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Coatings, Volume 8, Issue 4 (April 2018)

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Cover Story (view full-size image) Shellac is a renewable resource for eco-friendly treatment of wooden artefacts and furniture that [...] Read more.
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Open AccessArticle Comparative Study of the Corrosion Resistance of Air-Plasma-Sprayed Ca2SiO4 and Al2O3 Coatings in Salt Water
Coatings 2018, 8(4), 116; https://doi.org/10.3390/coatings8040116
Received: 11 January 2018 / Revised: 15 March 2018 / Accepted: 19 March 2018 / Published: 22 March 2018
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Abstract
In this study, Ca2SiO4 coating was sprayed on stainless steel substrate and the corrosion resistance of the as-sprayed coating was studied in salt water. At the same time, Al2O3 coatings were produced by air-plasma-sprayed technology as comparison.
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In this study, Ca2SiO4 coating was sprayed on stainless steel substrate and the corrosion resistance of the as-sprayed coating was studied in salt water. At the same time, Al2O3 coatings were produced by air-plasma-sprayed technology as comparison. Immersion test was carried out to evaluate the protection performance of coatings. Potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS) plots were also analyzed. The results indicated that Ca2SiO4 coatings showed a better protection performance than Al2O3 coatings. During the immersion, various calcium carbonate crystals appeared on the surface of Ca2SiO4 coatings. Ca(OH)2 was released from Ca2SiO4 coatings into NaCl aqueous solution, increasing the alkalinity, which is in favor of the formation of passivation film, and thus improves the corrosion resistance. Ca2SiO4 coatings became denser after immersion due to the fact that the pores and micro cracks were filled with hydration products i.e., hydrated calcium silicate (C–S–H) gel. On the contrary, the microstructure of Al2O3 coatings became loose and obvious rusty spots were observed on the surface after the immersion test. Full article
(This article belongs to the Special Issue Advanced Coatings for Corrosion Protection in Extreme Environments)
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Open AccessArticle The Electrical and Structural Properties of Nitrogen Ge1Sb2Te4 Thin Film
Coatings 2018, 8(4), 117; https://doi.org/10.3390/coatings8040117
Received: 24 January 2018 / Revised: 20 March 2018 / Accepted: 21 March 2018 / Published: 23 March 2018
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Abstract
The present work describes the process of obtaining thin films of Ge1Sb2Te4 by means of the short-pulse High Power Impulse Magnetron Sputtering (HiPIMS) technique. The Ge1Sb2Te4 (GST-124) and nitrogen Ge1Sb2
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The present work describes the process of obtaining thin films of Ge1Sb2Te4 by means of the short-pulse High Power Impulse Magnetron Sputtering (HiPIMS) technique. The Ge1Sb2Te4 (GST-124) and nitrogen Ge1Sb2Te4 (nitrogen GST-124) films were obtained in HiPIMS plasma ignited in Ar/GST-124 and Ar/N2/GST-124, respectively. In particular, the possibility of tailoring the electrical properties of films for applications in the phase change memory (PCM) cells was investigated. The IV measurements performed in a voltage sweeping mode on GST-124 and nitrogen GST-124 show that the threshold switching voltage varies as a function of nitrogen level in HiPIMS plasma. Amorphous-to-crystalline trigonal phase transition of the films was induced by thermal annealing, and structural changes were identified using X-ray diffraction and Raman scattering spectroscopy. The most intense bands appeared for the annealed layers in the range of 138–165 cm−1, for GST-124, and 138–150 cm−1 for nitrogen GST-124, respectively. Full article
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Open AccessArticle The Use of a Saturated Long Carbon Chain Sodium Monocarboxylate for the Corrosion Inhibition of Lead Objects in Atmospheric Conditions and in Acetic Acid Corrosive Solutions
Coatings 2018, 8(4), 118; https://doi.org/10.3390/coatings8040118
Received: 8 January 2018 / Revised: 15 March 2018 / Accepted: 18 March 2018 / Published: 23 March 2018
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Abstract
In this paper, a saturated long carbon chain sodium monocarboxylate containing 18 carbons—labeled NaC18—was used for the formation of a lead carboxylate coating to inhibit the corrosion of lead in atmospheric conditions and in acetic acid corrosive solutions. The effect of
[...] Read more.
In this paper, a saturated long carbon chain sodium monocarboxylate containing 18 carbons—labeled NaC18—was used for the formation of a lead carboxylate coating to inhibit the corrosion of lead in atmospheric conditions and in acetic acid corrosive solutions. The effect of stirring of the coating solution during the coating process on the inhibition efficiency was studied. The coating was characterized by scanning electron microscopy and Fourier transform infrared spectroscopy which have confirmed a formation of lead carboxylate layer on the lead metal surface. The corrosion inhibition properties of the coating were tested using linear sweep voltammetry and electrochemical impedance spectroscopy in a solution simulating the atmospheric conditions and in an acetic acid corrosive solution. Results show that the lead carboxylate forms a protective barrier that inhibits corrosion of lead in atmospheric conditions and in acetic acid corrosive solutions. Full article
(This article belongs to the Special Issue Communications from TechnoHeritage 2017)
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Open AccessArticle Comparison of Selected Properties of Shellac Varnish for Restoration and Polyurethane Varnish for Reconstruction of Historical Artefacts
Coatings 2018, 8(4), 119; https://doi.org/10.3390/coatings8040119
Received: 12 March 2018 / Revised: 20 March 2018 / Accepted: 21 March 2018 / Published: 24 March 2018
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Abstract
At present, many historical artefacts and furniture are only reconstructed and not restored. They are preserved in terms of material reparation, but their historical value decreases significantly. This work is focused on the comparison of the resistance of high-gloss polyurethane varnish with traditional
[...] Read more.
At present, many historical artefacts and furniture are only reconstructed and not restored. They are preserved in terms of material reparation, but their historical value decreases significantly. This work is focused on the comparison of the resistance of high-gloss polyurethane varnish with traditional shellac varnish. The varnishes were applied to oak wood and exposed to interior artificial accelerated ageing in Xenotest. Before and after ageing, cold liquid-resistance tests were performed on the tested specimens and gloss, colour, and adhesion were also evaluated. The structures of the surfaces were also analysed using a confocal laser scanning microscope. As expected, polyurethane varnish was much more durable than shellac varnish. Interestingly, shellac varnish was fairly resistant to water at the beginning, but this resistance was greatly reduced after artificial accelerated ageing. This illustrates the importance of sheltering the shellac treated artefacts in stable temperature-humidity conditions with the least possible effect of solar radiation. Full article
(This article belongs to the Special Issue Varnishes and Surface Treatments of Historical Wooden Artworks)
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Open AccessArticle SiO2@TiO2 Coating: Synthesis, Physical Characterization and Photocatalytic Evaluation
Coatings 2018, 8(4), 120; https://doi.org/10.3390/coatings8040120
Received: 2 February 2018 / Revised: 12 March 2018 / Accepted: 19 March 2018 / Published: 24 March 2018
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Abstract
Use of silicon dioxide (SiO2) and titanium dioxide (TiO2) have been widely investigated individually in coatings technology, but their combined properties promote compatibility for different innovative applications. For example, the photocatalytic properties of TiO2 coatings, when exposed to
[...] Read more.
Use of silicon dioxide (SiO2) and titanium dioxide (TiO2) have been widely investigated individually in coatings technology, but their combined properties promote compatibility for different innovative applications. For example, the photocatalytic properties of TiO2 coatings, when exposed to UV light, have interesting environmental applications, such as air purification, self-cleaning and antibacterial properties. However, as reported in different pilot projects, serious durability problems, associated with the adhesion between the substrate and TiO2, have been evidenced. Thus, the aim of this work is to synthesize SiO2 together with TiO2 to increase the durability of the photocatalytic coating without affecting its photocatalytic potential. Therefore, synthesis using sonochemistry, synthesis without sonochemistry, physical characterization, photocatalytic evaluation, and durability of the SiO2, SiO2@TiO2 and TiO2 coatings are presented. Results indicate that using SiO2 improved the durability of the TiO2 coating without affecting its photocatalytic properties. Thus, this novel SiO2@TiO2 coating shows potential for developing long-lasting, self-cleaning and air-purifying construction materials. Full article
(This article belongs to the Special Issue Nanocoatings with Air-Purifying Properties)
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Open AccessArticle Morphological Characteristics of Au Films Deposited on Ti: A Combined SEM-AFM Study
Coatings 2018, 8(4), 121; https://doi.org/10.3390/coatings8040121
Received: 3 March 2018 / Revised: 16 March 2018 / Accepted: 24 March 2018 / Published: 26 March 2018
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Abstract
Deposited Au films and coatings are, nowadays, routinely used as active or passive elements in several innovative electronic, optoelectronic, sensing, and energy devices. In these devices, the physical properties of the Au films are strongly determined by the films nanoscale structure. In addition,
[...] Read more.
Deposited Au films and coatings are, nowadays, routinely used as active or passive elements in several innovative electronic, optoelectronic, sensing, and energy devices. In these devices, the physical properties of the Au films are strongly determined by the films nanoscale structure. In addition, in these devices, often, a layer of Ti is employed to promote adhesion and, so, influencing the nanoscale structure of the deposited Au film. In this work, we present experimental analysis on the nanoscale cross-section and surface morphology of Au films deposited on Ti. In particular, we sputter-deposited thick (>100 nm thickness) Au films on Ti foils and we used Scanning Electron Microscopy to analyze the films cross-sectional and surface morphology as a function of the Au film thickness and deposition angle. In addition, we analyzed the Au films surface morphology by Atomic Force Microscopy which allowed quantifying the films surface roughness versus the film thickness and deposition angle. The results establish a relation between the Au films cross-sectional and surface morphologies and surface roughness to the film thickness and deposition angle. These results allow setting a general working framework to obtain Au films on Ti with specific morphological and topographic properties for desired applications in which the Ti adhesion layer is needed for Au. Full article
(This article belongs to the Special Issue Thin Films for Advance Applications)
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Open AccessArticle Cold-Sprayed AZ91D Coating and SiC/AZ91D Composite Coatings
Coatings 2018, 8(4), 122; https://doi.org/10.3390/coatings8040122
Received: 21 January 2018 / Revised: 23 March 2018 / Accepted: 23 March 2018 / Published: 26 March 2018
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Abstract
As an emerging coating building technique, cold spraying has many advantages to elaborate Mg alloy workpieces. In this study, AZ91D coatings and AZ91D-based composite coatings were deposited using cold spraying. Coatings were prepared using different gas temperatures to obtain the available main gas
[...] Read more.
As an emerging coating building technique, cold spraying has many advantages to elaborate Mg alloy workpieces. In this study, AZ91D coatings and AZ91D-based composite coatings were deposited using cold spraying. Coatings were prepared using different gas temperatures to obtain the available main gas temperature. Compressed air was used as the accelerating gas, and although magnesium alloy is oxidation-sensitive, AZ91D coatings with good performance were obtained. The results show that dense coatings can be fabricated until the gas temperature is higher than 500 °C. The deposition efficiency increases greatly with the gas temperature, but it is lower than 10% for all coating specimens. To analyze the effects of compressed air on AZ91D powder particles and the effects of gas temperature on coatings, the phase composition, porosity, cross-sectional microstructure, and microhardness of coatings were characterized. X-ray diffraction and oxygen content analysis clarified that no phase transformation or oxidation occurred on AZ91D powder particles during cold spraying processes with compressed air. The porosity of AZ91D coatings remained between 3.6% and 3.9%. Impact melting was found on deformed AZ91D particles when the gas temperature increased to 550 °C. As-sprayed coatings exhibit much higher microhardness than as-casted bulk magnesium, demonstrating the dense structure of cold-sprayed coatings. To study the effects of ceramic particles on cold-sprayed AZ91D coatings, 15 vol % SiC powder particles were added into the feedstock powder. Lower SiC content in the coating than in the feedstock powder means that the deposition efficiency of the SiC powder particles is lower than the deposition efficiency of AZ91D particles. The addition of SiC particles reduces the porosity and increases the microhardness of cold-sprayed AZ91D coatings. The corrosion behavior of AZ91D coating and SiC reinforced AZ91D composite coating were examined. The SiC-reinforced AZ91D composite coating reveals higher corrosion potential than magnesium substrate; therefore, it serves as a cathode for the magnesium substrate, the same as the AZ91D coating on magnesium substrate. As the SiC powder is semi-conductive, the embedded SiC particles reduce the electrochemical reaction of the AZ91D coating. The addition of SiC particles increases the corrosion potential of the coating, meanwhile increasing the galvanic potential and decreasing the negative galvanic current of the coating-substrate couple. Full article
(This article belongs to the Special Issue New Generation Coatings for Metals)
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Open AccessArticle Production of Antagonistic Compounds by Bacillus sp. with Antifungal Activity against Heritage Contaminating Fungi
Coatings 2018, 8(4), 123; https://doi.org/10.3390/coatings8040123
Received: 15 February 2018 / Revised: 15 March 2018 / Accepted: 21 March 2018 / Published: 28 March 2018
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Abstract
In recent years, the population has become acutely aware of the need to conserve the world’s resources. The study of new compounds produced by natural means is important in the search for alternative green solutions that act against biodeteriogenic fungi, which promote biodeterioration
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In recent years, the population has become acutely aware of the need to conserve the world’s resources. The study of new compounds produced by natural means is important in the search for alternative green solutions that act against biodeteriogenic fungi, which promote biodeterioration of built cultural heritage sites. The present paper reports new solutions, derived from Bacillus sp. CCLBH 1053 cultures, to produce lipopeptides (LPP) that can act as green biocides to promote the safeguarding of stone artwork. In the stationary phases of bacteria growth, peptone supplementation and sub-lethal heat activation improve the second cycle of sporulation, greatly enhancing LPP production. The bioactive compounds produced by Bacillus cultures suppress biodeteriogenic fungi growth on stone materials, and, hence, provide an important contribution to the development of new biocides for cultural heritage rehabilitation. Full article
(This article belongs to the Special Issue Communications from TechnoHeritage 2017)
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Open AccessArticle Laser-Assisted Removal of Graffiti from Granite: Advantages of the Simultaneous Use of Two Wavelengths
Coatings 2018, 8(4), 124; https://doi.org/10.3390/coatings8040124
Received: 27 February 2018 / Revised: 21 March 2018 / Accepted: 25 March 2018 / Published: 28 March 2018
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Abstract
Currently, removal of graffiti from stone monuments is a particularly challenging task. Lasers, being highly controllable and precise tools with minimal chemical waste, offer a key solution in this respect and a significant amount of research has been dedicated to this subject. Studies
[...] Read more.
Currently, removal of graffiti from stone monuments is a particularly challenging task. Lasers, being highly controllable and precise tools with minimal chemical waste, offer a key solution in this respect and a significant amount of research has been dedicated to this subject. Studies related to the laser cleaning of carbonate stones (such as limestone and marble) reported the extraction of the graffiti layer, although minimal damage to the substrate can be also detected. Recently, research efforts have been focused on the cleaning of granite, which is a complex stone due to its grained and polymineralic texture. Tests involving different wavelengths indicated that the effectiveness of the cleaning procedure is highly dependent on two components: The composition of the binding medium of the graffiti and the fissure system of the granite. In that direction, the aim of this paper is to investigate and to compare the cleaning effectiveness of two wavelengths emitted from a nanosecond (ns) Q-Switched Nd:YAG laser system (IR at 1064 nm and UV at 355 nm), as well as their simultaneous application at different energy density ratios FIR/FUV. The effectiveness of this combined methodology has been shown in several other cases; i.e., for the removal of pollution crusts from carbonate stones (marble). For this study, three different in composition graffiti paints (blue, black, and silver) were applied on a fine-grained granite originating from the NW Iberian Peninsula. Prior to the irradiation tests, the damage thresholds of the granite, as well as the extraction thresholds of the graffiti, were determined. Then, several tests involving a variety of parameters (fluence value, number of pulses, etc.) were performed and the most satisfactory irradiation conditions from each individual wavelength as well as their combination were compared, based on graffiti extraction level and any damage induced on the granite forming minerals. The analytical techniques used for the evaluation were stereomicroscopy, color measurements in CIELAB and CIELCH color spaces, Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS) and confocal microscopy. The experiments indicated the superiority of the combined laser cleaning regarding blue and black graffiti extraction. Full article
(This article belongs to the Special Issue Communications from TechnoHeritage 2017)
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Open AccessArticle The High-Temperature Resistance Properties of Polysiloxane/Al Coatings with Low Infrared Emissivity
Coatings 2018, 8(4), 125; https://doi.org/10.3390/coatings8040125
Received: 2 February 2018 / Revised: 2 March 2018 / Accepted: 24 March 2018 / Published: 28 March 2018
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Abstract
High-temperature-resistant coatings with low infrared emissivity were prepared using polysiloxane resin and flake aluminum as the adhesive and pigment, respectively. The heat resistance mechanisms of the polysiloxane/Al coating were systematically investigated. The composition, surface morphology, infrared reflectance spectra, and thermal expansion dimension (Δ
[...] Read more.
High-temperature-resistant coatings with low infrared emissivity were prepared using polysiloxane resin and flake aluminum as the adhesive and pigment, respectively. The heat resistance mechanisms of the polysiloxane/Al coating were systematically investigated. The composition, surface morphology, infrared reflectance spectra, and thermal expansion dimension (ΔL) of the coatings were characterized by X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FE-SEM), Fourier transform infrared spectroscopy, and thermal mechanical analysis (TMA), respectively. The results show that thermal decomposition of the resin and mismatch of ΔL between the coating and the substrate facilitate the high temperature failure of the coating. A suitable amount of flake aluminum pigments could restrain the thermal decomposition of the resin and could increase the match degree of ΔL between the coating and substrate, leading to an enhanced thermal resistance of the coating. Our results find that a coating with a pigment to binder ratio (P/B ratio) of 1.0 could maintain integrity until 600 °C, and the infrared emissivity was as low as 0.27. Hence, a coating with high-temperature resistance and low emissivity was obtained. Such coatings can be used for infrared stealth technology or energy savings in high-temperature equipment. Full article
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Open AccessArticle Application of Industrial XRF Coating Thickness Analyzer for Phosphate Coating Thickness on Steel
Coatings 2018, 8(4), 126; https://doi.org/10.3390/coatings8040126
Received: 6 February 2018 / Revised: 22 March 2018 / Accepted: 26 March 2018 / Published: 30 March 2018
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Abstract
The results of industrial application of an online X-ray fluorescence coating thickness analyzer for measuring the thickness of phosphate coatings on moving steel strips are considered in the article. The target range of coating thickness to be measured is from tens to hundreds
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The results of industrial application of an online X-ray fluorescence coating thickness analyzer for measuring the thickness of phosphate coatings on moving steel strips are considered in the article. The target range of coating thickness to be measured is from tens to hundreds of mg/m2 in a measurement time of 10 s. The measurement accuracy observed during long-duration factory acceptance test was 10–15%. The coating thickness analyzer consists of two XRF gauges, mounted above and below the steel strip and capable of moving across the moving strip system for their suspension and relocation and electronic control unit. Fully automated software was developed to automatically and continuously (24/7) control both gauges, scanning both sides of the steel strip, and develop and test methods for measuring new coatings. It allows performing offline storage and retrieval of the measurement results, remotely controlling the analyzer components and measurement modes from a control room. The developed XRF coating thickness analyzer can also be used for real-time measurement of other types of coatings, both metallic and non-metallic. Full article
(This article belongs to the Special Issue Advanced Nondestructive Evaluation and Characterization of Surface)
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Open AccessArticle Effects of Long-Term Static Bending Deformation on a Barrier Thin Film for Flexible Organic Optoelectronic Devices
Coatings 2018, 8(4), 127; https://doi.org/10.3390/coatings8040127
Received: 9 March 2018 / Revised: 26 March 2018 / Accepted: 29 March 2018 / Published: 30 March 2018
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Abstract
The objective of this study is to investigate the effect of long-term static bending on the encapsulation properties of a commercial barrier thin film for flexible optoelectronic devices. Encapsulation properties of the barrier film are evaluated under long-term static bending at various radii
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The objective of this study is to investigate the effect of long-term static bending on the encapsulation properties of a commercial barrier thin film for flexible optoelectronic devices. Encapsulation properties of the barrier film are evaluated under long-term static bending at various radii of curvature. Experimental results reveal that no significantly detrimental effect on the water vapor transmission rate (WVTR) at 40 °C and 90% RH is found for compressive bending up to 1000 h and for tensile bending up to 100 h with a radius of curvature of 5 mm or larger. However, WVTR of the barrier thin film is significantly increased and cracks are found in the barrier film when subjected to tensile bending of a radius of 10 mm or 5 mm for 1000 h. The expected WVTR of the given barrier thin film is numerically computed using a three-dimensional (3D) finite element model. Numerical results indicate that, with the presence of cracks in the barrier thin film, the WVTR increases for an apparent increase in moisture entrances. The WVTR calculated by the 3D cracking model concurs with the experimental results. Full article
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Open AccessArticle Thickness-Dependent Bioelectrochemical and Energy Applications of Thickness-Controlled Meso-Macroporous Antimony-Doped Tin Oxide
Coatings 2018, 8(4), 128; https://doi.org/10.3390/coatings8040128
Received: 31 December 2017 / Revised: 17 March 2018 / Accepted: 28 March 2018 / Published: 2 April 2018
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Abstract
Coatings of hierarchically meso-macroporous antimony-doped tin oxide (ATO) enable interfacing adsorbed species, such as biomacromolecules, with an electronic circuit. The coating thickness is a limiting factor for the surface coverage of adsorbates, that are electrochemically addressable. To overcome this challenge, a carbon black-based
[...] Read more.
Coatings of hierarchically meso-macroporous antimony-doped tin oxide (ATO) enable interfacing adsorbed species, such as biomacromolecules, with an electronic circuit. The coating thickness is a limiting factor for the surface coverage of adsorbates, that are electrochemically addressable. To overcome this challenge, a carbon black-based templating method was developed by studying the composition of the template system, and finding the right conditions for self-standing templates, preventing the reaction mixture from flowing out of the mask. The thicknesses of as-fabricated coatings were measured using stylus profilometry to establish a relationship between the mask thickness and the coating thickness. Cyclic voltammetry was performed on coatings with adsorbed cytochrome c to check whether the entire coating thickness was electrochemically addressable. Further, bacterial photosynthetic reaction centers were incorporated into the coatings, and photocurrent with respect to coating thickness was studied. The template mixture required enough of both carbon black and polymer, roughly 7% carbon black and 6% poly(ethylene glycol). Coatings were fabricated with thicknesses approaching 30 µm, and thickness was shown to be controllable up to at least 15 µm. Under the experimental conditions, photocurrent was found to increase linearly with the coating thickness, up to around 12 µm, above which were diminished gains. Full article
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Open AccessArticle Investigation of Element Effect on High-Temperature Oxidation of HVOF NiCoCrAlX Coatings
Coatings 2018, 8(4), 129; https://doi.org/10.3390/coatings8040129
Received: 14 March 2018 / Revised: 27 March 2018 / Accepted: 1 April 2018 / Published: 3 April 2018
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Abstract
MCrAlX (M: Ni or Co or both, X: minor elements) coatings have been used widely to protect hot components in gas turbines against oxidation and heat corrosion at high temperatures. Understanding the influence of the X-elements on oxidation behavior is important in the
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MCrAlX (M: Ni or Co or both, X: minor elements) coatings have been used widely to protect hot components in gas turbines against oxidation and heat corrosion at high temperatures. Understanding the influence of the X-elements on oxidation behavior is important in the design of durable MCrAlX coatings. In this study, NiCoCrAlX coatings doped with Y + Ru and Ce, respectively, were deposited on an Inconel-792 substrate using high velocity oxygen fuel (HVOF). The samples were subjected to isothermal oxidation tests in laboratory air at 900, 1000, and 1100 °C and a cyclic oxidation test between 100 and 1100 °C with a 1-h dwell time at 1100 °C. It was observed that the coating with Ce showed a much higher oxidation rate than the coating with Y + Ru under both isothermal and cyclic oxidation tests. In addition, the Y + Ru-doped coating showed significantly lower β phase depletion due to interdiffusion between the coating and the substrate, resulting from the addition of Ru. Simulation results using a moving phase boundary model and an established oxidation-diffusion model showed that Ru stabilized β grains, which reduced β-depletion of the coating due to substrate interdiffusion. This paper, combining experiment and simulation results, presents a comprehensive study of the influence of Ce and Ru on oxidation behavior, including an investigation of the microstructure evolution in the coating surface and the coating-substrate interface influenced by oxidation time. Full article
(This article belongs to the Special Issue Thermal Barrier Coatings)
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Open AccessArticle Realization of Graphene on the Surface of Electroless Ni–P Coating for Short-Term Corrosion Prevention
Coatings 2018, 8(4), 130; https://doi.org/10.3390/coatings8040130
Received: 3 March 2018 / Revised: 25 March 2018 / Accepted: 31 March 2018 / Published: 4 April 2018
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Abstract
Graphene was first fabricated on the surface of an electroless Ni–P coating/carbon steel (Ni–P–G) to improve its corrosion resistance. Meanwhile, an electroless Ni–P coating (Ni–P) was heated (Ni–P–H) under the same condition as Ni–P–G for comparison. The morphological results showed that a wavy
[...] Read more.
Graphene was first fabricated on the surface of an electroless Ni–P coating/carbon steel (Ni–P–G) to improve its corrosion resistance. Meanwhile, an electroless Ni–P coating (Ni–P) was heated (Ni–P–H) under the same condition as Ni–P–G for comparison. The morphological results showed that a wavy multilayer graphene was formed on the surface of Ni–P–G. The layer number of the graphene film was 5–10 according to the analysis of Raman spectra and observation by a high-resolution transmission electron microscope. The ID/IG ratio calculated from the Raman spectrum revealed that the graphene growing at the grain of Ni–P–H had larger grain size than that growing at the grain boundary. The electrochemical results showed a higher Rp, a lower CPEdl, and a lower corrosion rate of Ni–P–G than Q235 steel, Ni–P, and Ni–P–H, indicating a higher corrosion resistance. In addition, the surface potential map achieved by a scanning Kelvin probe presented a more positive surface potential of Ni–P–G than Ni–P with the difference being around 375–750 mV, demonstrating a lower corrosion tendency of Ni–P–G. Full article
(This article belongs to the Special Issue Advanced Coatings for Corrosion Protection in Extreme Environments)
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Open AccessArticle Recent Advances in Low-Temperature Deposition Methods of Transparent, Photocatalytic TiO2 Coatings on Polymers
Coatings 2018, 8(4), 131; https://doi.org/10.3390/coatings8040131
Received: 27 February 2018 / Revised: 30 March 2018 / Accepted: 4 April 2018 / Published: 4 April 2018
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Abstract
In this paper, we present an overview as well as current advances in the low-temperature deposition of highly crystalline suspensions of titania nanoparticles on polymers for photocatalytic applications. The presence of preformed titania nanoparticles yields the possibility of producing photocatalytically active coatings at
[...] Read more.
In this paper, we present an overview as well as current advances in the low-temperature deposition of highly crystalline suspensions of titania nanoparticles on polymers for photocatalytic applications. The presence of preformed titania nanoparticles yields the possibility of producing photocatalytically active coatings at reduced temperatures. Transparent and photocatalytically active TiO2 coatings that degrade organic matter, have been widely applied to bestow self-cleaning properties onto surfaces. This low-temperature deposition method and its transition to polymers would open an entire array of possible self-cleaning applications. During this research, incorporation of a silica buffer layer was applied to improve the compatibility of the inorganic coating on a substrate, such as polymethylmethacrylate (PMMA) and polyphenylsulphone (PPSU). The photocatalytic activity of the obtained coating was analyzed for its photocatalytic abilities by evaluating the color removal of a dye solution (methylene blue, MB) under UV irradiation and compared with commercial Pilkington Activ® self-cleaning glass. Our results indicate that the titania-coated silica-polymer systems yield a higher photocatalytic activity towards the degradation of organic pollutants. This method proves that the deposition of highly crystalline anatase suspensions on silica buffer layers is a viable method to produce photocatalytic coatings on heat-sensitive substrates. Full article
(This article belongs to the Special Issue Nanostructured Thin Films)
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Open AccessArticle Enhancement of the Corrosion Resistance of 304 Stainless Steel by Cr–N and Cr(N,O) Coatings
Coatings 2018, 8(4), 132; https://doi.org/10.3390/coatings8040132
Received: 27 February 2018 / Revised: 29 March 2018 / Accepted: 2 April 2018 / Published: 5 April 2018
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Abstract
Chromium nitride and oxynitride coatings were deposited as monolayers ((Cr–N), Cr(N,O)) and bilayers (Cr–N/Cr(N,O), Cr(N,O)/Cr–N) on 304 steel substrates by reactive cathodic arc method. The coatings were characterised by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDS), surface profilometry,
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Chromium nitride and oxynitride coatings were deposited as monolayers ((Cr–N), Cr(N,O)) and bilayers (Cr–N/Cr(N,O), Cr(N,O)/Cr–N) on 304 steel substrates by reactive cathodic arc method. The coatings were characterised by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDS), surface profilometry, and scratch tester. The anticorrosive properties of the coatings were assessed by electrochemical tests in 0.10 M NaCl + 1.96 M H2O2, carried out at 24 °C. Cr2N, CrN, and Cr(N,O) phases were identified in the coatings by grazing incidence X-ray diffraction (GI-XRD) measurements. The measured adhesion values ranged from 19 N to 35 N, the highest value being obtained for the bilayer with Cr(N,O) on top. Electrochemical tests showed that Cr(N,O) presence in both mono- and bilayered coatings determined the lowest damage in corrosive solution, as compared to the Cr–N coatings. This improvement was ascribed to the more compact structure, lower coatings porosity, and smoother surface. Full article
(This article belongs to the Special Issue Coatings for Harsh Environments)
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Open AccessArticle Chitosan Based Regenerated Cellulose Fibers Functionalized with Plasma and Ultrasound
Coatings 2018, 8(4), 133; https://doi.org/10.3390/coatings8040133
Received: 7 February 2018 / Revised: 29 March 2018 / Accepted: 4 April 2018 / Published: 5 April 2018
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Abstract
The great potential of regenerated cellulose fibers, which offer excellent possibilities as a matrix for the design of bioactive materials, was the lead for our research. We focused on the surface modification of fibers to improve the sorption properties of regenerated cellulose and
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The great potential of regenerated cellulose fibers, which offer excellent possibilities as a matrix for the design of bioactive materials, was the lead for our research. We focused on the surface modification of fibers to improve the sorption properties of regenerated cellulose and biocomposite regenerated cellulose/chitosan fibers, which are on the market. The purpose of our investigation was also the modification of regenerated cellulose fibers with the functionalization by chitosan as a means of obtaining similar properties to biocomposite regenerated cellulose/chitosan fibers on the market. Argon gas plasma was used for fiber surface activation and chitosan adsorption. Ultrasound was also used as a treatment procedure for the surface activation of regenerated cellulose fibers and treatment with chitosan. Analyses have shown that ultrasonic energy or plasma change the accessibility of free functional groups, structure and reactivity, especially in regenerated cellulose fibers. Changes that occurred in the morphology and in the structure of fibers were also reflected in their physical and chemical properties. Consequently, moisture content, sorption properties and water retention improved. Full article
(This article belongs to the Special Issue Surface Modification of Cellulose Fibres)
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Open AccessArticle Tribological Properties of New Cu-Al/MoS2 Solid Lubricant Coatings Using Magnetron Sputter Deposition
Coatings 2018, 8(4), 134; https://doi.org/10.3390/coatings8040134
Received: 10 February 2018 / Revised: 24 March 2018 / Accepted: 26 March 2018 / Published: 6 April 2018
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Abstract
The increasing demands of environmental protection have led to solid lubricant coatings becoming more and more important. A new type of MoS2-based coating co-doped with Cu and Al prepared by magnetron sputtering, including Cu/MoS2 and Cu-Al/MoS2 coatings, for lubrication
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The increasing demands of environmental protection have led to solid lubricant coatings becoming more and more important. A new type of MoS2-based coating co-doped with Cu and Al prepared by magnetron sputtering, including Cu/MoS2 and Cu-Al/MoS2 coatings, for lubrication applications is reported. To this end, the coatings were annealed in an argon atmosphere furnace. The microstructure and the tribological properties of the coatings prior to and following annealing were analyzed using scanning electron microscopy, energy dispersive spectrometry, X-ray diffractometry (XRD) and with a multi-functional tester for material surface properties. The results demonstrated that the friction coefficient of the Cu/MoS2 coating was able to reach as low as 0.07, due to the synergistic lubrication effect of the soft metal Cu with MoS2. However, the wear resistance of the coating was not satisfied. Although the lowest friction coefficient of the Cu-Al/MoS2 coatings was 0.083, the wear resistance was enhanced, which was attributed to the improved the toughness of the coatings due to the introduction of aluminum. The XRD results revealed that the γ2-Cu9Al4 phase was formed in the specimen of Cu-Al/MoS2 coatings. The comprehensive performance of the Cu-Al/MoS2 coatings after annealing was improved in comparison to substrate heating, since the heat-treatment was beneficial for the strengthening of the solid solution of the coatings. Full article
(This article belongs to the Special Issue Coatings Tribology)
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Open AccessArticle Physicochemical and Biological Activity Analysis of Low-Density Polyethylene Substrate Modified by Multi-Layer Coatings Based on DLC Structures, Obtained Using RF CVD Method
Coatings 2018, 8(4), 135; https://doi.org/10.3390/coatings8040135
Received: 6 March 2018 / Revised: 31 March 2018 / Accepted: 5 April 2018 / Published: 10 April 2018
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Abstract
In this paper, the surface properties and selected mechanical and biological properties of various multi-layer systems based on diamond-like carbon structure deposited on low-density polyethylene (LDPE) substrate were studied. Plasma etching and layers deposition (incl. DLC, N-DLC, Si-DLC) were carried out using the
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In this paper, the surface properties and selected mechanical and biological properties of various multi-layer systems based on diamond-like carbon structure deposited on low-density polyethylene (LDPE) substrate were studied. Plasma etching and layers deposition (incl. DLC, N-DLC, Si-DLC) were carried out using the RF CVD (radio frequency chemical vapor deposition) method. In particular, polyethylene with deposited N-DLC and DLC layers in one process was characterized by a surface hardness ca. seven times (up to ca. 2.3 GPa) higher than the unmodified substrate. Additionally, its surface roughness was determined to be almost two times higher than the respective plasma-untreated polymer. It is noteworthy that plasma-modified LDPE showed no significant cytotoxicity in vitro. Thus, based on the current research results, it is concluded that a multilayer system (based on DLC coatings) obtained using plasma treatment of the LDPE surface can be proposed as a prospective solution for improving mechanical properties while maintaining biocompatibility. Full article
(This article belongs to the Special Issue Functional Ceramic Coatings)
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Open AccessFeature PaperArticle Sharply Reduced Biofilm Formation from Cobetia marina and in Black Sea Water on Modified Siloxane Coatings
Coatings 2018, 8(4), 136; https://doi.org/10.3390/coatings8040136
Received: 6 February 2018 / Revised: 2 April 2018 / Accepted: 5 April 2018 / Published: 11 April 2018
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Abstract
Siloxane fouling release coatings are currently the only viable non-toxic commercial alternative to toxic biocide antifouling paints. However, they only partially inhibit biofouling since biofilms remain a major issue. With the aim to improve the bacterial resistance of siloxane coatings modified with non-ionic
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Siloxane fouling release coatings are currently the only viable non-toxic commercial alternative to toxic biocide antifouling paints. However, they only partially inhibit biofouling since biofilms remain a major issue. With the aim to improve the bacterial resistance of siloxane coatings modified with non-ionic surfactant (NIS), antioxidant (AO) or both NIS/AO, the ability of PEG-silane co-cross-linker was investigated to reduce Cobetia marina adhesion and multispecies biofilm formation from natural seawater. Surface physical-chemical and physical-mechanical parameters relevant to bio-adhesion were estimated before the testing of the biofilm formation. Slightly reduced biofilm from C. marina and sharply reduced multispecies biofilm, formed in natural sea water, were found on the PEG-silane co-cross-linked coatings without modifying additives. However, both C. marina growth and biofilm formation from natural sea water were sharply reduced on the PEG-silane co-cross-linked coatings containing NIS or AO, even more, no C. marina adhesion was seen on the coating containing NIS and AO simultaneously. Possible explanations of the observed effects are presented in this article. It was concluded that the PEG-silane co-cross-linker, toghether with NIS and AO, can be used as an efficient tool to additionally reduce the bioadhesion of Gram-negative marine bacteria and multispecies biofilm formation on siloxane antifouling coatings. Full article
(This article belongs to the Special Issue Novel Marine Antifouling Coatings)
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Open AccessFeature PaperArticle Lanthanum-Silica Sol-Gel Coatings for Protecting Metallic Materials in Museums: Approaches to Copper, Bronze, Lead and Steel
Coatings 2018, 8(4), 138; https://doi.org/10.3390/coatings8040138
Received: 9 February 2018 / Revised: 9 April 2018 / Accepted: 10 April 2018 / Published: 12 April 2018
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Abstract
Museum objects made from metals face the challenge of delaying corrosion in exhibition rooms, showcases and holdings. This study examined some innovative solutions used to protect such items based on sol-gel coatings doped with lanthanum. These coatings were prepared from sols based on
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Museum objects made from metals face the challenge of delaying corrosion in exhibition rooms, showcases and holdings. This study examined some innovative solutions used to protect such items based on sol-gel coatings doped with lanthanum. These coatings were prepared from sols based on TEOS as a precursor. Lanthanum acetate/nitrate was added as a doping agent and corrosion inhibitor. The coatings were deposited upon slabs of copper, bronze, lead and steel, since they are among the most common metals present in museums items. The coatings application was accomplished by immersion-extraction, and the remaining sols were gelled and characterized by Fourier transformed infrared spectroscopy and differential thermal analysis and thermogravimetry. To evaluate the behaviour and resistance of the coatings, tests of accelerated aging were carried out in climatic and Kesternich chambers, as well as under an atmosphere saturated with organic acids and under UV irradiation. The simulated conditions tested were undertaken to approach real conditions inside a conventional museum showcase. The microstructure of the coatings before and after accelerated aging tests was observed through optical and field emission scanning electron microscopies. The results indicated that these coatings can be a useful preventive, conservation avenue to protect copper, bronze and lead items exhibited in museums. Full article
(This article belongs to the Special Issue Communications from TechnoHeritage 2017)
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Open AccessArticle Effect of Reaction Conditions on the Surface Modification of Cellulose Nanofibrils with Aminopropyl Triethoxysilane
Coatings 2018, 8(4), 139; https://doi.org/10.3390/coatings8040139
Received: 7 March 2018 / Revised: 9 April 2018 / Accepted: 11 April 2018 / Published: 13 April 2018
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Abstract
Nine different surface modifications of cellulose nanofibrils (CNF) with 3-aminopropyl triethoxysilane (ATS) by using three different solvent systems (water, ethanol, and a mixture of both) were investigated. The effect of reaction conditions, such as silane to cellulose ratio and solvent type were evaluated
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Nine different surface modifications of cellulose nanofibrils (CNF) with 3-aminopropyl triethoxysilane (ATS) by using three different solvent systems (water, ethanol, and a mixture of both) were investigated. The effect of reaction conditions, such as silane to cellulose ratio and solvent type were evaluated to determine their contribution to the extent of the silane modification. Nanofibril properties were evaluated by infrared spectroscopy, powder X-ray diffraction, surface free energy, thermogravimetry, 13C and 29Si nuclear magnetic resonance, and electronic microscopy. The influence of the solvent in the solvolysis of the silane was reflected in the presence or absence of ethoxy groups in the silane. On the other hand, whereas the surface modification was increased directly proportionally to silane ratio on the reaction, the aggregation of nanofibrils was also increased, which can play a negative role in certain applications. The increment of silane modification also had substantial repercussions on the crystallinity of the nanofibrils by the addition of amorphous components to the crystalline unit; moreover, silane surface modifications enhanced the hydrophobic character of the nanofibrils. Full article
(This article belongs to the Special Issue Surface Modification of Cellulose Fibres)
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Open AccessArticle Microstructure Evolution of a Magnesium Phosphate Protective Layer on Concrete Structures in a Sulfate Environment
Coatings 2018, 8(4), 140; https://doi.org/10.3390/coatings8040140
Received: 6 February 2018 / Revised: 2 April 2018 / Accepted: 2 April 2018 / Published: 14 April 2018
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Abstract
This study investigates the resistance of an uncoated magnesium phosphate cement (MPC) protective layer to sulfate attacks through changes in its compressive strength and appearance. X-ray Diffraction (XRD) and scanning electron microscopy (SEM) microanalyses are conducted on the MPC layer concrete both before
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This study investigates the resistance of an uncoated magnesium phosphate cement (MPC) protective layer to sulfate attacks through changes in its compressive strength and appearance. X-ray Diffraction (XRD) and scanning electron microscopy (SEM) microanalyses are conducted on the MPC layer concrete both before and after etching, where changes in the microstructure of the magnesium phosphate protective layer are analyzed during the corrosion process. In addition, this study also explores the intrinsic mechanisms of the MPC protective layer in terms of the resistance of concrete to sulfate. The results showed that the erosion resistance of the concrete to sulfate can be dramatically improved by the MPC protective layer. The structure and composition of the MPC protective layer are different in the sulfate erosion environment compared with those exposed to other environments: the protective layer is more closely bonded to the concrete and has a more compact structure. Therefore, the MPC protective layer is verified to have a significant protective effect on concrete against sulfate corrosion. Full article
(This article belongs to the Special Issue Advanced Coatings for Corrosion Protection in Extreme Environments)
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Open AccessArticle Self-Assembled Composite Langmuir Films via Fluorine-Containing Bola-Type Derivative with Metal Ions
Coatings 2018, 8(4), 141; https://doi.org/10.3390/coatings8040141
Received: 17 January 2018 / Revised: 30 March 2018 / Accepted: 12 April 2018 / Published: 14 April 2018
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Abstract
The design and preparation of functional bolaamphiphile-based composite films are of key importance for application in a wide variety of fields. This study demonstrates a new approach to constructing composite films by the Langmuir-Blodgett (LB) method using a fluorine-containing bola-type diacid derivative with
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The design and preparation of functional bolaamphiphile-based composite films are of key importance for application in a wide variety of fields. This study demonstrates a new approach to constructing composite films by the Langmuir-Blodgett (LB) method using a fluorine-containing bola-type diacid derivative with different metal ions. The bola-type molecule we used could be spread on water surfaces and metal ion subphases to fabricate various nanostructured ultrathin films. The obtained data demonstrated that the employed metal ions, including Ag(I), Cu(II), and Eu(III) ions in subphase solutions, can regulate the organized molecular stacking and form interfacial nanostructures deposited in LB films. It was found that the interfacial coordinating interactions can easily occur between carboxyl groups in a molecular skeleton with metal ions in the formed composite films. The formation of composite films was confirmed by changes in the surface pressure-area isotherms, morphologies, and spectra of the transferred LB films. While various research works have achieved the regulation of functions and nanostructures of sophisticated bola-type compounds, we here demonstrate a simple routine to modulate the nanostructures and organized packing of bola-type compounds composite films by changing the metal ions in subphase solutions. Full article
(This article belongs to the Special Issue Nanostructured Thin Films)
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Open AccessArticle Efficiently Extracted Cellulose Nanocrystals and Starch Nanoparticles and Techno-Functional Properties of Films Made Thereof
Coatings 2018, 8(4), 142; https://doi.org/10.3390/coatings8040142
Received: 2 March 2018 / Revised: 6 April 2018 / Accepted: 12 April 2018 / Published: 14 April 2018
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Abstract
Cellulose nanocrystals (CNC) and starch nanoparticles (SNP) have remarkable physical and mechanical characteristics. These properties particularly facilitate their application as high-performance components of bio-based packaging films as alternatives to fossil-based counterparts. This study demonstrates a time-efficient and resource-saving extraction process of CNC and
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Cellulose nanocrystals (CNC) and starch nanoparticles (SNP) have remarkable physical and mechanical characteristics. These properties particularly facilitate their application as high-performance components of bio-based packaging films as alternatives to fossil-based counterparts. This study demonstrates a time-efficient and resource-saving extraction process of CNC and SNP by sulfuric acid hydrolysis and neutralization. The yields of the hydrolyzed products were 41.4% (CNC) and 32.2% (SNP) after hydrolysis times of 3 h and 120 h, respectively. The nanoparticle dispersions were wet-coated onto poly(lactic acid) (PLA) and paper substrates and were incorporated into starch films. No purification or functionalization of the nanoparticles was performed prior to their application. Techno-functional properties such as the permeability of oxygen and water vapor were determined. The oxygen permeability of 5–9 cm3 (STP) 100 µm m−2 d−1 bar−1 at 50% relative humidity and 23 °C on PLA makes the coatings suitable as oxygen barriers. The method used for the extraction of CNC and SNP contributes to the economic production of these nanomaterials. Further improvements, e.g., lower ion concentration and narrower particle size distribution, to achieve reproducible techno-functional properties are tangible. Full article
(This article belongs to the Special Issue Barrier Films and Coatings for Advanced Packaging)
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Open AccessArticle Evaluation of Thermal Degradation of DLC Film Using a Novel Raman Spectroscopy Technique
Coatings 2018, 8(4), 143; https://doi.org/10.3390/coatings8040143
Received: 5 March 2018 / Revised: 28 March 2018 / Accepted: 4 April 2018 / Published: 16 April 2018
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Abstract
Diamond-like carbon (DLC) films are extensively used in various industries due to their superior protective and lubrication properties. However, DLC films including sp2 and sp3 carbon bonding are metastable materials, which can be thermally degraded (or graphitized) at elevated temperature. In
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Diamond-like carbon (DLC) films are extensively used in various industries due to their superior protective and lubrication properties. However, DLC films including sp2 and sp3 carbon bonding are metastable materials, which can be thermally degraded (or graphitized) at elevated temperature. In this study, a novel Raman spectroscopy technique was developed to evaluate the in-situ thermal stability of DLC films. When a laser beam is applied onto a DLC film, the surface temperature can increase depending on the laser power, laser duration time, and surface reflectivity. Based on this laser heating concept, the Raman spectrum data of DLC films (i.e., G peak position and width) were obtained at the controlled Raman laser power, which enabled to determine the critical temperature to initiate the thermal degradation of DLC films. Two different designs of DLC film (i.e., types A and B with different initial sp2-to-sp3 ratio) were prepared and their thermal stability was evaluated using the proposed Raman spectroscopy technique. From the systematic data analysis and comparison, it could be observed that the type-A DLC film showed the significant change of Raman parameters (i.e., G peak position and width) at lower laser power value (=lower temperature) than the type-B DLC film, which indicated that the type-B DLC film had better thermal stability. Full article
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Open AccessArticle Fabrication of Self-healing Superhydrophobic Surfaces from Water-Soluble Polymer Suspensions Free of Inorganic Particles through Polymer Thermal Reconstruction
Coatings 2018, 8(4), 144; https://doi.org/10.3390/coatings8040144
Received: 11 March 2018 / Revised: 4 April 2018 / Accepted: 11 April 2018 / Published: 16 April 2018
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Abstract
Self-healing superhydrophobic surfaces have been fabricated by casting and drying water-soluble amphiphilic polymer suspensions at room temperature through thermal reconstruction. When compared with previous methods, this approach exploits modified natural hierarchical microstructures from wood instead of artificially constructing them for superhydrophobic morphology, which
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Self-healing superhydrophobic surfaces have been fabricated by casting and drying water-soluble amphiphilic polymer suspensions at room temperature through thermal reconstruction. When compared with previous methods, this approach exploits modified natural hierarchical microstructures from wood instead of artificially constructing them for superhydrophobic morphology, which involves neither organic solvent nor inorganic particles nor complex procedures. The obtained superhydrophobic surface has acceptable resistance to abrasion. The surface can recover superhydrophobicity spontaneously at room temperature upon damage, which can be accelerated at a higher temperature. After depleting healing agents, the polymer suspension can be sprayed or cast onto wood surfaces to replenish healing agents and to restore self-healing ability. The superhydrophobic surface greatly increases the mold inhibition and water resistance of wood, which would prolong the service life of wood based materials. Full article
(This article belongs to the Special Issue Superhydrophobic Coatings)
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Open AccessArticle Effects of Laser Microtexturing on the Wetting Behavior of Ti6Al4V Alloy
Coatings 2018, 8(4), 145; https://doi.org/10.3390/coatings8040145
Received: 20 March 2018 / Revised: 5 April 2018 / Accepted: 14 April 2018 / Published: 17 April 2018
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Abstract
Surface modification procedures by laser techniques allow the generation of specific topographies and microstructures that enable the adaptation of the external layers of materials for specific applications. In laser texturing processes, it is possible to maintain control over the microgeometry and dimensions of
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Surface modification procedures by laser techniques allow the generation of specific topographies and microstructures that enable the adaptation of the external layers of materials for specific applications. In laser texturing processes, it is possible to maintain control over the microgeometry and dimensions of the surface pattern through varying the processing parameters. One of the main areas of interest in the field of surface modification treatments is the ability to generate topographies that are associated with specific surface finishes, in terms of roughness, that can improve the manufactured part’s functional capabilities. In this aspect, several types of phenomena have been detected, such as the friction and sliding wear behavior or wetting capacity, which maintain a high dependence on surface roughness. In this research, surface texturing treatments have been developed by laser techniques through using the scanning speed of the beam (Vs) as a control parameter in order to generate samples that have topographies with different natures. Through assessments of surface finish using specialized techniques, the dimensional and geometrical features of the texturized tracks have been characterized, analyzing their influence on the wetting behavior of the irradiated layer. In this way, more defined texturing grooves has been developed by increasing the Vs, which also improves the hydrophobic characteristics of the treated surface. However, due to the lack of uniformity in the solidification process of the irradiated area, some deviations from the expected trends and singular points can be observed. Using the contact angle method to evaluate the wetting behavior of the applied treatments found increases in the contact angle values for high texturing speeds, finding a maximum value of 65.59° for Vs = 200 mm/s. Full article
(This article belongs to the Special Issue Laser Surface Treatment)
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Open AccessArticle Target Voltage Hysteresis Behavior and Control Point in the Preparation of Aluminum Oxide Thin Films by Medium Frequency Reactive Magnetron Sputtering
Coatings 2018, 8(4), 146; https://doi.org/10.3390/coatings8040146
Received: 16 March 2018 / Revised: 11 April 2018 / Accepted: 16 April 2018 / Published: 18 April 2018
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Abstract
Aluminum oxide thin films were prepared by medium frequency reactive magnetron sputtering. The target voltage hysteresis behavior under different argon partial pressure and target power conditions were studied. The results indicate that the target voltage hysteresis loop of aluminum oxide thin film preparation
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Aluminum oxide thin films were prepared by medium frequency reactive magnetron sputtering. The target voltage hysteresis behavior under different argon partial pressure and target power conditions were studied. The results indicate that the target voltage hysteresis loop of aluminum oxide thin film preparation has typical behavior of that for reactive sputtering deposition of compound films. The target voltage feedback control approach was applied to circumvent the hysteresis problem. The microstructure and chemical composition of the aluminum oxide thin films prepared at different target voltage control points were investigated by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy and Auger electron spectroscopy. The results indicated that the prepared aluminum oxide thin films, which are compact and mostly amorphous, can be obtained with target voltage control point in the range of 25~35%. Full article
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Open AccessArticle Hydrocolloid-Based Coatings are Effective at Reducing Acrylamide and Oil Content of French Fries
Coatings 2018, 8(4), 147; https://doi.org/10.3390/coatings8040147
Received: 6 March 2018 / Revised: 16 April 2018 / Accepted: 16 April 2018 / Published: 18 April 2018
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Abstract
French fries are popular products worldwide. However, this product is a sufferable source of high acrylamide due to high temperature and low moisture. The main objective of this study was to evaluate the effect of grass pea flour (GPF), transglutaminase (TGase)-treated (GPF +
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French fries are popular products worldwide. However, this product is a sufferable source of high acrylamide due to high temperature and low moisture. The main objective of this study was to evaluate the effect of grass pea flour (GPF), transglutaminase (TGase)-treated (GPF + TGase), chitosan (CH), and pectin (PEC) hydrocolloid coating solutions on the formation of acrylamide, water retention as well as on oil content. In addition, the Daily Intake (DI) and Margin of Exposure (MOE) were calculated to estimate variations in risk assessment by applying coating solutions before frying. Our results showed that the highest acrylamide content was detected in the control sample, reaching a value of 2089 µg kg−1. Hydrocolloid coating solutions were demonstrated to be an effective way to reduce acrylamide formation, with the percentage of acrylamide reduction equal to 48% for PEC, >38% for CH, ≥37% for GPF + TGase, and >31% for GPF, respectively. We hypothesized that the coatings were able to increase the water retention and, thus reduce the Maillard reaction, which is responsible for acrylamide formation. In fact, the MOE value for coated French fries was increase, resulting in being closer to the safety level to avoid carcinogenic risk. Moreover, our coatings were effective in reducing oil uptake. Full article
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Open AccessArticle One-Step Fabrication and Localized Electrochemical Characterization of Continuous Al-Alloyed Intermetallic Surface Layer on Magnesium Alloy
Coatings 2018, 8(4), 148; https://doi.org/10.3390/coatings8040148
Received: 2 March 2018 / Revised: 7 April 2018 / Accepted: 8 April 2018 / Published: 18 April 2018
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A continuous intermetallic compound coating was fabricated on AZ91D magnesium alloy via heat treatment at 400 °C in AlCl3-NaCl molten salts for 10 h. The microstructure and composition of the coating were characterized by scanning electron microscope and energy dispersive X-ray
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A continuous intermetallic compound coating was fabricated on AZ91D magnesium alloy via heat treatment at 400 °C in AlCl3-NaCl molten salts for 10 h. The microstructure and composition of the coating were characterized by scanning electron microscope and energy dispersive X-ray spectrometry. The results showed that the coating has a two-layer structure (the outer Mg2Al3 phase layer and the inner Mg17Al12 phase layer) up to 37 μm thick with compact and planar interfaces between the layers and the substrate. The corrosion property of the coating was investigated using electrochemical impedance spectroscopy (EIS) and two localized electrochemical techniques, i.e., localized electrochemical impedance spectroscopy (LEIS) and scanning vibrating electrode technique (SVET). The charge transfer resistance (Rct) of the Al-alloyed coating was 2119 Ω cm2. The localized impedance and current density maps obtained through LEIS and SVET indicate not only significantly improved corrosion resistance (the impedance modulus increased by one order of magnitude and the current density decreased to approximately 3.8%, compared with the substrate) but also defect-free surface condition. Full article
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Open AccessArticle Effects of Graphene-Oxide-Modified Coating on the Properties of Carbon-Fiber-Reinforced Polypropylene Composites
Coatings 2018, 8(4), 149; https://doi.org/10.3390/coatings8040149
Received: 27 March 2018 / Revised: 16 April 2018 / Accepted: 17 April 2018 / Published: 19 April 2018
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Abstract
Graphene oxide (GO) modified with ferrites (GO@Fe3O4) were studied to determine their effect on the interfacial properties of continuous carbon-fiber-reinforced thermoplastic composites. The GO@Fe3O4 were introduced by mixing them directly in an acrylic-styrene (AS) sizing emulsion
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Graphene oxide (GO) modified with ferrites (GO@Fe3O4) were studied to determine their effect on the interfacial properties of continuous carbon-fiber-reinforced thermoplastic composites. The GO@Fe3O4 were introduced by mixing them directly in an acrylic-styrene (AS) sizing emulsion suitable for the making of continuous carbon-fiber-reinforced thermoplastics and towpregs. A magnetic field was then generated during the online sizing using coils in order to change the morphology of the coating on the fiber. The effect on the obtained sizing quality and final properties of continuous carbon-fiber-reinforced thermoplastic composites was then studied. The results showed that the topography of the sized fibers was modified, showing a kind of “drag” effect and more than a 32% increase was obtained for interlaminar shear strength. Full article
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Open AccessArticle Effects of Annealing on Residual Stress in Ta2O5 Films Deposited by Dual Ion Beam Sputtering
Coatings 2018, 8(4), 150; https://doi.org/10.3390/coatings8040150
Received: 16 March 2018 / Revised: 16 April 2018 / Accepted: 16 April 2018 / Published: 20 April 2018
PDF Full-text (3579 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Optical coatings deposited by the dual ion beam sputtering (DIBS) method usually show high compressive stress, which results in severe wavefront deformation of optical elements. Annealing post-treatment has been widely used to control the residual stress of optical coatings. However, the effect of
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Optical coatings deposited by the dual ion beam sputtering (DIBS) method usually show high compressive stress, which results in severe wavefront deformation of optical elements. Annealing post-treatment has been widely used to control the residual stress of optical coatings. However, the effect of annealing on the stress of Ta2O5 films deposited by the IBS method has not been reported in detail. In this study, different thicknesses of Ta2O5 films were deposited by IBS and annealed at different temperatures from 473 to 973 K in air, and the effect of annealing on the stress of Ta2O5 films was investigated. The as-deposited Ta2O5 films deposited by IBS show high compressive stress, which are about 160 MPa. The compressive stress decreases linearly with the increasing temperature, and the wavefront deformation of Ta2O5 films increases linearly with film thickness (within 20 μm) at the same annealing temperature. When the temperature rises to 591 K, Ta2O5 films with zero-stress can be obtained. Ta2O5 films show tensile stress instead of compressive stress with further increasing annealing temperature, and the tensile stress increases with increasing temperature. Meanwhile, with the increasing annealing temperature, the refractive index of Ta2O5 film decreases, indicating the decreasing packing density. The atomic force microscope (AFM) test results show that surface roughness of Ta2O5 films slowly increases with the increasing of annealing temperature. Moreover, X-ray photoelectron spectroscopy (XPS) analysis shows that the Ta in Ta2O5 films can be further oxidized with increasing annealing temperature, namely, the absorption of Ta2O5 film can be reduced. X-ray diffraction (XRD) analysis shows that the annealing temperature should be below 923 K to maintain the amorphous structure of the Ta2O5 film. Full article
(This article belongs to the Special Issue Applications of Optical Thin Film Coatings)
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Open AccessArticle Anti-Icing Performance of Hydrophobic Silicone–Acrylate Resin Coatings on Wind Blades
Coatings 2018, 8(4), 151; https://doi.org/10.3390/coatings8040151
Received: 2 April 2018 / Revised: 15 April 2018 / Accepted: 19 April 2018 / Published: 23 April 2018
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Abstract
The icing of wind blades poses a serious threat to the operation of wind turbines. The application of superhydrophobic coatings on wind blades can serve as a potential anti-icing method. This study presents the findings of simulations of the icing environment of wind
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The icing of wind blades poses a serious threat to the operation of wind turbines. The application of superhydrophobic coatings on wind blades can serve as a potential anti-icing method. This study presents the findings of simulations of the icing environment of wind blades coated with hydrophobic silicone–acrylate resin in an artificial climate chamber. Artificial icing tests were performed on NACA7715 wind blades with four different silicone–acrylate resin coatings and on uncoated wind blades, with test performed at five different wind speeds and three different angles of attack. Results show that wind blade surfaces with higher hydrophobicity yield better anti-icing performance, and that the ice mass of the wind blades decreases with increasing wind speeds and angles of attack. In addition, variations in ice mass, shape, and distribution on different wind blades indicate that increased hydrophobicity can help limit the areas that are subject to freezing. Hydrophobicity can affect the air cavities of the ice deposited on the wind blades, and surfaces with increased hydrophobicity can lead to lower ice mass and less ice adhesion. In brief, surfaces with higher hydrophobicity demonstrate better anti-icing performance and benefit from active de-icing. Full article
(This article belongs to the Special Issue Superhydrophobic Coatings)
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Review

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Open AccessReview 2D Materials-Coated Plasmonic Structures for SERS Applications
Coatings 2018, 8(4), 137; https://doi.org/10.3390/coatings8040137
Received: 27 February 2018 / Revised: 3 April 2018 / Accepted: 10 April 2018 / Published: 12 April 2018
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Abstract
Two-dimensional (2D) materials, such as graphene and hexagonal boron nitride, are new kinds of materials that can serve as substrates for surface enhanced Raman spectroscopy (SERS). When combined with traditional metallic plasmonic structures, the hybrid 2D materials/metal SERS platform brings extra benefits, including
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Two-dimensional (2D) materials, such as graphene and hexagonal boron nitride, are new kinds of materials that can serve as substrates for surface enhanced Raman spectroscopy (SERS). When combined with traditional metallic plasmonic structures, the hybrid 2D materials/metal SERS platform brings extra benefits, including higher SERS enhancement factors, oxidation protection of the metal surface, and protection of molecules from photo-induced damages. This review paper gives an overview of recent progress in the 2D materials-coated plasmonic structure in SERS application, focusing on the fabrication of the hybrid 2D materials/metal SERS platform and its applications for Raman enhancement. Full article
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