Coatings

16 pages, 14065 KiB

Open AccessArticle

Optimised Performance of Non-Dispersive Infrared Gas Sensors Using Multilayer Thin Film Bandpass Filters

by Pinggui Wang, Xiuhua Fu, Des Gibson, Lewis Fleming, Sam Ahmadzadeh, Cheng Li, Manu Muhiyudin, Shigeng Song, David Hutson, David Moodie, Calum MacGregor and Matthew Steer

Coatings 2018, 8(12), 472; https://doi.org/10.3390/coatings8120472 - 19 Dec 2018

Cited by 10 | Viewed by 5381

Abstract

In this work, performance improvements are described for a low-power consumption non-dispersive infrared (NDIR) methane (CH₄) gas sensor using customised optical thin film bandpass filters (BPFs) centered at 3300 nm. BPFs shape the spectral characteristics of the combined mid-infrared III–V based [...] Read more.

In this work, performance improvements are described for a low-power consumption non-dispersive infrared (NDIR) methane (CH₄) gas sensor using customised optical thin film bandpass filters (BPFs) centered at 3300 nm. BPFs shape the spectral characteristics of the combined mid-infrared III–V based light emitting diode (LED)/photodiode (PD) light source/detector optopair, enhancing the NDIR CH₄ sensor performance. The BPFs, deposited using a novel microwave plasma-assisted pulsed DC sputter deposition process, provide room temperature deposition directly onto the temperature-sensitive PD heterostructure. BPFs comprise germanium (Ge) and niobium pentoxide (Nb₂O₅) alternating high and low refractive index layers, respectively. Two different optical filter designs are progressed with BPF bandwidths (BWs) of 160 and 300 nm. A comparison of the modelled and measured NDIR sensor performance is described, highlighting the maximised signal-to-noise ratio (SNR) and the minimised cross-talk performance benefits. The BPF spectral stability for various environmental temperature and humidity conditions is demonstrated. Full article

(This article belongs to the Special Issue Applications of Optical Thin Film Coatings)

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11 pages, 4721 KiB

Open AccessArticle

Determination of Optimum Concentration of Benzimidazole Improving the Cathodic Disbonding Resistance of Epoxy Coating

by Saghar Nabavian, Reza Naderi and Najmeh Asadi

Coatings 2018, 8(12), 471; https://doi.org/10.3390/coatings8120471 - 19 Dec 2018

Cited by 3 | Viewed by 3134

Abstract

This study is aimed to evaluate the effect of concentrated benzimidazole (BIM) on the cathodic disbonding (CP) of an epoxy coating applied on steel substrate. For this purpose, the polymeric coatings, formulated with different concentrations of BIM (0 wt.%, 0.5 wt.%, 0.75 wt.%, [...] Read more.

This study is aimed to evaluate the effect of concentrated benzimidazole (BIM) on the cathodic disbonding (CP) of an epoxy coating applied on steel substrate. For this purpose, the polymeric coatings, formulated with different concentrations of BIM (0 wt.%, 0.5 wt.%, 0.75 wt.%, and 1 wt.%, were subjected to the CP test at the potential of −1.2 V vs. Ag/AgCl during 24 h immersion in 3.5 wt.% NaCl solutions. The optimum formulation was found through taking advantage of the CP test results, FESEM/EDX, and EIS data. Moreover, a pull-off test was used to measure the wet adhesion strength. For insight into the inhibition function of the organic inhibitor, the behavior of steel in the sodium chloride solutions, with and without BIM, was compared using EIS and surface analysis. Full article

(This article belongs to the Special Issue Advances in Organic and Polymeric Coatings )

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20 pages, 5706 KiB

Open AccessArticle

Three-Dimensional Thermoelastic Contact Model of Coated Solids with Frictional Heat Partition Considered

by Tingjian Wang, Xinxin Ma, Liqin Wang, Le Gu, Longcheng Yin, Jingjing Zhang, Liwei Zhan and Dong Sun

Coatings 2018, 8(12), 470; https://doi.org/10.3390/coatings8120470 - 19 Dec 2018

Cited by 21 | Viewed by 2939

Abstract

In this paper, a three-dimensional thermoelastic contact model of coated solids with the frictional heat partition considered is developed by introducing a frictional heat partition model. The influence coefficients of the temperature rise, normal displacement and stress components in the three-dimensional thermoelastic contact [...] Read more.

In this paper, a three-dimensional thermoelastic contact model of coated solids with the frictional heat partition considered is developed by introducing a frictional heat partition model. The influence coefficients of the temperature rise, normal displacement and stress components in the three-dimensional thermoelastic contact model are converted from their corresponding frequency response functions (FRFs) with a conversion method based on the fast Fourier transform (FFT), and the FRFs of solids coated with a homogeneous coating subjected to a coupled action of the mechanical loading and the frictional heat flux on its surface are deduced in the frequency domain by introducing a two-dimensional Fourier integral transform. The contact pressure and the frictional heat partition between the two bodies are solved by employing a fast numerical algorithm based on the conjugate gradient method (CGM) and a discrete convolution fast Fourier transformation (DC-FFT). Comparison between the solutions of the present model and those of a thermoelastic contact model in literature is conducted in order to validate the present model. Several specific conclusions on the effect of the sliding speed, thermoelastic properties and thickness of the coating are drawn based on the result of numerical investigation by utilizing the present model. Full article

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18 pages, 3098 KiB

Open AccessArticle

Inter-Correlation among the Hydrophilic–Lipophilic Balance, Surfactant System, Viscosity, Particle Size, and Stability of Candelilla Wax-Based Dispersions

by Martina Lindner, Magdalena Bäumler and Andreas Stäbler

Coatings 2018, 8(12), 469; https://doi.org/10.3390/coatings8120469 - 19 Dec 2018

Cited by 22 | Viewed by 6864

Abstract

Owing to a decrease in mineral oil resources, it is crucial to develop packaging materials based on renewable resources. Hence, a water vapor-barrier coating is developed as a natural wax-based dispersion. This dispersion should be stable over the storage time. In this study, [...] Read more.

Owing to a decrease in mineral oil resources, it is crucial to develop packaging materials based on renewable resources. Hence, a water vapor-barrier coating is developed as a natural wax-based dispersion. This dispersion should be stable over the storage time. In this study, the physical stability of a wax-based melt dispersion was analyzed (24 h and 21 days after production), and instability phenomena such as agglomeration, coalescence, and flotation were identified. Furthermore, the inter-correlations among the particle size, viscosity of the continuous phase, physical stability, surfactant chemistry, and hydrophilic–lipophilic balance value were characterized. Particle sizes were described by volume/surface mean d_3,2, volume moment mean d_4,3, and number mean d_1,0 diameter, as well as the span of the volume and number distribution. Stability was characterized by the flotation rate, emulsion stability index, and Turbiscan stability index. Coalescence and agglomeration were not observed after the solidification of the wax particles. A significant correlation was observed for the emulsion stability index, with d_3,2, and for flotation rate, with d_1,0, d_4,3, and viscosity as well, with d_1,0, d_3,2. Surfactants with hydrophilic–lipophilic balance values of 11–13.5 seem to be the most suitable for stabilizing candelilla wax-in-water suspensions. Particles were smaller, and wax suspensions were better stabilized using Tween 20 and Span 20, compared with Tween 80 and Span 80. Full article

(This article belongs to the Special Issue Coating—A Sustainable Future)

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14 pages, 6099 KiB

Open AccessArticle

Cost-Effective Surface Modification of Carbon Cloth Electrodes for Microbial Fuel Cells by Candle Soot Coating

by Bor-Yann Chen, Yuan-Ting Tsao and Shih-Hang Chang

Coatings 2018, 8(12), 468; https://doi.org/10.3390/coatings8120468 - 17 Dec 2018

Cited by 14 | Viewed by 5035

Abstract

This study explored an economically-feasible and environmentally friendly attempt to provide more electrochemically promising carbon cloth anodes for microbial fuel cells (MFCs) by modifying them with candle soot coating. The sponge-like structure of the deposited candle soot apparently increased the surface areas of [...] Read more.

This study explored an economically-feasible and environmentally friendly attempt to provide more electrochemically promising carbon cloth anodes for microbial fuel cells (MFCs) by modifying them with candle soot coating. The sponge-like structure of the deposited candle soot apparently increased the surface areas of the carbon cloths for bacterial adhesion. The super-hydrophilicity of the deposited candle soot was more beneficial to bacterial propagation. The maximum power densities of MFCs configured with 20-s (13.6 ± 0.9 mW·m⁻²), 60-s (19.8 ± 0.2 mW·m⁻²), and 120-s (17.6 ± 0.8 mW·m⁻²) candle-soot-modified carbon cloth electrodes were apparently higher than that of an MFC configured with an unmodified electrode (10.2 ± 0.2 mW·m⁻²). The MFCs configured with the 20- and 120-s candle-soot-modified carbon cloth electrodes exhibited lower power densities than that of the MFC with the 60-s candle-soot-modified carbon cloth electrode. This suggested that the insufficient residence time of candle soot led to an incomplete formation of the hydrophilic surface, whereas protracted candle sooting would lead to a thick deposited soot film with a smaller conductivity. The application of candle soot for anode modification provided a simple, rapid, cost-effective, and environment-friendly approach to enhancing the electron-transfer capabilities of carbon cloth electrodes. However, a postponement in the MFC construction may lead to a deteriorated hydrophilicity of the candle-soot-modified carbon cloth. Full article

(This article belongs to the Special Issue Surface Chemical Modification)

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13 pages, 13399 KiB

Open AccessArticle

TEM Microstructural Evolution and Formation Mechanism of Reaction Layer for 22MnB5 Steel Hot-Dipped in Al–10% Si

by Dongik Shin, Jeong-Yong Lee, Hoejun Heo and Chung-Yun Kang

Coatings 2018, 8(12), 467; https://doi.org/10.3390/coatings8120467 - 15 Dec 2018

Cited by 7 | Viewed by 3361

Abstract

Microstructural evolution and formation mechanism of reaction layer for 22MnB5 steel hot-dipped in Al–10Si (in wt %) alloy was investigated. The microstructural identification of the reaction layer was characterized via transmission electron microscopy and electron backscatter diffraction. In addition, the formation mechanisms of [...] Read more.

Microstructural evolution and formation mechanism of reaction layer for 22MnB5 steel hot-dipped in Al–10Si (in wt %) alloy was investigated. The microstructural identification of the reaction layer was characterized via transmission electron microscopy and electron backscatter diffraction. In addition, the formation mechanisms of the phases were discussed with vertical section (isopleth) of the (Al–Si–Fe) ternary system. The solidified Al–Si coating layer consisted of three phases of Al, Si, and τ₅ (Al₈Fe₂Si). The reaction layer on the Al–Si coating layer side is a fine τ₅ phase (Al₈Fe₂Si) of 5 μm thickness. The layer on the steel side consisted of an η phase (Fe₂Al₅) of thickness of 500 nm or less. τ₁ (Al₂Fe₃Si₃, triclinic) phase of 200-nm-thickness was formed in the η phase, and κ phase (Fe₃AlC) of 40–50 nm thickness was formed between η phase and steel. The τ₅ phase was formed by isothermal solidification at 690 °C in the liquid Al–10 wt % Si when 3.73–29.0 wt % of Fe was dissolved from the boron steel into the Al–Si liquid bath. It was considered that the η phase was formed by the diffusion reaction of Al, Si, and Fe between τ₅ and ferrite steel. κ (Fe₃AlC) phase was formed by the reaction of the carbon, which is barely employed in η and τ phases, and diffused Al. Full article

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11 pages, 5033 KiB

Open AccessArticle

Spectroscopic and Structural Analyses of Opuntia Robusta Mucilage and Its Potential as an Edible Coating

by Aurea Bernardino-Nicanor, José Luis Montañez-Soto, Eloy Conde-Barajas, María de la Luz Xochilt Negrete-Rodríguez, Gerardo Teniente-Martínez, Enaim Aída Vargas-León, José Mayolo Simitrio Juárez-Goiz, Gerardo Acosta-García and Leopoldo González-Cruz

Coatings 2018, 8(12), 466; https://doi.org/10.3390/coatings8120466 - 15 Dec 2018

Cited by 14 | Viewed by 4038

Abstract

Mucilage extracted from the parenchymatous and chlorenchymatous tissues of Opuntia robusta were obtained using water or ethanol as the extraction solvent. The changes in the different tissues by using different extraction solvents were evaluated via scanning electron microscopy (SEM) and Fourier transform infrared [...] Read more.

Mucilage extracted from the parenchymatous and chlorenchymatous tissues of Opuntia robusta were obtained using water or ethanol as the extraction solvent. The changes in the different tissues by using different extraction solvents were evaluated via scanning electron microscopy (SEM) and Fourier transform infrared (FT-IR) and Raman spectroscopy; in addition, the effect of mucilage coating on the various quality characteristics of tomato (Lycopersicum sculentum) was evaluated. The SEM results showed that the mucilage extracted from the parenchyma had a higher aggregation level that the mucilage extracted from the chlorenchyma. The presence of three characteristic bands of pectic substances in the FT-IR spectra between 1050 and 1120 cm⁻¹ indicated that the mucilage extracted from the parenchymatous tissue had a higher content of pectic compounds than the mucilage extracted from the chlorenchymatous tissue. It was also observed in the Raman spectra that the level of pectic substances in the mucilage extracted from the parenchymatous was higher than that in the mucilage extracted from the chlorenchymatous tissue. The mucilage extracted from the parenchymatous tissue was more effective as an edible coating than the mucilage extracted from the chlorenchymatous tissue. Tomatoes covered with mucilage showed significantly enhanced firmness and reduced weight loss. The uncoated tomatoes showed higher lycopene content than the coated tomatoes on the 21st day. This study showed that the Opuntia robusta tissue and extraction solvent influence mucilage characteristics and that Opuntia robusta mucilage is a promising edible coating. Full article

(This article belongs to the Special Issue Advances in Organic and Polymeric Coatings )

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12 pages, 6827 KiB

Open AccessFeature PaperArticle

Extinction Properties of Obliquely Deposited TiN Nanorod Arrays

by Yi-Jun Jen, Wei-Chien Wang, Kai-Lun Wu and Meng-Jie Lin

Coatings 2018, 8(12), 465; https://doi.org/10.3390/coatings8120465 - 14 Dec 2018

Cited by 11 | Viewed by 3788

Abstract

Plasmonic titanium nitride (TiN) nanorod arrays (NRA) were fabricated by glancing angle deposition in a DC magnetron reactive sputtering system. The morphology of the TiN NRA was varied by collimating the vapor flux. The transmittance, reflectance, and extinctance of slanted TiN nanorods with [...] Read more.

Plasmonic titanium nitride (TiN) nanorod arrays (NRA) were fabricated by glancing angle deposition in a DC magnetron reactive sputtering system. The morphology of the TiN NRA was varied by collimating the vapor flux. The transmittance, reflectance, and extinctance of slanted TiN nanorods with different lengths as functions of wavelength and angle of incidence were measured and analyzed. The extinction peaks in the spectra reveal the transverse and longitudinal plasmonic modes of TiN NRA upon excitation by s-polarized and p-polarized light, respectively. The near-field simulation was performed to elucidate localized field enhancements that correspond to high extinction. The extension of the high extinction band with an increasing length of the nanorods results in broadband and wide-angle light extinction for a TiN NRA with a thickness greater than 426 nm. Full article

(This article belongs to the Special Issue Design, Manufacturing and Measurement of Optical Film Coatings)

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8 pages, 3113 KiB

Open AccessArticle

Microfiber Coating for Drag Reduction by Flocking Technology

by Mitsugu Hasegawa and Hirotaka Sakaue

Coatings 2018, 8(12), 464; https://doi.org/10.3390/coatings8120464 - 14 Dec 2018

Cited by 11 | Viewed by 4037

Abstract

The biomimicry of using a hair-like structure is introduced as a drag reduction coating. The hair-like structure consists of an array of microfiber that is introduced as a passive drag reduction device. An effective flow control for a transition delay or a flow [...] Read more.

The biomimicry of using a hair-like structure is introduced as a drag reduction coating. The hair-like structure consists of an array of microfiber that is introduced as a passive drag reduction device. An effective flow control for a transition delay or a flow attachment is expected via an interaction or counteraction of flexible fibers, compared to the existing passive methods that use a solid or rigid surface device. The effect of the microfiber coating on drag reduction over a bluff-body was experimentally investigated using a circular cylinder in a wind tunnel at Reynolds number of 6.1 × 10⁴. A drag reduction of 32% was obtained when the microfiber coating with a length of 0.012D was located at 40° from the stagnation point. Smoke flow visualization showed that flow separation delay was induced by the microfiber coating when the drag reduction occurred. Full article

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11 pages, 8350 KiB

Open AccessArticle

Effects of Cr and Nb Additions on Sliding Wear Behaviors of the FePSiB Coatings

by Yuan Feng, Jiangbo Cheng, Dan Liu and Xiubing Liang

Coatings 2018, 8(12), 463; https://doi.org/10.3390/coatings8120463 - 14 Dec 2018

Viewed by 2375

Abstract

The tribological properties of the FePSiB amorphous/nanocrystalline coatings with Cr and Nb additions were investigated in reciprocating mode against tungsten carbide friction coupling with different dry sliding conditions. The wear rates of the FePSiB-based coatings increase linearly with the normal load and sliding [...] Read more.

The tribological properties of the FePSiB amorphous/nanocrystalline coatings with Cr and Nb additions were investigated in reciprocating mode against tungsten carbide friction coupling with different dry sliding conditions. The wear rates of the FePSiB-based coatings increase linearly with the normal load and sliding speed. The coatings with Cr and Nb promote the formation of successive and compact oxide film on friction surface, which decreases significantly wear rate of the coating. Nano-mechanical characterization done to map the correlation between the elastic properties and wear resistance. The main damage mechanisms of the FePSiB-based coatings under dry friction conditions are abrasion wear, delamination failure and oxidation wear. Full article

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12 pages, 3987 KiB

Open AccessArticle

Transparent Amorphous Oxide Semiconductor as Excellent Thermoelectric Materials

by Seohan Kim, Doukyun Kim, Jayoung Byeon, Jaehong Lim, Jaeyong Song, Sunhwa Park, Chulhong Park and Pungkeun Song

Coatings 2018, 8(12), 462; https://doi.org/10.3390/coatings8120462 - 13 Dec 2018

Cited by 13 | Viewed by 4351

Abstract

It is demonstrated that transparent amorphous oxide semiconductors (TAOS) can be excellent thermoelectric (TE) materials, since their thermal conductivity (κ) through a randomly disordered structure is quite low, while their electrical conductivity and carrier mobility (μ) are high, compared to crystalline semiconductors through [...] Read more.

It is demonstrated that transparent amorphous oxide semiconductors (TAOS) can be excellent thermoelectric (TE) materials, since their thermal conductivity (κ) through a randomly disordered structure is quite low, while their electrical conductivity and carrier mobility (μ) are high, compared to crystalline semiconductors through the first-principles calculations and the various measurements for the amorphous In−Zn−O (a-IZO) thin film. The calculated phonon dispersion in a-IZO shows non-linear phonon instability, which can prevent the transport of phonon. The a-IZO was estimated to have poor κ and high electrical conductivity compared to crystalline In₂O₃:Sn (c-ITO). These properties show that the TAOS can be an excellent thin-film transparent TE material. It is suggested that the TAOS can be employed to mitigate the heating problem in transparent display devices. Full article

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10 pages, 6104 KiB

Open AccessFeature PaperArticle

Effects of Decaphenylcyclopentasilane Addition on Photovoltaic Properties of Perovskite Solar Cells

by Masaya Taguchi, Atsushi Suzuki, Takeo Oku, Sakiko Fukunishi, Satoshi Minami and Masanobu Okita

Coatings 2018, 8(12), 461; https://doi.org/10.3390/coatings8120461 - 13 Dec 2018

Cited by 14 | Viewed by 4112

Abstract

Perovskite solar cells, in which decaphenylcyclopentasilane (DPPS) layers were formed on the surface of the perovskite layer, were fabricated, and the influence on photovoltaic characteristics was investigated. The devices were fabricated by a spin-coating technique, and the surface morphology and crystal structures were [...] Read more.

Perovskite solar cells, in which decaphenylcyclopentasilane (DPPS) layers were formed on the surface of the perovskite layer, were fabricated, and the influence on photovoltaic characteristics was investigated. The devices were fabricated by a spin-coating technique, and the surface morphology and crystal structures were investigated by scanning electron microscopy and X-ray diffraction. By adding the DPPS, the fill factor and open circuit voltage were increased, and the photoelectric conversion efficiency was improved. A stability test in ambient air was carried out for seven weeks, and the photoelectric conversion efficiencies were remarkably improved for the devices with DPPS. Full article

(This article belongs to the Collection Surface and Interface Science and Engineering for the Society of the Future)

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7 pages, 209 KiB

Open AccessArticle

Bacterial Inactivation by Using Plastic Materials Activated with Combinations of Natural Antimicrobials

by Irene Ortega Blázquez, María José Grande Burgos, Rubén Pérez Pulido, Antonio Gálvez and Rosario Lucas

Coatings 2018, 8(12), 460; https://doi.org/10.3390/coatings8120460 - 12 Dec 2018

Cited by 2 | Viewed by 3151

Abstract

Natural antimicrobials have gained interest as possible inhibitors of biofilm formation. The aim of the present study was to determine the efficacy of antimicrobials derived from essential oils (carvacrol, thymol) plus bacteriocin AS-48 immobilized on two plastic supports (low density polyethylene and polyethylene–polyamide [...] Read more.

Natural antimicrobials have gained interest as possible inhibitors of biofilm formation. The aim of the present study was to determine the efficacy of antimicrobials derived from essential oils (carvacrol, thymol) plus bacteriocin AS-48 immobilized on two plastic supports (low density polyethylene and polyethylene–polyamide films) on bacterial inactivation. The polyethylene–polyamide vacuum-packaging plastic film activated with a combination of thymol plus enterocin AS-48 was the most effective in reducing the concentrations of viable planktonic and sessile cells for Listeria innocua, Lactobacillus fructivorans, Bacillus coagulans, and Bacillus licheniformis. Results from the study highlight the potential of polyethylene–polyamide film activated with thymol plus enterocin AS-48 for reducing the viable cell concentrations of spoilage Gram-positive bacteria and Listeria in both planktonic and sessile states. Full article

(This article belongs to the Collection Surface and Interface Science and Engineering for the Society of the Future)

22 pages, 14571 KiB

Open AccessArticle

Tribo-Mechanical Properties and Corrosion Behavior Investigation of Anodized Ti–V Alloy

by Bingrong Han, Erfan Zal Nezhad, Farayi Musharavati, Fadi Jaber and Sungchul Bae

Coatings 2018, 8(12), 459; https://doi.org/10.3390/coatings8120459 - 12 Dec 2018

Cited by 10 | Viewed by 3314

Abstract

In the work presented in this manuscript, a self-organized TiO₂ nanotube array film was produced by electrochemical anodization of a Ti–V alloy in an electrolyte containing NH₄F/H₃PO₄ and then annealed at different temperatures under different atmospheres. The [...] Read more.

In the work presented in this manuscript, a self-organized TiO₂ nanotube array film was produced by electrochemical anodization of a Ti–V alloy in an electrolyte containing NH₄F/H₃PO₄ and then annealed at different temperatures under different atmospheres. The effect of annealing temperature in different atmospheres on the morphology of the film was analyzed, and the tribo-mechanical property and corrosion behavior of TiO₂ were investigated. The morphological features and phase compositions were characterized using scanning electron microscopy (SEM) and X-ray diffraction (XRD) respectively. The results indicated that the TiO₂ characteristic peaks did not appear after anodization because of the intrinsic amorphous feature. However, highly crystalline TiO₂ (anatase and rutile) was produced after annealing from 200 to 600 °C. In addition, there was an improvement in the wear resistance of the Ti–V alloy due to the high hardness and low coefficient of friction of the TiO₂ nanotubes’ coating. Moreover, the corrosion behaviors of TiO₂ coated and uncoated substrates were evaluated in the synthetic medium, and it was confirmed that the corrosion resistance of the TiO₂-coated Ti–V alloy, annealed at 200 °C in the atmosphere, was significantly higher when compared to the uncoated sample. Full article

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10 pages, 3084 KiB

Open AccessArticle

Influence of C₂H₂ Flows on Microstructure and Corrosion Resistance of TiCN Films Doped with Carbon Atoms

by Haitao Li, Pengfei Sun, Yongchang Zhu, Mingzhong Wu and Qiang Wang

Coatings 2018, 8(12), 458; https://doi.org/10.3390/coatings8120458 - 12 Dec 2018

Cited by 5 | Viewed by 2853

Abstract

Nanosized TiCN/TiN films were deposited on AZ31 by reactive magnetron sputtering under different acetylene flows. The microstructures of obtained films were characterized, and their corrosion behaviors were also investigated. The films doped with carbon atoms under different acetylene flows own different structures and [...] Read more.

Nanosized TiCN/TiN films were deposited on AZ31 by reactive magnetron sputtering under different acetylene flows. The microstructures of obtained films were characterized, and their corrosion behaviors were also investigated. The films doped with carbon atoms under different acetylene flows own different structures and grain sizes. The grain size decreased to some extent, and the film structure changed from polycrystalline to nanocrystalline, with an increase of C₂H₂ flow. The surface morphology also changed from rough to smooth, with an increase of C₂H₂ flow. The Tafel curves and electrochemical impedance spectroscopy (EIS) demonstrated that the composite films could greatly improve the corrosion resistance of bare substrates in a 3.5% NaCl solution, and the films’ corrosion resistance is different, owing to their different structures and grain sizes. Full article

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10 pages, 2031 KiB

Open AccessArticle

Surface Preparation and Treatment for Large-Scale 3D-Printed Composite Tooling Coating Adhesion

by Philipp Sauerbier, James Anderson and Douglas J. Gardner

Coatings 2018, 8(12), 457; https://doi.org/10.3390/coatings8120457 - 11 Dec 2018

Cited by 14 | Viewed by 3699

Abstract

Recent advances in large-scale thermoplastic additive manufacturing (AM), using fused deposition modelling (FDM), have shown that the technology can effectively produce large aerospace tools with common feed stocks, costing 2.3 $/kg, such as a 20% carbon-filled acrylonitrile butadiene styrene (ABS). Large-scale additive manufacturing [...] Read more.

Recent advances in large-scale thermoplastic additive manufacturing (AM), using fused deposition modelling (FDM), have shown that the technology can effectively produce large aerospace tools with common feed stocks, costing 2.3 $/kg, such as a 20% carbon-filled acrylonitrile butadiene styrene (ABS). Large-scale additive manufacturing machines have build-volumes in the range of cubic meters and use commercially available pellet feedstock thermoplastics, which are significantly cheaper (5–10 $/kg) than the filament feedstocks for desktop 3D printers (20–50 $/kg). Additionally, large-scale AM machines have a higher material throughput on the order of 50 kg/h. This enables the cost-efficient tool production for several industries. Large-scale 3D-printed tooling will be computerized numerical control (CNC)-machined and -coated, to provide a surface suitable for demolding the composite parts. This paper outlines research undertaken to review and improve the adhesion of the coating systems to large, low-cost AM composite tooling, for marine or infrastructure composite applications. Lower cost tooling systems typically have a lower dimensional accuracy and thermal operating requirements than might be required for aerospace tooling. As such, they can use lower cost commodity grade thermoplastics. The polymer systems explored in the study included polypropylene (PP), styrene-maleic anhydride (SMA), and polylactic acid (PLA). Bio-based filler materials were used to reduce cost and increase the strength and stiffness of the material. Fillers used in the study included wood flour, at 30% by weight and spray-dried cellulose nano-fibrils, at 20% by weight. Applicable adhesion of the coating was achieved with PP, after surface treatment, and untreated SMA and PLA showed desirable coating adhesion results. PLA wood-filled composites offered the best properties for the desired application and, furthermore, they have environment-friendly advantages. Full article

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13 pages, 6959 KiB

Open AccessArticle

Wear and Corrosion Properties of Cold-Sprayed AISI 316L Coatings Treated by Combined Plasma Carburizing and Nitriding at Low Temperature

by Shinichiro Adachi and Nobuhiro Ueda

Coatings 2018, 8(12), 456; https://doi.org/10.3390/coatings8120456 - 10 Dec 2018

Cited by 25 | Viewed by 4452

Abstract

Cold-sprayed AISI 316L stainless steel coatings are treated to form an austenite phase with excessive dissolved nitrogen (known as the S-phase) by plasma nitriding at temperatures below 450 °C. The S-phase is a hard and wear-resistant layer with high corrosion resistance. However, the [...] Read more.

Cold-sprayed AISI 316L stainless steel coatings are treated to form an austenite phase with excessive dissolved nitrogen (known as the S-phase) by plasma nitriding at temperatures below 450 °C. The S-phase is a hard and wear-resistant layer with high corrosion resistance. However, the S-phase layer formed after only nitriding is thin and the hardness abruptly decreases at a certain depth; it lacks mechanical reliability. We examined two types of combined low-temperature plasma treatment to enhance the mechanical reliability of the S-phase layer: (i) sequential and (ii) simultaneous. In the sequential plasma treatment, the carburizing step was followed by nitriding. In the simultaneous treatment, the nitriding and carburizing steps were conducted at the same time. Both combined plasma treatments succeeded in thickening the S-phase layers and changed the hardness depth profiles to decrease smoothly. In addition, anodic polarization measurements indicated that sequential treatment involving carburizing followed by nitriding for 2 h each resulted in high corrosion resistance. Full article

(This article belongs to the Collection Surface and Interface Science and Engineering for the Society of the Future)

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18 pages, 3384 KiB

Open AccessArticle

Stress-Affected Lithiation Reactions in Elasto-Viscoplastic Si Particles with Hyperelastic Polymer Coatings: A Nonlinear Chemo-Mechanical Finite-Element Study

by Philip Lippmann, Michael Poluektov and Łukasz Figiel

Coatings 2018, 8(12), 455; https://doi.org/10.3390/coatings8120455 - 08 Dec 2018

Cited by 2 | Viewed by 3552

Abstract

Stress-affected two-phase lithiation reactions in spherical elasto-viscoplastic Si particles for Li-ion batteries are studied here to determine the effects of a hyperelastic polymer coating on particle stresses, reaction front velocity, and degree of lithiation. The problem is modelled using finite-strain chemo-mechanical equations that [...] Read more.

Stress-affected two-phase lithiation reactions in spherical elasto-viscoplastic Si particles for Li-ion batteries are studied here to determine the effects of a hyperelastic polymer coating on particle stresses, reaction front velocity, and degree of lithiation. The problem is modelled using finite-strain chemo-mechanical equations that couple stress, with Li-ion diffusion and reaction front velocity, and are solved using the finite-element (FE) approach, taking advantage of spherical symmetry of the problem. FE simulations and the sensitivity analysis reveal: (1) coating thickness is the most influential design parameter that affects the velocity of the reaction front, and (2) increasing values of the coating shear and bulk moduli, and the coating thickness reduce tensile circumferential stresses at the edge of the particle. The latter minimises the risk of particle cracking in the opening mode, but it can also accelerate the arrest of the reaction front, and thus reduce the particle lithiation degree in Li-ion battery anodes. Full article

(This article belongs to the Special Issue Modelling and Simulation of Coating 2019)

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16 pages, 14330 KiB

Open AccessArticle

From Waste to Valuable Resource: Lignin as a Sustainable Anti-Corrosion Coating

by Arman Dastpak, Kirsi Yliniemi, Mariana Cecilio De Oliveira Monteiro, Sarah Höhn, Sannakaisa Virtanen, Mari Lundström and Benjamin P. Wilson

Coatings 2018, 8(12), 454; https://doi.org/10.3390/coatings8120454 - 08 Dec 2018

Cited by 34 | Viewed by 6697

Abstract

In this study, a waste of biorefinery—lignin—is investigated as an anticorrosion coating on stainless steel. Corrosion behavior of two lignin types (hardwood beech and softwood spruce) was studied by electrochemical measurements (linear sweep voltammetry, open circuit potential, potentiostatic polarization, cyclic potentiodynamic polarization, and [...] Read more.

In this study, a waste of biorefinery—lignin—is investigated as an anticorrosion coating on stainless steel. Corrosion behavior of two lignin types (hardwood beech and softwood spruce) was studied by electrochemical measurements (linear sweep voltammetry, open circuit potential, potentiostatic polarization, cyclic potentiodynamic polarization, and electrochemical impedance measurements) during exposure to simulated body fluid (SBF) or phosphate buffer (PBS). Results from linear sweep voltammetry of lignin-coated samples, in particular, demonstrated a reduction in corrosion current density between 1 and 3 orders of magnitude cf. blank stainless steel. Furthermore, results from cross cut adhesion tests on lignin-coated samples demonstrated that the best possible adhesion (grade 0) of ISO 2409 standard was achieved for the investigated novel coatings. Such findings suggest that lignin materials could transform the field of organic coatings towards more sustainable alternatives by replacing non-renewable polymer coatings. Full article

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9 pages, 2814 KiB

Open AccessArticle

Relative Humidity Fiber Sensor Based on Multimode Interferometer Coated with Agarose-Gel

by Susana Novais, Marta S. Ferreira and João L. Pinto

Coatings 2018, 8(12), 453; https://doi.org/10.3390/coatings8120453 - 08 Dec 2018

Cited by 25 | Viewed by 2891

Abstract

In this work, a relative humidity (RH) sensor based on a structure with multimode interference is proposed and experimentally demonstrated. The multimode sensor is fabricated by fusion splicing a coreless fiber section to a single mode fiber. A hydrophilic agarose gel is coated [...] Read more.

In this work, a relative humidity (RH) sensor based on a structure with multimode interference is proposed and experimentally demonstrated. The multimode sensor is fabricated by fusion splicing a coreless fiber section to a single mode fiber. A hydrophilic agarose gel is coated on the coreless fiber, using the dip coating technique. By changing the surrounding RH, the refractive index of the coated agarose gel will change, causing a wavelength shift of the peak in the reflection spectra. For RH variations in the range between 60.0%RH and 98.5%RH, the sensor presents a maximum sensitivity of 44.2 pm/%RH, and taking in consideration the interrogation system, a resolution of 0.5%RH is acquired. This sensor has a great potential in real time RH monitoring and can be of interest for applications where a control of high levels of relative humidity is required. Full article

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2 pages, 167 KiB

Open AccessCorrection

Correction: Awino, C., et al. Investigation of Structural and Electronic Properties of CH₃NH₃PbI₃ Stabilized by Varying Concentrations of Poly(Methyl Methacrylate) (PMMA). Coatings 2017, 7, 115

by Celline Awino, Victor Odari, Thomas Dittrich, Pongthep Prajongtat, Thomas Sakwa and Bernd Rech

Coatings 2018, 8(12), 452; https://doi.org/10.3390/coatings8120452 - 07 Dec 2018

Cited by 1 | Viewed by 2442

Abstract

In the original version of article [1], the lists of authors and affiliations, and the Acknowledgements and Author Contributions were incomplete [...] Full article

10 pages, 10289 KiB

Open AccessArticle

Effects of Low-Temperature Tempering on Microstructure and Properties of the Laser-Cladded AISI 420 Martensitic Stainless Steel Coating

by Hongmei Zhu, Yongzuo Li, Baichun Li, Zhenyuan Zhang and Changjun Qiu

Coatings 2018, 8(12), 451; https://doi.org/10.3390/coatings8120451 - 07 Dec 2018

Cited by 20 | Viewed by 4078

Abstract

Post-treatment is crucial to improve the comprehensive performance of laser-cladded martensitic stainless steel coatings. In this work, a low-temperature tempering treatment (210 °C), for the first time, was performed on the laser-cladded AISI 420 martensitic stainless steel coating. The microstructure and properties of [...] Read more.

Post-treatment is crucial to improve the comprehensive performance of laser-cladded martensitic stainless steel coatings. In this work, a low-temperature tempering treatment (210 °C), for the first time, was performed on the laser-cladded AISI 420 martensitic stainless steel coating. The microstructure and properties of the pre- and post-tempering specimens were carefully investigated by XRD, SEM, TEM, a micro-hardness tester, a universal material testing machine and an electrochemical workstation. The results show that the as-cladded AISI 420 stainless steel coating mainly consisted of martensite, austenite, Fe₃C and M₂₃C₆ carbides. The phase constituent of the coating remained the same, however, the martensite decomposed into finer tempered martensite with the precipitation of numerous nano-sized Fe₃C carbides and reverted austenite in the as-tempered specimen. Moreover, a slight reduction was found in the micro-hardness and tensile strength, while a significant increase in elongation was achieved after tempering. The fractography showed a transition from brittle fracture to ductile fracture accordingly. The as-tempered coating exhibited a striking combination of mechanical properties and corrosion resistance. This work can provide a potential strategy to enhance the overall properties of the laser-deposited Fe-based coating for industrial applications. Full article

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8 pages, 1897 KiB

Open AccessArticle

Layer Formation from Polymer Carbon-Black Dispersions

by Fabian Scheepers, Andrea Stähler, Markus Stähler, Marcelo Carmo, Werner Lehnert and Detlef Stolten

Coatings 2018, 8(12), 450; https://doi.org/10.3390/coatings8120450 - 07 Dec 2018

Cited by 12 | Viewed by 4004

Abstract

It has been well-established that effects such as cracking are observable when wet layers are dried. In particular, the layer thickness, as well as the surface tension of the liquid, is responsible for this behavior. The layer formation of polymer electrolyte fuel cells [...] Read more.

It has been well-established that effects such as cracking are observable when wet layers are dried. In particular, the layer thickness, as well as the surface tension of the liquid, is responsible for this behavior. The layer formation of polymer electrolyte fuel cells and electrolyzer electrodes, however, has not yet been analyzed in relation to these issues, even though the effect of cracks on cell performance and durability has been frequently discussed. In this paper, water propanol polymer-containing carbon-black dispersions are analyzed in situ with regard to their composition during drying. We demonstrate that crack behavior can be steered by slight variations in the initial dispersion when the solvent mixture is near the dynamic azeotropic point. This minor adjustment may strongly affect the drying behavior, leading to either propanol or water-enriched liquid phases at the end of the drying process. If the evaporation of the solvent results in propanol enrichment, the critical layer thickness at which cracks occur will be increased by about 30% due to a decrease in the capillary pressure. Microscopic images indicate that the crack area ratio and width depend on the wet layer thickness and initial liquid phase composition. These results are of much value for future electrode fabrication, as cracks affect electrode properties. Full article

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9 pages, 2609 KiB

Open AccessFeature PaperCommunication

Strain-Mediated Substrate Effect on the Dielectric and Ferroelectric Response of Potassium Sodium Niobate Thin Films

by Alexander Tkach, André Santos, Sebastian Zlotnik, Ricardo Serrazina, Olena Okhay, Igor Bdikin, Maria Elisabete Costa and Paula M. Vilarinho

Coatings 2018, 8(12), 449; https://doi.org/10.3390/coatings8120449 - 06 Dec 2018

Cited by 11 | Viewed by 3936

Abstract

If piezoelectric thin films sensors based on K_0.5Na_0.5NbO₃ (KNN) are to achieve commercialization, it is critical to optimize the film performance using low-cost scalable processing and substrates. Here, sol–gel derived KNN thin films are deposited using a solution [...] Read more.

If piezoelectric thin films sensors based on K_0.5Na_0.5NbO₃ (KNN) are to achieve commercialization, it is critical to optimize the film performance using low-cost scalable processing and substrates. Here, sol–gel derived KNN thin films are deposited using a solution with 5% of potassium excess on Pt/TiO₂/SiO₂/Si and Pt/SrTiO₃ substrates, and rapid thermal annealed at 750 °C for 5 min. Despite an identical film morphology and thickness of ~335 nm, an in-plane stress/strain state is found to be tensile for KNN films on Pt/TiO₂/SiO₂/Si, and compressive for those on Pt/SrTiO₃ substrates, being related to thermal expansion mismatch between the substrate and the film. Correspondingly, KNN films under in-plane compressive stress possess superior dielectric permittivity and polarization in the parallel-plate-capacitor geometry. Full article

(This article belongs to the Special Issue Piezoresistive and Piezoelectric Thin Films for Sensors)

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14 pages, 5083 KiB

Open AccessArticle

Self-Stratification of Ternary Systems Including a Flame Retardant Liquid Additive

by Agnes Beaugendre, Stephanie Degoutin, Severine Bellayer, Christel Pierlot, Sophie Duquesne, Mathilde Casetta and Maude Jimenez

Coatings 2018, 8(12), 448; https://doi.org/10.3390/coatings8120448 - 06 Dec 2018

Cited by 9 | Viewed by 4131

Abstract

Particular coating compositions based on incompatible polymer blends can produce coatings having complex layered structures after film formation. The most traditional approaches to their structural modification are the introduction of additives (extenders, inorganic pigments, surface active agents, etc.). As minor additives, some are [...] Read more.

Particular coating compositions based on incompatible polymer blends can produce coatings having complex layered structures after film formation. The most traditional approaches to their structural modification are the introduction of additives (extenders, inorganic pigments, surface active agents, etc.). As minor additives, some are capable of substantially accelerating the phase separation process with a moderate or negligible influence on the composition equilibrium of solutions. In contrast, in order to be effective, some have to be introduced in significant amounts, thereby substantially changing the resulting distribution of components through the film. Up to now, most of the liquid additives that have been tested destabilized the solutions while impacting the layering process. In this work, two phosphorus based liquid fillers have been introduced (at 2.5 and 5 wt.%) in a partially incompatible polymer blend based on a silicone resin and a curable epoxy resin to fire retard a polycarbonate matrix. Self-stratification was evidenced by microscopic and chemical analyses, flammability by Limiting Oxygen Index (LOI) and UL-94 tests, fire performances by Mass Loss Calorimetry and thermal stability by using a tubular furnace and ThermoGravimetric Analysis. The ternary compositions including 5 wt.% of additives exhibit the best stratification and excellent adhesion onto polycarbonate. Improvements of the fire resistant properties were observed (+7% for the LOI compared to the virgin matrix) when a 200 µm wet thick coating was applied, due to reduced flame propagation and dripping. Full article

(This article belongs to the Special Issue Advances in Organic and Polymeric Coatings )

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14 pages, 8501 KiB

Open AccessArticle

Investigation into Performance of Multilayer Composite Nano-Structured Cr-CrN-(Cr_0.35Ti_0.40Al_0.25)N Coating for Metal Cutting Tools

by Sergey Grigoriev, Alexey Vereschaka, Alexander Metel, Nikolay Sitnikov, Filipp Milovich, Nikolay Andreev, Svetlana Shevchenko and Yulia Rozhkova

Coatings 2018, 8(12), 447; https://doi.org/10.3390/coatings8120447 - 06 Dec 2018

Cited by 4 | Viewed by 3078

Abstract

This paper deals with the Cr-CrN-(Cr_0.35Ti_0.40Al_0.25)N coating. It has a three-layered architecture with a nano-structured wear-resistant layer. The studies involved the investigation into the microstructure (with the use of SEM and TEM), elemental and phase composition (XRD [...] Read more.

This paper deals with the Cr-CrN-(Cr_0.35Ti_0.40Al_0.25)N coating. It has a three-layered architecture with a nano-structured wear-resistant layer. The studies involved the investigation into the microstructure (with the use of SEM and TEM), elemental and phase composition (XRD and SAED patterns), wear process pattern in scratch testing, crystal structure, as well as the microhardness of the coating. Cutting tests of tools with the above coating were carried out in dry turning of steel 1045 at cutting speeds of v_c = 200, 250, and 300 m·min⁻¹. The comparison included uncoated tools and tools with the commercial TiN and (Ti,Al)N coatings with the same thickness. The tool with the Cr-CrN-(Cr_0.35Ti_0.40Al_0.25)N coating showed the longest tool life at all the cutting speeds under consideration. Meanwhile, a tool with the coating under study can be recommended for use in turning constructional steel at the cutting speed of v_c = 250 m·min⁻¹. At this cutting speed, a tool shows the combination of a rather long tool life and balanced wear process, without any threat of catastrophic wear. Full article

(This article belongs to the Special Issue Coatings for Cutting Tools)

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13 pages, 3787 KiB

Open AccessArticle

POSS-Containing Polymethacrylates on Cellulose-Based Substrates: Immobilization and Ceramic Formation

by Christian Rüttiger, Steffen Vowinkel, Nicole Herzog, Kathrin Hofmann, Emanuel Ionescu and Markus Gallei

Coatings 2018, 8(12), 446; https://doi.org/10.3390/coatings8120446 - 06 Dec 2018

Cited by 1 | Viewed by 3594

Abstract

The combination of cellulose-based materials and functional polymers is a promising approach for the preparation of porous, biotemplated ceramic materials. Within this study, cellulose substrates were functionalized with a surface-attached initiator followed by polymerization of (3‑methacryloxypropyl)heptaisobutyl-T8-silsesquioxane (MAPOSS) by means of surface-initiated atom transfer [...] Read more.

The combination of cellulose-based materials and functional polymers is a promising approach for the preparation of porous, biotemplated ceramic materials. Within this study, cellulose substrates were functionalized with a surface-attached initiator followed by polymerization of (3‑methacryloxypropyl)heptaisobutyl-T8-silsesquioxane (MAPOSS) by means of surface-initiated atom transfer radical polymerization (ATRP). Successful functionalization was proven by infrared (IR) spectroscopy as well as by contact angle (CA) measurements. Thermal analysis of the polymer-modified cellulose substrates in different atmospheres (nitrogen and air) up to 600 °C led to porous carbon materials featuring the pristine fibre-like structure of the cellulose material as shown by scanning electron microscopy (SEM). Interestingly, spherical, silicon-containing domains were present at the surface of the cellulose-templated carbon fibres after further ceramisation at 1600 °C, as investigated by energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD) measurements. Full article

(This article belongs to the Special Issue Surface Modification of Cellulose Fibres)

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12 pages, 1376 KiB

Open AccessArticle

Chitosan-Based Coating Enriched with Hairy Fig (Ficus hirta Vahl.) Fruit Extract for “Newhall” Navel Orange Preservation

by Chuying Chen, Nan Cai, Jinyin Chen, Xuan Peng and Chunpeng Wan

Coatings 2018, 8(12), 445; https://doi.org/10.3390/coatings8120445 - 04 Dec 2018

Cited by 27 | Viewed by 4246

Abstract

A novel coating based on 1.5% chitosan (CH), enriched with or without hairy fig (Ficus hirta Vahl.) fruit extract (HFE), was applied to “Newhall” navel orange for improving the preservation effect. Changes in physicochemical indexes were analyzed over 120 days of cold [...] Read more.

A novel coating based on 1.5% chitosan (CH), enriched with or without hairy fig (Ficus hirta Vahl.) fruit extract (HFE), was applied to “Newhall” navel orange for improving the preservation effect. Changes in physicochemical indexes were analyzed over 120 days of cold storage. Uncoated fruit were used as the control. The CH-HFE coating, based on 1.5% CH enriched with HFE, exhibited the best preservation effect and showed the lowest decay rate (5.2%) and weight loss (5.16%). The CH-HFE coating could postpone the ripening and senescence of navel oranges, and maintain higher fruit quality by inhibiting respiration, decreasing the accumulation of malondialdehyde (MDA), and enhancing the activities of protective enzyme, including superoxide dismutase (SOD), peroxidase (POD), chitinase (CHI), and β-1,3-glucanase (GLU), which suggests that CH-HFE coating has the potential to improve the postharvest quality of “Newhall” navel orange and prolong the storage life. Full article

(This article belongs to the Special Issue Functional Coatings for Food Packaging Applications)

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21 pages, 10106 KiB

Open AccessReview

Lead Selenide Polycrystalline Coatings Sensitized Using Diffusion and Ion Beam Methods for Uncooled Mid-Infrared Photodetection

by Hao Yang, Xiaojiang Li, Guodong Wang and Jianbang Zheng

Coatings 2018, 8(12), 444; https://doi.org/10.3390/coatings8120444 - 04 Dec 2018

Cited by 23 | Viewed by 4855

Abstract

Polycrystalline lead selenide material that is processed after a sensitization technology offers the additional physical effects of carrier recombination suppression and carrier transport manipulation, making it sufficiently sensitive to mid-infrared radiation at room temperature. Low-cost and large-scale integration with existing electronic platforms such [...] Read more.

Polycrystalline lead selenide material that is processed after a sensitization technology offers the additional physical effects of carrier recombination suppression and carrier transport manipulation, making it sufficiently sensitive to mid-infrared radiation at room temperature. Low-cost and large-scale integration with existing electronic platforms such as complementary metal–oxide–semiconductor (CMOS) technology and multi-pixel readout electronics enable a photodetector based on polycrystalline lead selenide coating to work in high-speed, low-cost, and low-power consumption applications. It also shows huge potential to compound with other materials or structures, such as the metasurface for novel optoelectronic devices and more marvelous properties. Here, we provide an overview and evaluation of the preparations, physical effects, properties, and potential applications, as well as the optoelectronic enhancement mechanism, of lead selenide polycrystalline coatings. Full article

(This article belongs to the Special Issue Polycrystalline Coatings)

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22 pages, 4892 KiB

Open AccessArticle

Improving Corrosion and Corrosion-Fatigue Resistance of AZ31B Cast Mg Alloy Using Combined Cold Spray and Top Coatings

by Sugrib Kumar Shaha, Siavash Borhan Dayani, Yuna Xue, Xin Pang and Hamid Jahed

Coatings 2018, 8(12), 443; https://doi.org/10.3390/coatings8120443 - 04 Dec 2018

Cited by 21 | Viewed by 4664

Abstract

In this paper, we report the application of zinc phosphate electrostatic-painting top coating on cold sprayed AA7075 leading to a significant improvement in corrosion-fatigue performance. High strength AA7075 powder was sprayed on AZ31B substrate, followed by the application of the top coating. The [...] Read more.

In this paper, we report the application of zinc phosphate electrostatic-painting top coating on cold sprayed AA7075 leading to a significant improvement in corrosion-fatigue performance. High strength AA7075 powder was sprayed on AZ31B substrate, followed by the application of the top coating. The electrochemical corrosion and corrosion-fatigue tests of the coated and uncoated specimens were performed in 3.5% NaCl solution. Transmission electron microscopy (TEM) analysis showed that a continuous nanolayered mixture of Mg/Al was formed at the cold spray coating/substrate interface leading to high bonding strength. The results showed that the combined coatings improved the corrosion resistance remarkably, and significantly increased the fatigue life, with a fatigue strength of 80 MPa at 10⁷ cycles, as compared to the as-cast specimen. Surface topographic analysis of the corrosion-fatigue-tested specimens demonstrated the presence of deep macro-pits on the cold sprayed AA7075 coating after 3.7 million cycles, while there were no such pits on the top-coated specimens, even after 10⁷ cycles when tested at 30 Hz. The fractographic analysis of the fatigue-fractured specimens showed that the formation of pits allowed the NaCl solution to penetrate in the AZ31B substrate, creating localized corrosion pits resulting in premature failure, which eventually reduced the fatigue life. Full article

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Coatings, Volume 8, Issue 12 (December 2018) – 58 articles

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