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Coatings, Volume 9, Issue 10 (October 2019)

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Open AccessArticle
Electrical and Structural Properties of All-Sputtered Al/SiO2/p-GaN MOS Schottky Diode
Coatings 2019, 9(10), 685; https://doi.org/10.3390/coatings9100685 (registering DOI) - 21 Oct 2019
Abstract
The all-sputtered Al/SiO2/p-GaN metal-oxide-semiconductor (MOS) Schottky diode was fabricated by the cost-effective radio-frequency sputtering technique with a cermet target at 400 °C. Using scanning electron microscope (SEM), the thicknesses of the electrodes, insulator SiO2 layer, and p-GaN [...] Read more.
The all-sputtered Al/SiO2/p-GaN metal-oxide-semiconductor (MOS) Schottky diode was fabricated by the cost-effective radio-frequency sputtering technique with a cermet target at 400 °C. Using scanning electron microscope (SEM), the thicknesses of the electrodes, insulator SiO2 layer, and p-GaN were found to be ~250 nm, 70 nm, and 1 µm, respectively. By Hall measurement of a p-Mg-GaN film on an SiO2/Si (100) substrate at room temperature, the hole’s concentration (Np) and carrier mobility (μ) were found to be Np = 4.32 × 1016 cm−3 and μ = 7.52 cm2·V−1·s−1, respectively. The atomic force microscope (AFM) results showed that the surface topography of the p-GaN film had smoother, smaller grains with a root-mean-square (rms) roughness of 3.27 nm. By I–V measurements at room temperature (RT), the electrical properties of the diode had a leakage current of ~4.49 × 10−8 A at −1 V, a breakdown voltage of −6 V, a turn-on voltage of ~2.1 V, and a Schottky barrier height (SBH) of 0.67 eV. By C–V measurement at RT, with a frequency range of 100–1000 KHz, the concentration of the diode’s hole increased from 3.92 × 1016 cm−3 at 100 kHz to 5.36 × 1016 cm−3 at 1 MHz, while the Fermi level decreased slightly from 0.109 to 0.099 eV. The SBH of the diode at RT in the C–V test was higher than in the I–V test because of the induced charges by dielectric layer. In addition, the ideality factor (n) and series resistance (Rs) determined by Cheung’s and Norde’s methods, other parameters for MOS diodes were also calculated by C–V measurement at different frequencies. Full article
(This article belongs to the Special Issue Advanced Strategies in Thin Film Engineering by Magnetron Sputtering)
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Open AccessArticle
Effect of Carbon Fiber Addition on the Microstructure and Wear Resistance of Laser Cladding Composite Coatings
Coatings 2019, 9(10), 684; https://doi.org/10.3390/coatings9100684 (registering DOI) - 20 Oct 2019
Viewed by 141
Abstract
In this study, the effect of carbon fibers (CFs) on the microstructure and wear resistance of Fe-based alloy coating produced by laser cladding was investigated by X-ray diffractometer (XRD), scanning electron microscopy (SEM), energy-dispersive spectrometer (EDS), and wear tester. The results indicated that [...] Read more.
In this study, the effect of carbon fibers (CFs) on the microstructure and wear resistance of Fe-based alloy coating produced by laser cladding was investigated by X-ray diffractometer (XRD), scanning electron microscopy (SEM), energy-dispersive spectrometer (EDS), and wear tester. The results indicated that with the addition of CFs, the microstructure of the composite coating mainly transformed from α-Fe cellular dendrites and γ-Fe/(Cr, Fe)7C3/CrB eutectics to bulk-like (Cr, Fe)7C3, nano-size B4C, and γ-(Fe, Ni)/(Cr, Fe)23C6 lamellar eutectics. Additionally, the microhardness and wear resistance of the composite coating compared with the original coating both increased by approximately two times. The original coating showed the dominant wear mechanisms of micro-cutting and serious brittle spalling, while the composite coating with CFs showed the main wear mechanism of slight scratching. Full article
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Open AccessArticle
Influence of the Aspect Ratio of Sodium Iron Titanate Whiskers on the Mechanical and Tribological Performances of Fluorocarbon Composite Coatings
Coatings 2019, 9(10), 683; https://doi.org/10.3390/coatings9100683 (registering DOI) - 20 Oct 2019
Viewed by 163
Abstract
Inorganic–organic composite coatings with fluoroethylene vinyl ether (FEVE) resin as polymer matrix and sodium iron titanate (NFTO) whiskers with different aspect ratios as reinforcement filler are prepared by the liquid-phase blending method. The influence of aspect ratio and content of NFTO whiskers on [...] Read more.
Inorganic–organic composite coatings with fluoroethylene vinyl ether (FEVE) resin as polymer matrix and sodium iron titanate (NFTO) whiskers with different aspect ratios as reinforcement filler are prepared by the liquid-phase blending method. The influence of aspect ratio and content of NFTO whiskers on the morphology, and the mechanical and tribological performances, of NFTO-reinforced FEVE composite coatings are investigated. The addition of NFTO whiskers can obviously enhance the mechanical and wear resistance performances of the composite coatings and reduce the friction coefficient. The worn surface and wear debris of the composite coatings are studied with scanning electron microscopy (SEM) to reveal the friction-reducing and wear resistance mechanisms. The composite coating filled with ~10 wt.% NFTO whiskers has the best wear resistance performance, since the monodispersed hard whisker can carry the load applied on the sliding surface and reduce the adhesive wear of the polymer matrix. Among the three types of NFTO whiskers, the whiskers with a medium aspect ratio show the best reinforcement effect since they provide the optimum mechanical support to the polymer matrix and cannot be pulled out from the matrix easily. Full article
(This article belongs to the Section Corrosion, Wear and Erosion)
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Open AccessReview
Electrochemical Corrosion of Nano-Structured Magnetron-Sputtered Coatings
Coatings 2019, 9(10), 682; https://doi.org/10.3390/coatings9100682 (registering DOI) - 20 Oct 2019
Viewed by 130
Abstract
Magnetron sputtering has been employed for several decades to produce protective and multi-functional coatings, thanks to its versatility and ability to achieve homogeneous layers. Moreover, it is suitable for depositing coatings with very high melting points and that are thermodynamical unstable, which is [...] Read more.
Magnetron sputtering has been employed for several decades to produce protective and multi-functional coatings, thanks to its versatility and ability to achieve homogeneous layers. Moreover, it is suitable for depositing coatings with very high melting points and that are thermodynamical unstable, which is difficult to accomplish by other techniques. Among these types of coating, transition metal (Me) carbides/nitrides (MeC/N) and amorphous carbon (a-C) films are particularly interesting because of the possibility of tailoring their properties by selecting the correct amount of phase fractions, varying from pure MeN, MeC, MeCN to pure a-C phases. This complex phase mixture can be even enhanced by adding a fourth element such Ag, Pt, W, Ti, Si, etc., allowing the production of materials with a large diversity of properties. The mixture of phases, resulting from the immiscibility of phases, allows increasing the number of applications, since each phase can contribute with a specific property such as hardness, self-lubrication, antibacterial ability, to create a multifunctional material. However, the existence of different phases, their fractions variation, the type of transition metal and/or alloying element, can drastically alter the global electrochemical behaviour of these films, with a strong impact on their stability. Consequently, it is imperative to understand how the main features intrinsic to the production process, as well as induced by Me and/or the alloying element, influence the characteristics and properties of the coatings and how these affect their electrochemical behaviour. Therefore, this review will focus on the fundamental aspects of the electrochemical behaviour of magnetron-sputtered films as well as of the substrate/film assembly. Special emphasis will be given to the influence of simulated body fluids on the electrochemical behaviour of coatings. Full article
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Open AccessFeature PaperArticle
Synthesis of Nanoporous TiO2 with the Use of Diluted Hydrogen Peroxide Solution and Its Application in Gas Sensing
Coatings 2019, 9(10), 681; https://doi.org/10.3390/coatings9100681 (registering DOI) - 19 Oct 2019
Viewed by 130
Abstract
The chemical routes of metal oxidation in presence of hydrogen peroxide solutions are tailor-made for the synthesis of biocompatible metal oxide surfaces with clean intermediate and end products, such as oxides, hydroxides, hydrogen and water. The hydrolysis of titanium in hydrogen peroxide solutions [...] Read more.
The chemical routes of metal oxidation in presence of hydrogen peroxide solutions are tailor-made for the synthesis of biocompatible metal oxide surfaces with clean intermediate and end products, such as oxides, hydroxides, hydrogen and water. The hydrolysis of titanium in hydrogen peroxide solutions is particularly interesting for medical applications, forming micro- and nanoscale titania surfaces. In this paper, the content of the hydrolysis solution is revised, allowing the fabrication of gas sensor devices based on nanoporous titania. Nanopore and microcrack formations were discussed in detail by monitoring the structural changes on the thin film surface with field-emission scanning electron microscopy (FE-SEM). A stable rutile crystalline phase was detected by glancing incidence X-ray diffraction (GI-XRD) measurement after repetitive hydrothermal processes. Electrical conductance measurements were carried out at high temperatures (400–600 °C) under humid airflow (40% [email protected] °C) with the injection of various concentrations of a wide set of test compounds (C2H3N, CO, H2, NO2, C2H6O), to observe the sensing capabilities of the material. Furthermore, the humidity effects on the sensing properties toward H2, CO, and C2H6O have been discussed. Full article
(This article belongs to the Special Issue Metal Oxide Thin Films for Gas-Sensing and Optical Application)
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Open AccessArticle
Characterization of Polyorganosilazane-Derived Hybrid Coatings for the Corrosion Protection of Mild Steel in Chloride Solution
Coatings 2019, 9(10), 680; https://doi.org/10.3390/coatings9100680 (registering DOI) - 19 Oct 2019
Viewed by 166
Abstract
Polysilazane (PSZ) have been used for many years as precursors for the development of ceramic materials. Recently, hydrocarbon-substituted polysilazane, which is called organopolysilazane (OPSZ), has been proposed as possible alternative to silanes for the corrosion protection of metals by the sol gel route. [...] Read more.
Polysilazane (PSZ) have been used for many years as precursors for the development of ceramic materials. Recently, hydrocarbon-substituted polysilazane, which is called organopolysilazane (OPSZ), has been proposed as possible alternative to silanes for the corrosion protection of metals by the sol gel route. In this work, polymethyl(hydro)/polydimethylsilazane-derived coatings were deposited on low-carbon steel for corrosion protection purposes. The effect of the OPSZ precursor concentration (10–40 v/v %) in butyl-acetate on the final properties of the coatings was investigated. Coatings in the thickness range of 1 to 3.5 µm were obtained. The experimental results showed that the concentration of OPSZ in the solvent affects the structural properties as well as the dry film thickness of the hybrid layer. In particular, the network arrangement seems to be influenced by the dilution of the OPSZ precursors solution. The electrochemical characterization revealed that a minimum thickness of about 2 to 3 µm is needed to provide the mild steel substrate with enhanced corrosion protection properties compared to the bare substrate. Comparing the obtained results with literature data, it seems that OPSZs are a potential alternative to coatings derived from organisilicon precursors. Full article
(This article belongs to the Special Issue Advanced Hybrid Coatings and Thin Films for Surface Functionalization)
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Open AccessArticle
On the Icephobic Behavior of Organosilicon-Based Surface Structures Developed Through Atmospheric Pressure Plasma Deposition in Nitrogen Plasma
Coatings 2019, 9(10), 679; https://doi.org/10.3390/coatings9100679 - 18 Oct 2019
Viewed by 112
Abstract
In many regions around the world, atmospheric icing during freezing rains and ice storms can cause severe damage to exposed infrastructure. Subsequently, protective coatings capable of ice accumulation prevention or ice adhesion reduction, often referred to as icephobic coatings, have gained a significant [...] Read more.
In many regions around the world, atmospheric icing during freezing rains and ice storms can cause severe damage to exposed infrastructure. Subsequently, protective coatings capable of ice accumulation prevention or ice adhesion reduction, often referred to as icephobic coatings, have gained a significant amount of interest. In this study, we examine an atmospheric-pressure plasma jet technique for the development of organosilicon-based icephobic coatings on aluminum substrates. Initially, Al-6061 samples are exposed to multiple passes of air plasma treatment at very short jet-to-substrate distances to create a microporous alumina-based surface structure. These surfaces are then used for plasma deposition of superhydrophobic coatings in the same jet with hexamethyldisiloxane (HMDSO) as the precursor and nitrogen as the plasma gas. Several samples are created with varying plasma precursor flow rates and number of deposition passes. All samples are exposed to three cycles of icing/de-icing to estimate coatings’ stability in aggressive natural conditions. The effects of multiple icing/de-icing cycles on surface chemistry, surface morphology, and wetting behavior is studied. It is shown that the most remarkable mechanism through which icing affects surface properties is coating removal during aggressive de-icing procedure. Finally, the icephobic properties of the most efficient coating (referred to as PT5x3) is further studied through 10 cycles of icing/de-icing, and it is shown that this coating can reduce ice adhesion strength by a factor of at least two for up to nine cycles of icing/de-icing. Full article
(This article belongs to the Special Issue Surface Plasma Treatments)
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Open AccessArticle
Interlaboratory Study of Ice Adhesion Using Different Techniques
Coatings 2019, 9(10), 678; https://doi.org/10.3390/coatings9100678 - 18 Oct 2019
Viewed by 110
Abstract
Low ice adhesion surfaces are a promising anti-icing strategy. However, reported ice adhesion strengths cannot be directly compared between research groups. This study compares results obtained from testing the ice adhesion strength on two types of surfaces at two different laboratories, testing two [...] Read more.
Low ice adhesion surfaces are a promising anti-icing strategy. However, reported ice adhesion strengths cannot be directly compared between research groups. This study compares results obtained from testing the ice adhesion strength on two types of surfaces at two different laboratories, testing two different types of ice with different ice adhesion test methods at temperatures of −10 and −18 °C. One laboratory used the centrifuge adhesion test and tested precipitation ice and bulk water ice, while the other laboratory used a vertical shear test and tested only bulk water ice. The surfaces tested were bare aluminum and a commercial icephobic coating, with all samples prepared in the same manner. The results showed comparability in the general trends, surprisingly, with the greatest differences for bare aluminum surfaces at −10 °C. For bulk water ice, the vertical shear test resulted in systematically higher ice adhesion strength than the centrifugal adhesion test. The standard deviation depends on the surface type and seems to scale with the absolute value of the ice adhesion strength. The experiments capture the overall trends in which the ice adhesion strength surprisingly decreases from −10 to −18 °C for aluminum and is almost independent of temperature for a commercial icephobic coating. In addition, the study captures similar trends in the effect of ice type on ice adhesion strength as previously reported and substantiates that ice formation is a key parameter for ice adhesion mechanisms. Repeatability should be considered a key parameter in determining the ideal ice adhesion test method. Full article
(This article belongs to the Special Issue Anti-Icing Coatings and Surfaces)
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Open AccessArticle
Effect of Scanning Speed on the Interface Behavior and Dendrite Growth of Laser Remelted Fe-Based Ni/WC Coatings
Coatings 2019, 9(10), 677; https://doi.org/10.3390/coatings9100677 - 18 Oct 2019
Viewed by 96
Abstract
The flame sprayed Fe-based Ni/WC cermet coating was treated by laser remelting. The influence of scanning speeds on the interface behaviour was investigated. SEM, XRD and EDS were used to analyse the microstructure, phase composition and element distribution of the interface. The results [...] Read more.
The flame sprayed Fe-based Ni/WC cermet coating was treated by laser remelting. The influence of scanning speeds on the interface behaviour was investigated. SEM, XRD and EDS were used to analyse the microstructure, phase composition and element distribution of the interface. The results showed that the interface of the coating contained holes and interlayer cracks and showed typical mechanical bonding features. The coatings mainly consisted of [Fe, Ni], Cr, WC, Cr7C3, Fe0.04Ni0.36, and other phases. After laser remelting, the coatings were smooth and dense due to the existence of well-developed dendrite structures and metallurgical bonding and could reach the optimal performance at 200 mm/s. New phases such as Fe2Si, Cr2Si, and W2C appeared in the remelted layers. With the increase of scanning speed, the half-peak height and average grain size became wider and smaller. At the same time, the measured dendrite spacing decreased with increasing scanning speed. Full article
(This article belongs to the Special Issue Laser Surface Modification of Metallic Materials)
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Open AccessArticle
Surface Texture Evolution of Fused Silica in a Combined Process of Atmospheric Pressure Plasma Processing and Bonnet Polishing
Coatings 2019, 9(10), 676; https://doi.org/10.3390/coatings9100676 - 18 Oct 2019
Viewed by 125
Abstract
The increasing demand for precision optical components invokes the requirement of advanced fabrication techniques with high efficiency. Atmospheric pressure plasma processing (APPP), based on chemical etching, has a high material removal rate and a Gaussian-shaped influence function, which is suitable to generate complex [...] Read more.
The increasing demand for precision optical components invokes the requirement of advanced fabrication techniques with high efficiency. Atmospheric pressure plasma processing (APPP), based on chemical etching, has a high material removal rate and a Gaussian-shaped influence function, which is suitable to generate complex structures and correct form errors. Because of the pure chemical etching, an optically smooth surface cannot be achieved using only APPP. Thus, bonnet polishing (BP) with a flexible membrane tool, also delivering a Gaussian influence-function, is introduced to smooth the surface after APPP. In this paper, the surface texture evolution in the combined process of APPP and BP is studied. The etched texture with increased removal depth of APPP is presented and analyzed. Subsequently, the processed substrates are smoothed by BP. The texture smoothing and the roughness improvement is investigated in detail. The experimental results show that the APPP etched pits coalesce with each other and transform into irregular convex-concave structures, with roughness degraded to about 25 nm arithmetical mean deviation (Ra). The APPP etched texture can be successfully smoothed to 1.5 nm Ra, with 0.2–1 μm material removal of BP. Full article
(This article belongs to the Section Surface Characterization, Deposition and Modification)
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Open AccessArticle
New, Amino Acid Based Zwitterionic Polymers as Promising Corrosion Inhibitors of Mild Steel in 1 M HCl
Coatings 2019, 9(10), 675; https://doi.org/10.3390/coatings9100675 - 17 Oct 2019
Viewed by 114
Abstract
The zwitterionic monomers, N,N’-diallylamino propanephosphonate and amino acid residual N,N’-diallyl-l-methionine hydrochloride were synthesized, with excellent yields. These monomers were utilized in the preparation of zwitterionic homo and co-cyclopolymers 57 in aqueous solution using 2,2′-azobis (2-methylpropionamidine) [...] Read more.
The zwitterionic monomers, N,N’-diallylamino propanephosphonate and amino acid residual N,N’-diallyl-l-methionine hydrochloride were synthesized, with excellent yields. These monomers were utilized in the preparation of zwitterionic homo and co-cyclopolymers 57 in aqueous solution using 2,2′-azobis (2-methylpropionamidine) dihydrochloride as an initiator. The polymers were characterized by FT-IR, NMR, and TGA. The performance of these synthesized polymers on mild steel in acidic solution was investigated by gravimetric method, Tafel extrapolation, linear polarization resistance, and electrochemical impedance spectroscopy. At 313 K, the maximum inhibition efficiencies of corrosion inhibitors 57 at 4.50 × 10−4 mol L−1 were found to be 85.2%, 83.3%, and 99.5%, respectively. The inhibition efficiencies obtained from gravimetric weight loss, potentiodynamic polarization, and electrochemical impedance spectroscopy measurements were in good agreement. Different adsorption isotherms were also explored to find the best fit, and found to obey Langmuir adsorption isotherm. The thermodynamic parameters, such as activation energy (Ea), standard enthalpy of activation (ΔH*), standard entropy of activation (ΔS*), adsorption–desorption equilibrium constant (Kads), and standard free energy of adsorption (ΔGoads), were determined. Electrochemical data indicated that the zwitterionic copolymer 7 acts as a mixed type inhibitor under the influence of anodic control. The surface morphology of mild steel corrosion was evaluated without and with corrosion inhibitors by AFM, SEM-EDX, and XPS, which confirmed the adsorption of inhibitor molecules on the metal surface. Full article
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Open AccessArticle
Analysis of Paint Flow Pulsations during High-Speed Rotary Bell Atomization
Coatings 2019, 9(10), 674; https://doi.org/10.3390/coatings9100674 - 17 Oct 2019
Viewed by 107
Abstract
High-speed rotary bell atomization is the preeminent coating technique in the automotive industry. It is widely accepted that a narrow droplet size distribution and constant spray are necessary in order to guarantee uniform film thickness and high-quality appearance. This may be deteriorated by [...] Read more.
High-speed rotary bell atomization is the preeminent coating technique in the automotive industry. It is widely accepted that a narrow droplet size distribution and constant spray are necessary in order to guarantee uniform film thickness and high-quality appearance. This may be deteriorated by paint flow pulsations. So far, however, no studies exist regarding such fluctuations quantitatively for this type of atomizers. We fill this gap using image analysis of high-speed recordings close to the bell edge. We could show that the fundamental pulsation frequency increases linearly with rotational speed. A ratio of pulsation frequency and true rotational speed of about 3 was found, indicating that pulsations were initiated mainly by the three struts of the distributor disc. The coefficient of variation, i.e., the amplitude of fluctuation increased with decreasing liquid volume rate and rotational speed. Beyond that, we could show that the formation of droplets larger than 100 μm, which are assumed to cause paint defects, is promoted by the degree of fluctuation. These findings may stimulate development of bell cups showing less paint flow pulsations. Full article
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Open AccessArticle
The Effect of the Indium(III) Phthalocyanine Chloride Films on the Behavior of Flexible Devices of Flat and Disperse Heterojunction
Coatings 2019, 9(10), 673; https://doi.org/10.3390/coatings9100673 - 17 Oct 2019
Viewed by 238
Abstract
By means of flat-heterojunction structures based on small semiconductor molecules (MSCs), an analysis of the indium(III) phthalocyanine chloride (In(III)PcCl) film as a constituent of optoelectronic devices was performed. The study included the behavior of In(III)PcCl playing three different roles: a donor species, an [...] Read more.
By means of flat-heterojunction structures based on small semiconductor molecules (MSCs), an analysis of the indium(III) phthalocyanine chloride (In(III)PcCl) film as a constituent of optoelectronic devices was performed. The study included the behavior of In(III)PcCl playing three different roles: a donor species, an electronic acceptor, and a hole layer carrier. The flat-heterojunction structures were prepared by vacuum deposition method that permits a controlled layer-by-layer growth of high purity films. The investigated structures were characterized by scanning electron microscopy (SEM), Energy-dispersive X-ray spectroscopy (EDS), UV-vis spectroscopy and optical bandgaps were obtained by Tauc’s and Cody’s methods. As the structures exhibit a large spectral absorption in the visible range, they were incorporated into flat-heterojunction devices based on flexible and rigid substrates. However, during the synthesis of those structures, the disperse heterojunction arrangement was found and indeed it showed to be more efficient than the initial flat-heterojunction. In order to complement these results, disperse heterojunction arrangement structure as well as its bandgap value were obtained by DFT calculations. Finally, the electronic behavior of both fabricated devices, disperse heterojunction and flat-heterojunction were compared. Full article
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Open AccessArticle
The Corrosion Resistance of Aluminum Alloy Modified by Laser Radiation
Coatings 2019, 9(10), 672; https://doi.org/10.3390/coatings9100672 - 16 Oct 2019
Viewed by 121
Abstract
This study presents an analysis of the impact of the oxide layers, prepared utilizing fiber laser radiation (1062 nm) in ambient air with different process parameters, on the corrosion resistance of EN 5754 aluminum alloy. Due to both high corrosion resistance and high [...] Read more.
This study presents an analysis of the impact of the oxide layers, prepared utilizing fiber laser radiation (1062 nm) in ambient air with different process parameters, on the corrosion resistance of EN 5754 aluminum alloy. Due to both high corrosion resistance and high fatigue strength, a 5754 alloy is used, among others, in the marine, aerospace, automotive, and chemical industries. Nevertheless, it corrodes in aggressive environments (with high chloride ions concentration). The controlled delivery of laser radiation energy in the oxygen environment allows the formation of the oxide layer on the surface of the material. We have determined that it significantly affects the resistance of these materials to corrosion. As a result of laser irradiation, changes in the chemical structure of the surface layer (chemical composition as well as surface development) can be observed. It may exert both a positive and a negative consequence on the corrosion resistance. The electrochemical corrosion tests (potentiodynamic polarization and electrochemical impedance spectroscopy EIS) have been carried out in an aggressive environment (3% NaCl). Moreover, microscopic examination, chemical tests, and roughness were also performed. The study revealed that appropriate control of the laser process can significantly increase the original corrosion resistance of the 5754 aluminum alloy. Full article
(This article belongs to the Special Issue Laser Surface Modification of Metallic Materials)
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Open AccessArticle
Development of Vitroceramic Coatings and Analysis of Their Suitability for Biomedical Applications
Coatings 2019, 9(10), 671; https://doi.org/10.3390/coatings9100671 - 16 Oct 2019
Viewed by 94
Abstract
Within the field of tissue engineering, thin films have been studied to improve implant fixation of metallic or ceramic materials in bone, connective tissue, oral mucosa or skin. In this context, to enhance their suitability as implantable devices, titanium-based substrates received a superficial [...] Read more.
Within the field of tissue engineering, thin films have been studied to improve implant fixation of metallic or ceramic materials in bone, connective tissue, oral mucosa or skin. In this context, to enhance their suitability as implantable devices, titanium-based substrates received a superficial vitroceramic coating by means of laser ablation. Further, this study describes the details of fabrication and corresponding tests in order to demonstrate the bioactivity and biocompatibility of the newly engineered surfaces. Thus, the metallic supports were covered with a complex material composed of SiO2, P2O5, CaO, MgO, ZnO and CaF2, in the form of thin layers via a physical deposition techniques, namely pulsed laser deposition. The resulting products were characterized by X-ray diffraction, Fourier-transform infrared spectroscopy, scanning and transmission electron microscopy coupled with energy dispersive X-ray spectroscopy, selected area electron diffraction, and electron energy loss spectroscopy. It was found that a higher substrate temperature and a lower working pressure lead to the highest quality film. Finally, the samples biocompatibility was assessed and they were found to be bioactive after simulated body fluid soaking and biocompatible through the MTT cell viability test. Full article
(This article belongs to the Section Bioactive Coatings, Surfaces & Interfaces)
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Open AccessArticle
Evaluation of Bleeding Resistance in Chip Seal and Asphalt Emulsion Residue Rheology
Coatings 2019, 9(10), 670; https://doi.org/10.3390/coatings9100670 - 16 Oct 2019
Viewed by 97
Abstract
Chip seal bleeding is influenced by many factors, including design inputs, material properties, and project-specific conditions. It reduces the surface texture of the pavement and thus compromises the safety of the traveling public. Even though factors that bring about premature bleeding are known, [...] Read more.
Chip seal bleeding is influenced by many factors, including design inputs, material properties, and project-specific conditions. It reduces the surface texture of the pavement and thus compromises the safety of the traveling public. Even though factors that bring about premature bleeding are known, currently, no laboratory test methods for evaluating bleeding in chip seals have been specified. The objective of this paper is to present the results of an investigation of the influence factors of asphalt emulsion residue properties measured by the ASTM D7405 multiple stress creep and recovery (MSCR) test, as well as other factors related to chip seal bleeding resistance as measured by the modified loaded wheel test (MLWT). In this study, the MSCR test was used as a tool for evaluating the performance of asphalt emulsions because it has been identified as a potential test related to bleeding in the field. In addition, MLWT was selected as a tool for evaluating chip seal bleeding performance in the laboratory. The results of the MLWT showed that the emulsion application rate (EAR), aggregate gradation, and emulsion properties were significant factors affecting bleeding. The MSCR test was found to be a promising tool for the performance evaluation of asphalt emulsion residue, as the test was able to differentiate between emulsion chemistries and modifications in terms of sensitivity to both temperature and stress. In relation to chip seal bleeding resistance, only the creep compliance (Jnr) obtained from the MSCR test results was identified as a significant property affecting potential for bleeding. Full article
(This article belongs to the Special Issue Pavement Surface Coatings)
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Open AccessArticle
Thin Films of Tolane Aggregates for Faraday Rotation: Materials and Measurement
Coatings 2019, 9(10), 669; https://doi.org/10.3390/coatings9100669 - 16 Oct 2019
Viewed by 104
Abstract
We present organic, diamagnetic materials based on structurally simple (hetero-)tolane derivatives. They form crystalline thin-film aggregates that are suitable for Faraday rotation (FR) spectroscopy. The resulting new materials are characterized appropriately by common spectroscopic (NMR, UV-Vis), microscopy (POM), and XRD techniques. The spectroscopic [...] Read more.
We present organic, diamagnetic materials based on structurally simple (hetero-)tolane derivatives. They form crystalline thin-film aggregates that are suitable for Faraday rotation (FR) spectroscopy. The resulting new materials are characterized appropriately by common spectroscopic (NMR, UV-Vis), microscopy (POM), and XRD techniques. The spectroscopic studies give extremely high FR activities, thus making these materials promising candidates for future practical applications. Other than a proper explanation, we insist on the complexity of designing efficient FR materials starting from single molecules. Full article
(This article belongs to the Special Issue Optical Thin Films and Structures: Design and Advanced Applications)
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Open AccessEditorial
Special Issue on Superhydrophobic Coatings for Corrosion and Tribology
Coatings 2019, 9(10), 668; https://doi.org/10.3390/coatings9100668 - 14 Oct 2019
Viewed by 153
Abstract
Superhydrophobicity, showing strong water-repellency, has been widely investigated for many applications, especially in the fields of corrosion protection and antifouling. Water tends to roll off from superhydrophobic surfaces like natural lotus leaves[...] Full article
(This article belongs to the Special Issue Superhydrophobic Coatings for Corrosion and Tribology)
Open AccessArticle
Electrochemical Studies on CaP Electrodeposition on Three Dimensional Surfaces of Selective Laser Melted Titanium Scaffold
Coatings 2019, 9(10), 667; https://doi.org/10.3390/coatings9100667 - 14 Oct 2019
Viewed by 123
Abstract
In this work, calcium phosphate (CaP) coating was electrodeposited on the three dimensional surface of SLM-Ti scaffolds. The in situ measurement showed that the potential variation within 5 mm thickness porous selective laser melting (SLM)-Ti samples was about 80 mV as a result [...] Read more.
In this work, calcium phosphate (CaP) coating was electrodeposited on the three dimensional surface of SLM-Ti scaffolds. The in situ measurement showed that the potential variation within 5 mm thickness porous selective laser melting (SLM)-Ti samples was about 80 mV as a result of the low conductivity of CaP coatings. SEM observation results revealed that the coating morphology depended on the distance between the surface position of porous SLM-Ti electrode and the auxiliary electrode. Based on the compared electrochemical experiments, it was found that the top and the bottom surfaces of SLM-Ti scaffolds exhibited continuous nucleation and instantaneous nucleation behavior respectively. The Electrochemical impedance spectroscopy (EIS) results also revealed that the electrodeposition processes at different depth of SLM-Ti scaffolds were not synchronized. These differences were ultimately caused by the non-uniform distribution of the potential and the current inside porous SLM-Ti electrodes. The present work provides a basic research method for studying the mechanism of the electrochemical process on three dimensional surfaces of SLM-Ti scaffolds. Full article
(This article belongs to the Section Bioactive Coatings, Surfaces & Interfaces)
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Open AccessArticle
Reduced Graphene Oxide–Epoxy Grafted Poly(Styrene-Co-Acrylate) Composites for Corrosion Protection of Mild Steel
Coatings 2019, 9(10), 666; https://doi.org/10.3390/coatings9100666 - 14 Oct 2019
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Abstract
Reduced graphene oxide–epoxy grafted poly(styrene-co-acrylate) composites (GESA) were prepared by anchoring different amount of epoxy modified poly(styrene-co-acrylate) (EPSA) onto reduced graphene oxide (rGO) sheets through π–π electrostatic attraction. The GESA composites were characterized by Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, X-ray diffraction [...] Read more.
Reduced graphene oxide–epoxy grafted poly(styrene-co-acrylate) composites (GESA) were prepared by anchoring different amount of epoxy modified poly(styrene-co-acrylate) (EPSA) onto reduced graphene oxide (rGO) sheets through π–π electrostatic attraction. The GESA composites were characterized by Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The anti-corrosion properties of rGO/EPSA composites were evaluated by electro-chemical impedance spectroscopy (EIS) in hydroxyl-polyacrylate coating, and the results revealed that the corrosion rate was decreased from 3.509 × 10−1 to 1.394 × 10−6 mm/a. Full article
(This article belongs to the Section Thin Films)
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Open AccessArticle
Microstructure, Mechanical Properties, Abrasive Wear, and Corrosion Behavior in Molten Zinc of Boride-Based Coatings in Situ Synthesized by an HVOF Spraying Process
Coatings 2019, 9(10), 665; https://doi.org/10.3390/coatings9100665 - 14 Oct 2019
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Abstract
Hot-dip galvanizing has been used for anti-corrosion of various steel products; however, the corrosion of molten zinc in the galvanizing industry is the key problem to be solved. Three kinds of Mo–B–Co–Cr, Mo–B–Ni–Cr, and Ti–B–Co–Cr mixture powders were deposited on the surface of [...] Read more.
Hot-dip galvanizing has been used for anti-corrosion of various steel products; however, the corrosion of molten zinc in the galvanizing industry is the key problem to be solved. Three kinds of Mo–B–Co–Cr, Mo–B–Ni–Cr, and Ti–B–Co–Cr mixture powders were deposited on the surface of a 316L stainless-steel substrate by a HVOF spraying method to prepare MoB/CoCr, MoB/NiCr, and TiB/CoCr coatings. The microstructure, mechanical properties, abrasive wear, and corrosion behavior in molten zinc of the in situ synthesized boride-based coatings were investigated. The experimental results showed that MoB/NiCr coating with a denser microstructure had the lowest porosity (0.811%). The in situ synthesized boride-phase compositions of MoB/CoCr, MoB/NiCr, and TiB/CoCr coatings were CoMoB and CoMo2B2, NiMo2B2, and TiB2, respectively. The MoB/NiCr coating had the highest boride content among the coatings. The presence of binary (TiB2) or ternary boride phases (CoMoB, CoMo2B2, and NiMo2B2) with their excellent mechanical properties could obviously increase the microhardness values in the coatings. The in situ synthesized borides in the coatings also could improve the wear resistance properties; MoB/NiCr coating with shallower grooves and smaller craters/pits had the smoothest worn surface and the lowest weight loss (6.8 ± 0.84 mg) among the coatings. After immersion test in molten zinc for 360 h, no presence of zinc or intermetallic compounds in the three kinds of the coatings (MoB/CoCr, MoB/NiCr, and TiB/CoCr), and the element compositions of the three kinds of coatings after the immersion test were the same as the as-sprayed coatings. Compared to the other coatings, MoB/NiCr coatings had the higher durability in molten zinc. Full article
(This article belongs to the Special Issue Coatings and Interfaces)
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Open AccessArticle
Microfiber Coating for Flow Control over a Blunt Surface
Coatings 2019, 9(10), 664; https://doi.org/10.3390/coatings9100664 - 14 Oct 2019
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Abstract
A microfiber coating having a hair-like structure is investigated as a passive flow control device of a bluff body. The effect of microfiber length is experimentally studied to understand the impact of the coating on drag on a cylinder. A series of microfiber [...] Read more.
A microfiber coating having a hair-like structure is investigated as a passive flow control device of a bluff body. The effect of microfiber length is experimentally studied to understand the impact of the coating on drag on a cylinder. A series of microfiber coatings with different lengths are fabricated using flocking technology and applied to various locations over the cylinder surface under the constant Reynolds number of 6.1 × 104 based on the diameter of the cylinder. It is found that the length and the location both play important roles in the drag reduction. Two types of drag reduction can be seen: (1) when the relative length of the microfiber, k/D, is less than 1.8%, and the coating is applied before flow separates over the cylinder; and (2) k/D is over 3.3%, and the coating is applied after the flow separation location on the cylinder. The maximum drag reduction for the former type is 59% compared to that from the cylinder without the microfiber coating. For the latter type, the maximum drag reduction is 27%. Full article
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Open AccessEditorial
Tribology and Surface Engineering
Coatings 2019, 9(10), 663; https://doi.org/10.3390/coatings9100663 - 13 Oct 2019
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Abstract
The Special Issue on Tribology and Surface Engineering includes nine research articles and one review article. It concerns a very important problem of resistance to wear and shaping the properties of the surface layers of different materials by different methods and technologies. The [...] Read more.
The Special Issue on Tribology and Surface Engineering includes nine research articles and one review article. It concerns a very important problem of resistance to wear and shaping the properties of the surface layers of different materials by different methods and technologies. The topics of the presented research articles include reactive direct current magnetron sputtering of silicon nitrides on implants, laser surface modification of aeroengine turbine blades, laser micro-texturing of titanium alloy to increase the tribological characteristics, electroplating of Cu–Sn composite coatings incorporated with Polytetrafluoroethylene (PTFE) and TiO2 particles, arc spraying of self-lubricous coatings, high velocity oxygen fuel (HVOF) spraying and gas nitriding of stainless steel coatings, HVOF spraying composite WC-Co coatings, testing of coatings deposited by physical vapour deposition (PVD), and also analysis of material removal and surface creation in wood sanding. The special issue provides valuable knowledge based on theoretical and empirical study in the field of coating technologies, as well as characterization of coatings, and wear phenomena. Full article
(This article belongs to the Special Issue Tribology and Surface Engineering)
Open AccessArticle
Simple and Rapid High-Yield Synthesis of Sub-100 nm Nano-SiO2·0.5H2O Particles Based on Wollastonite
Coatings 2019, 9(10), 662; https://doi.org/10.3390/coatings9100662 - 13 Oct 2019
Viewed by 181
Abstract
Amorphous nano-SiO2·nH2O particles has drawn much attention in industrial applications because of the features of high purification, low density, large specific surface area, fine decentralization, good optical, and mechanical performances. However, the applications have been hindered by the exorbitant [...] Read more.
Amorphous nano-SiO2·nH2O particles has drawn much attention in industrial applications because of the features of high purification, low density, large specific surface area, fine decentralization, good optical, and mechanical performances. However, the applications have been hindered by the exorbitant price and the serious agglomeration. In this work, using wollastonite as reactant, H2SO4 as solvent, and adding sodium dodecyl benzene sulfonate (SDBS) as surfactant, sub-100 nm amorphous nano-SiO2·0.5H2O particles with good dispersibility, controllable agglomeration, narrow size distribution, and high yield were prepared by a low-cost and simple chemical method. The prepared sphere-like amorphous nano-SiO2·0.5H2O particles with average diameter of 70 nm were absorbed by the SDBS on the surface. The reaction conditions were systematically studied and the optimal technologic condition of the preparation was also confirmed. The achievement had a great perspective for the industrialization of high-quality nano-SiO2·nH2O particles, which hold great promise for various applications, such as plasmonic and catalytic nanoparticles supporting, polymeric matrices strengthening, drug delivery, and adsorption processes. Full article
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Open AccessCorrection
Correction: Yamamuro et al. Power Generation in Slope-Type Thin-Film Thermoelectric Generators by the Simple Contact of a Heat Source. Coatings 2019, 9, 63
Coatings 2019, 9(10), 661; https://doi.org/10.3390/coatings9100661 - 12 Oct 2019
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Abstract
In the original version of article [...] Full article
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Open AccessArticle
The Effect of Cathodic Arc Guiding Magnetic Field on the Growth of (Ti0.36Al0.64)N Coatings
Coatings 2019, 9(10), 660; https://doi.org/10.3390/coatings9100660 - 12 Oct 2019
Viewed by 174
Abstract
We use a modified cathodic arc deposition technique, including an electromagnetic coil that introduces a magnetic field in the vicinity of the source, to study its influence on the growth of (Ti0.36Al0.64)N coatings. By increasing the strength of the [...] Read more.
We use a modified cathodic arc deposition technique, including an electromagnetic coil that introduces a magnetic field in the vicinity of the source, to study its influence on the growth of (Ti0.36Al0.64)N coatings. By increasing the strength of the magnetic field produced by the coil, the cathode arc spots are steered toward the edge of the cathode, and the electrons are guided to an annular anode surrounding the cathode. As a result, the plasma density between the cathode and substrate decreased, which was observed as a lateral spread of the plasma plume, and a reduction of the deposition rate. Optical emission spectroscopy shows reduced intensities of all recorded plasma species when the magnetic field is increased due to a lower number of collisions resulting in excitation. We note a charge-to-mass ratio decrease of 12% when the magnetic field is increased, which is likely caused by a reduced degree of gas phase ionization, mainly through a decrease in N2 ionization. (Ti0.36Al0.64)N coatings grown at different plasma densities show considerable variations in grain size and phase composition. Two growth modes were identified, resulting in coatings with (i) a fine-grained glassy cubic and wurtzite phase mixture when deposited with a weak magnetic field, and (ii) a coarse-grained columnar cubic phase with a strong magnetic field. The latter conditions result in lower energy flux to the coating’s growth front, which suppresses surface diffusion and favors the formation of c-(Ti,Al)N solid solutions over phase segregated c-TiN and w-AlN. Full article
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Open AccessArticle
A Facile Route to Fabricate Superhydrophobic Cu2O Surface for Efficient Oil–Water Separation
Coatings 2019, 9(10), 659; https://doi.org/10.3390/coatings9100659 - 12 Oct 2019
Viewed by 139
Abstract
The mixture of insoluble organics and water seriously affects human health and environmental safety. Therefore, it is important to develop an efficient material to remove oil from water. In this work, we report a superhydrophobic Cu2O mesh that can effectively separate [...] Read more.
The mixture of insoluble organics and water seriously affects human health and environmental safety. Therefore, it is important to develop an efficient material to remove oil from water. In this work, we report a superhydrophobic Cu2O mesh that can effectively separate oil and water. The superhydrophobic Cu2O surface was fabricated by a facile chemical reaction between copper mesh and hydrogen peroxide solution without any low surface reagents treatment. With the advantages of simple operation, short reaction time, and low cost, the as-synthesized superhydrophobic Cu2O mesh has excellent oil–water selectivity for many insoluble organic solvents. In addition, it could be reused for oil–water separation with a high separation ability of above 95%, which demonstrated excellent durability and reusability. We expect that this fabrication technique will have great application prospects in the application of oil–water separation. Full article
(This article belongs to the Special Issue Water and Oil Repellent Surfaces)
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Open AccessFeature PaperArticle
Nanosecond Pulsed Laser Irradiation of Titanium Alloy Substrate: Effects of Periodic Patterned Topography on the Optical Properties of Colorizing Surfaces
Coatings 2019, 9(10), 658; https://doi.org/10.3390/coatings9100658 - 11 Oct 2019
Viewed by 141
Abstract
Most of the current works based on surface treatments of metals by laser marking technology are focused on the modification of the color tonality of flat surfaces, or the development of specific topography features, but the combination of both processes is not usually [...] Read more.
Most of the current works based on surface treatments of metals by laser marking technology are focused on the modification of the color tonality of flat surfaces, or the development of specific topography features, but the combination of both processes is not usually evaluated, mainly due to the complexity of controlling the optical properties on rough surfaces. This research presents an analysis of the influence of the micro-geometrical characteristics of periodic patterned laser tracks on the chromaticity and reflectance of Ti6Al4V substrates. The samples were irradiated with an infrared nanosecond pulsed laser in air atmosphere, taking as the control parameter the scan speed of the beam. A roughness evaluation, microscopic inspection, and absorption and chromaticity examination were conducted. Although micro-crack growth was detected in an isolated case (10 mm/s), the possibility of adjusting the result color was demonstrated by controlling the heat-affected zone thickness of the textures. The results of rough/colored combined textures allow new perspectives in industrial design to open, particularly in aesthetic applications with special properties. Full article
(This article belongs to the Special Issue Laser Surface Modification of Metallic Materials)
Open AccessArticle
Boron and Nitrogen Co-Doped Porous Carbons Synthesized from Polybenzoxazines for High-Performance Supercapacitors
Coatings 2019, 9(10), 657; https://doi.org/10.3390/coatings9100657 - 11 Oct 2019
Viewed by 142
Abstract
Boron and nitrogen co-doped porous carbons (BNPC-X) were synthesized from boron-containing polybenzoxazines through carbonization and chemical activation, where X represents the weight ratio of boric acid to benzoxazine resin. The as-prepared BNPC-X were characterized by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, [...] Read more.
Boron and nitrogen co-doped porous carbons (BNPC-X) were synthesized from boron-containing polybenzoxazines through carbonization and chemical activation, where X represents the weight ratio of boric acid to benzoxazine resin. The as-prepared BNPC-X were characterized by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, element analysis and electrochemical measurements. The results show that the BNPC-0.15 possesses relatively high weight fractions of boron (2.97 wt %) and nitrogen (2.43 wt %), a homogeneous pore distribution, and remarkable electrochemical capacitive performance. It exhibits high specific capacitance (286 F·g−1 at 0.05 A·g−1), excellent rate capability (at A·g−1), and good charge–discharge stability (>92% capacitance retention after 1,000 cycles at 1.0 A·g−1) in 6 M KOH aqueous solution. Full article
Open AccessArticle
Plasma Treatments to Improve the Bonding of Thermo-Treated Cherry Wood
Coatings 2019, 9(10), 656; https://doi.org/10.3390/coatings9100656 - 11 Oct 2019
Viewed by 110
Abstract
Thermal treatment can significantly improve the dimensional stability of wood, but it will decrease the bonding strength. In this work, the bonding strength of thermo-treated cherry wood boards was improved by plasma treatment. The change of wettability, surface morphology, and surface chemical property [...] Read more.
Thermal treatment can significantly improve the dimensional stability of wood, but it will decrease the bonding strength. In this work, the bonding strength of thermo-treated cherry wood boards was improved by plasma treatment. The change of wettability, surface morphology, and surface chemical property of cherry wood before and after plasma treatment was investigated by water contact angle measurement, Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), and X-ray photoelectron spectroscopy (XPS). The plasma treatment significantly improved the wettability of thermo-treated cherry wood by decreasing its water contact angle from 109.95° to 53.18°. N2 or O2 was used as the plasma atmosphere, and it was found that N2 plasma treatment afforded cherry wood a rougher surface. The AFM roughness of cherry wood was increased from 19 nm to 31.9 nm after N2 plasma treatment. XPS results revealed an additional C–N group for N2 plasma treatment and the content of C=O, O–C–O, and O–C=O increased for O2 plasma treatment, respectively, indicating that the surface chemical property of cherry wood was modified. Due to the surface character, the bonding strength increased by 21.17% for N2 plasma treatment and 15.32% for O2 plasma treatment. Full article
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