ti3SiC2 on the Microstructure and Properties of Laser Cladding Composite Coatings
Coatings 2020, 10(5), 498; https://doi.org/10.3390/coatings10050498 (registering DOI) - 22 May 2020
Viewed by 159
Abstract
This study explored the effects of Ti3SiC2 on the microstructure and properties of laser cladding coatings using X-ray diffractometer, scanning electron microscope, electrochemical workstation, and UMT-2 wear tester analyses. It was found that with the addition of Ti3SiC [...] Read more.
This study explored the effects of Ti3SiC2 on the microstructure and properties of laser cladding coatings using X-ray diffractometer, scanning electron microscope, electrochemical workstation, and UMT-2 wear tester analyses. It was found that with the addition of Ti3SiC2, the reinforcing phases in the composite coating were TiC, Ti(B,C)2, honeycomb-like (Cr, Fe)23C6, and a novel composite ceramic with an “eyeball” structure, which had an inside core of Al2O3 and TiC outer surrounding structure. The microhardness, wear, and corrosion resistance of the composite coating were about 1.35, 2, and 4.3 times those of the original coating, respectively. The main wear mechanisms of the original coating were severe fatigue spalling and microcutting, while the main mechanisms of the composite coating were slight microcutting and the formation of the transferred film. Full article
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Open AccessArticle
Chitosan Solution Containing Zein and Essential Oil as Bio Based Coating on Packaging Paper
Coatings 2020, 10(5), 497; https://doi.org/10.3390/coatings10050497 (registering DOI) - 22 May 2020
Viewed by 121
Abstract
Modifications of the packaging paper surface play an important role in a variety of industries, especially in the food sector. Uncoated paper has poor water and oil barrier properties due to its porous structure. In this study, packaging paper was successfully coated with [...] Read more.
Modifications of the packaging paper surface play an important role in a variety of industries, especially in the food sector. Uncoated paper has poor water and oil barrier properties due to its porous structure. In this study, packaging paper was successfully coated with six different coating solutions containing combinations of chitosan, zein and rosemary essential oil. The chitosan and zein were actually coated in two layers; the mixed chitosan–rosemary oil and the mixed zein–rosemary oil were each applied as one layer to the paper. The results showed increased oil barrier properties in the papers coated with mixed zein–rosemary oil and reduced water permeability in the papers coated with the chitosan–rosemary oil coating solution. The result of this two-layer coating showed excellent water (Cobb60 value of 2.18 g/m2) and oil barrier properties. All the coated papers showed a high thermal stability, especially those coated with chitosan, zein and rosemary oil layer by layer. Scanning electron microscopy was used to verify the surface differences of the coated papers, such as the closed structure, pores and smoother surface, especially in the layer-wise coated samples. Due to their good mechanical and chemical properties, coated papers with rosemary oil can be used in many applications, possibly also in the field of repellents. Full article
(This article belongs to the Special Issue Natural Materials in Functional Coatings)
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Open AccessArticle
Degradation Behavior, Transport Mechanism and Osteogenic Activity of Mg–Zn–RE Alloy Membranes in Critical-Sized Rat Calvarial Defects
Coatings 2020, 10(5), 496; https://doi.org/10.3390/coatings10050496 - 22 May 2020
Viewed by 143
Abstract
In this study, a specific Mg–Zn–RE alloy membrane with 6 wt.% zinc and 2.7 wt.% rare earth elements (Y, Gd, La and Ce) was prepared to investigate implant degradation, transport mechanism and guide bone regeneration in vivo. The Mg-membrane microstructure and precipitates were [...] Read more.
In this study, a specific Mg–Zn–RE alloy membrane with 6 wt.% zinc and 2.7 wt.% rare earth elements (Y, Gd, La and Ce) was prepared to investigate implant degradation, transport mechanism and guide bone regeneration in vivo. The Mg-membrane microstructure and precipitates were characterized by the scanning electron microscopy (SEM) and the transmission electron microscopy (TEM). The Mg-membrane degradation process and effect on osteogenesis were investigated in a critical-sized rat calvarial defect model via micro-CT examination and hard tissue slicing after 2-, 5- and 8-week implants. Then, the distribution of elements in organs after 1-, 2- and 4-weeks implantation was examined to explore their transportation routes. Results showed that two types of precipitates had formed in the Mg–membrane after a 10-h heat treatment at 175 °C: γ-phase MgZn precipitation with dissolved La, Ce and Gd, and W-phase Mg3(Y, Gd)2Zn3 precipitation rich in Y and Gd. In the degradation process of the Mg-membrane, the Mg matrix degraded first, and the rare earth-rich precipitation particles were transferred to a more stable phosphate compound. The element release rate was dependent on the precipitate type and composition. Rare earth elements may be transported mainly through the lymph system. The defects were repaired rapidly by the membranes. The Mg-membrane used in the present study showed excellent biocompatibility and enhanced bone formation in the vicinity of the implants. Full article
(This article belongs to the Special Issue Membrane Coatings for Surface Bio-Modifications)
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Open AccessArticle
Improvement of CoCr Alloy Characteristics by Ti-Based Carbonitride Coatings Used in Orthopedic Applications
Coatings 2020, 10(5), 495; https://doi.org/10.3390/coatings10050495 - 22 May 2020
Viewed by 149
Abstract
The response of the human body to implanted biomaterials involves several complex reactions. The potential success of implantation depends on the knowledge of the interaction between the biomaterials and the corrosive environment prior to the implantation. Thus, in the present study, the in [...] Read more.
The response of the human body to implanted biomaterials involves several complex reactions. The potential success of implantation depends on the knowledge of the interaction between the biomaterials and the corrosive environment prior to the implantation. Thus, in the present study, the in vitro corrosion behavior of biocompatible carbonitride-based coatings are discussed, based on microstructure, mechanical properties, roughness and morphology. TiCN and TiSiCN coatings were prepared by the cathodic arc deposition method and were analyzed as a possible solution for load bearing implants. It was found that both coatings have an almost stoichiometric structure, being solid solutions, which consist of a mixture of TiC and TiN, with a face-centered cubic (FCC) structure. The crystallite size decreased with the addition of Si into the TiCN matrix: the crystallite size of TiCN was 16.4 nm, while TiSiCN was 14.6 nm. The addition of Si into TiCN resulted in smaller Ra roughness values, indicating a beneficial effect of Si. All investigated surfaces have positive skewness, being adequate for the load bearing implants, which work in a corrosive environment. The hardness of the TiCN coating was 36.6 ± 2.9 GPa and was significantly increased to 47.4 ± 1 GPa when small amounts of Si were added into the TiCN layer structure. A sharp increase in resistance to plastic deformation (H3/E2 ratio) from 0.63 to 1.1 was found after the addition of Si into the TiCN matrix. The most electropositive value of corrosion potential was found for the TiSiCN coating (−14 mV), as well as the smallest value of corrosion current density (49.6 nA cm2), indicating good corrosion resistance in 90% DMEM + 10% FBS, at 37 ± 0.5 °C. Full article
(This article belongs to the Special Issue Physical Vapor Deposited Biomedical Coatings)
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Open AccessArticle
Synthesis and Characterization of Environmentally- Friendly Self-Matting Waterborne Polyurethane Coatings
Coatings 2020, 10(5), 494; https://doi.org/10.3390/coatings10050494 - 21 May 2020
Viewed by 185
Abstract
A series of self-matting waterborne polyurethanes (WPUs) were successfully prepared by introducing hydrophilic units into both soft and hard segments. By employing a polycaprolactone polyol containing carboxylate groups within the polymer chains to provide hydrophilicity directly, the matting performance of WPU films was [...] Read more.
A series of self-matting waterborne polyurethanes (WPUs) were successfully prepared by introducing hydrophilic units into both soft and hard segments. By employing a polycaprolactone polyol containing carboxylate groups within the polymer chains to provide hydrophilicity directly, the matting performance of WPU films was greatly improved. The chemical structures of the WPU resins were confirmed by FTIR spectroscopy, and the morphology of WPU films was observed by SEM. The parameters of WPU preparation were investigated in detail. It was found that the surface gloss of WPU films as well as the particle sizes of WPU dispersions were closely associated with the content of hydrophilic units. As the content of carboxylates or sulfonates increased, the particle sizes of WPU decreased, while the gloss increased gradually. When the particle sizes of dispersions were greater than 3 μm, the gloss of WPU films coated on a leather surface was lower than 1. The results of TG showed that, the initial decomposition temperatures of WPU films were higher than 280 °C, which indicated these films also had good thermal stability. The prepared self-matting WPU coatings would have potential application prospects in the field of leather finishing. Full article
Open AccessFeature PaperArticle
Corrosion Behavior of Si Diffusion Coating on an Austenitic Fe-Base Alloy in High Temperature Supercritical-Carbon Dioxide and Steam Environment
Coatings 2020, 10(5), 493; https://doi.org/10.3390/coatings10050493 - 21 May 2020
Viewed by 194
Abstract
In order to enhance corrosion resistance of stainless steel (SS) 316LN at high temperature environments, surface modification was carried out by Si deposition and subsequent heat treatment at 900 °C for 1 h. This resulted in the formation of Fe5Ni3 [...] Read more.
In order to enhance corrosion resistance of stainless steel (SS) 316LN at high temperature environments, surface modification was carried out by Si deposition and subsequent heat treatment at 900 °C for 1 h. This resulted in the formation of Fe5Ni3Si2 phase on the surface region. The surface-modified alloy was exposed to high temperature S-CO2 (650 °C, 20 MPa) and steam (650 °C, 0.1 MPa) for 500 h and evaluated for its corrosion behavior in comparison to the as-received alloy. In S-CO2 environment, the as-received SS 316LN showed severe oxide spallation and thick Fe-rich oxide formation, while the surface-modified alloy formed a continuous and adherent Si- and Cr-rich oxide layer. In steam, as-received SS 316LN formed very thick duplex Fe- and Cr-rich oxide layers. On the other hand, surface-modified SS 316LN formed notably thinner oxides, which could be attributed to the formation of Si-rich oxide under outer Fe-rich oxides on the surface-modified alloy. Thus, in view of the weight changes, oxide thickness, and morphologies of the two conditions, it was found that Si diffusion coating was effective in improving the corrosion resistance of SS 316LN in both S-CO2 and steam environments. Full article
(This article belongs to the Special Issue Advanced Coating for High Temperature Applications)
Open AccessArticle
Chromium Diffusion Coating on an ODS Ferritic-Martensitic Steel and Its Oxidation Behavior in Air and Steam Environments
Coatings 2020, 10(5), 492; https://doi.org/10.3390/coatings10050492 - 20 May 2020
Viewed by 179
Abstract
A chromium diffusion coating was applied on an oxide dispersion strengthened ferritic-martensitic (ODS-FM) steel to improve oxidation resistance at high temperature. By carrying out physical vapor deposition followed by inter-diffusion heat treatment, a thin Cr-rich carbide layer was produced on the ODS-FM steel. [...] Read more.
A chromium diffusion coating was applied on an oxide dispersion strengthened ferritic-martensitic (ODS-FM) steel to improve oxidation resistance at high temperature. By carrying out physical vapor deposition followed by inter-diffusion heat treatment, a thin Cr-rich carbide layer was produced on the ODS-FM steel. Both the as-received and surface-modified specimens were oxidation-tested at 650 °C in air and steam environments for 500 h. The surface-modified specimens showed improved oxidation resistance in both environments. In an air environment, both conditions exhibited a thin and continuous chromia layer, but the formation of Cr2O3 and (Mn, Cr)3O4 nodules resulted in greater weight gain for the as-received specimen. In a steam environment, weight gain increased for both the as-received and surface-modified specimen. Especially, the as-received specimen showed much greater weight gain with the formation of a thick oxide layer consisted of outer Fe-rich oxide and inner (Fe, Cr, Mn) oxide layers. On the other hand, a thin and continuous chromia layer was formed for the surface-modified specimen, which resulted in much less weight gain in a steam environment. Full article
(This article belongs to the Special Issue Advanced Coating for High Temperature Applications)
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Open AccessArticle
Surface Modification of the Ti-6Al-4V Alloy by Anodic Oxidation and Its Effect on Osteoarticular Cell Proliferation
Coatings 2020, 10(5), 491; https://doi.org/10.3390/coatings10050491 - 20 May 2020
Viewed by 187
Abstract
This investigation describes the formation of crystalline nanotubes of titanium oxide on the surface of a Ti-6Al-4V alloy and its biological evaluation. The formation of nanotubes was performed by the anodic oxidation technique with a constant work potential of 60 V but with [...] Read more.
This investigation describes the formation of crystalline nanotubes of titanium oxide on the surface of a Ti-6Al-4V alloy and its biological evaluation. The formation of nanotubes was performed by the anodic oxidation technique with a constant work potential of 60 V but with different anodizing times of 10, 20, 30, 40, 50, and 60 min used to evaluate their effects on the characteristics of the nanotubes and their biological activity. A mixture of ethylene glycol, water, and ammonium fluoride (NH4F) was used as the electrolytic fluid. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were applied to determine the morphology and crystalline nature of the nanotubes, showing a well-defined matrix of nanotubes of titanium oxide with a crystalline structure and a diameter in the range of 52.5 ± 5.13 to 95 ± 11.92 nm. In contrast, the XRD patterns showed an increase of defined peaks that directly correlated with treatment times. Moreover, in vitro assays using an innovative cell culture device demonstrated that the inner diameter of the nanotubes directly correlated with cell proliferation. Full article
(This article belongs to the Special Issue Bioactive Surfaces and Coatings for Bone Regeneration)
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Open AccessArticle
Evaluation of Experimental Multi-Particulate Polymer-Coated Drug Delivery Systems with Meloxicam
Coatings 2020, 10(5), 490; https://doi.org/10.3390/coatings10050490 - 20 May 2020
Viewed by 238
Abstract
The objectives of this study are the development and evaluation of modified release multi-particulate drug delivery systems containing a BCS class II drug (meloxicam), formulated as polymer-coated pellets. Inert seeds containing microcrystalline cellulose, lactose monohydrate, and polyvinylpyrrolidone were prepared by extrusion-spheronization. The obtained [...] Read more.
The objectives of this study are the development and evaluation of modified release multi-particulate drug delivery systems containing a BCS class II drug (meloxicam), formulated as polymer-coated pellets. Inert seeds containing microcrystalline cellulose, lactose monohydrate, and polyvinylpyrrolidone were prepared by extrusion-spheronization. The obtained cores were loaded with meloxicam using the drug layering technique, by spray coating in a fluidized bed with a liquid dispersion of the drug. The resulting drug pellets were film-coated with various polymers (Acryl-EZE® 93O, Eudragit® RS 30-D as well as experimental composite obtained by adding Methocel™ E5 Premium LV as pore forming agent to the extended release polymer Eudragit® RS 30-D). All experimental systems were evaluated by scanning electron microscopy and in vitro release testing, in an attempt to investigate the characteristics of the film coatings and their influence on drug release from the multi-particulate systems. The in vitro release study was performed in two stages, using two media with pH values corresponding to the gastric and intestinal environment (HCl 0.1N, pH = 1.2 for the first two hours of the test and phosphate buffer 50 mM, pH 6.8 for the next 4 h). The in vitro release data have highlighted the impact of the formulation factors on the drug release. Full article
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Open AccessArticle
Influence of AlN and GaN Pulse Ratios in Thermal Atomic Layer Deposited AlGaN on the Electrical Properties of AlGaN/GaN Schottky Diodes
Coatings 2020, 10(5), 489; https://doi.org/10.3390/coatings10050489 - 19 May 2020
Viewed by 241
Abstract
Atomic layer deposited AlGaN with different AlN and GaN pulse ratios (2:1, 1:1, and 1:2) was used to prepare AlGaN/GaN Schottky diodes, and their current transport mechanisms were investigated using current–voltage (I–V) and capacitance–voltage (C–V) measurements. Under low reverse [...] Read more.
Atomic layer deposited AlGaN with different AlN and GaN pulse ratios (2:1, 1:1, and 1:2) was used to prepare AlGaN/GaN Schottky diodes, and their current transport mechanisms were investigated using current–voltage (I–V) and capacitance–voltage (C–V) measurements. Under low reverse bias condition, the sample with the pulse ratio of 2:1 was explained by Poole–Frenkel emission and the negative temperature dependence for the sample with the pulse ratio of 1:2 was associated with the acceptor levels in the AlGaN layer. Fast interface traps at 0.24–0.29 eV were observed for the samples with the pulse ratios of 1:1 and 1:2, whereas bulk traps at ~0.34 eV were observed for the sample with the pulse ratio of 2:1. Higher trap densities were obtained from the C–V hysteresis measurements when the pulse ratios were 1:1 and 1:2, indicating the presence of a charge trapping interfacial layer. According to the X-ray photoelectron spectroscopy spectra, the pulse ratio of 2:1 was found to have less oxygen-related defects in the AlGaN layer. Full article
(This article belongs to the Special Issue Atomic Layer Deposition of Thin-Films)
Open AccessArticle
Effect of Modified Hexagonal Boron Nitride Nanoparticles on the Emulsion Stability, Viscosity and Electrochemical Behavior of Nanostructured Acrylic Coatings for the Corrosion Protection of AISI 304 Stainless Steel
Coatings 2020, 10(5), 488; https://doi.org/10.3390/coatings10050488 - 19 May 2020
Viewed by 300
Abstract
In this study, the effect of pure and modified hexagonal boron nitride (h-BN) nanosheet incorporation on the stability, viscosity, and electrochemical behavior of a waterborne emulsion acrylic coating was studied. The functionalization of h-BN nanoplatelets with polyacrylic acid (PAA) plasma polymerization was performed, [...] Read more.
In this study, the effect of pure and modified hexagonal boron nitride (h-BN) nanosheet incorporation on the stability, viscosity, and electrochemical behavior of a waterborne emulsion acrylic coating was studied. The functionalization of h-BN nanoplatelets with polyacrylic acid (PAA) plasma polymerization was performed, and the successful surface modification was determined through water dispersion testing, Fourier transform infrared spectroscopy and thermogravimetric analysis, X-ray photoelectron spectroscopy, and also by transmission electronic microscopy. Later, the stability and viscosity properties of emulsion nanostructured acrylic coatings, which were previously prepared by an ultrasound-assisted mixing system, were analyzed using zeta potential and rheometry testing, respectively. The electrochemical behavior was analyzed by electrochemical impedance spectroscopy. The results prove an effective deposition of PAA films on the h-BN surfaces, which enhanced the stability and viscosity acrylic of nanostructured coatings due to the interactions between the h-BN nanoplatelets surface and emulsion acrylic paint and also with the thickener additives. On the other hand, the electrochemical analysis demonstrated a significant increase (two orders of magnitude) in corrosion resistance in the acrylic nanostructured coatings with 1 wt.% of unmodified and modified h-BN nanoplatelets concerning pure acrylic paint due to a barrier protection mechanism of corrosion inhibition. Therefore, the results demonstrate that the surface modification of h-BN by plasma polymerization (green technology) helped to solve the low dispersibility issue of BN nanosheet surfaces in a waterborne polymer matrix to obtained green nanostructured acrylic coatings with the right balance in in-can properties and corrosion inhibition of AISI 304 stainless steel. Full article
(This article belongs to the Section Corrosion, Wear and Erosion)
Open AccessFeature PaperArticle
Experimental Study of the Influence of Deposition of Multilayer CrN/CrCN PVD Coating on Austenitic Steel on Resistance to Cavitation Erosion
Coatings 2020, 10(5), 487; https://doi.org/10.3390/coatings10050487 - 19 May 2020
Viewed by 246
Abstract
The impact of deposition of multilayer CrN/CrCN coating on X6CrNiTi18-10 steel by means of the PVD (physical vapour deposition) method on resistance to cavitation erosion has been investigated. Cavitation tests were performed using a cavitation chamber with a barricade system at the inlet [...] Read more.
The impact of deposition of multilayer CrN/CrCN coating on X6CrNiTi18-10 steel by means of the PVD (physical vapour deposition) method on resistance to cavitation erosion has been investigated. Cavitation tests were performed using a cavitation chamber with a barricade system at the inlet pressure p1 = 600 kPa and the outlet pressure p2 = 123 kPa. Deposition of CrN/CrCN coating allowed increasing duration of the incubation period and decreasing cumulative volume loss until 500 min of exposure. The erosion of the CrN/CrCN–X6CrNiTi18-10 system begins with the removal of microdroplets from the coating surface and surface undulation. The surface undulation increases with the exposure time leading to coating fracture in a brittle mode. Initiation sites of cracks were located inside the PVD coating. Measurements of surface roughness illustrate uneven degradation of the exposed surface and the location of slight and severe erosion zones. The Ra parameters obtained for the CrN/CrCN–X6CrNiTi18-10 system and X6CrNiTi18-10 steel after 180 min of erosion were comparable. An elongation of erosion test up to 600 min resulted in a higher increase in surface roughness of the CrN/CrCN coating–X6CrNiTi18-10 steel system in comparison to that of X6CrNiTi18-10 steel. With increasing exposition time, the rate of increase of the surface roughness decreased due to overlapping damage. Full article
(This article belongs to the Special Issue Erosion of Nanostructured Coatings)
Open AccessArticle
Comparison of the Clinical Results of Identically Designed Total Knee Prostheses with Different Surface Roughnesses
Coatings 2020, 10(5), 486; https://doi.org/10.3390/coatings10050486 - 19 May 2020
Viewed by 184
Abstract
The purpose of this study was to investigate the effects of the undersurface roughness of total knee prosthesis on clinical outcomes. We compared the clinical and radiological outcomes and prosthesis survivals in patients who underwent total knee arthroplasty using prosthesis with identical designs [...] Read more.
The purpose of this study was to investigate the effects of the undersurface roughness of total knee prosthesis on clinical outcomes. We compared the clinical and radiological outcomes and prosthesis survivals in patients who underwent total knee arthroplasty using prosthesis with identical designs but different surface roughness (average surface roughnesses (Ra), 5.0 μm vs. 11.6 μm). The results showed that the knee prostheses with a more roughened undersurface (Ra = 11.6 μm) produced significantly better functional results and enhanced prosthesis survival. The difference in surface roughness was associated with incidence of osteolysis and loosening at the tibial baseplate, but not at the femoral component. Overall, our results provided significant evidence that the use of roughened undersurface of tibial baseplate would be a way to prevent aseptic loosening. Full article
(This article belongs to the Special Issue Surface Modification of Medical Implants)
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Open AccessArticle
A Comprehensive Numerical Study on Friction Reduction and Wear Resistance by Surface Coating on Cam/Tappet Pairs under Different Conditions
Coatings 2020, 10(5), 485; https://doi.org/10.3390/coatings10050485 - 18 May 2020
Viewed by 207
Abstract
As a vital component in the valve train of internal combustion engines (ICEs), the cam/tappet pair undergoes high mechanical and thermal loads and usually works in a mixed and boundary lubrication regime. This leads to considerable friction loss and severe surface wear. Currently, [...] Read more.
As a vital component in the valve train of internal combustion engines (ICEs), the cam/tappet pair undergoes high mechanical and thermal loads and usually works in a mixed and boundary lubrication regime. This leads to considerable friction loss and severe surface wear. Currently, the applications of diamond-like carbon (DLC) coatings for automotive components are becoming a promising strategy to reduce the friction and lower the wear. However, the practical performance of the coating is related to many factors, including friction coefficient, thermal properties, load conditions, and surface topography. In order to investigate these factors and successively improve the fuel efficiency and durability of the cam/tappet pair, a comprehensive multi-physics analytical model considering the mechanical, thermal and tribological properties of DLC coatings is established in this paper. Simulations are carried out for the coated as well as the uncoated cam/tappet conjunctions with different roughness at various ambient temperatures. The results show that both the fluid and asperity contact friction for the coated cam/tappet conjunction are significantly reduced due to their favourable characteristics. As a result, the friction loss of the coated cam/tappet pair is noticeably lower by almost 40% than that of the uncoated, despite a slightly higher asperity contact. In addition, the wear resistance of DLC coatings is also impressive, although the wear condition becomes progressively more severe with the increasing ambient temperature. Moreover, the roughness has complex effects on the friction and wear under different conditions. Full article
(This article belongs to the Section Tribology)
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Open AccessArticle
Composite of PLA Nanofiber and Hexadecyl Trimethyl-Ammonium Chloride-Modified Montmorillonite Clay: Fabrication and Morphology
Coatings 2020, 10(5), 484; https://doi.org/10.3390/coatings10050484 - 18 May 2020
Viewed by 245
Abstract
Our research aim is to develop a new composite material via electrospinning and dip coating methodology. Among bioabsorbable polymers, Polylactic acid (PLA) is viewed as a suitable base material for biomedical usages such as drug delivery and wound dressing. Additionally, these bioabsorbable materials [...] Read more.
Our research aim is to develop a new composite material via electrospinning and dip coating methodology. Among bioabsorbable polymers, Polylactic acid (PLA) is viewed as a suitable base material for biomedical usages such as drug delivery and wound dressing. Additionally, these bioabsorbable materials can be used for filtration applications in terms of antibacterial activity the integration of hexadecyl trimethyl ammonium chloride-modified montmorillonite (CTAC-MMT) into PLA fibers would improve mechanical and absorption properties of the PLA fibers. This research aimed to investigated a new method of combining electrospun PLA with dip coating of CTAC-MMT solution. Precisely, electrospun PLA nanofibers were treated with methanol and dipped in a CTAC-MMT suspension. The resultant layer composite of PLA nanofibers and CTAC-MMT was then characterized by elemental analysis. For material characterization and morphological structure analysis, we performed FTIR, SEM-EDS, XPS, DSC, and X-ray diffraction. Through mechanical testing and contact angle measurements, it was found that CTAC-MMT shows a slight improvement in mechanical and absorption properties. Results of characterization techniques have shown that CTAC-MMT can be used as a good filler for composites processed through the dip-coating method. Moreover, results also showed that the diameter of microfibers is affected by concentrations of PLA. Full article
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Open AccessFeature PaperArticle
Electrophoretic Deposition and Characterization of Functional Coatings Based on an Antibacterial Gallium (III)-Chitosan Complex
Coatings 2020, 10(5), 483; https://doi.org/10.3390/coatings10050483 - 18 May 2020
Viewed by 256
Abstract
Despite their broad biomedical applications in orthopedics and dentistry, metallic implants are still associated with failures due to their lack of surface biofunctionality, leading to prosthesis-related microbial infections. In order to address this issue, the current study focuses on the fabrication and characterization [...] Read more.
Despite their broad biomedical applications in orthopedics and dentistry, metallic implants are still associated with failures due to their lack of surface biofunctionality, leading to prosthesis-related microbial infections. In order to address this issue, the current study focuses on the fabrication and characterization of a novel type of antibacterial coating based on gallium (III)-chitosan (Ga (III)-CS) complex layers deposited on metallic substrates via electrophoretic deposition (EPD). Aiming for the production of homogeneous and monophasic coatings, a two step-procedure was applied: the first step involved the synthesis of the Ga (III)-CS complex, followed by EPD from suitable solutions in an acetic acid–aqueous solvent. The influence of Ga (III) concentration on the stability of the suspensions was evaluated in terms of zeta potential. Fourier transform infrared (FTIR) and energy dispersive X-ray (EDX) spectroscopic analyses indicated the chelation of CS with Ga (III) within the coatings, while scanning electron microscopy (SEM) confirmed that no additional metallic gallium deposited during EPD. Furthermore, the results demonstrated that the wettability, mechanical properties, swelling ability, and enzymatic degradation of the coatings were affected by the quantity of Ga (III) ions. Colony forming unit (CFU) tests showed a strong synergistic effect between CS and Ga (III) in inhibiting Escherichia coli strain growth compared to control CS samples. An in vitro study with MG-63 cells showed that Ga (III)-containing coatings were not toxic after 24 h of incubation. Full article
(This article belongs to the Special Issue Electrochemical and Electrophoretic Deposition of Bioactive Coatings)
Open AccessArticle
Fabrication of Composite Ultrafiltration Membrane by Coating Urea Formaldehyde Resin on Filter Paper
Coatings 2020, 10(5), 482; https://doi.org/10.3390/coatings10050482 - 18 May 2020
Viewed by 221
Abstract
Urea-formaldehyde resin (UFR), a thermosetting resin, is used to prepare ultrafiltration membranes because of its excellent mechanical properties and filtration performance. Herein, a porous ultrafiltration membrane is prepared by coating a mixture of UFR and carboxymethylcellulose (CMC) on the surface of filter paper [...] Read more.
Urea-formaldehyde resin (UFR), a thermosetting resin, is used to prepare ultrafiltration membranes because of its excellent mechanical properties and filtration performance. Herein, a porous ultrafiltration membrane is prepared by coating a mixture of UFR and carboxymethylcellulose (CMC) on the surface of filter paper via a facile acid-curing treatment method. CMC is used as a thickening agent, and hydrochloric acid is used as a curing agent to accelerate composite membrane formation. The mesoporous UFR is embedded in the large pores of the paper matrix by coating treatment, and the presence of CMC can decrease the flowability of the resin. The effects of UFR concentration, CMC dosage, and hydrochloric acid concentration on the performance of the composite ultrafiltration membrane are studied. The ultrafiltration membrane demonstrates a rejection rate of 85% and a pure water flux of 850 L/(m2·h) with the optimized resin concentration, CMC dosage, hydrochloric acid concentration, and coating amount at 30%, 20% (resin dry), 12%, and 250 g/m2, respectively. Full article
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Open AccessArticle
Yttrium Oxyfluoride Coatings Deposited by Suspension Plasma Spraying Using Coaxial Feeding
Coatings 2020, 10(5), 481; https://doi.org/10.3390/coatings10050481 - 16 May 2020
Viewed by 304
Abstract
The recently discovered yttrium oxyfluoride (YOF) coating has been found to be a highly promising plasma-resistant material which can be coated onto the inner wall of the dry etching chambers used in the manufacturing of the three-dimensional stacking circuits of semiconductors, such as [...] Read more.
The recently discovered yttrium oxyfluoride (YOF) coating has been found to be a highly promising plasma-resistant material which can be coated onto the inner wall of the dry etching chambers used in the manufacturing of the three-dimensional stacking circuits of semiconductors, such as vertical NAND flash memory. Here, the coating behavior of the YOF coating which was deposited by suspension plasma spraying was investigated using a high-output coaxial feeding method. Both the deposition rate and density of YOF coatings increased with the plasma power, which was determined by the gas ratio of Ar/H2/N2 and the arc current. The coating thicknesses were 58 ± 3.4, 25.8 ± 2.1, 5.6 ± 0.6, and 0.93 ± 0.4 µm at plasma powers of 112, 83, 67, and 59 kW, respectively, for 20 scans with a feeding rate of the suspension at 0.045 standard liters per minute (slm). The porosities were 0.15% ± 0.01%, 0.25% ± 0.01%, and 5.50% ± 0.40% at corresponding plasma powers of 112, 83, and 67 kW. High-resolution X-ray diffraction (HRXRD) shows that the major and minor peaks of the coatings which were deposited at 112 kW stem from trigonal YOF and cubic Y2O3, respectively. Increasing the flow rate of the atomizing gas from 15 slm to 30 slm decreased the porosity of the YOF coating from 0.22% ± 0.03% to 0.07% ± 0.03%. The Vickers hardness of the YOF coating containing some Y2O3 deposited at 112 kW was 550 ± 70 HV. Full article
(This article belongs to the Special Issue Plasma Surface Engineering)
Open AccessArticle
Determination of the Complex Dielectric Function of Ion-Implanted Amorphous Germanium by Spectroscopic Ellipsometry
Coatings 2020, 10(5), 480; https://doi.org/10.3390/coatings10050480 - 16 May 2020
Viewed by 241
Abstract
Accurate reference dielectric functions play an important role in the research and development of optical materials. Libraries of such data are required in many applications in which amorphous semiconductors are gaining increasing interest, such as in integrated optics, optoelectronics or photovoltaics. The preparation [...] Read more.
Accurate reference dielectric functions play an important role in the research and development of optical materials. Libraries of such data are required in many applications in which amorphous semiconductors are gaining increasing interest, such as in integrated optics, optoelectronics or photovoltaics. The preparation of materials of high optical quality in a reproducible way is crucial in device fabrication. In this work, amorphous Ge (a-Ge) was created in single-crystalline Ge by ion implantation. It was shown that high optical density is available when implanting low-mass Al ions using a dual-energy approach. The optical properties were measured by multiple angle of incidence spectroscopic ellipsometry identifying the Cody-Lorentz dispersion model as the most suitable, that was capable of describing the dielectric function by a few parameters in the wavelength range from 210 to 1690 nm. The results of the optical measurements were consistent with the high material quality revealed by complementary Rutherford backscattering spectrometry and cross-sectional electron microscopy measurements, including the agreement of the layer thickness within experimental uncertainty. Full article
(This article belongs to the Special Issue Structure and Phase Transformations in Thin Films)
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Open AccessReview
Flame Resistant Silicone-Containing Coating Materials
Coatings 2020, 10(5), 479; https://doi.org/10.3390/coatings10050479 - 15 May 2020
Viewed by 220
Abstract
The flame resistance of applied coating materials affects the safety of innovative technological solutions. Silicone-containing polymeric materials are one of the most economical solutions in the field of coatings due to the effect of the unique combination of very good thermal, resistance, and [...] Read more.
The flame resistance of applied coating materials affects the safety of innovative technological solutions. Silicone-containing polymeric materials are one of the most economical solutions in the field of coatings due to the effect of the unique combination of very good thermal, resistance, and surface properties. The rich chemistry of silicon compounds, which results in their very good thermal stability, allows their use as flame-resistant coating materials or as flame retardants in polymer composites. In this review, the flame resistance of PDMS systems based on their thermal degradation data, as well as possible paths of thermal degradation depending on external conditions including the effect of additives, flame resistance of hybrid silicone-containing coating materials and most important innovative applications of these materials, are reviewed. Very good results from the use of organic silicon compounds as fire retardants in polymers obtained by many research teams are one of the promising ways of overcoming the health, safety, and availability concerns of traditional halogenated fire retardants. Full article
(This article belongs to the Special Issue Coatings and Interfaces)
Open AccessArticle
Thermal Initiators as Additives for Photopolymerization of Methacrylates upon Blue Light
Coatings 2020, 10(5), 478; https://doi.org/10.3390/coatings10050478 - 15 May 2020
Viewed by 290
Abstract
Free radical polymerization is often performed by thermal initiation but also more and more by light-assisted polymerization processes. This second approach allows the polymerization to be carried out under mild conditions (under air, upon blue light exposure, under low light intensity). The aim [...] Read more.
Free radical polymerization is often performed by thermal initiation but also more and more by light-assisted polymerization processes. This second approach allows the polymerization to be carried out under mild conditions (under air, upon blue light exposure, under low light intensity). The aim and the originality of the present paper is to perform photopolymerization in the presence of a thermal initiator, i.e., we can take advantage of the exothermicity of the photopolymerization process to decompose the thermal initiator, leading to enhanced polymerization rates. The performance of the photoinitiating system is discussed in the present study based on real-time Fourier-transform infrared spectroscopy measurements (following the C=C bond content evolution vs. time) and by thermal imaging experiments. Mechanisms of the new system proposed in this work are also fully detailed using cyclic voltammetry, electron spin resonance (ESR) spin trapping, and UV-visible absorption properties. Full article
(This article belongs to the Special Issue Light-Curable Coatings)
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Open AccessArticle
Effect of Interface Coating on High Temperature Mechanical Properties of SiC–SiC Composite Using Domestic Hi–Nicalon Type SiC Fibers
Coatings 2020, 10(5), 477; https://doi.org/10.3390/coatings10050477 - 15 May 2020
Viewed by 242
Abstract
Here we show that when the temperature exceeded 1200 °C, the tensile strength drops sharply with change of fracture mode from fiber pull-out to fiber-break. Theoretical analysis indicates that the reduction of tensile strength and change of fracture mode is due to the [...] Read more.
Here we show that when the temperature exceeded 1200 °C, the tensile strength drops sharply with change of fracture mode from fiber pull-out to fiber-break. Theoretical analysis indicates that the reduction of tensile strength and change of fracture mode is due to the variation of residual radial stress on the fiber–matrix interface coating. When the temperature exceeds the preparation temperature of the composites, the residual radial stress on the fiber–matrix interface coating changes from tensile to compressive, leading to the increase of the interface strength with increasing temperature. The fracture behavior of SiC–SiC composites changes from ductile to brittle when the strength of fiber–matrix interface coating exceeds the critical value. Theoretical analysis predicts that the high temperature tensile strength can increase with a decrease in fiber–matrix interface thickness, which is verified by experiments. Full article
(This article belongs to the Special Issue Mechanical Properties of Advanced Multifunctional Coatings)
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Open AccessArticle
Effects of Nitrogen Flow Ratio on Structures, Bonding Characteristics, and Mechanical Properties of ZrNx Films
Coatings 2020, 10(5), 476; https://doi.org/10.3390/coatings10050476 - 14 May 2020
Viewed by 236
Abstract
ZrNx (x = 0.67–1.38) films were fabricated through direct current magnetron sputtering by a varying nitrogen flow ratio [N2/(Ar + N2)] ranging from 0.4 to 1.0. The structural variation, bonding characteristics, and mechanical properties of the ZrN [...] Read more.
ZrNx (x = 0.67–1.38) films were fabricated through direct current magnetron sputtering by a varying nitrogen flow ratio [N2/(Ar + N2)] ranging from 0.4 to 1.0. The structural variation, bonding characteristics, and mechanical properties of the ZrNx films were investigated. The results indicated that the structure of the films prepared using a nitrogen flow ratio of 0.4 exhibited a crystalline cubic ZrN phase. The phase gradually changed to a mixture of crystalline ZrN and orthorhombic Zr3N4 followed by a Zr3N4 dominant phase as the N2 flow ratio increased up to >0.5 and >0.85, respectively. The bonding characteristics of the ZrNx films comprising Zr–N bonds of ZrN and Zr3N4 compounds were examined by X-ray photoelectron spectroscopy and were well correlated with the structural variation. With the formation of orthorhombic Zr3N4, the nanoindentation hardness and Young’s modulus levels of the ZrNx (x = 0.92–1.38) films exhibited insignificant variations ranging from 18.3 to 19.0 GPa and from 210 to 234 GPa, respectively. Full article
(This article belongs to the Special Issue Physical Vapor Deposition)
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