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Coatings, Volume 8, Issue 5 (May 2018)

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Cover Story (view full-size image) Colour is a distinctive feature of precious historical bowed string instruments. Old recipes have [...] Read more.
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Open AccessArticle Antibacterial Functionalization of PVD Coatings on Ceramics
Coatings 2018, 8(5), 197; https://doi.org/10.3390/coatings8050197
Received: 31 March 2018 / Revised: 14 May 2018 / Accepted: 17 May 2018 / Published: 22 May 2018
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Abstract
The application of surface treatments that incorporate silver or copper as antibacterial elements has become a common practice for a wide variety of medical devices and materials because of their effective activity against nosocomial infections. Ceramic tiles are choice materials for cladding the
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The application of surface treatments that incorporate silver or copper as antibacterial elements has become a common practice for a wide variety of medical devices and materials because of their effective activity against nosocomial infections. Ceramic tiles are choice materials for cladding the floors and walls of operation rooms and other hospital spaces. This study is focused on the deposition of biocide physical vapor deposition (PVD) coatings on glazed ceramic tiles. The objective was to provide antibacterial activity to the surfaces without worsening their mechanical properties. Silver and copper-doped chromium nitride (CrN) and titanium nitride (TiN) coatings were deposited on samples of tiles. A complete characterization was carried out in order to determine the composition and structure of the coatings, as well as their topographical and mechanical properties. The distribution of Ag and Cu within the coating was analyzed using glow discharge optical emission spectrometry (GD-OES) and field emission scanning electron microscope (FE-SEM). Roughness, microhardness, and scratch resistance were measured for all of the combinations of coatings and dopants, as well as their wettability. Finally, tests of antibacterial efficacy against Staphylococcus aureus and Escherichia coli were carried out, showing that all of the doped coatings had pronounced biocide activity. Full article
(This article belongs to the Special Issue Physical Vapor Deposition)
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Open AccessArticle On the Importance of Combined Scratch/Acoustic Emission Test Evaluation: SiC and SiCN Thin Films Case Study
Coatings 2018, 8(5), 196; https://doi.org/10.3390/coatings8050196
Received: 9 April 2018 / Revised: 10 May 2018 / Accepted: 21 May 2018 / Published: 22 May 2018
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Abstract
The scratch test, as probably the most widespread technique for assessment of the adhesive/cohesive properties of a film–substrate system, fully depends on reliable evaluation based on assessment of critical loads for systems’ failures. Traditionally used evaluation methods (depth change record and visual observation)
[...] Read more.
The scratch test, as probably the most widespread technique for assessment of the adhesive/cohesive properties of a film–substrate system, fully depends on reliable evaluation based on assessment of critical loads for systems’ failures. Traditionally used evaluation methods (depth change record and visual observation) may sometimes give misleading conclusions about the failure dynamics, especially in the case of opaque films. Therefore, there is a need for another independent evaluation technique with the potential to complete the existing approaches. The nondestructive method of acoustic emission, which detects the elastic waves emitted during film cracking and delamination, can be regarded as a convenient candidate for such a role even at nano/micro scale. The strength of the combination of microscopic observation of the residual groove and depth change record with the acoustic emission detection system proved to be a robust and reliable approach in analyzing adhesion/cohesion properties of thin films. The dynamics of the gradual damage taking place during the nano/micro scratch test revealed by the combined approach is presented for SiC and SiCN thin films. Comparison of critical load values clearly reflects the higher ability of the AE approach in detecting the initial material failure compared to the visual observation. Full article
(This article belongs to the Special Issue Coatings Tribology)
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Open AccessArticle Influences of Cr and Co on the Growth of Thermally Grown Oxide in Thermal Barrier Coating during High-Temperature Exposure
Coatings 2018, 8(5), 195; https://doi.org/10.3390/coatings8050195
Received: 7 February 2018 / Revised: 6 May 2018 / Accepted: 18 May 2018 / Published: 22 May 2018
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Abstract
Thermal barrier coating (TBC) is a critical material in the aerospace domain to increase the lifetime of gas turbine components subjected to thermal load. The properties of TBC are strongly related to the growth of thermally grown oxide (TGO) whose main constituent is
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Thermal barrier coating (TBC) is a critical material in the aerospace domain to increase the lifetime of gas turbine components subjected to thermal load. The properties of TBC are strongly related to the growth of thermally grown oxide (TGO) whose main constituent is Al2O3. However, the oxidation of Cr and Co can affect the growth of TGO, which is not studied sufficiently. In this paper, high-temperature exposure at 1000 °C was performed to investigate the effect of Cr and Co oxides on TGO growth. The morphology and composition analysis of the interface between the ceramic top coat and the bond coat (TC/BC) were investigated by using scanning electron microscopy (SEM) and the energy dispersion spectrum (EDS). The thermodynamics and kinetics of oxidation were analyzed. The results indicated that the oxidation kinetics basically followed the sub-parabolic law with exposure time. Additionally, the major factor affecting the formation of oxides was the diffusion rate at the initial stage of exposure, then oxides depended on thermodynamics, and the oxidation was influenced by both of them in the last stage. The major elements to be oxidized were different at different stages. Moreover, the replacement reaction of Cr2O3 and the phase conversion of Al2O3 resulted in thickness variations of the TGO and Al-depleted zone during high-temperature exposure. Full article
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Open AccessArticle Evolution of Calcareous Deposits and Passive Film on 304 Stainless Steel with Cathodic Polarization in Sea Water
Coatings 2018, 8(5), 194; https://doi.org/10.3390/coatings8050194
Received: 18 February 2018 / Revised: 17 May 2018 / Accepted: 18 May 2018 / Published: 21 May 2018
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Abstract
The change of protective current density, the formation and growth of calcareous deposits, and the evolution of passive film on 304 stainless steel (SS) were investigated at different potentials of cathodic polarization in sea water. Potentiostatic polarization, electrochemical impedance spectroscopy (EIS), and surface
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The change of protective current density, the formation and growth of calcareous deposits, and the evolution of passive film on 304 stainless steel (SS) were investigated at different potentials of cathodic polarization in sea water. Potentiostatic polarization, electrochemical impedance spectroscopy (EIS), and surface analysis techniques of scanning electron microscopy (SEM), energy dispersive X-ray (EDX) microanalysis and X-ray diffraction (XRD) were used to characterize the surface conditions. It was found that the protective current density was smaller for keeping polarization at −0.80 V (vs. saturated calomel electrode (SCE), same as below) than that at −0.65 V. The calcareous deposits could not be formed on 304 SS with polarization at −0.50 V while it was well protected. The formation rate, the morphology, and the constituent of the calcareous deposits depended on the applied potential. The resistance of passive film on 304 SS decreased at the first stage and then increased when polarized at −0.80 V and −0.65 V, which was related to the reduction and the repair of passive film. For the stainless steel polarized at −0.50 V, the film resistance increased with polarization time, indicating that the growth of oxide film was promoted. Full article
(This article belongs to the Special Issue Advanced Coatings for Corrosion Protection in Extreme Environments)
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Open AccessArticle Effect of Annealing Treatment on Microstructure and Properties of Cr-Coatings Deposited on AISI 5140 Steel by Brush-Plating
Coatings 2018, 8(5), 193; https://doi.org/10.3390/coatings8050193
Received: 1 May 2018 / Revised: 15 May 2018 / Accepted: 17 May 2018 / Published: 21 May 2018
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Abstract
Cr-coating was deposited on AISI 5140 steel by electro brush-plating, followed by annealing treatment at different temperatures, from 300 to 1100 °C. The microstructure evolution of the Cr-coating was characterized by backscattered electron imaging (BSEI) and energy dispersive spectrometry (EDS). The results show
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Cr-coating was deposited on AISI 5140 steel by electro brush-plating, followed by annealing treatment at different temperatures, from 300 to 1100 °C. The microstructure evolution of the Cr-coating was characterized by backscattered electron imaging (BSEI) and energy dispersive spectrometry (EDS). The results show that the brush-plated sample has a nodular shaped microstructure, which is very stable at 300 °C of annealing. At 500 °C of annealing, the constitution of the microstructure changes from nodules to grains. As the annealing temperature further increases, the grains grow significantly. When the temperature reaches 1100 °C, a Cr-Fe solid-solution layer is formed within the original pure Cr-coatings. With increasing annealing temperature, the number of micro-cracks in the coating increases first and then decreases, reaching a maximum at 500 °C. The hardness and wear-resistance of the coating are improved when the annealing temperature increases to 1100 °C, owing to the decrease of micro-cracks that formed during brush-plating. Full article
(This article belongs to the Special Issue Advanced Coatings for Corrosion Protection in Extreme Environments)
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Open AccessArticle Design and Preparation of a Micro-Pyramid Structured Thin Film for Broadband Infrared Antireflection
Coatings 2018, 8(5), 192; https://doi.org/10.3390/coatings8050192
Received: 8 April 2018 / Revised: 2 May 2018 / Accepted: 8 May 2018 / Published: 21 May 2018
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Abstract
A micro-pyramid structured thin film with a broad-band infrared antireflection property is designed and fabricated by using the single-point diamond turning (SPDT) technique and combined with nano-imprint lithography (NIL). A structure with dimensions of 10 μm pitch and 5 μm height is transferred
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A micro-pyramid structured thin film with a broad-band infrared antireflection property is designed and fabricated by using the single-point diamond turning (SPDT) technique and combined with nano-imprint lithography (NIL). A structure with dimensions of 10 μm pitch and 5 μm height is transferred from the copper mold to the silicon nitride optical film by using NIL and proportional inductively-coupled plasma (ICP) etching. Reflectance of the micro-optical surface is reduced below 1.0% over the infrared spectral range (800–2500 nm). A finite-difference-time-domain (FDTD) analysis indicates that this micro-structure can localize photons and enhance the absorption inside the micro-pyramid at long wavelengths. As described above, the micro-pyramid array has been integrated in an optical film successfully. Distinguishing from the traditional micro-optical components, considering the effect of refraction and diffraction, it is a valuable and flexible method to take account of the interference effect of optical film. Full article
(This article belongs to the Special Issue Applications of Optical Thin Film Coatings)
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Open AccessArticle Effects of Flow Rates and Density Matching on the Integrity of Solid Particles Coated by Water Phase Compound Droplets during the Transport Process
Coatings 2018, 8(5), 191; https://doi.org/10.3390/coatings8050191
Received: 8 April 2018 / Revised: 5 May 2018 / Accepted: 17 May 2018 / Published: 19 May 2018
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Abstract
To achieve the integrity of solid particles coated by water phase (S/W/O) compound droplets, it is important to investigate the transport process of the compound droplets in the horizontal straight channel. The experimental results show that the integrity is significantly influenced by the
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To achieve the integrity of solid particles coated by water phase (S/W/O) compound droplets, it is important to investigate the transport process of the compound droplets in the horizontal straight channel. The experimental results show that the integrity is significantly influenced by the flow rates and density difference. The water (W) phase is observed to be peeled off from the surface of the particles (polystyrene (PS) shells), mainly caused by the slip velocity of the W phase and the density mismatching among three phases. During the peeling off process, a relative motion between the solid (S) and W phases initially occurs, causing a decrease of the distance (δ) between them, and then, the PS shell is driven to pass through the W/O interface under the action of drag force and net gravity. It is also found that increasing flow rates of both phases contributes to obtaining integrated compound droplets. A boundary that separates the integrated from damaged compound droplets also exits when the fluid properties are fixed. Above the line of the boundary, compound droplets with integrity are prepared. Moreover, the absolute optimum density matching between the S and W phases is less than 0.003 g/cm3, while that between the W and oil (O) phases is less than 0.005 g/cm3. Full article
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Open AccessFeature PaperArticle Stabilized SPEEK Membranes with a High Degree of Sulfonation for Enthalpy Heat Exchangers
Coatings 2018, 8(5), 190; https://doi.org/10.3390/coatings8050190
Received: 18 April 2018 / Revised: 10 May 2018 / Accepted: 16 May 2018 / Published: 19 May 2018
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Abstract
In this investigation, we explored for the first time the use of cross-linked sulfonated poly (ether ether ketone) (SPEEK) membranes in the fabrication of enthalpy heat exchangers. SPEEK is very sensitive to changes in relative humidity, especially when featuring high degrees of sulfonation
[...] Read more.
In this investigation, we explored for the first time the use of cross-linked sulfonated poly (ether ether ketone) (SPEEK) membranes in the fabrication of enthalpy heat exchangers. SPEEK is very sensitive to changes in relative humidity, especially when featuring high degrees of sulfonation (DS), though a poor mechanical stability may be observed in the latter case. Cross-linking is crucial in overcoming this issue, and here, we firstly employed the INCA method (ionomer counter-elastic pressure “nc” analysis) to assess the improvements in the mechanical properties. The cross-link was achieved following a simple thermal-assisted process that occurs directly on the performed membranes. After an initial screening, a degree of cross-link = 0.1 was selected as the better compromise between absorption of water vapor and mechanical properties. When implemented in the enthalpy heat exchanger system, these cross-linked SPEEK membranes enabled a high level of sensible heat exchange, as well as a remarkable variation in the mass (water vapor) transfer between the individual air flows. The performances resulted in being better than those for the system based on a benchmark commercially available perfluorinated Nafion membrane. Full article
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Open AccessFeature PaperArticle Comparing Colorfastness to Light of Wood-Staining Fungal Pigments and Commercial Dyes: An Alternative Light Test Method for Color Fastness
Coatings 2018, 8(5), 189; https://doi.org/10.3390/coatings8050189
Received: 17 April 2018 / Revised: 12 May 2018 / Accepted: 18 May 2018 / Published: 19 May 2018
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Abstract
Colorfastness to light is an essential quality for textiles exposed to sunlight for a significant length of time. In this study, the colorfastness (specifically to light) of fabrics dyed with wood-staining (spalting) fungal pigments was compared to the colorfastness of commercial dyes. A
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Colorfastness to light is an essential quality for textiles exposed to sunlight for a significant length of time. In this study, the colorfastness (specifically to light) of fabrics dyed with wood-staining (spalting) fungal pigments was compared to the colorfastness of commercial dyes. A short-duration immersion dying method without heat was used to minimize both water and energy usage. Both mordanted and unmordanted fabrics were tested and compared for colorfastness. Additionally, a new method of testing for colorfastness to light was developed. Results indicate that the wood-staining fungal pigments demonstrate superior colorfastness to light over commercial dyes when the employed dyeing method is used. Additionally, the colorfastness to light testing method developed using the L-2 Blue Wool Standard and QUV Accelerated Weathering Machine is a viable alternative to current standard colorfastness to light testing methods. Full article
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Open AccessArticle Effects of Coating Film Parameters on Thermal and Stress Distributions of Glass-Based Phosphor-Converted Color Wheels
Coatings 2018, 8(5), 188; https://doi.org/10.3390/coatings8050188
Received: 28 April 2018 / Revised: 14 May 2018 / Accepted: 14 May 2018 / Published: 17 May 2018
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Abstract
To protect the environment, the use of mercury tubes has been prohibited in Europe since 2000. As an alternative, phosphor-doped silicone resin wheels have been used to convert blue-ray laser diodes. However, high-temperature photonic decay and cracking on the lens surface significantly degrade
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To protect the environment, the use of mercury tubes has been prohibited in Europe since 2000. As an alternative, phosphor-doped silicone resin wheels have been used to convert blue-ray laser diodes. However, high-temperature photonic decay and cracking on the lens surface significantly degrade transmission. Recent research has explored the possibility of replacing the silicone encapsulant material of the phosphor layer with glass. In this study, the thermal effects of a glass-based phosphor-converted color wheel (GP wheel) and a silicone-based phosphor-converted color wheel (SP wheel) were investigated using various parameters and geometries. A thermal-structural coupling finite element (FE) model of the color wheels was employed to simulate the thermal and stress distributions. To construct the FE model, experiments were conducted and the inverse engineering approach was employed to extract the optical-to-heat conversion coefficient and the heat convection coefficient. In addition, an arc-shaped moving input heat flux was used to simulate a moving laser input and reduce the calculation time of the FE model. Based on the numerical and experimental results, the FE model developed can simulate the steady/transient behavior of the resin and the GP wheel. In addition, the results reveal that thermal failures of the SP wheel are very likely to occur under all parameters employed in this study, whereas the maximum temperature of the GP wheel reaches only approximately 40% of the glass transition temperature. The numerical results indicate that the GP wheel may be useful for overcoming all of these thermal disadvantages in a high-power laser-lit projector. Full article
(This article belongs to the Special Issue Selected Papers from IEEE ICASI 2018)
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Open AccessArticle Influence of Lamellar Interface Morphology on Cracking Resistance of Plasma-Sprayed YSZ Coatings
Coatings 2018, 8(5), 187; https://doi.org/10.3390/coatings8050187
Received: 21 March 2018 / Revised: 4 May 2018 / Accepted: 11 May 2018 / Published: 15 May 2018
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Abstract
Splat morphology is an important factor that influences the mechanical properties and durability of thermal barrier coatings (TBCs). In this study, yttria-stabilized zirconia (YSZ) coatings with different lamellar interface morphologies were deposited by atmospheric plasma spraying (APS) using feedstocks with different particle sizes.
[...] Read more.
Splat morphology is an important factor that influences the mechanical properties and durability of thermal barrier coatings (TBCs). In this study, yttria-stabilized zirconia (YSZ) coatings with different lamellar interface morphologies were deposited by atmospheric plasma spraying (APS) using feedstocks with different particle sizes. The influence of lamellar interface roughness on the cracking resistance of the coatings was investigated. Furthermore, the thermal shock and erosion resistance of coatings deposited by two different powders was evaluated. It was found that the particle size of the feedstock powder affects the stacking morphology of the splat that forms the coating. Coatings fabricated from coarse YSZ powders (45–60 μm) show a relatively rough inter-lamellar surface, with a roughness about 3 times greater than those faricated from fine powders (15–25 μm). Coatings prepared with fine powders tend to form large cracks parallel to the substrate direction under indentation, while no cracking phenomena were found in coatings prepared with coarse powders. Due to the higher cracking resistance, coatings prepared with coarse powders show better thermal shock and erosion resistances than those with fine powders. The results of this study provide a reference for the design and optimization of the microstructure of TBCs. Full article
(This article belongs to the Special Issue Coatings for Harsh Environments)
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Open AccessArticle Improvement of Aluminium Film Adhesion on PMMA Using Pre-Layer and Specific Annealing
Coatings 2018, 8(5), 186; https://doi.org/10.3390/coatings8050186
Received: 29 March 2018 / Revised: 5 May 2018 / Accepted: 11 May 2018 / Published: 15 May 2018
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Abstract
During the electron beam evaporation for deposition of an aluminium film, high-speed electrons decelerate when they bombard the material and part of the electron energy contributes to radiation. Due to the high sensitivity of polymethyl methacrylate (PMMA) to such radiation (in UV), the
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During the electron beam evaporation for deposition of an aluminium film, high-speed electrons decelerate when they bombard the material and part of the electron energy contributes to radiation. Due to the high sensitivity of polymethyl methacrylate (PMMA) to such radiation (in UV), the PMMA surface is degraded. This results in a weak surface of PMMA layer and decreases film adhesion. Based on the film interface adhesion mechanism and the relationship between film structure and stress, this research proposed and investigated a method for producing high quality Al reflective thin film on a PMMA surface with good adhesion. This was done by depositing a pre-layer of 20 nm Al using resistant evaporation to protect the PMMA surface from radiation damage, followed by the deposition of 80 nm Al using e-beam evaporation with ion assisted deposition. Using this method, an average reflectance of 88.6% was achieved in the wavelength range of 400–800 nm. The elastic modulus and hardness were tested by nanoindentation for the calculation of the thermal stress of the film. Adhesion was tested using the pressure strip peeling test and meets the military national standard. Full article
(This article belongs to the Special Issue Applications of Optical Thin Film Coatings)
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Open AccessArticle Corrosion Resistance of Pipeline Steel with Damaged Enamel Coating and Cathodic Protection
Coatings 2018, 8(5), 185; https://doi.org/10.3390/coatings8050185
Received: 20 February 2018 / Revised: 12 April 2018 / Accepted: 9 May 2018 / Published: 14 May 2018
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Abstract
This paper presents the first report on the corrosion resistance of pipeline steel with damaged enamel coating and cathodic protection in 3.5 wt % NaCl solution. In particular, dual cells are set up to separate the solution in contact with the damaged and
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This paper presents the first report on the corrosion resistance of pipeline steel with damaged enamel coating and cathodic protection in 3.5 wt % NaCl solution. In particular, dual cells are set up to separate the solution in contact with the damaged and intact enamel coating areas, to produce a local corrosion resistance measurement for the first time. Enamel-coated steel samples, with two levels of cathodic protection, are tested to investigate their impedance by electrochemical impedance spectroscopy (EIS) and their cathodic current demand by a potentiostatic test. Due to its glass transition temperature, the enamel-coated pipeline can be operated on at temperatures up to 400 °C. The electrochemical tests show that cathodic protection (CP) can decelerate the degradation process of intact coating and delay the electrochemical reactions at the enamel-steel interface. However, CP has little effect on the performance of coating once damaged and can prevent the exposed steel from corrosion around the damaged site, as verified by visual inspections. Scanning electron microscopy (SEM) indicated no delamination at the damaged enamel–steel interface due to their chemical bond. Full article
(This article belongs to the Special Issue Coatings for Harsh Environments)
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Open AccessArticle Hydrophilic Self-Replenishing Coatings with Long-Term Water Stability for Anti-Fouling Applications
Coatings 2018, 8(5), 184; https://doi.org/10.3390/coatings8050184
Received: 14 March 2018 / Revised: 19 April 2018 / Accepted: 30 April 2018 / Published: 14 May 2018
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Abstract
Hydrophilic coatings have recently emerged as a new approach to avoiding the adhesion of (bio)organisms on surfaces immersed in water. In these coatings the hydrophilic character is crucial for the anti-fouling (AF) performance. However, this property can be rapidly lost due to the
[...] Read more.
Hydrophilic coatings have recently emerged as a new approach to avoiding the adhesion of (bio)organisms on surfaces immersed in water. In these coatings the hydrophilic character is crucial for the anti-fouling (AF) performance. However, this property can be rapidly lost due to the inevitable damages which occur at the surface, reducing the long-term effectiveness of the AF functionality. We report hydrophilic polycarbonate-poly(ethylene glycol) methyl ether (mPEG) polyurethane coatings with tunable hydrophilic properties as well as an excellent and long-term stability in water. The coatings exhibit low protein adhesion values and are able to self-replenish their hydrophilicity after damage, due to the existence of a reservoir of hydrophilic dangling chains incorporated in the bulk. The combination of low Tg and sufficient mobility of the mPEG dangling chains (enabled by chains with higher molecular weight) proved to be crucial to ensure autonomous surface hydrophilicity recovery when the coatings were immersed in water. This coatings and design approach offers new possibilities towards high-performance AF coatings with an extended service life-time which can be used in several major applications areas, such as marine and biomedical coatings, with major economic and environmental benefits. Full article
(This article belongs to the Special Issue Progress in Self-Healing Coatings)
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Open AccessArticle Semitransparent Decorative Coatings Based on Optical Interference of Metallic and Dielectric Thin Films for High Temperature Applications
Coatings 2018, 8(5), 183; https://doi.org/10.3390/coatings8050183
Received: 12 April 2018 / Revised: 2 May 2018 / Accepted: 9 May 2018 / Published: 11 May 2018
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Abstract
This paper introduces a thin film multilayer structure composed of dielectric and metallic layers that allows for a wide range of aesthetic appearances using the phenomenon of optical interference. In addition, this multilayer structure allows the reflection and transmission coefficients to be controlled
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This paper introduces a thin film multilayer structure composed of dielectric and metallic layers that allows for a wide range of aesthetic appearances using the phenomenon of optical interference. In addition, this multilayer structure allows the reflection and transmission coefficients to be controlled independently. The application of these decorative coatings to induction stoves is also studied. The aim is to provide an attractive aesthetic appearance for the transparent glass-ceramic, and allow the visualization of blue and white lighting systems. Moreover, degradation of these decorative coatings is studied at high temperatures, so as to ensure that the coating does not change its aesthetic appearance during normal operation of the stove. It has been found to be necessary to use dielectric materials with low diffusion coefficients of oxygen, or not containing oxygen, to prevent oxidation of the metal layers when subjecting the coating to high temperatures. Full article
(This article belongs to the Special Issue Applications of Optical Thin Film Coatings)
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Open AccessArticle Electrodeposition of a Pd-Ni/TiO2 Composite Coating on 316L SS and Its Corrosion Behavior in Hot Sulfuric Acid Solution
Coatings 2018, 8(5), 182; https://doi.org/10.3390/coatings8050182
Received: 2 April 2018 / Revised: 27 April 2018 / Accepted: 3 May 2018 / Published: 11 May 2018
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Abstract
Pd-Ni/TiO2 composite coatings were elaborated on 316L stainless steel by an electrodeposition method. The specimens were obtained from an electrolytic bath that contained various contents (5, 10, and 15 g L−1) of nanosized TiO2 particles. X-ray diffraction (XRD) characterization
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Pd-Ni/TiO2 composite coatings were elaborated on 316L stainless steel by an electrodeposition method. The specimens were obtained from an electrolytic bath that contained various contents (5, 10, and 15 g L−1) of nanosized TiO2 particles. X-ray diffraction (XRD) characterization showed that increasing the TiO2 content in the coatings can decrease the crystal grain size. The surface morphology and chemical composition of the composite coatings were modified by the addition of TiO2 particles in the electrolyte, as shown by scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS) methods, respectively. The TiO2 content also significantly affected the mechanical and electrochemical properties of the Pd-Ni/TiO2 composite coatings. The microhardness of the Pd-Ni/TiO2 composite coatings can be enhanced by increasing the TiO2 content in the coatings. With the addition of 5 g L−1 TiO2 particles to the electrolyte, the deposited Pd-Ni/TiO2 composite coating presented a remarkably increased corrosion resistance when exposed to a sulfuric acid solution at 60 °C compared with that of the Pd-Ni alloy coating. Nevertheless, the further addition of TiO2 particles into the electrolytic bath did not further improve the corrosion resistance of the composite coating. Full article
(This article belongs to the Special Issue Advanced Coatings for Corrosion Protection in Extreme Environments)
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Open AccessArticle Bonding Characteristics and Chemical Inertness of Zr–Si–N Coatings with a High Si Content in Glass Molding
Coatings 2018, 8(5), 181; https://doi.org/10.3390/coatings8050181
Received: 15 April 2018 / Revised: 5 May 2018 / Accepted: 8 May 2018 / Published: 11 May 2018
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Abstract
High-Si-content transition metal nitride coatings, which exhibited an X-ray amorphous phase, were proposed as protective coatings on glass molding dies. In a previous study, the Zr–Si–N coatings with Si contents of 24–30 at.% exhibited the hardness of Si3N4, which
[...] Read more.
High-Si-content transition metal nitride coatings, which exhibited an X-ray amorphous phase, were proposed as protective coatings on glass molding dies. In a previous study, the Zr–Si–N coatings with Si contents of 24–30 at.% exhibited the hardness of Si3N4, which was higher than those of the middle-Si-content (19 at.%) coatings. In this study, the bonding characteristics of the constituent elements of Zr–Si–N coatings were evaluated through X-ray photoelectron spectroscopy. Results indicated that the Zr 3d5/2 levels were 179.14–180.22 and 180.75–181.61 eV for the Zr–N bonds in ZrN and Zr3N4 compounds, respectively. Moreover, the percentage of Zr–N bond in the Zr3N4 compound increased with increasing Si content in the Zr–Si–N coatings. The Zr–N bond of Zr3N4 dominated when the Si content was >24 at.%. Therefore, high Si content can stabilize the Zr–N compound in the M3N4 bonding structure. Furthermore, the thermal stability and chemical inertness of Zr–Si–N coatings were evaluated by conducting thermal cycle annealing at 270 °C and 600 °C in a 15-ppm O2–N2 atmosphere. The results indicated that a Zr22Si29N49/Ti/WC assembly was suitable as a protective coating against SiO2–B2O3–BaO-based glass for 450 thermal cycles. Full article
(This article belongs to the Special Issue Coatings for Dies and Molds)
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Open AccessArticle Fabrication of Poly(o/m-Toluidine)–SiC/Zinc Bilayer Coatings and Evaluation of Their Corrosion Resistances
Coatings 2018, 8(5), 180; https://doi.org/10.3390/coatings8050180
Received: 1 April 2018 / Revised: 2 May 2018 / Accepted: 5 May 2018 / Published: 9 May 2018
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Abstract
The purpose of this research was to study the structure and corrosion resistance of poly(o/m-toluidine)-SiC/zinc (Zn) bilayer coatings. Poly(o/m-toluidine) films, such as poly(o-toluidine) (POT) and poly(m-toluidine) (PMT), were chemically deposited on the surface of composite SiC/Zn coating using the solution evaporation method. The
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The purpose of this research was to study the structure and corrosion resistance of poly(o/m-toluidine)-SiC/zinc (Zn) bilayer coatings. Poly(o/m-toluidine) films, such as poly(o-toluidine) (POT) and poly(m-toluidine) (PMT), were chemically deposited on the surface of composite SiC/Zn coating using the solution evaporation method. The structures of poly(o/m-toluidine) were characterized by various optic techniques and the electrochemical behavior was studied by cyclic voltammetry (CV). The structures and morphologies of the SiC/Zn coating were detected by Fourier transformation infrared spectroscopy (FTIR), X-ray diffraction (XRD), energy dispersive spectrometer (EDS), and scanning electron microscopy (SEM). Thereafter, the corrosion resistances of electrodeposited and bilayer coatings were investigated in 3.5% NaCl solution by electrochemical corrosion techniques and an accelerated immersion test. The results showed that the outer POT film exhibits a lower corrosion behavior with respect to PMT, which significantly reduces the corrosion rate of SiC/Zn coating and prolongs the service life of the zinc matrix. The conclusion demontrates that the stronger adsorptive POT film ensures the formed POT–SiC/Zn bilayer coatings possess a compact and low-defect surface, which facilitates POT film to develop its excellent barrier and passivation properties against corrosion. Full article
(This article belongs to the Special Issue Polymer Thin Films)
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Open AccessArticle Effect of Graphene Oxide/ZSM-5 Hybrid on Corrosion Resistance of Waterborne Epoxy Coating
Coatings 2018, 8(5), 179; https://doi.org/10.3390/coatings8050179
Received: 18 March 2018 / Revised: 25 April 2018 / Accepted: 26 April 2018 / Published: 7 May 2018
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Abstract
In this study, the preparation of modified graphene oxide (GO) synergistic structure (ZSM-5-NH-GO) and the effect of this structure on the corrosion performance of epoxy coatings were investigated. The structural and morphological properties of ZSM-5-NH-GO were characterized by Fourier transform infrared spectroscopy (FT-IR),
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In this study, the preparation of modified graphene oxide (GO) synergistic structure (ZSM-5-NH-GO) and the effect of this structure on the corrosion performance of epoxy coatings were investigated. The structural and morphological properties of ZSM-5-NH-GO were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), and scanning electron microscopy (SEM). The corrosion performances were studied by electrochemical impedance spectroscopy (EIS) and salt spray tests. The EIS results showed that the corrosion resistance of steel substrate was considerably improved by ZSM-5-NH-GO. The salt spray tests demonstrated that the ZSM-5-NH-GO coating provided strong corrosion performance for steel substrate. The mechanical properties of the epoxy-composite coatings containing ZSM-5-NH-GO were studied by adhesion tests. The above results indicated that the composite coating containing 0.7 wt % ZSM-5-NH-GO composite possessed most excellent anti-corrosion performance compared with other epoxy coatings. Full article
(This article belongs to the Special Issue Advanced Surface Coating of Nanoparticles)
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Open AccessShort Note An Analysis of Effect of CO2 Laser Treatment on Carbon Fibre Fabric
Coatings 2018, 8(5), 178; https://doi.org/10.3390/coatings8050178
Received: 14 March 2018 / Revised: 30 April 2018 / Accepted: 2 May 2018 / Published: 6 May 2018
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Abstract
The colour of carbon fibre fabric is black which limits its aesthetic properties. CO2 laser has been used for cutting carbon fibres. The impact of CO2 laser treatment to modify the surface of carbon fibre fabric is investigated in this work.
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The colour of carbon fibre fabric is black which limits its aesthetic properties. CO2 laser has been used for cutting carbon fibres. The impact of CO2 laser treatment to modify the surface of carbon fibre fabric is investigated in this work. Different combinations of laser process parameters, i.e., pixel time (110, 120, 130, 140, 150, 160, 170, 180, 190 and 200 µs, with 10 µs intervals) and resolution (70, 80, 90 and 100 dpi (dots per inch), with 10 dpi intervals), were used for treating carbon fibre fabric surface. Since the laser process is a surface treatment, contact angle measurement was used for evaluating the wetting property imparted after laser processing. The resistivity of the laser-treated carbon fibre fabric was measured to evaluate any effect on the original electrical property of the carbon fibre fabric. Moreover, surface morphology and functionality of laser-treated carbon fibre fabric were assessed by scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy-attenuated total internal reflectance (FTIR-ATR), respectively. SEM assessment was to examine the physical change in the carbon fibre surface after laser processing. On the other hand, the FTIR-ATR measurement can help to evaluate the chemical change in the carbon fibre surface after laser processing. Full article
(This article belongs to the Special Issue Laser Surface Treatment)
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Open AccessArticle Shelf Life Assessment of Fresh Poultry Meat Packaged in Novel Bionanocomposite of Chitosan/Montmorillonite Incorporated with Ginger Essential Oil
Coatings 2018, 8(5), 177; https://doi.org/10.3390/coatings8050177
Received: 31 March 2018 / Revised: 26 April 2018 / Accepted: 3 May 2018 / Published: 5 May 2018
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Abstract
Active packaging incorporated with natural extracts is a promising technology to extend shelf life of perishable food. Therefore, this study aimed to produce a bionanocomposite based on chitosan reinforced with sodium montmorillonite (MMT) and incorporated with ginger essential oil (GEO). In vitro activity
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Active packaging incorporated with natural extracts is a promising technology to extend shelf life of perishable food. Therefore, this study aimed to produce a bionanocomposite based on chitosan reinforced with sodium montmorillonite (MMT) and incorporated with ginger essential oil (GEO). In vitro activity was assessed through migration assay and antimicrobial study against foodborne bacteria. Phenolic compounds were diffused within 48 h of contact, and retained some of their antioxidant activity. Films demonstrated antimicrobial activity against both Gram-positive and -negative bacteria tested. The effect on the shelf life of fresh poultry meat was determined on samples wrapped in the biopolymers and stored under refrigeration for 15 days, through physicochemical and microbiological analyses. Compared to unwrapped poultry meat, samples wrapped in the bionanocomposites showed a reduction in microorganisms count of 1.2–2.6 log CFU/g, maintained color and pH values and thiobarbituric acid reactive substances (TBARS) index increased at a lower rate, extending fresh poultry meat shelf life. The incorporation of GEO enhanced the biopolymer activity, by reducing lipid oxidation and microbiological growth of the poultry meat. In contrast, reinforcement with MMT imprisoned the active compounds in the polymeric chain, hindering its activity. In conclusion, the bionanocomposites tested represent promising substitutes to commercial and unsustainable plastic films. Full article
(This article belongs to the Special Issue Edible Films and Coatings)
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Open AccessArticle Laser Cladding of Embedded Sensors for Thermal Barrier Coating Applications
Coatings 2018, 8(5), 176; https://doi.org/10.3390/coatings8050176
Received: 12 March 2018 / Revised: 20 April 2018 / Accepted: 25 April 2018 / Published: 4 May 2018
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Abstract
The accurate real-time monitoring of surface or internal temperatures of thermal barrier coatings (TBCs) in hostile environments presents significant benefits to the efficient and safe operation of gas turbines. A new method for fabricating high-temperature K-type thermocouple sensors on gas turbine engines using
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The accurate real-time monitoring of surface or internal temperatures of thermal barrier coatings (TBCs) in hostile environments presents significant benefits to the efficient and safe operation of gas turbines. A new method for fabricating high-temperature K-type thermocouple sensors on gas turbine engines using coaxial laser cladding technology has been developed. The deposition of the thermocouple sensors was optimized to provide minimal intrusive features to the TBC, which is beneficial for the operational reliability of the protective coatings. Notably, this avoids a melt pool on the TBC surface. Sensors were deposited onto standard yttria-stabilized zirconia (7–8 wt % YSZ) coated substrates; subsequently, they were embedded with second YSZ layers by the Atmospheric Plasma Spray (APS) process. Morphology of cladded thermocouples before and after embedding was optimized in terms of topography and internal homogeneity, respectively. The dimensions of the cladded thermocouple were in the order of 200 microns in thickness and width. The thermal and electrical response of the cladded thermocouple was tested before and after embedding in temperatures ranging from ambient to approximately 450 °C in a furnace. Seebeck coefficients of bared and embedded thermocouples were also calculated correspondingly, and the results were compared to that of a commercial standard K-type thermocouple, which demonstrates that laser cladding is a prospective technology for manufacturing microsensors on the surface of or even embedded into functional coatings. Full article
(This article belongs to the Special Issue Thermal Barrier Coatings)
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Open AccessArticle Kinetic Research on the Curing Reaction of Hydroxyl-Terminated Polybutadiene Based Polyurethane Binder System via FT-IR Measurements
Coatings 2018, 8(5), 175; https://doi.org/10.3390/coatings8050175
Received: 5 April 2018 / Revised: 24 April 2018 / Accepted: 30 April 2018 / Published: 4 May 2018
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Abstract
Polyurethane binder systems based on hydroxyl-terminated polybutadiene (HTPB) possess several superior properties such as superior adhesion, high solid-loading capacity, outstanding mechanical performance, etc. They have been widely used in coatings and adhesives as well as in medical and military industries. The cure reaction
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Polyurethane binder systems based on hydroxyl-terminated polybutadiene (HTPB) possess several superior properties such as superior adhesion, high solid-loading capacity, outstanding mechanical performance, etc. They have been widely used in coatings and adhesives as well as in medical and military industries. The cure reaction between hydroxyl-terminated polybutadiene (HTPB) and diisocyanates plays a key role in the properties of final products as well as the adjustment of process parameters. FT-IR spectroscopy is applied to investigate the kinetics of the curing reaction of HTPB and isophorone diisocyanate (IPDI) in the presence of a low toxic and low viscosity catalyst, stannous isooctoate (TECH). The concentrations of the isocyanate groups (NCO) characterized by FT-IR during the cure reaction with respect to time were recorded at different temperatures and at constant stoichiometric ratio Rn[NCO]/n[OH] = 1.0. The kinetic parameters, i.e., activation energy (Ea), pre-exponential factor (A), activation enthalpy (ΔH) and activation entropy (ΔS) were determined. In addition, the curing process and mechanism of the HTPB-IPDI reaction are discussed. Full article
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Open AccessArticle Study of Near-Cup Droplet Breakup of an Automotive Electrostatic Rotary Bell (ESRB) Atomizer Using High-Speed Shadowgraph Imaging
Coatings 2018, 8(5), 174; https://doi.org/10.3390/coatings8050174
Received: 9 March 2018 / Revised: 5 April 2018 / Accepted: 29 April 2018 / Published: 3 May 2018
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Abstract
Electrostatic Rotary bell (ESRB) atomizers are used as the dominant means of paint application by the automotive industry. They utilize the high rotational speed of a cup to induce primary atomization of a liquid along with shaping air to provide secondary atomization and
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Electrostatic Rotary bell (ESRB) atomizers are used as the dominant means of paint application by the automotive industry. They utilize the high rotational speed of a cup to induce primary atomization of a liquid along with shaping air to provide secondary atomization and transport. In order to better understand the fluid breakup mechanisms involved in this process, high-speed shadowgraph imaging was used to visualize the edge of a serrated rotary bell at speeds varying between 5000 and 12,000 RPM and with a water flow rate of 250 ccm. A multi-step image processing algorithm was developed to differentiate between ligaments and droplets during the primary atomization process. The results from this experiment showed that higher bell speeds resulted in a 26.8% reduction in ligament and 22.3% reduction in droplet Sauter Mean Diameters (SMD). Additionally, the ligament (ranging from 40 to 400 μm) diameters formed bimodal distributions, while the droplet (ranging from 40 to 300 μm) diameters formed a normal distribution. Velocities were also measured using particle tracking velocimetry, in which size-dependent velocities could then be computed. Droplet velocities were affected more by rotational speed than droplet SMD, while ligaments were affected by other factors than the rotational speed and ligament SMD. Full article
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Open AccessArticle Superhydrophobic Bilayer Coating Based on Annealed Electrospun Ultrathin Poly(ε-caprolactone) Fibers and Electrosprayed Nanostructured Silica Microparticles for Easy Emptying Packaging Applications
Coatings 2018, 8(5), 173; https://doi.org/10.3390/coatings8050173
Received: 1 April 2018 / Revised: 28 April 2018 / Accepted: 30 April 2018 / Published: 3 May 2018
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Abstract
A coating rendering superhydrophobic properties to low-density polyethylene (LDPE) films used in packaging applications was herein generated by means of the electrohydrodynamic processing (EHDP) technique. To this end, electrospun ultrathin poly(ε-caprolactone) (PCL) fibers, followed by electrosprayed nanostructured silica (SiO2) microparticles, were
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A coating rendering superhydrophobic properties to low-density polyethylene (LDPE) films used in packaging applications was herein generated by means of the electrohydrodynamic processing (EHDP) technique. To this end, electrospun ultrathin poly(ε-caprolactone) (PCL) fibers, followed by electrosprayed nanostructured silica (SiO2) microparticles, were deposited on top of the LDPE film. Various electrospinning and electrospraying times were tested and optimized followed by a thermal post-treatment to provide physical adhesion between the bilayer coating and the LDPE substrate. The morphology, hydrophobicity, permeance to limonene, and thermal stability of the resultant nanostructured coatings were characterized. It was observed that by controlling both the deposition time of the electrospun ultrathin PCL fibers and the electrosprayed SiO2 microparticles, as well as the conditions of the thermal post-treatment, effective superhydrophobic coatings were developed onto the LDPE films. The resultant multilayer presented a hierarchical micro/nanostructured surface with an apparent contact angle of 157° and a sliding angle of 8°. The addition of silica reduced, to some extent, the limonene (aroma) barrier, likely due to the increased surface-to-volume ratio, which allowed permeant sorption to occur but improved the thermal stability of the LDPE/PCL film. As a result, the developed multilayer system of LDPE/PCL/SiO2 has significant potential for use in easy-to-empty packaging applications of high water activity products. Full article
(This article belongs to the Special Issue Superhydrophobic Coatings)
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Open AccessFeature PaperArticle HFCVD Diamond-Coated Mechanical Seals
Coatings 2018, 8(5), 172; https://doi.org/10.3390/coatings8050172
Received: 31 March 2018 / Revised: 24 April 2018 / Accepted: 2 May 2018 / Published: 3 May 2018
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Abstract
A mechanical seal promotes the connection between systems or mechanisms, preventing the escape of fluids to the exterior. Nonetheless, due to extreme working conditions, premature failure can occur. Diamond, due to its excellent properties, is heralded as an excellent choice to cover the
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A mechanical seal promotes the connection between systems or mechanisms, preventing the escape of fluids to the exterior. Nonetheless, due to extreme working conditions, premature failure can occur. Diamond, due to its excellent properties, is heralded as an excellent choice to cover the surface of these devices and extend their lifetime. Therefore, the main objective of this work was to deposit diamond films over mechanical seals and test the coated seals on a water pump, under real working conditions. The coatings were created by hot filament chemical vapor deposition (HFCVD) and two consecutive layers of micro- and nanocrystalline diamond were deposited. One of the main difficulties is the attainment of a good adhesion between the diamond films and the mechanical seal material (WC-Co). Nucleation, deposition conditions, and pre-treatments were studied to enhance the coating. Superficial wear or delamination of the film was investigated using SEM and Raman characterization techniques, in order to draw conclusions about the feasibility of these coatings in the WC-Co mechanical seals with the purpose of increasing their performance and life time. The results obtained gave a good indication about the feasibility of this process and the deposition conditions used, with the mechanical seals showing no wear and no film delamination after a real work environment test. Full article
(This article belongs to the Special Issue Plasma Etching and Deposition)
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Open AccessArticle Approaches for Detecting Madder Lake in Multi-Layered Coating Systems of Historical Bowed String Instruments
Coatings 2018, 8(5), 171; https://doi.org/10.3390/coatings8050171
Received: 19 March 2018 / Revised: 15 April 2018 / Accepted: 28 April 2018 / Published: 3 May 2018
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Abstract
Musical instrument coatings are generally made by multi-layered systems of organic and inorganic materials, applied on the wood substrate by the violin makers during the finishing process. This coating has paramount relevance for several aspects: protection from sweat and dirt, increase of specific
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Musical instrument coatings are generally made by multi-layered systems of organic and inorganic materials, applied on the wood substrate by the violin makers during the finishing process. This coating has paramount relevance for several aspects: protection from sweat and dirt, increase of specific acoustic features, and especially aesthetic effects. In fact, the colour of historical bowed string instruments represents a very peculiar characteristic of each workshop. Among the various colourants, lakes are the most challenging to detect because of their sensibility to the alteration processes. In this work, non-invasive and micro-invasive procedures were applied to a set of mock-ups mimicking historical coatings systems prior and after artificial ageing, in order to highlight the overall information that can be recovered for the detection of madder lake in historical bowed instruments. A set of techniques, including colourimetry, visible and UV-light imaging, stereomicroscopy, Fibre Optics Diffuse Reflectance spectroscopy (FORS), X-ray Fluorescence spectroscopy (XRF), Scanning Electron Microscopy coupled with Energy-Dispersive X-ray microprobe (SEM-EDX), and Fourier-Transform Infrared spectroscopy (FTIR) were used in order to evaluate the pros and cons in the detection of organic and inorganic component of madder lake at low concentration levels. Full article
(This article belongs to the Special Issue Varnishes and Surface Treatments of Historical Wooden Artworks)
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Open AccessFeature PaperArticle New Consolidant-Hydrophobic Treatment by Combining SiO2 Composite and Fluorinated Alkoxysilane: Application on Decayed Biocalcareous Stone from an 18th Century Cathedral
Coatings 2018, 8(5), 170; https://doi.org/10.3390/coatings8050170
Received: 8 March 2018 / Revised: 30 April 2018 / Accepted: 1 May 2018 / Published: 2 May 2018
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Abstract
An effective procedure has been developed to consolidate and hydrophobize decayed monumental stones by a simple sol-gel process. The sol contains silica oligomer, silica nanoparticles and a surfactant, preventing gel cracking. The effectiveness of the process on biocalcareous stone samples from an 18th
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An effective procedure has been developed to consolidate and hydrophobize decayed monumental stones by a simple sol-gel process. The sol contains silica oligomer, silica nanoparticles and a surfactant, preventing gel cracking. The effectiveness of the process on biocalcareous stone samples from an 18th century cathedral has been evaluated, and it was found that the gel creates effective linking bridges between mineral grains of the stone. Silica nanoparticles produced a significant increase in the mechanical resistance and cohesion of the stone. The application of an additional fluorinated oligomer onto the consolidated stone gave rise to a surface with lasting hydrophobicity, preventing water absorption. Full article
(This article belongs to the Special Issue Communications from TechnoHeritage 2017)
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Open AccessArticle The Gain of Low Thermal Expansivity via Phase Transition in Electroformed Invar
Coatings 2018, 8(5), 169; https://doi.org/10.3390/coatings8050169
Received: 5 March 2018 / Revised: 24 April 2018 / Accepted: 1 May 2018 / Published: 2 May 2018
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Abstract
In the organic light-emitting diode display industry, Invar exhibits anomalously low thermal expansivity and is, therefore, used as a material for fine metal masks, which are necessary components for the evaporation process of diode materials. We present an electroforming method for fabricating Fe-Ni
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In the organic light-emitting diode display industry, Invar exhibits anomalously low thermal expansivity and is, therefore, used as a material for fine metal masks, which are necessary components for the evaporation process of diode materials. We present an electroforming method for fabricating Fe-Ni alloys with a coefficient of thermal expansion lower than that of conventional Invar. The principle of controlling the thermal expansivity of electroformed Fe-Ni alloys is clarified in terms of the behavior of the phases constituting them. The cause of the Invar anomalies, which has not yet been fully elucidated, is explained by combining the Weiss model based on the electron configurations of Fe atoms and a model that we propose based on atom configurations. Full article
(This article belongs to the Special Issue Thin Films and Patterned Structures by Electrochemical Methods)
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Open AccessArticle The Influence of Oxygen Flow Ratio on the Optoelectronic Properties of p-Type Ni1−xO Films Deposited by Ion Beam Assisted Sputtering
Coatings 2018, 8(5), 168; https://doi.org/10.3390/coatings8050168
Received: 26 March 2018 / Revised: 20 April 2018 / Accepted: 25 April 2018 / Published: 30 April 2018
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Abstract
In this work, p-type non-stoichiometric Ni1−xO thin films were deposited by oxygen ion beam assisted RF sputtering on glass substrates. The influence of the oxygen flow ratio (0–100%) on the films’ optoelectronic properties was investigated. In our experimental conditions, all
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In this work, p-type non-stoichiometric Ni1−xO thin films were deposited by oxygen ion beam assisted RF sputtering on glass substrates. The influence of the oxygen flow ratio (0–100%) on the films’ optoelectronic properties was investigated. In our experimental conditions, all the films are crystallized in the cubic NiO phase. However, their crystallinity and mean grain size decreases with increasing oxygen flow ratios. Meanwhile, the films’ conductivity improves from 9.1 to 25.4 S·cm−1. This is due to the fact that the nickel vacancies along with hole carriers can be introduced into NiO films when they are deposited under higher oxygen flow ratio conditions. Thus, the O-rich environment is beneficial in enhancing the films’ carrier concentrations. In addition, with an increasing oxygen flow ratio, the film’s transmittance degrades. The direct optical band gap of Ni1−xO films declines slightly from 3.99 to 3.95 eV, with the oxygen flow ratio increasing from 0% to 100%. Full article
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