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Coatings, Volume 12, Issue 3 (March 2022) – 129 articles

Cover Story (view full-size image): The electroplating industry market has a turnover of tens of billions of US dollars. The applications of metal coatings span a range of applications, from the automotive and aerospace industries to electronics and jewellery. Unfortunately, this industrial sector is infamous for the use of numerous substances harmful to both human health and the environment. A hot topic of research concerns the development of new formulations able to be deposited in addition to more sustainable metals and alloys, reducing the toxic compounds present in solutions. One of the biggest challenges is to remove cyanides, which are used as complexing agents in numerous electroplating baths. However, simple removal is not a trivial task: valid substitutes must be found to maintain the functional and aesthetic characteristics for which the metal deposit was designed. View this paper
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Article
Research on Fault Feature Extraction Method Based on Parameter Optimized Variational Mode Decomposition and Robust Independent Component Analysis
Coatings 2022, 12(3), 419; https://doi.org/10.3390/coatings12030419 - 21 Mar 2022
Cited by 4 | Viewed by 826
Abstract
The variational mode decomposition mode (VMD) has a reliable mathematical derivation and can decompose signals adaptively. At present, it has been widely used in mechanical fault diagnosis, financial analysis and prediction, geological signal analysis, and other fields. However, VMD has the problems of [...] Read more.
The variational mode decomposition mode (VMD) has a reliable mathematical derivation and can decompose signals adaptively. At present, it has been widely used in mechanical fault diagnosis, financial analysis and prediction, geological signal analysis, and other fields. However, VMD has the problems of insufficient decomposition and modal aliasing due to the unclear selection method of modal component k and penalty factor α. Therefore, it is difficult to ensure the accuracy of fault feature extraction and fault diagnosis. To effectively extract fault feature information from bearing vibration signals, a fault feature extraction method based on VMD optimized with information entropy, and robust independent component analysis (RobustICA) was proposed. Firstly, the modal component k and penalty factor α in VMD were optimized by the principle of minimum information entropy to improve the effect of signal decomposition. Secondly, the optimal parameters weresubstituted into VMD, and several intrinsic mode functions (IMFs) wereobtained by signal decomposition. Secondly, the kurtosis and cross-correlation coefficient criteria were comprehensively used to evaluate the advantages and disadvantages of each IMF.And then, the optimal IMFs were selected to construct the observation signal channel to realize the signal-to-noise separation based on RobustICA. Finally, the envelope demodulation analysis of the denoised signal was carried out to extract the fault characteristic frequency. Through the analysis of bearing simulation signal and actual data, it shows that this method can extract the weak characteristics of rolling bearing fault signal and realize the accurate identification of fault. Meanwhile, in the bearing simulation signal experiment, the results of kurtosis value, cross-correlation coefficient, root mean square error, and mean absolute error are 6.162, 0.681, 0.740, and 0.583, respectively. Compared with other traditional methods, better index evaluation value is obtained. Full article
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Article
Experimental Study on the Scouring Rate of Cohesive Soil in the Lower Yellow River
Coatings 2022, 12(3), 418; https://doi.org/10.3390/coatings12030418 - 21 Mar 2022
Viewed by 607
Abstract
The different soil anti scourability in the lower reaches of the Yellow River leads to different scouring and retreating speeds, which has a great influence on river regime evolution. Through the incipient motion scouring test of cemented cohesive soil in the lower reaches [...] Read more.
The different soil anti scourability in the lower reaches of the Yellow River leads to different scouring and retreating speeds, which has a great influence on river regime evolution. Through the incipient motion scouring test of cemented cohesive soil in the lower reaches of the Yellow River, the physical phenomena of the incipient motion of cohesive soil were expounded, the scouring rate of cohesive soil was calculated, and the relationship between the scouring rate and its influencing factors was established. The results show that when the moisture content of cohesive soil is 43%~61%, the scouring rate is about 0.001~0.03 kg/(m2·s). The scouring rate of cohesive soil with the same particle size varies with the flow shear stress under different deposition duration conditions. Under the same flow rate, the scouring rate of cohesive soil increases with the increase of water content, showing an exponential relationship of increment. Under the same shear stress condition, the scouring rate decreases with the increase of dry density, while the exponential relationship between dry density and scouring rate is not clear when the shear stress is small. With the increase of shear stress, there is an obvious exponential relationship between dry density and scouring rate. Finally, the relationship between the scouring rate and relative residual shear stress was established, and the scouring rate formula suitable for cohesive extremely fine sediment was fitted. The formula can better estimate the scouring rate of the riverbank composed of very fine cohesive sediment and provide support for predicting the scouring and retreating rate of riverbanks in natural rivers. Full article
(This article belongs to the Section Selected Papers from International Conferences and Workshops)
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Article
Natural Dyes Used as Organic Coatings UV Protecting for Food Packages
Coatings 2022, 12(3), 417; https://doi.org/10.3390/coatings12030417 - 21 Mar 2022
Viewed by 823
Abstract
Nowadays, the use of biodegradable and bio-derived plastics such as poly(lactic acid) (PLA) and cellulose in food packaging applications are replacing the use of different and more conventional oil-derived polymers that are much more expensive and unsuitable for the environment. However, their high [...] Read more.
Nowadays, the use of biodegradable and bio-derived plastics such as poly(lactic acid) (PLA) and cellulose in food packaging applications are replacing the use of different and more conventional oil-derived polymers that are much more expensive and unsuitable for the environment. However, their high transparency to ultraviolet (UV) radiation limits their current commercialization. Therefore, this study focuses on the deposition of organic thin films on commercial PLA and cellulose in order to enhance their performance, in particular for UV shielding. Coatings with different natural and biocompatible (edible) molecules, quinine and p-Coumaric acid, dispersed in different matrices are deposited by comparing different deposition techniques such as spray coating and spin coating. Morphological characterizations are carried out with atomic force microscopy (AFM) and scanning electron microscopy (SEM), with spectroscopic characterizations performed by light transmission measurements. Our results show that it is possible to enhance the UV protection of packaging using a suitable deposition with these biocompatible materials. Full article
(This article belongs to the Special Issue Multifunctional Coating for Packaging Applications)
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Article
Fabrication and Performance Analysis of 3D Inkjet Flexible Printed Touch Sensor Based on AgNP Electrode for Infotainment Display
Coatings 2022, 12(3), 416; https://doi.org/10.3390/coatings12030416 - 21 Mar 2022
Cited by 1 | Viewed by 688
Abstract
It is possible to employ printed capacitive sensors in car bezel applications because of its lower cost and higher detecting capabilities. In this paper, a flexible sensor for automotive entertainment applications has been developed using an electrode flexible sensor with an interdigitated pattern [...] Read more.
It is possible to employ printed capacitive sensors in car bezel applications because of its lower cost and higher detecting capabilities. In this paper, a flexible sensor for automotive entertainment applications has been developed using an electrode flexible sensor with an interdigitated pattern printed on it using screen printing and 3D printing fabrication processes. Design concerns such as electrode overlap, electrode gap and width on capacitance changes, and production costs were studied. In addition, a new generation of flexible printed sensors has been developed that can outperform conventional human–machine interface (HMI) sensors. The capacitance of the design pattern may be optimized by using a 15mm overlap and 0.5mm electrode line width. Due to the precision of interpolation, overlap has a larger effect on sensor performance than it would have without it. Full article
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Communication
Partitional Behavior of Janus Dumbbell Microparticles in a Polyethylene Glycol (PEG)-Dextran (DEX) Aqueous Two-Phase System (ATPS)
Coatings 2022, 12(3), 415; https://doi.org/10.3390/coatings12030415 - 21 Mar 2022
Viewed by 584
Abstract
Janus particles are known to be useful to various fields such as biomolecule-probing sensors, reaction catalysts, surfactants, and so on. They have two chemically different surfaces which possess contradictory characteristics such as polarity, hydrophobicity, etc. Here, a simple fabrication of dumbbell-shaped Janus microparticles [...] Read more.
Janus particles are known to be useful to various fields such as biomolecule-probing sensors, reaction catalysts, surfactants, and so on. They have two chemically different surfaces which possess contradictory characteristics such as polarity, hydrophobicity, etc. Here, a simple fabrication of dumbbell-shaped Janus microparticles was tested by the chemical reaction of carboxyl groups and amino groups to form amide bonds. They were distributed to the interface between polyethylene glycol (PEG)-rich phase and dextran (DEX)-rich phase, while the unreacted particles having carboxyl groups located at the top PEG-rich phase and particles having amine ligands went to the bottom DEX-rich phase of an aqueous two-phase system (ATPS). The fabrication procedures, observations, and possible applications of results are discussed. Full article
(This article belongs to the Special Issue Surface Chemical Modification II)
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Article
Surface Modification of Titanium by Femtosecond Laser in Reducing Bacterial Colonization
Coatings 2022, 12(3), 414; https://doi.org/10.3390/coatings12030414 - 20 Mar 2022
Cited by 2 | Viewed by 935
Abstract
In the past few decades, titanium and its alloys have been widely used in the orthopaedic field. However, because titanium is bioinert and lacks antibacterial properties, infection may happen when bacteria attach to implant surfaces and form biofilms. It has been studied that [...] Read more.
In the past few decades, titanium and its alloys have been widely used in the orthopaedic field. However, because titanium is bioinert and lacks antibacterial properties, infection may happen when bacteria attach to implant surfaces and form biofilms. It has been studied that some naturally existing micron-scale topographies can reduce bacterial attachment such as cicada wings and gecko skins. The aim of this in vitro study was to find an implant with good biocompatibility and antimicrobial properties by the modification of micron-scale topographies. In this paper, a femtosecond laser was used to provide microtopography coatings on Ti substrates. The surface morphology of Ti substrates was observed by scanning electron microscopy (SEM). XPS was used to fulfil the chemical compositional analysis. The surface wettability was measured by contact angle measurement system. The effect of microtopography coatings with different surface microstructures on bacterial activities and bone marrow mesenchymal stem cells (BMSC) functions was investigated. The results of in vitro study revealed that microtopography coatings restrain the adhesion of Staphylococcus aureus (S. aureus) and Staphylococcus epidermidis (S. epidermidis), which are common pathogens of orthopaedic implant infections. In addition, microtopography coatings stimulated BMSC adhesion and proliferation. Our studies suggest that a microtopography-coated sample modified by femtosecond laser showed promising antibacterial properties and favourable biocompatibility. The femtosecond laser technique provides an accurate and valid way to produce microtopography coatings with outstanding biocompatibility and antimicrobial properties, and could be widely used to modify the surface of orthopaedic metal implants with great potential. Full article
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Article
Optimization of Parameters for Protection of Materials by Primer Application
Coatings 2022, 12(3), 413; https://doi.org/10.3390/coatings12030413 - 20 Mar 2022
Viewed by 512
Abstract
The protective properties of coating systems usually depend on their base layer, since its characteristics and chemical composition are greatly responsible for prevention of corrosion development. Moreover, a good primer as a base coating has to provide good adhesion between the coating system [...] Read more.
The protective properties of coating systems usually depend on their base layer, since its characteristics and chemical composition are greatly responsible for prevention of corrosion development. Moreover, a good primer as a base coating has to provide good adhesion between the coating system and the substrate material, as well as good cohesion, i.e., coating strength. The described experiment aimed to determine the influence of input parameters (anticorrosive pigment content, conditioning time, dry film thickness) on the adhesion properties of the coating. The optimization of input parameters was achieved by the pull-off test in order to determine their maximum values. For the purpose of imitating aggressive atmosphere of service conditions, the experiment was run in a salt spray chamber, in which samples were cyclically sprayed with 5% sodium chloride (NaCl) solution for 120 h. The obtained mathematical model makes it possible to define the optimal values of the input variables for the defined values of the required property, i.e., the adhesion properties of the applied primer for certain exploitative conditions. Full article
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Article
Microstructure and Wear Properties of IN718/WC Composite Coating Fabricated by Ultrasonic Vibration-Assisted Laser Cladding
Coatings 2022, 12(3), 412; https://doi.org/10.3390/coatings12030412 - 20 Mar 2022
Viewed by 816
Abstract
Laser cladding coating with wolfram carbide (WC) as enhanced particles can improve the performance of nickel-based materials. However, there still exists several problems, such as serious element segregation and unequal distribution of the reinforcement phase. In order to improve the mechanical properties further, [...] Read more.
Laser cladding coating with wolfram carbide (WC) as enhanced particles can improve the performance of nickel-based materials. However, there still exists several problems, such as serious element segregation and unequal distribution of the reinforcement phase. In order to improve the mechanical properties further, IN718/WC coatings were prepared by ultrasonic vibration-assisted laser cladding. The effects of ultrasonic vibration on the ceramic distribution, microstructure, and wear performance were systematically studied. The results show that ultrasonic vibration can promote the uniform distribution of WC particles without changing the phase composition of the coating. The cavitation and acoustic flow induced by ultrasonic vibration interrupt the growth of columnar dendrites and refine the grains. In addition, the microhardness of the ultrasonic vibration-assisted coating is enhanced by 15.6% to 475 HV0.2. The average coefficient of friction (COF) of the ultrasonic vibration-assisted coating is 0.452, which is 17.5% lower than that of the unassisted coating. The wear volume of the coating is decreased significantly, and the wear characteristics change from severe adhesive wear to the slight coexistence of abrasive wear and adhesive wear. Full article
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Article
Friction and Wear Properties of Silicon Nitride-Based Composites with Different hBN Content Sliding against Polyether-Etherketone at Different Speeds under Artificial Seawater Lubrication
Coatings 2022, 12(3), 411; https://doi.org/10.3390/coatings12030411 - 19 Mar 2022
Viewed by 713
Abstract
In the present study, the friction and wear behaviors of Si3N4-hBN(Hexagonal boron nitride) ceramic composites against polyether-etherketone in artificial seawater were investigated, and the sliding speed was varied from 0.52 to 1.73 m/s to study the effect. It was [...] Read more.
In the present study, the friction and wear behaviors of Si3N4-hBN(Hexagonal boron nitride) ceramic composites against polyether-etherketone in artificial seawater were investigated, and the sliding speed was varied from 0.52 to 1.73 m/s to study the effect. It was found that the friction coefficients and wear rates decreased with the increase in sliding speed for Si3N4-hBN (with the hBN content ranging from 5% to 20%) against PEEK(Polyether-ether-ketone); the sliding pairs represented an upward trend as the speed increased for Si3N4-hBN (with an hBN content of 0 and 30%) against PEEK. This result was mainly attributed to complex friction resistance sources, such as mechanical meshing and the shear strength of soft tribofilm. On the other hand, both the hBN content and sliding speed had a significant effect on the tribological performance of the Si3N4-hBN/PEEK pairs. Meanwhile, the lowest friction coefficient of 0.07 and wear rates below 10−6 mm3/Nm were obtained from the Si3N4-20%hBN/PEEK pair at the speed of 1.73 m/s. Full article
(This article belongs to the Special Issue Trends and Advances in Anti-wear Materials)
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Article
Analytical Investigation of Jiatang Scroll Paintings in the Seventh Year of the Guangxu Era
Coatings 2022, 12(3), 410; https://doi.org/10.3390/coatings12030410 - 19 Mar 2022
Cited by 1 | Viewed by 618
Abstract
Jiatang scroll paintings listed in the Chinese intangible cultural heritage list are an important form of family trees. In this paper, a Jiatang scroll painting drawn in the seventh year of Guangxu (AD 1881) was chosen as a prototype to analyze its components. [...] Read more.
Jiatang scroll paintings listed in the Chinese intangible cultural heritage list are an important form of family trees. In this paper, a Jiatang scroll painting drawn in the seventh year of Guangxu (AD 1881) was chosen as a prototype to analyze its components. Samples were taken from different parts of the Jiatang scroll painting to analyze the composition of fibers, pigments, and adhesives. Herein, fiber analyzer, Fourier transform infrared spectroscopy (FTIR), and Herzberg stain were conducted to identify the type of fiber used. Microstructural and microchemical analyses by means of SEM-EDX and Raman spectroscopy were performed to characterize the pigments present in the painting, while the nature of the adhesive was examined using pyrolysis gas chromatography–mass spectrometry (Py-GC/MS). The results show that the painting fiber is from cotton, while the red, black, and green pigments were identified as cinnabar, carbon black, and emerald green, respectively. Finally, the adhesive is a mixture of animal glue, benzoin gum, and starch. The research results provide a basis for the protection and restoration of this precious cultural heritage in the future. Full article
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Article
Electrochemical Behavior of Cu-MWCNT Nanocomposites Manufactured by Powder Technology
Coatings 2022, 12(3), 409; https://doi.org/10.3390/coatings12030409 - 19 Mar 2022
Cited by 1 | Viewed by 692
Abstract
This paper presents an experimental investigation of the fabrication of Cu–multi-walled carbon nanotube (MWCNT) nanocomposites prepared via the electroless chemical deposition technique followed by the powder metallurgy (PM) method. To enhance the dispersion and wettability of MWCNTs with a Cu matrix, MWCNTs were [...] Read more.
This paper presents an experimental investigation of the fabrication of Cu–multi-walled carbon nanotube (MWCNT) nanocomposites prepared via the electroless chemical deposition technique followed by the powder metallurgy (PM) method. To enhance the dispersion and wettability of MWCNTs with a Cu matrix, MWCNTs were given an electroless coating of Ag nanoparticles. MWCNTs with 0.4, 0.8, and 1.2 wt.% were first coated with 5 wt.% Ag nanoparticles, then mechanically milled with Cu nanoparticles using a 10:1 ball-to-powder ratio for 60 min at 300 rpm. The mixed samples (35 g) were subjected to a compression pressure of 700 MPa and sintered at 950 °C in a hydrogen-inert gas furnace. Mapping and microstructure analyses were conducted to analyze the constituents’ homogeneity. In addition, the electrochemical properties and corrosion resistance of specimens were investigated. The results revealed that the relative density decreased by raising the MWCNTs’ content. Electrical resistivity increased gradually with the addition of MWCNTs coated by Ag nanoparticles, and the thermal conductivity decreased. It was also revealed that the smallest corrosion rate could be obtained for the sample with 1.2 wt.% MWCNTs, which is the appropriate rate for the electrochemical deposition. Full article
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Article
Analysis of Color Fastness and Shrinkage of Dyed and Printed Linen/Silk Fabrics
Coatings 2022, 12(3), 408; https://doi.org/10.3390/coatings12030408 - 19 Mar 2022
Viewed by 605
Abstract
In this study, we analyzed the impact of the dyeing and the digital printing processes of linen/silk fabric (70% linen/30% silk) on its color fastness and shrinkage in the directions of warp and weft. This is a highly relevant topic because a single [...] Read more.
In this study, we analyzed the impact of the dyeing and the digital printing processes of linen/silk fabric (70% linen/30% silk) on its color fastness and shrinkage in the directions of warp and weft. This is a highly relevant topic because a single fabric combines two natural fibers of different origins—silk, a protein, is animal-based, whereas linen is derived from cellulose and is, thus, plant-based. Therefore, the different natures of the two fibers determine distinctive chemical properties. As a result, selecting the optimal technological course of processing for blended yarn fabrics and their yarn is a challenging task. The quality of the conducted finishing is determined by the physical properties of fabrics, such as color fastness to perspiration; soap; dry friction and wet friction; the pH of the fabric after finishing; and the shrinkage of the fabric in the directions of warp and weft. Here, color fastness was assigned the top grade with respect to all potentially harmful factors, except for wet friction. The evaluation proves that the technological regimes employed for digital printing and dyeing in the production item’s fabrics were properly selected. Full article
(This article belongs to the Special Issue Surface Treatment for Fabrics and Textiles)
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Article
A Simple Scheme for Extraction of Asphaltenes from Asphalt at Room Temperature
Coatings 2022, 12(3), 407; https://doi.org/10.3390/coatings12030407 - 19 Mar 2022
Viewed by 542
Abstract
This paper proposes a simple scheme to separate asphaltenes from asphalt at room temperature without heating or refluxing. The proposed scheme can solve the problems of high energy cost, expensive devices, and safety risks of flammable steam in standard methods of asphaltene extraction. [...] Read more.
This paper proposes a simple scheme to separate asphaltenes from asphalt at room temperature without heating or refluxing. The proposed scheme can solve the problems of high energy cost, expensive devices, and safety risks of flammable steam in standard methods of asphaltene extraction. First, the asphalt is dissolved in a good solvent to obtain a solution containing asphaltenes, and the inorganic impurity as well as residual carbons are removed by filtration. Then, the solution containing asphaltenes is dropped into poor solvent to let asphaltenes flocculate into suspended solids. Finally, the suspension is filtered, and the filter cake is dried to obtain asphaltene solid. The CHNS elements and 1H-Nuclear magnetic resonance were characterized for the obtained product. Compared with asphalt, the C/H element ratios and the aromatic carbon ratios of the product were higher, which matched the elemental and structural characteristics of asphaltenes. The asphaltene yields obtained from different solvents were compared, and the reasons for the yield differences were analyzed. Recovered solvent could be used to extract asphaltenes, and the yield was found to decrease with the extraction times. Full article
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Article
The Corrosion Behaviors of an As-Rolled Mg-8Li (in wt.%) Alloy in Two Differently Concentrated NaCl Solutions
Coatings 2022, 12(3), 406; https://doi.org/10.3390/coatings12030406 - 18 Mar 2022
Cited by 3 | Viewed by 599
Abstract
By means of an electrochemical workstation, hydrogen evolution device, optical microscope (OM) and scanning electron microscope (SEM), the corrosion behaviors of an as-rolled Mg-8%Li alloy with a dual phase structure in 0.9 wt.% NaCl and 3.5 wt.% NaCl solutions have been investigated and [...] Read more.
By means of an electrochemical workstation, hydrogen evolution device, optical microscope (OM) and scanning electron microscope (SEM), the corrosion behaviors of an as-rolled Mg-8%Li alloy with a dual phase structure in 0.9 wt.% NaCl and 3.5 wt.% NaCl solutions have been investigated and compared. The results show that when the immersion time exceeds 8 h, the hydrogen evolution rate of the alloy in the 0.9 wt.% NaCl is 3 times higher than that in the 3.5 wt.% NaCl solution. Moreover, the corrosion behaviors of the alloy are obviously different in the two differently concentrated NaCl solutions. In the 3.5 wt.% NaCl solution, the localized corrosion is much more severe and can occur simultaneously in the interior of both the α-Mg and β-Li matrix phases. However, the localized corrosion in the 0.9 wt.% NaCl solution is obviously weak and mainly occurs at the α-Mg phase. Full article
(This article belongs to the Special Issue Corrosion and Degradation of Materials)
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Article
Comparison of Various Thin-Film-Based Absorber Materials: A Viable Approach for Next-Generation Solar Cells
Coatings 2022, 12(3), 405; https://doi.org/10.3390/coatings12030405 - 18 Mar 2022
Cited by 2 | Viewed by 830
Abstract
Thin-film solar cells are simple and affordable to produce, but their efficiency is low compared to crystalline-silicon solar cells, and needs to be improved. This study investigates the photovoltaic performance of different absorber materials (CdTe, CIGS, Sb2Se3, and CZTS) with [...] Read more.
Thin-film solar cells are simple and affordable to produce, but their efficiency is low compared to crystalline-silicon solar cells, and needs to be improved. This study investigates the photovoltaic performance of different absorber materials (CdTe, CIGS, Sb2Se3, and CZTS) with simple structure Au/absorber/CdS/ITO. The research uses the SCAPS (Solar Cell Capacitance Simulator), a mathematical model based on Poisson and continuity equations. The impact of various parameters on cell performance, such as absorber layer thickness, acceptor density, electron affinity, back contact work function, and temperature, are examined. As per the simulation results, an absorber thickness of 4 µm is suitable for achieving the maximum efficiency for all the absorber materials. The optimized acceptor density for CdTe/CIGS/ Sb2Se3 and CZTS is taken as 1016 cm−3 and 1017 cm−3, respectively. The back contact work function and device temperature were set to be 5.1 eV and 300 K, respectively, to achieve excellent performance. Among all the absorber materials, the highest efficiency of 28.2% was achieved for CZTS. The aim is to highlight the various absorber layers’ performances by optimizing the device parameters. The obtained results can be used in solar energy harvesting applications due to the improved performance characteristics. Full article
(This article belongs to the Special Issue Nanomaterials and Thin Films for Energy Applications)
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Article
Influence to Hardness of Alternating Sequence of Atomic Layer Deposited Harder Alumina and Softer Tantala Nanolaminates
Coatings 2022, 12(3), 404; https://doi.org/10.3390/coatings12030404 - 18 Mar 2022
Cited by 1 | Viewed by 631
Abstract
Atomic layer deposited amorphous 70 nm thick Al2O3-Ta2O5 double- and triple-layered films were investigated with the nanoindentation method. The sequence of the oxides from surface to substrate along with the layer thickness had an influence on [...] Read more.
Atomic layer deposited amorphous 70 nm thick Al2O3-Ta2O5 double- and triple-layered films were investigated with the nanoindentation method. The sequence of the oxides from surface to substrate along with the layer thickness had an influence on the hardness causing rises and declines in hardness along the depth yet did not affect the elastic modulus. Hardness varied from 8 to 11 GPa for the laminates having higher dependence on the structure near the surface than at higher depths. Triple-layered Al2O3/Ta2O5/Al2O3 laminate possessed the most even rise of hardness along the depth and possessed the highest hardness out of the laminates (11 GPa at 40 nm). Elastic modulus had steady values along the depth of the films between 145 and 155 GPa. Full article
(This article belongs to the Special Issue Mechanical Properties of Advanced Multifunctional Coatings)
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Article
Molecular Dynamics Study of the Diffusion between Virgin and Aged Asphalt Binder
Coatings 2022, 12(3), 403; https://doi.org/10.3390/coatings12030403 - 18 Mar 2022
Cited by 4 | Viewed by 692
Abstract
The diffusion between the virgin and aged asphalt binder in the recycled asphalt mixture is a crucial factor affecting its macro-mechanical performance. In this study, a combined model of the virgin-aged layered asphalt structure was assembled based on the molecular dynamics (MD) method. [...] Read more.
The diffusion between the virgin and aged asphalt binder in the recycled asphalt mixture is a crucial factor affecting its macro-mechanical performance. In this study, a combined model of the virgin-aged layered asphalt structure was assembled based on the molecular dynamics (MD) method. A four-component and twelve-category molecule were used to model the asphalt. The diffusion behaviors of the virgin and aged asphalt were characterized by mean square displacement (MSD), diffusion coefficient, relative concentration and cohesive energy density (CED). Results indicated that at the same temperature, the diffusion coefficient of the virgin asphalt was the largest, followed by the virgin-aged asphalt and the aged asphalt. As the temperature increased, the relative concentration on both sides of the virgin-aged asphalt overlapped to a certain extent. The covered lengths of the virgin asphalt were larger than those of the aged asphalt, indicating the diffusion between the virgin asphalt and aged asphalt was mainly manifested as the diffusion from the virgin asphalt to the aged asphalt. The development of CED and the fraction of free volume (FFV) indicated the mutual attractive interactions among the molecules in virgin and aged asphalt layers became strong and the cohesion properties inside the model became better. Full article
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Article
Acoustic Emission Monitoring of High-Entropy Oxyfluoride Rock-Salt Cathodes during Battery Operation
Coatings 2022, 12(3), 402; https://doi.org/10.3390/coatings12030402 - 18 Mar 2022
Cited by 2 | Viewed by 995
Abstract
High-entropy materials with tailorable properties are receiving increasing interest for energy applications. Among them, (disordered) rock-salt oxyfluorides hold promise as next-generation cathodes for use in secondary batteries. Here, we study the degradation behavior of a high-entropy oxyfluoride cathode material in lithium cells in [...] Read more.
High-entropy materials with tailorable properties are receiving increasing interest for energy applications. Among them, (disordered) rock-salt oxyfluorides hold promise as next-generation cathodes for use in secondary batteries. Here, we study the degradation behavior of a high-entropy oxyfluoride cathode material in lithium cells in situ via acoustic emission (AE) monitoring. The AE signals allow acoustic events to be correlated with different processes occurring during battery operation. The initial cycle proved to be the most acoustically active due to significant chemo-mechanical degradation and gas evolution, depending on the voltage window. Irrespective of the cutoff voltage on charge, the formation and propagation of cracks in the electrode was found to be the primary source of acoustic activity. Taken together, the findings help advance our understanding of the conditions that affect the cycling performance and provide a foundation for future investigations on the topic. Full article
(This article belongs to the Special Issue 10th Anniversary of Coatings: Invited Papers for Thin Films Section)
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Article
Duplex Surface Modification of 304-L SS Substrates by an Electron-Beam Treatment and Subsequent Deposition of Diamond-like Carbon Coatings
Coatings 2022, 12(3), 401; https://doi.org/10.3390/coatings12030401 - 18 Mar 2022
Viewed by 810
Abstract
In this study, we present the results of the effect of duplex surface modification of 304-L stainless steel substrates by an electron-beam treatment (EBT) and subsequent deposition of diamond-like carbon coatings on the surface roughness and corrosion behavior. During the EBT process, the [...] Read more.
In this study, we present the results of the effect of duplex surface modification of 304-L stainless steel substrates by an electron-beam treatment (EBT) and subsequent deposition of diamond-like carbon coatings on the surface roughness and corrosion behavior. During the EBT process, the beam power was varied from 1000 to 1500 W. The successful deposition of the DLC coatings was confirmed by FTIR and Raman spectroscopy experiments. The results showed a presence of C–O, C=N, graphite-like sp2, and mixed sp2-sp3 C–C bond vibrations. The surface topography was studied by atomic force microscopy. The rise in the beam power leads to a decrease in the surface roughness of the deposited DLC coatings. The studies on the corrosion resistance of the samples have been performed using three electrochemical techniques: open circuit potential (OCP), cyclic voltammetry (polarization measurements), and non-destructive electrochemical impedance spectroscopy (EIS). The measured corrosion potentials suggest that these samples are corrosion-resistant even in a medium, containing corrosive agents such as chloride ions. It can be concluded that the most corrosion-resistant specimen is DLC coating deposited on electron-beam-treated 304-L SS substrate by a beam power of 1500 W. Full article
(This article belongs to the Special Issue Advanced Coatings for Biomedical Applications)
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Article
Interlaminar Shear Characteristics, Energy Consumption, and Carbon Emissions of Polyurethane Mixtures
Coatings 2022, 12(3), 400; https://doi.org/10.3390/coatings12030400 - 17 Mar 2022
Cited by 2 | Viewed by 677
Abstract
The interlaminar shear characteristics of a polyurethane (PU) mixture composite structure, quantitatively calculating its energy consumption and carbon emissions were analyzed in this study. Inclined shear tests were carried out on thirteen structures without interlaminar treatment, and high-temperature water bath accelerated loading tests [...] Read more.
The interlaminar shear characteristics of a polyurethane (PU) mixture composite structure, quantitatively calculating its energy consumption and carbon emissions were analyzed in this study. Inclined shear tests were carried out on thirteen structures without interlaminar treatment, and high-temperature water bath accelerated loading tests were conducted on three composite structures; further, the interlaminar shear strength of the tire trace position after the accelerated loading test was tested to analyze the influence of both the high-temperature water bath environment and loading on the structure. In addition, based on the medium repair project of the Qingdao-Yinchuan expressway, the construction log of PU mixture pavement and asphalt pavement was investigated. Combined with the calculation parameters provided by the United Nations Intergovernmental Panel on Climate Change (IPCC), the consumption and carbon emissions of the two types of mixtures were calculated and compared quantitatively. The results showed that the shear strength between layers of asphalt mixtures, PU mixture and asphalt mixture was less than 2 MPa; however, the shear strength between PU mixture–cement-stabilized macadam and PU mixture–PU mixture was greater than 3 MPa. Therefore, it was recommended to spread a 0.4 L/m2 two-component PU adhesive layer as the interlayer treatment scheme for the structure of asphalt mixture-PU mixture and PU mixture-asphalt mixture; the high-temperature water area and accelerated loading had different effects on the interlaminar shear strength of the three structures. The PUM-16 mixture could effectively reduce energy consumption by 88.3 and 87.2%, carbon emissions by 81.1% and 79.1% in comparison to Stone Matrix asphalt with Nominal maximum particle size of 13.2 mm (SMA-13) and Stone Matrix asphalt with Nominal maximum particle size of 19.0 mm (SMA-20). Thus, the PU mixture was confirmed to be an environmentally friendly road pavement material. Full article
(This article belongs to the Special Issue Asphalt Pavement Materials and Surface)
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Article
The Effect of Different Surface Conditioning Techniques on the Bonding between Resin Cement & Ceramic
Coatings 2022, 12(3), 399; https://doi.org/10.3390/coatings12030399 - 17 Mar 2022
Viewed by 664
Abstract
Surface etching before cementation is a vital step that determines the clinical performance of ceramic restorations. Etching alters surface topography that contributes effective bonding between ceramic restoration and resin cement. This study aimed to compare etching techniques to determine the most effective etching [...] Read more.
Surface etching before cementation is a vital step that determines the clinical performance of ceramic restorations. Etching alters surface topography that contributes effective bonding between ceramic restoration and resin cement. This study aimed to compare etching techniques to determine the most effective etching method contributing the highest bond strength that helps in improving dental implants. Materials and methods: sixty discs of feldspathic ceramic measuring 10 mm diameter and 4 mm thickness were prepared. The 60 samples were divided into four equal groups based on the surface treatment technique used: group A: 9.6% hydrofluoric acid; group B: coarse diamond burs; group C: CO2 laser; and group D: no treatment. Ceramic disc specimens were examined under a Scanning Electron microscope (SEM) after surface treatment to characterize their surface morphology. Further, the specimens were luted with a resin luting agent and incubated for 24 h at a temperature of 37 °C simulating the oral environment. After 24 h, shear bond strength (SBS) and the nature of bond failure was determined for each specimen using a universal Instron testing machine. Results: significant change in surface morphology was noticed on hydrofluoric acid treatment forming larger irregular roughness (4.83 ± 1.78 µm) with multiple patterns of grooves and pores compared to other groups. Further, the highest SBS value was measured on hydrofluoric acid etching that display the highest bond strength due to the high surface roughness. In conclusion, our findings report a strong association between the surface roughness and bond strength upon hydrofluoric acid compared to other methods. Further work in this direction will enhance the utility of the etching technique on the improvement of dental implants. Full article
(This article belongs to the Special Issue Advances and Innovations in Dental Materials and Coatings)
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Article
Surface Modification of Polyester/Viscose Fabric with Silica Hydrosol and Amino-Functionalized Polydimethylsiloxane for the Preparation of a Fluorine-Free Superhydrophobic and Breathable Textile
Coatings 2022, 12(3), 398; https://doi.org/10.3390/coatings12030398 - 17 Mar 2022
Cited by 2 | Viewed by 795
Abstract
This work attempted to fabricate superhydrophobic fabric via a simple immersion technique. Textile fabrics were coated with silica nanoparticles prepared from tetraethoxysilane (TEOS) to obtain sufficient roughness with hydrophobic surface chemistry. Then, the coated fabrics were treated with polydimethylsiloxane (PDMS) and aminopropyltriethoxysilane (APTES) [...] Read more.
This work attempted to fabricate superhydrophobic fabric via a simple immersion technique. Textile fabrics were coated with silica nanoparticles prepared from tetraethoxysilane (TEOS) to obtain sufficient roughness with hydrophobic surface chemistry. Then, the coated fabrics were treated with polydimethylsiloxane (PDMS) and aminopropyltriethoxysilane (APTES) to reduce the surface energy. The effects of the PDMS concentration on the surface morphology and superhydrophobicity of as-prepared fabric were investigated. The morphology and the composition of superhydrophobic fabric were characterized by scanning electron microscopy (SEM), energy dispersive X-ray (EDS), and Fourier transform infrared (FTIR) spectroscopy. The results revealed the formation of spherical silica nanoparticles with an average particle size of 250 nm throughout the fabric surface. The possible interactions between silica nanoparticles and APTES, as well as the fabrics, were elucidated. Investigating the hydrophobicity of fabrics via water contact angle (WCA) measurement showed that the treated fabric exhibits excellent water repellency with a water contact angle as high as 151° and a very low water sliding angle. It was also found that the treated fabric maintained most of its hydrophobicity against repeated washing, as the WCA of superhydrophobic fabrics decreased to 141° after 25 repeated washing cycles. The comfort properties of the obtained superhydrophobic fabrics in terms of air permeability and bending length did not reveal any significant changes. Full article
(This article belongs to the Special Issue Surface Treatment of Textiles Vol. 2)
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Review
Influence of Defects and Heteroatoms on the Chemical Properties of Supported Graphene Layers
Coatings 2022, 12(3), 397; https://doi.org/10.3390/coatings12030397 - 17 Mar 2022
Cited by 1 | Viewed by 577
Abstract
A large and growing number of theoretical papers report the possible role of defects and heteroatoms on the chemical properties of single-layer graphene. Indeed, they are expected to modify the electronic structure of the graphene film, allow for chemisorption of different species, and [...] Read more.
A large and growing number of theoretical papers report the possible role of defects and heteroatoms on the chemical properties of single-layer graphene. Indeed, they are expected to modify the electronic structure of the graphene film, allow for chemisorption of different species, and enable more effective functionalisation. Therefore, from theoretical studies, we get the suggestion that single and double vacancies, Stone–Wales defects and heteroatoms are suitable candidates to turn nearly chemically inert graphene into an active player in chemistry, catalysis, and sensoristics. Despite these encouraging premises, experimental proofs of an enhanced reactivity of defected/doped graphene are limited because experimental studies addressing adsorption on well-defined defects and heteroatoms in graphene layers are much less abundant than theoretical ones. In this paper, we review the state of the art of experimental findings on adsorption on graphene defects and heteroatoms, covering different topics such as the role of vacancies on adsorption of oxygen and carbon monoxide, the effect of the presence of N heteroatoms on adsorption and intercalation underneath graphene monolayers, and the role of defects in covalent functionalisation and defect-induced gas adsorption on graphene transistors. Full article
(This article belongs to the Special Issue Application of Graphene and Two-Dimensional Materials in Thin Films)
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Article
Effect of Low-CTE Oxide-Dispersion-Strengthened Bond Coats on Columnar-Structured YSZ Coatings
Coatings 2022, 12(3), 396; https://doi.org/10.3390/coatings12030396 - 17 Mar 2022
Cited by 1 | Viewed by 554
Abstract
Thermal barrier coatings (TBCs) are commonly used to protect gas turbine components from high temperatures and oxidation. Such coatings consist of ceramic top coats and metallic bond coats. The mismatch in thermal expansion of the top coat, the bond coat and the component [...] Read more.
Thermal barrier coatings (TBCs) are commonly used to protect gas turbine components from high temperatures and oxidation. Such coatings consist of ceramic top coats and metallic bond coats. The mismatch in thermal expansion of the top coat, the bond coat and the component material is one main factor leading to the failure of the coating system. Columnar-structured top coats offer an enhanced tolerance to the strain during thermal cycling. On a flat bond coated surface, these TBCs reach higher thermal cycling performance. However, on rough surfaces, as used for thermal spray coatings, the performance of these thermal barrier coatings seems to be restricted or even stays below the performance of atmospheric-plasma-sprayed (APS) thermal barrier coatings. This low performance is linked to out-of-plane stresses at the interface between the top coat and the bond coat. In this study, a thin additional oxide-dispersion-strengthened (ODS) bond coat with high alumina content provides a reduced mismatch of the coefficient of thermal expansion (CTE) between the top coat and the bond coat. Columnar suspension plasma sprayed (SPS), yttria-stabilized zirconia (YSZ) TBCs were combined with low-CTE ODS bond coats. The behavior of these TBCs was characterized with respect to thermal cycling performance and degradation in a burner-rig facility. The comparison showed an up-to-four-fold increase in the performance of the new system. Full article
(This article belongs to the Topic Multiple Application for Novel and Advanced Materials)
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Article
A Study on Functional Hydrophobic Stainless Steel 316L Using Single-Step Anodization and a Self-Assembled Monolayer Coating to Improve Corrosion Resistance
Coatings 2022, 12(3), 395; https://doi.org/10.3390/coatings12030395 - 16 Mar 2022
Cited by 1 | Viewed by 800
Abstract
Stainless steel fabricated using chromium is widely being used in various industries due to its superior corrosion resistance compared to light metals such as aluminum, titanium, and magnesium. However, despite its excellent properties, a problem of poor corrosion resistance in harsh environments remains. [...] Read more.
Stainless steel fabricated using chromium is widely being used in various industries due to its superior corrosion resistance compared to light metals such as aluminum, titanium, and magnesium. However, despite its excellent properties, a problem of poor corrosion resistance in harsh environments remains. In this study, an economical and environmentally friendly anodizing process was applied to the surface of stainless steel (SUS 316L) to create porous nanostructures to improve its water-repellent properties. In these experiments, voltages of 30, 50, 70, and 90 V were applied to stainless steel for 3 h to form an oxide film, prior to immersion in 0.1 M phosphoric acid for 10 min to expand the oxide pores. In addition, the change of the oxide structure was observed through field-emission scanning electron microscopy (FE-SEM). In terms of the contact angle, hydrophilicity was observed at applied voltages of 70 and 90 V, in which a porous film was formed; the best water repellency was observed at a 90 V applied voltage, after the application of an FDTS (1H,1H,2H,2H-perfluorodecyltrichlorosilane) coating, a self-assembled monolayer. Finally, the corrosion behavior of a hydrophobic specimen was tested using potentiodynamic polarization (PDP) experiments. The hydrophobic SUS 316L alloy subsequently displayed improved corrosion resistance in a 3.5 wt% NaCl solution. Full article
(This article belongs to the Special Issue Recent Advances in Functional Surfaces and Interfaces)
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Article
Influence of Target Current on Structure and Performance of Cu Films Deposited by Oscillating Pulse Magnetron Sputtering
Coatings 2022, 12(3), 394; https://doi.org/10.3390/coatings12030394 - 16 Mar 2022
Viewed by 536
Abstract
To improve the deposition rate of thin films, a novel oscillating pulse magnetron sputtering technology (OPMS) was developed to substitute the traditional high-power impulse magnetron sputtering (HiPIMS). Meanwhile, the relative density and the mechanical properties were also significantly enhanced by this method. In [...] Read more.
To improve the deposition rate of thin films, a novel oscillating pulse magnetron sputtering technology (OPMS) was developed to substitute the traditional high-power impulse magnetron sputtering (HiPIMS). Meanwhile, the relative density and the mechanical properties were also significantly enhanced by this method. In this study, OPMS was used to prepare the pure Cu film, and the effect of the target current on the mode of copper atoms leaving the target (off-target method) under argon gas atmosphere was also investigated. The results showed that with the increase of the target current, the off-target method of copper atoms was transformed from sputtering to evaporation, the surface cracks’ width of the deposited films gradually decreased, and the lattice constants of the Cu films were close to the bulk materials. Furthermore, the deposition rate of Cu films obviously increased from 19 to 103 nm/min. The crystal structures of Cu films showed a face-centered cubic structure, and the grain size increased from 13 to 18 nm, with the target current increased from 2 to 18 A. Moreover, Cu films deposited at currents of 8 and 13 A exhibited excellent adhesion. Full article
(This article belongs to the Topic Surface Engineered Materials)
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Article
Organic–Inorganic Hybrid Film MLAs Built on the Silicon Solar Cells to Improve the Photoelectric Conversion Efficiency
Coatings 2022, 12(3), 393; https://doi.org/10.3390/coatings12030393 - 16 Mar 2022
Viewed by 741
Abstract
Light trapping micro-nano structures have been widely used to optimize the function of solar cell devices, especially microlens arrays (MLAs). In this article, we first prepared composite films by using sol-gel technology and the spin coating method, and then constructed heteromorphic MLAs on [...] Read more.
Light trapping micro-nano structures have been widely used to optimize the function of solar cell devices, especially microlens arrays (MLAs). In this article, we first prepared composite films by using sol-gel technology and the spin coating method, and then constructed heteromorphic MLAs on the surface of the composite films by using thermal reflow and UV nanoimprint technology; the substrate used was the silicon solar cell. Finally, the performance of the cells was improved. Optical transmission properties and surface morphology of the organic–inorganic hybrid films were detected by using a UV-Vis spectrometer and atomic force microscopy, respectively; it was revealed that the hybrid films had relatively excellent optical transmission performance in the visible light range. Surface structure of the hybrid film MLAs were detected by using SEM. At the same time, the optical imaging capabilities of MLAs were studied by using optical microscopy. Besides, the contact angles of the MLAs were also measured. It can be clearly seen that the prepared MLAs have a regular arrangement, clean appearance, and good imaging capabilities (from the actual test results). Finally, the various parameters of the silicon solar cells with hybrid film MLAs were studied. In addition, the power conversion efficiency (PCE) values increased by about 10.48% for the silicon solar cell with circular MLAs, compared to the silicon solar cell without a structure. The results show a concise and effective method to prepare organic–inorganic hybrid film MLAs on silicon solar cells, with significant improvement in photoelectric conversion efficiency. Full article
(This article belongs to the Topic Optical and Optoelectronic Materials and Applications)
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Editorial
Acknowledgment to Reviewers of Coatings in 2021
Coatings 2022, 12(3), 392; https://doi.org/10.3390/coatings12030392 - 15 Mar 2022
Viewed by 637
Abstract
Rigorous peer-reviews are the basis of high-quality academic publishing [...] Full article
Article
Mathematical Modelling of Ree-Eyring Nanofluid Using Koo-Kleinstreuer and Cattaneo-Christov Models on Chemically Reactive AA7072-AA7075 Alloys over a Magnetic Dipole Stretching Surface
Coatings 2022, 12(3), 391; https://doi.org/10.3390/coatings12030391 - 15 Mar 2022
Cited by 5 | Viewed by 694
Abstract
In the current study, since nanofluids have a high thermal resistance, and because non-Newtonian (Ree-Eyring) fluid movement on a stretching sheet by means of suspended nanoparticles AA7072-AA7075 is used, the proposed mathematical model takes into account the [...] Read more.
In the current study, since nanofluids have a high thermal resistance, and because non-Newtonian (Ree-Eyring) fluid movement on a stretching sheet by means of suspended nanoparticles AA7072-AA7075 is used, the proposed mathematical model takes into account the influence of magnetic dipoles and the Koo-Kleinstreuer model. The Cattaneo-Christov model is used to calculate heat transfer in a two-dimensional flow of Ree-Eyring nanofluid across a stretching sheet, and viscous dissipation is taken into account. The base liquid water with suspended nanoparticles AA7072-AA7075 is considered in this study. The PDEs are converted into ODEs by exhausting similarity transformations. The numerical solution of the altered equations is then performed utilising the HAM. To examine the performance of velocity, temperature profiles, concentration profiles, skin friction, the Nusselt number, and the Sherwood number, a graphical analysis is carried out for various parameters. The new model’s key conclusions are that the AA7075 alloy outperforms the AA7072 alloy in terms of thermal performance as the volume fraction and ferro-magnetic interaction constraint rise. Additionally, the rate of heat transmission and the skin friction coefficient improve as the volume fraction rises. Full article
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Article
Nondestructive Evaluation of Thermal Barrier Coatings Thickness Using Terahertz Technique Combined with PCA–GA–ELM Algorithm
Coatings 2022, 12(3), 390; https://doi.org/10.3390/coatings12030390 - 15 Mar 2022
Cited by 2 | Viewed by 775
Abstract
Thermal barrier coatings (TBCs) are usually used in high temperature and harsh environment, resulting in thinning or even spalling off. Hence, it is vital to detect the thickness of the TBCs. In this study, a hybrid machine learning model combined with terahertz time-domain [...] Read more.
Thermal barrier coatings (TBCs) are usually used in high temperature and harsh environment, resulting in thinning or even spalling off. Hence, it is vital to detect the thickness of the TBCs. In this study, a hybrid machine learning model combined with terahertz time-domain spectroscopy technology was designed to predict the thickness of TBCs. The terahertz signals were obtained from the samples prepared in laboratory and actual turbine blade. The principal component analysis (PCA) method was used to decrease the data dimensions. Finally, an extreme learning machine (ELM) was proposed to establish the thickness of TBCs prediction model. Genetic algorithm (GA) was selected to optimize the model to make it more accurate. The results showed that the root correlation coefficient (R2) exceeded 0.97 and the errors (root mean square error and mean absolute percentage error) were less than 2.57. This study proposes that terahertz time-domain technology combined with PCA–GA–ELM model is accurate and feasible for evaluating the thickness of the TBCs. Full article
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