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Coatings, Volume 9, Issue 2 (February 2019)

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Cover Story (view full-size image) The incorporation of SiC nanoparticles (NPs) into the zinc matrix is proposed as a way to improve [...] Read more.
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Open AccessArticle Comprehensive Study of Au Nano-Mesh as a Catalyst in the Fabrication of Silicon Nanowires Arrays by Metal-Assisted Chemical Etching
Coatings 2019, 9(2), 149; https://doi.org/10.3390/coatings9020149
Received: 5 December 2018 / Revised: 11 February 2019 / Accepted: 16 February 2019 / Published: 25 February 2019
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Abstract
Silicon nanowires (SiNWs) arrays have become one of low-dimensional structural nanomaterials for the preparation of high-performance optoelectronic devices with the advantages of highly efficient light trapping effect, carrier multiplication, and adjustable optical bandgap. The controlled growth of SiNWs determines their electrical and optical [...] Read more.
Silicon nanowires (SiNWs) arrays have become one of low-dimensional structural nanomaterials for the preparation of high-performance optoelectronic devices with the advantages of highly efficient light trapping effect, carrier multiplication, and adjustable optical bandgap. The controlled growth of SiNWs determines their electrical and optical properties. The morphology of silicon nanowires fabricated by conventional metal-assisted chemical etching (MACE) involving the Ag-based etching process cannot be precisely controlled. Ultra-thin anodic aluminum oxide (AAO) is one of the new-pattern nanostructure assembly systems for the synthesis of nanomaterials. The synthesized nanostructure arrays can be tuned to exhibit different optical and electrical properties in a certain wavelength range by adjusting the AAO membrane parameters. In this paper, we demonstrate an ultra-thin Au nano-meshes array from a single hexagonal AAO membrane as a replication master instead of conventional Ag particles as etching catalyst. The extended ordered silicon nanowires arrays are fabricated by the selective chemical dissolution of nanoscale noble metal meshes that exhibit excellent anti-reflection performance in broadband wavelengths and a wide incidence angle. Full article
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Open AccessArticle Synthesis and Properties of Electrodeposited Ni–Co/WS2 Nanocomposite Coatings
Coatings 2019, 9(2), 148; https://doi.org/10.3390/coatings9020148
Received: 17 January 2019 / Revised: 11 February 2019 / Accepted: 13 February 2019 / Published: 25 February 2019
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Abstract
Ni–Co coatings have gained widespread attention due to their potential in replacing hard chromium deposits (which have traditionally utilized toxic and corrosive chromic acid baths). A major challenge is to lower the high coefficient of friction of coated surfaces against steel, under dry [...] Read more.
Ni–Co coatings have gained widespread attention due to their potential in replacing hard chromium deposits (which have traditionally utilized toxic and corrosive chromic acid baths). A major challenge is to lower the high coefficient of friction of coated surfaces against steel, under dry sliding conditions. In this research, low friction Ni–Co/WS2 nanocomposite coatings have been prepared by a convenient, one-pot electrodeposition from aqueous Ni–Co plating baths containing WS2 particles. The embedment of the WS2 lubricants is found to reduce the friction coefficient of coating significantly, and an ultra-low friction coefficient of 0.16 is obtained for the coating having a WS2 content of 7.1 wt.%. Morphology and composition characterization of wear tracks reveal that the formation of a WS2-rich lubricating tribofilm on the contact surfaces is beneficial to a low friction coefficient and good oxidation resistance. The wettability of electrodeposited coatings was also investigated. Compared to pure Ni-Co coating, the Ni–Co/7.1 wt.% WS2 coating has an excellent hydrophobicity with a high water contact angle (WCA) of 157°, due to a rough surface with dual scale protrusions and the low surface energy of WS2. Full article
(This article belongs to the Special Issue Superhydrophobic Coatings for Corrosion and Tribology)
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Open AccessArticle Manufacturing of Double Layer Optical Fiber Coating Using Phan-Thien-Tanner Fluid as Coating Material
Coatings 2019, 9(2), 147; https://doi.org/10.3390/coatings9020147
Received: 9 November 2018 / Revised: 10 January 2019 / Accepted: 14 January 2019 / Published: 24 February 2019
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Abstract
Modern optical fiber required a double-layer resin coating on the glass fiber to provide protection from signal attenuation and mechanical damage. The most important plastics resin used in coating of fiber optics are plasticized polyvinyle (PVC), low/high density polyethylene (LDPE/HDPE), nylon, and polysulfone. [...] Read more.
Modern optical fiber required a double-layer resin coating on the glass fiber to provide protection from signal attenuation and mechanical damage. The most important plastics resin used in coating of fiber optics are plasticized polyvinyle (PVC), low/high density polyethylene (LDPE/HDPE), nylon, and polysulfone. Polymer flow during optical fiber coating in a pressure type coating die has been simulated under non-isothermal conditions. The flow dependent on the wire or fiber velocity, geometry of the die, and the viscosity of the polymer. The wet-on-wet coating process is an efficient process for two-layer coating on the fiber optics. In the present study, the constitutive equation of polymer flow satisfies viscoelastic Phan-Thien-Tanner (PTT) fluid, is used to characterize rheology of the polymer melt. Based on the assumption of the fully developed incompressible and laminar flow, the viscoelastic fluid model of two-immiscible resins-layers modeled for simplified-geometry of capillary-annulus where the glass fiber drawing inside the die at high speed. The equation describing the flow of the polymer melt inside the die was solved, analytically and numerically, by the Runge-Kutta method. The effect of physical characteristics in the problem has been discussed in detail through graphs by assigning numerical values for several parameters of interest. It is observed that velocity increases with increasing values of ε D 1 2 , ε D 2 2 , X 1 , and X 2 . The volume flow rate increases with an increasing Deborah number. The thickness of coated fiber optic increases with increasing ε D 1 2 , ε D 2 2 , and δ . Increase in Brinkman number and Deborah number enhances the rate of heat transfer. It is our first attempt to model PTT fluid as a coating material for double-layer optical fiber coating using the wet-on-wet coating process. At the end, the present study is also compared with the published work as a particular case, and good agreement is found. Full article
(This article belongs to the Special Issue Recent Trends in Coatings and Thin Film–Modeling and Application)
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Open AccessArticle Analysis of Linear Non-Destructive Testing and Evaluation Methods for Thin-Walled Structure Inspection Using Ultrasonic Array
Coatings 2019, 9(2), 146; https://doi.org/10.3390/coatings9020146
Received: 20 January 2019 / Revised: 16 February 2019 / Accepted: 18 February 2019 / Published: 22 February 2019
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Abstract
The ultrasonic array used for thin-walled structure non-destructive inspection usually has a high central frequency so that the thickness-to-acoustic wavelength ratio is greater than 10. When the ratio is much smaller than 10, the reliability of the conventional ultrasonic array method will dramatically [...] Read more.
The ultrasonic array used for thin-walled structure non-destructive inspection usually has a high central frequency so that the thickness-to-acoustic wavelength ratio is greater than 10. When the ratio is much smaller than 10, the reliability of the conventional ultrasonic array method will dramatically decrease due to the influence of the acoustic near-field. This situation is unavoidable since the available central frequency of the array transducer cannot be an arbitrarily large value. To optimize the inspection performance in this case, the testing of an ultrasonic array and the evaluation of a structure whose thickness is smaller than five-times the longitudinal wavelength are analyzed in this paper. Linear ultrasonic array methods using different combinations of wave patterns, reflection times, and coupling conditions are uniformly expressed as full matrix algorithms. Simulated and experimental full matrices of 6 mm-thick aluminum plates using a 5-MHz array transducer are captured to analyze their imaging performances and sizing abilities with respect to various defects. Analyses show that the inspection results of the wedge coupling method have a much higher signal-to-noise ratio (SNR) than the results of conventional direct contact methods. Circular defects and rectangular defects can be distinguished by comparing the imaging results of different modes. For the simulated circular defect, the diameter can be measured according to the maximum image amplitude of the defect. To simulate a rectangular defect located in the lower half of the region, the nominal length can be measured using a linear function whose input is a −6 dB drop in length of the SS-S mode image. For a real sample, the material anisotropy and complex self-reflections will decrease the SNR by about 10 dB. Full article
(This article belongs to the Special Issue Advanced Nondestructive Evaluation and Characterization of Surface)
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Open AccessArticle Modification of Polyethylene by RF Plasma in Different/Mixture Gases
Coatings 2019, 9(2), 145; https://doi.org/10.3390/coatings9020145
Received: 21 January 2019 / Revised: 5 February 2019 / Accepted: 11 February 2019 / Published: 22 February 2019
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Abstract
Herein, low-density polyethylene (LDPE) films were treated using radio-frequency plasma discharge in the presence of air, nitrogen, oxygen, argon, and their mixtures to introduce new chemical functionalities. The surface properties of treated LDPE were qualitatively and quantitatively characterized using various analytical and microscopic [...] Read more.
Herein, low-density polyethylene (LDPE) films were treated using radio-frequency plasma discharge in the presence of air, nitrogen, oxygen, argon, and their mixtures to introduce new chemical functionalities. The surface properties of treated LDPE were qualitatively and quantitatively characterized using various analytical and microscopic techniques. It was found that the optimum plasma treatment for LDPE occurs in the presence of air plasma at an exposure time of 120 s and 80 W of nominal power. The plasma formed layer had tendency to increasing thickness with increasing treatment time up to 60 s using air and oxygen and even more with inert gases. An aging study of plasma-treated LDPE samples stored in ambient air or water medium revealed the partial hydrophobic recovery. Full article
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Open AccessArticle A Single-Ended Ultra-Thin Spherical Microbubble Based on the Improved Critical-State Pressure-Assisted Arc Discharge Method
Coatings 2019, 9(2), 144; https://doi.org/10.3390/coatings9020144
Received: 29 January 2019 / Revised: 17 February 2019 / Accepted: 19 February 2019 / Published: 22 February 2019
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Abstract
Hollow core microbubble structures are good candidates for the construction of high performance whispering gallery microresonator and Fabry-Perot (FP) interference devices. In the previous reports, most of interest was just focused on the dual-ended microbubble, but not single-ended microbubble, which could be used [...] Read more.
Hollow core microbubble structures are good candidates for the construction of high performance whispering gallery microresonator and Fabry-Perot (FP) interference devices. In the previous reports, most of interest was just focused on the dual-ended microbubble, but not single-ended microbubble, which could be used for tip sensing or other special areas. The thickness, symmetry and uniformity of the single-ended microbubble in previous reports were far from idealization. Thus, a new ultra-thin single-ended spherical microbubble based on the improved critical-state pressure-assisted arc discharge method was proposed and fabricated firstly in this paper, which was fabricated simply by using a commercial fusion splicer. The improvement to former paper was using weak discharge and releasing pressure gradually during the discharging process. Thus, the negative influence of gravity towards bubble deformation was decreased, and the fabricated microbubble structure had a thin, smooth and uniform surface. By changing the arc discharge parameters and the fiber position, the wall thicknesses of the fabricated microbubble could reach the level of 2 μm or less. The fiber Fabry-Perot (FP) interference technique was also used to analyze the deformation characteristic of microbubble under difference filling pressures. Finding the ends of the microbubbles had a trend of elongation with axial compression when the filling pressure was increasing. Its sensitivity to the inner pressure of microbubble samples was about ~556 nm/MPa, the bubble wall thickness was only of about 2 μm. Besides, a high whispering gallery mode (WGM) quality factor that up to 107 was realized by using this microbubble-based resonator. To explain the upper phenomenon, the microbubble was modeled and simulated with the ANSYS software. Results of this study could be useful for developing new single-ended whispering gallery mode micro-cavity structure, pressure sensors, etc. Full article
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Open AccessArticle The Effect of Texturing of the Surface of Concrete Substrate on the Pull-Off Strength of Epoxy Resin Coating
Coatings 2019, 9(2), 143; https://doi.org/10.3390/coatings9020143
Received: 30 November 2018 / Revised: 3 February 2019 / Accepted: 18 February 2019 / Published: 21 February 2019
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Abstract
This paper describes a study conducted to evaluate the effect of texturing of the surface of concrete substrate on the pull-off strength (fb) of epoxy resin coating. The paper investigates a total of seventeen types of textures: after grooving, imprinting, [...] Read more.
This paper describes a study conducted to evaluate the effect of texturing of the surface of concrete substrate on the pull-off strength (fb) of epoxy resin coating. The paper investigates a total of seventeen types of textures: after grooving, imprinting, patch grabbing and brushing. The texture of the surface of the concrete substrate was prepared during the first 15 min after pouring fresh concrete into molds. The epoxy resin coating was laid after 28 days on hardened concrete substrates. To investigate the pull-off strength of the epoxy resin coating to the concrete substrate, the pull-off method was used. The results were compared with the results obtained for a sample prepared by grinding, normative minimal pull-off strength values and the values declared by the manufacturer. During this study twelve out of fifteen tested samples achieved a pull-off strength higher than 1.50 MPa. It was found that one of the imprinting texturing methods was especially beneficial. Full article
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Open AccessErratum Erratum: Wang et al. Optimised Performance of Non-Dispersive Infrared Gas Sensors Using Multilayer Thin Film Bandpass Filters. Coatings 2018, 8, 472
Coatings 2019, 9(2), 142; https://doi.org/10.3390/coatings9020142
Received: 20 February 2019 / Accepted: 20 February 2019 / Published: 21 February 2019
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Abstract
The authors wish to modify the funding section as follows to this paper [...] Full article
Open AccessArticle Effects of Strontium-Hydroxyapatite Mediated Active Compounds from Hippocampus Kuda Bleeler (HKB) on Osteogenesis
Coatings 2019, 9(2), 141; https://doi.org/10.3390/coatings9020141
Received: 23 January 2019 / Revised: 15 February 2019 / Accepted: 18 February 2019 / Published: 21 February 2019
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Abstract
Porous hydroxyapatite as a drug carrier is very popular and has many clinical applications. However, traditional hydroxyapatite materials have limited osteogenic capacity. Therefore, the development of a new hydroxyapatite drug delivery system is essential for bone tissue engineering. In this study, the metal [...] Read more.
Porous hydroxyapatite as a drug carrier is very popular and has many clinical applications. However, traditional hydroxyapatite materials have limited osteogenic capacity. Therefore, the development of a new hydroxyapatite drug delivery system is essential for bone tissue engineering. In this study, the metal element Sr was used to replace Ca, and the SrHA microspheres were successfully prepared by hydrothermal reaction. Scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) were used to characterize SrHA (strontium-doped hydroxyapatite) microspheres obtained from hydrothermal reaction conditions. In addition, the drug utility was enhanced by loading the marine active compound 1-(5-bromo-2-hydroxy-4-methoxyphenyl)-ethanone (HKB). Furthermore, after co-culture with preosteoblasts, experiments indicated that HKB/SrHA composite microspheres had a more significant effect on the proliferation and differentiation of cells compared to pure SrHA. These HKB/SrHA composite microspheres may be applied to the drug delivery system of bone tissue repair. Full article
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Open AccessArticle Torsional Fretting Wear Behavior of PVD TiCN Coated CuNiAl Blade Bearing in Oil and Artificial Seawater
Coatings 2019, 9(2), 140; https://doi.org/10.3390/coatings9020140
Received: 23 January 2019 / Revised: 11 February 2019 / Accepted: 19 February 2019 / Published: 20 February 2019
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Abstract
The feasibility of alleviating torsional fretting wear of the blade bearing by preparing PVD TiCN coating was studied. The results show that the friction torque was highly influenced by the wear debris acting as the solid lubricant. The TiCN coating reduced the wear [...] Read more.
The feasibility of alleviating torsional fretting wear of the blade bearing by preparing PVD TiCN coating was studied. The results show that the friction torque was highly influenced by the wear debris acting as the solid lubricant. The TiCN coating reduced the wear volume by 97.6% and 62.3% in oil and artificial seawater, respectively, which was mainly due to an increase in surface hardness. In oil, the produced sulfates and phosphates prevent seizures between the friction pair and the worn surface was characterized by polishing wear. In artificial seawater, the wear mechanism was a combination of mechanical wear and corrosion wear. This study reveals that the TiCN coating is suitable for alleviation of fretting wear in the blade bearing. Full article
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Open AccessArticle Surface Modification on Cellulose Nanofibers by TiO2 Coating for Achieving High Capture Efficiency of Nanoparticles
Coatings 2019, 9(2), 139; https://doi.org/10.3390/coatings9020139
Received: 4 January 2019 / Revised: 6 February 2019 / Accepted: 18 February 2019 / Published: 20 February 2019
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Abstract
Cellulose nanofibers were modified by TiO2 gel layer (~25 nm in thickness) via hydrolysis reaction on the surface of the cellulose nanofibers. After the TiO2 coating, the surface charge of the nanofiber dramatically changed from negative to positive. A high efficiency [...] Read more.
Cellulose nanofibers were modified by TiO2 gel layer (~25 nm in thickness) via hydrolysis reaction on the surface of the cellulose nanofibers. After the TiO2 coating, the surface charge of the nanofiber dramatically changed from negative to positive. A high efficiency (~100%) of capturing negatively charged Au nanoparticles (5 nm) was successfully obtained by effectively utilizing the electrostatic interaction of surface charge between the TiO2-coated cellulose nanofibers and Au nanoparticles. Therefore, this technique of surface modification will be potentially used in improving filtration efficiency for membrane applications. Full article
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Open AccessArticle Effect of Different Types of Pores on Thermal Conductivity of YSZ Thermal Barrier Coatings
Coatings 2019, 9(2), 138; https://doi.org/10.3390/coatings9020138
Received: 23 January 2019 / Revised: 12 February 2019 / Accepted: 15 February 2019 / Published: 20 February 2019
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Abstract
Atmospheric plasma spray (APS) yttria-stabilized zirconia coatings have a complex microstructure with a variety of pores that significantly reduce the thermal conductivity. APS thermal barrier coatings (TBCs) with a similar monoclinic phase were prepared. The pore sizes and distributions of the coatings were [...] Read more.
Atmospheric plasma spray (APS) yttria-stabilized zirconia coatings have a complex microstructure with a variety of pores that significantly reduce the thermal conductivity. APS thermal barrier coatings (TBCs) with a similar monoclinic phase were prepared. The pore sizes and distributions of the coatings were obtained by scanning their cross-section via SEM; the scanned areas were over 1 mm × 2 mm and more than 23,000 pores for each coating were analyzed. Multiple linear regression was used to analyze the porosity data and then to determine the quantitative relationship between different types of pores and thermal conductivity. Results revealed that the different pores have different effects on decreasing the thermal conductivity. The small, vertical pores have the biggest effect, while the horizontal pores also play a significant role in decreasing the thermal conductivity. Full article
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Open AccessFeature PaperReview Transparent p-Type Semiconductors: Copper-Based Oxides and Oxychalcogenides
Coatings 2019, 9(2), 137; https://doi.org/10.3390/coatings9020137
Received: 31 January 2019 / Revised: 15 February 2019 / Accepted: 16 February 2019 / Published: 20 February 2019
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Abstract
While p-type transparent conducting materials (TCMs) are crucial for many optoelectronic applications, their performance is still not satisfactory. This has impeded the development of many devices such as photovoltaics, sensors, and transparent electronics. Among the various p-type TCMs proposed so far, Cu-based oxides [...] Read more.
While p-type transparent conducting materials (TCMs) are crucial for many optoelectronic applications, their performance is still not satisfactory. This has impeded the development of many devices such as photovoltaics, sensors, and transparent electronics. Among the various p-type TCMs proposed so far, Cu-based oxides and oxychalcogenides have demonstrated promising results in terms of their optical and electrical properties. Hence, they are the focus of this current review. Their basic material properties, including their crystal structures, conduction mechanisms, and electronic structures will be covered, as well as their device applications. Also, the development of performance enhancement strategies including doping/co-doping, annealing, and other innovative ways to improve conductivity will be discussed in detail. Full article
(This article belongs to the Special Issue Thin Films for Electronic Applications)
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Open AccessArticle The Properties of Zn-Doped AlSb Thin Films Prepared by Pulsed Laser Deposition
Coatings 2019, 9(2), 136; https://doi.org/10.3390/coatings9020136
Received: 24 December 2018 / Revised: 4 February 2019 / Accepted: 8 February 2019 / Published: 20 February 2019
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Abstract
Aluminum antimony (AlSb) is a promising photovoltaic material with a band gap of about 1.62 eV. However, AlSb is highly deliquescent and not stable, which has brought great difficulties to the applications. Based on the above situation, there are two purposes for preparing [...] Read more.
Aluminum antimony (AlSb) is a promising photovoltaic material with a band gap of about 1.62 eV. However, AlSb is highly deliquescent and not stable, which has brought great difficulties to the applications. Based on the above situation, there are two purposes for preparing our Zn-doped AlSb (AlSb:Zn) thin films: One is to make P-type AlSb and the other is to find a way to suppress the deliquescence of AlSb. The AlSb:Zn thin films were prepared on glass substrates at different substrate temperatures by using the pulsed laser deposition (PLD) method. The structural, surface morphological, optical, and electrical properties of AlSb:Zn films were investigated. The crystallization of AlSb:Zn thin films was enhanced and the electrical resistivity decreased as the substrate temperature increased. The scanning electron microscopy (SEM) images indicated that the grain sizes became bigger as the substrate temperatures increased. The Raman vibration mode AlSb:Zn films were located at ~107 and ~142 cm−1 and the intensity of Raman peaks was stronger at higher substrate temperatures. In the experiment, a reduced band gap (1.4 eV) of the AlSb:Zn thin film was observed compared to the undoped AlSb films, which were more suitable for thin-film solar cells. Zn doping could reduce the deliquescent speed of AlSb thin films. The fabricated heterojunction device showed the good rectification behavior, which indicated the PN junction formation. The obvious photovoltaic effect has been observed in an FTO/ZnS/AlSb:Zn/Au device. Full article
(This article belongs to the Special Issue Electrochromic Thin Films and Devices)
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Open AccessArticle Corrosiveness of Palm Biodiesel in Gray Cast Iron Coated by Thermoreactive Diffusion Vanadium Carbide (VC) Coating
Coatings 2019, 9(2), 135; https://doi.org/10.3390/coatings9020135
Received: 13 January 2019 / Revised: 11 February 2019 / Accepted: 18 February 2019 / Published: 20 February 2019
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Abstract
Palm biodiesel is a currently used biofuel, principally as an additive or substitute of diesel fuel in vehicular internal combustion engines. In the present work, vanadium carbide (VC) coatings were deposited on gray cast iron (GCI) using the thermoreactive diffusion process (TRD) to [...] Read more.
Palm biodiesel is a currently used biofuel, principally as an additive or substitute of diesel fuel in vehicular internal combustion engines. In the present work, vanadium carbide (VC) coatings were deposited on gray cast iron (GCI) using the thermoreactive diffusion process (TRD) to evaluate the corrosiveness of palm biodiesel and compare it with gray cast iron corrosion behavior. VC coated and uncoated gray cast iron samples were tested by immersion corrosion tests (291 K and 313 K), cyclic oxidation test (CO), and the electrochemical impedance spectrometry test (EIS). The corrosion test showed the reduction of the corrosion rate for the VC coating when compared to gray cast iron. EIS tests of coated samples showed higher values of polarization resistance when compared with uncoated gray cast iron samples. Results confirmed that while biodiesel was more corrosive than diesel on both coated and uncoated gray cast iron, the VC coating was efficient in protecting the substrate exposed to both fuels. Full article
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Open AccessArticle Argon Plasma Surface Modified Porcine Bone Substitute Improved Osteoblast-Like Cell Behavior
Coatings 2019, 9(2), 134; https://doi.org/10.3390/coatings9020134
Received: 14 December 2018 / Revised: 16 February 2019 / Accepted: 16 February 2019 / Published: 19 February 2019
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Low-temperature plasma-treated porcine grafts (PGPT) may be an effective means for treating demanding osseous defects and enhance our understanding of plasma-tissue engineering. We chemically characterized porcine grafts under low-temperature Argon plasma treatment (CAP) and evaluated their biocompatibility in-vitro. Our results showed that PGPT [...] Read more.
Low-temperature plasma-treated porcine grafts (PGPT) may be an effective means for treating demanding osseous defects and enhance our understanding of plasma-tissue engineering. We chemically characterized porcine grafts under low-temperature Argon plasma treatment (CAP) and evaluated their biocompatibility in-vitro. Our results showed that PGPT did not differ in roughness, dominant crystalline phases, absorption peaks corresponding to phosphate band peaks, or micro-meso pore size, compared to non-treated porcine grafts. The PGPT Ca/P ratio was 2.16; whereas the porcine control ratio was 2.04 (p < 0.05). PGPT’s [C 1s], [P 2p] and [Ca 2p] values were 24.3%, 5.6% and 11.0%, respectively, indicating that PGPT was an apatite without another crystalline phase. Cell viability and alkaline phosphatase assays revealed enhanced proliferation and osteoblastic differentiation for the cells cultivated in the PGPT media after 5 days (p < 0.05). The cells cultured in PGPT medium had higher bone sialoprotein and osteocalcin relative mRNA expression compared to cells cultured in non-treated porcine grafts (p < 0.05). CAP treatment of porcine particles did not modify the biomaterial’s surface and improved the proliferation and differentiation of osteoblast-like cells. Full article
(This article belongs to the Special Issue Surface Chemical Modification)
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Open AccessReview Ångström-Scale, Atomically Thin 2D Materials for Corrosion Mitigation and Passivation
Coatings 2019, 9(2), 133; https://doi.org/10.3390/coatings9020133
Received: 11 December 2018 / Revised: 11 February 2019 / Accepted: 11 February 2019 / Published: 19 February 2019
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Abstract
Metal deterioration via corrosion is a ubiquitous and persistent problem. Ångström-scale, atomically thin 2D materials are promising candidates for effective, robust, and economical corrosion passivation coatings due to their ultimate thinness and excellent mechanical and electrical properties. This review focuses on elucidating the [...] Read more.
Metal deterioration via corrosion is a ubiquitous and persistent problem. Ångström-scale, atomically thin 2D materials are promising candidates for effective, robust, and economical corrosion passivation coatings due to their ultimate thinness and excellent mechanical and electrical properties. This review focuses on elucidating the mechanism of 2D materials in corrosion mitigation and passivation related to their physicochemical properties and variations, such as defects, out-of-plane deformations, interfacial states, temporal and thickness variations, etc. In addition, this review discusses recent progress and developments of 2D material coatings for corrosion mitigation and passivation as well as the significant challenges to overcome in the future. Full article
(This article belongs to the Special Issue Corrosion Characterization and Surface Analysis of Metallic Materials)
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Open AccessArticle Method of Stabilizing Heavily Spalted Big Leaf Maple as a Decorative Coating Veneer Layer for Engineered Wood Flooring
Coatings 2019, 9(2), 132; https://doi.org/10.3390/coatings9020132
Received: 27 December 2018 / Revised: 28 January 2019 / Accepted: 13 February 2019 / Published: 19 February 2019
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Abstract
Spalted wood, wood colored by fungi, has been popular in woodcraft for centuries. Most spalted wood, however, is found in an advanced state of decay and cannot be utilized. This project describes the use of viscoelastic thermal compression (VTC) to investigate the potential [...] Read more.
Spalted wood, wood colored by fungi, has been popular in woodcraft for centuries. Most spalted wood, however, is found in an advanced state of decay and cannot be utilized. This project describes the use of viscoelastic thermal compression (VTC) to investigate the potential increase in spalted woods’ strength and stiffness, with the main objective of converting so-called “punky” wood into the top layer (veneer layer or “coating”) on commercial flooring. Spalted Acer macrophyllum logs were cut into veneers of size 7 mm × 7.8 cm × 25 cm and were then VTC-treated at 150 °C and 50 psi for 11.5 min. Statistical analysis on the mixed linear models showed significant increases for both the density and hardness of spalted wood (p < 0.0001). Density and Brinell hardness increased by 84% and 209%, respectively. FTIR analysis revealed that the wood polymers present in spalted wood were more susceptible to degradation imposed by the heat of the VTC treatment compared to sound wood. Additionally, the color analysis of the wood specimens showed statistically significant changes in color after the VTC treatment (p < 0.0001), which turned the wood surface darker and redder. The use of the VTC technology to transform spalted wood into wood flooring is viable. However, when exposed to moisture, the VTC-treated spalted wood showed a high percentage of set recovery (78%), which was significantly different from the set recovery of the sound wood (71%, p = 0.004). Successful use of VTC-treated spalted wood for flooring will require addressing of the swelling issue, and additional studies are needed to fully characterize the anatomy of VTC-treated spalted wood. Full article
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Open AccessArticle Laser Surface Blasting of Granite Stones Using a Laser Scanning System
Coatings 2019, 9(2), 131; https://doi.org/10.3390/coatings9020131
Received: 3 December 2018 / Revised: 28 January 2019 / Accepted: 18 February 2019 / Published: 19 February 2019
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Abstract
Granite stones are the most abundant rock of the crust. Due to their beauty, durability, and virtually zero maintenance, they have been used widely since ancient times in all types of construction, as a structural or decorative element. Commonly, this material is used [...] Read more.
Granite stones are the most abundant rock of the crust. Due to their beauty, durability, and virtually zero maintenance, they have been used widely since ancient times in all types of construction, as a structural or decorative element. Commonly, this material is used with a polished finishing, but there has been an increased interest in giving it a rustic aspect, mainly for decorative or functional reasons, e.g., to reduce slipping. Rough surfaces are usually produced by means of bush hammering, but this is an extremely noisy and inefficient process. In this work we have explored the capabilities and limits of a laser blasting process assisted by a scanning system in order to produce precise and controllable roughness on two varieties of granite plates. It was found that laser blasting of thin granite tiles can be accomplished with processing widths up to 250 mm at medium-low laser power, obtaining a rustic aspect suitable for use in façades, paving, or flooring. Moreover, laser scanner systems are capable of enhancing the productivity of this process up to ten times greater than that found in previous works. Full article
(This article belongs to the Special Issue Surface Treatment by Laser-Assisted Techniques)
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Open AccessArticle Fabrication of Cu2ZnSnS4 Thin Films Based on Facile Nanocrystals-Printing Approach with Rapid Thermal Annealing (RTA) Process
Coatings 2019, 9(2), 130; https://doi.org/10.3390/coatings9020130
Received: 15 December 2018 / Revised: 1 February 2019 / Accepted: 13 February 2019 / Published: 19 February 2019
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Abstract
In the current study, Cu2ZnSnS4 (CZTS) thin film was successfully fabricated by the facile nanocrystals (NCs)-printing approach combined with rapid thermal annealing (RTA) process. Firstly, the CZTS NCs were synthesized by a thermal solution method and the possible formation mechanism [...] Read more.
In the current study, Cu2ZnSnS4 (CZTS) thin film was successfully fabricated by the facile nanocrystals (NCs)-printing approach combined with rapid thermal annealing (RTA) process. Firstly, the CZTS NCs were synthesized by a thermal solution method and the possible formation mechanism was analyzed briefly. Then the influences of RTA toleration temperature and duration time on the various properties of as-printed thin films were examined via XRD, Raman, FE-SEM, UV-vis-IR spectroscopy, EDS and XPS treatments in detail. As observed, the RTA factors of temperature and time had significant impacts on the structure and morphology of as-prepared thin films, while there were no obvious effects on the band gap energy in studied conditions. The results showed that the obtained thin film at optimal RTA conditions of (600 °C, 20 min) featured a kesterite structure in pure phase and an irregular morphology consisting of large grains. Moreover, the satisfactory composition of a Cu-poor, Zn-rich state and an ideal band gap energy of 1.4 eV suggests that as-fabricated CZTS thin film is a suitable light-absorbing layer candidate for the application in thin film solar cells. Full article
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Open AccessReview Research Status and Prospect of Friction Stir Processing Technology
Coatings 2019, 9(2), 129; https://doi.org/10.3390/coatings9020129
Received: 31 December 2018 / Revised: 10 February 2019 / Accepted: 16 February 2019 / Published: 19 February 2019
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Abstract
Friction stir processing (FSP) is a novel solid-phase processing technique that is derived from friction stir welding (FSW). The microstructure of the base metal can be modified with the friction heat and stir function during processing. It can be used to fabricate surface [...] Read more.
Friction stir processing (FSP) is a novel solid-phase processing technique that is derived from friction stir welding (FSW). The microstructure of the base metal can be modified with the friction heat and stir function during processing. It can be used to fabricate surface composites and in situ composites by adding reinforced particles into the metal matrix via FSP. Friction stir processing can significantly improve the hardness, wear resistance, ductility, etc., while preventing defects caused by material melting. It is an ideal material processing technology and has good prospects in the field of superplastic materials and for the preparation of metal matrix composites. This paper reviews research developments into the principle, process, and applications of FSP technology as well as its future research directions and development prospects. Full article
(This article belongs to the Special Issue Recent Advances in Friction Stir Processed Coatings)
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Open AccessArticle A Deep Insight into the Electronic Properties of CIGS Modules with Monolithic Interconnects Based on 2D Simulations with TCAD
Coatings 2019, 9(2), 128; https://doi.org/10.3390/coatings9020128
Received: 30 January 2019 / Revised: 15 February 2019 / Accepted: 17 February 2019 / Published: 19 February 2019
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Abstract
The aim of this work is to provide an insight into the impact of the P1 shunt on the performance of ZnO/CdS/Cu(In,Ga)Se2/Mo modules with monolithic interconnects. The P1 scribe is a pattern that separates the back contact of two adjacent cells [...] Read more.
The aim of this work is to provide an insight into the impact of the P1 shunt on the performance of ZnO/CdS/Cu(In,Ga)Se2/Mo modules with monolithic interconnects. The P1 scribe is a pattern that separates the back contact of two adjacent cells and is filled with Cu(In,Ga)Se2 (CIGS). This scribe introduces a shunt that can affect significantly the behavior of the device, especially under weak light conditions. Based on 2D numerical simulations performed with TCAD, we postulate a mechanism that affects the current flow through the P1 shunt. This mechanism is similar to that of a junction field effect transistor device with a p-type channel, in which the current flow can be modulated by varying the thickness of the channel and the doping concentration. The results of these simulations suggest that expanding the space charge region (SCR) into P1 reduces the shunt conductance in this path significantly, thus decreasing the current flow through it. The presented simulations demonstrate that two fabrication parameters have a direct influence on the extension of the SCR, which are the thickness of the absorber layer and its acceptor concentration. Full article
(This article belongs to the Special Issue Advanced Thin Film Materials for Photovoltaic Applications)
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Open AccessArticle Tridoped TiO2 Composite Films for Improved Photocatalytic Activities
Coatings 2019, 9(2), 127; https://doi.org/10.3390/coatings9020127
Received: 27 December 2018 / Revised: 10 February 2019 / Accepted: 13 February 2019 / Published: 19 February 2019
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Abstract
The Fe/B/F tridoped TiO2-ZnO composite films attached to glass substrates were prepared via a simple sol–gel method. We appraised all samples’ photocatalytic activities by the degradation of methyl green and formaldehyde solutions. The samples were characterized by photoluminescence (PL) spectra, UV-Vis [...] Read more.
The Fe/B/F tridoped TiO2-ZnO composite films attached to glass substrates were prepared via a simple sol–gel method. We appraised all samples’ photocatalytic activities by the degradation of methyl green and formaldehyde solutions. The samples were characterized by photoluminescence (PL) spectra, UV-Vis diffraction reflectance absorption spectra (DRS), X-ray diffraction (XRD), differential thermal analysis-thermogravimetry (DTA-TG), field emission scanning electron microscopy (FE-SEM) equipped with energy-dispersive spectroscopy (EDS), and Brunner–Emmet–Teller (BET) measurements. According to the results of DRS and PL spectroscopy, the multi-modification could not only enhance visible light absorption intensity, but also decrease the recombination rate of photo-generated electron-hole pairs. XRD results revealed that the sample was mainly in anatase crystal type. FE-SEM results shown that the sample had fewer particle aggregates and almost no cracks. The specific surface area of the Fe/B/F tridoped TiO2-ZnO was 104.9 m2·g−1, while that of the pure TiO2 was 84.0 m2·g−1. Compared to pure TiO2 and TiO2-ZnO, the Fe/B/F tridoped TiO2-ZnO composite film had the highest photocatalytic activity due to their synergies. Full article
(This article belongs to the Special Issue Photocatalytic Thin Films)
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Open AccessFeature PaperArticle Technical and Economic Criteria to Select Pavement Surfaces of Port Handling Plants
Coatings 2019, 9(2), 126; https://doi.org/10.3390/coatings9020126
Received: 31 December 2018 / Revised: 12 February 2019 / Accepted: 14 February 2019 / Published: 18 February 2019
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Abstract
A port is an intermodal system in which many logistics activities requiring properly constructed areas occur. The large extension of these areas poses a major problem in choosing materials with technical and economic implications. Choice and design of pavements are directly related to [...] Read more.
A port is an intermodal system in which many logistics activities requiring properly constructed areas occur. The large extension of these areas poses a major problem in choosing materials with technical and economic implications. Choice and design of pavements are directly related to the port handling systems and procedures for the disposal of the cargo units. The paper presents the design and verification procedures for three equivalent pavements for a handling pavement in an Italian medium-sized port trafficked by reach stackers moving containers. An asphalt pavement, a concrete pavement, and a concrete block pavement have been considered during the 20-year service life. Empirical and analytical methods have been adopted to design and verify the pavements. The structures have been examined in terms of economic concerns during the overall service life, considering both construction and maintenance costs, in order to determine the most cost-effective option. The results demonstrate the inappropriateness of asphalt pavement, in the examined case, from a construction costs point of view. Furthermore, the overall discounted costs show an inversion of convenience between block concrete pavement and cast in situ concrete: the latter is the cheaper solution. The proposed methodology can balance often conflicting objectives in matters of durability and funds management, providing answers to a complex topic. Full article
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Open AccessArticle Surface Structuring of Diamond-Like Carbon Films by Chemical Etching of Zinc Inclusions
Coatings 2019, 9(2), 125; https://doi.org/10.3390/coatings9020125
Received: 31 December 2018 / Revised: 14 February 2019 / Accepted: 15 February 2019 / Published: 18 February 2019
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Abstract
A diamond-like carbon (DLC) film with a nanostructured surface can be produced in a two-step process. At first, a metal-containing DLC film is deposited. Here, the combination of plasma source ion implantation using a hydrocarbon gas and magnetron sputtering of a zinc target [...] Read more.
A diamond-like carbon (DLC) film with a nanostructured surface can be produced in a two-step process. At first, a metal-containing DLC film is deposited. Here, the combination of plasma source ion implantation using a hydrocarbon gas and magnetron sputtering of a zinc target was used. Next, the metal particles within the surface are dissolved by an etchant (HNO3:H2O solution in this case). Since Zn particles in the surface of Zn-DLC films have a diameter of 100–200 nm, the resulting surface structures possess the same dimensions, thus covering a range that is accessible neither by mask deposition techniques nor by etching of other metal-containing DLC films, such as Cu-DLC. The surface morphology of the etched Zn-DLC films depends on the initial metal content of the film. With a low zinc concentration of about 10 at.%, separate holes are produced within the surface. Higher zinc concentrations (40 at.% or above) lead to a surface with an intrinsic roughness. Full article
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Open AccessArticle Coating Sand with New Hydrophobic and Superhydrophobic Silica/Paraffin Wax Nanocapsules for Desert Water Storage and Transportation
Coatings 2019, 9(2), 124; https://doi.org/10.3390/coatings9020124
Received: 6 January 2019 / Revised: 30 January 2019 / Accepted: 13 February 2019 / Published: 17 February 2019
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Abstract
Paraffin wax emulsions have gained immense attention as a cheap, environment-friendly, and aroma-free material for preparing superhydrophobic coatings. In this work, paraffin wax (PWs) capsules consisting of hydrophobic silica nanoparticles were used for coating desert sand. Different types of the hydrophobic silica nanoparticles, [...] Read more.
Paraffin wax emulsions have gained immense attention as a cheap, environment-friendly, and aroma-free material for preparing superhydrophobic coatings. In this work, paraffin wax (PWs) capsules consisting of hydrophobic silica nanoparticles were used for coating desert sand. Different types of the hydrophobic silica nanoparticles, modified with new oleylamino- and oleylamide silane precursors, were prepared in the presence and absence of paraffin waxes. The particle sizes, surface charges, thermal stability, surface morphologies, and wetting characteristics of these nanoparticles were investigated. The combination of these superhydrophobic silica nanoparticles and desert sand, showed excellent water repellency; stable water droplets remained on the sand surface, without any wetting or permeation. Furthermore, the mixing of the superhydrophobic sand with untreated sand (mixing ratio 1:10 wt %), with a thickness of 2 cm, sustained a great water-holding capacity with a water column height of 35 cm. The good thermal stability of the PWs capsules containing hydrophobic silica nanoparticles, along with their good water-holding capacity, make them potential candidates for developing superhydrophobic sand for desert water storage and transportation. Full article
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Open AccessArticle Functional Performance of Stone Mastic Asphalt Pavements in Spain: Acoustic Assessment
Coatings 2019, 9(2), 123; https://doi.org/10.3390/coatings9020123
Received: 18 January 2019 / Revised: 9 February 2019 / Accepted: 13 February 2019 / Published: 16 February 2019
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Abstract
Environmental noise is one of the problems modern societies face today. Traffic noise, especially the noise produced from tire/pavement interaction, plays a main role in environmental noise. Pavement rehabilitation with new bituminous mixtures is a good option for combatting noise pollution in urban [...] Read more.
Environmental noise is one of the problems modern societies face today. Traffic noise, especially the noise produced from tire/pavement interaction, plays a main role in environmental noise. Pavement rehabilitation with new bituminous mixtures is a good option for combatting noise pollution in urban areas. This paper studies the functional performance of two bituminous mixtures of stone mastic asphalt (SMA), fabricated with the same polymer modified binder, but with different maximum aggregate size (MAS) (SMA11 and SMA16). The acoustic absorption, the dynamic stiffness, the surface texture and the tire/pavement noise were assessed. The bituminous mixture type SMA16 has higher texture levels at nearly every depicted wavelength of the texture spectra. This characteristic may lead to its higher average tire/pavement sound level compared to the mixture SMA11. The influence of each texture wavelength on the different frequency bands of the tire/pavement noise spectrum was studied, however, this relation is not a simple matter. This paper also presents low-noise pavement labeling methodology (LNP labelingLA²IC). The mixtures SMA11 and SMA16 are labeled at 50 and 80 km/h. An acoustic label is a valuable tool for construction companies and urban planners to use in order to define the best option against noise when pavement rehabilitation must be carried out. Full article
(This article belongs to the Special Issue Pavement Surface Coatings)
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Open AccessArticle Modeling Self-Healing Mechanisms in Coatings: Approaches and Perspectives
Coatings 2019, 9(2), 122; https://doi.org/10.3390/coatings9020122
Received: 24 December 2018 / Revised: 1 February 2019 / Accepted: 8 February 2019 / Published: 15 February 2019
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Abstract
There is a wide range of self-healing mechanisms that provide the recovery of specific functionalities in coatings. Moreover, it is well known that computational simulation is a complementary tool that can help in the optimization and cost reduction of the experimental development of [...] Read more.
There is a wide range of self-healing mechanisms that provide the recovery of specific functionalities in coatings. Moreover, it is well known that computational simulation is a complementary tool that can help in the optimization and cost reduction of the experimental development of materials. This work critically discusses the current status of the models that are of interest for the advance of self-healing coatings, and proposes future paths of improvement. Full article
(This article belongs to the Special Issue Progress in Self-Healing Coatings)
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Open AccessArticle Evaluation of the Impacts of Four Weathering Methods on Two Acrylic Paints: Showcasing Distinctions and Particularities
Coatings 2019, 9(2), 121; https://doi.org/10.3390/coatings9020121
Received: 14 November 2018 / Revised: 25 January 2019 / Accepted: 30 January 2019 / Published: 15 February 2019
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Abstract
Two commercial waterborne wood acrylic paints were applied to wood samples and the weathering resistance of samples was tested using four different weathering methods: outdoor exposure in Arizona (USA), Florida (USA), and the province of Quebec (Canada), and accelerated weathering in a QUV [...] Read more.
Two commercial waterborne wood acrylic paints were applied to wood samples and the weathering resistance of samples was tested using four different weathering methods: outdoor exposure in Arizona (USA), Florida (USA), and the province of Quebec (Canada), and accelerated weathering in a QUV (fluorescent) weatherometer. Degradation was characterised by colorimetric and FTIR analyses. FTIR confirmed the importance of paint composition in the resistance of samples to weathering. Polymer sensitivity to UV radiation was clearly evident. An interpretation of discoloration in terms of either the energy received by the samples or the length of exposure is presented. Strong differences existed between the four weathering methods. Particularities of each method are discussed and recommendations regarding their application for effective testing are proposed. Overall, in addition to accelerated weathering tests, we conclude that it is necessary to test paints in an end-use environment for accurate assessment of their likely performance. This study confirms the multifactorial aspect of the weathering process. Full article
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Open AccessArticle Thermoelectric Properties of Thin Films of Germanium-Gold Alloy Obtained by Magnetron Sputtering
Coatings 2019, 9(2), 120; https://doi.org/10.3390/coatings9020120
Received: 3 December 2018 / Revised: 12 February 2019 / Accepted: 13 February 2019 / Published: 15 February 2019
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Abstract
In this paper, the electric and thermoelectric properties of thin films of germanium–gold alloy (Ge–Au) are discussed in terms of choosing the optimal deposition process and post-processing conditions to obtain Ge–Au layers with the best thermoelectric parameters. Thin films were fabricated by magnetron [...] Read more.
In this paper, the electric and thermoelectric properties of thin films of germanium–gold alloy (Ge–Au) are discussed in terms of choosing the optimal deposition process and post-processing conditions to obtain Ge–Au layers with the best thermoelectric parameters. Thin films were fabricated by magnetron sputtering using the Ge–Au alloy target onto glass substrates at two various conditions; during one of the sputtering processes, the external substrate bias voltage (Ub = −150 V) was used. After deposition thin films were annealed in the atmosphere of N2 at various temperatures (473, 523 and 573 K) to investigate the influence of annealing temperature on the electric and thermoelectric properties of films. Afterwards, the thermocouples were created by deposition of the NiCrSi/Ag contact pads onto Ge–Au films. In this work, particular attention has been paid to thermoelectric properties of fabricated thin films—the thermoelectric voltage, Seebeck coefficient, power factor PF and dimensionless figure of merit ZT were determined. Full article
(This article belongs to the Special Issue Novel Thin Film Materials for Thermoelectric Applications)
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