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Coatings, Volume 11, Issue 6 (June 2021) – 129 articles

Cover Story (view full-size image): The metamagnetic phase transition from antiferromagnetic to ferromagnetic in FeRh thin films has drawn considerable interest in recent years. Investigation into high-speed triggers for the transition via piezo strain, temperature and high-frequency lasing bring to light its possible uses in novel antiferromagnetic and phase change spintronic memory. The field is now focused on understanding how to precisely control the metamagnetic transition temperature using methods such as ion irradiation, epitaxial substrate strain, film thickness and crystalline morphology. These works accelerate its possible application in neuromorphic-centered memory architectures based on spintronic and memristive logic. View this paper
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Review
A Review on Additive Manufacturing of Pure Copper
Coatings 2021, 11(6), 740; https://doi.org/10.3390/coatings11060740 - 21 Jun 2021
Viewed by 432
Abstract
With the development of the aerospace and automotive industries, high heat exchange efficiency is a challenge facing the development of various industries. Pure copper has excellent mechanical and physical properties, especially high thermal conductivity and electrical conductivity. These excellent properties make pure copper [...] Read more.
With the development of the aerospace and automotive industries, high heat exchange efficiency is a challenge facing the development of various industries. Pure copper has excellent mechanical and physical properties, especially high thermal conductivity and electrical conductivity. These excellent properties make pure copper the material of choice for the manufacture of heat exchangers and other electrical components. However, the traditional processing method is difficult to achieve the production of pure copper complex parts, so the production of pure copper parts through additive manufacturing has become a problem that must be overcome in industrial development. In this article, we not only reviewed the current status of research on the structural design and preparation of complex pure copper parts by researchers using selective laser melting (SLM), selective electron beam melting (SEBM) and binder jetting (BJ) in recent years, but also reviewed the forming, physical properties and mechanical aspects of pure copper parts prepared by different additive manufacturing methods. Finally, the development trend of additive manufacturing of pure copper parts is also prospected. Full article
(This article belongs to the Special Issue The Applications of Laser Processing and Additive Manufacturing)
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Article
Internal Coating of Ureteral Stents with Chemical Vapor Deposition of Parylene
Coatings 2021, 11(6), 739; https://doi.org/10.3390/coatings11060739 - 21 Jun 2021
Viewed by 370
Abstract
Ureteral balloon catheters and ureteral stents are implanted in large quantities on a daily basis. They are the suspected cause for about a quarter of all the nosocomial infections, which lead to approx. 20,000 deaths in Germany alone. To fight these infections, catheters [...] Read more.
Ureteral balloon catheters and ureteral stents are implanted in large quantities on a daily basis. They are the suspected cause for about a quarter of all the nosocomial infections, which lead to approx. 20,000 deaths in Germany alone. To fight these infections, catheters should be made antibacterial. A technique for an antibacterial coating of catheters exhibiting an aspect ratio of up to 200 consists of a thin silver layer, which is deposited out of an aqueous solution, which is followed by a second step: chemical vapor deposition (CVD) of an organic polymeric film, which moderates the release rate of silver ions. The main concern of the second step is the longitudinal evenness of the film. For tubes with one opening as balloon catheters, this issue can be solved by applying a descendent temperature gradient from the opening to the end of the catheter. An alternative procedure can be applied to commercially available ureteral stents, which exhibit small drainage openings in their middle. The same CVD as before leads to a longitudinal homogeneity of about ±10%—at very low costs. This deposition can be modeled using viscous flow. Full article
(This article belongs to the Section Functional Polymer Coatings and Films)
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Article
Effect of Chitosan Composite Coatings with Salicylic Acid and Titanium Dioxide Nanoparticles on the Storage Quality of Blackcurrant Berries
Coatings 2021, 11(6), 738; https://doi.org/10.3390/coatings11060738 - 21 Jun 2021
Viewed by 419
Abstract
The use of chitosan and chitosan composite coatings for the preservation of fruits and vegetables during storage is attracting increasing attention. In this study, a chitosan-based edible coating, as well as a second chitosan-based edible coating containing salicylic acid (CTS + SA), a [...] Read more.
The use of chitosan and chitosan composite coatings for the preservation of fruits and vegetables during storage is attracting increasing attention. In this study, a chitosan-based edible coating, as well as a second chitosan-based edible coating containing salicylic acid (CTS + SA), a third containing nanosized titanium dioxide particles (CTS + TiO2), and a fourth containing a combination of these two (CTS + SA + TiO2) were evaluated in terms of their effects on the postharvest quality of blackcurrant fruit during storage at 4 °C. The results showed that compared with the other three treatment groups, the blackcurrants treated with CTS + SA + TiO2 underwent the smallest changes in weight loss, total soluble solids, titratable acidity, vitamin C, and total anthocyanin content, and retained the highest total flavonoid content. This combined treatment significantly inhibited polyphenol oxidase activity during storage, and the CTS + SA + TiO2 samples also displayed the lowest malondialdehyde content. These results, thus, indicate that the CTS + SA + TiO2 composite coating could maintain the nutrient composition of blackcurrants, thereby playing a significant role in preserving the quality of this fruit at 4 °C. Full article
(This article belongs to the Section Coatings for Food Technology and System)
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Article
Identification of the Wear Process of a Silver-Plating Layer by Dual Acoustic Emission Sensing
Coatings 2021, 11(6), 737; https://doi.org/10.3390/coatings11060737 - 21 Jun 2021
Viewed by 505
Abstract
A method based on acoustic emission (AE) sensing in which two AE sensors are used to measure the tribological characteristics of two interacting friction materials simultaneously in real time was assessed for the in situ measurement and evaluation of the wear process of [...] Read more.
A method based on acoustic emission (AE) sensing in which two AE sensors are used to measure the tribological characteristics of two interacting friction materials simultaneously in real time was assessed for the in situ measurement and evaluation of the wear process of silver plating. AE sensors were attached to a silver-plated pin and a silver-plated plate, and the two AE signals were measured simultaneously on a pin-on-plate-type reciprocating sliding tester. The resulting changes in the AE signal could be classified into three phases. Surface observations and energy-dispersive X-ray spectroscopy analyses showed that the wear of the silver-plating layer progressed in Phase I, the nickel intermediate layer was exposed and wear of the nickel progressed in Phase II, and the contact electrical resistance increased and the copper substrate was exposed in Phase III. In summary, the wear process of a silver-plating layer, which cannot be identified from the changes in the frictional resistance or the contact electric resistance, can be detected from changes in the dual AE signals. Furthermore, changes in the wear state of both the pin and plate specimens can be identified from differences in the amplitudes of the AE signals and the timing of their detection. Full article
(This article belongs to the Special Issue Characterization and Mechanism of Friction and Wear Phenomena)
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Article
Discrete Coating of CNT on Carbon Fiber Surfaces and the Effect on Improving the Electrochemical Performance of VRFB Systems
Coatings 2021, 11(6), 736; https://doi.org/10.3390/coatings11060736 - 18 Jun 2021
Viewed by 426
Abstract
Carbon fiber, as an electrode material, has been widely used in all-vanadium liquid flow batteries. In order to further reduce the size of the all-vanadium storage system, it is imperative to increase the current density of the battery and to achieve high conductivity [...] Read more.
Carbon fiber, as an electrode material, has been widely used in all-vanadium liquid flow batteries. In order to further reduce the size of the all-vanadium storage system, it is imperative to increase the current density of the battery and to achieve high conductivity and large electrostatic capacitance. The graphitization of the electrode material and the improvement in the specific surface area of the electrode surface also greatly affect the performance of all-vanadium redox liquid flow batteries. Therefore, in this paper, carbon nanotubes (CNTs) with a small diameter and a large specific surface area were coated on the electrode surface of the VRFB system by the dispersion method to improve the cell performance. The performance of the surface-modified electrode was also verified by Raman spectroscopy, XRD and SEM surface observations and charge/discharge experiments. Full article
(This article belongs to the Special Issue Surface Modification and Functionalization for Advanced Materials)
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Article
Seasonal Signals Observed in Non-Contact Long-Term Road Texture Measurements
Coatings 2021, 11(6), 735; https://doi.org/10.3390/coatings11060735 - 18 Jun 2021
Viewed by 376
Abstract
Texture is required on road pavements for safe vehicle braking and manoeuvres. This paper provides a unique analysis of long-term texture obtained using traffic speed condition survey (TRACS) data from 14 sites, located along a north to south transect spanning the longest highway [...] Read more.
Texture is required on road pavements for safe vehicle braking and manoeuvres. This paper provides a unique analysis of long-term texture obtained using traffic speed condition survey (TRACS) data from 14 sites, located along a north to south transect spanning the longest highway in the UK. A total of 19 years of sensor measured texture depth (SMTD) data have been analyzed using spatial filtering techniques and compared with meteorological and traffic datasets. The results for hot rolled asphalt (HRA) surfaces reveal that changes to SMTD follow a linearly increasing trend with time. The “rate of change” is influenced by the order of magnitude of annual average daily traffic (AADT), when factored for the percentage of heavy goods vehicles. This linear trend is disrupted by environmental parameters, such as rainfall events and seasonal conditioning. In the summer, this signal is evident as a transient peak in the “rate of change” of texture greater than 0.04 mm, and in the winter as a reduction. The transient changes in texture corresponded to above average rainfall occurring in the week prior to SMTD measurement. The signal observed demonstrates an inverse pattern to the classically understood seasonal variation of skid resistance in the UK, where values are low in the summer and high in the winter. The findings demonstrate for the first time that texture measurements experience a seasonal signal, and provide compelling evidence pointing toward surface processes (such as polishing and the wetting and drying of surface contaminants) causing changes to texture that are affecting seasonal variation in skid resistance. Full article
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Article
Roughing Milling with Ceramic Tools in Comparison with Sintered Carbide on Nickel-Based Alloys
Coatings 2021, 11(6), 734; https://doi.org/10.3390/coatings11060734 - 18 Jun 2021
Viewed by 379
Abstract
Productivity in the manufacture of aircrafts components, especially engine components, must increase along with more sustainable conditions. Regarding machining, a solution is proposed to increase the cutting speed, but engines are made with very difficult-to-cut alloys. In this work, a comparison between two [...] Read more.
Productivity in the manufacture of aircrafts components, especially engine components, must increase along with more sustainable conditions. Regarding machining, a solution is proposed to increase the cutting speed, but engines are made with very difficult-to-cut alloys. In this work, a comparison between two cutting tool materials, namely (a) cemented carbide and (b) SiAlON ceramics, for milling rough operations in Inconel® 718 in aged condition was carried out. Furthermore, both the influence of coatings in cemented carbide milling tools and the cutting speed in the ceramic tools were analysed. All tools were tested until the end of their useful life. The cost performance ratio was used to compare the productivity of the tested tools. Despite the results showing higher durability of the coated carbide tool, the ceramic tools presented a better behavior in terms of productivity at higher speed. Therefore, ceramic tools should be used for higher productivity demands, while coated carbide tools for low speed-high volume material removal. Full article
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Article
Development of Electrospun Films from Wastewater Treatment Plant Sludge
Coatings 2021, 11(6), 733; https://doi.org/10.3390/coatings11060733 - 18 Jun 2021
Viewed by 498
Abstract
Electrospinning is a versatile method for producing continuous polymer nanofibers, including from wastewater treatment plant sludge (WTPS). In this context, purified WTPS was successfully used to produce electrospun fibers. The main objective of our research was to produce new, local, circular, renewable and [...] Read more.
Electrospinning is a versatile method for producing continuous polymer nanofibers, including from wastewater treatment plant sludge (WTPS). In this context, purified WTPS was successfully used to produce electrospun fibers. The main objective of our research was to produce new, local, circular, renewable and environmentally friendly packaging material. The aim of the research was to purify and treat WTPS to make it suitable for the electrospinning process, thus producing a new material and chemically characterizing it in the first step. One of the major advantages of our process was that the electrospinning process could be carried out with water and ethylenediaminetetraacetic acid. The optimal viscosity was determined to be 20,000 mPas in order to produce sufficient nanofibers. Analyses such as Fourier-Transform Infrared Spectroscopy (FTIR) and 1H-NMR (proton nuclear magnetic resonance) were used to determine the substances of unpurified and purified WTPS. The tensile properties, contact angle, surface properties and differential scanning calorimetry of the final material were determined and used. The 1H-NMR analysis confirmed the presence of a small quantity of polyhydroxyalkanoates in the samples. Based on the properties, the final material was brittle and less stretchable compared to electrospun packaging films available in the market. Full article
(This article belongs to the Special Issue Natural Fiber Based Composites)
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Article
Tribological Behaviour of Graphene Nanoplatelets as Additive in Pongamia Oil
Coatings 2021, 11(6), 732; https://doi.org/10.3390/coatings11060732 - 18 Jun 2021
Viewed by 382
Abstract
This study investigated the tribological behaviour of Pongamia oil (PO) and 15W–40 mineral engine oil (MO) with and without the addition of graphene nanoplatelets (GNPs). The friction and wear characteristics were evaluated in four-ball anti-wear tests according to the ASTM D4172 standard. The [...] Read more.
This study investigated the tribological behaviour of Pongamia oil (PO) and 15W–40 mineral engine oil (MO) with and without the addition of graphene nanoplatelets (GNPs). The friction and wear characteristics were evaluated in four-ball anti-wear tests according to the ASTM D4172 standard. The morphology of worn surfaces and the lubrication mechanism of GNPs were investigated via SEM and EDS. This study also focuses on the tribological effect of GNP concentration at various concentrations. The addition of 0.05 wt % GNPs in PO and MO exhibits the lowest friction and wear with 17.5% and 12.24% friction reduction, respectively, and 11.96% and 5.14% wear reduction, respectively. Through SEM and EDS surface analysis, the surface enhancement on the worn surface by the polishing effect of GNPs was confirmed. The deposition of GNPs on the friction surface and the formation of a protective film prevent the interacting surfaces from rubbing, resulting in friction and wear reduction. Full article
(This article belongs to the Special Issue Erosion of Nanostructured Coatings)
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Article
Effect of Assembly Unit of Expansive Agents on the Mechanical Performance and Durability of Cement-Based Materials
Coatings 2021, 11(6), 731; https://doi.org/10.3390/coatings11060731 - 18 Jun 2021
Viewed by 504
Abstract
This paper studies the influence of assembly unit of expansive agents (CaO and calcium sulphoaluminate) on the limited and free compressive strengths, the limited expansion rate, carbonation resistance, chloride ion penetration resistance and corrosion resistance of reinforcement concrete. The dosages of expansive agent [...] Read more.
This paper studies the influence of assembly unit of expansive agents (CaO and calcium sulphoaluminate) on the limited and free compressive strengths, the limited expansion rate, carbonation resistance, chloride ion penetration resistance and corrosion resistance of reinforcement concrete. The dosages of expansive agent were 0%, 3%, 6%, 9%, and 12% by the total amount of cementitious materials. Two kinds of mineral admixture (blast furnace slag and fly ash) were applied in this study. Results show that suitable dosage (lower than or equal to 9%) of double expansion agent with a large amount of mineral admixtures can improve the limited and free compressive strengths. However, when the dosage of the double expansion agent is higher than 9%, the addition of the double expansion agent leads to the reduction of limited and free compressive strengths. The variation of the limit expansion rate reaches the maximum value when the curing age is 14 days. The increasing addition of expansive agents and lower water-binder ratio demonstrate positive effect on the limited expansion rate. Concrete with 60% mineral admixtures (fly ash and ground granulated blast furnace slag) shows lower limited expansion rate and higher compressive strength than the concrete with 50% mineral admixtures. Finally, the incorporation of double expansion agent can improve the resistance to carbonation, chloride ion penetration resistance, anti-corrosion of steel bars and mechanical strengths (the limited and free compressive strengths). Full article
(This article belongs to the Special Issue Interface and Surface Modification for Durable Concretes)
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Article
Manipulation of Magnetization Reversal by Electric Field in a FePt/(011)PMN-PT/Au
Coatings 2021, 11(6), 730; https://doi.org/10.3390/coatings11060730 - 17 Jun 2021
Viewed by 411
Abstract
Electric field manipulation of magnetism and 180° magnetization reversal are crucial for realizing magnetic storage devices with low-power consumption. Here, we demonstrate that electric-field manipulation of magnetic anisotropy rotation is achieved by the strain-mediated magnetoelectric effect in a Fe50Pt50/(011)0.7Pb(Mg [...] Read more.
Electric field manipulation of magnetism and 180° magnetization reversal are crucial for realizing magnetic storage devices with low-power consumption. Here, we demonstrate that electric-field manipulation of magnetic anisotropy rotation is achieved by the strain-mediated magnetoelectric effect in a Fe50Pt50/(011)0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3/Au. The remanent magnetization and magnetic coercivity of the Fe50Pt50 film exhibit an obvious response with the change of the electric fields. Moreover, the reversible in-plane 180° magnetization reversal can be controlled by alternating on or off the electric field under a small bias magnetic field. These results suggest a promising application for realizing magnetoelectric random access memory (MeRAM) devices with low-power consumption. Full article
(This article belongs to the Special Issue Thick and Thin Films for Functional Device Applications)
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Article
Characterization of Ultra-Thin Diamond-Like Carbon Films by SEM/EDX
Coatings 2021, 11(6), 729; https://doi.org/10.3390/coatings11060729 - 17 Jun 2021
Viewed by 520
Abstract
A novel, high throughput method to characterize the chemistry of ultra-thin diamond-like carbon films is discussed. The method uses surface sensitive SEM/EDX to provide substrate-specific, semi-quantitative silicon nitride/DLC stack composition of protective films extensively used in the hard disk drives industry and at [...] Read more.
A novel, high throughput method to characterize the chemistry of ultra-thin diamond-like carbon films is discussed. The method uses surface sensitive SEM/EDX to provide substrate-specific, semi-quantitative silicon nitride/DLC stack composition of protective films extensively used in the hard disk drives industry and at Angstrom-level. SEM/EDX output is correlated to TEM to provide direct, gauge-capable film thickness information using multiple regression models that make predictions based on film constituents. The best model uses the N/Si ratio in the films, instead of separate Si and N contributions. Topography of substrate/film after undergoing wear is correlatively and compositionally described based on chemical changes detected via the SEM/EDX method without the need for tedious cross-sectional workflows. Wear track regions of the substrate have a film depleted of carbon, as well as Si and N in the most severe cases, also revealing iron oxide formation. Analysis of film composition variations around industry-level thicknesses reveals a complex interplay between oxygen, silicon and nitrogen, which has been reflected mathematically in the regression models, as well as used to provide valuable insights into the as-deposited physics of the film. Full article
(This article belongs to the Section Surface Characterization, Deposition and Modification)
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Article
Impact Evaluation of High Energy Ball Milling Homogenization Process in the Phase Distribution of Hydroxyapatite-Barium Titanate Plasma Spray Biocoating
Coatings 2021, 11(6), 728; https://doi.org/10.3390/coatings11060728 - 17 Jun 2021
Viewed by 521
Abstract
Air plasma spray technique (APS) is widely used in the biomedical industry for the development of HA-based biocoatings. The present study focuses on the influence of powder homogenization treatment by high-energy ball milling (HEBM) in developing a novel hydroxyapatite-barium titanate (HA/BT) composite coating [...] Read more.
Air plasma spray technique (APS) is widely used in the biomedical industry for the development of HA-based biocoatings. The present study focuses on the influence of powder homogenization treatment by high-energy ball milling (HEBM) in developing a novel hydroxyapatite-barium titanate (HA/BT) composite coating deposited by APS; in order to compare the impact of the milling process, powders were homogenized by mechanical stirring homogenization (MSH) too. For the two-homogenization process, three weight percent ratios were studied; 10%, 30%, and 50% w/w of BT in the HA matrix. The phase and crystallite size were analyzed by X-ray diffraction patterns (XRD); the BT-phase distribution in the coating was analyzed by backscattered electron image (BSE) with a scanning electron microscope (SEM); the energy-dispersive X-ray spectroscopy (EDS) analysis was used to determinate the Ca/P molar ratio of the coatings, the degree of adhesion (bonding strength) of coatings was determinate by pull-out test according to ASTM C633, and finally the nanomechanical properties was determinate by nanoindentation. In the results, the HEBM powder processing shows better efficiency in phase distribution, being the 30% (w/w) of BT in HA matrix that promotes the best bonding strength performance and failure type conduct (cohesive-type), on the other hand HEBM powder treatment promotes a slightly greater crystal phase stability and crystal shrank conduct against MSH; the HEBM promotes a better behavior in the nanomechanical properties of (i) adhesive strength, (ii) cohesive/adhesive failure-type, (iii) stiffness, (iv) elastic modulus, and (v) hardness properties. Full article
(This article belongs to the Special Issue New Advances in Thermal Spraying)
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Article
In Vitro Microleakage Evaluation of Bioceramic and Zinc-Eugenol Sealers with Two Obturation Techniques
Coatings 2021, 11(6), 727; https://doi.org/10.3390/coatings11060727 - 17 Jun 2021
Viewed by 380
Abstract
Aim of the study is to compare the quality of the apical seal offered by a zinc-eugenol and a tricalcium-silicate-based sealer, both used with the single-cone or with the continuous wave of condensation technique. Forty central incisors were divided into four groups (n [...] Read more.
Aim of the study is to compare the quality of the apical seal offered by a zinc-eugenol and a tricalcium-silicate-based sealer, both used with the single-cone or with the continuous wave of condensation technique. Forty central incisors were divided into four groups (n = 10), according to the two sealers and the two obturation techniques under investigation, and their outer surface was isolated with nail varnish. After endodontic treatment, samples were immersed in methylene blue dye for 72 h, then included in self-curing resin and sectioned to longitudinally expose the canal apical third. The depth of dye penetration was measured in each group. Mean values were compared by two-way-ANOVA test. Multiple comparisons were performed by Tukey test. The level of significance was set at 0.05 in all tests. The continuous wave of condensation technique led to reduced microleakage. Moreover, dye penetration values were reduced for the tricalcium-silicate sealer. In terms of microleakage, the warm continuous wave of condensation technique seems promising even when combined to a bioceramic sealer. Full article
(This article belongs to the Special Issue Dentistry and Dental Biomaterials)
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Article
Numerical Simulation of Plasma Jet Characteristics under Very Low-Pressure Plasma Spray Conditions
Coatings 2021, 11(6), 726; https://doi.org/10.3390/coatings11060726 - 17 Jun 2021
Viewed by 464
Abstract
Plasma spray-physical vapor deposition (PS-PVD) is an emerging technology for the deposition of uniform and large area coatings. As the characteristics of plasma jet are difficult to measure in the whole chamber, computational fluid dynamics (CFD) simulations could predict the plasma jet temperature, [...] Read more.
Plasma spray-physical vapor deposition (PS-PVD) is an emerging technology for the deposition of uniform and large area coatings. As the characteristics of plasma jet are difficult to measure in the whole chamber, computational fluid dynamics (CFD) simulations could predict the plasma jet temperature, velocity and pressure fields. However, as PS-PVD is generally operated at pressures below 500 Pa, a question rises about the validity of the CFD predictions that are based on the continuum assumption. This study dealt with CFD simulations for a PS-PVD system operated either with an argon-hydrogen plasma jet at low-power (<50 kW) or with an argon-helium plasma jet at high-power (≥50 kW). The effect of the net arc power and chamber pressure on the plasma jet characteristics and local gradient Knudsen number (Kn) was systematically investigated. The Kn was found to be lower than 0.2, except in the region corresponding to the first expansion shock wave. The peak value in this region decreased rapidly with an increase in the arc net power and the width of this region decreased with an increase in the deposition chamber pressure. Based on the results of the study, the local Knudsen number was introduced for detecting conditions where the continuum approach is valid under PS-PVD conditions for the first time and the CFD simulations could be reasonably used to determine a process parameter window under the conditions of this study. Full article
(This article belongs to the Special Issue Plasma Sprayed Coatings)
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Article
Thermally Sprayed Nickel-Based Repair Coatings for High-Pressure Turbine Blades: Controlling Void Formation during a Combined Brazing and Aluminizing Process
Coatings 2021, 11(6), 725; https://doi.org/10.3390/coatings11060725 - 16 Jun 2021
Viewed by 389
Abstract
Turbine blades must withstand severe loading conditions and damage can occur during operation due to heat, pressure, foreign objects and hot gas corrosion, despite the protective coatings applied onto the turbine blades. Instead of replacing the damaged components, maintenance, repair and overhaul are [...] Read more.
Turbine blades must withstand severe loading conditions and damage can occur during operation due to heat, pressure, foreign objects and hot gas corrosion, despite the protective coatings applied onto the turbine blades. Instead of replacing the damaged components, maintenance, repair and overhaul are key to extend the total service life. Besides welding, the repair of turbine blades by brazing is an established repair process in the industry and involves many individual steps that often require a high degree of manual work. In the present study, a hybrid joining and coating technology was developed to shorten the state-of-the-art process chain for repairing turbine blades. With this approach, a repair coating, which consists of a filler metal, a hot gas corrosion protective layer and an aluminum top layer, is applied by atmospheric plasma spraying. The coated turbine blade then undergoes a heat-treatment so that a brazing and aluminizing process is carried out simultaneously. Due to diffusion and segregation processes, pores can occur in the heat-treated coating. In the present study, a full factorial design of experiment was performed to reduce the pores in the coating. The microstructure of the repair coating was investigated by optical- and scanning electron microscopy (SEM), and the impact of the process parameters on the resulting microstructure is discussed. Full article
(This article belongs to the Section Plasma Coatings, Surfaces & Interfaces)
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Review
High Pressure X-ray Diffraction as a Tool for Designing Doped Ceria Thin Films Electrolytes
Coatings 2021, 11(6), 724; https://doi.org/10.3390/coatings11060724 - 16 Jun 2021
Viewed by 432
Abstract
Rare earth-doped ceria thin films are currently thoroughly studied to be used in miniaturized solid oxide cells, memristive devices and gas sensors. The employment in such different application fields derives from the most remarkable property of this material, namely ionic conductivity, occurring through [...] Read more.
Rare earth-doped ceria thin films are currently thoroughly studied to be used in miniaturized solid oxide cells, memristive devices and gas sensors. The employment in such different application fields derives from the most remarkable property of this material, namely ionic conductivity, occurring through the mobility of oxygen ions above a certain threshold temperature. This feature is in turn limited by the association of defects, which hinders the movement of ions through the lattice. In addition to these issues, ionic conductivity in thin films is dominated by the presence of the film/substrate interface, where a strain can arise as a consequence of lattice mismatch. A tensile strain, in particular, when not released through the occurrence of dislocations, enhances ionic conduction through the reduction of activation energy. Within this complex framework, high pressure X-ray diffraction investigations performed on the bulk material are of great help in estimating the bulk modulus of the material, and hence its compressibility, namely its tolerance toward the application of a compressive/tensile stress. In this review, an overview is given about the correlation between structure and transport properties in rare earth-doped ceria films, and the role of high pressure X-ray diffraction studies in the selection of the most proper compositions for the design of thin films. Full article
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Article
A Comprehensive Study of Al0.6Ti0.4N Coatings Deposited by Cathodic Arc and HiPIMS PVD Methods in Relation to Their Cutting Performance during the Machining of an Inconel 718 Alloy
Coatings 2021, 11(6), 723; https://doi.org/10.3390/coatings11060723 - 16 Jun 2021
Viewed by 439
Abstract
The structural, physical–chemical, and micromechanical characteristics of Al0.6Ti0.4N coatings deposited by different physical vapor deposition (PVD) methods, such as cathodic arc deposition (CAD), as well as advanced HiPIMS techniques were investigated in terms of their cutting performance during the [...] Read more.
The structural, physical–chemical, and micromechanical characteristics of Al0.6Ti0.4N coatings deposited by different physical vapor deposition (PVD) methods, such as cathodic arc deposition (CAD), as well as advanced HiPIMS techniques were investigated in terms of their cutting performance during the machining of an Inconel 718 alloy. XRD studies had revealed that the HiPIMS coating featured lower residual stresses and more fine-grained structure. Electrochemical characterization with the potentiostat-impendence method shows that the HiPIMS coating has a significantly lower porosity than CAD. SEM and AFM studies of the surface morphology demonstrate that the HiPIMS coating has a smoother surface and an absence of droplet phases, in contrast with CAD. XRD, combined with FIB/TEM studies, shows a difference in the crystal structure of both coatings. The micromechanical characteristics of each coating, such as hardness, elastic modulus, fracture toughness, and adhesion to the substrate, were evaluated. The HiPIMS coating was found to possess a more beneficial combination of micromechanical properties compared to CAD. The beneficial characteristics of the HiPIMS coating alleviated the damage of the coated layer under operation. Combined with grain size refinement, this results in the improved adaptive performance of the HiPIMS coating through the formation of a greater amount of thermal barrier sapphire tribo-films on the friction surface. All of these characteristics contribute to the reduction of flank and crater wear intensity, as well as notching, leading to an improvement of the HiPIMS coating’s tool life. Full article
(This article belongs to the Special Issue Micro- and Nano- Mechanical Testing of Coatings and Surfaces)
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Article
Effects of Organic Solvent on Curing Behavior and Storage Stability for Waterborne Paint Containing Catalyst Encapsulated in Micelles
Coatings 2021, 11(6), 722; https://doi.org/10.3390/coatings11060722 - 16 Jun 2021
Viewed by 357
Abstract
In this study, a 2-pack isocyanate curing waterborne paint (without organic solvents) encapsulating dibutyltin dilaurate (hereinafter, DBTL) in nonionic surfactant micelles with an hydrophilic–lipophilic balance of 13–14 in advance releases DBTL when the micelles are collapsed at 80 °C or higher, whereby the [...] Read more.
In this study, a 2-pack isocyanate curing waterborne paint (without organic solvents) encapsulating dibutyltin dilaurate (hereinafter, DBTL) in nonionic surfactant micelles with an hydrophilic–lipophilic balance of 13–14 in advance releases DBTL when the micelles are collapsed at 80 °C or higher, whereby the curing progresses rapidly. On the other hand, the viscosity levels of the paint before and after being left at 40 °C for 1 h are almost the same. Organic solvents are mandatory for waterborne paints to provide paint and film properties, but they might collapse the micelles when they are formulated in the paint. In this study, we investigate whether the abovementioned paint containing organic solvents can develop switching functionality in terms of maintaining the storage stability at 40 °C and expressing a catalytic function at 80 °C to progress the curing. As a result, we find that if the solubility of the organic solvent in water at 20 °C is at least 10 g/100 mL and the boiling point is ≤200 °C, both curing and storage stability can be achieved. Full article
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Article
Design and Optimization of the Antireflective Coating Properties of Silicon Solar Cells by Using Response Surface Methodology
Coatings 2021, 11(6), 721; https://doi.org/10.3390/coatings11060721 - 16 Jun 2021
Viewed by 369
Abstract
The design and optimization of a nanostructured antireflective coatings for Si solar cells were performed by using response surface methodology (RSM). RSM was employed to investigate the effect on the overall optical performance of silicon solar cells coated with three different nanoparticle materials [...] Read more.
The design and optimization of a nanostructured antireflective coatings for Si solar cells were performed by using response surface methodology (RSM). RSM was employed to investigate the effect on the overall optical performance of silicon solar cells coated with three different nanoparticle materials of titanium dioxide, aluminum oxide, and zinc oxide nanostructures. Central composite design was used for the optimization of the reflectance process and to study the main effects and interactions between the three process variables: nanomaterial type, the radius of nanoparticles, and wavelength of visible light. In this theoretical study, COMSOL Multiphysics was utilized to design the structures by using the wave optics module. The optical properties of the solar cell’s substrate and the three different nanomaterial types were studied. The results indicated that ZnO nanoparticles were the best antireflective coating candidate for Si, as the ZnO nanoparticles produced the lowest reflection values among the three nanomaterial types. The study reveals that the optimum conditions to reach minimum surface reflections for silicon solar cell were established by using ZnO nanoparticles with a radius of ~38 nm. On average, the reflectance reached ~5.5% along the visible spectral range, and approximately zero reflectance in the 550–600 nm range. Full article
(This article belongs to the Special Issue Thin Films and Coatings for Energy Application)
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Article
Tailoring Periodic Vertical Cracks in Thermal Barrier Coatings Enabling High Strain Tolerance
Coatings 2021, 11(6), 720; https://doi.org/10.3390/coatings11060720 - 16 Jun 2021
Viewed by 553
Abstract
Lifetime is a basic support for the thermal insulation function of thermal barrier coatings (TBCs). Therefore, extending the life span is essential to develop next-generation TBCs. For this objective, the columnar structure formed by vertical cracks appears to make sense. However, the underlying [...] Read more.
Lifetime is a basic support for the thermal insulation function of thermal barrier coatings (TBCs). Therefore, extending the life span is essential to develop next-generation TBCs. For this objective, the columnar structure formed by vertical cracks appears to make sense. However, the underlying mechanism is still unclear. This work scrutinizes the influence of periodic vertical cracks on cracking behavior in order to tailor high strain tolerant TBCs. A finite element model was evolved to explore the crack behavior influenced by thermal mismatch strain between substrate and coating. The virtual crack closure technique (VCCT) was used to describe the propagation of crack under load. It is found clearly that the space between two vertical cracks (short for SVC) along the in-plane direction has a noteworthy influence on the strain tolerance of TBCs. Results indicate that the strain energy release rate (SERR) and stresses at the pre-crack tip increase continuously with the increase of the SVC, suggesting that the driving force for cracks is increasing. The crack is not propagated when the SVC is very small, whereas the crack grows continuously with the increase of the SVC. The growth of a crack can be prevented by reducing the SVC. A critical value for the SVC was found. When the SVC is less than the critical value, the SERR can be dramatically reduced. Thus, the SVC of periodic cracks can be tailored to obtain TBCs with high strain tolerance. Full article
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Article
Influence of Alternative and Conventional Surface Treatments on the Bonding Mechanism between PEEK and Veneering Resin for Dental Application
Coatings 2021, 11(6), 719; https://doi.org/10.3390/coatings11060719 - 16 Jun 2021
Viewed by 445
Abstract
This study evaluated the influence of conventional and alternative surface treatments on wettability and the bond strength between polyether ether ketone (PEEK) and veneering resin. PEEK samples were randomly divided into five groups: sandblasting, tribochemical silica coating, etching with 98% sulfuric acid for [...] Read more.
This study evaluated the influence of conventional and alternative surface treatments on wettability and the bond strength between polyether ether ketone (PEEK) and veneering resin. PEEK samples were randomly divided into five groups: sandblasting, tribochemical silica coating, etching with 98% sulfuric acid for 5 s, etching with 98% sulfuric acid for 30 s, and tribochemical silica coating plus heated silane. One of them was subjected to analysis by energy-dispersive X-ray spectroscopy (EDS) and ten were analyzed by goniometry (n = 5) and scanning electron microscopy (n = 5). Shear bond strength (SBS) was tested, and failure types were assessed. Data were analyzed using one-way ANOVA, followed by the Tukey and Duncan tests (all, α = 5%). Treatment with sandblasting and silica coating had the lowest SBS means (4.2 MPa and 4.4 MPa respectively), while sulfuric acid for 5 s showed the highest mean value (12.6 MPa), followed by sulfuric acid for 30 s and tribochemical + heated silane. All failures were classified as adhesive. The lowest mean contact angle was found for the polished (control) and etched group with 98% sulfuric acid for 30 s (83.9°). Etching with 98% sulfuric acid for 5 s increased the SBS between resin and PEEK. Full article
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Article
MOCVD Growth of GeTe/Sb2Te3 Core–Shell Nanowires
Coatings 2021, 11(6), 718; https://doi.org/10.3390/coatings11060718 - 15 Jun 2021
Viewed by 506
Abstract
We report the self-assembly of core–shell GeTe/Sb2Te3 nanowires (NWs) on Si (100), and SiO2/Si substrates by metalorganic chemical vapour deposition, coupled to the vapour–liquid–solid mechanism, catalyzed by Au nanoparticles. Scanning electron microscopy, X-ray diffraction, micro-Raman mapping, high-resolution transmission [...] Read more.
We report the self-assembly of core–shell GeTe/Sb2Te3 nanowires (NWs) on Si (100), and SiO2/Si substrates by metalorganic chemical vapour deposition, coupled to the vapour–liquid–solid mechanism, catalyzed by Au nanoparticles. Scanning electron microscopy, X-ray diffraction, micro-Raman mapping, high-resolution transmission electron microscopy, and electron energy loss spectroscopy were employed to investigate the morphology, structure, and composition of the obtained core and core–shell NWs. A single crystalline GeTe core and a polycrystalline Sb2Te3 shell formed the NWs, having core and core–shell diameters in the range of 50–130 nm and an average length up to 7 µm. Full article
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Review
Medicinal Plants and Biogenic Metal Oxide Nanoparticles: A Paradigm Shift to Treat Alzheimer’s Disease
Coatings 2021, 11(6), 717; https://doi.org/10.3390/coatings11060717 - 15 Jun 2021
Viewed by 428
Abstract
Alzheimer’s disease (AD) is the most prevalent form of dementia. Improving the amount of acetylcholine in the brain is an efficient way to treat the illness. The global incidence of dementia is estimated to be as high as 50 million, and it is [...] Read more.
Alzheimer’s disease (AD) is the most prevalent form of dementia. Improving the amount of acetylcholine in the brain is an efficient way to treat the illness. The global incidence of dementia is estimated to be as high as 50 million, and it is expected to increase every 20 years until 2040, resulting in a costly burden of disease. Early-life risk factors for pathology include genes, chromosomal abnormalities, head injury, insulin resistance, and inflammation. Potentially modifiable risk factors including obesity, diabetes, hypertension, and smoking are associated with Alzheimer’s disease (AD) and represent promising targets for intervention. The drugs currently being used to manage AD have various drawbacks. The chemical inhibition of cholinesterase enzymes is an effective technique for treating signal related neuropathology, and possible sources of compounds with these properties are natural products and biogenic metal oxide nanoparticles. There is a potential source of AChE and BChE inhibitors in the abundance of plants in nature, and natural goods appear to offer useful medications and templates for the development of other compounds. This dissertation represents a review of the literature on species of medicinal plants and nanomaterial related plants tested for their inhibitory action of AChE and BChE. Plant species and the plant-mediated metal oxide nanoparticles referred to are possible cholinesterase inhibitors and can assist researchers in their study of natural products that may be beneficial in the treatment of AD. Full article
(This article belongs to the Special Issue New Advance in Nanoparticles, Fiber, and Coatings)
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Article
Silver-Releasing Micro-/Nanoporous Coating on Additively Manufactured Macroporous Ti-Ta-Nb-Zr Scaffolds with High Osseointegration and Antibacterial Properties
Coatings 2021, 11(6), 716; https://doi.org/10.3390/coatings11060716 - 15 Jun 2021
Viewed by 427
Abstract
The two major problems of titanium alloy surface of bone/dental implants were the lack of native tissue integration and associated infection. To solve these problems, the development of self-defending implants with intrinsic osteogenic properties has been highlighted, in which titanium alloy surfaces of [...] Read more.
The two major problems of titanium alloy surface of bone/dental implants were the lack of native tissue integration and associated infection. To solve these problems, the development of self-defending implants with intrinsic osteogenic properties has been highlighted, in which titanium alloy surfaces of bone/dental implants are endowed with antibacterial property by silver (Ag) incorporated in biomaterials. In this study, we biofunctionalized the surface of selective laser melting (SLM) manufactured volume-porous Ti-Ta-Nb-Zr scaffolds by using plasma electrolytic oxidation (PEO) as a way to eliminate the peri-operative bacterial load and promote osseointegration. In the experiment, the PEO process operated with three different concentration (1, 1, and 2 g/L) of a AgNO3 solution. As a result, a titanium oxide coating embedded with calcium and phosphorous and Ag was formed by one-step PEO treatment, and a presence of HAp was detected by X-ray diffraction (XRD) and XPS. In addition, Ag ions were found to be released from the scaffolds for at least 28 days, resulting in an effective prevention of bacterial adhesion and a decrease of the number of planktonic bacteria, with no sign of cytotoxicity shown simultaneously. Highly porosity micropores were formed on the surface of scaffolds after oxidation, and the mechanical properties did not show any signs of change. Besides, a strong calcium deposition and osteoconductive effect were found on the surface of PEO-treated Ag scaffolds. To sum up, this study reveals the potential of PEO coatings to biofunctionalize SLM Ti-Ta-Nb-Zr scaffolds with antibacterial agents. The biomaterials developed here, therefore, exploit the biofunctionalized behavior of Ag to offer strong antibacterial behavior and osteogenic promotion without cytotoxicity of Ag against mammalian cells. Full article
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Article
Friction and Wear Performance of CoCrFeMnNiW Medium-Entropy Alloy Coatings by Plasma-Arc Surfacing Welding on Q235 Steel
Coatings 2021, 11(6), 715; https://doi.org/10.3390/coatings11060715 - 15 Jun 2021
Viewed by 360
Abstract
In this study, CoCrFeMnNiW medium-entropy alloy coating on Q235 was fabricated by plasma surfacing technology. The wear performance of the prepared one-layer coating and the two-layer coating was studied by a friction and abrasion tester. The microstructure and performance of the CoCrFeMnNiW coating [...] Read more.
In this study, CoCrFeMnNiW medium-entropy alloy coating on Q235 was fabricated by plasma surfacing technology. The wear performance of the prepared one-layer coating and the two-layer coating was studied by a friction and abrasion tester. The microstructure and performance of the CoCrFeMnNiW coating were researched by optical microscope, a nano-indentation test, SEM, and hardness tester. The results show that the microstructure of the coating is made up of a fusion zone, equiaxed dendrites near the fusion zone, coarse columnar crystals, and near-surface with a certain direction between the near-fusion zone and near-surface fine equiaxed grains. The wear mechanism of one layer coating was abrasive with wear and fatigue wear. The wear mechanism of the two-layer coating was adhesive with wear and fatigue wear. For CoCrFeMnNiW MEA coating, the main factors determining their wear resistance were the value of its depth recovery ratio (ηh) and EIT. Full article
(This article belongs to the Special Issue Plasma Processing of Thin Films, Coatings, and Advanced Materials)
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Article
Influence of Lightly Burned MgO on the Mechanical Properties and Anticarbonization of Cement-Based Materials
Coatings 2021, 11(6), 714; https://doi.org/10.3390/coatings11060714 - 15 Jun 2021
Viewed by 356
Abstract
This study aims to study the influence of a lightly burned magnesium oxide (LBMO) expansion agent on the rheological properties (the slump flow, plastic viscosity and variation of shear stress) of cement-based materials. Four different mass contents (i.e., 0%, 3%, 6% and 9%) [...] Read more.
This study aims to study the influence of a lightly burned magnesium oxide (LBMO) expansion agent on the rheological properties (the slump flow, plastic viscosity and variation of shear stress) of cement-based materials. Four different mass contents (i.e., 0%, 3%, 6% and 9%) of LBMO were selected. The following compressive strength and expansion value of the corresponding cement concrete were tested. Cement concrete with two strength grades of 30 MPa and 50 MPa (C30 and C50) was selected. Results indicated that the addition of LBMO can effectively decrease the fluidity and increase the plastic viscosity of fresh cement paste. An optimum dosage (3%) of LBMO is the most advantageous to the compressive strength of cement concrete. The addition of LBMO can increase the expansion rate of cement concrete, thus preventing inside cracks. Moreover, the incorporation of LBMO led to a reduction in the fluidity of the cement paste and an increase in plastic viscosity. The addition of LBMO can increase the expansion rate of cement concrete, thus preventing inside cracks. It can be found that little difference exists in the compressive strength and the expansion rate of cement concrete with strength grades of 30 MPa and 50 MPa. Finally, the increased dosage of LBMO, curing age and compressive strength led to improving the carbonization resistance of cement concrete. Full article
(This article belongs to the Special Issue Interface and Surface Modification for Durable Concretes)
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Article
High Sensitivity to Salinity-Temperature Using One-Dimensional Deformed Photonic Crystal
Coatings 2021, 11(6), 713; https://doi.org/10.3390/coatings11060713 - 14 Jun 2021
Viewed by 491
Abstract
This paper aims to theoretically study the concept of a photonic salinity and temperature sensor according to a deformed one-dimensional photonic structure. The fundamental capability of the proposed sensor is studied. Simultaneously we search to optimize the thickness of the structure and to [...] Read more.
This paper aims to theoretically study the concept of a photonic salinity and temperature sensor according to a deformed one-dimensional photonic structure. The fundamental capability of the proposed sensor is studied. Simultaneously we search to optimize the thickness of the structure and to get the maximum salinity and temperature sensitivity. The structure is constructed by alternating layers of TiO2 and fused-silica P times. In the middle of the structure, a cavity containing seawater is inserted to measure its salinity and temperature. The transfer matrix method (TMM) is used to simulate the wave-transmittance spectra. It is shown that the quality factor (Q-factor) of the resonance peaks depends on the number (P) of layers. After that, the thickness of the layers is deformed by changing the deformation degree (h). The parameters P and h are optimized to get the maximal Q-factor with the minimal number of layers and structure thickness. The best sensitivity SS of the proposed salinity sensor is 558.82 nm/RFIU with a detection limit of 0.0034 RFIU. In addition, the best sensitivity ST of the designed temperature sensor is 600 nm/RFIU with a detection limit of 0.0005 RFIU. Full article
(This article belongs to the Section Thin Films)
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Article
Electrodeposition Based Preparation of Zn–Ni Alloy and Zn–Ni–WC Nano-Composite Coatings for Corrosion-Resistant Applications
Coatings 2021, 11(6), 712; https://doi.org/10.3390/coatings11060712 - 13 Jun 2021
Viewed by 583
Abstract
Zinc (Zn) is one of the five most widely consumed metals in the world. Indeed, more than 50% of all the zinc produced is used in zinc-galvanizing processes to protect steel from corrosion. Zn-based coatings have the potential for use as a corrosion-resistant [...] Read more.
Zinc (Zn) is one of the five most widely consumed metals in the world. Indeed, more than 50% of all the zinc produced is used in zinc-galvanizing processes to protect steel from corrosion. Zn-based coatings have the potential for use as a corrosion-resistant barrier, but their wider use is restricted due to the poor mechanical properties of Zn that are needed to protect steel and other metals from rusting. The addition of other alloying elements such as Ni (Nickle) and WC (Tungsten Carbide) to Zn coating can improve its performance. This study investigates, the corrosion performance of Zn–Ni coating and Zn–Ni–WC composite nanocoatings fabricated on mild steel substrate in an environmentally friendly bath solution. The influence of WC nanoparticles on Zn–Ni deposition was also investigated. The surface morphologies, texture coefficients via XRD (X-ray diffraction), SEM (Scanning Electron Microscopy), and EDS (Energy-dispersive X-ray spectroscopy) were analyzed. The electrochemical test such as polarization curves (PC) and electrochemical impedance spectroscopy (EIS) resulted in a corrosion rate of 0.6948 Å/min for Zn–Ni–WC composite nanocoating, and 1.192 Å/min for Zn–Ni coating. The results showed that the Zn–Ni–WC composite nanocoating reduced the corrosion rate by 41.71% and showed an 8.56% increase in microhardness compared to the hardness of the Zn–Ni coating. These results are augmented to better wettable characteristics of zinc, which developed good interfacial metallurgical adhesion amongst the Ni and WC elements. The results of the novel Zn–Ni–WC nanocomposite coatings achieved a great improvement of mechanical property and corrosion protection to the steel substrate surface. Full article
(This article belongs to the Special Issue Surface Engineering for Corrosion Protection)
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Article
Effects of Coating on the Dimensional Stability of Wood-Polymer Composites
Coatings 2021, 11(6), 711; https://doi.org/10.3390/coatings11060711 - 13 Jun 2021
Viewed by 537
Abstract
Wood polymer composites (WPC) are sensitive to moisture because of the hydrophilic nature of the wood fibers. The main objective of this study was to improve the dimensional stability of WPCs by coating. Polypropylene and polylactic acid were reinforced by three pulp fibers [...] Read more.
Wood polymer composites (WPC) are sensitive to moisture because of the hydrophilic nature of the wood fibers. The main objective of this study was to improve the dimensional stability of WPCs by coating. Polypropylene and polylactic acid were reinforced by three pulp fibers (kraft, thermomechanical (TMP), and chemothermomechanical (CTMP)) at three fiber contents (50, 60, and 70% w/w). The resulting WPCs were coated using two commercial coatings, epoxy and acrylic. Kraft fiber WPCs were less sensitive to moisture than TMP and CTMP WPCs. These differences were explained by the crystallinity of the kraft fibers and their better interfacial adhesion to the polymers. The epoxy coating proved to be more effective than the acrylic coating and significantly reduced the water absorption and the thickness swell for all formulations. Negative relationships between the contact angle and water absorption were obtained. These relationships depend on the fiber content and type, the matrix nature, and the coating. Full article
(This article belongs to the Special Issue Recent Developments and Trends in Wood Coatings)
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