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Coatings, Volume 8, Issue 9 (September 2018)

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Cover Story (view full-size image) The use of AP plasma jet systems might be a suitable approach to produce photo catalysts, thereby [...] Read more.
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Open AccessFeature PaperArticle Photoactivated Self-Sanitizing Chlorophyllin-Containing Coatings to Prevent Microbial Contamination in Packaged Food
Coatings 2018, 8(9), 328; https://doi.org/10.3390/coatings8090328
Received: 27 August 2018 / Revised: 12 September 2018 / Accepted: 19 September 2018 / Published: 19 September 2018
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Abstract
Chlorophyllins are semi-synthetic porphyrins obtained from chlorophyll that—when exposed to visible light—generate radical oxygen substances with antimicrobial activity. In this work, chlorophyllins incorporated with polyethylene (PE), polyvinyl alcohol (PVOH), (hydroxypropyl)methyl cellulose (HPMC), and gelatin (G) were formulated for application as coatings in packages
[...] Read more.
Chlorophyllins are semi-synthetic porphyrins obtained from chlorophyll that—when exposed to visible light—generate radical oxygen substances with antimicrobial activity. In this work, chlorophyllins incorporated with polyethylene (PE), polyvinyl alcohol (PVOH), (hydroxypropyl)methyl cellulose (HPMC), and gelatin (G) were formulated for application as coatings in packages providing antimicrobial activity after photoactivation. First, the antimicrobial properties of two porphyrins (sodium magnesium chlorophyllin, E-140, and sodium copper chlorophyllin, E-141) were analyzed against L. monocytogenes and Escherichia coli. The results indicated that E-140 was more active than E-141 and that chlorophyllins were more effective against Gram-positive bacteria. In addition, both chlorophyllins were more efficient when irradiated with halogen lamps than with LEDs, and they were inactive in dark conditions. Then, coatings on polyethylene terephthalate (PET) film were prepared, and their effect against the test bacteria was similar to that shown previously with pure chlorophyllins, i.e., greater activity in films containing E-140. Among the coating matrices, those based on PE presented the least effect (1 log reduction), whereas PVOH, HPMC, and G were lethal (7 log reduction). The self-sanitizing effect of these coatings was also analyzed by contaminating the surface of the coatings and irradiating them through the PET surface, which showed high efficiency, although the activity of the coatings was limited to L. monocytogenes. Finally, coated films were applied as separators of bologna slices. After irradiation, all the films showed count reductions of L. monocytogenes and the usual microbial load; the gelatin coating was the most effective, with an average of 3 log reduction. Full article
(This article belongs to the Special Issue Recent Progress in Food and Beverage Packaging Coatings)
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Open AccessArticle Influence of Particle Velocity When Propelled Using N2 or N2-He Mixed Gas on the Properties of Cold-Sprayed Ti6Al4V Coatings
Coatings 2018, 8(9), 327; https://doi.org/10.3390/coatings8090327
Received: 12 July 2018 / Revised: 30 August 2018 / Accepted: 7 September 2018 / Published: 18 September 2018
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Abstract
Cold-spraying is a relatively new low-temperature coating technology which produces coatings by the deposition of metallic micro-particles at supersonic speed onto target substrate surfaces. This technology has the potential to enhance or restore damaged parts made of light metal alloys, such as Ti6Al4V
[...] Read more.
Cold-spraying is a relatively new low-temperature coating technology which produces coatings by the deposition of metallic micro-particles at supersonic speed onto target substrate surfaces. This technology has the potential to enhance or restore damaged parts made of light metal alloys, such as Ti6Al4V (Ti64). Particle deposition velocity is one of the most crucial parameters for achieving high-quality coatings because it is the main driving force for particle bonding and coating formation. In this work, studies were conducted on the evolution of the properties of cold-sprayed Ti64 coatings deposited on Ti64 substrates with particle velocities ranging from 730 to 855 m/s using pure N2 and N2-He mixture as the propellant gases. It was observed that the increase in particle velocity significantly reduced the porosity level from about 11 to 1.6% due to greater densification. The coatings’ hardness was also improved with increased particle velocity due to the intensified grain refinement within the particles. Interestingly, despite the significant differences in the coating porosities, all the coatings deposited within the velocity range (below and above critical velocity) achieved a high adhesion strength exceeding 60 MPa. The fractography also showed changes in the degree of dimple fractures on the particles across the deposition velocities. Finite element modelling was carried out to understand the deformation behaviour of the impacting particles and the evolutions of strain and temperature in the formed coatings during the spraying process. This work also showed that the N2-He gas mixture was a cost-effective propellant gas (up to 3-times cheaper than pure He) to deliver the high-quality Ti64 coatings. Full article
(This article belongs to the Special Issue From Metallic Coatings to Additive Manufacturing)
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Open AccessArticle Porosity Characterization of Cold Sprayed Stainless Steel Coating Using Three-Dimensional X-ray Microtomography
Coatings 2018, 8(9), 326; https://doi.org/10.3390/coatings8090326
Received: 24 July 2018 / Revised: 27 August 2018 / Accepted: 15 September 2018 / Published: 17 September 2018
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Abstract
Cold gas-dynamic spray (cold spray) is an evolving coating deposition and restoration technology in which particles are deposited above the sonic speed. This paper presents the non-destructive three-dimensional characterization of cold sprayed stainless steel coating. The visualization of coating morphology and volumetric porosity
[...] Read more.
Cold gas-dynamic spray (cold spray) is an evolving coating deposition and restoration technology in which particles are deposited above the sonic speed. This paper presents the non-destructive three-dimensional characterization of cold sprayed stainless steel coating. The visualization of coating morphology and volumetric porosity and the analyses of porosity size and spatial distributions confirmed that dense stainless steel coating with non-connected, micron-sized gradient porosity can be successfully produced by cold spray. The suitability of X-ray tomography for characterizing cold sprayed coatings was also assessed. Full article
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Open AccessReview Simulation and Optimization of Film Thickness Uniformity in Physical Vapor Deposition
Coatings 2018, 8(9), 325; https://doi.org/10.3390/coatings8090325
Received: 8 July 2018 / Revised: 30 July 2018 / Accepted: 12 September 2018 / Published: 16 September 2018
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Abstract
Optimization of thin film uniformity is an important aspect for large-area coatings, particularly for optical coatings where error tolerances can be of the order of nanometers. Physical vapor deposition is a widely used technique for producing thin films. Applications include anti-reflection coatings, photovoltaics
[...] Read more.
Optimization of thin film uniformity is an important aspect for large-area coatings, particularly for optical coatings where error tolerances can be of the order of nanometers. Physical vapor deposition is a widely used technique for producing thin films. Applications include anti-reflection coatings, photovoltaics etc. This paper reviews the methods and simulations used for improving thin film uniformity in physical vapor deposition (both evaporation and sputtering), covering characteristic aspects of emission from material sources, projection/mask effects on film thickness distribution, as well as geometric and rotational influences from apparatus configurations. Following the review, a new program for modelling and simulating thin film uniformity for physical vapor deposition was developed using MathCAD. Results from the program were then compared with both known theoretical analytical equations of thickness distribution and experimental data, and found to be in good agreement. A mask for optimizing thin film thickness distribution designed using the program was shown to improve thickness uniformity from ±4% to ±0.56%. Full article
(This article belongs to the Special Issue Applications of Optical Thin Film Coatings)
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Open AccessArticle Torsional Fretting Wear Properties of Thermal Oxidation-Treated Ti3SiC2 Coatings
Coatings 2018, 8(9), 324; https://doi.org/10.3390/coatings8090324
Received: 1 July 2018 / Revised: 4 September 2018 / Accepted: 12 September 2018 / Published: 14 September 2018
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Abstract
In this study, efforts were made to oxidize the Ti3SiC2 coating surface to improve its wear resistance by producing oxide layers and healing microcracks that initiated from the thermal sprayed process. Tribological behaviors of the thermal oxidation-treated Ti3SiC
[...] Read more.
In this study, efforts were made to oxidize the Ti3SiC2 coating surface to improve its wear resistance by producing oxide layers and healing microcracks that initiated from the thermal sprayed process. Tribological behaviors of the thermal oxidation-treated Ti3SiC2 coatings subjected to various temperatures (200, 300, and 400 °C) and durations (1, 3, and 5 h) were investigated comparatively by fretting wear. The results showed that the thickness of the oxide layer and the average content of element O on the surface were gradually increased with increasing temperature. Lower friction coefficients were observed in coatings at 200–400 °C for 1 h. Better performance of crack-healing features was demonstrated at 400 °C, whereas fresh microcracks were formed under the fretting condition due to the fragility of oxides at the same time. The tribological behavior of thermal oxidation-treated Ti3SiC2 coatings was mainly controlled by delamination and abrasive wear. The volume losses induced by wear scars decreased with the increase in oxidation time under the oxidation treatment at 200 °C and increased with increasing oxidation time under the oxidation temperatures of 300 and 400 °C. Full article
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Open AccessArticle Online Characterization Algorithms for Optical Coating Production with Broadband Monitoring
Coatings 2018, 8(9), 323; https://doi.org/10.3390/coatings8090323
Received: 28 July 2018 / Revised: 6 September 2018 / Accepted: 13 September 2018 / Published: 14 September 2018
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Abstract
Algorithms for the online determination of thicknesses of already-deposited layers are important for the reliable control of optical coating production. Possible ways of constructing such algorithms in the case of coating production with direct broadband monitoring are discussed. A modified triangular algorithm is
[...] Read more.
Algorithms for the online determination of thicknesses of already-deposited layers are important for the reliable control of optical coating production. Possible ways of constructing such algorithms in the case of coating production with direct broadband monitoring are discussed. A modified triangular algorithm is proposed. In contrast to the well-known triangular algorithm, the new algorithm does not determine all thicknesses of previously deposited layers but only those for which an increase in the accuracy of their determination is to be expected. The most promising algorithms are compared in terms of their accuracy and operational speed. It is shown that the modified triangular algorithm is much faster than the triangular algorithm, and both algorithms have close accuracy. The operational speed of the modified triangular algorithm can be a decisive factor for its use in modern broadband monitoring systems. Full article
(This article belongs to the Special Issue Applications of Optical Thin Film Coatings)
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Open AccessArticle Improvement of Corrosion Resistance of Hastelloy-N Alloy in LiF-NaF-KF Molten Salt by Laser Cladding Pure Metallic Coatings
Coatings 2018, 8(9), 322; https://doi.org/10.3390/coatings8090322
Received: 9 August 2018 / Revised: 6 September 2018 / Accepted: 12 September 2018 / Published: 14 September 2018
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Abstract
The corrosion protection of Hastelloy-N alloy in LiF-NaF-KF (commonly referred to as FLiNaK) molten salt has been developed by pure Ni and Co coatings using the laser cladding technique. An immersion experiment with samples was performed in molten FLiNaK salt at 900 °C
[...] Read more.
The corrosion protection of Hastelloy-N alloy in LiF-NaF-KF (commonly referred to as FLiNaK) molten salt has been developed by pure Ni and Co coatings using the laser cladding technique. An immersion experiment with samples was performed in molten FLiNaK salt at 900 °C for 100 h. It was found that the corrosion rates of the pure Ni-coated specimen and the pure Co-coated specimen are 39.9% and 35.7% of that of Hastelloy-N alloy, respectively. A careful microstructural characterization indicates that a selective dissolution of the elemental Cr occurred in the surface of bare Hastelloy-N alloy, showing a severe intergranular corrosion. For pure metal-coated specimens, in contrast, only metal oxide formed during the laser cladding process dissolved into the molten fluoride salt. The dense pure metal (Ni or Co) coatings exhibit a slightly general corrosion and protect the Hastelloy-N substrate effectively. The possible corrosion mechanism for both coated and uncoated Hastelloy-N under the current experimental condition are discussed in this work. Full article
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Open AccessArticle On the Effect of Thin Film Growth Mechanisms on the Specular Reflectance of Aluminium Thin Films Deposited via Filtered Cathodic Vacuum Arc
Coatings 2018, 8(9), 321; https://doi.org/10.3390/coatings8090321
Received: 31 July 2018 / Revised: 10 September 2018 / Accepted: 12 September 2018 / Published: 13 September 2018
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Abstract
The optimisation of the specular reflectance of solar collectors is a key parameter to increase the global yield of concentrated solar power (CSP) plants. In this work, the influence of filtered cathodic vacuum arc deposition parameters, particularly working pressure and deposition time, on
[...] Read more.
The optimisation of the specular reflectance of solar collectors is a key parameter to increase the global yield of concentrated solar power (CSP) plants. In this work, the influence of filtered cathodic vacuum arc deposition parameters, particularly working pressure and deposition time, on the specular and diffuse reflectance of aluminium thin films, was studied. Changes in specular reflectance, measured by ultraviolet–visible and near-infrared spectroscopy (UV-vis-NIR) spectrophotometry, were directly correlated with thin film elemental concentration depth profiles, obtained by Rutherford backscattering spectrometry (RBS), and surface and cross-sectional morphologies as measured by scanning electron microscopy (SEM) and profilometry. Finally, atomic force microscopy (AFM) provided information on the roughness and growth mechanism of the films. The two contributions to the total reflectance of the films, namely diffuse and specular reflectance, were found to be deeply influenced by deposition conditions. It was proven that working pressure and deposition time directly determine the predominant factor. Specular reflectance varied from 12 to 99.8% of the total reflectance for films grown at the same working pressure of 0.1 Pa and with different deposition times. This transformation could not be attributed to an oxidation of the films as stated by RBS, but was correlated with a progressive modification of the roughness, surface, and bulk morphology of the samples over the deposition time. Hence, the evolution in the final optical properties of the films is driven by different growth mechanisms and the resulting microstructures. In addition to the originally addressed CSP applications the potential of the developed aluminium films for other application rather than CSP, such as, for example, reference material for spectroscopic diffuse reflectance measurements, is also discussed. Full article
(This article belongs to the Special Issue Surface Engineering and Nanofilms)
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Open AccessArticle Capturing the Competing Influence of Thermal and Mechanical Loads on the Strain of Turbine Blade Coatings via High Energy X-rays
Coatings 2018, 8(9), 320; https://doi.org/10.3390/coatings8090320
Received: 12 July 2018 / Revised: 22 August 2018 / Accepted: 30 August 2018 / Published: 10 September 2018
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Abstract
This paper presents findings of synchrotron diffraction measurements on tubular specimens with a thermal barrier coating (TBC) system applied by electron beam physical vapor deposition (EB-PVD), having a thermally grown oxide (TGO) layer due to aging in hot air. The diffraction measurements were
[...] Read more.
This paper presents findings of synchrotron diffraction measurements on tubular specimens with a thermal barrier coating (TBC) system applied by electron beam physical vapor deposition (EB-PVD), having a thermally grown oxide (TGO) layer due to aging in hot air. The diffraction measurements were in situ while applying a thermal cycle with high temperature holds at 1000 °C and varying internal air cooling mass flow and mechanical load. It was observed that, during high temperature holds at 1000 °C, the TGO strain approached zero if no mechanical load or internal cooling was applied. When applying a mechanical load, the TGO in-plane strain (e22) changed to tensile and the out of plane TGO strain (e11) became compressive. The addition of internal cooling induced a thermal gradient, yielding a competing effect, driving the e22 strain to compressive and e11 strain to tensile. Quantifying TGO strain variations in response to competing factors will provide a path to controlling the TGO strain, and further improving the lifetime assessment and durability design strategies for TBC systems. Full article
(This article belongs to the Special Issue Thermal Barrier Coatings)
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Open AccessReview Novel Attribute of Organic–Inorganic Hybrid Coatings for Protection and Preservation of Materials (Stone and Wood) Belonging to Cultural Heritage
Coatings 2018, 8(9), 319; https://doi.org/10.3390/coatings8090319
Received: 4 July 2018 / Revised: 5 September 2018 / Accepted: 6 September 2018 / Published: 10 September 2018
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Abstract
In order to protect a material belonging to Cultural Heritage (i.e., stone, wood) from weathering, and in turn to preserve its beauty and historical value for the future generations, the contact with external harmful agents, particularly water, must be avoided, or at least
[...] Read more.
In order to protect a material belonging to Cultural Heritage (i.e., stone, wood) from weathering, and in turn to preserve its beauty and historical value for the future generations, the contact with external harmful agents, particularly water, must be avoided, or at least limited. This task can be successfully obtained with the use of a protective organic coating. The use of nano-metric reinforcing agents in conventional polymeric coatings demonstrated to be a successful route in achieving better protective performance of the films and improved physical properties, even in extreme environments. The present paper would, therefore, review the more recent findings in this field. Generally speaking, when a hydrophobic product is applied on its surface, the stone material will absorb less water and consequently, less substances which may be harmful to it. An efficient organic coating should also supply wear and abrasion resistance, resistance to aggressive chemicals, excellent bond to the substrate; finally, it should be also able to guarantee vapor exchange between the environment and the material interior, i.e., the material should keep the same water vapor permeability as if it was un-protected. To regard to the conservation of wood artifacts, protective treatments for wood will preserve the material from environmental agents and biological attack. Hence, potential advantages of hybrid (organic–inorganic) nano-composite coatings for stone/wood have been found to be: Enhanced mechanical properties in comparison to the pure polymeric matrix, due to the reinforcing effect of the nano-filler; superior barrier properties (the presence of the nano-filler hinders the ingress of water and/or potentially harmful chemicals); optical clarity and transparency. It has been found that the efficacy of a nano-filled coating strongly depends on the effectiveness of the method used to uniformly disperse the nano-filler in the polymeric matrix. Furthermore, the presence of nano-particles should not impair the viscosity of the organic matrix, in order to employ the conventional techniques of application for coatings. Full article
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Open AccessArticle Effect of an Edible Coating Based on Chitosan and Oxidized Starch on Shelf Life of Carica papaya L., and Its Physicochemical and Antimicrobial Properties
Coatings 2018, 8(9), 318; https://doi.org/10.3390/coatings8090318
Received: 9 August 2018 / Revised: 31 August 2018 / Accepted: 6 September 2018 / Published: 7 September 2018
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Abstract
Papaya production plays an important economic role in Mexico’s economy. After harvest, it continues to ripen, leading to softening, skin color changes, development of strong aroma, and microbial spoilage. The objective of this work was to apply an active coating of chitosan–starch to
[...] Read more.
Papaya production plays an important economic role in Mexico’s economy. After harvest, it continues to ripen, leading to softening, skin color changes, development of strong aroma, and microbial spoilage. The objective of this work was to apply an active coating of chitosan–starch to increase papaya shelf life and to evaluate physicochemical and antimicrobial properties of the coating. Papaya surfaces were coated with a chitosan-oxidized starch (1:3 w/w) solution and stored at room temperature (25 ± 1 °C) for 15 days. Variables measured were color, titratable acidity, vitamin C, pH, soluble solids, volatile compounds by gas chromatography, texture, homogeneity by image analysis, and coating antimicrobial activity. At the end of the storage time, there were no significant differences (p > 0.05) between coated and uncoated papayas for pH (4.3 ± 0.2), titratable acidity (0.12% ± 0.01% citric acid), and soluble solids (12 ± 0.2 °Bx). Papaya firmness decreased to 10 N for coated and 0.5 N for uncoated papayas. Volatile compounds identified in uncoated papaya (acetic acid, butyric acid, ethyl acetate, ethyl butanoate) are related to fermentation. Total microbial population of coated papaya decreased after 15 days, whereas population of uncoated papaya increased. This active coating permitted longer shelf life of papaya than that of the uncoated fruit. Full article
(This article belongs to the Special Issue Recent Progress in Food and Beverage Packaging Coatings)
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Open AccessArticle Effects of Chitosan Coating Structure and Changes during Storage on Their Egg Preservation Performance
Coatings 2018, 8(9), 317; https://doi.org/10.3390/coatings8090317
Received: 8 August 2018 / Revised: 28 August 2018 / Accepted: 3 September 2018 / Published: 7 September 2018
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Abstract
To explore the influences of chitosan coating structure and structure changes during storage on egg preservation, eggs coated by chitosan solution for single time (CS1), two times (CS2), and three times (CS3) were prepared separately and stored with untreated eggs (CK1), eggs washed
[...] Read more.
To explore the influences of chitosan coating structure and structure changes during storage on egg preservation, eggs coated by chitosan solution for single time (CS1), two times (CS2), and three times (CS3) were prepared separately and stored with untreated eggs (CK1), eggs washed by water (CK2) and eggs treated by acetic acid solution (CK3) at 25 °C, 80% RH. The weight loss, Haugh unit, yolk index, albumen pH, eggshell morphologies and infrared (FTIR—Fourier Transform Infrared) spectra of all the samples were monitored. CS2 and CS3 presented the lowest weight loss, highest Haugh unit and yolk index, stabilized pH, and the highest thickness of chitosan coating layers (>2 μm) among all the groups, which extended egg shelf life for 20 days longer compared to CK1 and CK2. CS1 with very thin chitosan coating showed similar egg qualities with CK3, which are second only to CS2 and CS3. Furthermore, destructions were found on chitosan coatings during storage as revealed by the eggshell morphologies and FTIR spectra, which caused the quality deterioration of eggs. The results demonstrated that eggs with the thickest coating showed the best qualities during storage, while destructions on coating layers led to the quality drop of eggs. Full article
(This article belongs to the Special Issue Recent Progress in Food and Beverage Packaging Coatings)
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Open AccessRetraction Retraction: Gao, W., et al. Exploration of Growth Window for Phase-Pure Cubic Boron Nitride Films Prepared in a Pure N2 Plasma. Coatings 2018, 8, 82, doi:10.3390/coatings8020082
Coatings 2018, 8(9), 316; https://doi.org/10.3390/coatings8090316
Received: 4 September 2018 / Accepted: 5 September 2018 / Published: 7 September 2018
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The published article [1] has been retracted at the request of the corresponding author due to a dispute regarding the authorship of the paper[...] Full article
Open AccessArticle Corrosion Protection of N80 Steel in Hydrochloric Acid Medium Using Mixed C15H15NO and Na2WO4 Inhibitors
Coatings 2018, 8(9), 315; https://doi.org/10.3390/coatings8090315
Received: 10 July 2018 / Revised: 8 August 2018 / Accepted: 3 September 2018 / Published: 6 September 2018
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Abstract
A novel inhibitor based on mixed Mannich base (C15H15NO) and Na2WO4 was developed for the corrosion prevention of N80 steel in hydrochloric acid solution. Infra-red spectrum, electrochemical measurements, X-ray Photoelectron Spectroscopy, and Scanning Electron Microscopy were
[...] Read more.
A novel inhibitor based on mixed Mannich base (C15H15NO) and Na2WO4 was developed for the corrosion prevention of N80 steel in hydrochloric acid solution. Infra-red spectrum, electrochemical measurements, X-ray Photoelectron Spectroscopy, and Scanning Electron Microscopy were used to understand the inhibition efficiency and mechanism. The results showed that the mixed inhibitors reduced the corrosion current density and increased the interface resistance. The inhibition efficiency is the highest when the ratio of C15H15NO to Na2WO4 is 1:1 in the mixture. Observed from the surfaces, the number of pits and small cracks was reduced on the surface in the presence of the optimized inhibitors. The inhibition film can successfully hinder the chloride ions from reaching the bulk steel. Full article
(This article belongs to the Special Issue Advanced Coatings for Corrosion Protection in Extreme Environments)
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Open AccessArticle Facile Solution Spin-Coating SnO2 Thin Film Covering Cracks of TiO2 Hole Blocking Layer for Perovskite Solar Cells
Coatings 2018, 8(9), 314; https://doi.org/10.3390/coatings8090314
Received: 4 August 2018 / Revised: 28 August 2018 / Accepted: 3 September 2018 / Published: 6 September 2018
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The hole blocking layer plays an important role in suppressing recombination of holes and electrons between the perovskite layer and fluorine-doped tin oxide (FTO). Morphological defects, such as cracks, at the compact TiO2 hole blocking layer due to rough FTO surface seriously
[...] Read more.
The hole blocking layer plays an important role in suppressing recombination of holes and electrons between the perovskite layer and fluorine-doped tin oxide (FTO). Morphological defects, such as cracks, at the compact TiO2 hole blocking layer due to rough FTO surface seriously affect performance of perovskite solar cells (PSCs). Herein, we employ a simple spin-coating SnO2 thin film solution to cover cracks of TiO2 hole blocking layer for PSCs. The experiment results indicate that the TiO2/SnO2 complementary composite hole blocking layer could eliminate the serious electrical current leakage existing inside the device, extremely reducing interface defects and hysteresis. Furthermore, a high efficiency of 13.52% was achieved for the device, which is the highest efficiency ever recorded in PSCs with spongy carbon film deposited on a separated FTO-substrate as composite counter electrode under one sun illumination. Full article
(This article belongs to the Special Issue Advanced Thin Film Materials for Photovoltaic Applications)
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Open AccessArticle Microstructure and Corrosion Characterization of Cr Film on Carburized CSS-42L Aerospace Bearing Steel by Filtered Cathodic Vacuum Arc Deposition
Coatings 2018, 8(9), 313; https://doi.org/10.3390/coatings8090313
Received: 18 July 2018 / Revised: 11 August 2018 / Accepted: 3 September 2018 / Published: 6 September 2018
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Abstract
For present and future advanced aerospace bearing applications, it is significant and necessary to improve the corrosion resistance of carburized CSS-42L steel. In this study, Cr films of about 1 μm in thickness were fabricated onto carburized CSS-42L bearing steel using a filtered
[...] Read more.
For present and future advanced aerospace bearing applications, it is significant and necessary to improve the corrosion resistance of carburized CSS-42L steel. In this study, Cr films of about 1 μm in thickness were fabricated onto carburized CSS-42L bearing steel using a filtered cathodic vacuum arc deposition system. The corrosion behavior of carburized CSS-42L steel with Cr films was investigated. The Cr film was composed of nanocrystalline α–Cr. The electrochemical experimental results indicated that the current density had two orders of magnitude decrease and the corrosion potential evidently increased after Cr film deposition. The protective efficiency of this Cr film was as high as 99.7%. Nanocrystalline exhibits a higher corrosion resistance and enhances the modification effect of Cr film on carburized CSS-42L steel. Full article
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Open AccessFeature PaperArticle Atmospheric Pressure Plasma Coating of Bismuth Oxide Circular Droplets
Coatings 2018, 8(9), 312; https://doi.org/10.3390/coatings8090312
Received: 12 July 2018 / Revised: 15 August 2018 / Accepted: 29 August 2018 / Published: 4 September 2018
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Abstract
In this study, bismuth oxide powder (Bi2O3) was deposited by an atmospheric pressure plasma jet onto borosilicate glass. The layer produced through this method is to be used as a photo catalyst in later applications. The deposited coating was
[...] Read more.
In this study, bismuth oxide powder (Bi2O3) was deposited by an atmospheric pressure plasma jet onto borosilicate glass. The layer produced through this method is to be used as a photo catalyst in later applications. The deposited coating was analyzed by X-ray diffraction (XRD) to determine the crystal structure, and X-ray photoelectron spectroscopy (XPS) to analyze the chemical state. The results showed a change in crystal and chemical structure during the deposition process. The morphological properties of the layer were examined with scanning electron microscopy (SEM) and laser scanning microscopy (LSM). The band gap structure of the coating was investigated by UV-Vis spectroscopy. The layer produced by the plasma spraying process consisted of circular multi-phase bismuth oxide droplets (monoclinic Bi2O3 and tetragonal Bi2O2.33), showing a direct band gap of Eg = 2.72 eV, which allows their use as a photocatalyst. Full article
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Open AccessArticle The Temperature Distribution in Plasma-Sprayed Thermal-Barrier Coatings During Crack Propagation and Coalescence
Coatings 2018, 8(9), 311; https://doi.org/10.3390/coatings8090311
Received: 7 August 2018 / Revised: 25 August 2018 / Accepted: 3 September 2018 / Published: 4 September 2018
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A Finite-Element Model (FEM) for thermal-barrier coatings was employed to elaborate the temperature distribution on yttria-stabilized zirconia (YSZ) free surface during cracks coalescing, then the influence of sintering of YSZ induced by heat-transfer overlapping on energy release rate was quantificationally evaluated. A three-dimensional
[...] Read more.
A Finite-Element Model (FEM) for thermal-barrier coatings was employed to elaborate the temperature distribution on yttria-stabilized zirconia (YSZ) free surface during cracks coalescing, then the influence of sintering of YSZ induced by heat-transfer overlapping on energy release rate was quantificationally evaluated. A three-dimensional model including three layers was fabricated. Two types of cracks, with and without depth variations in YSZ coating, were introduced into the model, respectively. The temperature rise of YSZ coating over the crack is independent of each other at the beginning of crack propagation. As crack distance shortens, the independent temperature-rise regions begin to overlap, while maximum temperature is still located at the crack center before crack coalescence. The critical distance that the regions of temperature rise, just overlapping, is the sum of half lengths of two coalescing cracks (i.e., a1 + a2), which is independent of cracking path. The maximum temperature in YSZ sharply increases once cracks coalesce. Compared with one delamination crack, the effective energy-release rate induced by heat-transfer overlapping increases in the range of 0.2%–15%, depending on crack length and crack distance, which is on some level comparable to that of deterioration of thermal expansion misfit induced by temperature jump between crack faces. Full article
(This article belongs to the Special Issue From Metallic Coatings to Additive Manufacturing)
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Open AccessCommunication Determination of Nonconductive Coating Thickness Using Electrical Contact Conductance and Surface Profile
Coatings 2018, 8(9), 310; https://doi.org/10.3390/coatings8090310
Received: 2 August 2018 / Revised: 19 August 2018 / Accepted: 3 September 2018 / Published: 4 September 2018
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Abstract
This paper describes a method to determine the thickness of a nonconductive coating by identifying the transition of material by a change in electrical properties. A slide-hold-slide test was conducted with a worn specimen including an electrodeposited coating layer. Relative displacement was imposed
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This paper describes a method to determine the thickness of a nonconductive coating by identifying the transition of material by a change in electrical properties. A slide-hold-slide test was conducted with a worn specimen including an electrodeposited coating layer. Relative displacement was imposed between a metallic stylus tip and a worn steel specimen. After an initial sliding, the tip was held for a certain time to measure electrical contact resistance. During the test, the vertical displacement of the stylus tip was also recorded to draw a surface profile of the worn specimen. Coating thickness on the specimen was determined with a surface profile at the transition of electrical contact conductance. Optical cross-section measurement of the specimen was applied to identify actual coating thickness. Measured results reveal that calculated coating thicknesses are in good agreement with measured values by an optical microscope. The proposed method allows determination of both nonconductive coating thickness and surface profile in a single measurement. Full article
(This article belongs to the Special Issue Advanced Coatings for Resisting Fretting Damage)
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Open AccessArticle Effect of Particle In-Flight Behavior on the Microstructure and Fracture Toughness of YSZ TBCs Prepared by Plasma Spraying
Coatings 2018, 8(9), 309; https://doi.org/10.3390/coatings8090309
Received: 29 July 2018 / Revised: 20 August 2018 / Accepted: 30 August 2018 / Published: 4 September 2018
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Abstract
The present study aims to elaborate particle in-flight behavior during plasma spraying and its significance in determining the microstructure and mechanical properties of plasma sprayed yttria partially stabilized zirconia (YSZ) thermal barrier coatings (TBCs). The as-sprayed YSZ coatings were characterized in terms of
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The present study aims to elaborate particle in-flight behavior during plasma spraying and its significance in determining the microstructure and mechanical properties of plasma sprayed yttria partially stabilized zirconia (YSZ) thermal barrier coatings (TBCs). The as-sprayed YSZ coatings were characterized in terms of defects (such as pores, unmelted particles and cracks) and fracture toughness. The results showed that, due to the higher temperature and velocity of in-flight particles in a supersonic atmospheric plasma spraying (SAPS) compared to that of atmospheric plasma spraying (APS), denser coatings were formed leading to a better fracture toughness. The percentage of defects of the microstructure was similar to the temperature and velocity of particles in-flight during plasma spraying. Furthermore, the structural defects had a strong effect on its mechanical behavior. The total defect percentage and fracture toughness in SAPS-TBCs spanned 6.9 ± 0.17%–13.26 ± 0.22% and 2.52 ± 0.06 MPa m1/2–1.78 ± 0.19 MPa m1/2; and 11.11 ± 0.36%–17.15 ± 0.67% and 2.13 ± 0.08 MPa m1/2–1.4 ± 0.12 MPa m1/2 in APS-TBCs. Full article
(This article belongs to the Special Issue Advanced Ceramic Coatings and Interfaces)
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Open AccessArticle Preparation and Spectrum Characterization of a High Quality Linear Variable Filter
Coatings 2018, 8(9), 308; https://doi.org/10.3390/coatings8090308
Received: 4 July 2018 / Revised: 21 August 2018 / Accepted: 24 August 2018 / Published: 31 August 2018
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Abstract
To meet the requirements for lightweight, miniaturized dispersive optical systems for space applications, linear variable filters with a high transmittance and spatial dispersion coefficient are proposed. The filters were produced with dual ion beam sputtering, where a single layer thickness variation was achieved
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To meet the requirements for lightweight, miniaturized dispersive optical systems for space applications, linear variable filters with a high transmittance and spatial dispersion coefficient are proposed. The filters were produced with dual ion beam sputtering, where a single layer thickness variation was achieved with a deposition rate adjustment based on a linear variable correction formula. A linear variable trend matching method was used to correct the film thickness based on the reduction of the mismatch error between two materials: Ta2O5 and SiO2. The influence of the spectral and spatial measuring average effects was addressed by sampling the spot size optimization. This paper presents an all-dielectric linear variable filter that operates between 520 and 1000 nm, with an excellent linear dependence of 40 nm/mm over 12 mm. The linear variable filter possessed a 2.5% bandwidth, and its transmittance was found to be >80% at the central wavelength of the band, with a 0.1% transmittance in the cut-off region. These results indicate great potential for optical devices for space applications, and the developed process has good reproducibility and stability. Full article
(This article belongs to the Special Issue Applications of Optical Thin Film Coatings)
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Open AccessArticle Microstructure and Cavitation Erosion Resistance of HVOF Deposited WC-Co Coatings with Different Sized WC
Coatings 2018, 8(9), 307; https://doi.org/10.3390/coatings8090307
Received: 25 July 2018 / Revised: 15 August 2018 / Accepted: 24 August 2018 / Published: 29 August 2018
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Abstract
Conventional, multimodal and nanostructured WC-12Co coatings with different WC sizes and distributions were prepared by high velocity oxy-fuel spray (HVOF). The micrographs and structures of the coatings were analyzed by scanning electron microscope (SEM), X-ray diffractometer (XRD) et al. The porosity, microhardness and
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Conventional, multimodal and nanostructured WC-12Co coatings with different WC sizes and distributions were prepared by high velocity oxy-fuel spray (HVOF). The micrographs and structures of the coatings were analyzed by scanning electron microscope (SEM), X-ray diffractometer (XRD) et al. The porosity, microhardness and fracture toughness of the WC-Co coatings were measured. The coating resistance to cavitation erosion (CE) was investigated by ultrasonic vibration cavitation equipment and the cavitation mechanisms were explored. Results show that there is serious WC decarburization in nanostructured and multimodal WC-Co coatings with the formation of W2C and W phases. The nanostructured WC-Co coating has the densest microstructure with lowest porosity compared to the other two WC-Co coatings, as well as the highest fracture toughness among the three coatings. It was also discovered that the nanostructured WC-Co coating exhibits the best CE resistance and that the CE rate is approximately one-third in comparison with conventional coating. Full article
(This article belongs to the Special Issue Tribology and Surface Engineering)
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Open AccessArticle Influence of SiO2 Particles on the Corrosion and Wear Resistance of Plasma Electrolytic Oxidation-Coated AM50 Mg Alloy
Coatings 2018, 8(9), 306; https://doi.org/10.3390/coatings8090306
Received: 10 July 2018 / Revised: 31 July 2018 / Accepted: 20 August 2018 / Published: 29 August 2018
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Abstract
The influence of SiO2 particles on the microstructure, phase composition, corrosion and wear performance of plasma electrolytic oxidation (PEO) coatings on AM50 Mg was investigated. Different treatment durations were applied to fabricate coatings in an alkaline, phosphate-based electrolyte (1 g/L KOH +
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The influence of SiO2 particles on the microstructure, phase composition, corrosion and wear performance of plasma electrolytic oxidation (PEO) coatings on AM50 Mg was investigated. Different treatment durations were applied to fabricate coatings in an alkaline, phosphate-based electrolyte (1 g/L KOH + 20 g/L Na3PO4 + 5 g/L SiO2), aiming to control the incorporated amount of SiO2 particles in the layer. It was found that the uptake of particles was accompanied by the coating growth at the initial stage, while the particle content remained unchanged at the final stage, which is dissimilar to the evolution of the coating thickness. The incorporation mode of the particles and phase composition of the layer was not affected by the treatment duration under the voltage-control regime. The corrosion performance of the coating mainly depends on the barrier property of the inner layer, while wear resistance primarily relies on the coating thickness. Full article
(This article belongs to the Special Issue Plasma Electrolytic Oxidation (PEO) Coatings)
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Open AccessArticle Preparation and Properties of Ginger Essential Oil β-Cyclodextrin/Chitosan Inclusion Complexes
Coatings 2018, 8(9), 305; https://doi.org/10.3390/coatings8090305
Received: 16 July 2018 / Revised: 23 August 2018 / Accepted: 28 August 2018 / Published: 29 August 2018
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Abstract
The ginger essential oil/β-cyclodextrin (GEO/β-CD) composite, ginger essential oil/β-cyclodextrin/chitosan (GEO/β-CD/CTS) particles and ginger essential oil/β-cyclodextrin/chitosan (GEO/β-CD/CTS) microsphere were prepared with the methods of inclusion, ionic gelation and spray drying. Their properties were studied by using scanning electron microscopy (SEM), differential scanning calorimetry (DSC),
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The ginger essential oil/β-cyclodextrin (GEO/β-CD) composite, ginger essential oil/β-cyclodextrin/chitosan (GEO/β-CD/CTS) particles and ginger essential oil/β-cyclodextrin/chitosan (GEO/β-CD/CTS) microsphere were prepared with the methods of inclusion, ionic gelation and spray drying. Their properties were studied by using scanning electron microscopy (SEM), differential scanning calorimetry (DSC), thermo-gravimetry analysis (TGA), Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD). The results showed that the particle size of GEO/β-CD composite was smaller than that of β-CD and GEO/β-CD/CTS particles were loose and porous, while the microsphere obtained by spray drying had certain cohesiveness and small particle size. Besides, results also indicated that β-CD/CTS could modify properties and improve the thermal stability of GEO, which would improve its application value in food and medical industries. Full article
(This article belongs to the Special Issue Films and Coatings for Food and Health Applications)
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Open AccessArticle Influence of Ge Incorporation from GeSe2 Vapor on the Properties of Cu2ZnSn(S,Se)4 Material and Solar Cells
Coatings 2018, 8(9), 304; https://doi.org/10.3390/coatings8090304
Received: 18 July 2018 / Revised: 15 August 2018 / Accepted: 24 August 2018 / Published: 28 August 2018
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Abstract
Cu2ZnSn(S,Se)4 (CZTSSe) and Cu2Zn(Sn,Ge)(S,Se)4 (CZTGSSe) thin films were prepared based on a non-vacuum solution method. The CZTSSe films were obtained by annealing the solution-deposited precursor films with Se, while the CZTGSSe films were obtained by annealing the
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Cu2ZnSn(S,Se)4 (CZTSSe) and Cu2Zn(Sn,Ge)(S,Se)4 (CZTGSSe) thin films were prepared based on a non-vacuum solution method. The CZTSSe films were obtained by annealing the solution-deposited precursor films with Se, while the CZTGSSe films were obtained by annealing the similar precursor films with Se and GeSe2. We found that Ge could be incorporated into the annealed films when GeSe2 was present during the annealing process. The Ge incorporation obviously enlarged the sizes of the crystalline grains in the annealed films. However, the energy dispersive spectrometry (EDS) measurements revealed that the element distribution was not uniform in the CZTGSSe films. We fabricated solar cells based on the CZTSSe and CZTGSSe films. It was found the Ge incorporation decreases the Eu energy of the absorber material. The solar cell efficiency was increased from 5.61% (CZTSSe solar cell) to 7.14% (CZTGSSe solar cell) by the Ge incorporation. Compared to CZTSSe solar cells, the CZTGSSe solar cells exhibited a lower diode ideality factor and lower reverse saturation current density. Full article
(This article belongs to the Special Issue Thin Films for Energy Harvesting, Conversion, and Storage)
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Open AccessArticle Improvement of Thin Film Adhesion Due to Bombardment by Fast Argon Atoms
Coatings 2018, 8(9), 303; https://doi.org/10.3390/coatings8090303
Received: 4 July 2018 / Revised: 24 August 2018 / Accepted: 28 August 2018 / Published: 28 August 2018
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Abstract
A new hollow cathode sputtering system is used for beam-assisted deposition of thin films on dielectric substrates. A copper target placed at the hollow cathode bottom is uniformly sputtered by argon ions from the glow discharge plasma filling the cathode. Through an emissive
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A new hollow cathode sputtering system is used for beam-assisted deposition of thin films on dielectric substrates. A copper target placed at the hollow cathode bottom is uniformly sputtered by argon ions from the glow discharge plasma filling the cathode. Through an emissive grid, sputtered copper atoms leave the cathode together with accelerated argon ions. On their way to the substrate, the ions—due to charge exchange collisions—turn into fast argon atoms bombarding the growing film. With increasing argon ion energy, continuous bombardment results in the film adhesion improvement and reduction of the deposition rate down to zero, at an energy of about 2 keV. The pulsed bombardment does not influence the film deposition rate, and results in a monotonic growth of the film adhesion up to 20 MPa when increasing the fast atom energy up to 10 keV. Full article
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Open AccessArticle Electrochemical Performance of Few-Layer Graphene Nano-Flake Supercapacitors Prepared by the Vacuum Kinetic Spray Method
Coatings 2018, 8(9), 302; https://doi.org/10.3390/coatings8090302
Received: 1 July 2018 / Revised: 16 August 2018 / Accepted: 24 August 2018 / Published: 27 August 2018
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Abstract
A few-layer graphene nano-flake thin film was prepared by an affordable vacuum kinetic spray method at room temperature and modest low vacuum conditions. In this economical approach, graphite microparticles, a few layers thick, are deposited on a stainless-steel substrate to form few-layer graphene
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A few-layer graphene nano-flake thin film was prepared by an affordable vacuum kinetic spray method at room temperature and modest low vacuum conditions. In this economical approach, graphite microparticles, a few layers thick, are deposited on a stainless-steel substrate to form few-layer graphene nano-flakes using a nanoparticle deposition system (NPDS). The NPDS allows for a large area deposition at a low cost and can deposit various metal oxides at room temperature and low vacuum conditions. The morphology and structure of the deposited thin films are alterable by changing the scan speed of the deposition. These changes were verified by field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and Raman spectroscopy. The electrochemical performances of the supercapacitors, fabricated using the deposited films and H3PO4–PVA gel electrolytes with different concentrations, were measured using a 2-electrode cell. The electrochemical performance was evaluated by cyclic voltammetry, galvanostatic Charge–discharge, and electrochemical impedance spectroscopy. The proposed affordable fabricated supercapacitors show a high areal capacitance and a small equivalent series resistance. Full article
(This article belongs to the Special Issue Thin Films for Energy Harvesting, Conversion, and Storage)
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Open AccessArticle Non-Stick Coatings in Aluminium Molds for the Production of Polyurethane Foam
Coatings 2018, 8(9), 301; https://doi.org/10.3390/coatings8090301
Received: 17 July 2018 / Revised: 12 August 2018 / Accepted: 24 August 2018 / Published: 27 August 2018
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Abstract
The manufacturing of polyurethane foam is a process of great industrial importance in the automotive and furniture sector. The operation of demolding is the most delicate, since the foam sticks firmly to the walls of the mold onto which it has spread. In
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The manufacturing of polyurethane foam is a process of great industrial importance in the automotive and furniture sector. The operation of demolding is the most delicate, since the foam sticks firmly to the walls of the mold onto which it has spread. In order to avoid the use of demolding agents, the proposal is to coat the inside of the molds with non-stick coatings. In this work, three types of different coatings were studied: fluoropolymers, ceramics, and elastomers. After carrying out different tests in the laboratory, two fluoropolymer coatings (PFA (perfluoroalkoxy) and PTFE (polytetrafluoroethylene)) were selected for a test at the industrial level and, after 1500 cycles of demolding, it was experimentally proven that the PFA coating is the most adequate for the use studied. Full article
(This article belongs to the Special Issue Coatings for Dies and Molds)
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Open AccessArticle Functionalized Electrospun Fibers for the Design of Novel Hydrophobic and Anticorrosive Surfaces
Coatings 2018, 8(9), 300; https://doi.org/10.3390/coatings8090300
Received: 25 July 2018 / Revised: 13 August 2018 / Accepted: 24 August 2018 / Published: 25 August 2018
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Abstract
In this work, a novel coating was deposited on aluminum alloy samples by using a combination of electrospinning and chemical vapor deposition (CVD-silanization) techniques in order to create a functionalized film with an enhancement of both corrosion resistance and hydrophobicity. The electrospinning technique
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In this work, a novel coating was deposited on aluminum alloy samples by using a combination of electrospinning and chemical vapor deposition (CVD-silanization) techniques in order to create a functionalized film with an enhancement of both corrosion resistance and hydrophobicity. The electrospinning technique makes the fabrication of highly crosslinked electrospun fibers possible by the combination of both poly(acrylic acid) and β-cyclodextrin, respectively, which can be easily functionalized in a further step by using the CVD-silanization process due to the evaporation of a hydrophobic molecule such as 1H,1H,2H,2H-Perflurodecyltriethoxysilane. In addition, the resultant electrospun fibers with a high degree of insolubility have been successfully fabricated and metal oxide nanoparticles (TiO2NPs) have been incorporated into the electrospun polymeric solution in order to improve the corrosion protection. The surface morphology has been determined by using light optical microscopy, atomic force microscopy, scanning electron microscopy, and water contact angle (WCA) measurements. The corrosion resistance has been evaluated by using both potentiodynamic polarization and pitting corrosion tests. Finally, the results related to WCA measurements after CVD-silanization corroborate that the surfaces have been successfully functionalized with a hydrophobic behavior in comparison with the electrospinning process, showing a considerable difference in the roughness. Full article
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Open AccessArticle Electrodeposition Behavior of Polycrystalline Ni–Mo–La Composite in Alkaline Solution
Coatings 2018, 8(9), 299; https://doi.org/10.3390/coatings8090299
Received: 7 June 2018 / Revised: 9 August 2018 / Accepted: 12 August 2018 / Published: 24 August 2018
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Abstract
The polycrystalline Ni–Mo–La composite coating was obtained by electrodeposition through the addition of La3+ ions into Ni, Mo ions main salt weak alkaline solution. The obtained composite contain 0.92 at.% La. According to the law of ionic activity, the redox reaction of
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The polycrystalline Ni–Mo–La composite coating was obtained by electrodeposition through the addition of La3+ ions into Ni, Mo ions main salt weak alkaline solution. The obtained composite contain 0.92 at.% La. According to the law of ionic activity, the redox reaction of three kinds of metal atoms was studied by polarography and cyclic voltammetry. It was found that the addition of lanthanum ions changed the composite structural, phase, and element, and the OH ions were deduced during the electrodeposition in alkaline solution. The introduction of lanthanum and molybdenum ions negatively shifted the reduction potential of nickel ions and broadened the peaks significantly in the deposition process, retarding the reduction and deposition rate of Ni ions, which was characterized by a multi-step reduction process of Mo and La metal atoms. Full article
(This article belongs to the Special Issue Nanocomposite Coatings)
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