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Coatings, Volume 11, Issue 2 (February 2021) – 149 articles

Cover Story (view full-size image): Superhydrophobic coatings, as smart coatings, have captured the attention of researchers worldwide, as their excellent water repellence makes them applicable to all walks of life. The prominent functional requirements and performance conformities of superhydrophobic coatings in particular play essential roles in the development of various application fields, including automobile, marine, aircraft, solar energy, and architecture. The optimization and design of superhydrophobic coatings by diverse fabrication technologies are contemporary hot spots to meet the demand growth of the coating industry. View this paper
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Editorial
Special Issue “Surface Modification of Metals and Alloys”
Coatings 2021, 11(2), 260; https://doi.org/10.3390/coatings11020260 - 23 Feb 2021
Viewed by 743
Abstract
Recently surface modification has become necessary for the scientific community because of surface properties of new materials are usually inadequate in terms of wettability, adhesion, corrosion resistance or even drag reduction [...] Full article
(This article belongs to the Special Issue Surface Modification of Metals and Alloys)
Article
Kinetics of the Boride Layers Obtained on AISI 1018 Steel by Considering the Amount of Matter Involved
Coatings 2021, 11(2), 259; https://doi.org/10.3390/coatings11020259 - 23 Feb 2021
Cited by 8 | Viewed by 1027
Abstract
Boride layers are typically used to combat the wear and corrosion of metals. For this reason, to improve our knowledge of the boriding process, this research studied the effect of the size of the treated material on the kinetics of the growth of [...] Read more.
Boride layers are typically used to combat the wear and corrosion of metals. For this reason, to improve our knowledge of the boriding process, this research studied the effect of the size of the treated material on the kinetics of the growth of the boride layers obtained during a solid diffusion process. The purpose was to elucidate how the layers’ growth kinetics could be affected by the size of the samples since, as the amount of matter increases, the amount of energy necessary to make the process occur also increases. Furthermore, the level of activation energy seems to change as a function of the sample size, although it is considered an intrinsic parameter of each material. Six cylindrical samples with different diameters were exposed to the boriding process for three different exposure times (1.5, 3, and 5 h). The treatment temperatures used were 900, 950, and 1000 °C for each size and duration of treatment. The results show that the layer thickness increased not only as a function of the treatment conditions but also as a function of the sample diameter. The influence of the sample size on the growth kinetics of the boride layers is clear, because the growth rate increased even though the treatment conditions (time and temperature) remained constant. Full article
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Article
Optical Evidence for the Assembly of Sensors Based on Reduced Graphene Oxide and Polydiphenylamine for the Detection of Epidermal Growth Factor Receptor
Coatings 2021, 11(2), 258; https://doi.org/10.3390/coatings11020258 - 23 Feb 2021
Cited by 2 | Viewed by 805
Abstract
Using Raman scattering and FTIR spectroscopy, new optical evidence for the assembly of sensors based on reduced graphene oxide (RGO) and polydiphenylamine (PDPA) for the electrochemical detection of the epidermal growth factor receptor (EGFR) are reported. The assembly process of the RGO sheets [...] Read more.
Using Raman scattering and FTIR spectroscopy, new optical evidence for the assembly of sensors based on reduced graphene oxide (RGO) and polydiphenylamine (PDPA) for the electrochemical detection of the epidermal growth factor receptor (EGFR) are reported. The assembly process of the RGO sheets electrochemical functionalized with PDPA involves the chemical adsorption of 1,4-phenylene diisothiocyanate (PDITC), followed by an incubation with protein G in phosphate buffer (PB) solution and after that the interaction with EGFR antibodies solution. Taking into account the changes reported by Raman scattering and FTIR spectroscopy, a chemical mechanism of the assembling process for this sensor is proposed. The preliminary testing of the electrochemical activity of the sensors based on RGO and PDPA was reported by cyclic voltammetry. Full article
(This article belongs to the Special Issue Surface Chemical Modification)
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Article
Electro-Oxidation of Ammonia at Novel Ag2O−PrO2/γ-Al2O3 Catalysts
Coatings 2021, 11(2), 257; https://doi.org/10.3390/coatings11020257 - 22 Feb 2021
Cited by 19 | Viewed by 1862
Abstract
An Ag2O(x)−PrO2(y)/γ-Al2O3 electrocatalyst series (X:Y is for Ag:Pr from 0 to 10) was synthesized, to use synthesized samples in electrochemical applications, a step in fuel cells advancements. [...] Read more.
An Ag2O(x)−PrO2(y)/γ-Al2O3 electrocatalyst series (X:Y is for Ag:Pr from 0 to 10) was synthesized, to use synthesized samples in electrochemical applications, a step in fuel cells advancements. Ag2O(x)−PrO2(y)/γ-Al2O3/Glassy-Carbon was investigated for electrochemical oxidation of ammonia in alkaline medium and proved to be highly effective, having high potential utility, as compared to commonly used Pt-based electrocatalysts. In this study, gamma alumina as catalytic support was synthesized via precipitation method, and stoichiometric wt/wt.% compositions of Ag2O−PrO2 were loaded on γ-Al2O3 by co-impregnation method. The desired phase of γ-Al2O3 and supported nanocatalysts was obtained after heat treatment at 800 and 600 °C, respectively. The successful loadings of Ag2O−PrO2 nanocatalysts on surface of γ-Al2O3 was determined by X-rays diffraction (XRD), Fourier-transform Infrared Spectroscopy (FTIR), and energy dispersive analysis (EDX). The nano-sized domain of the sample powders sustained with particle sizes was calculated via XRD and scanning electron microscopy (SEM). The surface morphology and elemental compositions were examined by SEM, transmission electron microscopy (TEM) and EDX. The conductive and electron-transferring nature was investigated by cyclic voltammetry and electrochemical impedance (EIS). Cyclic voltammetric profiles were observed, and respective kinetic and thermodynamic parameters were calculated, which showed that these synthesized materials are potential catalysts for ammonia electro-oxidation. Ag2O(6)−PrO2(4)/γ-Al2O3 proved to be the most proficient catalyst among all the members of the series, having greater diffusion coefficient, heterogeneous rate constant and lesser Gibbs free energy for this system. The catalytic activity of these electrocatalysts is revealed from electrochemical studies which reflected their potentiality as electrode material in direct ammonia fuel cell technology for energy production. Full article
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Article
Synthesis and Frost Suppression Performance of PDMS-SiO2/PFA Hybrid Coating
Coatings 2021, 11(2), 256; https://doi.org/10.3390/coatings11020256 - 22 Feb 2021
Viewed by 896
Abstract
In this article, a simple synthesis method was applied to form a branch and tendril structure using hydroxyl-terminated silicone sol modified silica nanoparticles at high temperature, followed by mixing with fluoro-containing polyacrylate emulsion (PFA) to obtained a polydimethylsiloxane (PDMS)-SiO2/PFA hybrid coating. [...] Read more.
In this article, a simple synthesis method was applied to form a branch and tendril structure using hydroxyl-terminated silicone sol modified silica nanoparticles at high temperature, followed by mixing with fluoro-containing polyacrylate emulsion (PFA) to obtained a polydimethylsiloxane (PDMS)-SiO2/PFA hybrid coating. The hydrophobic performance of the PDMS-SiO2/PFA coating was further enhanced through the synergistic action of Si-O and F group. The obtained coating has a similar surface structure of lotus leaf and the contact angle can reach 142.2 ± 2.4°. The PDMS-SiO2/PFA coating could delay the formation of frost crystal and the growth of frost layer. The defrosting droplets were difficult to adhere on the coating and could be easily rolled off for long frosting and defrosting cycles, which indicates the potential application of this coating in the field of frost suppression. Full article
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Editorial
Metal Surfaces
Coatings 2021, 11(2), 255; https://doi.org/10.3390/coatings11020255 - 22 Feb 2021
Viewed by 695
Abstract
Surface phenomena such as corrosion, wear, heterogeneous catalysis, segregation, etc [...] Full article
(This article belongs to the Special Issue Metal Surfaces)
Article
Investigation of the Anti-Corrosion Properties of Fluorinated Graphene-Modified Waterborne Epoxy Coatings for Carbon Steel
Coatings 2021, 11(2), 254; https://doi.org/10.3390/coatings11020254 - 21 Feb 2021
Cited by 12 | Viewed by 1490
Abstract
Waterborne epoxy resin (WEP) has been widely used as an anti-corrosive coating for metals. However, it is still a big challenge to further improve its anti-corrosion performance due to the poor barrier properties to corrosive media. In this study, fluorinated graphene (FG) was [...] Read more.
Waterborne epoxy resin (WEP) has been widely used as an anti-corrosive coating for metals. However, it is still a big challenge to further improve its anti-corrosion performance due to the poor barrier properties to corrosive media. In this study, fluorinated graphene (FG) was used as a filler in WEP to improve its barrier properties, which contributes to corrosion resistance enhancement. The chemical composition and microstructures of FG and FG-modified WEP were systematically analyzed, and its corrosion resistance was also studied. Results reveal that the addition of FG sheet to WEP not only can significantly improve the tensile strength of WEP coating, but also increase the barrier properties of WEP coating and block the penetration of corrosive agent throughout the coating to the interface between coating and substrate. Meanwhile, the results also declare that the F content of FG has a significant effect on mechanical properties and long-term corrosion resistance, and the performance of FG-modified WEP coating will deteriorate with the increase of F content. Full article
(This article belongs to the Special Issue Modern Trends in Corrosion Protection of Steels)
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Article
Increasing the Strength of the Glue Line in the Production of Thermally Modified Wood Paneling
Coatings 2021, 11(2), 253; https://doi.org/10.3390/coatings11020253 - 20 Feb 2021
Cited by 1 | Viewed by 717
Abstract
This work is devoted to the study of the effect of ultraviolet rays for the surface activation of pine wood thermally modified at temperatures of 180−240 °C in order to increase the surface roughness, enhance the wettability of thermal wood and the adhesive [...] Read more.
This work is devoted to the study of the effect of ultraviolet rays for the surface activation of pine wood thermally modified at temperatures of 180−240 °C in order to increase the surface roughness, enhance the wettability of thermal wood and the adhesive strength of the glue in the production of wood block furniture panels. Studies were carried out to measure the contact angle of wettability of thermally modified wood samples of pine, as a result of which it was determined that the ultraviolet treatment process contributes to an increase in the adhesion properties of the surface layer of thermally modified wood by more than 13% due to the reactivity of ultraviolet rays to oxidize and degrade ligno-containing wood products. At the same time, the most active process of surface activation takes place during 60 min of ultraviolet irradiation of wood with a total irradiation of at least 125 W/cm2. It was revealed that the combined effect of two-stage wood processing, including preliminary volumetric thermal modification followed by surface ultraviolet treatment, causes an increase in the moisture resistance of glued wood products by 24%. So, if the strength of the glue seam when gluing natural wood samples after boiling decreased by 46%, then the samples that underwent two-stage processing showed a decrease only by 22%. In connection with the results obtained, an improved technology for the production of furniture boards for the manufacture of moisture-resistant wood products is proposed. Full article
(This article belongs to the Special Issue Physicochemical Surface Treatment of Wood Raw Materials)
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Article
Physical, Optical, and Visual Performance of Coated Cross-Laminated Timber during Natural and Artificial Weathering
Coatings 2021, 11(2), 252; https://doi.org/10.3390/coatings11020252 - 20 Feb 2021
Cited by 4 | Viewed by 1279
Abstract
Cross-laminated timber (CLT) market demand is on the rise in the United States. Adequate protective measures have not been extensively studied. The objective of this study was to investigate the weathering performance of exterior wood coatings. We evaluated coated CLT sample surfaces based [...] Read more.
Cross-laminated timber (CLT) market demand is on the rise in the United States. Adequate protective measures have not been extensively studied. The objective of this study was to investigate the weathering performance of exterior wood coatings. We evaluated coated CLT sample surfaces based on visual appearance, color change (CIE*L*a*b), gloss changes, and water intrusion. From the five exterior wood coatings evaluated, only two showed adequate performance after twelve months field exposure. Based on visual ratings following the ASTM procedures, coating failure occurs more quickly in Mississippi than in Wisconsin, due to its greater decay zone. Both location and coating type impacted the aging of the samples. Artificial weathering results were consistent with natural weathering indicating the two adequate coatings were the most resistant to failure, color, and gloss change. For future studies, new coatings designed for the protection of end-grain in CLT panels should be a target of research and development. Full article
(This article belongs to the Special Issue Wood Modification: Characterization, Modelling and Applications)
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Article
Waterborne Polyurea Coatings Filled with Sulfonated Graphene Improved Anti-Corrosion Performance
Coatings 2021, 11(2), 251; https://doi.org/10.3390/coatings11020251 - 20 Feb 2021
Cited by 3 | Viewed by 897
Abstract
In this paper, an environmentally friendly waterborne polyurea (WPUA) emulsion and its corresponding coating were prepared, which was characterized by dynamic light scattering (DLS), Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR), and scanning electron microscopy (SEM). To improve the performance of [...] Read more.
In this paper, an environmentally friendly waterborne polyurea (WPUA) emulsion and its corresponding coating were prepared, which was characterized by dynamic light scattering (DLS), Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR), and scanning electron microscopy (SEM). To improve the performance of the coating, we doped sulfonated graphene (SG) into WPUA to prepare composite coating (SG/WPUA). SG can be uniformly dispersed in WPUA emulsion and is stable for a long time (28 days) without delamination. The water resistance of the composite coating with 0.3 wt.% SG nanofiller was improved; the water contact angle (WCA) result was SG/WPUA (89°) > WPUA (48.5°), and water absorption result was SG/WPUA (2.90%) < WPUA (9.98%). After water immersion treatment, SEM observation revealed that the SG/WPUA film only generated enlarged microcracks (100 nm) instead of holes (150–400 nm, WPUA film). Polarization curves and electrochemical impedance spectroscopy (EIS) tests show that SG nanosheets with low doping content (0.3 wt.%) are more conducive to the corrosion resistance of WPUA coatings, and the model was established to explain the mechanism. Full article
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Article
Effect of Annealing on the Characteristics of CoFeBY Thin Films
Coatings 2021, 11(2), 250; https://doi.org/10.3390/coatings11020250 - 20 Feb 2021
Cited by 2 | Viewed by 724
Abstract
In this study, the addition of Y to CoFeB alloy can refine the grain size to study the magnetic, adhesion and optical properties of as-deposited and annealed CoFeB alloy. XRD analysis shows that CoFeB(110) has a BCC CoFeB (110) nanocrystalline structure with a [...] Read more.
In this study, the addition of Y to CoFeB alloy can refine the grain size to study the magnetic, adhesion and optical properties of as-deposited and annealed CoFeB alloy. XRD analysis shows that CoFeB(110) has a BCC CoFeB (110) nanocrystalline structure with a thickness of 10–50 nm under four heat-treatment conditions, and a CoFeB(110) peak at 44° (2θ). The measurements of saturation magnetization (MS) and low frequency alternate-current magnetic susceptibility (χac) revealed a thickness effect owed to exchange coupling. The maximum MS of the 300 °C annealed CoFeBY film with a thickness of 50 nm was 925 emu/cm3 (9.25 × 105 A/m). The maximum χac value of the 300 °C annealed CoFeBY nanofilms with a thickness of 50 nm was 0.165 at 50 Hz. After annealing at 300 °C, CoFeBY nanofilms exhibited the highest surface energy of 31.07 mJ/mm2, where the thickness of the nanofilms was 40 nm. Compared with the as-deposited CoFeBY nanofilms, due to the smaller average grain size after annealing, the transmittance of the annealed nanofilms increased. Importantly, when a CoFeB seed or buffer layer was replaced by a CoFeBY nanofilm, the thermal stability of the CoFeBY nanofilms was improved, promoting themselves on the practical MTJ applications. Full article
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Article
Adhesion of Electrospun Poly(acrylonitrile) Nanofibers on Conductive and Isolating Foil Substrates
Coatings 2021, 11(2), 249; https://doi.org/10.3390/coatings11020249 - 19 Feb 2021
Cited by 6 | Viewed by 1011
Abstract
Electrospinning can be used to prepare nanofibers from various polymers and polymer blends. The adhesion of nanofibers to the substrates on which they are electrospun varies greatly with the substrate material and structure. In some cases, good adhesion is desired to produce sandwich [...] Read more.
Electrospinning can be used to prepare nanofibers from various polymers and polymer blends. The adhesion of nanofibers to the substrates on which they are electrospun varies greatly with the substrate material and structure. In some cases, good adhesion is desired to produce sandwich structures by electrospinning one material directly onto another. This is the case, e.g., with dye-sensitized solar cells (DSSCs). While both pure foil DSSCs and pure electrospun DSSCs have been examined, a combination of both technologies can be used to combine their advantages, e.g., the lateral strength of foils with the large surface-to-volume ratio of electrospun nanofibers. Here, we investigate the morphology and adhesion of electrospun nanofibers on different foil substrates containing materials commonly used in DSSCs, such as graphite, poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) or TiO2. The results show that the foil material strongly influences the adhesion, while a plasma pretreatment of the foils showed no significant effect. Moreover, it is well known that conductive substrates can alter the morphology of nanofiber mats, both at microscopic and macroscopic levels. However, these effects could not be observed in the current study. Full article
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Article
Spherical Droplet Deposition—Mechanistic Model
Coatings 2021, 11(2), 248; https://doi.org/10.3390/coatings11020248 - 19 Feb 2021
Cited by 1 | Viewed by 661
Abstract
In the currently existing physical models of wetting a solid substrate by a liquid drop, the contact angle is determined on the basis of the equilibrium of forces acting tangentially to the wetted surface at any point in the perimeter of the wetted [...] Read more.
In the currently existing physical models of wetting a solid substrate by a liquid drop, the contact angle is determined on the basis of the equilibrium of forces acting tangentially to the wetted surface at any point in the perimeter of the wetted area, ignoring the forces (or their components) acting perpendicular to this area. In the solution shown in the paper, the equilibrium state of forces acting on a droplet was determined based on the minimum mechanical energy that the droplet achieves in the state of equilibrium. This approach allows one to take into account in the model, in addition to the forces tangential to the wetted surface, also forces perpendicular to it (also the force of adhesion), moreover, these may be dispersed forces acting on the entire interface, not on a single point. The correctness of this approach is confirmed by the derived equations concerning the forces acting on the liquid both tangentially and perpendicularly to the wetted surface. The paper also identifies the areas of solutions in which the obtained equilibrium of forces is stable and areas of unstable equilibrium of forces. The solution is formulated both for isothermal and isochoric system. Based on the experimental data accessible in the literature, the condition that has to be met by the droplets (and their surroundings) during measurements performed under gravity conditions was formulated. Full article
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Article
Contribution of Different Pretreatments to the Thermal Stability and UV Resistance Performance of Cellulose Nanofiber Films
Coatings 2021, 11(2), 247; https://doi.org/10.3390/coatings11020247 - 19 Feb 2021
Cited by 2 | Viewed by 762
Abstract
Hot water (HW), green liquor (GL), and sodium chlorite (SC) pretreatments were used to pretreat sugarcane bagasse (SCB) and spruce (SP) and then to prepare cellulose nanofibers (CNFs) through high-pressure homogenization to explore the effect of physicochemical properties on the thermal stability and [...] Read more.
Hot water (HW), green liquor (GL), and sodium chlorite (SC) pretreatments were used to pretreat sugarcane bagasse (SCB) and spruce (SP) and then to prepare cellulose nanofibers (CNFs) through high-pressure homogenization to explore the effect of physicochemical properties on the thermal stability and ultraviolet (UV) resistance performance of CNF films. The results indicated that the lignin content of HW-pretreated CNFs was higher than that of GL- and SC-pretreated CNFs, and the hemicellulose content of HW-pretreated CNFs was lower than that of GL- and SC-pretreated CNFs. The synergy of lignin and hemicellulose impacted the thermal stability of CNF films. The thermal stability of all the SP CNF films was higher than that of all the SCB CNF films. Hot water pretreatment improved the thermal stability of CNF films, and green liquor and sodium chlorite pretreatment decreased the thermal stability of CNF films. The highest thermal stability of SP-HW CNF films reached 392 °C, which was 5.4% higher than that of SP-SC CNF films. Furthermore, the ultraviolet resistance properties of different CNF films were as follows: SCB-HW > SCB-GL > SCB-SC and SP-HW > SP-GL > SP-SC. Green liquor pretreatment is an effective method to prepare CNFs. Conclusively, this research provides a basic theory for the preparation of CNFs and allows the improvement of CNF films in the application of thermal stability management and UV resistance fields. Full article
(This article belongs to the Special Issue Natural Fiber Based Composites)
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Article
Influence of Phosphoric Acid on the Adhesion Strength between Rusted Steel and Epoxy Coating
Coatings 2021, 11(2), 246; https://doi.org/10.3390/coatings11020246 - 19 Feb 2021
Cited by 1 | Viewed by 884
Abstract
In this work, we evaluated the influence of phosphoric acid in conjunction with a tannic converter formula on the adhesion of the coating system by employing the epoxy coating as the top coating. The morphology and the composition of the rusted steel before [...] Read more.
In this work, we evaluated the influence of phosphoric acid in conjunction with a tannic converter formula on the adhesion of the coating system by employing the epoxy coating as the top coating. The morphology and the composition of the rusted steel before and after treatment were determined by scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) spectroscopy. The adhesion test result showed that the adhesion strength between the rust and the epoxy coating was enhanced from 1.93 MPa to 11.63 MPa with the treatment by 50 g/L phosphoric acid in conjunction with a tannic converter formula. Further investigation of the working mechanism of such treatment revealed that the adhesion improvement could be attributed to the formation of a micro-cracked and compact conversion layer. This layer could reinforce the anchoring of epoxy coating through the pinning effect. It was also found that both the pH and the phosphate radical were the important factors to improve the adhesion strength. Full article
(This article belongs to the Special Issue Mechanical Properties of Polymer Materials and Coatings)
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Article
Measurement of the Elastic Modulus and Residual Stress of Thermal Barrier Coatings Using a Digital Image Correlation Technique
Coatings 2021, 11(2), 245; https://doi.org/10.3390/coatings11020245 - 19 Feb 2021
Cited by 3 | Viewed by 923
Abstract
This paper presents an experimental study on simultaneously measuring the elastic modulus and residual stress of a thermal barrier coating (TBC) after different isothermal heat treatments. The elastic modulus and residual stress of TBCs were theoretically analyzed based on composite beam bending theory. [...] Read more.
This paper presents an experimental study on simultaneously measuring the elastic modulus and residual stress of a thermal barrier coating (TBC) after different isothermal heat treatments. The elastic modulus and residual stress of TBCs were theoretically analyzed based on composite beam bending theory. Thereafter, an experimental setup was established combining the 3D digital image correlation method with the bending test to obtain the curvature changes in the TBC sample. Finally, the elastic modulus and residual stress of the ceramic layer with different isothermal heat treatments were obtained. The results show that the elastic modulus of the ceramic layer measured under compression is greater than that under tension, and the elastic modulus of the ceramic layer increases first and then tends to be stable as the heat treatment time increases. In addition, the residual stress of the TBCs ceramic layer quickly changes from compressive stress to tensile stress with heat treatment, and the tensile stress increases with the increase in thermal exposure time. Furthermore, the reasons for the change tendency were analyzed according to the variation in porosity and microstructures by processing the scanning electron microscope (SEM) figures. The results demonstrate that simultaneously determining the elastic modulus and residual stress of TBC based on combining the 3D digital image correlation method with the bending test is effective and reliable. Full article
(This article belongs to the Section Ceramic Coatings and Engineering Technology)
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Article
Nondestructive Evaluation of Heritage Object Coatings with Four Hyperspectral Imaging Systems
Coatings 2021, 11(2), 244; https://doi.org/10.3390/coatings11020244 - 18 Feb 2021
Cited by 4 | Viewed by 1410
Abstract
Advanced imaging techniques can noninvasively characterise, monitor, and evaluate how conservation treatments affect cultural heritage objects. In this specific field, hyperspectral imaging allows nondestructive characterisation of materials by identifying and characterising colouring agents, binders, and protective coatings as components of an object’s original [...] Read more.
Advanced imaging techniques can noninvasively characterise, monitor, and evaluate how conservation treatments affect cultural heritage objects. In this specific field, hyperspectral imaging allows nondestructive characterisation of materials by identifying and characterising colouring agents, binders, and protective coatings as components of an object’s original construction or later historic additions. Furthermore, hyperspectral imaging can be used to monitor deterioration or changes caused by environmental conditions. This paper examines the potential of hyperspectral imaging (HSI) for the evaluation of heritage objects. Four cameras operating in different spectral ranges were used to nondestructively scan a beehive panel painting that originated from the Slovene Ethnographic Museum collection. The specific objective of this research was to identify pigments and binders present in the samples and to spatially map the presence of these across the surface of the art piece. Merging the results with databases created in parallel using other reference methods allows for the identification of materials originally used by the artist on the panel. Later interventions to the original paintings can also be traced as part of past conservation campaigns. Full article
(This article belongs to the Special Issue Surface and Interface Analysis of Cultural Heritage)
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Article
Development of Adhesive, Bioactive and Antibacterial Titania Sol-Gel Coating on Titanium Substrate by Dip-Coating Technique
Coatings 2021, 11(2), 243; https://doi.org/10.3390/coatings11020243 - 18 Feb 2021
Cited by 3 | Viewed by 932
Abstract
The sol-gel method provides a wide variety of applications in the medical field. One of these applications is the formation of coatings on the metal implants. The coatings containing specific additive can enhance or improve the existing surface properties of the substrate. In [...] Read more.
The sol-gel method provides a wide variety of applications in the medical field. One of these applications is the formation of coatings on the metal implants. The coatings containing specific additive can enhance or improve the existing surface properties of the substrate. In this work, titania sol-gel coatings were doped with two forms of silver (AgNO3, Ag3PO4) and synthetic hydroxyapatite and applied on the titanium samples by dip-coating technique. After drying and slow firing, all coatings were characterized with scanning electron microscopy. Thin coatings were successfully prepared with excellent adhesion to the substrate (measured by ASTM D 3359-2), despite cracks. Coatings containing silver and hydroxyapatite demonstrated a 100% antibacterial effect against Escherichia coli after 24 h. The bioactivity of the coatings containing hydroxyapatite tested in modified simulated body fluid under static-dynamic conditions was confirmed by bone-like hydroxyapatite precipitation. To better understand the interaction of the coatings with simulated body fluid (SBF), changes of Ca2+ and (PO4)3− ions concentrations and pH values were studied. Full article
(This article belongs to the Special Issue Glass/Ceramic Coatings for Biomaterials and Biomedical Applications)
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Article
Tribocorrosion Performance of Cr/CrN Hybrid Layer as a Coating for Machine Components Used in a Chloride Ions Environment
Coatings 2021, 11(2), 242; https://doi.org/10.3390/coatings11020242 - 18 Feb 2021
Cited by 6 | Viewed by 883
Abstract
The aim of the article was to identify the effect of material hardness on the tribocorrosion process by comparing two material solutions. The analysis concerned the assessment of the process intensity and the identification of the mechanisms responsible for material loss. Possible mechanisms [...] Read more.
The aim of the article was to identify the effect of material hardness on the tribocorrosion process by comparing two material solutions. The analysis concerned the assessment of the process intensity and the identification of the mechanisms responsible for material loss. Possible mechanisms of tribocorrosion common for materials of high hardness were determined. Two classic material solutions (based on AISI 1045 steel) ensuring high hardness of the subsurface layers were tested: nitriding with an additional oxidation and impregnation process, and Physical Vapour Deposition (PVD) coating. In order to better identify the impact of hardness on the tribocorrosion process in each individual test, the pressures in the contact zone were increased. The tribocorrosion tests were carried out in 3.5% NaCl with free corrosion potential (OCP) for the ball-on-plate system. The results of the tribocorrosion tests presented in the article indicate that the synergy effect of friction and corrosion can be generated by the same mechanisms of material removal in both the material solutions tested. The intensity of these mechanisms is determined by material hardness. The likely mechanism of generating the synergy effect may be related to the formation of local pits along the friction path. The corrosion processes that are initiated by the cracking of the hard surface layer create local cavities, which most probably intensify frictional wear in successive time intervals. The area around the cavities facilitates plastic deformation, the initiation of cracking of the cyclically deformed layer and the tearing of larger pieces of material (especially at higher unit pressures in the frictional contact zone). Full article
(This article belongs to the Special Issue Tribological Behavior of Functional Surface: Models and Methods)
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Article
Experimental Analysis of Reinforcement Rust in Cement under Corrosive Environment
Coatings 2021, 11(2), 241; https://doi.org/10.3390/coatings11020241 - 18 Feb 2021
Cited by 2 | Viewed by 900
Abstract
In this work, the microstructure characteristics of corrosion products of reinforcement under a corrosive environment with chloride, carbonation and the combination of chloride-carbonization were studied by x-ray photoelectron spectroscopy (XPS) and scanning electron microscopy/energy spectroscopy (SEM-EDX). The results indicate that the outside of [...] Read more.
In this work, the microstructure characteristics of corrosion products of reinforcement under a corrosive environment with chloride, carbonation and the combination of chloride-carbonization were studied by x-ray photoelectron spectroscopy (XPS) and scanning electron microscopy/energy spectroscopy (SEM-EDX). The results indicate that the outside of the passivation film reacts with the cement slurry to produce Fe–SiO4 in all three corrosive environments. The inner side is not completely corroded. The morphology of the corrosion is different in the three environments. In a chloride environment, corrosion products have obvious cracks, and the local layered structure is dense. In a carbonation environment, the surface of the steel corrosion shows a uniform granular structure and loose texture. With the combination of chloride and combination, the surface of the structural layer of steel corrosion was uneven and accompanied by protrusions, cracking and spalling occurred. The composition of the corrosion substances in the three corrosion environments are mainly composed of FeO, Fe3O4, Fe2O3 and Fe–SiO4. The content of iron oxide increases from a chloride salt, carbonization to the composite environment, indicating that the corrosion degree intensifies successively. Full article
(This article belongs to the Special Issue Interface and Surface Modification for Durable Concretes)
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Article
Polymer Coating Effects: Study of Material Properties and Architectural Application Characteristics of Aluminum Template
Coatings 2021, 11(2), 240; https://doi.org/10.3390/coatings11020240 - 17 Feb 2021
Cited by 1 | Viewed by 1432
Abstract
In construction process, the formwork must be in contact with concrete to help the concrete solidify and fix the shape. Coating the formwork with a polymer can prolong its service life by reducing the amount of concrete sticking to the mold. Herein, an [...] Read more.
In construction process, the formwork must be in contact with concrete to help the concrete solidify and fix the shape. Coating the formwork with a polymer can prolong its service life by reducing the amount of concrete sticking to the mold. Herein, an aluminum template substrate was coated with polyvinylidene difluoride (PVDF) or polyurethane (PU). Aluminum template material analysis was conducted, polymer film thickness was measured, and weather, moisture, pollution, salt spray, abrasion, impact, and acid and alkali resistance tests were conducted, as were tensile, bending, adhesion, hardness, and salt water resistance tests. Cement adhesion resistance was repeatedly tested. The experimental results indicated that the PVDF-coated template was superior. The novel PVDF Aluminum template exhibited high corrosion resistance and can be used in building materials, for example, in ceilings, partition walls, curtain walls, roof panels, and roof trusses. For reference, it can also be applied to ship structures and seaside and wind power generation projects. Full article
(This article belongs to the Special Issue Advances in Thin Film Transistors: Properties and Applications)
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Article
Light Output, Thermal Properties, and Reliability of Using Glass Phosphors in WLED Packages
Coatings 2021, 11(2), 239; https://doi.org/10.3390/coatings11020239 - 17 Feb 2021
Cited by 3 | Viewed by 918
Abstract
White-light-emitting diodes (WLED) based on yttrium aluminum garnet (YAG) phosphors sintered with glass (PiG) and with silicone (PiS) are compared in terms of their light properties, temperature properties and reliability.The complete YAG phosphor was doped with an encapsulant traditional WLED (PiS WLED), and [...] Read more.
White-light-emitting diodes (WLED) based on yttrium aluminum garnet (YAG) phosphors sintered with glass (PiG) and with silicone (PiS) are compared in terms of their light properties, temperature properties and reliability.The complete YAG phosphor was doped with an encapsulant traditional WLED (PiS WLED), and the WLED was covered with PiG (PiG WLED). PiG was made by sintering glass powder and YAG phosphor at the ratio of 87:13 (%), and the correlated color temperature (CCT) was 5564 K. The CCT of the PiG WLED with the YAG doping concentration of 8.5 wt.% approximated 5649 K. The initial light output of the PiG WLED was 6.4% lower than that of the PiS WLED. Under 1008 h and 350 mA aging, PiG WLED and PiS WLED’ light output, CCT and color rendering index variation rates were all within 1%. In the saturated vapor-pressure test, no sample exhibited red ink infiltration, light nor peeling between the encapsulant and the lead-frame. Compared with that of the PiS WLED, the junction temperature of the PiG WLED reduced from 88.4 °C to 81.3 °C. Thermal resistance dropped from 37.4 °C/W to 35.6 °C/W. The PiG WLED presented a better CIE (Commission Internationale de l’Eclairage) 1931 chromaticity coordinate (x,y) concentration and thermal properties than the PiS WLED. Full article
(This article belongs to the Special Issue Advances in Thin Film Transistors: Properties and Applications)
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Article
Biomimetic Slippery PDMS Film with Papillae-Like Microstructures for Antifogging and Self-Cleaning
Coatings 2021, 11(2), 238; https://doi.org/10.3390/coatings11020238 - 17 Feb 2021
Cited by 3 | Viewed by 1048
Abstract
Transparent materials with antifogging and self-cleaning ability are of extreme significance for utilization in outdoor solar cell devices to alleviate the performance loss and maintenance costs. Herein, with inspiration from the anti-wetting surfaces in nature, regular papillae-like microstructure arrays (PMAs) inspired by lotus [...] Read more.
Transparent materials with antifogging and self-cleaning ability are of extreme significance for utilization in outdoor solar cell devices to alleviate the performance loss and maintenance costs. Herein, with inspiration from the anti-wetting surfaces in nature, regular papillae-like microstructure arrays (PMAs) inspired by lotus leaves were designed via a common UV lithography combined with a soft replication. Subsequently, the biomimetic slippery polydimethylsiloxane (PDMS) film (BSPF) inspired by the pitcher plant was fabricated successfully by infusing with hydrophobic liquid lubricant. The resultant surface has hydrophobic surface chemistry, a slippery interface, PMAs structure. The wettability, optical characteristic, antifogging property and self-cleaning ability of the PMAs-based BSPF were characterized experimentally. The film displays excellent optical transmittance, antireflection, antifogging, and self-cleaning properties, which is superior to the flat PDMS film (FPF). Remarkably, an average reflection of ∼11.3% in the FPF was reduced to ∼8.9% of the BSPF. In addition, after gradient spray test for 120 s, the antifogging efficiency was close to 100% for the BSPF surface in comparison with the flat PDMS film (FPF), biomimetic PDMS film (BPF) and flat slippery PDMS film (FSPF) (35%, 70% and 85%). Furthermore, we also discovered that the BSPF surface exhibited a better self-cleaning performance toward a variety of liquids than solid dust. Full article
(This article belongs to the Section Functional Polymer Coatings and Films)
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Article
Long-Term Atmospheric Aging and Corrosion of Epoxy Primer-Coated Aluminum Alloy in Coastal Environments
Coatings 2021, 11(2), 237; https://doi.org/10.3390/coatings11020237 - 17 Feb 2021
Cited by 4 | Viewed by 1124
Abstract
Aircraft are subjected to extreme weather conditions in coastal areas. This study reports long-term atmospheric exposure tests carried out on an epoxy primer-coated aluminum alloy in a coastal environment for 7, 12, and 20 years. The micromorphology and characteristics of the section and [...] Read more.
Aircraft are subjected to extreme weather conditions in coastal areas. This study reports long-term atmospheric exposure tests carried out on an epoxy primer-coated aluminum alloy in a coastal environment for 7, 12, and 20 years. The micromorphology and characteristics of the section and surface, the products of corrosion, electrochemical impedance, and molecular structure of the coated specimens were examined through a spectrophotometer, scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), electrochemical impedance spectroscopy (EIS), and X-ray photoelectron spectrometer (XPS). The results showed that the angles of contact of the specimens with different numbers of years of atmospheric exposure satisfied the normal distribution. Their fractal dimensions increased with an increase in the duration of exposure. Intergranular corrosion and exfoliation corrosion appeared in the specimens after 20 years, where the product of corrosion was Al(OH)3. The impedances and thermal properties of the epoxy coatings were influenced by the synergistic effects of aging and post-curing. The impedances of the coatings decreased greatly after long-term atmospheric exposure. After 20 years of corrosion, the specimen showed the characteristics of the substrate being corroded. The mechanism of corrosion and the electrochemical equivalent circuit were also analyzed. Full article
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Article
Effect of Riveting Angle and Direction on Fatigue Performance of Riveted Lap Joints
Coatings 2021, 11(2), 236; https://doi.org/10.3390/coatings11020236 - 16 Feb 2021
Cited by 4 | Viewed by 661
Abstract
Riveting is the most commonly used connection method in aircraft assembly, and its quality has a crucial effect on the fatigue performance of aircraft. Many factors affect the riveting quality, among which the influence of the riveting angle and direction is not clear. [...] Read more.
Riveting is the most commonly used connection method in aircraft assembly, and its quality has a crucial effect on the fatigue performance of aircraft. Many factors affect the riveting quality, among which the influence of the riveting angle and direction is not clear. In this paper, a three-dimensional finite element model of single-rivet lap joints is established and verified by the driven head geometry and the riveting force data obtained from the riveting experiments. Then, by adjusting the angle and direction of the punch in the finite element model, the riveting process is simulated at the angles of 0°, 1°, 2°, and 3° and the directions of 0° and 180° to investigate the deformation of the lap joints, the stress distribution around the hole, and the stress distribution of the rivet. Finally, the fatigue tests of the single-rivet lap joints are performed and the influence of the riveting angle and direction on the connection quality and fatigue performance of the riveting joints is analyzed. Full article
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Article
Bacterial Adhesion on Glass–Ionomer Cements and Micro/Nano Hybrid Composite Dental Surfaces
Coatings 2021, 11(2), 235; https://doi.org/10.3390/coatings11020235 - 16 Feb 2021
Viewed by 1255
Abstract
Dental restorations need to reproduce the aspect of the natural teeth of the patient, and must be non-toxic, biocompatible, and have good mechanical properties so that they can last for longer. The aim of this study was to determine the extent of bacterial [...] Read more.
Dental restorations need to reproduce the aspect of the natural teeth of the patient, and must be non-toxic, biocompatible, and have good mechanical properties so that they can last for longer. The aim of this study was to determine the extent of bacterial adhesion of Streptococcus mutans on four different dental material surfaces, i.e., two glass–ionomer cements (Fuji conventional and Fuji hybrid) and two ceramic composites (Micro hybrid composite and Nano hybrid composite). To understand the bacterial adhesion on these four different dental materials, various surface properties were measured: roughness, contact angle, CIE color parameters and zeta potential. We found that the greatest adhesion extent was obtained for the Nano hybrid composite surface. The pronounced adhesion is the interplay between the relatively high roughness and hydrophilicity of the Nano hybrid composite surface. Color changes upon immersing ceramic composites in red wine and black tea proved that both beverages adhered to them. Black tea adhered more intensively than wine, and showed a higher inhibitory effect on the growth of Streptococcus mutans and Staphylococcus aureus. Full article
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Article
Effects of Cr2O3 Content on Microstructure and Mechanical Properties of Al2O3 Matrix Composites
Coatings 2021, 11(2), 234; https://doi.org/10.3390/coatings11020234 - 16 Feb 2021
Cited by 37 | Viewed by 2101
Abstract
Al2O3-Cr2O3 refractories are completely substitution solid solutions and can effectively resist slag erosion when used as an industrial furnace lining. In order to provide suitable chromium corundum refractory with excellent slag resistance and mechanical properties for [...] Read more.
Al2O3-Cr2O3 refractories are completely substitution solid solutions and can effectively resist slag erosion when used as an industrial furnace lining. In order to provide suitable chromium corundum refractory with excellent slag resistance and mechanical properties for smelting reduction ironmaking, Al2O3-Cr2O3 samples with different mass percentages (0, 10, 20, 30, 40 wt.%) of Cr2O3 were prepared by a normal pressure sintering process to study its sintering properties, mechanical properties, thermal shock resistance, and microstructure. The results of densification behavior showed that the introduction of Cr2O3 deteriorates the compactness, the relative density and volume shrinkage rate of the composite material decrease with the increase of the Cr2O3 content, and the apparent porosity increases accordingly. In terms of mechanical properties, the hardness, compressive strength, and flexural strength of Al2O3-Cr2O3 material decrease gradually with the increase of Cr2O3. After 10 and 20 thermal shock cycles, the flexural strengths of the samples all decreased. With the increase of Cr2O3 in these samples, the loss rate of flexural strength gradually increased. Considering the slag resistance and mechanical properties of the composite material, the Al2O3-Cr2O3 composite refractory with Cr2O3 content of 20–30% can meet the requirements of smelting reduction iron making kiln lining. Full article
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Article
Tailoring Crystalline Structure of Titanium Oxide Films for Optical Applications Using Non-Biased Filtered Cathodic Vacuum Arc Deposition at Room Temperature
Coatings 2021, 11(2), 233; https://doi.org/10.3390/coatings11020233 - 15 Feb 2021
Cited by 2 | Viewed by 974
Abstract
Titanium oxide films were deposited at room temperature and with no applied bias using a filtered cathodic vacuum arc (FCVA) system in a reactive oxygen environment. The dependence of film growth on two process parameters, the working pressure (Pw) and the [...] Read more.
Titanium oxide films were deposited at room temperature and with no applied bias using a filtered cathodic vacuum arc (FCVA) system in a reactive oxygen environment. The dependence of film growth on two process parameters, the working pressure (Pw) and the O2 partial pressure (pO2), is described in detail. The composition, morphological features, crystalline structure, and optical properties of the deposited films were systematically studied by Rutherford Back Scattering (RBS), Scanning Electron Microscopy (SEM), X-Ray diffraction (XRD), Raman Spectroscopy, UV-vis spectroscopy, and spectroscopic ellipsometry. This systematic investigation allowed the identification of three different groups or growth regimes according to the stoichiometry and the phase structure of the titanium oxide films. RBS analysis revealed that a wide range of TiOx stoichiometries (0.6 < × < 2.2) were obtained, including oxygen-deficient, stoichiometric TiO2 and oxygen-rich films. TiO, Ti2O3, rutile-type TiO2, and amorphous TiO2 phase structures could be achieved, as confirmed both by Raman and XRD. Therefore, the results showed a highly versatile approach, in which different titanium oxide stoichiometries and crystalline phases especially suited for diverse optical applications can be obtained by changing only two process parameters, in a process at room temperature and without applied bias. Of particular interest are crystalline rutile films with high density to be used in ultra-high reflectance metal-dielectric multilayered mirrors, and reduced-TiO2 rutile samples with absorption in the visible range as a very promising photocatalyst material. Full article
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Review
The Role of Carbon Quantum Dots in Organic Photovoltaics: A Short Overview
Coatings 2021, 11(2), 232; https://doi.org/10.3390/coatings11020232 - 15 Feb 2021
Cited by 13 | Viewed by 1496
Abstract
Carbon quantum dots (CDs) are a new class of fluorescent carbonaceous nanomaterials that were casually discovered in 2004. Since then, they have become object of great interest in the scientific community because of their peculiar optical properties (e.g., size-dependent and excitation wavelength-dependent fluorescence), [...] Read more.
Carbon quantum dots (CDs) are a new class of fluorescent carbonaceous nanomaterials that were casually discovered in 2004. Since then, they have become object of great interest in the scientific community because of their peculiar optical properties (e.g., size-dependent and excitation wavelength-dependent fluorescence), which make them very similar to the well-known semiconductor quantum dots and suitable for application in photovoltaic devices (PVs). In fact, with appropriate structural engineering, it is possible to modulate CDs photoluminescence properties, band gap, and energy levels in order to realize the band matching suitable to enable the desired directional flow of charge carriers within the PV device architecture in which they are implanted. Considering the latest developments, in the present short review, the employment of CDs in organic photovoltaic devices (OPVs) will be summarized, in order to study the role played by these nanomaterials in the improvement of the performances of the devices. After a first brief summary of the strategies of structural engineering of CDs and the effects on their optical properties, the attention will be devoted to the recent highlights of CDs application in organic solar cells (OSCs) and in dye sensitized solar cells (DSSCs), in order to guide the users towards the full exploitation of the use of these nanomaterials in such OPV devices. Full article
(This article belongs to the Special Issue Advanced Thin Films for Opto-Electronic and Photovoltaic Applications)
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Article
Effects of Variable Transport Properties on Heat and Mass Transfer in MHD Bioconvective Nanofluid Rheology with Gyrotactic Microorganisms: Numerical Approach
Coatings 2021, 11(2), 231; https://doi.org/10.3390/coatings11020231 - 15 Feb 2021
Cited by 29 | Viewed by 1175
Abstract
Rheology of MHD bioconvective nanofluid containing motile microorganisms is inspected numerically in order to analyze heat and mass transfer characteristics. Bioconvection is implemented by combined effects of magnetic field and buoyancy force. Gyrotactic microorganisms enhance the heat and transfer as well as perk [...] Read more.
Rheology of MHD bioconvective nanofluid containing motile microorganisms is inspected numerically in order to analyze heat and mass transfer characteristics. Bioconvection is implemented by combined effects of magnetic field and buoyancy force. Gyrotactic microorganisms enhance the heat and transfer as well as perk up the nanomaterials’ stability. Variable transport properties along with assisting and opposing flow situations are taken into account. The significant influences of thermophoresis and Brownian motion have also been taken by employing Buongiorno’s model of nanofluid. Lie group analysis approach is utilized in order to compute the absolute invariants for the system of differential equations, which are solved numerically using Adams-Bashforth technique. Validity of results is confirmed by performing error analysis. Graphical and numerical illustrations are prepared in order to get the physical insight of the considered analysis. It is observed that for controlling parameters corresponding to variable transport properties c2, c4, c6, and c8, the velocity, temperature, concentration, and bioconvection density distributions accelerates, respectively. While heat and mass transfer rates increases for convection parameter and bioconvection Rayleigh number, respectively. Full article
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