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Coatings, Volume 8, Issue 7 (July 2018)

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Cover Story (view full-size image) EN-GJS-500-7 spheroidal graphite (SG) cast iron was coated with chemical Ni-P. The kinetic study [...] Read more.
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Open AccessCommentary Revisiting the Birth of 7YSZ Thermal Barrier Coatings: Stephan Stecura
Coatings 2018, 8(7), 255; https://doi.org/10.3390/coatings8070255
Received: 6 July 2018 / Revised: 11 July 2018 / Accepted: 20 July 2018 / Published: 22 July 2018
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Abstract
Thermal barrier coatings are widely used in all turbine engines, typically using a 7 wt.% Y2O3–ZrO2 formulation. Extensive research and development over many decades have refined the processing and structure of these coatings for increased durability and reliability.
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Thermal barrier coatings are widely used in all turbine engines, typically using a 7 wt.% Y2O3–ZrO2 formulation. Extensive research and development over many decades have refined the processing and structure of these coatings for increased durability and reliability. New compositions demonstrate some unique advantages and are gaining in application. However, the “7YSZ” (7 wt.% yttria stabilized zirconia) formulation predominates and is still in widespread use. This special composition has been universally found to produce nanoscale precipitates of metastable t’ tetragonal phase, giving rise to a unique toughening mechanism via ferro-elastic switching under stress. This note recalls the original study that identified superior properties of 6–8 wt.% yttria stabilized zirconia (YSZ) plasma sprayed thermal barrier coatings, published in 1978. The impact of this discovery, arguably, continues in some form to this day. At one point, 7YSZ thermal barrier coatings were used in every new aircraft and ground power turbine engine produced worldwide. 7YSZ is a tribute to its inventor, Dr. Stephan Stecura, NASA retiree. Full article
(This article belongs to the Special Issue Thermal Barrier Coatings)
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Open AccessArticle Cavitation Erosion Resistance and Wear Mechanism Model of Flame-Sprayed Al2O3-40%TiO2/NiMoAl Cermet Coatings
Coatings 2018, 8(7), 254; https://doi.org/10.3390/coatings8070254
Received: 5 June 2018 / Revised: 13 July 2018 / Accepted: 19 July 2018 / Published: 21 July 2018
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Abstract
This manuscript deals with the cavitation erosion resistance of flame-sprayed Al2O3-40%TiO2/NiMoAl cermet coatings (low-velocity oxy-fuel (LVOF)), a new functional application of cermet coatings. The aim of the study was to investigate the cavitation erosion mechanism and determine
[...] Read more.
This manuscript deals with the cavitation erosion resistance of flame-sprayed Al2O3-40%TiO2/NiMoAl cermet coatings (low-velocity oxy-fuel (LVOF)), a new functional application of cermet coatings. The aim of the study was to investigate the cavitation erosion mechanism and determine the effect of feedstock powder ratio (Al2O3-TiO2/NiMoAl) of LVOF-sprayed cermet coatings on their cavitation erosion resistance. As-sprayed coatings were investigated for roughness, porosity, hardness, and Young’s modulus. Microstructural characteristics of the cross section and the surface of as-sprayed coatings were examined by light optical microscopy (LOM), scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD) methods. Coating cavitation tests were conducted in accordance with the ASTM G32 standard using an alternative stationary specimen testing method with usage of reference samples made from steel, copper, and aluminum alloys. Cavitation erosion resistance was measured by weight and volume loss, and normalised cavitation erosion resistance was calculated. Surface eroded due to cavitation was examined in successive time intervals by LOM and SEM-EDS. On the basis of coating properties and cavitation investigations, a phenomenological model of the cavitation erosion of Al2O3-40%TiO2/NiMoAl cermet coatings was elaborated. General relationships between their properties, microstructure, and cavitation wear resistance were established. The Al2O3-40%TiO2/NiMoAl composite coating containing 80% ceramic powder has a higher cavitation erosion resistance than the reference aluminium alloy. Full article
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Open AccessArticle Phase Composition, Thermal Conductivity, and Toughness of TiO2-Doped, Er2O3-Stabilized ZrO2 for Thermal Barrier Coating Applications
Coatings 2018, 8(7), 253; https://doi.org/10.3390/coatings8070253
Received: 26 May 2018 / Revised: 5 July 2018 / Accepted: 17 July 2018 / Published: 20 July 2018
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Abstract
TiO2 was doped into Er2O3-stabilized ZrO2 (ErSZ) to obtain desirable properties for thermal barrier coating (TBC) applications. The phase composition, thermal conductivity, and mechanical properties of TiO2-doped ErSZ were investigated. ErSZ had a non-transformable metastable
[...] Read more.
TiO2 was doped into Er2O3-stabilized ZrO2 (ErSZ) to obtain desirable properties for thermal barrier coating (TBC) applications. The phase composition, thermal conductivity, and mechanical properties of TiO2-doped ErSZ were investigated. ErSZ had a non-transformable metastable tetragonal (t′) phase, the compound with 5 mol % TiO2 consisted of t′ and cubic (c) phases, while 10 mol % TiO2 doped ErSZ had t′, c, and about 3.5 mol % monoclinic (m) phases. Higher TiO2 doping contents caused more m phase, and the compounds were composed of t′ and m phases. When the dopant content was below 10 mol %, TiO2 doping could decrease the thermal conductivity and enhance the toughness of the compounds. At higher doping levels, the compounds exhibited an increased thermal conductivity and a reduction in the toughness, mainly attribable to the formation of the undesirable m phase. Hence, 10 mol % TiO2-doped ErSZ could be a promising candidate for TBC applications. Full article
(This article belongs to the Special Issue Advanced Ceramic Coatings and Interfaces)
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Open AccessArticle The Surface Anodization of Titanium Dental Implants Improves Blood Clot Formation Followed by Osseointegration
Coatings 2018, 8(7), 252; https://doi.org/10.3390/coatings8070252
Received: 2 June 2018 / Revised: 28 June 2018 / Accepted: 16 July 2018 / Published: 20 July 2018
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Abstract
The anodization of titanium dental implant influences the biologic processes of osseointegration. 34 grit-blasted and acid-etched titanium specimens were used to evaluate micro- and nano-roughness (Ra), contact angle (θ) and blood clot extension (bce). 17 samples were anodized
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The anodization of titanium dental implant influences the biologic processes of osseointegration. 34 grit-blasted and acid-etched titanium specimens were used to evaluate micro- and nano-roughness (Ra), contact angle (θ) and blood clot extension (bce). 17 samples were anodized (test) while the remaining were used as control. The bce, was measured using 10 µL of human blood left in contact with titanium for 5 min at room temperature. The micro- and nano-scale Ra were measured under CLSM and AFM, respectively, while the θ was analyzed using the sessile drop technique. The bone-implant contact (BIC) rate was measured on two narrow implants retrieved for fracture. bce was 42.5 (±22) for test and 26.6% (±13)% for control group (p = 0.049). The micro-Ra was 6.0 (±1.5) for the test and 5.8 (±1.8) µm for control group (p > 0.05). The θ was 98.5° (±18.7°) for test and 103° (±15.2°) for control group (p > 0.05). The nano-Ra was 286 (±40) for the test and 226 (±40) nm for control group (p < 0.05). The BIC rate was 52.5 (±2.1) for test and 34.5% (±2.1%) for control implant (p = 0.014). (Conclusions) The titanium anodized surface significantly increases blood clot retention, significantly increases nano-roughness, and favors osseointegration. When placing dental implants in poor bone quality sites or with immediate loading protocol anodized Ti6Al4V dental implants should be preferred. Full article
(This article belongs to the Special Issue Advanced Bioadhesive and Bioabhesive Coatings)
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Open AccessEditorial To Do List for Research and Development and International Standardization to Achieve the Goal of Running a Majority of Electric Vehicles on Solar Energy
Coatings 2018, 8(7), 251; https://doi.org/10.3390/coatings8070251
Received: 15 May 2018 / Revised: 2 June 2018 / Accepted: 13 July 2018 / Published: 17 July 2018
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Abstract
A car-roof photovoltaic has enormous potential to change our society. With this technology, 70% of a car can run on the solar energy collected by the solar panel on its roof. Unfortunately, it is not a simple extension of conventional photovoltaic technology. This
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A car-roof photovoltaic has enormous potential to change our society. With this technology, 70% of a car can run on the solar energy collected by the solar panel on its roof. Unfortunately, it is not a simple extension of conventional photovoltaic technology. This paper lists what we need to do to achieve the goal of running a majority of cars on renewable solar energy, after clarification of the difference to conventional photovoltaic technology. In addition to technological development, standardization will be important and this list was made highlighting standardization. Full article
(This article belongs to the Special Issue Thin Film Solar Cells: Fabrication, Characterization and Applications)
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Open AccessArticle Development and Characterization of Anticorrosion and Antifriction Properties for High Performance Polyurethane/Graphene Composite Coatings
Coatings 2018, 8(7), 250; https://doi.org/10.3390/coatings8070250
Received: 13 June 2018 / Revised: 12 July 2018 / Accepted: 13 July 2018 / Published: 16 July 2018
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Abstract
This work contributes to the development and characterization of the corrosion resistance and antifriction properties of high performance polyurethane (PU)/graphene (Gr) composite coating. In this study, PU composite coatings containing 0, 2, 4 and 8 wt.% of Gr were prepared and evaluated using
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This work contributes to the development and characterization of the corrosion resistance and antifriction properties of high performance polyurethane (PU)/graphene (Gr) composite coating. In this study, PU composite coatings containing 0, 2, 4 and 8 wt.% of Gr were prepared and evaluated using various corrosion and mechanical tests, namely electrochemical impedance spectroscopy, salt spray tests, cross-cut tape tests and dynamic mechanical analysis. Antifriction properties of the coatings were evaluated using a tribometer with a ball-on-disc mode at room temperature. The corrosion resistance and adhesion property of the PU coatings were found to be enhanced by adding 4 and 8 wt.% of Gr. The coefficient of friction revealed that the antifriction properties of the PU/Gr composite coatings were 61% lower than those of the conventional coating when the Gr content was increased to 8 wt.%. Full article
(This article belongs to the Special Issue Advanced Coatings for Corrosion Protection in Extreme Environments)
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Open AccessArticle Significantly Reduced Secondary-Electron-Yield of Aluminum Sheet with Fluorocarbon Coating
Coatings 2018, 8(7), 249; https://doi.org/10.3390/coatings8070249
Received: 3 June 2018 / Revised: 11 July 2018 / Accepted: 13 July 2018 / Published: 16 July 2018
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Abstract
In this work, the surface of Al sheet was coated with a fluorocarbon (FC) thin film by radio frequency (RF) sputtering of polytetrafluoroethylene (PTFE) to investigate the influence of dielectric coatings on the secondary electron yield (SEY) behavior of Al sheets. Atomic-force microscopy
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In this work, the surface of Al sheet was coated with a fluorocarbon (FC) thin film by radio frequency (RF) sputtering of polytetrafluoroethylene (PTFE) to investigate the influence of dielectric coatings on the secondary electron yield (SEY) behavior of Al sheets. Atomic-force microscopy (AFM) and energy-dispersive spectroscopy (EDS) were employed to identify the surface topographies and elemental contents of the samples with FC coatings. Water contact angle (WCA) measurements were performed to characterize the surface tension as well as the polar and dispersion components of the samples’ surface. The secondary electron- mission (SEE) behavior of the samples was determined by measuring the SEY coefficients in an ultra-high vacuum chamber with three electron guns. The experimental results indicated that the longer sputtering time effectively led to the increase in coating thickness and a higher ratio of F/C, as well as the continued decrease of surface tension. A quite thin FC coating of about 11.3 nm on Al sheet resulted in the value of maximum SEY (δmax) dropping from 3.02 to 1.85. The further increase in coating thickness beneficially decreased δmax down to 1.60, however, at the cost of a ten-fold thicker coating (ca. 113 nm). It is found that increasing the coating thickness contributes to reducing SEY coefficients as well as suppressing SEE. The results are expected to guide the design of dielectric-coating for SEY reduction as well as multipactor suppression on Al. Full article
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Open AccessArticle Combination of Zinc Oxide and Antimony Doped Tin Oxide Nanocoatings for Glazing Application
Coatings 2018, 8(7), 248; https://doi.org/10.3390/coatings8070248
Received: 24 May 2018 / Revised: 10 July 2018 / Accepted: 10 July 2018 / Published: 12 July 2018
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Abstract
Multilayered nanocoatings allow outstanding properties with broad potential for glazing applications. Here, we report on the development of a multilayer nanocoating for zinc oxide (ZnO) and antimony doped tin oxide (ATO). The combination of ZnO and ATO thin films with their promising optical
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Multilayered nanocoatings allow outstanding properties with broad potential for glazing applications. Here, we report on the development of a multilayer nanocoating for zinc oxide (ZnO) and antimony doped tin oxide (ATO). The combination of ZnO and ATO thin films with their promising optical properties is a cost-efficient alternative for the production of energy-efficient glazing. It is an effective modification of the building envelope to reduce current high domestic demand of electrical power for air conditioning, especially in hot climates like Saudi Arabia. In this paper, we report the development of a nanocoating based on the combination of ZnO and ATO. Principle material and film investigations were carried out on lab-scale by dip coating with chemical solution deposition (CSD), while with regard to production processes, chemical vapor deposition (CVD) processes were evaluated in a second stage of the film development. It was found that with both processes, high-quality thin films and multilayer coatings with outstanding optical properties can be prepared. While keeping the optical transmission in the visible range at around 80%, only 10% of the NIR (near infrared) and below 1% of UV (ultraviolet) light passes these coatings. However, in contrast to CSD, the CVD process allows a free combination of the multilayer film sequence, which is of high relevance for production processes. Furthermore, it can be potentially integrated in float glass production lines. Full article
(This article belongs to the Special Issue Chemical Vapor Deposition 2018)
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Open AccessArticle Structure and Properties of High-Hardness Silicide Coatings on Cemented Carbides for High Temperature Applications
Coatings 2018, 8(7), 247; https://doi.org/10.3390/coatings8070247
Received: 29 April 2018 / Revised: 8 June 2018 / Accepted: 4 July 2018 / Published: 12 July 2018
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Abstract
Cemented tungsten carbides (cWCs) are routinely used in mining and manufacturing but are also candidate materials for compact radiation shielding in fusion power generation. In both applications, there is a need for oxidation to be minimized at operating temperatures. In a recent study,
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Cemented tungsten carbides (cWCs) are routinely used in mining and manufacturing but are also candidate materials for compact radiation shielding in fusion power generation. In both applications, there is a need for oxidation to be minimized at operating temperatures. In a recent study, Si-based coatings deposited by pack cementation were demonstrated to improve the oxidation resistance of cWCs by up to a factor of 1000. In this work, these coatings are further characterized, with the focus on growth kinetics, phase composition, and hardness. By combining quantitative X-ray diffraction, electron microscopy, and instrumented micro-indentation, it is shown that the coating layer has a 20% higher hardness than the substrate, which is explained by the presence of a previously-unknown distribution of very hard SiC laths. To interpret the coating stability, a coating growth map is developed. The map shows that the structure is stable under a broad range of processing temperatures and cWC compositions, demonstrating the wide-ranging applicability of these coatings. Full article
(This article belongs to the Special Issue Thermal Barrier Coatings)
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Open AccessArticle Corrosion Potential Modulation on Lead Anodes Using Water Oxidation Catalyst Coatings
Coatings 2018, 8(7), 246; https://doi.org/10.3390/coatings8070246
Received: 25 May 2018 / Revised: 18 June 2018 / Accepted: 4 July 2018 / Published: 11 July 2018
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Abstract
The oxidation of water to form oxygen gas provides charge balance for the cathodic deposition of metals, such as zinc, in the electrorefining industry. This is a corrosive, four-electron electrochemical reaction that causes deterioration of lead-silver alloy anodes employed in these processes. A
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The oxidation of water to form oxygen gas provides charge balance for the cathodic deposition of metals, such as zinc, in the electrorefining industry. This is a corrosive, four-electron electrochemical reaction that causes deterioration of lead-silver alloy anodes employed in these processes. A sacrificial manganese oxide layer on the anode surface, formed in-situ from manganese sulfate, is used in industry to reduce the corrosion rate of these anodes by preferentially enabling water oxidation rather than lead dissolution. Still, it is poorly understood how the activity of manganese oxide as a water oxidation catalyst relates to its anticorrosive properties. Here, we show how the presence of water oxidation catalysts both formed in-situ (including the industry standard manganese oxide) and heterogenized prior to electrolysis on lead anodes affect the corrosion potential of these anodes. We find that corrosion potential under dynamic polarization conditions is the parameter most affected by the coatings formed in-situ and applied ex-situ prior to electrolysis. Full article
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Open AccessArticle Preparation of Yttria-Stabilized Zirconia Hollow Sphere with Reduced Shell Thickness by Controlling Ambient Temperature during Plasma Process
Coatings 2018, 8(7), 245; https://doi.org/10.3390/coatings8070245
Received: 30 May 2018 / Revised: 29 June 2018 / Accepted: 8 July 2018 / Published: 11 July 2018
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Abstract
Yttria-stabilized zirconia (YSZ) hollow sphere (HS) powder is a novel potential feedstock material for the plasma spraying of next generation advanced thermal barrier coatings with low thermal conductivity and high sintering resistibility. In this study, YSZ HS powders were prepared by plasma treatment
[...] Read more.
Yttria-stabilized zirconia (YSZ) hollow sphere (HS) powder is a novel potential feedstock material for the plasma spraying of next generation advanced thermal barrier coatings with low thermal conductivity and high sintering resistibility. In this study, YSZ HS powders were prepared by plasma treatment with/without a heat preservation zone around the flying path of the particles during plasma flame. The results of the scanning electron microscopy of YSZ HS powders showed that HS prepared with a heat preservation zone during the plasma process exhibited a regular spherical morphology and a homogeneous thin shell structure. Due to the sufficient heating of the shell regions, the HS powder presented a well densified shell structure. Furthermore, the mechanism of formation of the HS powder with reduced shell thickness was also discussed based on the analysis of the evolution of the powder structure. This kind of hollow sphere powder with a very thin shell structure provides a new alternative feedstock material for the development of next generation high performance thermal barrier coatings. Full article
(This article belongs to the Special Issue From Metallic Coatings to Additive Manufacturing)
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Open AccessReview Thin Film Thermoelectric Materials: Classification, Characterization, and Potential for Wearable Applications
Coatings 2018, 8(7), 244; https://doi.org/10.3390/coatings8070244
Received: 22 May 2018 / Revised: 28 June 2018 / Accepted: 9 July 2018 / Published: 10 July 2018
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Abstract
Thermoelectric technology has the ability to convert heat directly into electricity and vice versa. With the rapid growth of portable and wearable electronics and miniature devices, the self-powered and maintenance of free thermoelectric energy harvester is highly desired as a potential power supply.
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Thermoelectric technology has the ability to convert heat directly into electricity and vice versa. With the rapid growth of portable and wearable electronics and miniature devices, the self-powered and maintenance of free thermoelectric energy harvester is highly desired as a potential power supply. Thin film thermoelectric materials are lightweight, mechanically flexible, and they can be synthesized from abundant resources and processed with a low-cost procedure, which offers the potential to develop the novel thermoelectric devices and hold unique promise for future electronics and miniature accessories. Here, a general classification for thin film thermoelectric materials varied by material compositions, and thermoelectric properties depended on different measurement technique. Several new flexible thermoelectric strategies are summarized with the hope that they can inspire further development of novel thermoelectric applications. Full article
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Open AccessArticle Effect of Electrode Coating with Graphene Suspension on Power Generation of Microbial Fuel Cells
Coatings 2018, 8(7), 243; https://doi.org/10.3390/coatings8070243
Received: 1 April 2018 / Revised: 3 June 2018 / Accepted: 18 June 2018 / Published: 10 July 2018
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Abstract
Microbial fuel cells (MFCs), which can generate low-pollution power through microbial decomposition, are a potentially vital technology with applications in environmental protection and energy recovery. The electrode materials used in MFCs are crucial determinants of their capacity to generate electricity. In this study,
[...] Read more.
Microbial fuel cells (MFCs), which can generate low-pollution power through microbial decomposition, are a potentially vital technology with applications in environmental protection and energy recovery. The electrode materials used in MFCs are crucial determinants of their capacity to generate electricity. In this study, we proposed an electrode surface modification method to enhance the bacterial adhesion and increase the power generation in MFCs. Graphene suspension (GS) is selected as modifying reagent, and thin films of graphene are fabricated on an electrode substrate by spin-coating. Application of this method makes it easy to control the thickness of graphene film. Moreover, the method has the advantage of low cost and large-area fabrication. To understand the practicality of the method, the effects of the number of coating layers and drying temperature of the graphene films on the MFCs’ performance levels are investigated. The results indicate that when the baking temperature is increased from 150 to 325 °C, MFC power generation can increase approximately 4.5 times. Besides, the maximum power density of MFCs equipped with a four-layer graphene anode is approximately four times that of MFCs equipped with a two-layer graphene anode. An increase in baking temperature or number of coating layers of graphene films enhances the performance of MFC power generation. The reason can be attributed to the graphene purity and amount of graphene adhering to the surface of electrode. Full article
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Open AccessAddendum Addendum: Amadori, S., et al. Experimental Evaluation and Modeling of the Damping Properties of Multi-Layer Coated Composites. Coatings 2018, 8, 53
Coatings 2018, 8(7), 242; https://doi.org/10.3390/coatings8070242
Received: 28 June 2018 / Accepted: 4 July 2018 / Published: 9 July 2018
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Abstract
We wish to add the following statement to the published article [1].[...] Full article
Open AccessArticle Effect of Laser Scanning Speed on the Wear Behavior of Nano-SiC-Modified Fe/WC Composite Coatings by Laser Remelting
Coatings 2018, 8(7), 241; https://doi.org/10.3390/coatings8070241
Received: 6 June 2018 / Revised: 24 June 2018 / Accepted: 28 June 2018 / Published: 7 July 2018
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Abstract
A supersonic plasma sprayed nano-SiC-modified WC/Fe metal–cermet composite coating was remelted with a fibre-pulsed laser at four different laser scanning speeds (100, 150, 200 and 250 mm·min−1) while the other parameters were kept constant. The microstructures, microhardness, and tribological properties of
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A supersonic plasma sprayed nano-SiC-modified WC/Fe metal–cermet composite coating was remelted with a fibre-pulsed laser at four different laser scanning speeds (100, 150, 200 and 250 mm·min−1) while the other parameters were kept constant. The microstructures, microhardness, and tribological properties of the coatings were analysed by means of SEM (scanning electron microscopy), XRD (X-ray diffractometer), and a friction tester, respectively. The results show that, when the laser scanning speed is 100 mm·min−1, the remelted coating is most dense with regard to the coverage of the substrate. The coating with nano-particles became more smooth, and elements Si and C in the nano-particles reacted with Fe, Ni, or Cr and formed a hard mesophase that enhanced the strength and hardness of the coating. With the increase of laser scanning speed, the hardness of the four coatings increased first and then decreased, and the nano-SiC-modified remelted coating showed a maximum microhardness of about HV0.51350, and the nano-particles made the coating’s micro-structure finer, at a laser scanning speed of 150 mm·min−1. The friction coefficient and wear rate of the four coatings were 0.58 and 12.01 × 10−5 mm3/(N·m), 0.21 and 8.50 × 10−5 mm3/(N·m), 0.62 and 20.04 × 10−5 mm3/(N·m), and 1.23 and 25.13 × 10−5 mm3/(N·m). The remelted coating at a laser scanning speed of 150 mm·min−1 exhibits the best wear resistance and its wear mechanism is governed by slight adhesion wear and plastic deformation. Full article
(This article belongs to the Special Issue Nanocomposite Coatings)
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Open AccessArticle Fabrication of Transparent Very Thin SiOx Doped Diamond-Like Carbon Films on a Glass Substrate
Coatings 2018, 8(7), 240; https://doi.org/10.3390/coatings8070240
Received: 5 June 2018 / Revised: 27 June 2018 / Accepted: 4 July 2018 / Published: 7 July 2018
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Abstract
A novel direct current (DC) magnetron sputtering system via radio frequency (RF) bias with hexamethyldisiloxane (HMDSO) plasma polymerization was developed for the deposition of SiOx-doped diamond-like carbon (DLC) films on a glass substrate. As the RF bias increased, the ratio of
[...] Read more.
A novel direct current (DC) magnetron sputtering system via radio frequency (RF) bias with hexamethyldisiloxane (HMDSO) plasma polymerization was developed for the deposition of SiOx-doped diamond-like carbon (DLC) films on a glass substrate. As the RF bias increased, the ratio of intensity of D peak and G peak (I(D)/I(G)) decreased and the G peak shifted to a low position, leading to high hardness and a large portion of sp3 bonds. Additionally, weak sp2 graphite bonds were broken and sp3 diamond bonds formed because the RF bias attracted hydrogen ion bombarding the DLC films. Increasing DC power was helpful to improve the hardness of the DLC films because the proportion of sp3 bonds and the I(D)/I(G) ration was increased. HMDSO was introduced into this process to form SiOx:DLC films with enhanced optical performance. The average transmittance in the visible region of these very thin SiOx:DLC films with a thickness of 37.5 nm was 80.3% and the hardness of the SiOx:DLC films was increased to 7.4 GPa, which was 23.3% higher than that of B270 substrates. Full article
(This article belongs to the Special Issue Advances in Functional Inorganic Coatings)
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Open AccessFeature PaperArticle Study of Electroless Nickel Coatings on EN-GJS-500-7 Spheroidal Graphite Cast Iron
Coatings 2018, 8(7), 239; https://doi.org/10.3390/coatings8070239
Received: 25 May 2018 / Revised: 17 June 2018 / Accepted: 4 July 2018 / Published: 6 July 2018
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Abstract
EN-GJS-500-7 spheroidal graphite (SG) cast iron was coated with chemical Ni-P. The kinetic study reveals that the limiting step corresponds to a classical surface process, but the morphological study shows, at short times, an imperfect Ni-P coating on the graphite spheroids. The initial
[...] Read more.
EN-GJS-500-7 spheroidal graphite (SG) cast iron was coated with chemical Ni-P. The kinetic study reveals that the limiting step corresponds to a classical surface process, but the morphological study shows, at short times, an imperfect Ni-P coating on the graphite spheroids. The initial Ni-P growth appears to be blocked. This problem has been solved by the application of a cathodic polarization for a few minutes as a pretreatment of the surface. It was observed after this first step that both chemical and electrochemical reduction of nickel cation and hypophosphite on the SG cast iron took place at the same time, leading to the growth of a homogeneous Ni-P scale, in particular on graphite spheroids. Full article
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Open AccessArticle In Situ Plasma Monitoring of PECVD nc-Si:H Films and the Influence of Dilution Ratio on Structural Evolution
Coatings 2018, 8(7), 238; https://doi.org/10.3390/coatings8070238
Received: 12 April 2018 / Revised: 25 June 2018 / Accepted: 2 July 2018 / Published: 6 July 2018
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Abstract
We report plasma-enhanced chemical vapor deposition (PECVD) hydrogenated nano-crystalline silicon (nc-Si:H) thin films. In particular, the effect of hydrogen dilution ratio (R = H2/SiH4) on structural and optical evolutions of the deposited nc-Si:H films were systematically investigated including
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We report plasma-enhanced chemical vapor deposition (PECVD) hydrogenated nano-crystalline silicon (nc-Si:H) thin films. In particular, the effect of hydrogen dilution ratio (R = H2/SiH4) on structural and optical evolutions of the deposited nc-Si:H films were systematically investigated including Raman spectroscopy, Fourier-transform infrared spectroscopy (FTIR) and low angle X-ray diffraction spectroscopy (XRD). Measurement results revealed that the nc-Si:H structural evolution, primarily the transition of nano-crystallization from the amorphous state to the nanocrystalline state, can be carefully induced by the adjustment of hydrogen dilution ratio (R). In addition, an in situ plasma diagnostic tool of optical emission spectroscopy (OES) was used to further characterize the crystallization rate index (Hα*/SiH*) that increases when hydrogen dilution ratio (R) rises, whereas the deposition rate decreases. Another in situ plasma diagnostic tool of quadruple mass spectrometry (QMS) also confirmed that the “optimal” range of hydrogen dilution ratio (R = 30–40) can yield nano-crystalline silicon (n-Si:H) growth due to the depletion of higher silane radicals. A good correlation between the plasma characteristics by in situ OES/QMS and the film characteristics by XRD, Raman and FTIR, for the transition of a-Si:H to nc-Si:H film from the hydrogen dilution ratio, was obtained. Full article
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Open AccessFeature PaperArticle Catalytic Performance of Ag2O and Ag Doped CeO2 Prepared by Atomic Layer Deposition for Diesel Soot Oxidation
Coatings 2018, 8(7), 237; https://doi.org/10.3390/coatings8070237
Received: 31 May 2018 / Revised: 28 June 2018 / Accepted: 28 June 2018 / Published: 4 July 2018
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Abstract
The catalytic behaviour of Ag2O and Ag doped CeO2 thin films, deposited by atomic layer deposition (ALD), was investigated for diesel soot oxidation. The silver oxide was deposited from pulses of the organometallic precursor (hfac)Ag(PMe3) and ozone at
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The catalytic behaviour of Ag2O and Ag doped CeO2 thin films, deposited by atomic layer deposition (ALD), was investigated for diesel soot oxidation. The silver oxide was deposited from pulses of the organometallic precursor (hfac)Ag(PMe3) and ozone at 200 °C with growth rate of 0.28 Å/cycle. Thickness, crystallinity, elemental composition, and morphology of the Ag2O and Ag doped CeO2 films deposited on Si (100) were characterized by ellipsometry, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and field emission scanning electron microscopy (FESEM), respectively. The catalytic effect on diesel soot combustion of pure Ag2O, CeO2, and Ag doped CeO2 films grown on stainless steel foil supports was measured with oxidation tests. Nominally CeO2:Ag 10:1 doped CeO2 films were most effective and oxidized 100% of soot at 390 °C, while the Ag2O films were 100% effective at 410 °C. The doped films also showed much higher stability; their performance remained stable after five tests with only a 10% initial reduction in efficiency whereas the performance of the Ag2O films reduced by 50% after the first test. It was concluded that the presence of Ag+ sites on the catalyst is responsible for the high soot oxidation activity. Full article
(This article belongs to the Special Issue Atomic Layer Deposition)
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Open AccessFeature PaperArticle A Ladder-Type Organosilicate Copolymer Gate Dielectric Materials for Organic Thin-Film Transistors
Coatings 2018, 8(7), 236; https://doi.org/10.3390/coatings8070236
Received: 31 May 2018 / Revised: 27 June 2018 / Accepted: 2 July 2018 / Published: 3 July 2018
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Abstract
A ladder-type organosilicate copolymer based on trimethoxymethylsilane (MTMS) and 1,2-bis(triethoxysilyl)alkane (BTESn: n = 2–4) were synthesized for use as gate dielectrics in organic thin-film transistors (OTFTs). For the BTESn, the number of carbon chains (2–4) was varied to elucidate
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A ladder-type organosilicate copolymer based on trimethoxymethylsilane (MTMS) and 1,2-bis(triethoxysilyl)alkane (BTESn: n = 2–4) were synthesized for use as gate dielectrics in organic thin-film transistors (OTFTs). For the BTESn, the number of carbon chains (2–4) was varied to elucidate the relationship between the chemical structure of the monomer and the resulting dielectric properties. The developed copolymer films require a low curing temperature (≈150 °C) and exhibit good insulating properties (leakage current density of ≈10−8–10−7 A·cm−2 at 1 MV·cm−1). Copolymer films were employed as dielectric materials for use in top-contact/bottom-gate organic thin-film transistors and the resulting devices exhibited decent electrical performance for both p- and n-channel organic semiconductors with mobility as high as 0.15 cm2·V−1·s−1 and an Ion/Ioff of >105. Furthermore, dielectric films were used for the fabrication of TFTs on flexible substrates. Full article
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Open AccessArticle Alginate and Chitosan as a Functional Barrier for Paper-Based Packaging Materials
Coatings 2018, 8(7), 235; https://doi.org/10.3390/coatings8070235
Received: 30 May 2018 / Revised: 21 June 2018 / Accepted: 27 June 2018 / Published: 3 July 2018
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Abstract
Paper-based food packaging materials are widely used, renewable, and biodegradable. Because of its porous structure, paper has poor or no barrier performance against grease, water vapor, water, and volatile organic compounds. Moreover, recycled paperboard can be a source of organic residuals that are
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Paper-based food packaging materials are widely used, renewable, and biodegradable. Because of its porous structure, paper has poor or no barrier performance against grease, water vapor, water, and volatile organic compounds. Moreover, recycled paperboard can be a source of organic residuals that are able to migrate into packed food. Two different types of paperboard produced from primary and secondary cellulosic fibers were coated using renewable materials, such as alginate and chitosan, and comprehensive barrier measurements showed multifunctional barrier properties of these two biomaterials. Both paper substrates were successfully coated using a draw-down coater, and the measured air permeability of the coated samples was 0 mL·min−1. Grease resistance was improved, while it was possible to reduce water vapor transmission, the migration of mineral oil saturated hydrocarbons and mineral oil aromatic hydrocarbons (MOSH/MOAH), and the permeation of volatile compounds for both paper substrates when compared with uncoated substrates. Wettability and water absorptiveness of chitosan- and alginate-coated papers were found to be substrate-dependent properties, and could be significantly affected by bio-based coatings. In summary, industrially produced paperboard was upgraded by coating it with the naturally biodegradable biopolymers, alginate and chitosan, thus achieving extraordinary barrier performance for various applications within the packaging industry. Full article
(This article belongs to the Special Issue Recent Progress in Food and Beverage Packaging Coatings)
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Open AccessFeature PaperArticle Electrochemical and Surface Analysis of 2-Phenylimidazole Adsorbed on Copper from Chloride Solution
Coatings 2018, 8(7), 234; https://doi.org/10.3390/coatings8070234
Received: 16 May 2018 / Revised: 20 June 2018 / Accepted: 2 July 2018 / Published: 3 July 2018
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Abstract
The electroanalytical and surface characterization of copper immersed in 3 wt.% NaCl solution containing 1 mM of 2-phenylimidazole (2PhI) is presented. It was proven that 2PhI can be employed as corrosion inhibitor for copper using various electrochemical analyses, such as cyclic voltammetry, chronopotentiometry,
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The electroanalytical and surface characterization of copper immersed in 3 wt.% NaCl solution containing 1 mM of 2-phenylimidazole (2PhI) is presented. It was proven that 2PhI can be employed as corrosion inhibitor for copper using various electrochemical analyses, such as cyclic voltammetry, chronopotentiometry, electrochemical impedance spectroscopy, and potentiodynamic curve measurements. The adsorption of 2PhI on copper was further analyzed by 3D-profilometry, attenuated total reflectance Fourier transform infrared spectroscopy, contact angle measurements, and scanning electron microscopy equipped with an energy dispersive X-ray spectrometer. This system was therefore comprehensively described by various analytical approaches. Full article
(This article belongs to the Special Issue Corrosion Characterization and Surface Analysis of Metallic Materials)
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Open AccessFeature PaperArticle Electrochemical Deposition of Ni–W Crack-Free Coatings
Coatings 2018, 8(7), 233; https://doi.org/10.3390/coatings8070233
Received: 1 June 2018 / Revised: 21 June 2018 / Accepted: 25 June 2018 / Published: 30 June 2018
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Abstract
The main features of electrochemical deposition of coatings based on Ni–W binary alloy in the pulse current mode using pyrophosphate electrolytes were studied. Two electrolytes with a pH of 8.7 and 9.5 were used. The deposition was carried out with the current density
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The main features of electrochemical deposition of coatings based on Ni–W binary alloy in the pulse current mode using pyrophosphate electrolytes were studied. Two electrolytes with a pH of 8.7 and 9.5 were used. The deposition was carried out with the current density varying in the range of 0.01–0.1 A·cm−2, and the duty cycle (the relative pulse duration) was changed within the range 20–100%. The surface morphology and elemental and phase composition of the coatings were studied by scanning electron microscopy, energy-dispersive X-ray microanalysis and X-ray diffractometry. The experimental conditions allowing us to achieve the maximum Faradaic efficiency and W content in the coatings were determined. It was found that the pulse current mode enabled the fabrication of crack-free coatings with a thickness greater than 6 μm. Full article
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Open AccessArticle Effect of Sensitization on the Electrochemical Properties of Nanostructured NiO
Coatings 2018, 8(7), 232; https://doi.org/10.3390/coatings8070232
Received: 7 February 2018 / Revised: 11 June 2018 / Accepted: 25 June 2018 / Published: 29 June 2018
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Abstract
Screen-printed NiO electrodes were sensitized with 11 different dyes and the respective electrochemical properties were analyzed in a three-electrode cell with the techniques of cyclic voltammetry and electrochemical impedance spectroscopy. The dye sensitizers of NiO were organic molecules of different types (e.g., squaraines,
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Screen-printed NiO electrodes were sensitized with 11 different dyes and the respective electrochemical properties were analyzed in a three-electrode cell with the techniques of cyclic voltammetry and electrochemical impedance spectroscopy. The dye sensitizers of NiO were organic molecules of different types (e.g., squaraines, coumarins, and derivatives of triphenyl-amines and erythrosine B), which were previously employed as sensitizers of the same oxide in dye-sensitized solar cells of p-type (p-DSCs). Depending on the nature of the sensitizer, diverse types of interactions occurred between the immobilized sensitizer and the screen-printed NiO electrode at rest and under polarization. The impedance data recorded at open circuit potential were interpreted in terms of two different equivalent circuits, depending on the eventual presence of the dye sensitizer on the mesoporous electrode. The fitting parameter of the charge transfer resistance through the electrode/electrolyte interface varied in accordance to the differences of the passivation action exerted by the various dyes against the electrochemical oxidation of NiO. Moreover, it has been observed that the resistive term RCT associated with the process of dark electron transfer between the dye and NiO substrate is strictly correlated to the overall efficiency of the photoconversion (η) of the corresponding p-DSC, which employs the same dye-sensitized electrode as photocathode. Full article
(This article belongs to the Special Issue Thin Films for Energy Harvesting, Conversion, and Storage)
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Open AccessArticle Design and Fabrication of a Narrow Bandpass Filter with Low Dependence on Angle of Incidence
Coatings 2018, 8(7), 231; https://doi.org/10.3390/coatings8070231
Received: 31 May 2018 / Revised: 23 June 2018 / Accepted: 27 June 2018 / Published: 29 June 2018
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Abstract
A multilayer narrow bandpass filter that consists of silver and silicon thin films is designed using the admittance tracing method. Owing to the low loss of silicon in the infrared range, the peak transmittance at a wavelength of 950 nm exceeds 85%. To
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A multilayer narrow bandpass filter that consists of silver and silicon thin films is designed using the admittance tracing method. Owing to the low loss of silicon in the infrared range, the peak transmittance at a wavelength of 950 nm exceeds 85%. To eliminate the sidebands that are adjacent to the passband, a compact four-layered structure is proposed to generate an angle-insensitive spectrum. In fabrication, a silver-silicon multilayer is deposited to approach the design. Full article
(This article belongs to the Special Issue Design, Manufacturing and Measurement of Optical Film Coatings)
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Open AccessArticle Repair Bond Strength of a Resin Composite to Plasma-Treated or UV-Irradiated CAD/CAM Ceramic Surface
Coatings 2018, 8(7), 230; https://doi.org/10.3390/coatings8070230
Received: 6 May 2018 / Revised: 19 June 2018 / Accepted: 24 June 2018 / Published: 28 June 2018
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Abstract
The aim of this study was to investigate whether atmospheric-pressure plasma (APP) or ultraviolet (UV) irradiation could alter the hydrophilicity of a computer-aided design/computer-aided manufacturing (CAD/CAM) glass ceramic surface, and thereby enhance the repair bond strength between the ceramic and a resin composite.
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The aim of this study was to investigate whether atmospheric-pressure plasma (APP) or ultraviolet (UV) irradiation could alter the hydrophilicity of a computer-aided design/computer-aided manufacturing (CAD/CAM) glass ceramic surface, and thereby enhance the repair bond strength between the ceramic and a resin composite. Forty-eight leucite-reinforced glass ceramic discs were treated with 40% phosphoric acid and randomly assigned into one of six groups: Group 1, control; Group 2, treated with a mixture of Clearfil SE Bond primer (SEP) and Clearfil Porcelain Bond Activator (PBA); Group 3, subjected to APP irradiation for 10 s; Group 4, subjected to UV irradiation for 60 min; Group 5, APP irradiation followed by SEP/PBA; and Group 6, UV irradiation followed by SEP/PBA. After treatment, discs were bonded with resin composite using Clearfil SE Bond and stored in water at 37 °C for 1 week. We then tested how these treatments affected the microtensile bond strength (µTBS) and measured changes in the water contact angle (CA). Samples from Group 2 showed the highest µTBS (44.3 ± 6.0 MPa) and CA (33.8 ± 2.3°), with no significant differences measured between Groups 1, 3, and 4 (p < 0.05). Furthermore, the additional treatments of APP or UV before SEP/PBA had no effect (Group 5, p = 0.229) or a reduced effect (Group 6, p = 0.006), respectively, on µTBS. Overall, APP or UV irradiation before SEP/PBA treatment did not enhance the repair bond strength. Full article
(This article belongs to the Special Issue Advanced Bioadhesive and Bioabhesive Coatings)
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Open AccessArticle Raman Spectroscopy for Reliability Assessment of Multilayered AlCrN Coating in Tribo-Corrosive Conditions
Coatings 2018, 8(7), 229; https://doi.org/10.3390/coatings8070229
Received: 18 May 2018 / Revised: 11 June 2018 / Accepted: 20 June 2018 / Published: 26 June 2018
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Abstract
In this study, a multilayered AlCrN coating has been employed as a protective layer for steel used in tribo-corrosive conditions. The coating was deposited by a lateral rotating cathode arc PVD technology on a AISI 316L stainless steel substrate. A ratio of Al/(Al
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In this study, a multilayered AlCrN coating has been employed as a protective layer for steel used in tribo-corrosive conditions. The coating was deposited by a lateral rotating cathode arc PVD technology on a AISI 316L stainless steel substrate. A ratio of Al/(Al + Cr) was varied from 0.5 up to 0.6 in the AlCrN layer located above Cr adhesion and gradient CrN interlayers. A Raman spectroscopy and potentiodynamic polarization scan were used to determine the resistance in tribo-corrosive (3.5 wt % NaCl) conditions. Correlation between sliding contact surface chemistry and measured tribological properties of material was supported with static corrosion experiments. The corrosion mechanisms responsible for surface degradation are reported. Full article
(This article belongs to the Special Issue Coatings Tribology)
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Open AccessArticle Enhanced Transmittance Modulation of SiO2-Doped Crystalline WO3 Films Prepared from a Polyethylene Oxide (PEO) Template
Coatings 2018, 8(7), 228; https://doi.org/10.3390/coatings8070228
Received: 26 May 2018 / Revised: 15 June 2018 / Accepted: 23 June 2018 / Published: 26 June 2018
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Abstract
Polyethylene oxide (PEO)-modified silicon dioxide (SiO2)-doped crystalline tungsten trioxide (WO3) films for use as electrochromic layers were prepared on indium tin oxide (ITO) glass by the sol–gel spin coating technique. The effects of the PEO template and SiO2
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Polyethylene oxide (PEO)-modified silicon dioxide (SiO2)-doped crystalline tungsten trioxide (WO3) films for use as electrochromic layers were prepared on indium tin oxide (ITO) glass by the sol–gel spin coating technique. The effects of the PEO template and SiO2 on the electrochromic transmittance modulation ability of crystalline WO3 films were investigated. Fourier transform infrared spectroscopy (FT-IR) spectra analysis indicated that PEO was decomposed after annealing at 500 °C for 3 h. X-ray diffraction (XRD) pattern analysis showed that both SiO2 and PEO helped reduce the crystalline grain size of the WO3 films. Atomic force microscope (AFM) images showed that the combined action of SiO2 and PEO was helpful for achieving high surface roughness and a macroporous structure. An electrochromic test indicated that PEO-modified SiO2-doped crystalline WO3 films intercalated more charges (0.0165 C/cm2) than pure WO3 crystalline films (0.0095 C/cm2). The above effects resulted in a good transmittance modulation ability (63.2% at 628 nm) of PEO-modified SiO2-doped crystalline WO3 films, which was higher than that of pure WO3 crystalline films (9.4% at 628 nm). Full article
(This article belongs to the Special Issue Thin Films for Advance Applications)
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Open AccessArticle Hot Embossing for Whole Teflon Superhydrophobic Surfaces
Coatings 2018, 8(7), 227; https://doi.org/10.3390/coatings8070227
Received: 30 May 2018 / Revised: 16 June 2018 / Accepted: 16 June 2018 / Published: 22 June 2018
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Abstract
In this paper, we report a simple fabrication process of whole Teflon superhydrophobic surfaces, featuring high-aspect-ratio (>20) nanowire structures, using a hot embossing process. An anodic aluminum oxide (AAO) membrane is used as the embossing mold for the fabrication of high-aspect-ratio nanowires directly
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In this paper, we report a simple fabrication process of whole Teflon superhydrophobic surfaces, featuring high-aspect-ratio (>20) nanowire structures, using a hot embossing process. An anodic aluminum oxide (AAO) membrane is used as the embossing mold for the fabrication of high-aspect-ratio nanowires directly on a Teflon substrate. First, high-aspect-ratio nanowire structures of Teflon are formed by pressing a fluorinated ethylene propylene (FEP) sheet onto a heated AAO membrane at 340 °C, which is above the melting point of FEP. Experimental results show that the heating time and aspect ratios of nanopores in the AAO mold are critical to the fidelity of the hot embossed nanowire structures. It has also been found that during the de-molding step, a large adhesive force between the AAO mold and the molded FEP greatly prolongs the length of nanowires. Contact angle measurements indicate that Teflon nanowires make the surface superhydrophobic. The reliability and robustness of superhydrophobicity is verified by a long-term (~6.5 h) underwater turbulent channel flow test. After the first step of hot-embossing the Teflon nanowires, microstructures are further superimposed by repeating the hot embossing process, but this time with microstructured silicon substrates as micromolds and at a temperature lower than the melting temperature of the FEP. The results indicate that the hot embossing process is also an effective way to fabricate hierarchical micro/nanostructures of whole Teflon, which can be useful for applications of Teflon material, such as superhydrophobic surfaces. Full article
(This article belongs to the Special Issue Superhydrophobic Coatings)
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