Editor's Choice Articles

Editor’s Choice articles are based on recommendations by the scientific editors of MDPI journals from around the world. Editors select a small number of articles recently published in the journal that they believe will be particularly interesting to authors, or important in this field. The aim is to provide a snapshot of some of the most exciting work published in the various research areas of the journal.

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Article
Sputter-Deposited Ag Nanoparticles on Electrospun PCL Scaffolds: Morphology, Wettability and Antibacterial Activity
Coatings 2021, 11(3), 345; https://doi.org/10.3390/coatings11030345 - 18 Mar 2021
Cited by 2
Abstract
Porous scaffolds made of biocompatible and environmental-friendly polymer fibers with diameters in the nano/micro range can find applications in a wide variety of sectors, spanning from the biomedical field to textiles and so on. Their development has received a boost in the last [...] Read more.
Porous scaffolds made of biocompatible and environmental-friendly polymer fibers with diameters in the nano/micro range can find applications in a wide variety of sectors, spanning from the biomedical field to textiles and so on. Their development has received a boost in the last decades thanks to advances in the production methods, such as the electrospinning technique. Conferring antimicrobial properties to these fibrous structures is a primary requirement for many of their applications, but the addition of antimicrobial agents by wet methods can present a series of drawbacks. In this work, strong antibacterial action is successfully provided to electrospun polycaprolactone (PCL) scaffolds by silver (Ag) addition through a simple and flexible way, namely the sputtering deposition of silver onto the PCL fibers. SEM-EDS analyses demonstrate that the polymer fibers get coated by Ag nanoparticles without undergoing any alteration of their morphological integrity upon the deposition process. The influence on wettability is evaluated with polar (water) and non-polar (diiodomethane) liquids, evidencing that this coating method allows preserving the hydrophobic character of the PCL polymer. Excellent antibacterial action (reduction > 99.995% in 4 h) is demonstrated against Escherichia coli. The easy fabrication of these PCL-Ag mats can be applicable to the production of biomedical devices, bioremediation and antifouling systems in filtration, personal protective equipment (PPE), food packaging materials, etc. Full article
(This article belongs to the Special Issue Antibacterial Surfaces, Thin Films, and Nanostructured Coatings)
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Article
Low-Density Insulation Blocks and Hardboards from Amaranth (Amaranthus cruentus) Stems, a New Perspective for Building Applications
Coatings 2021, 11(3), 349; https://doi.org/10.3390/coatings11030349 - 18 Mar 2021
Cited by 1
Abstract
Nowadays, amaranth appears as a promising source of squalene of vegetable origin. Amaranth oil is indeed one of the most concentrated vegetable oils in squalene, i.e., up to 6% (w/w). This triterpene is highly appreciated in cosmetology, especially for [...] Read more.
Nowadays, amaranth appears as a promising source of squalene of vegetable origin. Amaranth oil is indeed one of the most concentrated vegetable oils in squalene, i.e., up to 6% (w/w). This triterpene is highly appreciated in cosmetology, especially for the formulation of moisturizing creams. It is almost exclusively extracted from the liver of sharks, causing their overfishing. Thus, providing a squalene of renewable origin is a major challenge for the cosmetic industry. The amaranth plant has thus experienced renewed interest in recent years. In addition to the seeds, a stem is also produced during cultivation. Representing up to 80% (w/w) of the plant aerial part, it is composed of a ligneous fraction, the bark, on its periphery, and a pith in its middle. In this study, a fractionation process was developed to separate bark and pith. These two fractions were then used to produce renewable materials for building applications. On the one hand, the bark was used to produce hardboards, with the deoiled seeds acting as natural binder. Such boards are a viable alternative to commercial wood-based panels. On the other hand, the pith was transformed into cohesive and machinable low-density insulation blocks revealing a low thermal conductivity value. Full article
(This article belongs to the Special Issue Natural Fiber Based Composites)
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Article
Polymer-Cement Composites Glazing by Concentrated Solar Energy
Coatings 2021, 11(3), 350; https://doi.org/10.3390/coatings11030350 - 18 Mar 2021
Cited by 1
Abstract
Macro defect free (MDF) cements are polymer-cement composites characterized by high biaxial flexural strength compared to traditional concrete, having as a drawback a low water resistance. Glazing these composite materials with an inorganic enamel containing TiO2 nano-particles has led to a high [...] Read more.
Macro defect free (MDF) cements are polymer-cement composites characterized by high biaxial flexural strength compared to traditional concrete, having as a drawback a low water resistance. Glazing these composite materials with an inorganic enamel containing TiO2 nano-particles has led to a high water-stable material with advanced photocatalytic properties. Classic glazing by thermal treatment of samples, at 1050 °C, requires energy consumption and long-time performing. The purpose of this paper is to test the use of solar radiation as a source of energy in the glazing process. A vertical axis solar furnace has been used, from PROMES-CNRS Solar Laboratory, Font-Romeu Odeillo, France, and it has been observed that a uniform appearance of the glaze coating has been achieved; it shows high scratch resistance, meaning a good hardness and adhesion to the substrate. The obtained film was also characterized by SEM, EDS and XRD, aiming to evidence the coat morphology, the TiO2 distribution and its crystallinity alteration, when compared to the samples obtained by classic thermal treatment. The conclusion of the paper is that using solar radiation in the MDF cement glazing process is a promising approach for obtaining multifunctional materials. Full article
(This article belongs to the Special Issue Thermal Spray Coatings)
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Article
Efficacy of Mesenchymal Stem Cell and Vitamin D in the Treatment of Diabetes Mellitus Induced in a Rat Model: Pancreatic Tissues
Coatings 2021, 11(3), 317; https://doi.org/10.3390/coatings11030317 - 10 Mar 2021
Cited by 3
Abstract
Treatment with mesenchyme stem cells (MSCs) plays a significant role in the therapies of many diseases such as diabetics. Vitamin D plays a significant role in the development of insulin and can increase the insulin action sensitivity of peripheral tissues. Moreover, there is [...] Read more.
Treatment with mesenchyme stem cells (MSCs) plays a significant role in the therapies of many diseases such as diabetics. Vitamin D plays a significant role in the development of insulin and can increase the insulin action sensitivity of peripheral tissues. Moreover, there is limited research concerning the mechanism of the therapeutic action of MSCs with the combination of vitamin D (vit. D). Therefore, we evaluated the effect of MSC intervention in a diabetic animal model. Diabetes was induced by streptozotocin (STZ) injection at a dose of 50 mg/kg in adult male rats The diabetic rats were injected with MSCs derived from bone marrow (2 × 106 per rat), either alone or in combination with vit. D through the tail vein for four weeks. Serum insulin, glucose, C-peptide, glycosylated hemoglobin, and lipid profile levels were determined. Pancreatic oxidative stress, histology, and electron microscopy were evaluated, and the gene expression of cytokines was assessed by real-time polymerase chain reaction PCR. MSC treatment suppressed pancreatic inflammatory cytokine secretion and oxidative stress in diabetic rats, resulting in improved pancreatic histology and cellular structure, and the complication of hyperglycemia was observed. Engrafted MSCs were found inside degraded pancreatic regions and regulated inflammatory cytokines. Our results demonstrated that treatment with MSCs and vit. D in combination prevented pancreatic injury via antioxidant and immune regulation in diabetic rats, contributing to the prevention of pancreatic dysfunction, improvement of lipid metabolism, and regulation of cytokine gene expression compared with each one separately. All these mechanisms also improved the histological structure of the pancreas based on transmission electron microscopy. The combination of MSCs and vit. D appears to have contributed to a greater improvement in the diabetic pancreatic complication of rats than was observed by each one separately. Therefore, this association can be used as antidiabetic therapy. Full article
(This article belongs to the Special Issue Biomedical Application of Natural Plant Extracts)
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Article
Antifungal Hydroxypropyl Methylcellulose (HPMC)-Lipid Composite Edible Coatings and Modified Atmosphere Packaging (MAP) to Reduce Postharvest Decay and Improve Storability of ‘Mollar De Elche’ Pomegranates
Coatings 2021, 11(3), 308; https://doi.org/10.3390/coatings11030308 - 09 Mar 2021
Cited by 1
Abstract
Pomegranate exhibits important postharvest quality losses that limit its storage potential, caused mainly by weight loss, chilling injury and fungal diseases. In this work, we evaluated the effect of novel hydroxypropyl methylcellulose (HPMC) edible coatings (ECs) formulated with three different lipids (beeswax (BW), [...] Read more.
Pomegranate exhibits important postharvest quality losses that limit its storage potential, caused mainly by weight loss, chilling injury and fungal diseases. In this work, we evaluated the effect of novel hydroxypropyl methylcellulose (HPMC) edible coatings (ECs) formulated with three different lipids (beeswax (BW), carnauba wax, and glycerol monostearate), as hydrophobic components, and two different GRAS salts (potassium bicarbonate (PBC) and sodium benzoate (SB)), as antifungal ingredients, to control weight loss and natural fungal decay of ‘Mollar de Elche’ pomegranates during storage at 20 °C. Afterwards, selected antifungal ECs and commercial modified atmosphere packaging (MAP) films were assayed alone or in combination to control natural decay and preserve fruit quality of pomegranates stored at 5 °C for 4 months plus 1 week at 20 °C. Results showed that ECs amended with SB reduced pomegranate latent infections caused by Botrytis cinerea and wound diseases caused by Penicillium spp. Moreover, MAP technologies were confirmed as an efficient mean to preserve freshness, prevent fruit shriveling and rind browning, and reduce fungal decay, thus extending storage life of pomegranates. The combination HPMC-BW-SB + MAP was the most promising treatment as it reduced weight loss and decay, without negatively affecting the fruit physicochemical and sensory quality. Full article
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Article
Interplay of Hydrophobic Thiol and Polar Epoxy Silicate Groups on Microstructural Development in Low-Alcohol, Crosslinked Sol–Gel Coatings for Corrosion Prevention
Coatings 2021, 11(3), 306; https://doi.org/10.3390/coatings11030306 - 08 Mar 2021
Abstract
We have demonstrated that our patented, crosslinked, sol–gel, epoxy–thiol silicates made from the combination of (a) tetraethoxysilane (TEOS, T), 3-glycidoxypropyltrimethoxysilane (GPTMS, G), and the (b) sulfur-containing 3-mercaptopropyltrimethoxysilane (MPTMS, S) with TEOS in a 1:1 stoichiometric ratio form the 1:1 TGST [...] Read more.
We have demonstrated that our patented, crosslinked, sol–gel, epoxy–thiol silicates made from the combination of (a) tetraethoxysilane (TEOS, T), 3-glycidoxypropyltrimethoxysilane (GPTMS, G), and the (b) sulfur-containing 3-mercaptopropyltrimethoxysilane (MPTMS, S) with TEOS in a 1:1 stoichiometric ratio form the 1:1 TGST (crosslinked epoxy and thiol silicates) coating, which can be successfully utilized for the corrosion protection of low-carbon steel. Alcohols that are a by-product of sol–gel reactions influence the network formation, crosslinking density, and formulation stability, are volatile organic contents, and are regulated in the coatings industry. To improve environmental sustainability, a series of low-alcohol (LA) formulations with TG:ST ratios of 3:1 to 1:3 was prepared to investigate the microstructural development and crosslinking reactions emerging from the interplay of the hydrophobic thiol and polar epoxy silicates induced by the low-alcohol environment. The impact on crosslinking density was characterized by Fourier Transform Infrared (FTIR), Raman, XPS, viscosity, and pot-life measurements. Low-alcohol TGST (LA(TGST)) formulations were compared, using the example of 1:1 TGST, to corresponding TGST formulations where alcohols were retained. The reduced impact of LA(TGST) formulations on global warming was quantified. The glossy and scratch-resistant LA(TGST) coatings showed 71% enhanced corrosion protection compared to the non-crosslinked hybrids. Full article
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Article
Characterization and Identification of Varnishes on Copper Alloys by Means of UV Imaging and FTIR
Coatings 2021, 11(3), 298; https://doi.org/10.3390/coatings11030298 - 05 Mar 2021
Cited by 3
Abstract
The application of varnishes on the surface of metal objects has been a very common practice since antiquity, both for protective and aesthetic purposes. One specific case concerns the use of tinted varnishes on copper alloys in order to mimic gilding. This practice, [...] Read more.
The application of varnishes on the surface of metal objects has been a very common practice since antiquity, both for protective and aesthetic purposes. One specific case concerns the use of tinted varnishes on copper alloys in order to mimic gilding. This practice, especially flourishing in the 19th century for scientific instruments, decorative objects, and liturgical items, results in large museum collections of varnished copper alloys that need to be preserved. One of the main challenges for conservators and restorers deals with the identification of the varnishes through non-invasive and affordable analytical techniques. We hereby present the experimental methodology developed in the framework of the LacCA and VERILOR projects at the Haute École ARC of Neuchâtel for the identification of gold varnishes on brass. After extensive documentary research and analytical campaigns on varnished museum objects, various historic shellac-based varnishes were created and applied by different methods on a range of brass substrates with different finishes. The samples were then characterized by UV imaging and infrared spectroscopy before and after artificial ageing. The comparative study of these two techniques was performed for different thicknesses of the same varnish and for different shellac grades in order to implement an identification methodology based on simple non-invasive examination and analytical tools, which are accessible to conservators. Full article
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Article
Multifunctional Nanocrystalline Cu–Ti Thin Films Enhance Survival and Induce Proliferation of Mouse Fibroblasts In Vitro
Coatings 2021, 11(3), 300; https://doi.org/10.3390/coatings11030300 - 05 Mar 2021
Abstract
This paper describes the effect of a nanocrystalline thin film based on copper and titanium on mouse fibroblast cells. Cu–Ti coatings were prepared using magnetron sputtering. In their composition was 25 at.% Cu and 75 at.% Ti. The goal of the study was [...] Read more.
This paper describes the effect of a nanocrystalline thin film based on copper and titanium on mouse fibroblast cells. Cu–Ti coatings were prepared using magnetron sputtering. In their composition was 25 at.% Cu and 75 at.% Ti. The goal of the study was to evaluate the effect of the material on the survival, migration, and proliferative capabilities of mouse L929 fibroblasts. The Cu25Ti75 material had no effect on the induction of cell death and did not disturb the cell cycle phase. The study showed a unique effect of a Cu25Ti75 thin film on mouse fibroblast cells, and the results concerning mitochondrial activity, cell proliferation, and migration proved that the material is nontoxic and shows proliferative properties in a wound healing test. The possible biomedical applications of the new nanocrystalline thin film biomaterial with multifunctional properties are described. Full article
(This article belongs to the Special Issue Biomaterials and Antimicrobial Coatings)
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Article
Direct-ARPES and STM Investigation of FeSe Thin Film Growth by Nd:YAG Laser
Coatings 2021, 11(3), 276; https://doi.org/10.3390/coatings11030276 - 26 Feb 2021
Cited by 1
Abstract
Research on ultrathin quantum materials requires full control of the growth and surface quality of the specimens in order to perform experiments on their atomic structure and electron states leading to ultimate analysis of their intrinsic properties. We report results on epitaxial FeSe [...] Read more.
Research on ultrathin quantum materials requires full control of the growth and surface quality of the specimens in order to perform experiments on their atomic structure and electron states leading to ultimate analysis of their intrinsic properties. We report results on epitaxial FeSe thin films grown by pulsed laser deposition (PLD) on CaF2 (001) substrates as obtained by exploiting the advantages of an all-in-situ ultra-high vacuum (UHV) laboratory allowing for direct high-resolution surface analysis by scanning tunnelling microscopy (STM), synchrotron radiation X-ray photoelectron spectroscopy (XPS) and angle-resolved photoemission spectroscopy (ARPES) on fresh surfaces. FeSe PLD growth protocols were fine-tuned by optimizing target-to-substrate distance d and ablation frequency, atomically flat terraces with unit-cell step heights are obtained, overcoming the spiral morphology often observed by others. In-situ ARPES with linearly polarized horizontal and vertical radiation shows hole-like and electron-like pockets at the Γ and M points of the Fermi surface, consistent with previous observations on cleaved single crystal surfaces. The control achieved in growing quantum materials with volatile elements such as Se by in-situ PLD makes it possible to address the fine analysis of the surfaces by in-situ ARPES and XPS. The study opens wide avenues for the PLD based heterostructures as work-bench for the understanding of proximity-driven effects and for the development of prospective devices based on combinations of quantum materials. Full article
(This article belongs to the Special Issue Pulsed Laser Deposition of Thin Films: Recent Advances and Challenges)
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Article
Effect of Irradiation with Si+ Ions on Phase Transformations in Ti–Al System during Thermal Annealing
Coatings 2021, 11(2), 205; https://doi.org/10.3390/coatings11020205 - 10 Feb 2021
Abstract
The article deals with the effect of irradiation with Si+ ions on phase transformations in the Ti–Al system during thermal annealing. An aluminum film with a thickness of 500 nm was deposited on VT1-00 titanium samples by magnetron sputtering, followed by ion implantation. [...] Read more.
The article deals with the effect of irradiation with Si+ ions on phase transformations in the Ti–Al system during thermal annealing. An aluminum film with a thickness of 500 nm was deposited on VT1-00 titanium samples by magnetron sputtering, followed by ion implantation. Samples before and after irradiation with Si ions were annealed in a vacuum of 10−4 Pa in the temperature range 600–1000 °C. It was established that ion implantation reduces the dissolution of Al in α-Ti with the formation of titanium silicides (TiSi2, Ti5Si3) and stabilizes aluminide phases Ti3Al rich in aluminum. As a result, a composite structure based on titanium silicide/aluminide was obtained on the surface of the sample synthesized by complex treatment: deposition, irradiation with Si+, and thermal annealing at the near-surface layers. The formation of the phase-structural state of the implanted layers is associated with the displacement of atoms of the crystal lattice, a result that is reflected in an increase in the size of the crystal lattice and a decrease in microdistortion of the lattice. The opposite effect is observed with increasing temperature. This fact is explained by the relaxation of unstable large grains with an excess of internal energies. At the annealing temperature of 900–1000 °C, a significant increase in microhardness was observed due to silicide phases. Full article
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Article
Sputter Deposited Metal Layers Embedded in Composites—From Fundamentals to Applications
Coatings 2021, 11(2), 190; https://doi.org/10.3390/coatings11020190 - 06 Feb 2021
Cited by 1
Abstract
Due to the low heat flux towards the substrate, magnetron sputter deposition offers the possibility to deposit thin films on heat sensitive materials such as fiber-reinforced polymers, also known as composite materials. Passive thermal probe measurements during the sputter deposition of metal layers [...] Read more.
Due to the low heat flux towards the substrate, magnetron sputter deposition offers the possibility to deposit thin films on heat sensitive materials such as fiber-reinforced polymers, also known as composite materials. Passive thermal probe measurements during the sputter deposition of metal layers show indeed that the temperature increase remains well below 25 °C for film thicknesses up to 600 nm. The latter thickness threshold is based on the influence of embedded metal films on the adhesion of the composite plies. Films thicker than this threshold deteriorate the mechanical integrity of the composite. The introduction of the uncured composite in the vacuum chamber strongly affects the base pressure by outgassing of impurities from the composite. The impurities affect the film properties as illustrated by their impact on the Seebeck coefficient of sputter deposited thermocouples. The restrictions to embed thin films in composites, as illustrated by both the heat flux measurements, and the study on the influence of impurities, are however not insurmountable. The possibility to use embedded thin films will be briefly demonstrated in different applications such as digital volume image correlation, thermocouples, and de-icing. Full article
(This article belongs to the Section Thin Films)
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Article
Microstructural Charactistics of Plasma Sprayed NiCrBSi Coatings and Their Wear and Corrosion Behaviors
Coatings 2021, 11(2), 170; https://doi.org/10.3390/coatings11020170 - 31 Jan 2021
Cited by 1
Abstract
Nickel-based alloys are commonly used as protective coating materials for surface protection applications owing to their superior resistance to corrosion, wear and high-temperature oxidation. It is urgent to study the fundamental mechanism between the structure and corrosion properties of the Nickel-base composite coatings. [...] Read more.
Nickel-based alloys are commonly used as protective coating materials for surface protection applications owing to their superior resistance to corrosion, wear and high-temperature oxidation. It is urgent to study the fundamental mechanism between the structure and corrosion properties of the Nickel-base composite coatings. This paper, therefore, focuses on clarifying the mechanisms of the microstructure influencing the acid corrosion and mechanical characteristics of the as-sprayed NiCrBSi coating and post-heat-treated coating. The formation mechanisms of the amorphous phase of flat particles during the plasma spray process were studied by using X-ray diffraction analysis, Raman spectroscopy and confocal laser scanning microscope at first. Then the evolutionary process of the corrosion structure and phase of the coating in the accelerated corrosion experiment is directly visualized by using scanning electron microscopy and energy spectrum analysis. The mechanical properties of the amorphous NiCrBSi coatings are lastly measured by microhardness and friction wear tests. The critical phenomena and results help to elucidate the relative influence of the surface features of atmospheric plasma sprayed coatings on acid corrosion responses and wear resistance, aiming at contributing to the development of a protective technique for electrical engineering. Full article
(This article belongs to the Special Issue New Advances in Thermal Spraying)
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Article
Surface Functionalization Utilizing Mesoporous Silica Nanoparticles for Enhanced Evanescent-Field Mid-Infrared Waveguide Gas Sensing
Coatings 2021, 11(2), 118; https://doi.org/10.3390/coatings11020118 - 21 Jan 2021
Cited by 1
Abstract
This work focuses on the development of nanoparticle-based layer-by-layer (LbL) coatings for enhancing the detection sensitivity and selectivity of volatile organic compounds (VOCs) using on-chip mid-infrared (MIR) waveguides (WGs). First, we demonstrate construction of conformal coatings of polymer/mesoporous silica nanoparticles (MSNs) on the [...] Read more.
This work focuses on the development of nanoparticle-based layer-by-layer (LbL) coatings for enhancing the detection sensitivity and selectivity of volatile organic compounds (VOCs) using on-chip mid-infrared (MIR) waveguides (WGs). First, we demonstrate construction of conformal coatings of polymer/mesoporous silica nanoparticles (MSNs) on the surface of Si-based WGs using the LbL technique and evaluate the coating deposition conditions, such as pH and substrate withdrawal speed, on the thickness and homogeneity of the assemblies. We then use the modified WGs to achieve enhanced sensitivity and selectivity of polar organic compounds, such as ethanol, versus non-polar ones, such as methane, in the MIR region. In addition, using density functional theory calculations, we show that such an improvement in sensing performance is achieved due to preferential adsorption of ethanol molecules within MSNs in the vicinity of the WG evanescent field. Full article
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Article
One-Step Methods to Fabricate Durable Superhydrophobic Coatings for Flexible Electronic Sensors
Coatings 2021, 11(1), 95; https://doi.org/10.3390/coatings11010095 - 16 Jan 2021
Abstract
Inspired by lotus leaves in nature, superhydrophobic surfaces have attracted extensive attention in many fields. However, their complex preparation process, poor durability and high cost seriously restrict their large-scale application in industrial production. Based on the good flexibility and durability of carbon nanofibers, [...] Read more.
Inspired by lotus leaves in nature, superhydrophobic surfaces have attracted extensive attention in many fields. However, their complex preparation process, poor durability and high cost seriously restrict their large-scale application in industrial production. Based on the good flexibility and durability of carbon nanofibers, several simple modifier-free one-step approaches were adopted to fabricate a durable CNF/PVDF/PDMS conductive superhydrophobic coating. The fabricated coating not only possesses good superhydrophobicity to many kinds of liquids, but also has excellent self-cleaning and anti-fouling properties. In addition, the superhydrophobicity of the obtained multifunctional coating is stable even after harsh bending fatigue deformation, long immersion times and high-temperature treatment. Due to its strong adhesion and excellent conductivity, the CNF/PVDF/PDMS coating displays reliable mechanical stability and superior sensitivity. These distinct features make the obtained conductive superhydrophobic coating a good candidate for multifunctional smart sensors, with great application prospects in gesture detectors, waterproof wearable electronics and health monitors. Full article
(This article belongs to the Section Bioactive Coatings and Biointerfaces)
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Article
Surface and Interface Treatments on Wooden Artefacts: Potentialities and Limits of a Non-Invasive Multi-Technique Study
Coatings 2021, 11(1), 29; https://doi.org/10.3390/coatings11010029 - 29 Dec 2020
Cited by 4
Abstract
Wooden artefacts embrace wide-ranging types of objects, like paintings on panel, sculptures, musical instruments, and furniture. Generally, in the manufacturing process of an artwork, wood is firstly treated with organic and inorganic materials to make it nonporous and morphologically homogeneous, and, at last, [...] Read more.
Wooden artefacts embrace wide-ranging types of objects, like paintings on panel, sculptures, musical instruments, and furniture. Generally, in the manufacturing process of an artwork, wood is firstly treated with organic and inorganic materials to make it nonporous and morphologically homogeneous, and, at last, the surface treatment consists of varnishes or coatings applied with the aims of conferring aesthetic properties and protecting wood from biological growth and external degradation agents, as well as mechanical damage. In this work, different wooden mock-ups were prepared by varying some parameters: concentration of filler and pigment, respectively, in the ground and paint layers, thickness of the protective varnish coat, and sequence of the layers. The mock-ups were subsequently exposed to time-varying artificial aging processes. The multi-analytical non-invasive approach involved spectroscopic (reflection FT-IR, Raman, and X-ray fluorescence), tomographic (optical coherence tomography) and colorimetric techniques. Data were interpreted using both univariate and multivariate methods. The aim was to evaluate potential and limits of each non-invasive technique into the study of different stratigraphies of wooden artworks. This approach was supported by microscopic observations of cross-sections obtained from selected mock-ups. The methodological approach proposed here would add valuable technical know-how and information about the non-invasive techniques applied to the study of wooden artworks. Full article
(This article belongs to the Special Issue Surface and Interface Analysis of Cultural Heritage)
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Article
Pulsed Magnetron Sputtering of Strongly Thermochromic VO2-Based Coatings with a Transition Temperature of 22 °C onto Ultrathin Flexible Glass
Coatings 2020, 10(12), 1258; https://doi.org/10.3390/coatings10121258 - 19 Dec 2020
Cited by 4
Abstract
The reversible semiconductor-to-metal transition of vanadium dioxide (VO2) makes VO2-based coatings a promising candidate for thermochromic smart windows, reducing the energy consumption of buildings. This paper deals with maximizing the application potential of these coatings in terms of their [...] Read more.
The reversible semiconductor-to-metal transition of vanadium dioxide (VO2) makes VO2-based coatings a promising candidate for thermochromic smart windows, reducing the energy consumption of buildings. This paper deals with maximizing the application potential of these coatings in terms of their performance, an industry-friendly preparation technique, and an industrially relevant substrate. We present a scalable sputter deposition technique for the preparation of strongly thermochromic ZrO2/V0.984W0.016O2/ZrO2 coatings on ultrathin flexible glass and standard glass at a relatively low substrate surface temperature (330 °C) and without any substrate bias voltage. The V0.984W0.016O2 layers were deposited by a controlled high-power impulse magnetron sputtering of a V target, combined with a simultaneous pulsed dc magnetron sputtering of a W target. We explain the fundamental principles of this technique using the discharge characteristics measured for both discharges. We characterize the coating structure (X-ray diffraction) and a wide range of optical properties (spectrophotometry and spectroscopic ellipsometry). We find that the coatings combine a transition temperature of 22 °C, a luminous transmittance approaching 50%, a modulation of the solar energy transmittance over 10% and a temperature-independent color. The results in general, and the successful transfer from a standard glass to the ultrathin flexible glass in particular, are crucial for future applications of the coatings on smart windows. Full article
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Article
Analysis of Surface Roughness and Flank Wear Using the Taguchi Method in Milling of NiTi Shape Memory Alloy with Uncoated Tools
Coatings 2020, 10(12), 1259; https://doi.org/10.3390/coatings10121259 - 19 Dec 2020
Cited by 4
Abstract
The aim of this study was to optimize machining parameters to obtain the smallest average surface roughness (Ra) and flank wear (Vb) values as a result of the surface milling of a nickel-titanium (NiTi) shape memory alloy (SMA) with uncoated cutting tools with [...] Read more.
The aim of this study was to optimize machining parameters to obtain the smallest average surface roughness (Ra) and flank wear (Vb) values as a result of the surface milling of a nickel-titanium (NiTi) shape memory alloy (SMA) with uncoated cutting tools with different nose radius (rε) under dry cutting conditions. Tungsten carbide cutting tools with different rε (0.4 mm and 0.8 mm) were used in milling operations. The milling process was performed as lateral/surface cutting at three different cutting speeds (Vc) (20, 35 and 50 m/min), feed rates (fz) (0.03, 0.07 and 0.14 mm/tooth) and a constant axial cutting depth (0.7 mm). The effects of machining parameters in milling experiments were investigated based on the Taguchi L18 (21 × 32) orthogonal sequence, and the data obtained were analyzed using the Minitab 17 software. To determine the effects of processing parameters on Ra and Vb, analysis of variance (ANOVA) was used. The analysis results reveal that the dominant factor affecting the Ra is the cutting tool rε, while the main factor affecting Vb is the fz. Since the predicted values and measured values are very close to each other, it can be said that optimization is correct according to the validation test results. Full article
(This article belongs to the Special Issue Advanced Coating Materials for Machining Processes)
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Article
Distribution of Characteristic Times: A High-Resolution Spectrum Approach for Visualizing Chemical Relaxation and Resolving Kinetic Parameters of Ionic-Electronic Conducting Ceramic Oxides
Coatings 2020, 10(12), 1240; https://doi.org/10.3390/coatings10121240 - 17 Dec 2020
Cited by 3
Abstract
Surface exchange coefficient (k) and bulk diffusion coefficient (D) are important properties to evaluate the performance of mixed ionic-electronic conducting (MIEC) ceramic oxides for use in energy conversion devices, such as solid oxide fuel cells. The values of k [...] Read more.
Surface exchange coefficient (k) and bulk diffusion coefficient (D) are important properties to evaluate the performance of mixed ionic-electronic conducting (MIEC) ceramic oxides for use in energy conversion devices, such as solid oxide fuel cells. The values of k and D are usually estimated by a non-linear curve fitting procedure based on electrical conductivity relaxation (ECR) measurement. However, the rate-limiting mechanism (or the availability of k and D) and the experimental imperfections (such as flush delay for gaseous composition change, τf) are not reflected explicitly in the time–domain ECR data, and the accuracy of k and D demands a careful sensitivity analysis of the fitting error. Here, the distribution of characteristic times (DCT) converted from time–domain ECR data is proposed to overcome the above challenges. It is demonstrated that, from the DCT spectrum, the rate-limiting mechanism and the effect of τf are easily recognized, and the values of k, D and τf can be determined conjunctly. A strong robustness of determination of k and D is verified using noise-containing ECR data. The DCT spectrum opens up a way towards visible and credible determination of kinetic parameters of MIEC ceramic oxides. Full article
(This article belongs to the Special Issue Surface Engineering of C/N/O Functionalized Materials)
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Article
Strong Coupling between Tamm and Surface Plasmons for Advanced Optical Bio-Sensing
Coatings 2020, 10(12), 1187; https://doi.org/10.3390/coatings10121187 - 05 Dec 2020
Cited by 2
Abstract
The total internal reflection ellipsometry method was used to analyse the angular spectra of the hybrid Tamm and surface plasmon modes and to compare their results with those obtained using the conventional single SPR method. As such type of measurement is quite common [...] Read more.
The total internal reflection ellipsometry method was used to analyse the angular spectra of the hybrid Tamm and surface plasmon modes and to compare their results with those obtained using the conventional single SPR method. As such type of measurement is quite common in commercial SPR devices, more detailed attention was paid to the analysis of the p-polarization reflection intensity dependence. The conducted study showed that the presence of strong coupling in the hybrid plasmonic modes increases the sensitivity of the plasmonic-based sensors due to the reduced losses in the metal layer. The experimental results and analysis of the optical responses of three different plasmonic-based samples indicated that the optimized Tamm plasmons ΔRp(TP) and optimized surface plasmons ΔRp(SP) samples produce a response that is about five and six times greater than the conventional surface plasmon resonance ΔRp(SPR) in angular spectra. The sensitivity of the refractive index unit of the spectroscopic measurements for the optimized Tamm plasmon samples was 1.5 times higher than for conventional SPR, while for wavelength scanning, the SPR overcame the optimized TP by 1.5 times. Full article
(This article belongs to the Special Issue Thin Films and Surface Optics)
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Article
Influence of Plasma Electrolytic Oxidation on Fatigue Behaviour of ZK60A-T5 Magnesium Alloy
Coatings 2020, 10(12), 1180; https://doi.org/10.3390/coatings10121180 - 02 Dec 2020
Cited by 3
Abstract
Magnesium alloys are used in the motorsport and aerospace fields because of their high specific strength. However, due to their low corrosion resistance, protective surface treatments, such as conversion coating or electroless plating, are necessary when they are used in humid or corrosive [...] Read more.
Magnesium alloys are used in the motorsport and aerospace fields because of their high specific strength. However, due to their low corrosion resistance, protective surface treatments, such as conversion coating or electroless plating, are necessary when they are used in humid or corrosive environments. The present study aimed at evaluating the effect of plasma electrolytic oxidation (PEO), followed by the deposition of a polymeric layer by powder coating, on the rotating bending fatigue behaviour of the wrought magnesium alloy ZK60A-T5. The specimens were extracted from forged wheels of racing motorbikes and were PEO treated and powder coated. Microstructural characterization was carried out by optical (OM) and scanning electron microscopy (SEM) to analyse both the bulk material and the multilayer, consisting of the anodic oxide interlayer with the powder coating top layer (about 40 µm total thickness). Rotating bending fatigue tests were carried out to obtain the S–N curve of PEO-treated specimens. The results of the rotating bending tests evidenced fatigue strength equal to 104 MPa at 106 cycles and 90 MPa at 107 cycles. The results of the investigation pointed out that PEO led to a reduction in fatigue strength between 14% and 17% in comparison to the untreated alloy. Fracture surface analyses of the fatigue specimens, carried out by SEM and by 3D digital microscopy, highlighted multiple crack initiation sites at the interface between the PEO layer and substrate, induced by the concurrent effects of coating defects, local tensile stresses in the substrate, and increased roughness at the substrate–coating interface. Full article
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Article
Surface Characterization and Tribological Behavior of Graphene-Reinforced Cellulose Composites Prepared by Large-Area Spray Coating on Flexible Substrate
Coatings 2020, 10(12), 1176; https://doi.org/10.3390/coatings10121176 - 01 Dec 2020
Cited by 1
Abstract
A large-area spray coating process is introduced to efficiently apply a graphene/Cu/cellulose composite on a flexible glass substrate. The dispersion characteristics of nano-additives are measured and the Tyndall effect observed. The characteristics of the composite coating such as the film thickness, surface roughness, [...] Read more.
A large-area spray coating process is introduced to efficiently apply a graphene/Cu/cellulose composite on a flexible glass substrate. The dispersion characteristics of nano-additives are measured and the Tyndall effect observed. The characteristics of the composite coating such as the film thickness, surface roughness, water contact angle, and lubricating characteristics are measured. The tribological properties of the composite coating are measured using a ball-on-disk. The wear width of the abrasive parts, as well as the wear and friction coefficient of the grinding balls, are investigated. Adding graphene/Cu helps to improve the anti-wear ability of cellulose. The transfer layer was observed using the Raman spectroscopy and mapping technology. Finally, the lubricating mechanism is discussed, and the wear mechanism is proposed. Nanoparticles existed in the wear track as the third-body particles and improved the load capacity of the composites. The wear mechanism of the composites is discussed in terms of the worn surfaces and the analysis of the transfer film with the third-body approach. Full article
(This article belongs to the Special Issue New Advances in Functional Optical Thin Films)
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Article
Optimizing Heat Treatment for Electroplated NiP and NiP/SiC Coatings
Coatings 2020, 10(12), 1179; https://doi.org/10.3390/coatings10121179 - 01 Dec 2020
Cited by 3
Abstract
NiP (P > 10 wt.%) coatings are amorphous coatings whose structure can be transformed by heat treatment into a crystalline structure and hardened by precipitation of Ni3P. In this study, NiP coatings and composite ones with SiC nanoparticles were produced by [...] Read more.
NiP (P > 10 wt.%) coatings are amorphous coatings whose structure can be transformed by heat treatment into a crystalline structure and hardened by precipitation of Ni3P. In this study, NiP coatings and composite ones with SiC nanoparticles were produced by electrodeposition, and their structural transformation by heat treatment was studied using differential scanning calorimetry (DSC) and X-ray diffraction (XRD). The microhardness and the scratch and corrosion resistance of the coatings were evaluated and compared before and after different heat treatments. The results showed that in as-plated condition, the addition of SiC particles in the coatings did not modify the microstructure, microhardness, or electrochemical behavior. However, the SiC particles’ role was disclosed in combination with heat treatment. Composite coatings that were heat treated at 300 °C had higher microhardness and scratch resistance than the pure NiP one. In addition, composite coatings maintained their scratch resistance up to 400 °C, while in the case of the NiP ones, there was a reduction in scratch resistance by heating at 400 °C. It was also concluded that heating temperature has the main role in hardness and corrosion resistance of NiP and composite coatings, rather than heating time. The optimum heat-treatment protocol was found to be heating at 360 °C for 2 h, which resulted in a maximum microhardness of about 1500 HV0.02 for NiP and its composite coating without sacrificing the corrosion resistance. Full article
(This article belongs to the Section Surface Characterization, Deposition and Modification)
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Article
Bio-Inspired Facile Synthesis of Graphene-Based Nanocomposites: Elucidation of Antimicrobial and Biofilm Inhibitory Potential against Foodborne Pathogenic Bacteria
Coatings 2020, 10(12), 1171; https://doi.org/10.3390/coatings10121171 - 29 Nov 2020
Cited by 2
Abstract
Herein, a new and simple biogenic method for the preparation of gold nanoparticles (AuNPs) and their reduced graphene oxide based nanocomposites (Au-RGO) by using microwave irradiation method for antimicrobial and biofilm inhibition against foodborne pathogenic bacteria was reported. X-ray diffraction (XRD), Raman, and [...] Read more.
Herein, a new and simple biogenic method for the preparation of gold nanoparticles (AuNPs) and their reduced graphene oxide based nanocomposites (Au-RGO) by using microwave irradiation method for antimicrobial and biofilm inhibition against foodborne pathogenic bacteria was reported. X-ray diffraction (XRD), Raman, and transmission electron microscopy (TEM) analyses confirmed that the AuNPs with face centered cubic (FCC) structure were indeed anchored onto the RGO sheets. Ultraviolet-Vis (UV-VIS) spectrum showed a shifting and broadening of absorption peaks of AuNPs when attached on the surface of RGO sheets. The effect of sub-inhibitory concentrations of Au-RGO nanocomposites on biofilm formation in five foodborne pathogens was assessed. Au-RGO nanocomposites reduced the formation of biofilm by 75%, 78%, 68%, 80% and 79% in L. monocytogenes, MRSA, E. coli, S. marcescens and P. aeruginosa, respectively. Exopolysaccharides (EPS), a vital component of the biofilm was also inhibited significantly and pre-formed mature biofilms were also reduced considerably. Further, this study demonstrated that the reactive oxygen species (ROS) generation induced in bacterial cells as a result of Au-RGO treatment could be the plausible mechanism for biofilm inhibitory action. The tested concentrations were found non-toxic to human embryonic kidney cell lines (HEK-293). The investigation highlights the broad-spectrum biofilm inhibitory properties of Au-RGO nanocomposites that could be exploited in the food industry to prevent biofilm-based food contamination. Full article
(This article belongs to the Section Coatings for Food Technology and System)
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Article
Significant Improvement of Anticorrosion Properties of Zinc-Containing Coating Using Sodium Polystyrene Sulfonate Noncovalent Modified Graphene Dispersions
Coatings 2020, 10(12), 1150; https://doi.org/10.3390/coatings10121150 - 25 Nov 2020
Cited by 1
Abstract
High-quality graphene zinc-containing anticorrosive coatings are highly and urgently desirable for effective, economical anticorrosion of metals and alloys in industrial products. The realization of such coatings is, however, hindered by the dispersibility and compatibility of the graphene in them. This work reports a [...] Read more.
High-quality graphene zinc-containing anticorrosive coatings are highly and urgently desirable for effective, economical anticorrosion of metals and alloys in industrial products. The realization of such coatings is, however, hindered by the dispersibility and compatibility of the graphene in them. This work reports a novel direct modification of graphene using sodium polystyrene sulfonate (PSS) without reduction of graphene oxide, leading to homogeneous dispersion of graphene in water. The agglomeration of graphene is prevented thanks to the formation of π−π interaction between PSS and graphene sheets. Such graphene dispersion can effectively improve the anticorrosion performance of the zinc-containing epoxy coatings. With the addition of graphene modified by PSS into the 20% zinc-containing epoxy coating (graphene is 0.05% by weight of the coating), its anticorrosion properties revealed by both electrochemical characterization and the neutral salt spray tolerance analysis are rather close to those of 60% zinc-containing epoxy coating. These results demonstrate that direct PSS modification is an effective method for graphene dispersion and thus open a pathway to achieve graphene zinc-containing anticorrosive coatings with high performance. Full article
(This article belongs to the Special Issue Coatings for Corrosion Mitigation)
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Article
Effect of Rb+ Doping on Tunable Luminescence in Yb3+/Er3+–Y2O3 Film
Coatings 2020, 10(11), 1137; https://doi.org/10.3390/coatings10111137 - 23 Nov 2020
Cited by 3
Abstract
In this paper, a series of Rb+-doped Er3+/Yb3+–Y2O3 films were synthesized via a sol-gel method and spin coating. The structure and morphology of the samples were investigated by X-ray diffraction and scanning electron microscopy. [...] Read more.
In this paper, a series of Rb+-doped Er3+/Yb3+–Y2O3 films were synthesized via a sol-gel method and spin coating. The structure and morphology of the samples were investigated by X-ray diffraction and scanning electron microscopy. The Rb+-doped films with nanoparticles, in the size range of 20–40 nm, were obtained. The spectroscopic analysis of the samples was investigated by using the emission spectra and the intensity of luminescence. All the samples exhibited a green emission ascribed to 2H11/2/4S3/2 to 4I15/2 of Er3+ and a red one ascribed to 4F9/2 and its stark level to 4I15/2 of Er3+. As the Rb+ concentration increased, the intensities of the green light and red light were enhanced 16.97- and 5.81-fold relative to that of the undoped sample. Moreover, by controlling the Rb+ concentration, the samples were capable of generating color-tunable luminescence from red to green linearly. The tunable emission was caused by the change of ion distribution ratio in 4F7/2(Er) and 4F9/2(Er) levels. The results suggest that the as-prepared Rb+-doped Er3+/Yb3+–Y2O3 films have a great potential for applications of luminescence. Full article
(This article belongs to the Section Thin Films)
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Article
Production of Microbial Cellulose Films from Green Tea (Camellia Sinensis) Kombucha with Various Carbon Sources
Coatings 2020, 10(11), 1132; https://doi.org/10.3390/coatings10111132 - 22 Nov 2020
Cited by 1
Abstract
The aim of this study was to evaluate the production of microbial cellulose films (MCFs) in culture media based on green tea and different carbon sources, using two microbial consortia (COr and CFr). During the fermentation process, there was a reduction in the [...] Read more.
The aim of this study was to evaluate the production of microbial cellulose films (MCFs) in culture media based on green tea and different carbon sources, using two microbial consortia (COr and CFr). During the fermentation process, there was a reduction in the total soluble solids (TSS) content and pH, as well as an increase in the acidity in all treatments. Furthermore, fluctuations in the total sugar content and proteins during the fermentation process were associated with the consumption of carbon and nitrogen sources, as well as the production of MCFs. In the color analysis, a decrease in the L* value was observed while the rest of the parameters remained stable. Production of films was observed between days 6 and 9 of fermentation; the preferred substrate for COr was glucose (wet base yields = 603.61% and dry base yields = 22.37%), whereas for CFr was dextrose (wet base yields = 601.49% and dry base yields = 28.14%). Finally, the MCFs produced by COr and CFr showed a homogeneous, thick appearance, slight flexibility, and the characteristic brown color of the fermentation medium. Full article
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Article
Strain-Dependent Resistivity of Granular Manganite Systems: A Simple Quantitative Approach
Coatings 2020, 10(11), 1081; https://doi.org/10.3390/coatings10111081 - 10 Nov 2020
Abstract
The effects of an applied strain tensor on the electrical resistivity of a manganite granular system are investigated using a simple approach describing the induced deformation in terms of the tilt angle between adjacent grains. The results obtained assuming the resistivity of each [...] Read more.
The effects of an applied strain tensor on the electrical resistivity of a manganite granular system are investigated using a simple approach describing the induced deformation in terms of the tilt angle between adjacent grains. The results obtained assuming the resistivity of each grain as given by a metallic part, coming from the inner grain, and a surface-related tunnel contribution, allow us to estimate appreciable resistivity variations even in the case of small deformation angles. Full article
(This article belongs to the Special Issue Advance in Perovskite Thin Films)
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Article
Mathematical Modeling of Carbon Flux Parameters for Low-Pressure Vacuum Carburizing with Medium-High Alloy Steel
Coatings 2020, 10(11), 1075; https://doi.org/10.3390/coatings10111075 - 09 Nov 2020
Cited by 1
Abstract
Low-pressure vacuum carburizing adopts a pulse process mode to improve the carburizing efficiency and reduces gas and energy consumption. Carbon flux is the key to accurately control the time of strong infiltration and diffusion in each pulse. In order to obtain the carbon [...] Read more.
Low-pressure vacuum carburizing adopts a pulse process mode to improve the carburizing efficiency and reduces gas and energy consumption. Carbon flux is the key to accurately control the time of strong infiltration and diffusion in each pulse. In order to obtain the carbon fluxes with various materials under diffident carburizing process conditions, an evenly segmented carbon flux method is proposed. A systematic study with each model using different materials (12Cr2Ni4A, 16Cr3NiWMoVNbE, and 18Cr2Ni4WA represent different initial carbon concentrations and different alloy compositions), carburizing temperatures, and carburizing pressures to determine the effect of these conditions on carbon flux is conducted. Compared with traditional segmented carbon flux method, an evenly segmented carbon flux method can predict the actual carbon flux more precisely and effectively in order to finely control the pulse carburization process. The paper also indicates that carbon fluxes increase with the increase of pressure. The optimal carburization pressure for low-pressure vacuum carburization is 300 Pa. Raising the carburization temperature to 980 °C instead of 920 °C can increase effective carbon flux by more than 30%. Among the material compositions, alloy content has the biggest impact over the carbon, initial carbon concentration the second, and saturated carbon concentration the third biggest impact. Full article
(This article belongs to the Special Issue Technologies of Coatings and Surface Hardening for Tool Industry)
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Article
Residual Stresses on Various PVD Hard Coatings on Tube and Plate Substrates
Coatings 2020, 10(11), 1054; https://doi.org/10.3390/coatings10111054 - 30 Oct 2020
Cited by 1
Abstract
In this study, the average residual stresses were determined in hard PVD nACRo (nc-AlCrN/a-Si3N4), nACo (nc-AlTiN/a-Si3N4), AlCrN, TiAlN, and TiCN commercial coatings through the deflection of the plate substrates and the simultaneous measurement of length [...] Read more.
In this study, the average residual stresses were determined in hard PVD nACRo (nc-AlCrN/a-Si3N4), nACo (nc-AlTiN/a-Si3N4), AlCrN, TiAlN, and TiCN commercial coatings through the deflection of the plate substrates and the simultaneous measurement of length variation in thin-walled tubular substrates. The length measuring unit was used for the measurement of any length change in the tubular substrate. A change in tube length was reduced to the deflection of the middle cross-section of the elastic element for which deformation was measured using four strain gauges. The cross-sectional microstructure and thickness of the coatings were investigated by means of scanning electron microscopy (SEM), and a determination was made of the chemical composition of the coatings and substrate by means of energy dispersive X-ray spectroscopy (EDS). The values of average compressive residual stresses, as determined by both methods, were very high (with a variation of between 2.05 and 6.63 GPa), irrespective of coating thickness, but were dependent upon the shape of the substrate and on its position in relation to the axis of the rotating cathode. The thicknesses of the coatings that were deposited on the plates with two parallel fixings (such as the nACRo coatings on the front surface at 6.8 μm and on the rear surface at 2.9 μm) and on the tubular substrates (10.0 μm) were significantly different. The higher average compressive residual stresses in the coating correlate to the higher average relative wear resistance that was obtained during field wear testing. Full article
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Article
Biodegradation and Antimicrobial Properties of Zinc Oxide–Polymer Composite Materials for Urinary Stent Applications
Coatings 2020, 10(10), 1002; https://doi.org/10.3390/coatings10101002 - 20 Oct 2020
Abstract
Research advancements in the field of urinary stents have mainly been in the selection of materials and coatings to address commonly faced problems of encrustation and bacterial adhesion. In this study, polylactic acid (PLA) and polypropylene (PP) were evaluated with zinc oxide (ZnO) [...] Read more.
Research advancements in the field of urinary stents have mainly been in the selection of materials and coatings to address commonly faced problems of encrustation and bacterial adhesion. In this study, polylactic acid (PLA) and polypropylene (PP) were evaluated with zinc oxide (ZnO) coating to assess its ability to reduce or eliminate the problems of encrustation and bacteria adhesion. PLA and PP films were prepared via twin screw extrusion. ZnO microparticles were prepared using sol-gel hydrothermal synthesis. The as-prepared ZnO microparticles were combined in the form of a functional coating and deposited on both polymer substrates using a doctor blade technique. The ZnO-coated PP and PLA samples as well as their uncoated counterparts were characterized from the physicochemical standpoints, antibacterial and biodegradation properties. The results demonstrated that both the polymers preserved their mechanical and thermal properties after coating with ZnO, which showed a better adhesion on PLA than on PP. Moreover, the ZnO coating successfully enhanced the antibacterial properties with respect to bare PP/PLA substrates. All the samples were investigated after immersion in simulated body fluid and artificial urine. The ZnO layer was completely degraded following 21 days immersion in artificial urine irrespective of the substrate, with encrustations more evident in PP and ZnO-coated PP films than PLA and ZnO-coated PLA films. Overall, the addition of ZnO coating on PLA displayed better adhesion, antibacterial activity and delayed the deposition of encrustations in comparison to PP substrates. Full article
(This article belongs to the Special Issue Recent Developments in Antibacterial and/or Antifouling Surfaces)
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Article
A Comparative Study of Adhesion Evaluation Methods on Ophthalmic AR Coating Lens
Coatings 2020, 10(10), 979; https://doi.org/10.3390/coatings10100979 - 14 Oct 2020
Abstract
Ophthalmic resin lenses are widely used to correct myopia and defend harmful light waves. Ophthalmic lens with anti-reflective (AR) coating has become the mainstream product in the lens market. The AR coating is composed by inorganic metal oxides, which is very different to [...] Read more.
Ophthalmic resin lenses are widely used to correct myopia and defend harmful light waves. Ophthalmic lens with anti-reflective (AR) coating has become the mainstream product in the lens market. The AR coating is composed by inorganic metal oxides, which is very different to the organic lens substrate in thermal expansion coefficients. In a normal wearing environment, coating delaminating often occurs resulting that AR function is disabled. How to evaluate adhesion of the AR coating is important. In this paper, a specially designed cutting tool was used to scratch two grids on each surface of the lens. The peel off operation was carried out with the tape within specified adhesion range. The coating detachment was evaluated by visual inspection and microscopy based on the methods defined in ISO 2409 and GB 10810.4, the applicability was compared and discussed. Full article
(This article belongs to the Special Issue Manufacturing and Surface Engineering II)
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Article
The Effect of Electrolytic Solution Composition on the Structure, Corrosion, and Wear Resistance of PEO Coatings on AZ31 Magnesium Alloy
Coatings 2020, 10(10), 937; https://doi.org/10.3390/coatings10100937 - 30 Sep 2020
Cited by 7
Abstract
Plasma electrolytic oxidation coatings were prepared in aluminate, phosphate, and silicate-based electrolytic solutions using a soft-sparking regime in a multi-frequency stepped process to compare the structure, corrosion, and wear characteristics of the obtained coatings on AZ31 magnesium alloy. The XRD results indicated that [...] Read more.
Plasma electrolytic oxidation coatings were prepared in aluminate, phosphate, and silicate-based electrolytic solutions using a soft-sparking regime in a multi-frequency stepped process to compare the structure, corrosion, and wear characteristics of the obtained coatings on AZ31 magnesium alloy. The XRD results indicated that all coatings consist of MgO and MgF2, while specific products such as Mg2SiO4, MgSiO3, Mg2P2O7, and MgAl2O4 were also present in specimens based on the selected solution. Surface morphology of the obtained coatings was strongly affected by the electrolyte composition. Aluminate-containing coating showed volcano-like, nodular particles and craters distributed over the surface. Phosphate-containing coating presented a sintering-crater structure, with non-uniform distributions of micro-pores and micro-cracks. Silicate-containing coating exhibited a scaffold surface involving a network of numerous micro-pores and oxide granules. The aluminate-treated sample offered the highest corrosion resistance and the minimum wear rate (5 × 10−5 mm3 N−1 m−1), owing to its compact structure containing solely 1.75% relative porosity, which is the lowest value in comparison with other samples. The silicate-treated sample was degraded faster in long-term corrosion and wear tests due to its porous structure, and with more delay in the phosphate-containing coating due to its larger thickness (30 µm). Full article
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On the Role of γ-Fe2O3 Nanoparticles and Reduced Graphene Oxide Nanosheets in Enhancing Self-Cleaning Properties of Composite TiO2 for Cultural Heritage Protection
Coatings 2020, 10(10), 933; https://doi.org/10.3390/coatings10100933 - 29 Sep 2020
Abstract
The durability of novel metallic artifacts and buildings is an open issue, and the role of smart protecting coatings in extending these artifacts’ lifetimes is crucial. In this paper, the role of γ-Fe2O3 nanoparticles and reduced graphene oxide (rGO) nanosheets [...] Read more.
The durability of novel metallic artifacts and buildings is an open issue, and the role of smart protecting coatings in extending these artifacts’ lifetimes is crucial. In this paper, the role of γ-Fe2O3 nanoparticles and reduced graphene oxide (rGO) nanosheets on enhancing the self-cleaning properties of composite TiO2 films and reducing metal alterations due to contact with acid rain and pollutants is investigated. The photocatalytic assessment of the TiO2 based films indicates that there are optimum contents for γ-Fe2O3 and rGO, which confer the film lower bandgap and tune the TiO2 anatase/rutile ratio. By adding a proper content of γ-Fe2O3, wettability is reduced both in dark and under illumination, which could be related to higher roughness. γ-Fe2O3 overloading causes increasing crack density and eventually a fully cracked structure. Adding an appropriate amount of rGO causes a sharp increase in roughness, due to the stacking of rGO nanosheets, while simultaneously avoiding cracking. At higher contents of rGO, wettability further decreases due to higher amounts of hydroxyl groups bound onto rGO; also in this case, overloading causes film cracking. Evaluation of self-cleaning performance and discoloration resistance under soiling and acid rain simulated tests demonstrates that proper loadings of γ-Fe2O3 and rGO present higher efficiency thanks to higher superhydrophilic tendency and higher photocatalytic activities, as well as an efficient barrier effect. Full article
(This article belongs to the Special Issue Photocatalytic Thin Films)
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Article
Anti-Corrosive Coating of Carbon-Steel Assisted by Polymer-Camphorsulfonic Acid Embedded within Graphene
Coatings 2020, 10(9), 879; https://doi.org/10.3390/coatings10090879 - 13 Sep 2020
Cited by 2
Abstract
A novel, economic and environmentally friendly anticorrosion coating material for metals is introduced and investigated in this paper. For this purpose, camphor-sulfonic-acid/graphene-doped poly(o-toluidine) composites (MG/[email protected]) were fabricated using in-situ polymerization with (NH4)2S2O8 as an oxidant. The [...] Read more.
A novel, economic and environmentally friendly anticorrosion coating material for metals is introduced and investigated in this paper. For this purpose, camphor-sulfonic-acid/graphene-doped poly(o-toluidine) composites (MG/[email protected]) were fabricated using in-situ polymerization with (NH4)2S2O8 as an oxidant. The structure and the morphology of MG/[email protected] were analyzed using FTIR (Fourier-transform infrared spectroscopy), XRD (X-ray diffraction), and SEM (Scanning Electron Microscope). Multilayer graphene (MG)/[email protected] composite coatings (MG/[email protected]) were prepared on the surface of a carbon steel substrate by mixing MG/[email protected] with waterborne polyurethane via blending. The corrosion performance of the MG/[email protected] composite coatings in a 3.5% NaCl solution was studied with a corrosion electrochemical method. The results showed that 5-MG/[email protected] had the best shielding effect on corrosive media and the lowest corrosion rate (1.02 × 10−6 mm/year) compared to other coatings while its inhibition efficiency reached 99.96%. Full article
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Article
Stress Analysis of Multilayered Coatings Subjected to Surface Point Contact Loading Based on Its Three-Dimensional Elastic Field Solution
Coatings 2020, 10(9), 838; https://doi.org/10.3390/coatings10090838 - 28 Aug 2020
Abstract
In order to investigate the effect of the structural layout of multilayered coatings on its mechanical behavior, a three-dimensional elastic field solution is developed for multilayered solids subjected to surface point contact loading, which is converted from the elastic field solution in frequency [...] Read more.
In order to investigate the effect of the structural layout of multilayered coatings on its mechanical behavior, a three-dimensional elastic field solution is developed for multilayered solids subjected to surface point contact loading, which is converted from the elastic field solution in frequency domain by using a numerical conversion algorithm. The elastic field solution in frequency domain is obtained by numerically solving a group of linear equations involving the unknown constants in the general elastic field solution of layered material that is obtained by using Fourier integral transform technique. The present solution is validated by comparing with the exact analytical solution for uncoated solids and finite element solution for solids coated with 30 layers. Lastly, the effect of structural layout of multilayered coatings is further investigated with present solution. The result shows that the gradient structural layout with elasticity modulus decreasing gradually from the top layer to the substrate, which is preferable to a larger friction coefficient for multilayered solids subjected to surface line contact loading, is preferable for a smaller friction coefficient <0.1 for multilayered solids subjected to surface point contact loading, and the gradient structural layout with elasticity modulus increasing first in the top layers and then decreasing in the bottom layers, which is preferable to a smaller friction coefficient for multilayered solids subjected to surface line contact loading, is preferable for a friction coefficient >0.2. Full article
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Article
Evaporated MoOx as General Back-Side Hole Collector for Solar Cells
Coatings 2020, 10(8), 763; https://doi.org/10.3390/coatings10080763 - 06 Aug 2020
Cited by 1
Abstract
Substoichiometric molybdenum oxide (MoOx) has good potential as a hole-collecting layer in solar cells. In this paper, we report on the application of ultrathin evaporated MoOx as a hole collector at the back side of two distinct photovoltaic technologies: polymeric [...] Read more.
Substoichiometric molybdenum oxide (MoOx) has good potential as a hole-collecting layer in solar cells. In this paper, we report on the application of ultrathin evaporated MoOx as a hole collector at the back side of two distinct photovoltaic technologies: polymeric and silicon heterojunction (SHJ). In the case of polymer solar cells, we test MoOx as a hole transport layer in devices with inverted architecture. The higher transparency of the MoOx film, compared to the commonly used poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), allows an enhanced back reflected light into the photoactive layer, thus boosting the photogeneration, as found from the illuminated J-V and external quantum efficiency (EQE) curves. The higher fill factor (FF) of the MoOx-based device also suggests an improved charge collection efficiency compared to the cells with PEDOT:PSS. As for SHJ solar cells, we show that MoOx offers the means for dopant-free hole collection with both p-type and n-type Si wafers. In the present comparison over planar test structures with Ag back reflecting electrodes, we observe an efficiency gain of approximately 1% absolute against a baseline with a conventional p-type amorphous silicon hole collector. The gain is linked to the increased VOC, which is likely due to the reduced recombination at the Si wafer. Full article
(This article belongs to the Special Issue Advances in Thin Films for Photovoltaic Applications)
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Versatility of Nanocrystalline Silicon Films: from Thin-Film to Perovskite/c-Si Tandem Solar Cell Applications
Coatings 2020, 10(8), 759; https://doi.org/10.3390/coatings10080759 - 03 Aug 2020
Cited by 2
Abstract
Doped hydrogenated nanocrystalline (nc-Si:H) and silicon oxide (nc-SiOx:H) materials grown by plasma-enhanced chemical vapor deposition have favourable optoelectronic properties originated from their two-phase structure. This unique combination of qualities, initially, led to the development of thin-film Si solar cells allowing the [...] Read more.
Doped hydrogenated nanocrystalline (nc-Si:H) and silicon oxide (nc-SiOx:H) materials grown by plasma-enhanced chemical vapor deposition have favourable optoelectronic properties originated from their two-phase structure. This unique combination of qualities, initially, led to the development of thin-film Si solar cells allowing the fabrication of multijunction devices by tailoring the material bandgap. Furthermore, nanocrystalline silicon films can offer a better carrier transport and field-effect passivation than amorphous Si layers could do, and this can improve the carrier selectivity in silicon heterojunction (SHJ) solar cells. The reduced parasitic absorption, due to the lower absorption coefficient of nc-SiOx:H films in the relevant spectral range, leads to potential gain in short circuit current. In this work, we report on development and applications of hydrogenated nanocrystalline silicon oxide (nc-SiOx:H) from material to device level. We address the potential benefits and the challenges for a successful integration in SHJ solar cells. Finally, we prove that nc-SiOx:H demonstrated clear advantages for maximizing the infrared response of c-Si bottom cells in combination with perovskite top cells. Full article
(This article belongs to the Special Issue Advances in Thin Films for Photovoltaic Applications)
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Article
Nanowire Aptamer-Sensitized Biosensor Chips with Gas Plasma-Treated Surface for the Detection of Hepatitis C Virus Core Antigen
Coatings 2020, 10(8), 753; https://doi.org/10.3390/coatings10080753 - 01 Aug 2020
Cited by 12
Abstract
Herein, we have demonstrated highly sensitive real-time biospecific detection of a protein marker of hepatitis C—the core antigen of hepatitis C virus (HCVcoreAg)—using a nanowire (NW) biosensor. The primary element of the NW-biosensor is a chip with p-type conductance, bearing silicon-on-insulator (SOI) nanowire [...] Read more.
Herein, we have demonstrated highly sensitive real-time biospecific detection of a protein marker of hepatitis C—the core antigen of hepatitis C virus (HCVcoreAg)—using a nanowire (NW) biosensor. The primary element of the NW-biosensor is a chip with p-type conductance, bearing silicon-on-insulator (SOI) nanowire structures on its surface. The nanowire structures are fabricated by gas-plasma treatment and electron beam lithography. The detection specificity was provided by sensitization of the sensor surface with aptamers against HCVcoreAg. The influence of buffer pH on the sensor response signal was studied. The effect of reverse polarity of the biosensor response signal with change from the acidic buffer pH to the neutral one was found. The lowest detectable HCVcoreAg concentration was determined to be 2.0 × 10−15 M in both acidic (pH 5.1) and neutral (pH 7.4) buffer solution. The proposed aptamer-sensitized sensor was also successfully applied to detect HCVcoreAg in serum samples of hepatitis C patients. Full article
(This article belongs to the Section Surface Coatings for Biomedicine and Bioengineering)
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Article
The Assessment of Finishing Properties on the Mass per Unit Area, Pilling, Bursting Strength, and Wicking Behavior of Polyester Weft-Knitted Jersey Fabric
Coatings 2020, 10(8), 723; https://doi.org/10.3390/coatings10080723 - 23 Jul 2020
Cited by 2
Abstract
Finishes bring an alteration to the physical and comfort properties of the textiles. That’s why various finishes are used to impart various functionalities to the fabric surface. However, it may also affect some properties. The purpose of this study is to investigate the [...] Read more.
Finishes bring an alteration to the physical and comfort properties of the textiles. That’s why various finishes are used to impart various functionalities to the fabric surface. However, it may also affect some properties. The purpose of this study is to investigate the effect of various finishes on pilling, mass per unit area, bursting strength, and wicking behavior of the polyester weft-knitted jersey fabric. Herein, 100% spun polyester weft-knitted plain jersey fabric was exposed to different finish treatments to check their effect on the some physical and comfort properties of the fabric like mass per unit area, pilling behavior, bursting strength, and wicking properties of the weft-knitted jersey fabric. The fabric used was knit from 24/1, 100% spun polyester yarn on the single knit circular knitting machine. The developed fabric was washed on Fong machine. Finishes are applied on fabric by “Monofort Stanter” machine. The resultant fabric was characterized by random tumble pilling tester, bursting strength tester, and wicking tester to analyze their pilling grade, bursting strength, and wicking behavior respectively. A significant increase has been found in wicking behavior, mass per unit area, and bursting strength of the fabric after finishing treatments. Moreover, the wicking finish shows the highest reduction in pilling grade from 3.5 to 2.5. Significant improvement has been observed in bursting strength by all finish’s treatment. However, wicking finish treatment results in the highest increase in bursting strength of 4.2%. Significant improvement has been observed in the vertical wicking speed of all treatment except silicon finish which significantly reduces vertical wicking rate. However, the wicking finish (Recipe E) shows the highest increase in wicking rate by 13.75 times as compared to grey fabric. Full article
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Article
Top Coating Anti-Erosion Performance Analysis in Wind Turbine Blades Depending on Relative Acoustic Impedance. Part 2: Material Characterization and Rain Erosion Testing Evaluation
Coatings 2020, 10(8), 709; https://doi.org/10.3390/coatings10080709 - 22 Jul 2020
Cited by 3
Abstract
Under droplet impingement, surface leading edge protection (LEP) coating materials for wind turbine blades develop high-rate transient pressure build-up and a subsequent relaxation in a range of strain rates. The stress-strain coating LEP behavior at a working frequency range depends on the specific [...] Read more.
Under droplet impingement, surface leading edge protection (LEP) coating materials for wind turbine blades develop high-rate transient pressure build-up and a subsequent relaxation in a range of strain rates. The stress-strain coating LEP behavior at a working frequency range depends on the specific LEP and on the material and operational conditions, as described in this research in a previous work. Wear fatigue failure analysis, based on the Springer model, requires coating and substrate speed of sound measurements as constant input material parameters. It considers a linear elastic response of the polymer subjected to drop impact loads, but does not account for the frequency dependent viscoelastic effects for the materials involved. The model has been widely used and validated in the literature for different liquid impact erosion problems. In this work, it is shown the appropriate definition of the viscoelastic materials properties with ultrasonic techniques. It is broadly used for developing precise measurements of the speed of sound in thin coatings and laminates. It also allows accurately evaluating elastic moduli and assessing mechanical properties at the high frequencies of interest. In the current work, an investigation into various LEP coating application cases have been undertaken and related with the rain erosion durability factors due to suitable material impedance definition. The proposed numerical procedures to predict wear surface erosion have been evaluated in comparison with the rain erosion testing, in order to identify suitable coating and composite substrate combinations. LEP erosion performance at rain erosion testing (RET) technique is used widely in the wind industry as the key metric, in an effort to assess the response of the varying material and operational parameters involved. Full article
(This article belongs to the Special Issue Recent Trends in Coatings and Thin Film–Modeling and Application)
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Article
Algorithm Scheme to Simulate the Distortions during Gas Quenching in a Single-Piece Flow Technology
Coatings 2020, 10(7), 694; https://doi.org/10.3390/coatings10070694 - 19 Jul 2020
Cited by 2
Abstract
Low-pressure carburizing followed by high-pressure quenching in single-piece flow technology has shown good results in avoiding distortions. For better control of specimen quality in these processes, developing numerical simulations can be beneficial. However, there is no commercial software able to simulate distortion formation [...] Read more.
Low-pressure carburizing followed by high-pressure quenching in single-piece flow technology has shown good results in avoiding distortions. For better control of specimen quality in these processes, developing numerical simulations can be beneficial. However, there is no commercial software able to simulate distortion formation during gas quenching that considers the complex fluid flow field and heat transfer coefficient as a function of space and time. For this reason, this paper proposes an algorithm scheme that aims for more refined results. Based on the physical phenomena involved, a numerical scheme was divided into five modules: diffusion module, fluid module, thermal module, phase transformation module, and mechanical module. In order to validate the simulation, the results were compared with the experimental data. The outcomes showed that the average difference between the numerical and experimental data for distortions was 1.7% for the outer diameter and 12% for the inner diameter of the steel element. Numerical simulation also showed the differences between deformations in the inner and outer diameters as they appear in the experimental data. Therefore, a numerical model capable of simulating distortions in the steel elements during high-pressure gas quenching after low-pressure carburizing using a single-piece flow technology was obtained, whereupon the complex fluid flow and variation of the heat transfer coefficient was considered. Full article
(This article belongs to the Special Issue Surface Treatment for Alloys)
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Article
Microstructural Characteristics in Babbitt Coatings Deposited by LPCS
Coatings 2020, 10(7), 689; https://doi.org/10.3390/coatings10070689 - 17 Jul 2020
Abstract
Studies have already established that the mechanical properties of Babbitt coatings significantly depend on the microstructural characteristics, such as the amount and distribution of intermetallic compounds dispersed in a soft solid solution matrix. For Sn–Sb–Cu-based Babbitt coatings, the formation of SbSn- and CuSn-based [...] Read more.
Studies have already established that the mechanical properties of Babbitt coatings significantly depend on the microstructural characteristics, such as the amount and distribution of intermetallic compounds dispersed in a soft solid solution matrix. For Sn–Sb–Cu-based Babbitt coatings, the formation of SbSn- and CuSn-based precipitates has a substantial influence on the resulting microhardness and thus determines the maximum load carrying capacity. Thermal spraying of Sn-based Babbitt coatings results in a relatively more refined structure of these precipitates than in common manufacturing processes, such as casting, due to the thermal processing conditions. This study aims to evaluate the effect of the temperature of the propellant gas and substrate temperature on the microstructural characteristics of Sn–Sb–Cu-based Babbitt coatings deposited by low pressure cold spraying (LPCS). The deposits were examined for their phase composition, microhardness and mesoscopic structure. It was found that the coatings were mainly composed of Sb2Sn23, Sb0.49Sn0.51 and Sorosite (CuSn or CuSb0.115Sn0.835), regardless of the substrate temperature or temperature of the propellant gas to be investigated. For a gas temperature above 300 °C, an increased microhardness was observed, which correlates with the appearance of a more homogenous distribution of Sb0.49Sn0.51 dispersed in a soft Sn-rich solid solution matrix. Full article
(This article belongs to the Special Issue Recent Developments of Cold Spray Coating)
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Article
Top Coating Anti-Erosion Performance Analysis in Wind Turbine Blades Depending on Relative Acoustic Impedance. Part 1: Modelling Approach
Coatings 2020, 10(7), 685; https://doi.org/10.3390/coatings10070685 - 16 Jul 2020
Cited by 4
Abstract
Top coating are usually moulded, painted or sprayed onto the wind blade Leading-Edge surface to prevent rain erosion due to transverse repeated droplet impacts. Wear fatigue failure analysis based on Springer model has been widely referenced and validated to quantitatively predict damage initiation. [...] Read more.
Top coating are usually moulded, painted or sprayed onto the wind blade Leading-Edge surface to prevent rain erosion due to transverse repeated droplet impacts. Wear fatigue failure analysis based on Springer model has been widely referenced and validated to quantitatively predict damage initiation. The model requires liquid, coating and substrate speed of sound measurements as constant input parameters to define analytically the shockwave progression due to their relative vibro-acoustic properties. The modelling assumes a pure elastic material behavior during the impact event. Recent coating technologies applied to prevent erosion are based on viscoelastic materials and develop high-rate transient pressure build-up and a subsequent relaxation in a range of strain rates. In order to analyze the erosion performance by using Springer model, appropriate impedance characterization for such viscoelastic materials is then required and represents the main objective of this work to avoid lack of accuracy. In the first part of this research, it is proposed a modelling methodology that allows one to evaluate the frequency dependent strain-stress behavior of the multilayer coating system under single droplet impingement. The computational tool ponders the operational conditions (impact velocity, droplet size, layer thickness, etc.) with the appropriate variable working frequency range for the speed of sound measurements. The second part of this research defines in a complementary paper, the ultrasonic testing characterization of different viscoelastic coatings and the methodology validation. The modelling framework is then used to identify suitable coating and substrate combinations due to their acoustic matching optimization and to analyze the anti-erosion performance of the coating protection system. Full article
(This article belongs to the Special Issue Recent Trends in Coatings and Thin Film–Modeling and Application)
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Article
New Antimicrobial Biomaterials for the Reconstruction of Craniofacial Bone Defects
Coatings 2020, 10(7), 678; https://doi.org/10.3390/coatings10070678 - 15 Jul 2020
Cited by 1
Abstract
Reconstructive bone surgery of the head and neck could prove challenging in terms of postoperative healing and recovery. Fighting infection during the healing period is one of the critical factors of the long-term survival of an implant. The aim of the study was [...] Read more.
Reconstructive bone surgery of the head and neck could prove challenging in terms of postoperative healing and recovery. Fighting infection during the healing period is one of the critical factors of the long-term survival of an implant. The aim of the study was to develop an innovative composition suitable for an antibacterial craniofacial implant that should have the capacity to continuously and constantly release the amount of gentamicin necessary to prevent the post-surgical infections. For this purpose, a series of composite materials based on dimethacrylic monomers, hydroxyapatite and ZrO2, with (series B) or without the addition of polymethyl methacrylate (series A), reinforced with woven E-glass fibers (FRC) were obtained using the laminate lay-up process. Gentamicin was included in all FRC sample matrices to confer an antimicrobial effect. The results show that after extraction of the residual monomers from the FRC samples in different solvents (chloroform, acetone and ethyl alcohol), the cumulative amount of released gentamicin after 12 days was between 7.05–11.38 mg for A samples and 11.21–14.52 mg for B samples. The microbiological protocol showed that gentamicin induces a two weeks-lasting antimicrobial effect maintained over the minimal inhibitory concentration for P. aeruginosa and S. aureus. Full article
(This article belongs to the Special Issue Polymer Coatings for Biomaterials)
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Article
Corrosion Resistance of Al/SiC Laser Cladding Coatings on AA6082
Coatings 2020, 10(7), 673; https://doi.org/10.3390/coatings10070673 - 14 Jul 2020
Cited by 1
Abstract
Aluminum matrix composites reinforced with silicon carbide particles (SiCp) were deposited by laser cladding on AA6082 aluminum alloy. Different compositions of the matrix of the composites coating were used and different amounts of Si and Ti were added to a base [...] Read more.
Aluminum matrix composites reinforced with silicon carbide particles (SiCp) were deposited by laser cladding on AA6082 aluminum alloy. Different compositions of the matrix of the composites coating were used and different amounts of Si and Ti were added to a base of Al-12Si in order to control the reactivity between molten aluminum and SiCp during laser cladding. The corrosion behavior of the coatings deposited was evaluated in 3.5 wt.% NaCl solution using gravimetric analyses and electrochemical polarization tests. The corrosion products observed were Al(OH)3 and Al2O3, and they formed a layer that limited the evolution of corrosion. However, the presence of discontinuities in it reduced the corrosion resistance of the coating. The corrosion mechanisms were different depending on the coating composition. The addiction of Ti to the alloy allowed for better corrosion behavior for the composite coating than that of the aluminum substrate. Full article
(This article belongs to the Special Issue Anticorrosion Protection of Nonmetallic and Metallic Coatings II)
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Article
In Vitro Corrosion and Tribocorrosion Performance of Biocompatible Carbide Coatings
Coatings 2020, 10(7), 654; https://doi.org/10.3390/coatings10070654 - 07 Jul 2020
Cited by 1
Abstract
The present study aims to explain the corrosion and the tribocorrosion performance in simulated conditions of the human body by the level of stress, adhesion of coating to substrate, roughness, and hardness. The coatings were synthesized by the cathodic arc evaporation method on [...] Read more.
The present study aims to explain the corrosion and the tribocorrosion performance in simulated conditions of the human body by the level of stress, adhesion of coating to substrate, roughness, and hardness. The coatings were synthesized by the cathodic arc evaporation method on 316L stainless steel substrates to be used for load bearing implants. Structure, elemental, and phase compositions were studied by means of energy dispersive spectrometry and X-ray diffraction, respectively. The grain size and strain of the coatings were determined by the Williamson–Hall plot method. Tests on hardness, adhesion, roughness, and electrochemical behavior in 0.9% NaCl solution at 37 ± 0.5 °C were carried out. Tribocorrosion performances, evaluated by measuring the friction coefficient and wear rate, were conducted in 0.9% NaCl solution using the pin on disc method at 37 ± 0.5 °C. TiC and ZrC exhibited a (111) preferred orientation, while TiNbC had a (200) orientation and the smallest crystallite size (8.1 nm). TiC was rougher than ZrC and TiNbC; the lowest roughness was found for TiNbC coatings. The highest hardness and adhesion values were found for TiNbC, followed by TiC and the ZrC. All coatings improved the corrosion resistance of 316L steels, but TiNbC showed the best corrosion behavior. TiNbC had the lowest friction coefficient (1.6) and wear rate (0.99 × 10−5 mm3·N−1∙m−1) values, indicating the best tribocorrosive performance in 0.9% NaCl at 37 ± 0.5 °C. Full article
(This article belongs to the Special Issue Surface Modification of Medical Implants)
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Article
Femtosecond Laser-Induced Damage Characterization of Multilayer Dielectric Coatings
Coatings 2020, 10(6), 603; https://doi.org/10.3390/coatings10060603 - 26 Jun 2020
Cited by 5
Abstract
The laser-induced damage threshold (LIDT) of optical components is one of the major constraints in developing high-power ultrafast laser systems. Multi-layer dielectric (MLD) coatings-based optical components are key parts of high-power laser systems because of their high damage resistance. Therefore, understanding and characterizing [...] Read more.
The laser-induced damage threshold (LIDT) of optical components is one of the major constraints in developing high-power ultrafast laser systems. Multi-layer dielectric (MLD) coatings-based optical components are key parts of high-power laser systems because of their high damage resistance. Therefore, understanding and characterizing the laser-induced damage of MLD coatings are of paramount importance for developing ultrahigh-intensity laser systems. In this article, we overview the possible femtosecond laser damage mechanisms through damage morphologies in various MLD optical coatings tested in our facility. To evaluate the major contributions to the coating failure, different LIDT test methods (R-on-1, ISO S-on-1 and Raster Scan) were carried out for a high reflective hybrid Ta2O5/HfO2/SiO2 MLD mirror coating at a pulse duration of 37 fs. Different LIDT test methods were compared due to the fact that each test method exposes the different underlying damage mechanisms. For instance, the ISO S-on-1 test at a higher number of laser pulses can bring out the fatigue effects, whereas the Raster Scan method can reveal the non-uniform defect clusters in the optical coating. The measured LIDT values on the sample surface for the tested coating in three test methods are 1.1 J/cm2 (R-on-1), 0.9 J/cm2 (100k-on-1) and 0.6 J/cm2 (Raster Scan) at an angle of incidence of 45 deg. The presented results reveal that the performance of the tested sample is limited by coating defects rather than fatigue effects. Hence, the Raster Scan method is found to be most accurate for the tested coating in evaluating the damage threshold for practical applications. Importantly, this study demonstrates that the testing of different LIDT test protocols is necessary in femtosecond regime to assess the key mechanisms to the coating failure. Full article
(This article belongs to the Special Issue Visual Effects Coatings and Surfaces)
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Article
Facile Route for Synthesis of Novel Flame Retardant, Reinforcement and Antibacterial Textile Fabrics Coatings
Coatings 2020, 10(6), 576; https://doi.org/10.3390/coatings10060576 - 19 Jun 2020
Cited by 1
Abstract
New and innovative textile fabrics coatings were facilely developed. The coating was developed based on synthesis of novel charring and antibacterial organic agent in conjunction with chitosan. N-[2,3-dibromo-4-(4-methoxy-3-methylphenyl)-4-oxobutanoyl]anthranilic acid was synthesized as organic antibacterial, reinforcement, and charring agent (OA) and then, dispersed [...] Read more.
New and innovative textile fabrics coatings were facilely developed. The coating was developed based on synthesis of novel charring and antibacterial organic agent in conjunction with chitosan. N-[2,3-dibromo-4-(4-methoxy-3-methylphenyl)-4-oxobutanoyl]anthranilic acid was synthesized as organic antibacterial, reinforcement, and charring agent (OA) and then, dispersed in chitosan solution followed by coating on textile fabrics using immersion route forming new flame retardant coating layer. The developed organic molecule structure was elucidated using spectroscopic techniques. The mass loadings of developed organic agent dispersed in chitosan solution were varied between 20–60 wt.%. The coated textile fabrics have special surface morphology of fiber shape aligned on textile fibers surface. The thermal stability and charring residues of the coated textile fabrics were enhanced when compared to blank and organic agent free coated samples. Furthermore, the flammability properties were evaluated using LOI (limiting oxygen index) and UL94 tests. Therefore, the coated textile fabrics record significant enhancement in flame retardancy achieving first class flame retardant textile of zero mm/min rate of burning and 23.8% of LOI value compared to 118 mm/min. rate of burning and 18.2% for blank textile, respectively. The tensile strength of the coated textile fabrics was enhanced, achieving 51% improvement as compared to blank sample. Additionally, the developed coating layer significantly inhibited the bacterial growth, recording 18 mm of clear inhibition zone for coated sample when compared to zero for blank and chitosan coated ones. Full article
(This article belongs to the Special Issue Novel Coatings for Smart Textile Fabrics for Enhanced Functions)
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Article
Gas Technique of Simultaneous Borocarburizing of Armco Iron Using Trimethyl Borate
Coatings 2020, 10(6), 564; https://doi.org/10.3390/coatings10060564 - 14 Jun 2020
Cited by 2
Abstract
The gas boriding process is an appropriate technique used for increasing the hardness and wear resistance of iron and steels. However, the boron halides (e.g., BCl3, BF3) are rarely used as a boron source during gas boriding in industry [...] Read more.
The gas boriding process is an appropriate technique used for increasing the hardness and wear resistance of iron and steels. However, the boron halides (e.g., BCl3, BF3) are rarely used as a boron source during gas boriding in industry due to the toxic character of these reagents. The possibility of the use of organic compounds as a boron source in plasma assisted processes was the instigation to determine the possibility of applying these agents for gas boriding. In the present work trimethyl borate was used as an organic boron source. The use of a N2–H2–B(CH3O)3 atmosphere ensured the appropriate conditions for the simultaneous gas borocarburizing of Armco iron. The process was carried out at 1223 K (950 °C) for 2 h. The produced layer consisted of two zones: an outer zone containing a diffusion of boron atoms and an inner zone containing a diffusion of carbon atoms, under the outer zone. Due to the reduction of trimethyl borate with hydrogen, free atoms of carbon were released for the gas atmosphere. Therefore, there existed favorable conditions for carburizing. Unfortunately, the formation of a carburized layer was the reason for the difficult diffusion of boron atoms. As a consequence, the boron diffusion front was hindered, and the outer boride layer was relatively thin (ca. 7.8 µm). The boride layer contained only Fe2B phase, which was characterized by high hardness in the range from 1103 HV0.01 to 1546 HV0.01. The presence of iron borides in the outer layer was also the reason for increased wear resistance in comparison with untreated Armco iron. Full article
(This article belongs to the Section Surface Characterization, Deposition and Modification)
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Article
Effects of Cathode Voltage Pulse Width in High Power Impulse Magnetron Sputtering on the Deposited Chromium Thin Films
Coatings 2020, 10(6), 542; https://doi.org/10.3390/coatings10060542 - 02 Jun 2020
Cited by 3
Abstract
Environmentally-safe high-power impulse magnetron sputtering (HiPIMS) technology was utilized to deposit chromium films. This research focused on the influences of the HiPIMS pulse widths on the microstructure of films deposited at different deposition pressures and substrate bias voltages. Under the conditions of the [...] Read more.
Environmentally-safe high-power impulse magnetron sputtering (HiPIMS) technology was utilized to deposit chromium films. This research focused on the influences of the HiPIMS pulse widths on the microstructure of films deposited at different deposition pressures and substrate bias voltages. Under the conditions of the same average HiPIMS power and duty cycle, the deposition rate of the Cr thin film at working pressure 0.8 Pa is slightly higher than at 1.2 Pa. Also, the difference between deposition rates under two pressures decreases with the discharge pulse width. The deposition rate of the short pulse width 60 μs is lowest, but those of 200 and 360 μs are approximately the same. With no or small direct current substrate biasing, the microstructure of films coated at short pulse width is similar to the typical magnetron sputtering deposited films. Elongating the pulse width enhances the ion flux toward the substrate and changes the film structure from individual prism-like columns into tangled 3-point/4-point star columns. Substantial synchronized substrate biasing and longer pulse width changes the preferred orientation of Cr films from Cr (110) to Cr (200) and Cr (211). The films deposited at longer pulse width exhibit a higher hardness due to the reducing of intercolumn voids. Full article
(This article belongs to the Section Thin Films)
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Article
Polyethylene Glycol (PEG) Modified Porous Ca5(PO4)2SiO4 Bioceramics: Structural, Morphologic and Bioactivity Analysis
Coatings 2020, 10(6), 538; https://doi.org/10.3390/coatings10060538 - 31 May 2020
Cited by 4
Abstract
Bioceramics are class of biomaterials that are specially developed for application in tissue engineering and regenerative medicines. Sol-gel method used for producing bioactive and reactive bioceramic materials more than those synthesized by traditional methods. In the present research study, the effect of polyethylene [...] Read more.
Bioceramics are class of biomaterials that are specially developed for application in tissue engineering and regenerative medicines. Sol-gel method used for producing bioactive and reactive bioceramic materials more than those synthesized by traditional methods. In the present research study, the effect of polyethylene glycol (PEG) on Ca5(PO4)2SiO4 (CPS) bioceramics was investigated. The addition of 5% and 10% PEG significantly affected the porosity and bioactivity of sol-gel derived Ca5(PO4)2SiO4. The morphology and physicochemical properties of pure and modified materials were evaluated using scanning electron microscopy (SEM), X-ray powder diffraction (XRD), transmission electron microscopy (TEM) and Fourier-transform infrared spectroscopy (FTIR), respectively. The effect of PEG on the surface area and porosity of Ca5(PO4)2SiO4 was measured by Brunauer–Emmett–Teller (BET). The results obtained from XRD and FTIR studies confirmed the interactions between PEG and CPS. Due to the high concentration of PEG, the CPS-3 sample showed the largest-sized particle with an average of 200.53 µm. The porous structure of CPS-2 and CPS-3 revealed that they have a better ability to generate an appetite layer on the surface of the sample when immersed in simulated body fluid (SBF) for seven days. The generation of appetite layer showed the bioactive nature of CPS which makes it a suitable material for hard tissue engineering applications. The results have shown that the PEG-modified porous CPS could be a more effective material for drug delivery, implant coatings and other tissue engineering applications. The aim of this research work is to fabricate SBF treated and porous polyethylene glycol-modified Ca5(PO4)2SiO4 material. SBF treatment and porosity of material can provide a very useful target for bioactivity and drug delivery applications in the future. Full article
(This article belongs to the Special Issue Mesoporous Metal Oxide Films)
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Article
Atomic Layer-Deposited Al-Doped ZnO Thin Films for Display Applications
Coatings 2020, 10(6), 539; https://doi.org/10.3390/coatings10060539 - 31 May 2020
Cited by 8
Abstract
The integration of high uniformity, conformal and compact transparent conductive layers into next generation indium tin oxide (ITO)-free optoelectronics, including wearable and bendable structures, is a huge challenge. In this study, we demonstrate the transparent and conductive functionality of aluminum-doped zinc oxide (AZO) [...] Read more.
The integration of high uniformity, conformal and compact transparent conductive layers into next generation indium tin oxide (ITO)-free optoelectronics, including wearable and bendable structures, is a huge challenge. In this study, we demonstrate the transparent and conductive functionality of aluminum-doped zinc oxide (AZO) thin films deposited on glass as well as on polyethylene terephthalate (PET) flexible substrates by using an atomic layer deposition (ALD) technique. AZO thin films possess high optical transmittance at visible and near-infrared spectral range and electrical properties competitive to commercial ITO layers. AZO layers deposited on flexible PET substrates demonstrate stable sheet resistance over 1000 bending cycles. Based on the performed optical and electrical characterizations, several applications of ALD AZO as transparent conductive layers are shown—AZO/glass-supported liquid crystal (LC) display and AZO/PET-based flexible polymer-dispersed liquid crystal (PDLC) devices. Full article
(This article belongs to the Special Issue Optical Thin Films and Structures: Design and Advanced Applications)
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Article
A Comprehensive Numerical Study on Friction Reduction and Wear Resistance by Surface Coating on Cam/Tappet Pairs under Different Conditions
Coatings 2020, 10(5), 485; https://doi.org/10.3390/coatings10050485 - 18 May 2020
Abstract
As a vital component in the valve train of internal combustion engines (ICEs), the cam/tappet pair undergoes high mechanical and thermal loads and usually works in a mixed and boundary lubrication regime. This leads to considerable friction loss and severe surface wear. Currently, [...] Read more.
As a vital component in the valve train of internal combustion engines (ICEs), the cam/tappet pair undergoes high mechanical and thermal loads and usually works in a mixed and boundary lubrication regime. This leads to considerable friction loss and severe surface wear. Currently, the applications of diamond-like carbon (DLC) coatings for automotive components are becoming a promising strategy to reduce the friction and lower the wear. However, the practical performance of the coating is related to many factors, including friction coefficient, thermal properties, load conditions, and surface topography. In order to investigate these factors and successively improve the fuel efficiency and durability of the cam/tappet pair, a comprehensive multi-physics analytical model considering the mechanical, thermal and tribological properties of DLC coatings is established in this paper. Simulations are carried out for the coated as well as the uncoated cam/tappet conjunctions with different roughness at various ambient temperatures. The results show that both the fluid and asperity contact friction for the coated cam/tappet conjunction are significantly reduced due to their favourable characteristics. As a result, the friction loss of the coated cam/tappet pair is noticeably lower by almost 40% than that of the uncoated, despite a slightly higher asperity contact. In addition, the wear resistance of DLC coatings is also impressive, although the wear condition becomes progressively more severe with the increasing ambient temperature. Moreover, the roughness has complex effects on the friction and wear under different conditions. Full article
(This article belongs to the Section Tribology)
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Article
Pectin-Based Films Loaded with Hydroponic Nopal Mucilages: Development and Physicochemical Characterization
Coatings 2020, 10(5), 467; https://doi.org/10.3390/coatings10050467 - 10 May 2020
Cited by 3
Abstract
Nopal is a potential source of mucilage that can be used in different food applications. One of its potential use is the development of films and coatings where it can act as a packaging material but also as a source of bioactive compounds. [...] Read more.
Nopal is a potential source of mucilage that can be used in different food applications. One of its potential use is the development of films and coatings where it can act as a packaging material but also as a source of bioactive compounds. Therefore, this work aimed to develop and characterize pectin-based films loaded with mucilage extracted from two species of nopal, Copena F1 (Cop) and Villanueva (Vi). The obtained mucilages were denominated as materials without fibre (Copwtf and Viwtf) and with fibre (Copwf and Viwf), according to the fibre’s size. Films were produced with pectin (2% w/v), mucilage (2.5% w/v) and glycerol (0.5% w/v) by the casting method. The addition of mucilages was shown to influence the visual appearance, optical properties and morphology of the films. The presence of mucilage also changed the moisture content, water contact angle and water vapour permeability of the films. The pectin-based films without mucilage presented the best mechanical properties. Fourier-transform infrared (FTIR) spectroscopy showed similar signals in terms of frequency and intensity, for all the films, not showing any chemical modification. Results show that the mucilage obtained from different nopal fractions can be used in pectin-based films foreseeing their use as films or coatings in food applications. Full article
(This article belongs to the Special Issue Bio-Based Active Packaging for Shelf Life Extension)
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