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Coatings, Volume 9, Issue 6 (June 2019)

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Cover Story (view full-size image) Force-spinning is a versatile and low-cost alternative to electrospinning. PHBV is a microbial [...] Read more.
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Open AccessReview
A Brief Overview on the Anticorrosion Performances of Sol-Gel Zeolite Coatings
Coatings 2019, 9(6), 409; https://doi.org/10.3390/coatings9060409
Received: 24 May 2019 / Revised: 19 June 2019 / Accepted: 20 June 2019 / Published: 24 June 2019
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Abstract
Research activity concerning nanoporous zeolites has grown considerably in recent decades. The structural porosity of zeolites provides versatile functional properties such as molecular selectivity, ion and molecule storage capacity, high surface area, and pore volume which combined with excellent thermal and chemical stability [...] Read more.
Research activity concerning nanoporous zeolites has grown considerably in recent decades. The structural porosity of zeolites provides versatile functional properties such as molecular selectivity, ion and molecule storage capacity, high surface area, and pore volume which combined with excellent thermal and chemical stability can extend its application fields in several industrial sectors. In such a context, anti-corrosion zeolite coatings are an emerging technology able to offer a reliable high performing and environmental friendly alternative to conventional chromate-based protective coatings. In this article, a focused overview on anti-corrosion performances of sol-gel composite zeolite coatings is provided. The topic of this review is addressed to assess the barrier and self-healing properties of composite zeolite coating. Based on results available in the literature, a property–structure relationship of this class of composites is proposed summarizing, furthermore, the competing anti-corrosion active and passive protective mechanisms involved during coating degradation. Eventually, a brief summary and a future trend evaluation is also reported. Full article
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Open AccessArticle
Custom-Made Chemically Modified Graphene Oxide to Improve the Anti-Scratch Resistance of Urethane-Acrylate Transparent Coatings
Coatings 2019, 9(6), 408; https://doi.org/10.3390/coatings9060408
Received: 4 June 2019 / Revised: 18 June 2019 / Accepted: 20 June 2019 / Published: 24 June 2019
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Abstract
In this work, a thermoset ultraviolet (UV)-cured polyurethane-acrylate resin was doped with different chemically-modified graphene obtained from a commercial graphene oxide (GO): as-received GO, chemically reduced GO (rGO), GO functionalized with vinyltriethoxysilane (VTES) (GOvtes), and GO functionalized with VTES and subsequently reduced with [...] Read more.
In this work, a thermoset ultraviolet (UV)-cured polyurethane-acrylate resin was doped with different chemically-modified graphene obtained from a commercial graphene oxide (GO): as-received GO, chemically reduced GO (rGO), GO functionalized with vinyltriethoxysilane (VTES) (GOvtes), and GO functionalized with VTES and subsequently reduced with a chemical agent (rGOvtes). Modified graphene was introduced in the oligomer component via solvent-assisted process using acetone, which was recovered after completion of the process. Results indicate that the GO-doped oligomers produce cured coatings with improved anti-scratch resistance (above the resistance of conventional coatings), without surface defects and high transparency. The anti-scratch resistance was measured with atomic force microscopy (AFM). Additionally, results are presented in terms of Wolf–Wilburn scale, a straightforward method widely accepted and employed in the coating industry. Full article
(This article belongs to the Special Issue Graphene-Based Composite Films)
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Open AccessArticle
TiBCN-Ceramic-Reinforced Ti-Based Coating by Laser Cladding: Analysis of Processing Conditions and Coating Properties
Coatings 2019, 9(6), 407; https://doi.org/10.3390/coatings9060407
Received: 21 May 2019 / Revised: 11 June 2019 / Accepted: 19 June 2019 / Published: 24 June 2019
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Abstract
In this paper, TiBCN-ceramic-reinforced Ti-based coating was fabricated on a Ti6Al4V substrate surface by laser cladding. The correlations between the main processing parameters and the geometrical characteristics of single clad tracks were predicted by linear regression analysis. On this basis, the microstructure, microhardness, [...] Read more.
In this paper, TiBCN-ceramic-reinforced Ti-based coating was fabricated on a Ti6Al4V substrate surface by laser cladding. The correlations between the main processing parameters and the geometrical characteristics of single clad tracks were predicted by linear regression analysis. On this basis, the microstructure, microhardness, corrosion resistance, and wear resistance of the coating and the substrate were investigated. The results showed that the clad height, clad width, clad depth, and dilution rate depended mainly on the laser power, the powder feeding rate, and the scanning speed. TiBCN-ceramic-reinforced Ti-based coating was mainly composed of directional dendritic TiBCN phases, equiaxed TiN phases, needle-like Al3Ti phases, and Ti phases. The microhardness gradually increased from the bottom to the top of the coating. The highest microhardness of coating was 1025 HV, which was three times higher than that of the Ti6Al4V substrate (350 HV). Furthermore, the coating exhibited excellent corrosion resistance and wear resistance. The corrosion potential (Ecorr) reached −1.258 V, and the corrosion density (Icorr) was 4.035 × 10−5 A/cm2, which was one order lower than that of the Ti6Al4V substrate (1.172 × 10−4 A/cm2). The coating wear mass loss was 4.35 mg, which was about two-third of the wear mass loss of the Ti6Al4V substrate (6.71 mg). Full article
(This article belongs to the Special Issue Laser Surface Modification of Metallic Materials)
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Open AccessArticle
Phase Evolution and Microstructure Analysis of CoCrFeNiMo High-Entropy Alloy for Electro-Spark-Deposited Coatings for Geothermal Environment
Coatings 2019, 9(6), 406; https://doi.org/10.3390/coatings9060406
Received: 20 May 2019 / Revised: 14 June 2019 / Accepted: 18 June 2019 / Published: 21 June 2019
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Abstract
In this work, a CoCrFeNiMo high-entropy alloy (HEA) material was prepared by the vacuum arc melting (VAM) method and used for electro-spark deposition (ESD). The purpose of this study was to investigate the phase evolution and microstructure of the CoCrFeNiMo HEA as as-cast [...] Read more.
In this work, a CoCrFeNiMo high-entropy alloy (HEA) material was prepared by the vacuum arc melting (VAM) method and used for electro-spark deposition (ESD). The purpose of this study was to investigate the phase evolution and microstructure of the CoCrFeNiMo HEA as as-cast and electro-spark-deposited (ESD) coating to assess its suitability for corrosvie environments encountered in geothermal energy production. The composition, morphology, and structure of the bulk material and the coating were analyzed using scanning electron microscopy (SEM) coupled with energy-dispersive spectroscopy (EDS), and X-ray diffraction (XRD). The hardness of the bulk material was measured to access the mechanical properties when preselecting the composition to be pursued for the ESD coating technique. For the same purpose, electrochemical corrosion tests were performed in a 3.5 wt.% NaCl solution on the bulk material. The results showed the VAM CoCrFeNiMo HEA material had high hardness (593 HV) and low corrosion rates (0.0072 mm/year), which is promising for the high wear and corrosion resistance needed in the harsh geothermal environment. The results from the phase evolution, chemical composition, and microstructural analysis showed an adherent and dense coating with the ESD technique, but with some variance in the distribution of elements in the coating. The crystal structure of the as-cast electrode CoCrFeNiMo material was identified as face centered cubic with XRD, but additional BCC and potentially σ phase was formed for the CoCrFeNiMo coating. Full article
(This article belongs to the Special Issue Coatings for Harsh Environments)
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Open AccessFeature PaperArticle
Corrosion Resistance Test of Electroplated Gold and Palladium Using Fast Electrochemical Analysis
Coatings 2019, 9(6), 405; https://doi.org/10.3390/coatings9060405
Received: 16 May 2019 / Revised: 14 June 2019 / Accepted: 19 June 2019 / Published: 21 June 2019
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Abstract
Noble metal coatings are commonly employed to improve corrosion resistance of metals in the electronic and jewellery industry. The corrosion resistance of electroplated goods is currently determinate with long, destructive and almost subjective interpretation corrosion tests in artificial atmosphere. In this study we [...] Read more.
Noble metal coatings are commonly employed to improve corrosion resistance of metals in the electronic and jewellery industry. The corrosion resistance of electroplated goods is currently determinate with long, destructive and almost subjective interpretation corrosion tests in artificial atmosphere. In this study we present the application of electrochemical analysis to obtain fast and numerical information of the antiaging coating. We performed open circuit potential (OCP) and corrosion current measurement; we employed also the electrochemical impedance spectroscopy (EIS), commonly applied to organic or passivated metal with high-impedance, to find the best option for noble low-impedance coating analysis. For comparison, traditional standardized tests (damp heat ISO 17228, salt spray ISO 9227 and sulphur dioxide ISO 4524) were also performed. Full article
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Open AccessArticle
Double-Sided Anti-Reflection Nanostructures on Optical Convex Lenses for Imaging Applications
Coatings 2019, 9(6), 404; https://doi.org/10.3390/coatings9060404
Received: 2 May 2019 / Revised: 18 June 2019 / Accepted: 19 June 2019 / Published: 21 June 2019
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Abstract
Anti-reflection coatings (ARCs) from the cornea nipple array of the moth-eye remarkably suppress the Fresnel reflection at the interface in broadband wavelength ranges. ARCs on flat glass have been studied to enhance the optical transmittance. However, little research on the implementation of ARCs [...] Read more.
Anti-reflection coatings (ARCs) from the cornea nipple array of the moth-eye remarkably suppress the Fresnel reflection at the interface in broadband wavelength ranges. ARCs on flat glass have been studied to enhance the optical transmittance. However, little research on the implementation of ARCs on curved optical lenses, which are the core element in imaging devices, has been reported. Here, we report double-sided, bio-inspired ARCs on bi-convex lenses with high uniformity. We theoretically optimize the nanostructure geometry, such as the height, period, and morphology, since an anti-reflection property results from the gradually changed effective refractive index by the geometry of nanostructures. In an experiment, the transmittance of an ARCs lens increases up to 10% for a broadband spectrum without distortion in spot size and focal length. Moreover, we demonstrate ~30% improved transmittance of an imaging system composed of three bi-convex lenses, in series with double-sided ARCs (DARCs). Full article
(This article belongs to the Special Issue Semiconductor Thin Films)
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Open AccessArticle
The Antibacterial Properties and Safety of a Nanoparticle-Coated Parquet Floor
Coatings 2019, 9(6), 403; https://doi.org/10.3390/coatings9060403
Received: 27 April 2019 / Revised: 16 June 2019 / Accepted: 17 June 2019 / Published: 21 June 2019
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Abstract
Floor antibacterial technology prevents the human body from cross-infection with bacterial diseases. The most commonly used approach to endow daily-used floors with antibacterial properties is to apply a thin film of antibacterial agents on the parquet floor surface. In the present study, five [...] Read more.
Floor antibacterial technology prevents the human body from cross-infection with bacterial diseases. The most commonly used approach to endow daily-used floors with antibacterial properties is to apply a thin film of antibacterial agents on the parquet floor surface. In the present study, five commercial antibacterial nanoparticles were first dispersed in melamine resin solution, and then applied on a floor. Afterwards, the antibacterial properties of the nanoparticle-coated floor were investigated, in which Escherichia coli was used as the target bacteria. The impact of the nanoparticle dispersing agents on the ultimate antibacterial properties of the floor were also investigated. The results showed that silver nanoparticle-loaded hydroxyl zirconium sodium phosphate (Ag-HZDP) was most suitable as the antibacterial agent of a melamine coating for parquet flooring. With the help of sodium hexametaphosphate, the antibacterial agent was able to disperse well in the melamine resin solution and was also able to disperse well on the floor surface. When the loading amount of Ag-HZDP was 1 wt % or higher, the prepared antibacterial floor was able kill almost all the bacteria cultivated on its surface. Moreover, the prepared antibacterial floor had a lower toxicity compared with a pristine cedar substrate. The present study provides an effective way to provide daily-used parquet floors with excellent antibacterial properties. Full article
(This article belongs to the Special Issue Recent Developments in Antibacterial and/or Antifouling Surfaces)
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Open AccessArticle
HA Coating on Ti6Al7Nb Alloy Using an Electrophoretic Deposition Method and Surface Properties Examination of the Resulting Coatings
Coatings 2019, 9(6), 402; https://doi.org/10.3390/coatings9060402
Received: 21 May 2019 / Revised: 12 June 2019 / Accepted: 18 June 2019 / Published: 21 June 2019
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Abstract
Ti and its alloys, which are commonly used in biomedical applications, are often preferred due to their proximity to the mechanical properties of bone. In order to increase the biocompatibility and bioactivities of these materials, biomaterials based on ceramic are used in coating [...] Read more.
Ti and its alloys, which are commonly used in biomedical applications, are often preferred due to their proximity to the mechanical properties of bone. In order to increase the biocompatibility and bioactivities of these materials, biomaterials based on ceramic are used in coating operations. In this study, by using an electrophoretic deposition method, instead of on the Ti6Al4V alloy which is commonly used in the literature, a hydroxyapatite (HA) coating operation was applied on the surface of the Ti6Al7Nb alloy, and the surface properties of the coatings were examined. Ti6Al7Nb is a new-generation implant on which there have not been many studies. The voltage values which were used in the coating operation were 50, 100, 150 and 200 V, and the time parameter was stabilized at 1 min. In our method, when preparing the solution, HA, ethanol, and polyvinyl alcohol (PVA) were used. At the end of the study, by using an electron microscope (SEM) the microstructures of the coatings were examined; elemental analyses (EDS) of the coating surfaces were performed; and by using an X-radiation diffraction (XRD) method, the phases which the coatings contained and the concentration of these phases were determined, and the coating thickness, roughness, and hardness values were also determined. Also, by conducting a Scratch test, the strength of the surface combination was examined. At the end of the study, in each parameter, a successful HA coating was seen. By comparing parameters with each other, the ideal voltage value in this coating was determined. It was determined that the most suitable coating was obtained at 100 V voltage and 1 min deposition time. Full article
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Open AccessArticle
The Relationship between Solid Content and Particle Size Ratio of Waterborne Polyurethane
Coatings 2019, 9(6), 401; https://doi.org/10.3390/coatings9060401
Received: 21 May 2019 / Revised: 15 June 2019 / Accepted: 18 June 2019 / Published: 21 June 2019
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Abstract
A series of high solid content carboxylic acid/sulfonic acid waterborne polyurethanes was prepared by the emulsion dispersion method. The particle size and solid content were measured. By changing the particle size of the large particles to achieve different particle size ratios, high solid [...] Read more.
A series of high solid content carboxylic acid/sulfonic acid waterborne polyurethanes was prepared by the emulsion dispersion method. The particle size and solid content were measured. By changing the particle size of the large particles to achieve different particle size ratios, high solid content waterborne polyurethanes were obtained at specific particle size ratios. When the particle size ratio was >7, 4–5 or 2–3, the aqueous polyurethane could reach a higher solid content (more than 56%). This indicated that solid content is related to particle size distribution in high solid content waterborne polyurethane. Moreover, the corresponding three-dimensional stacked models (simple cubic accumulation, face-centered cubic accumulation, cubic close packing and hexagonal closest packing) were established. Full article
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Open AccessReview
Nanocrystalline Cermet Coatings for Erosion–Corrosion Protection
Coatings 2019, 9(6), 400; https://doi.org/10.3390/coatings9060400
Received: 3 May 2019 / Revised: 3 June 2019 / Accepted: 6 June 2019 / Published: 20 June 2019
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Abstract
The processing techniques, microstructural characteristics, and erosion corrosion behaviour of Cr3C2–NiCr and tungsten carbide (WC)-based cermet coatings are reviewed in this work. Conventional and nanocrystalline Cr3C2–NiCr and WC-based cermet coatings are generally synthesized using thermal [...] Read more.
The processing techniques, microstructural characteristics, and erosion corrosion behaviour of Cr3C2–NiCr and tungsten carbide (WC)-based cermet coatings are reviewed in this work. Conventional and nanocrystalline Cr3C2–NiCr and WC-based cermet coatings are generally synthesized using thermal spray technique. The wear, erosion, and corrosion protection ability of conventional and nanocermet coatings are compared based on available literature. In Cr3C2–NiCr coatings, the corrosion resistance is offered by NiCr metal matrix while the wear resistance is provided by the carbide ceramic phase, making it suitable for erosion–corrosion protection. The nanocrystalline cermet coatings exhibits better erosion–corrosion resistance as compared to the conventional coatings. The nanocrystalline coatings reduces the erosion–corrosion rate significantly compared to conventional coatings. It is attributed to the presence of the protective NiCr metallic binder that allows easier and faster re-passivation when the coating is subjected to wear and the fine-grain structure with homogeneous distribution of the skeleton network of hard carbide phases. In addition, corrosion-accelerated erosion dominates the reaction mechanism of erosion–corrosion and, therefore, higher hardness, strength, and better wear resistance of nanocermet coating along with its faster repassivation kinetics accounts for improved corrosion resistance as compared to conventional coatings. Full article
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Open AccessArticle
Preparation and Anticorrosive Property of Soluble Aniline Tetramer
Coatings 2019, 9(6), 399; https://doi.org/10.3390/coatings9060399
Received: 17 May 2019 / Revised: 11 June 2019 / Accepted: 17 June 2019 / Published: 20 June 2019
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Abstract
Soluble aniline tetramer (AT) was successfully prepared by chemical oxidation method. Fourier transform infrared spectroscopy (FTIR) and ultraviolet-visible spectroscopy (UV-vis) were used to characterize its structure. The redox behavior of AT was identified through the electrochemical cyclic voltammetry studies. Then, the epoxy coating [...] Read more.
Soluble aniline tetramer (AT) was successfully prepared by chemical oxidation method. Fourier transform infrared spectroscopy (FTIR) and ultraviolet-visible spectroscopy (UV-vis) were used to characterize its structure. The redox behavior of AT was identified through the electrochemical cyclic voltammetry studies. Then, the epoxy coating was prepared by using AT as inhibitor. Its anticorrosive property was evaluated by salt solution resistance test, polarization curve, and electrochemical impedance spectroscopy (EIS). Salt solution resistance test, polarization curves, and EIS measurements indicate that the obtained epoxy anticorrosive coating, containing 1.0% AT, exhibits remarkably enhanced corrosion protection properties on Q235 steel electrodes as compared to pure epoxy anticorrosive coating without AT. The significantly improved anticorrosion performance may be owing to the redox behavior of the AT, adsorption and inhibition effect of AT on Q235 steel surface, as well as synergistic curing effect by AT and polyamide. Full article
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Open AccessArticle
Preparation of Superhydrophobic Steel Surfaces with Chemical Stability and Corrosion
Coatings 2019, 9(6), 398; https://doi.org/10.3390/coatings9060398
Received: 25 May 2019 / Revised: 16 June 2019 / Accepted: 18 June 2019 / Published: 20 June 2019
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Abstract
Corrosion seriously limits the long-term application of Q235 carbon steel. Herein, a simple fabrication method was used to fabricate superhydrophobic surfaces on Q235 carbon steel for anticorrosion application. The combination of structure and the grafted low-surface-energy material contributed to the formation of superhydrophobic [...] Read more.
Corrosion seriously limits the long-term application of Q235 carbon steel. Herein, a simple fabrication method was used to fabricate superhydrophobic surfaces on Q235 carbon steel for anticorrosion application. The combination of structure and the grafted low-surface-energy material contributed to the formation of superhydrophobic steel surfaces, which exhibited a water contact angle of 161.6° and a contact angle hysteresis of 0.8°. Meanwhile, the as-prepared superhydrophobic surface showed repellent toward different solutions with pH ranging from 1 to 14, presenting excellent chemical stability. Moreover, the acid corrosive liquid (HCl solution with pH of 1) maintained sphere-like shape on the as-prepared superhydrophobic surface at room temperature, indicating superior corrosion resistance. This work provides a simple method to fabricate superhydrophobic steel surfaces with chemical stability and corrosion resistance. Full article
(This article belongs to the Special Issue Superhydrophobic Coatings for Corrosion and Tribology)
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Open AccessArticle
Surface Properties of Pine Scrimber Panels with Varying Density
Coatings 2019, 9(6), 397; https://doi.org/10.3390/coatings9060397
Received: 2 May 2019 / Revised: 11 June 2019 / Accepted: 18 June 2019 / Published: 20 June 2019
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Abstract
Coating quality for scrimber products against exterior conditions is largely dependent on the surface properties. The wettability, morphology, and chemical composition of pine scrimber surfaces were investigated to better understand the surface properties. The scrimber was found to be a hydrophilic material because [...] Read more.
Coating quality for scrimber products against exterior conditions is largely dependent on the surface properties. The wettability, morphology, and chemical composition of pine scrimber surfaces were investigated to better understand the surface properties. The scrimber was found to be a hydrophilic material because the water contact angles were less than 90°. The panels with a density of 1.20 g/cm3 had the largest angle change rate (k = 0.212). As the panel density increased, the instantaneous contact angle of each test liquid (i.e., water, formamide, and diiodomethane) on the panels decreased, and so did surface free energy. Panels with higher density showed lower surface roughness. Surface roughness across the wood grain was greater than that along the grain. SEM observations showed the high-density panels had a smoother surface with fewer irregular grooves in comparison with the low-density panels. X-ray photoelectron spectroscopy (XPS) analysis indicated that more unoxygenated groups appeared on the surface of high-density panels. Full article
(This article belongs to the Special Issue Recent Developments and Trends in Wood Coatings)
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Open AccessArticle
Evaluation of the Corrosion Resistance and Cytocompatibility of a Bioactive Micro-Arc Oxidation Coating on AZ31 Mg Alloy
Coatings 2019, 9(6), 396; https://doi.org/10.3390/coatings9060396
Received: 13 May 2019 / Revised: 13 June 2019 / Accepted: 14 June 2019 / Published: 20 June 2019
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Abstract
Magnesium alloys have recently been attracting attention as a degradable biomaterial. They have advantages including non-toxicity, biocompatibility, and biodegradability. To develop magnesium alloys into biodegradable medical materials, previous research has quantitatively analyzed magnesium alloy corrosion by focusing on the overall changes in the [...] Read more.
Magnesium alloys have recently been attracting attention as a degradable biomaterial. They have advantages including non-toxicity, biocompatibility, and biodegradability. To develop magnesium alloys into biodegradable medical materials, previous research has quantitatively analyzed magnesium alloy corrosion by focusing on the overall changes in the alloy. Therefore, the objective of this study is to develop a bioactive material by applying a ceramic oxide coating (magnesia) on AZ31 magnesium alloy through micro-arc oxidation (MAO) process. This MAO process is conducted under pulsed bipolar constant current conditions in a Si- and P-containing electrolyte and the optimal processing parameters in corrosion protection are obtained by the Taguchi method to design a coating with good anti-corrosion performance. The negative duty cycle and treatment time are two deciding factors of the coating’s capability in corrosion protection. Microstructure characterizations are investigated by means of SEM and XRD. The simulation body-fluid solution is utilized for testing the corrosion resistance with the potentiodynamic polarization and the electrochemical impedance test data. Finally, an in vivo testing shows that the MAO-coated AZ31 has good cytocompatibility and anticorrosive properties. Full article
(This article belongs to the Special Issue Plasma Electrolytic Oxidation (PEO) Coatings)
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Open AccessArticle
Investigations on Forming Ether Coated Iron Nanoparticle Materials by First-Principle Calculations and Molecular Dynamic Simulations
Coatings 2019, 9(6), 395; https://doi.org/10.3390/coatings9060395
Received: 6 May 2019 / Revised: 29 May 2019 / Accepted: 17 June 2019 / Published: 19 June 2019
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Abstract
The mechanism of coating effects between ether molecules and iron (Fe) nanoparticles was generally estimated using first-principle calculations and molecular dynamic (MD) simulations coupling with Fe (110) crystal layers and sphere models. In the present work, the optimized adsorption site and its energy [...] Read more.
The mechanism of coating effects between ether molecules and iron (Fe) nanoparticles was generally estimated using first-principle calculations and molecular dynamic (MD) simulations coupling with Fe (110) crystal layers and sphere models. In the present work, the optimized adsorption site and its energy were confirmed. The single sphere model in MD simulations was studied for typical adsorption behaviors, and the double sphere model was built to be more focused on the gap impact between two particles. In those obtained results, it is demonstrated that ether molecules were prone to be adsorbed on the long bridge site of the Fe (110) crystal while comparing with other potential sites. Although the coating was not completely uniform at early stages, the formation of ether layer ended up being equilibrated finally. Accompanied with charge transfer, those coated ether molecules exerted much binding force on the shell Fe atoms. Additionally, when free ether molecules were close to the gap between two nanoparticles, they were found to come under double adsorption effects. Although this effect might not be sufficient to keep them adsorbed, the movement of these ether molecules were hindered to some extent. Full article
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Open AccessFeature PaperArticle
Surface Functionalization of Bioactive Glasses with Polyphenols from Padina pavonica Algae and In Situ Reduction of Silver Ions: Physico-Chemical Characterization and Biological Response
Coatings 2019, 9(6), 394; https://doi.org/10.3390/coatings9060394
Received: 30 April 2019 / Revised: 11 June 2019 / Accepted: 15 June 2019 / Published: 19 June 2019
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Abstract
Bioactive glasses (BGs) are attractive materials for bone replacement due to their tailorable chemical composition that is able to promote bone healing and repair. Accordingly, many attempts have been introduced to further improve BGs’ biological behavior and to protect them from bacterial infection, [...] Read more.
Bioactive glasses (BGs) are attractive materials for bone replacement due to their tailorable chemical composition that is able to promote bone healing and repair. Accordingly, many attempts have been introduced to further improve BGs’ biological behavior and to protect them from bacterial infection, which is nowadays the primary reason for implant failure. Polyphenols from natural products have been proposed as a novel source of antibacterial agents, whereas silver is a well-known antibacterial agent largely employed due to its broad-ranged activity. Based on these premises, the surface of a bioactive glass (CEL2) was functionalized with polyphenols extracted from the Egyptian algae Padina pavonica and enriched with silver nanoparticles (AgNPs) using an in situ reduction technique only using algae extract. We analyzed the composite’s morphological and physical-chemical characteristics using FE-SEM, EDS, XPS and Folin–Ciocalteau; all analyses confirmed that both algae polyphenols and AgNPs were successfully loaded together onto the CEL2 surface. Antibacterial analysis revealed that the presence of polyphenols and AgNPs significantly reduced the metabolic activity (>50%) of Staphylococcus aureus biofilm in comparison with bare CEL2 controls. Finally, we verified the composite’s cytocompatibility with human osteoblasts progenitors that were selected as representative cells for bone healing advancement. Full article
(This article belongs to the Special Issue Surfaces Modification and Analysis for Innovative Biomaterials)
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Open AccessArticle
Tunable Perfect Narrow-Band Absorber Based on a Metal-Dielectric-Metal Structure
Coatings 2019, 9(6), 393; https://doi.org/10.3390/coatings9060393
Received: 17 May 2019 / Revised: 17 June 2019 / Accepted: 17 June 2019 / Published: 18 June 2019
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Abstract
In this paper, a metal-dielectric-metal structure based on a Fabry–Perot cavity was proposed, which can provide near 100% perfect narrow-band absorption. The lossy ultrathin silver film was used as the top layer spaced by a lossless silicon oxide layer from the bottom silver [...] Read more.
In this paper, a metal-dielectric-metal structure based on a Fabry–Perot cavity was proposed, which can provide near 100% perfect narrow-band absorption. The lossy ultrathin silver film was used as the top layer spaced by a lossless silicon oxide layer from the bottom silver mirror. We demonstrated a narrow bandwidth of 20 nm with 99.37% maximum absorption and the absorption peaks can be tuned by altering the thickness of the middle SiO2 layer. In addition, we established a deep understanding of the physics mechanism, which provides a new perspective in designing such a narrow-band perfect absorber. The proposed absorber can be easily fabricated by the mature thin film technology independent of any nano structure, which make it an appropriate candidate for photodetectors, sensing, and spectroscopy. Full article
(This article belongs to the Special Issue Thin Films for Energy Harvesting, Conversion, and Storage)
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Open AccessArticle
Machining GX2CrNiMoN26-7-4 DSS Alloy: Wear Analysis of TiAlN and TiCN/Al2O3/TiN Coated Carbide Tools Behavior in Rough End Milling Operations
Coatings 2019, 9(6), 392; https://doi.org/10.3390/coatings9060392
Received: 4 May 2019 / Revised: 27 May 2019 / Accepted: 14 June 2019 / Published: 17 June 2019
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Abstract
In the last decade, it has been common to observe a competition between coatings achieved via physical vapor deposition (PVD) and chemical vapor deposition (CVD) techniques on cutting tools used in machining processes. The tool’s substrate material can immediately condition the coating process [...] Read more.
In the last decade, it has been common to observe a competition between coatings achieved via physical vapor deposition (PVD) and chemical vapor deposition (CVD) techniques on cutting tools used in machining processes. The tool’s substrate material can immediately condition the coating process selection. However, there are also materials capabe of adapting to any of the coating processes. Hence, the capabilities demonstrated by a given coating when created with one technique or another are usually different due to the intrinsic characteristics of each coating process, such as temperature and stress levels. In this work, to study the machining behavior of a super duplex stainless steel, PVD- and CVD-coated tungsten carbide inserts with different coatings were used in order to identify the wear mechanisms that affect each of the coatings and the workpiece’s surface quality, evaluated through different roughness parameters. The vibration level produced throughout the various tests was also registered in an attempt to associate the type of coating or insert failure with the level of vibrations generated in the CNC (Computer Numeric Control) machining spindle. This allowed us to conclude that the tools coated with TiAlN via PVD showed better wear behavior, as well as creating workpiece surfaces with less roughness. Thus, it was clear that this coating presents strong advantages in the machining of the super duplex stainless steel chosen for this work, being an innovative work due to the combination of materials used and the approach in terms of vibration analysis applied to milling. Full article
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Open AccessArticle
Numerical Simulation of Thermal Evolution and Solidification Behavior of Laser Cladding AlSiTiNi Composite Coatings
Coatings 2019, 9(6), 391; https://doi.org/10.3390/coatings9060391
Received: 12 May 2019 / Revised: 5 June 2019 / Accepted: 14 June 2019 / Published: 17 June 2019
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Abstract
In order to better understand how a high energy input and a fast cooling rate affect the geometric morphology and microstructure of laser cladding aluminum composite coatings, a three-dimensional (3D) transient finite element model (FEM) has been established to study the temperature field [...] Read more.
In order to better understand how a high energy input and a fast cooling rate affect the geometric morphology and microstructure of laser cladding aluminum composite coatings, a three-dimensional (3D) transient finite element model (FEM) has been established to study the temperature field evolution during laser cladding of AlSiTiNi coatings on a 304 stainless steel substrate. In this model, a planar Gauss heat source and a temperature selection judgment mechanism are used to simulate the melting and solidification process as well as the geometric morphology of the laser cladding coatings. The differences in physical characteristics of the cladding materials before and after melting are considered. The results of thermal simulations, including temperature history, temperature gradient, and solidification rate, of the laser cladding coatings are investigated. Corresponding experiments, conducted using an IPG-YLS-5000 fiber laser, are used to verify the simulation results. The experimental observations agree well with the theoretical predictions, which indicates that the established model is valid. Full article
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Open AccessArticle
First Principles Study of Gas Molecules Adsorption on Monolayered β-SnSe
Coatings 2019, 9(6), 390; https://doi.org/10.3390/coatings9060390
Received: 30 April 2019 / Revised: 8 June 2019 / Accepted: 13 June 2019 / Published: 17 June 2019
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Abstract
For the purpose of exploring the application of two-dimensional (2D) material in the field of gas sensors, the adsorption properties of gas molecules, CO, CO2, CH2O, O2, NO2, and SO2 on the surface of [...] Read more.
For the purpose of exploring the application of two-dimensional (2D) material in the field of gas sensors, the adsorption properties of gas molecules, CO, CO2, CH2O, O2, NO2, and SO2 on the surface of monolayered tin selenium in β phase (β-SnSe) has been researched by first principles calculation based on density functional theory (DFT). The results indicate that β-SnSe sheet presents weak physisorption for CO and CO2 molecules with small adsorption energy and charge transfers, which show that a β-SnSe sheet is not suitable for sensing CO and CO2. The adsorption behavior of CH2O molecules adsorbed on a β-SnSe monolayer is stronger than that of CO and CO2, revealing that the β-SnSe layer can be applied to detect CH2O as physical sensor. Additionally, O2, NO2, and SO2 are chemically adsorbed on a β-SnSe monolayer with moderate adsorption energy and considerable charge transfers. All related calculations reveal that β-SnSe has a potential application in detecting and catalyzing O2, NO2, and SO2 molecules. Full article
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Open AccessArticle
In Vitro Activity Assays of Sputtered HAp Coatings with SiC Addition in Various Simulated Biological Fluids
Coatings 2019, 9(6), 389; https://doi.org/10.3390/coatings9060389
Received: 13 May 2019 / Revised: 11 June 2019 / Accepted: 13 June 2019 / Published: 15 June 2019
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Abstract
Considering the requirements of medical implantable devices, it is pointed out that biomaterials should play a more sophisticated, longer-term role in the customization and optimization of the material–tissue interface in order to ensure the best long-term clinical outcomes. The aim of this contribution [...] Read more.
Considering the requirements of medical implantable devices, it is pointed out that biomaterials should play a more sophisticated, longer-term role in the customization and optimization of the material–tissue interface in order to ensure the best long-term clinical outcomes. The aim of this contribution was to assess the performance of silicon carbide–hydroxyapatite in various simulated biological fluids (Dulbecco’s modified Eagle’s medium (DMEM), simulated body fluid (SBF), and phosphate buffer solution (PBS)) through immersion assays for 21 days at 37 ± 0.5 °C and to evaluate the electrochemical behavior. The coatings were prepared on Ti6Al4V alloy substrates by magnetron sputtering method using two cathodes made of hydroxyapatite and silicon carbide (SiC). After immersion assays the coating’s surface was analyzed in terms of morphology, chemical and phase composition, and chemical bonds. According to the electrochemical behavior in the media investigated at 37 ± 0.5 °C, SiC addition inhibits the dissolution of the hydroxyapatite in DMEM acellular media. Furthermore, after adding SiC, the slow degradation of hydroxyapatite in PBS and SBF media as well as biomineralization in DMEM were observed. Full article
(This article belongs to the Special Issue Surface Modification of Medical Implants)
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Open AccessArticle
Rectifying Characteristics of Thermally Treated Mo/SiC Schottky Contact
Coatings 2019, 9(6), 388; https://doi.org/10.3390/coatings9060388
Received: 27 May 2019 / Revised: 12 June 2019 / Accepted: 13 June 2019 / Published: 15 June 2019
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Abstract
The rectifying characteristics of a Mo/SiC Schottky contact fabricated by facing targets sputtering system were investigated through current–voltage measurement. The Schottky diode parameters were extracted from the forward current–voltage characteristic curve by the Cheung and Cheung method and the Norde method. The as-deposited [...] Read more.
The rectifying characteristics of a Mo/SiC Schottky contact fabricated by facing targets sputtering system were investigated through current–voltage measurement. The Schottky diode parameters were extracted from the forward current–voltage characteristic curve by the Cheung and Cheung method and the Norde method. The as-deposited Mo/SiC Schottky contacts possessed Schottky barrier heights of 1.17 and 1.22 eV, respectively. The Schottky barrier heights of the diodes were decreased to 1.01 and 0.91 eV after annealing at 400 °C for 30 min. The ideality factor was increased from 1.14 and 1.08 to 1.51 and 1.41, respectively. This implies the presence of non-ideal behaviors due to a current transport mechanism other than ideal thermionic emission, and the non-ideal behaviors increased as a result of excessive thermal annealing. In contrast, only a negligible change was observed in the crystallographic characteristics. This result suggests that the reason for the deviation from the ideal rectifying characteristics of the Mo/SiC Schottky contact through the annealing process was the variation in the current transport mechanism, including recombination, tunneling, and/or minority carrier injection. Full article
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Open AccessCommunication
Modifying Plasmonic-Field Enhancement and Resonance Characteristics of Spherical Nanoparticles on Metallic Film: Effects of Faceting Spherical Nanoparticle Morphology
Coatings 2019, 9(6), 387; https://doi.org/10.3390/coatings9060387
Received: 22 April 2019 / Revised: 12 June 2019 / Accepted: 13 June 2019 / Published: 15 June 2019
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Abstract
A three-dimensional finite-difference time-domain study of the plasmonic structure of nanoparticles on metallic film (NPOM) is presented in this work. An introduction to nanoparticle (NP) faceting in the NPOM structure produced a variety of complex transverse cavity modes, which were labeled S11 [...] Read more.
A three-dimensional finite-difference time-domain study of the plasmonic structure of nanoparticles on metallic film (NPOM) is presented in this work. An introduction to nanoparticle (NP) faceting in the NPOM structure produced a variety of complex transverse cavity modes, which were labeled S11 to S13. We observed that the dominant S11 mode resonance could be tuned to the desired wavelength within a broadband range of ~800 nm, with a maximum resonance up to ~1.42 µm, as a function of NP facet width. Despite being tuned at the broad spectral range, the S11 mode demonstrated minimal decrease in its near field enhancement characteristics, which can be advantageous for surface-enhanced spectroscopy applications and device fabrication perspectives. The identification of mode order was interpreted using cross-sectional electric field profiles and three-dimensional surface charge mapping. We realized larger local field enhancement in the order of ~109, even for smaller NP diameters of 50 nm, as function of the NP faceting effect. The number of radial modes were dependent upon the combination of NP diameter and faceting length. We hope that, by exploring the sub-wavelength complex optical properties of the plasmonic structures of NPOM, a variety of exciting applications will be revealed in the fields of sensors, non-linear optics, device engineering/processing, broadband tunable plasmonic devices, near-infrared plasmonics, and surface-enhanced spectroscopy. Full article
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Open AccessFeature PaperReview
Pulsed Laser Deposited Films for Microbatteries
Coatings 2019, 9(6), 386; https://doi.org/10.3390/coatings9060386
Received: 10 May 2019 / Revised: 6 June 2019 / Accepted: 10 June 2019 / Published: 14 June 2019
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Abstract
This review article presents a survey of the literature on pulsed laser deposited thin film materials used in devices for energy storage and conversion, i.e., lithium microbatteries, supercapacitors, and electrochromic displays. Three classes of materials are considered: Positive electrode materials (cathodes), solid electrolytes, [...] Read more.
This review article presents a survey of the literature on pulsed laser deposited thin film materials used in devices for energy storage and conversion, i.e., lithium microbatteries, supercapacitors, and electrochromic displays. Three classes of materials are considered: Positive electrode materials (cathodes), solid electrolytes, and negative electrode materials (anodes). The growth conditions and electrochemical properties are presented for each material and state-of-the-art of lithium microbatteries are also reported. Full article
(This article belongs to the Special Issue Current Research in Pulsed Laser Deposition)
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Open AccessArticle
Improvement of the Sphericity and the Thickness Uniformity of the Polystyrene (PS) Shell Microsphere during Curing Process
Coatings 2019, 9(6), 385; https://doi.org/10.3390/coatings9060385
Received: 14 April 2019 / Revised: 6 June 2019 / Accepted: 13 June 2019 / Published: 14 June 2019
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Abstract
To improve the quality of dispersed polystyrene (PS) compound droplets, a new random rotating curing system is designed. In addition, the qualities of the curing products of the PS compound droplets of this new system are compared with those of the traditional curing [...] Read more.
To improve the quality of dispersed polystyrene (PS) compound droplets, a new random rotating curing system is designed. In addition, the qualities of the curing products of the PS compound droplets of this new system are compared with those of the traditional curing system with a constant rotating speed, so as to verify the effectiveness of the new system on the quality improvement of the PS compound droplets. The effect of the liquid level, rotation rate and the density difference on the curing process is also analyzed to reveal the mechanism of the curing process in a rotating flow field. The results indicate that, in the new rotating curing system, the disturbance of the fluid increases the deformation recovery ability of the compound droplets. Furthermore, the vortex with different directions in the external flow fields, make the compound droplets spin in many directions, which improves the spheroidization and concentricity of the compound droplets. Compared with using the traditional rotating curing system, when utilizing the random rotating curing system, the sensitivity of the microspheres’ quality to the density mismatch between the phases is smaller, and the sphericity and the thickness uniformity of the polystyrene (PS) microsphere increase by 10.2% and 4.5%, respectively. In addition, there is an optimal rotation rate for the random rotating curing device, which can optimize the survival rate and quality of the hollow microspheres. Full article
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Open AccessReview
Crumb Rubber Modifier in Road Asphalt Pavements: State of the Art and Statistics
Coatings 2019, 9(6), 384; https://doi.org/10.3390/coatings9060384
Received: 12 February 2019 / Revised: 31 May 2019 / Accepted: 5 June 2019 / Published: 13 June 2019
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Abstract
Tire rubber recycling for civil engineering applications and products is developing faster, achieving increasingly higher levels of maturation. The improvements in the material circle, where crumb rubber, generated as a by-product of the tire rubber making process, becomes the resource used for the [...] Read more.
Tire rubber recycling for civil engineering applications and products is developing faster, achieving increasingly higher levels of maturation. The improvements in the material circle, where crumb rubber, generated as a by-product of the tire rubber making process, becomes the resource used for the construction of road asphalt pavement, is absolutely necessary for increasing the sustainability of the entire supply chain. The paper reports the results of an accurate data analysis derived from an extensive literature review of existing processes, technologies, and materials within construction of infrastructure. The current position, the direction, and rate of progress of the scientific efforts towards the reuse and recycling of tire rubber worldwide have been shown. Furthermore, an in-depth analysis of a set of important properties of Crumb Rubber Modified Asphalt has been carried out—fabrication parameters, standard properties, high and low-temperature performance, and rheological properties. Statistics over a sample of selected publications have been presented to understand the main processes adopted, rubber particle size, temperatures, and possible further modifications of crumb rubber modified binder. Full article
(This article belongs to the Special Issue Pavement Surface Coatings)
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Open AccessFeature PaperArticle
Degradation Behaviour of Mg0.6Ca and Mg0.6Ca2Ag Alloys with Bioactive Plasma Electrolytic Oxidation Coatings
Coatings 2019, 9(6), 383; https://doi.org/10.3390/coatings9060383
Received: 14 May 2019 / Revised: 4 June 2019 / Accepted: 11 June 2019 / Published: 13 June 2019
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Abstract
Bioactive Plasma Electrolytic Oxidation (PEO) coatings enriched in Ca, P and F were developed on Mg0.6Ca and Mg0.6Ca2Ag alloys with the aim to impede their fast degradation rate. Different characterization techniques (SEM, TEM, EDX, SKPFM, XRD) were used to analyze the surface characteristics [...] Read more.
Bioactive Plasma Electrolytic Oxidation (PEO) coatings enriched in Ca, P and F were developed on Mg0.6Ca and Mg0.6Ca2Ag alloys with the aim to impede their fast degradation rate. Different characterization techniques (SEM, TEM, EDX, SKPFM, XRD) were used to analyze the surface characteristics and chemical composition of the bulk and/or coated materials. The corrosion behaviour was evaluated using hydrogen evolution measurements in Simulated Body Fluid (SBF) at 37 °C for up to 60 days of immersion. PEO-coated Mg0.6Ca showed a 2–3-fold improved corrosion resistance compared with the bulk alloy, which was more relevant to the initial 4 weeks of the degradation process. In the case of the Mg0.6Ag2Ag alloy, the obtained corrosion rates were very high for both non-coated and PEO-coated specimens, which would compromise their application as resorbable implants. The amount of F ions released from PEO-coated Mg0.6Ca during 24 h of immersion in 0.9% NaCl was also measured due to the importance of F in antibacterial processes, yielding 33.7 μg/cm2, which is well within the daily recommended limit of F consumption. Full article
(This article belongs to the Special Issue Plasma Electrolytic Oxidation (PEO) Coatings)
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Open AccessArticle
Plasmonic Nanoparticles and Island Films for Solar Energy Harvesting: A Comparative Study of Cu, Al, Ag and Au Performance
Coatings 2019, 9(6), 382; https://doi.org/10.3390/coatings9060382
Received: 15 May 2019 / Revised: 5 June 2019 / Accepted: 8 June 2019 / Published: 13 June 2019
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Abstract
Alternative materials that can potentially replace Au and Ag in plasmonics and broaden its application potential have been actively investigated over the last decade. Cu and Al have been usually overlooked as plasmonic material candidates because they are prone to oxidisation. In this [...] Read more.
Alternative materials that can potentially replace Au and Ag in plasmonics and broaden its application potential have been actively investigated over the last decade. Cu and Al have been usually overlooked as plasmonic material candidates because they are prone to oxidisation. In this work the plasmonic performance of Cu and Al is investigated using numerical simulations of different nanostructures (spheres, cubes, rods and particle dimers) and taking into account the presence of oxidisation. It is shown that geometry can play a dominant role over material properties and the performance of Cu and Al becomes comparable to that of Ag and Au for systems of non-spherical particles and strong electromagnetic coupling among particles. This observation is experimentally confirmed by the fabrication and characterisation of Cu and Al metal island films. Optical characterisation of the samples reveals a comparable performance of these metals to that obtained for Ag and Au and suggests that Cu and Al metal island films can offer an efficient low-cost platform for solar energy harvesting, as shown in water vapour generation proof of concept experiments. Full article
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Open AccessArticle
Relevance of the Preparation of the Target for PLD on the Magnetic Properties of Films of Iron-Doped Indium Oxide
Coatings 2019, 9(6), 381; https://doi.org/10.3390/coatings9060381
Received: 2 May 2019 / Revised: 5 June 2019 / Accepted: 10 June 2019 / Published: 13 June 2019
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Abstract
This paper concerns the importance of the preparation of the targets that may be used for pulsed laser deposition of iron-doped indium oxide films. Targets with a fixed concentration of iron are fabricated from indium oxide and iron metal or one of the [...] Read more.
This paper concerns the importance of the preparation of the targets that may be used for pulsed laser deposition of iron-doped indium oxide films. Targets with a fixed concentration of iron are fabricated from indium oxide and iron metal or one of the oxides of iron, FeO, Fe3O4 and Fe2O3. Films from each target were ablated onto sapphire substrates at the same temperature under different oxygen pressures such that the thickness of the films was kept approximately constant. The films were studied using X-ray diffraction, X-ray absorption (both XANES and EXAFS), optical absorption and magnetic circular dichroism. The magnetic properties were measured with a SQUID magnetometer. At the lowest oxygen pressure, there was evidence that some of the iron ions in the films were in the state Fe2+, rather than Fe3+, and there was also a little metallic iron; these properties were accompanied by a substantial magnetisation. As the amount of the oxygen was increased, the number of defect phases and the saturation magnetisation was reduced and the band gap increased. In each case, we found that the amount of the oxygen that had been included in the target from the precursor added to the effect of adding oxygen in the deposition chamber. It was concluded that the amount of oxygen in the target due to the precursor was an important consideration but not a defining factor in the quality of the films. Full article
(This article belongs to the Special Issue Current Research in Pulsed Laser Deposition)
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Open AccessArticle
The Corrosion Inhibition of AA6082 Aluminium Alloy by Certain Azoles in Chloride Solution: Electrochemistry and Surface Analysis
Coatings 2019, 9(6), 380; https://doi.org/10.3390/coatings9060380
Received: 15 May 2019 / Revised: 30 May 2019 / Accepted: 10 June 2019 / Published: 13 June 2019
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Abstract
The corrosion inhibition effect of five azole compounds on the corrosion of an AA6082 aluminium alloy in 5 wt.% NaCl solution at 25 and 50 °C was investigated using weight loss and electrochemical measurements. Only 2-mercaptobenzothiazole (MBT) showed a corrosion inhibition effect at [...] Read more.
The corrosion inhibition effect of five azole compounds on the corrosion of an AA6082 aluminium alloy in 5 wt.% NaCl solution at 25 and 50 °C was investigated using weight loss and electrochemical measurements. Only 2-mercaptobenzothiazole (MBT) showed a corrosion inhibition effect at both temperatures and was further studied in detail, including with the addition of potassium iodide as a possible intensifier. Surface analysis of the MBT surface layer was performed by means of attenuated total reflectance Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and time-of-flight secondary ion mass spectrometry techniques. The hydrophobicity of the MBT surface layer was also investigated. Full article
(This article belongs to the Special Issue Anticorrosion Protection of Nonmetallic and Metallic Coatings)
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