Coatings

16 pages, 3643 KiB

Open AccessEditor’s ChoiceArticle

Evaluation of the Mechanical and Corrosion Behavior of Twin Wire Arc Sprayed Ni-Al Coatings with Different Al and Mo Content

by Jaehui Bang and Eunkyung Lee

Coatings 2023, 13(6), 1069; https://doi.org/10.3390/coatings13061069 - 9 Jun 2023

Cited by 2 | Viewed by 1402

Abstract

In this study, the surface properties of marine structures were improved by applying a twin wire arc spray process to high-strength low alloys. The effect of Al and Mo contents in Ni-Al coatings on their mechanical and corrosion behaviors was analyzed using hardness [...] Read more.

In this study, the surface properties of marine structures were improved by applying a twin wire arc spray process to high-strength low alloys. The effect of Al and Mo contents in Ni-Al coatings on their mechanical and corrosion behaviors was analyzed using hardness tests, electrochemical experiments, and immersion tests. The increase in Al content resulted in the formation of oxides and intermetallic compounds, leading to a significant improvement in the mechanical properties by approximately 222 HV. Despite a fine galvanic phenomenon causing a decrease in corrosion resistance by up to 8.91%, a higher Al content demonstrated the highest corrosion resistance after high-temperature exposure, with an enhancement of approximately 20.9%, attributed to the formation of an oxide film generated by intermetallic phase transformation. However, the mechanical properties experienced a reduction of 134.3 HV. This study demonstrated a correlation between the microstructure of the coating layers that form passivation films and their respective mechanical and corrosion properties. It also revealed that the content of Al and Mo significantly affects the mechanical and corrosion behavior of Ni-Al coatings. Full article

(This article belongs to the Special Issue Corrosion Resistance, Mechanical Properties and Characterization of Metallic Materials and Coatings)

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10 pages, 4936 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Effect of the Working Pressure and Oxygen Gas Flow Rate on the Fabrication of Single-Phase Ag₂O Thin Films

by Jiyoon Choi, Jiha Seong, Sangbin Park, Hyungmin Kim, Sangmo Kim, Kyung Hwan Kim and Jeongsoo Hong

Coatings 2023, 13(6), 1061; https://doi.org/10.3390/coatings13061061 - 7 Jun 2023

Viewed by 1570

Abstract

Ag₂O thin films have been applied in various devices, such as photodetectors, photocatalysts, and gas sensors, because of their excellent thermal stability, strong electrical properties, and stable structures. However, because various phases of silver oxide exist, the fabrication of single-phase Ag [...] Read more.

Ag₂O thin films have been applied in various devices, such as photodetectors, photocatalysts, and gas sensors, because of their excellent thermal stability, strong electrical properties, and stable structures. However, because various phases of silver oxide exist, the fabrication of single-phase Ag₂O thin films using a general deposition system is difficult. In this study, Ag₂O thin films were deposited on glass substrates at different working pressures and O₂ gas flow rates using a facing-target sputtering (FTS) system. After optimizing the working pressure and O₂ gas flow rate, the Ag₂O thin films were post-annealed at different temperatures ranging from 100 to 400 °C to improve their crystallographic properties. The X-ray diffraction patterns of the as-fabricated Ag₂O thin films indicated the presence of a single phase of Ag₂O, and the ultraviolet–visible (UV–vis) spectral analysis indicated transmittance of 65% in the visible light region. The optimum working pressure and O₂ gas flow rate were determined to be 4 mTorr and 3.4 sccm, respectively. Finally, the effect of the post-annealing temperature on the thin film was investigated; the Ag₂O peak had high intensity at 300 °C, suggesting this as the optimum post-annealing temperature. Full article

(This article belongs to the Special Issue Optical Thin Film and Photovoltaic (PV) Related Technologies, Volume II)

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12 pages, 7543 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Refined Grain Enhancing Lithium-Ion Diffusion of LiFePO₄ via Air Oxidation

by Xinjie Shen, Zijun Qin, Peipei He, Xugang Ren, Yunjiao Li, Feixiang Wu, Yi Cheng and Zhenjiang He

Coatings 2023, 13(6), 1038; https://doi.org/10.3390/coatings13061038 - 2 Jun 2023

Viewed by 1454

Abstract

LiFePO₄ is a type of cathode material with good safety and long service life. However, the problems of the low Li ion diffusion rate and low electron conductivity limit the application of LiFePO₄ in the field of electric vehicles. In this [...] Read more.

LiFePO₄ is a type of cathode material with good safety and long service life. However, the problems of the low Li ion diffusion rate and low electron conductivity limit the application of LiFePO₄ in the field of electric vehicles. In this paper, FePO₄ with different grain sizes was prepared via the air oxidation precipitation method and then sintered to prepare LiFePO₄. The refined grain can shorten the diffusion distance of Li⁺, accelerate the diffusion of Li⁺, and improve the diffusion coefficient of Li⁺. The results show that LiFePO₄ with a smaller grain size has better electrochemical performance. The discharge capacity of the first cycle is 151.3 mAh g⁻¹ at 1 C, and the capacity retention rate is 95.04% after 230 cycles. Its rate performance is more outstanding, not only at 0.2 C, where the discharge capacity is as high as 155 mAh g⁻¹, but also at 10 C, the capacity fade is less, and it can still reach 131 mAh g⁻¹. The air oxidation precipitation method reduces the production cost, shortens the production process, and prepares FePO₄ with small grains, which provides a reference for further improving the properties of precursors and LiFePO₄. Full article

(This article belongs to the Section Surface Engineering for Energy Harvesting, Conversion, and Storage)

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18 pages, 5917 KiB

Open AccessEditor’s ChoiceArticle

Effects of Wet and Dry Treatments on Surface Functional Groups and Mechanical Properties of Flax Fiber Composites

by Ghane Moradkhani, Jacopo Profili, Mathieu Robert, Gaétan Laroche and Saïd Elkoun

Coatings 2023, 13(6), 1036; https://doi.org/10.3390/coatings13061036 - 2 Jun 2023

Cited by 10 | Viewed by 3131

Abstract

Flax fibers have found widespread use in eco-composite materials because of their remarkable mechanical properties compared to glass fibers. However, their low stability limits their use on a larger scale when employed in hot or humid environments. Therefore, the surfaces should be modified [...] Read more.

Flax fibers have found widespread use in eco-composite materials because of their remarkable mechanical properties compared to glass fibers. However, their low stability limits their use on a larger scale when employed in hot or humid environments. Therefore, the surfaces should be modified before the composite process to provide the best interfacial interactions and increase the dispersion of natural fibers. To tackle this problem, two kinds of modifications can be considered: wet and dry modifications. This research explores different methods to improve the adhesion between flax fibers and the poly lactic acid (PLA) polymer. Morphological and chemical modifications in the presence of acetone, alkali (as a wet modification), and with air atmospheric pressure plasma (as a dry modification) are compared in this research. The results revealed that altering the chemical characteristics on the surface significantly changed the mechanical properties of the final composite. More specifically, the Fourier transform infrared spectroscopy (FTIR) data indicate that wax-related peaks (2850 and 2920 cm⁻¹) were eliminated by both wet and dry treatments. Dynamic mechanical analysis (DMA) results also highlighted that a better bond between the flax fibers and the PLA matrix is obtained with the plasma modification. Full article

(This article belongs to the Special Issue Sustainable Coatings for Functional Textile and Packaging Materials)

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12 pages, 6196 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Permeability of Skin-Mimicking Cell Coatings by Polymers of Complex Architecture Based on Polyoxazolines

by Gia Storti, Giulia Romano, Kristen Gilmore, Nicholas Sadowski, Andrii Tiiara, Igor Luzinov and Alexander Sidorenko

Coatings 2023, 13(6), 1007; https://doi.org/10.3390/coatings13061007 - 29 May 2023

Cited by 2 | Viewed by 2187

Abstract

In the scope of drug delivery, the transdermal route is desirable because it provides attainable therapeutic concentrations and has minimal systemic side effects. To make the skin a feasible route for the delivery of therapeutic agents, the biggest challenge is overcoming its natural [...] Read more.

In the scope of drug delivery, the transdermal route is desirable because it provides attainable therapeutic concentrations and has minimal systemic side effects. To make the skin a feasible route for the delivery of therapeutic agents, the biggest challenge is overcoming its natural coating. In this paper, we investigate the effect of the architectures (homopolymer vs. block copolymer vs. hybrid block–graft copolymer) of several amphiphilic polymeric derivatives of poly(2-oxazoline) on skin permeability. The block copolymers are composed of a hydrophobic poly(2-oxazoline) block and a hydrophilic PEG block. The hybrid block–graft copolymers are obtained by grafting hydrophobic side chains of polycaprolactone to a poly(2-oxazoline) backbone. We used the commercially available EpiDerm™ by MatTek, composed of human epidermal cells, as a model of human skin. Two parameters of skin permeation are reported: penetration rate and lag time. We hypothesize that the skin permeation characteristics correlate with the critical micelle concentration and particle size of the studied polymers, while both parameters are a function of the complex architectures of the presented macromolecular constructs. While homopolymer poly(2-oxazolines) show the least permeation, the block copolymers demonstrate partial permeation. The hybrid block–graft copolymers exhibited full penetration through the model skin samples. Full article

(This article belongs to the Special Issue Toward Sustainability through Bio-Based Materials at the Interfaces with Living Systems)

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13 pages, 3344 KiB

Open AccessEditor’s ChoiceArticle

Complex Bioactive Chitosan–Bioglass Coatings on a New Advanced TiTaZrAg Medium–High-Entropy Alloy

by Andrei Bogdan Stoian, Radu Nartita, Georgeta Totea, Daniela Ionita and Cristian Burnei

Coatings 2023, 13(5), 971; https://doi.org/10.3390/coatings13050971 - 22 May 2023

Cited by 2 | Viewed by 1595

Abstract

High-entropy alloys (HEAs), also known as multicomponent or multi-principal element alloys (MPEAs), differ from traditional alloys, which are usually based only on one principal element, in that they are usually fabricated from five or more elements in large percentages related to each other, [...] Read more.

High-entropy alloys (HEAs), also known as multicomponent or multi-principal element alloys (MPEAs), differ from traditional alloys, which are usually based only on one principal element, in that they are usually fabricated from five or more elements in large percentages related to each other, in the range of 5%–35%. Despite the usually outstanding characteristics of HEAs, based on a properly selected design, many such alloys are coated with advanced composites after their elaboration to further improve their qualities. In this study, 73Ti-20Zr-5Ta-2Ag samples were covered with chitosan and a mixture of chitosan, bioglass, and ZnO particles to improve the materials’ antibacterial properties. A variety of methods, including scanning electron microscopy, atomic force microscopy, and mechanical and electrochemical determinations, has permitted a quantified comparison between the coated and uncoated surfaces of this medium–high-entropy alloy. The materials’ properties were enhanced by the complex coating, giving the alloys not only high antibacterial activity, but also good corrosion protection. Full article

(This article belongs to the Special Issue New Strategies and Recent Advances in Investigations of Micro- and Nano-Coatings for Technological and Biomedical Applications)

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18 pages, 13890 KiB

Open AccessEditor’s ChoiceArticle

Aluminium-Based Dissimilar Alloys Surface Composites Reinforced with Functional Microparticles Produced by Upward Friction Stir Processing

by Filipe Moreira, Pedro M. Ferreira, Rui J. C. Silva, Telmo G. Santos and Catarina Vidal

Coatings 2023, 13(5), 962; https://doi.org/10.3390/coatings13050962 - 21 May 2023

Cited by 10 | Viewed by 1886

Abstract

Surface metal matrix composites offer an excellent solution for applications where surface properties play a crucial role in components’ performance and durability, such as greater corrosion resistance, better wear resistance, and high formability. Solid-state processing techniques, such as friction surfacing and friction stir [...] Read more.

Surface metal matrix composites offer an excellent solution for applications where surface properties play a crucial role in components’ performance and durability, such as greater corrosion resistance, better wear resistance, and high formability. Solid-state processing techniques, such as friction surfacing and friction stir welding/processing, offer several advantages over conventional liquid-phase processing methods. This research investigated the feasibility of producing surface composites of aluminium-based dissimilar alloys reinforced with functional microparticles through experimental validation, determined the process parameters that resulted in a more homogeneous distribution of the particles in the surface composites, and enhanced the understanding of Upward Friction Stir Processing (UFSP) technology. The production of aluminium-based dissimilar alloys (AA 7075-T651 and AA 6082-T651) surface composites reinforced with SiC particles was studied, and it was concluded that the macrography and micrography analyses, scanning electron microscopy (SEM) analysis, microhardness measurements, and eddy currents technique reveal an extensive and homogeneous incorporation of SiC particles. In the stirred zone, a decrease of approximately 20 HV 0.5 in hardness was observed compared to the base material. This reduction is attributed to the weakening effect caused by low-temperature annealing during UFSP, which reduces the strengthening effect of the T651 heat treatment. Additionally, the presence of particles did not affect the surface composite hardness in the stirred zone. Furthermore, despite the presence of significant internal defects, SEM analyses revealed evidence of the lower alloy merging with the upper zone, indicating that the lower plate had a role beyond being merely sacrificial. Therefore, the production of bimetallic composites through UFSP may offer advantages over composites produced from a monometallic matrix. The results of the eddy currents testing and microhardness measurements support this finding and are consistent with the SEM/EDS analyses. Full article

(This article belongs to the Special Issue Surface Engineering Treatments and Innovative Coatings for Additive Manufacturing Materials)

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15 pages, 8013 KiB

Open AccessEditor’s ChoiceArticle

Facile Fabrication of Robust and Fluorine-Free Superhydrophobic PDMS/STA-Coated Cotton Fabric for Highly Efficient Oil-Water Separation

by Daibin Tang and Enzhou Liu

Coatings 2023, 13(5), 954; https://doi.org/10.3390/coatings13050954 - 19 May 2023

Cited by 7 | Viewed by 1921

Abstract

Oil–water separation using special wettability materials has received much attention due to its low energy consumption and high separation efficiency. Herein, a fluorine-free superhydrophobic cotton fabric (PDMS/STA-coated cotton fabric) was successfully prepared by a simple impregnation method using hydroxyl-capped polydimethylsiloxane (PDMS-OH), tetraethoxysilane (TEOS), [...] Read more.

Oil–water separation using special wettability materials has received much attention due to its low energy consumption and high separation efficiency. Herein, a fluorine-free superhydrophobic cotton fabric (PDMS/STA-coated cotton fabric) was successfully prepared by a simple impregnation method using hydroxyl-capped polydimethylsiloxane (PDMS-OH), tetraethoxysilane (TEOS), and stearic acid (STA) as precursors. The investigation found that the cross-linking reactions between the hydroxyl groups of PDMS-OH and hydrolyzed TEOS enabled a strong interaction between PDMS-OH and cotton fabric. Furthermore, a suitable roughness surface of coated cotton fabric was established by introducing STA due to its long chain structure. The contact angle of this composite can reach 158.7° under optimal conditions due to its low surface energy and desired roughness. The oil/water separation efficiency of PDMS/STA-coated cotton fabric is higher than 90% even after 10 cycles of oil–water separation, and the oil flux can reach 11862.42 L m⁻² h⁻¹. In addition, PDMS/STA-coated cotton fabric exhibits excellent chemical stability and durability under extreme conditions such as strong acid (HCl, pH = 1~2) and alkali (NaOH, pH = 13~14), and the hydrophobicity of PDMS/STA-coated cotton fabric was decreased to 147° after 300 cycles of abrasion testing. Full article

(This article belongs to the Special Issue Sustainable Coatings for Functional Textile and Packaging Materials)

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26 pages, 11891 KiB

Open AccessEditor’s ChoiceArticle

The Electrodeposition of Derivatives of Pyrrole and Thiophene on Brass Alloy in the Presence of Dodecane-1-Sulfonic Acid Sodium Salt in Acidic Medium and Its Anti-Corrosive Properties

by Florina Branzoi and Simona Petrescu

Coatings 2023, 13(5), 953; https://doi.org/10.3390/coatings13050953 - 19 May 2023

Cited by 1 | Viewed by 1441

Abstract

In this paper, potentiostatic and galvanostatic deposition (electrochemical deposition) processes have been used for the obtained of a new composite polymer: N-methylpyrrole-sodium 1-dodecanesulfonate/poly 2-methylthiophene (PNMPY-1SSD/P2MT) coatings over brass electrode for corrosion protection. The sodium 1-dodecanesulfonate as a dopant ion employed in the electropolymerization [...] Read more.

In this paper, potentiostatic and galvanostatic deposition (electrochemical deposition) processes have been used for the obtained of a new composite polymer: N-methylpyrrole-sodium 1-dodecanesulfonate/poly 2-methylthiophene (PNMPY-1SSD/P2MT) coatings over brass electrode for corrosion protection. The sodium 1-dodecanesulfonate as a dopant ion employed in the electropolymerization procedure can have a meaningful effect on the anti-corrosion protection of the composite polymeric film by stopping the penetration of corrosive ions. The composite coatings have been characterized by cyclic voltammetry, Fourier transform infrared (FT-IR) spectroscopy, and scanning electron microscopy (SEM) procedures. The anti-corrosion performance of PNMPY-1SSD/P2MT coated brass has been investigated by potentiostatic and potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) practices in 0.5 M H₂SO₄ medium. The corrosion assessment of PNMPY-1SSD/P2MT coated brass was noticed to be ~9 times diminished than of uncoated brass, and the efficiency of these protective coatings of this coating is above 90%. The highest effectiveness is realized by the electrochemical deposition of PNMPY-1SSD/P2MT obtained at 1.1 V and 1.4 V potential applied and at 0.5 mA/cm² and 1 mA/cm² current densities applied in molar ratio 5:3. The outcomes of the corrosion tests denoted that PNMPY-1SSD/P2MT coatings assure good anti-corrosion protection of brass in corrosive media. Full article

(This article belongs to the Special Issue New Developments of Protective Coatings, Organic Polymers, and Surface Analysis)

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13 pages, 5486 KiB

Open AccessEditor’s ChoiceArticle

Fabrication and Characterization of Ti/TiC Composite Layers by an Electron-Beam Surface Modification

by Stefan Valkov, Daniela Nedeva, Vladimir Dunchev, Fatme Padikova, Maria Ormanova, Borislav Stoyanov and Nikolay Nedyalkov

Coatings 2023, 13(5), 951; https://doi.org/10.3390/coatings13050951 - 19 May 2023

Cited by 2 | Viewed by 2423

Abstract

In this study, the possibilities for modification and improvement of the surface structure and properties of titanium substrates by a formation of composite Ti/TiC layers are presented. The layers were fabricated by a two-step electron-beam surface modification technique. The first step consists of [...] Read more.

In this study, the possibilities for modification and improvement of the surface structure and properties of titanium substrates by a formation of composite Ti/TiC layers are presented. The layers were fabricated by a two-step electron-beam surface modification technique. The first step consists of injection of C powder within the pure Ti substrates by electron-beam alloying technology. The second step is the refinement and homogenization of the microstructure by the electron-beam remelting procedure. During the remelting, the speed of the motion of the samples was varied, and two (most representative) velocities were chosen: 5 and 15 mm/s. Considering both speeds of the motion of the specimens, a composite structure in the form of fine TiC particles distributed within the base titanium matrix was formed. The remelting speed of 5 mm/s led to the formation of a much thicker composite layer, where the TiC particles were significantly more homogeneously distributed. The results obtained for the Vickers microhardness exhibit a significant increase in the value in the mentioned mechanical characteristic in comparison with the base Ti substrate. In the case of the lower speed of the motion of the specimen during the remelting procedure, the microhardness is 510 HV, or about 2.5 times higher than that of the titanium substrate. The application of a higher speed of the specimen motion leads to a decrease in the microhardness in comparison with the case of lower velocity. However, it is still much higher than that of the base Ti material. The mean microhardness of the sample obtained by the remelting speed of motion of 15 mm/s is 360 HV, or it is 1.8 times higher than that of the base material. Full article

(This article belongs to the Special Issue Surface Modification for Improving the Performance of Engineering Components)

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17 pages, 2552 KiB

Open AccessEditor’s ChoiceArticle

Plasma-Deposited Organosilicon Hydrophobic Coatings on Cellulosic Materials for Wet Packaging Applications

by Jacopo Profili, Sara Babaei, Mariam Al Rashidi, Annie Dorris, Siavash Asadollahi, Andranik Sarkissian and Luc Stafford

Coatings 2023, 13(5), 924; https://doi.org/10.3390/coatings13050924 - 15 May 2023

Cited by 3 | Viewed by 2093

Abstract

Non-toxic organosilicon coatings with hydrophobic properties were deposited on Kraft paper films using atmospheric-pressure dielectric barrier discharge. In order to assess the applicability of the plasma-deposited coating in the food packaging industry, its stability in different liquids (i.e., food simulants) was studied. Chemical [...] Read more.

Non-toxic organosilicon coatings with hydrophobic properties were deposited on Kraft paper films using atmospheric-pressure dielectric barrier discharge. In order to assess the applicability of the plasma-deposited coating in the food packaging industry, its stability in different liquids (i.e., food simulants) was studied. Chemical analyses reveal that the food simulants, namely, de-ionized water, acetic acid, ethanol, and heptane, do not significantly alter the chemical composition or the hydrophobicity of the coatings. Based on inductively coupled plasma-optical emission spectroscopy analyses, the amount of Si released from the plasma-deposited coating is less than that typically detected in tap water. Overall, the results obtained suggest that hydrophobic plasma-deposited organosilicon coatings have great potential for use in food and wet packaging applications, especially considering their environmentally friendly character. Full article

(This article belongs to the Special Issue Recent Advances in Functional Biopolymers for Food Packaging and Biomedical Applications)

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16 pages, 5107 KiB

Open AccessEditor’s ChoiceArticle

Efficacy Evaluation of Cu- and Ag-Based Antibacterial Treatments on Polypropylene Fabric and Comparison with Commercial Products

by Nunzia Gallo, Giorgia Natalia Iaconisi, Mauro Pollini, Federica Paladini, Sudipto Pal, Concetta Nobile, Loredana Capobianco, Antonio Licciulli, Giovanna Giuliana Buonocore, Antonella Mansi, Luca Salvatore and Alessandro Sannino

Coatings 2023, 13(5), 919; https://doi.org/10.3390/coatings13050919 - 14 May 2023

Cited by 2 | Viewed by 2500

Abstract

Filter masks are disposable devices intended to be worn in order to reduce exposure to potentially harmful foreign agents of 0.1–10.0 microns. However, to perform their function correctly, these devices should be replaced after a few hours of use. Because of this, billions [...] Read more.

Filter masks are disposable devices intended to be worn in order to reduce exposure to potentially harmful foreign agents of 0.1–10.0 microns. However, to perform their function correctly, these devices should be replaced after a few hours of use. Because of this, billions of non-biodegradable face masks are globally discarded every month (3 million/minute). The frequent renewal of masks, together with the strong environmental impact of non-biodegradable plastic-based mask materials, highlights the need to find a solution to this emerging ecological problem. One way to reduce the environmental impact of masks, decrease their turnover, and, at the same time, increase their safety level is to make them able to inhibit pathogen proliferation and vitality by adding antibacterial materials such as silver, copper, zinc, and graphene. Among these, silver and copper are the most widely used. In this study, with the aim of improving commercial devices’ efficacy and eco-sustainability, Ag-based and Cu-based antibacterial treatments were performed and characterized from morphological, compositional, chemical–physical, and microbiological points of view over time and compared with the antibacterial treatments of selected commercial products. The results demonstrated the good distribution of silver and copper particles onto the surface of the masks, along with almost 100% antibacterial capabilities of the coatings against both Gram-positive and Gram-negative bacteria, which were still confirmed even after several washing cycles, thus indicating the good potential of the developed prototypes for mask application. Full article

(This article belongs to the Special Issue Advances in Antibacterial Coatings: From Materials to Applications)

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16 pages, 4588 KiB

Open AccessEditor’s ChoiceArticle

Al₂O₃ Ceramic/Nanocellulose-Coated Non-Woven Separator for Lithium-Metal Batteries

by Dong-Min Shin, Hyunsu Son, Ko Un Park, Junyoung Choi, Jungdon Suk, Eun Seck Kang, Dong-Won Kim and Do Youb Kim

Coatings 2023, 13(5), 916; https://doi.org/10.3390/coatings13050916 - 13 May 2023

Cited by 3 | Viewed by 3356

Abstract

Separators play an essential role in lithium (Li)-based secondary batteries by preventing direct contact between the two electrodes and providing conduction pathways for Li-ions in the battery cells. However, conventional polyolefin separators exhibit insufficient electrolyte wettability and thermal stability, and in particular, they [...] Read more.

Separators play an essential role in lithium (Li)-based secondary batteries by preventing direct contact between the two electrodes and providing conduction pathways for Li-ions in the battery cells. However, conventional polyolefin separators exhibit insufficient electrolyte wettability and thermal stability, and in particular, they are vulnerable to Li dendritic growth, which is a significant weakness in Li-metal batteries (LMBs). To improve the safety and electrochemical performance of LMBs, Al₂O₃ nanoparticles and nanocellulose (NC)-coated non-woven poly(vinylidene fluoride)/polyacrylonitrile separators were fabricated using a simple, water-based blade coating method. The Al₂O₃/NC-coated separator possessed a reasonably porous structure and a significant number of hydroxyl groups (-OH), which enhanced electrolyte uptake (394.8%) and ionic conductivity (1.493 mS/cm). The coated separator also exhibited reduced thermal shrinkage and alleviated uncontrollable Li dendritic growth compared with a bare separator. Consequently, Li-metal battery cells with a LiNi_0.8Co_0.1Mn_0.1O₂ cathode and an Al₂O₃/NC-coated separator using either liquid or solid polymer electrolytes exhibited improved rate capability, cycle stability, and safety compared with a cell with a bare separator. The present study demonstrates that combining appropriate materials in coatings on separator surfaces can enhance the safety and electrochemical performance of LMBs. Full article

(This article belongs to the Special Issue Advanced Materials for Energy Storage and Conversion)

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17 pages, 9111 KiB

Open AccessEditor’s ChoiceArticle

Atmospheric Pressure Plasma Treatment of Magnesium Alloy for Enhanced Coating Adhesion and Corrosion Resistance

by Gyoung Gug Jang, Jiheon Jun, Sinchul Yeom, Mina Yoon, Yi Feng Su, John Wade, Michael S. Stephens and Jong K. Keum

Coatings 2023, 13(5), 897; https://doi.org/10.3390/coatings13050897 - 10 May 2023

Cited by 5 | Viewed by 2467

Abstract

Atmospheric pressure plasma (AP) treatment, using an open-air jet of ionized CO_2, N₂, or air, was applied to AZ91D Mg alloy surfaces to investigate its effects on primer coating adhesion and corrosion resistance. The CO₂ and air AP treatments [...] Read more.

Atmospheric pressure plasma (AP) treatment, using an open-air jet of ionized CO_2, N₂, or air, was applied to AZ91D Mg alloy surfaces to investigate its effects on primer coating adhesion and corrosion resistance. The CO₂ and air AP treatments formed an O- and C-rich surface layer (Mg-O-C) consisting of agglomerated nanoparticles and pits with a depth of a few microns and increasing the surface roughness by 6–8 times compared with the reference 600 grit-finished surface. Then, three commercial primers, zinc phosphate (ZnP), chromate-containing epoxy, and MIL23377, were applied on the treated surfaces to evaluate the corrosion resistance associated with the coating adhesion. Microscopic analysis demonstrated stronger interlocking between the primer layer and the nano-/microrough Mg-O-C surface compared to the untreated (600 grit-finished) surfaces, indicating improved coating adhesion and corrosion resistance. Crosscut tests of the MIL23377 primer on the CO₂ and air AP-treated surfaces showed the highest level of adhesion, ASTM class 5B. Salt spray corrosion tests showed that after 8 days of exposure, the primer coatings on air AP-treated surfaces had corrosion areas that were more than four times smaller than that of the 600 grit-finished surface. The N₂ AP treatment showed similar adhesion enhancement. The preliminary operation expenses for AP treatment using CO₂, N₂, and air were estimated at USD 30.62, USD 35.45, and USD 29.75 (from an air cylinder)/USD 0.66 (from an air compressor) per m², respectively. Full article

(This article belongs to the Section Plasma Coatings, Surfaces & Interfaces)

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18 pages, 4956 KiB

Open AccessEditor’s ChoiceArticle

Migration of TiO₂ from PET/TiO₂ Composite Films Used for Polymer-Laminated Steel Cans in Acidic Solution

by Jingying Cui, Jinyang Chen, Jie Gu, Xiaomin Hong, Menghan Hong, Zheying Wu and Yu Hu

Coatings 2023, 13(5), 887; https://doi.org/10.3390/coatings13050887 - 8 May 2023

Cited by 2 | Viewed by 1734

Abstract

Nano-TiO₂ is widely used as a commercial food contact material (FCM), which poses potential risks to food. Therefore, the migration of TiO₂ is crucial for the safety of FCM. Since PET/TiO₂ composite films are food contact layers used for producing [...] Read more.

Nano-TiO₂ is widely used as a commercial food contact material (FCM), which poses potential risks to food. Therefore, the migration of TiO₂ is crucial for the safety of FCM. Since PET/TiO₂ composite films are food contact layers used for producing polymer-laminated steel cans and the majority of beverages contained in cans are acidic, it is necessary to study the migration of TiO₂ from PET/TiO₂ composite films in acidic solutions. The migration of TiO₂ in 4% (v/v) acetic acid was studied through the ICP-OES method. The corrosion process that occurred during the migration process was studied using electrochemical impedance spectroscopy (EIS). The morphology of Ti nanoparticles and films was measured by SEM, TEM, and dynamic light scattering (DLS) techniques. The results indicate that, at a temperature of 60 °C, the maximum migration concentration of TiO₂ is 0.32 mg/kg. The TiO₂ particles released during the migration process are unstable and tend to aggregate in the simulated material, with most of the Ti being present in the form of particles. Therefore, the migration of TiO₂ does not follow the Fick law of diffusion but rather conforms to the Weibull model based on the non-Fick law of diffusion. Full article

(This article belongs to the Special Issue New Developments of Protective Coatings, Organic Polymers, and Surface Analysis)

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16 pages, 5640 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Comparison of Tribological Characteristics of AA2024 Coated by Plasma Electrolytic Oxidation (PEO) Sealed by Different sol–gel Layers

by Hafiza Ayesha Khalid, Sajjad Akbarzadeh, Yoann Paint, Véronique Vitry and Marie-Georges Olivier

Coatings 2023, 13(5), 871; https://doi.org/10.3390/coatings13050871 - 5 May 2023

Cited by 2 | Viewed by 2383

Abstract

The application of sol–gel on plasma electrolytic oxidation (PEO) coatings can increase wear resistance by sealing the surface defects such as pores and cracks in the outer layer of the PEO layer and strengthen the coating. Four different sol–gel formulations based on precursors—(3-glycidyloxypropyl)trimethoxysilane [...] Read more.

The application of sol–gel on plasma electrolytic oxidation (PEO) coatings can increase wear resistance by sealing the surface defects such as pores and cracks in the outer layer of the PEO layer and strengthen the coating. Four different sol–gel formulations based on precursors—(3-glycidyloxypropyl)trimethoxysilane (GPTMS), methyltriethoxysilane (MTES), methacryloxypropyltrimethoxysilane (MAPTMS), (3-aminopropyl)triethoxysilane (APTES), and zirconium(IV) propoxide (ZTP) along with tetraethoxysilane (TEOS)—were used to seal PEO pores, and the samples were tested tribologically. A sliding reciprocating tribometer was used to carry out a wear test with an alumina ball as the counter body in two different conditions: (a) 2.5 N load for 20 min, and (b) 3 N load for 40 min. The coefficient of friction and wear rate as volume loss per unit sliding length were obtained for all sol–gel-sealed specimens and unsealed PEO-coated and bare AA2024 substrate. 3D mechanical profilometer surface scans were used to compare the depth of wear traces. The elemental color mapping using SEM and EDS revealed that silicon remains present in the wear tracks of PEO coatings sealed with sol–gel layers containing GPTMS (PSG) and ZTP (PSG-ZT). GPTMS (PSG) was able to fill the pores of the PEO layer efficiently due to its cross-linked network. Moreover, sol–gel containing ZTP (PSG-ZT) was deposited as a thick layer on top of the PEO layer which provided good lubrication and resistance to wear. However, other sol–gel formulations (PSG-MT and PSG-AP) were worn out during tests at a higher load (3 N). The most stable friction coefficient (COF) and specific wear rates were observed with sol–gels with GPTMS and ZTP. Full article

(This article belongs to the Special Issue Plasma Electrolytic Oxidation (PEO) Coatings, 2nd Edition)

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16 pages, 749 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Optical Characterization of Inhomogeneous Thin Films Deposited onto Non-Absorbing Substrates

by Jan Dvořák, Jiří Vohánka, Vilma Buršíková, Daniel Franta and Ivan Ohlídal

Coatings 2023, 13(5), 873; https://doi.org/10.3390/coatings13050873 - 5 May 2023

Cited by 1 | Viewed by 2403

Abstract

In this study, a novel approach for characterizing the optical properties of inhomogeneous thin films is presented, with a particular focus on samples exhibiting absorption in some part of the measured spectral range. Conventional methods of measuring the samples only from the film [...] Read more.

In this study, a novel approach for characterizing the optical properties of inhomogeneous thin films is presented, with a particular focus on samples exhibiting absorption in some part of the measured spectral range. Conventional methods of measuring the samples only from the film side can be limited by incomplete information at the lower boundary of the film, leading to potentially unreliable results. To address this issue, depositing the thin films onto non-absorbing substrates to enable measurements from both sides of the sample is proposed. To demonstrate the efficacy of this approach, a combination of variable-angle spectroscopic ellipsometry and spectrophotometry at near-normal incidence was employed to optically characterize three inhomogeneous polymer-like thin films. The spectral dependencies of the optical constants were modeled using the Kramers–Kronig consistent model. It was found that it is necessary to consider thin, weakly absorbing transition layers between the films and the substrates. The obtained results show excellent agreement between the fits and the measured data, providing validation of the structural and dispersion models, as well as the overall characterization procedure. The proposed approach offers a method for optically characterizing a diverse range of inhomogeneous thin films, providing more reliable results when compared to traditional one-sided measurements. Full article

(This article belongs to the Special Issue Recent Advancement in Thin Film Deposition, Characterization, and Surface Engineering (Second Volume))

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17 pages, 8974 KiB

Open AccessEditor’s ChoiceArticle

Corrosion Evolution of Nickel Aluminum Bronze in Clean and Sulfide-Polluted Solutions

by Liu Yang and Yinghua Wei

Coatings 2023, 13(5), 846; https://doi.org/10.3390/coatings13050846 - 28 Apr 2023

Cited by 1 | Viewed by 1835

Abstract

Nickel aluminum bronze (NAB) alloys are reported to suffer accelerated local corrosion in sulfide-polluted seawater. In this work, the real-time in situ scanning vibrating electrode technique (SVET) was employed to monitor the evolution of the corrosion product film of a typical NAB alloy [...] Read more.

Nickel aluminum bronze (NAB) alloys are reported to suffer accelerated local corrosion in sulfide-polluted seawater. In this work, the real-time in situ scanning vibrating electrode technique (SVET) was employed to monitor the evolution of the corrosion product film of a typical NAB alloy immersed in the clean and sulfide-polluted 3.5% NaCl solutions. In the sulfide-free condition, the corrosion current peak surged at the individual point of the NAB surface and receded to calm in 2 h. In the presence of the sulfide, however, multiple active points on the measured metal surface released high corrosion current for a long time, indicating that intense corrosion had occurred. The corrosion mass loss was more than four times the former. Global electrochemical techniques, scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) were adopted to perform a comprehensive analysis of the composition of the corrosion product films. The results show that a dense layer of aluminum and cuprous oxide forms on the NAB surface in the sulfide-free solution, while a loose mixture of cuprous sulfide and cuprous oxide is detected in the sulfide-contaminated solution. This finding is believed to account for the observed distinction between the corrosion behavior of NAB in the two solutions. Full article

(This article belongs to the Section Corrosion, Wear and Erosion)

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10 pages, 6646 KiB

Open AccessEditor’s ChoiceArticle

3D Multilayered Metamaterials with High Plasmonic Hotspot Density for Surface—Enhanced Raman Spectroscopy

by Jun Chen, Chai Zhang, Feng Tang, Xin Ye, Yubin Zhang, Jingjun Wu, Kaixuan Wang, Ning Zhang and Liming Yang

Coatings 2023, 13(5), 844; https://doi.org/10.3390/coatings13050844 - 28 Apr 2023

Viewed by 1373

Abstract

Three-dimensional (3D) plasmonic metamaterials have become a trend in the application of nanophotonic devices. In this paper, a convenient and inexpensive method for the design of 3D multilayer plasmonic metamaterials is constructed using a one-step self-shielded reactive-ion-etching process (OSRP) and a thermal evaporation [...] Read more.

Three-dimensional (3D) plasmonic metamaterials have become a trend in the application of nanophotonic devices. In this paper, a convenient and inexpensive method for the design of 3D multilayer plasmonic metamaterials is constructed using a one-step self-shielded reactive-ion-etching process (OSRP) and a thermal evaporation system, which provides an efficient and low-cost method for the preparation of surface-enhanced Raman spectroscopy (SERS) substrates. The near-field enhancement of the 3D plasmonic metamaterials provides highly efficient electromagnetic resonance, and highly sensitive and uniform SERS sensing capabilities. The SERS detection results of rhodamine B (Rh. B) and rhodamine 6G (R6G) on this substrate show that the detection limit could reach 10^–13 mol/L, and the signal could give expression to excellent uniform stability. The results show that high sensitivity and high robustness SERS substrates can be prepared with high efficiency and low cost. Full article

(This article belongs to the Special Issue Micro-Nano Optics and Its Applications)

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19 pages, 17846 KiB

Open AccessEditor’s ChoiceArticle

Effect of Scanning Strategies on Anisotropy of YCF104 Alloy Mechanical Properties by Laser Cladding

by Yu Zhao, Wenkai Shi, Liaoyuan Chen, Wenzheng Wu and Tianbiao Yu

Coatings 2023, 13(5), 842; https://doi.org/10.3390/coatings13050842 - 28 Apr 2023

Cited by 1 | Viewed by 1708

Abstract

YCF104 alloy specimens were fabricated by laser cladding on #45 steel following three different scanning strategies. The microstructure, phase composition, friction coefficient, microhardness, tensile strength, and compressive strength of the specimens formed by different scanning strategies were investigated. The results show that the [...] Read more.

YCF104 alloy specimens were fabricated by laser cladding on #45 steel following three different scanning strategies. The microstructure, phase composition, friction coefficient, microhardness, tensile strength, and compressive strength of the specimens formed by different scanning strategies were investigated. The results show that the uniformity of laser remelting of solidified layers improved the uniformity of microstructure and refined the grains. The strengthening effect of the Fe–Cr/Mo solid solution was primarily responsible for the high strength. YCF104 cladding specimens exhibit brittle failure, and with the change of metallurgical bonding form in the overlap area, the compressive strength (the maximum value is 3235 MPa) and the tensile strength (specimen via strategy 3 is 527.44 MPa), there appears significant anisotropy. With the improvement of the uniformity of temperature distribution, the friction coefficient as well as the microhardness decreased when the GCr15 was used as the friction pair. The mechanical anisotropy of the coating is related to both the microstructure and metallurgical bonding strength in the overlap area. Full article

(This article belongs to the Special Issue Laser Cladding Coatings: Microstructure, Properties, and Applications)

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17 pages, 11521 KiB

Open AccessEditor’s ChoiceArticle

Microstructure and Properties of Direct Laser-Deposited CeO₂-Modified Cobalt-Based Composite Coatings

by Yan Liu, Hui Han, Tao Ding, Dengwen Hu, Zhenlin Zhang, Hang Lv and Hui Chen

Coatings 2023, 13(5), 834; https://doi.org/10.3390/coatings13050834 - 26 Apr 2023

Viewed by 1547

Abstract

The seawater circulation pump is a significant piece of equipment in coastal nuclear power plants that is susceptible to erosion and corrosion in the seawater. In this work, CeO₂-modified cobalt-based composite coatings were prepared on the surface of martensitic stainless steel [...] Read more.

The seawater circulation pump is a significant piece of equipment in coastal nuclear power plants that is susceptible to erosion and corrosion in the seawater. In this work, CeO₂-modified cobalt-based composite coatings were prepared on the surface of martensitic stainless steel by direct laser deposition. The effect of CeO₂ on the phase composition, microstructure, microhardness, corrosion resistance, and erosion properties of the cobalt-based composite coatings was systematically investigated. While the addition of CeO₂ did not affect the phase composition of the coatings that comprised γ-Co, γ-Ni, M₇C₃, and M₂₃C₆ (M = Cr, W, Fe) metallic carbides, the eutectic organization showed an obvious phenomenon of contiguous aggregation. Microscopic pores were found in the coatings with 2 wt.% CeO₂, and the number of pores increased with the increase in CeO₂ content. Despite the higher self-corrosion potential (−0.27668 V) of cobalt-based alloy coating compared to the substrate (−0.37019 V), indicating enhanced corrosion resistance, the difference in self-corrosion potential among coatings with varying CeO₂ addition amounts is small (0.027 V), and the corrosion current densities are within one order of magnitude (10⁻⁸ A/cm²). These findings suggest that the addition of CeO₂ has no significant impact on the coating’s corrosion resistance. Full article

(This article belongs to the Section Laser Coatings)

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18 pages, 8616 KiB

Open AccessEditor’s ChoiceArticle

Synthesis of CaCO₃-Based Hyperdispersants and Their Application in Aqueous Coatings

by Jue Bai and Yu Li

Coatings 2023, 13(5), 819; https://doi.org/10.3390/coatings13050819 - 23 Apr 2023

Cited by 1 | Viewed by 2225

Abstract

As an essential pigment particle in white water-based coatings, light calcium carbonate (CaCO₃) is difficult to disperse in water-based systems. The hard-to-disperse particles agglomerate, causing the viscosity of the coating to rise, which in turn affects the quality of the coating. [...] Read more.

As an essential pigment particle in white water-based coatings, light calcium carbonate (CaCO₃) is difficult to disperse in water-based systems. The hard-to-disperse particles agglomerate, causing the viscosity of the coating to rise, which in turn affects the quality of the coating. Therefore, in order to obtain efficient dispersion, the hyperdispersant SSS–MPEGA–DMAEA (SMD) has been prepared in this study using sodium styrene sulfonate (SSS), polyethylene glycol monomethyl ether acrylate (MPEGA), and dimethylaminoethyl acrylate (DMAEA) as monomers through aqueous solution polymerization. Firstly, we utilized the central composite design method to conduct mathematical modeling of the monomer ratios so as to optimize the dispersion performance of the hyperdispersants. Secondly, the structural characteristics and molecular weight distribution of SMD were characterized by ¹H NMR spectroscopy and GPC. Then, the effect of SMD on the dispersion of the CaCO₃ slurry was investigated through particle size distribution and TEM measurements. Finally, we applied the SMD in aqueous white coatings and tested the surface properties of the paint film by SEM as well as the stability of the paint film. The results showed that SMD can significantly reduce the viscosity and particle size of the CaCO₃ slurry. The waterborne coatings prepared by SMD had good storage stability and corrosion resistance, so the materials owned broad application prospects. Full article

(This article belongs to the Section Functional Polymer Coatings and Films)

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24 pages, 3314 KiB

Open AccessEditor’s ChoiceArticle

Influence of Drop Viscosity and Surface Wettability on Impact Outcomes

by Ghokulla Haran Krishnan, Kevin Fletcher and Eric Loth

Coatings 2023, 13(5), 817; https://doi.org/10.3390/coatings13050817 - 23 Apr 2023

Cited by 5 | Viewed by 2966

Abstract

To understand the effects of liquid viscosity and surface wettability on the outcomes for a drop impacting perpendicularly on a dry, clean surface at a normal temperature and pressure, experiments were conducted for a wide variety of droplets and substrate surfaces. These experiments [...] Read more.

To understand the effects of liquid viscosity and surface wettability on the outcomes for a drop impacting perpendicularly on a dry, clean surface at a normal temperature and pressure, experiments were conducted for a wide variety of droplets and substrate surfaces. These experiments included a range of receding contact angles (from ~18° to ~150°) and liquid viscosities (from 1 cp to 45 cp); the broadest such combination is yet published. The surface wettabilities were quantitatively characterized using a new set of definitions: superphillic (θ_rec < 30°), phillic (30° < θ_rec < 90°), phobic (90° < θ_rec < 150°), and superphobic (θ_rec > 150°). Six different outcome regimes were found (including a new beaded deposition outcome) as a function of Ohnesorge number, Weber number, and the cosine of the receding contact angle. The beaded deposition is a hybrid of the well-known splash and deposition outcomes. The critical Weber number that separates the outcome boundaries was found to be significantly influenced by both the Ohnesorge numbers and the receding contact angle. In particular, there is a consistent reduction in the critical Weber number from superphilic to philic to neutral wettability conditions. Interestingly, this same decreasing trend line continues from neutral to phobic to superphobic conditions, but instead, it separates the regimes of deposition and bouncing. At higher Weber numbers, an additional boundary regime was found between splashing and bounce, which also decreased as the surface wettability decreased. This same type of trend was seen for several Ohnesorge numbers, indicating that wetting characterization should be based on the contact angles for the combination of the droplet liquid and the surface. In addition, a new regime map for droplet rebound on superphobic surfaces was obtained from the present and previous results indicating (for the first time) that the total rebound generally occurs for Weber numbers between 2.2 and 32 with Ohnesorge numbers less than 0.17. Additional studies are recommended to explore an even broader range of test conditions (especially intermediate wettability conditions), the separate influence of advancing and/or hysteresis contact angles, and to include the effects of the inclination angle, gas pressure, and heat transfer. Full article

(This article belongs to the Special Issue Liquid–Fluid Interfaces and Dynamics)

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14 pages, 2288 KiB

Open AccessEditor’s ChoiceArticle

Linear and Nonlinear Optical Properties of Iridium Nanoparticles Grown via Atomic Layer Deposition

by Paul Schmitt, Pallabi Paul, Weiwei Li, Zilong Wang, Christin David, Navid Daryakar, Kevin Hanemann, Nadja Felde, Anne-Sophie Munser, Matthias F. Kling, Sven Schröder, Andreas Tünnermann and Adriana Szeghalmi

Coatings 2023, 13(4), 787; https://doi.org/10.3390/coatings13040787 - 18 Apr 2023

Cited by 3 | Viewed by 2596

Abstract

Nonlinear optical phenomena enable novel photonic and optoelectronic applications. Especially, metallic nanoparticles and thin films with nonlinear optical properties offer the potential for micro-optical system integration. For this purpose, new nonlinear materials need to be continuously identified, investigated, and utilized for nonlinear optical [...] Read more.

Nonlinear optical phenomena enable novel photonic and optoelectronic applications. Especially, metallic nanoparticles and thin films with nonlinear optical properties offer the potential for micro-optical system integration. For this purpose, new nonlinear materials need to be continuously identified, investigated, and utilized for nonlinear optical applications. While noble-metal nanoparticles, nanostructures, and thin films of silver and gold have been widely studied, iridium (Ir) nanoparticles and ultrathin films have not been investigated for nonlinear optical applications yet. Here, we present a combined theoretical and experimental study on the linear and nonlinear optical properties of iridium nanoparticles deposited via atomic layer deposition (ALD). Linear optical constants, such as the effective refractive index and extinction coefficient, were evaluated at different growth stages of nanoparticle formation. Both linear and nonlinear optical properties of these Ir ALD coatings were calculated theoretically using the Maxwell Garnett theory. The third-order susceptibility of iridium nanoparticle samples was experimentally investigated using the z-scan technique. According to the experiment, for an Ir ALD coating with 45 cycles resulting in iridium nanoparticles, the experimentally determined nonlinear third-order susceptibility is about χ_Ir⁽³⁾ = (2.4 − i2.1) × 10⁻¹⁷ m²/V² at the fundamental wavelength of 700 nm. The theory fitted to the experimental results predicts a 5 × 10⁶-fold increase around 230 nm. This strong increase is due to the proximity to the Mie resonance of iridium nanoparticles. Full article

(This article belongs to the Special Issue Optical Properties of Crystals and Thin Films)

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13 pages, 3371 KiB

Open AccessEditor’s ChoiceArticle

Bacterial Detection and Differentiation of Staphylococcus aureus and Escherichia coli Utilizing Long-Period Fiber Gratings Functionalized with Nanoporous Coated Structures

by Shuyue He, Jue Wang, Fan Yang, Tzu-Lan Chang, Ziyu Tang, Kai Liu, Shuli Liu, Fei Tian, Jun-Feng Liang, Henry Du and Yi Liu

Coatings 2023, 13(4), 778; https://doi.org/10.3390/coatings13040778 - 17 Apr 2023

Cited by 5 | Viewed by 1844

Abstract

A biosensor utilizing long-period fiber gratings (LPFG) functionalized with nanoporous coated structures was developed for the rapid detection of Staphylococcus aureus (S. aureus) bacteria. The nanoporous structure coatings on the LPFG surface facilitated specific adhesion and interaction with S. aureus, [...] Read more.

A biosensor utilizing long-period fiber gratings (LPFG) functionalized with nanoporous coated structures was developed for the rapid detection of Staphylococcus aureus (S. aureus) bacteria. The nanoporous structure coatings on the LPFG surface facilitated specific adhesion and interaction with S. aureus, resulting in an instantaneous shift in the resonance wavelength (RW) in the transmission spectrum of the LPFG. The LPFG with nanoporous polyelectrolyte coatings exhibited an approximately seven-fold RW shift compared to the bare LPFG under the optimal experiment conditions. By tracking the RW shifts, we were able to monitor the real-time S. aureus adhesion to study the interaction process in detail. The bacterial differentiation and S. aureus specificity of the method was confirmed through a series of studies using Escherichia coli (E. coli). This nanoporous structure-enabled LPFG-based biosensor scheme holds significant promise for rapid, reliable, and low-cost detection of S. aureus for biomedical applications. Full article

(This article belongs to the Special Issue New Advance in Nanoparticles, Fiber, and Coatings)

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21 pages, 2587 KiB

Open AccessEditor’s ChoiceReview

Thermal Barrier Coatings for High-Temperature Performance of Nickel-Based Superalloys: A Synthetic Review

by Izabela Barwinska, Mateusz Kopec, Dominik Kukla, Cezary Senderowski and Zbigniew L. Kowalewski

Coatings 2023, 13(4), 769; https://doi.org/10.3390/coatings13040769 - 14 Apr 2023

Cited by 23 | Viewed by 6384

Abstract

With the rising demands of industry to increase the working temperature of gas turbine blades and internal combustion engines, thermal barrier coatings (TBC) were found to be an effective way to further enhance the lifetime of aero components through the improvement of mechanical [...] Read more.

With the rising demands of industry to increase the working temperature of gas turbine blades and internal combustion engines, thermal barrier coatings (TBC) were found to be an effective way to further enhance the lifetime of aero components through the improvement of mechanical properties and oxidation-resistance. Thus, this paper aims to review coating technologies with special emphasis on plasma-sprayed thermal barrier coatings (PS), and those produced by physical vapor deposition (PVD) and chemical vapor deposition (CVD) methods. Each technology was assessed in terms of its effectiveness to enhance the mechanical response and oxidation resistance of nickel-based parts working at high temperature. The effect of coating technology on mechanical strength, hardness, fatigue and creep of nickel alloys was discussed to reveal the potential candidates for future applications in aggressive environments. Full article

(This article belongs to the Section Ceramic Coatings and Engineering Technology)

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22 pages, 6668 KiB

Open AccessEditor’s ChoiceReview

Biobased Anti-Adhesive Marine Coatings from Polyhydroxyalkanoates and Polysaccharides

by Fabienne Faÿ, Marie Champion, Alexandra Guennec, Xavier Moppert, Christelle Simon-Colin and Mathieu Elie

Coatings 2023, 13(4), 766; https://doi.org/10.3390/coatings13040766 - 13 Apr 2023

Cited by 6 | Viewed by 3233

Abstract

Due to environmental regulations, antifouling marine coatings must be gradually replaced by biocide-free coatings. Marine organisms weakly adhere to fouling release coatings, presenting a low surface free energy and a high elasticity, so they can be readily removed by the sheer force of [...] Read more.

Due to environmental regulations, antifouling marine coatings must be gradually replaced by biocide-free coatings. Marine organisms weakly adhere to fouling release coatings, presenting a low surface free energy and a high elasticity, so they can be readily removed by the sheer force of water. Currently, these materials are mainly composed of petrochemical polymers, such as silicone or fluoropolymers, with hydrophilic polymers as additives. However, following the ever-increasing environmental concerns, the research on new, alternative, eco-friendly coatings is oriented towards the use of biobased polymers from renewable resources. Two main families have been studied: polyhydroxyalkanoates (PHAs) and polysaccharides. PHAs are produced by bacteria in stressful conditions, while polysaccharides are extracted from plants, animals, or micro-organisms such as bacteria, in which case they are called exopolysaccharides (EPS). Since the use of these polymers is a non-toxic approach to controlling fouling colonization, this review provides an overview of these biobased polymers for their applications in new anti-adhesive marine coatings. Full article

(This article belongs to the Special Issue Environmentally-Friendly Coatings towards Biofouling Control and Microbiologically Influenced Corrosion (MIC) Inhibition)

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17 pages, 4240 KiB

Open AccessEditor’s ChoiceArticle

Novel Hybrid Organic–Inorganic Polymeric Coatings Containing Phosphonium or Acidic Groups for Improving Flame Retardancy of Wood

by Vasilis Koukoumtzis, Georgia C. Lainioti, George A. Voyiatzis and Joannis K. Kallitsis

Coatings 2023, 13(4), 754; https://doi.org/10.3390/coatings13040754 - 9 Apr 2023

Cited by 2 | Viewed by 1765

Abstract

Flame-retardant polymeric coatings with high limiting oxygen index (LOI) were prepared by combining inorganic mineral huntite (H5) and polymeric additives synthesized in the present work into a polymeric formulation. In order to improve the dispersion of the Mg- (and Ca)-based H5 particles, additives [...] Read more.

Flame-retardant polymeric coatings with high limiting oxygen index (LOI) were prepared by combining inorganic mineral huntite (H5) and polymeric additives synthesized in the present work into a polymeric formulation. In order to improve the dispersion of the Mg- (and Ca)-based H5 particles, additives containing phosphonium and acidic groups were employed to homogenize the inorganic fillers into the polymer matrix. Specific blend combinations of the commercial matrix Ecrovin^® LV 340 eco with huntite and the additives poly(benzyltriphenylphosphonium-co-4-styrene sulfonic acid) P(SSH-co-SSBTPB60) and poly(hexadecyltributylphosphonium-co-4-styrene sulfonic acid) P(SSH-co-SSTBHDPB80), combining acidic and phosphonium groups, led to LOI values of 34.5% and 33.5%, respectively. The novel flame-retardant polymeric coatings inhibited the combustion of the coated wood substrates, which is attributed to the combination of acidic groups that promote the dispersion of inorganic filler in the polymer matrix and phosphonium groups that support the increase in LOI values. Full article

(This article belongs to the Section Functional Polymer Coatings and Films)

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18 pages, 4683 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Comparison of the Mechanical Properties and Corrosion Resistance of the Cr-CrN, Ti-TiN, Zr-ZrN, and Mo-MoN Coatings

by He Tao, Valery Zhylinski, Alexey Vereschaka, Vadzim Chayeuski, Huo Yuanming, Filipp Milovich, Catherine Sotova, Anton Seleznev and Olga Salychits

Coatings 2023, 13(4), 750; https://doi.org/10.3390/coatings13040750 - 8 Apr 2023

Cited by 8 | Viewed by 2409

Abstract

In this work, the mechanical properties and corrosion resistance of Cr-CrN, Ti-TiN, Zr-ZrN, and Mo-MoN coatings deposited by the physical vapor deposition (PVD) method on Ti-6Al-4V alloy were compared. The phase composition of the coatings, their hardness and fracture resistance in scratch tests [...] Read more.

In this work, the mechanical properties and corrosion resistance of Cr-CrN, Ti-TiN, Zr-ZrN, and Mo-MoN coatings deposited by the physical vapor deposition (PVD) method on Ti-6Al-4V alloy were compared. The phase composition of the coatings, their hardness and fracture resistance in scratch tests were determined, and their structural characteristics were also studied using a scanning electron microscope (SEM) and a transmission electron microscope (TEM). The diffraction spectra were made using an automatic X-ray diffractometer. The value of the adhesive component of the friction coefficient f_adh of the pair “coated and uncoated Ti-6Al-4V alloy” was investigated in the temperature range of 20–900 °C. The lowest value of f_adh was detected for the Zr-ZrN coating at temperatures below 400 °C, while for the Mo-MoN coating it was observed at temperatures above 700 °C. The polarization curves of the coated and uncoated samples were performed in a 3% aqueous NaCl solution. The level of corrosion of the Ti-6Al-4V alloy samples with Cr-CrN, Ti-TiN, Zr-ZrN, and Mo-MoN coatings was evaluated using the Tafel extrapolation method, the iteration method, and the polarization resistance method. The results obtained with these methods indicate that the Zr-ZrN coated sample has the best corrosion resistance in the 3 wt.% NaCl solution, with a corrosion current density of 0.123 μA/cm². Full article

(This article belongs to the Special Issue Corrosion Effects and Smart Coatings of Corrosion Protection)

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21 pages, 8544 KiB

Open AccessEditor’s ChoiceArticle

Thermoelectric and Structural Properties of Transparent Sb-Doped ZnO Thin Films Sputtered in a Confocal Geometry

by Helder Filipe Faria, Joana Margarida Ribeiro, Torben Boll and Carlos José Tavares

Coatings 2023, 13(4), 735; https://doi.org/10.3390/coatings13040735 - 4 Apr 2023

Cited by 6 | Viewed by 2522

Abstract

This study focuses on understanding the influence of low Sb doping on ZnO’s electrical, optical, and thermoelectrical properties, while also studying its structural and morphological parameters. For this, several ZnO films with varying Sb target current densities, in the range of 0–0.27 mA/cm [...] Read more.

This study focuses on understanding the influence of low Sb doping on ZnO’s electrical, optical, and thermoelectrical properties, while also studying its structural and morphological parameters. For this, several ZnO films with varying Sb target current densities, in the range of 0–0.27 mA/cm², were produced by DC magnetron sputtering in a confocal geometry. As a result, thin ZnO:Sb films with an average transparency in the visible region greater than 80% are obtained, revealing for optimized conditions an absolute Seebeck coefficient of 100 μV/K and a respective power factor of 1.1 mW∙m⁻¹∙K⁻² at 300 K, effectively modifying the electrical, optical, and thermoelectrical properties of the material and ensuring its suitability for heat harvesting applications. From atom probe tomography experiments, a larger Zn content is registered at triple junctions of the grain boundary, which matches the approximately 25 nm crystallite grain size derived from the X-ray diffraction analysis. Full article

(This article belongs to the Collection Feature Papers of Coatings for Energy Applications)

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20 pages, 7211 KiB

Open AccessEditor’s ChoiceArticle

Impact of High Concentrations of Cellulose Fibers on the Morphology, Durability and Protective Properties of Wood Paint

by Massimo Calovi and Stefano Rossi

Coatings 2023, 13(4), 721; https://doi.org/10.3390/coatings13040721 - 31 Mar 2023

Cited by 13 | Viewed by 1901

Abstract

This work aims to reveal the effect of a high amount of cellulose fibers on the durability and protective behavior of a bio-based wood paint. The influence of the filler on the morphology of the coatings was investigated by scanning electron microscopy observations, [...] Read more.

This work aims to reveal the effect of a high amount of cellulose fibers on the durability and protective behavior of a bio-based wood paint. The influence of the filler on the morphology of the coatings was investigated by scanning electron microscopy observations, while the durability of the paint was evaluated by exposing the samples to UV-B radiation and continuous thermal shocks. Infrared spectroscopy analysis, colorimetric inspections, adhesion tests and scanning electron microscope observations were employed to assess the role of the high concentrations of fillers in affecting the resilience of the acrylic matrix. Moreover, the impact of the filler on the barrier performance of the coatings was estimated using a liquid resistance test and a water uptake test. Finally, the mechanical properties of hardness and abrasion resistance of the layers were evaluated by means of the Buchholz Hardness Indentation test and the Scrub test. Ultimately, this study demonstrates the pros and cons of using large amounts of cellulose fibers as filler in wood paint: the work warns against the excessive use of these fibers, which need a threshold limit so as not to significantly change the coating’s structure and thereby weaken its protective properties. Full article

(This article belongs to the Special Issue Recent Advances in Wood Coatings)

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13 pages, 4614 KiB

Open AccessEditor’s ChoiceArticle

Atmospheric Plasma and UV Polymerisation for Developing Sustainable Anti-Adhesive Polyethylene Terephthalate (PET) Surfaces

by Tugce Caykara, Sara Fernandes, Adelaide Braga, Joana Rodrigues, Ligia Raquel Rodrigues and Carla Joana Silva

Coatings 2023, 13(4), 715; https://doi.org/10.3390/coatings13040715 - 31 Mar 2023

Cited by 3 | Viewed by 1886

Abstract

Enhancing the hydrophilicity of polymeric materials is an important step for achieving anti-adhesiveness. Thus, in this study, atmospheric plasma as a pre-treatment was combined with a UV grafting process to obtain a durable surface modification on polyethylene terephthalate (PET). The most promising conditions [...] Read more.

Enhancing the hydrophilicity of polymeric materials is an important step for achieving anti-adhesiveness. Thus, in this study, atmospheric plasma as a pre-treatment was combined with a UV grafting process to obtain a durable surface modification on polyethylene terephthalate (PET). The most promising conditions for the atmospheric plasma process were found to be 15 kW power and 4 m/min speed, leading to a contact angle reduction from 70 ± 6° to approximately 30°. However, it was observed that these values increased over time due to the ageing and washing of the PET surface, ultimately causing it to recover its initial contact angle. Therefore, the plasma-pre-treated PET samples were further modified through a UV grafting process using sodium acrylate (NaAc) and 3-sulfopropyl acrylate potassium salts (KAc). The grafted acrylate PET samples exhibited contact angles of 8 ± 3° and 28 ± 13° for NaAc and KAc, respectively, while showing durability in ageing and washing tests. The dry film thicknesses for both samples were found to be 28 ± 2 μm. Finally, the anti-adhesive properties of the NaAc- and KAc-treated surfaces were evaluated using an Escherichia coli expressing YadA, an adhesive protein from Yersinia. The modified PET surfaces were highly effective in reducing bacterial adhesion by more than 90%. Full article

(This article belongs to the Special Issue Functional Coatings for Textile Applications)

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33 pages, 35756 KiB

Open AccessEditor’s ChoiceArticle

The Influence of Galvanizing on the Surface Quality and Part Precision of S235J0 Alloy Machined by Turning

by Sandor Ravai-Nagy, Aurel Mihail Titu and Alina Bianca Pop

Coatings 2023, 13(4), 701; https://doi.org/10.3390/coatings13040701 - 30 Mar 2023

Cited by 1 | Viewed by 2196

Abstract

This scientific paper aims to determine the optimal economic roughness of galvanized surfaces by studying the influence of turning surface roughness on the quality of galvanizing. The thickness of the zinc layer, its corrosion resistance, and the precision of the galvanized parts were [...] Read more.

This scientific paper aims to determine the optimal economic roughness of galvanized surfaces by studying the influence of turning surface roughness on the quality of galvanizing. The thickness of the zinc layer, its corrosion resistance, and the precision of the galvanized parts were also examined. S235J0 steel samples were processed using a turning operation to obtain different roughness values. Three galvanizing technologies, galvanic galvanizing, hot dip galvanizing, and hot dip galvanizing with centrifugation, were used in the experiments. The surface evolution from turning to zinc layer deposition was monitored, and parts were subjected to salt spray corrosion resistance testing. Statistical analysis confirmed the stability of the technologies used and the accuracy of the experimental data. Optimal roughness ranges for galvanizing were determined based on the quality of the surface before galvanizing and the galvanizing technology used. The findings show that avoiding small roughness values leads to savings in the machining phases. From the dimensional accuracy perspective, the parts have smaller dimensions after galvanizing, and the dimensional accuracy decreases. The study confirms that steel parts are protected from corrosion, and degradation of the zinc layer is more advanced in sections with less roughness. The optimal surface roughness values before galvanizing were determined to be Ra < 3.657 m in the case of HDG, Ra < 3.344 m in the case of HDG+C, and Ra > 2.928 μm in the case of ZP. The conclusions drawn from this study introduce new directions of research. Full article

(This article belongs to the Special Issue Surface Modification of Magnesium, Aluminum Alloys, and Steel)

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15 pages, 5093 KiB

Open AccessEditor’s ChoiceArticle

Multiscale Wear Simulation in Textured, Lubricated Contacts

by Michael Maier, Michael Pusterhofer and Florian Grün

Coatings 2023, 13(4), 697; https://doi.org/10.3390/coatings13040697 - 29 Mar 2023

Cited by 4 | Viewed by 2105

Abstract

Specific surface textures may reduce the friction and increase the lifting forces in lubricated contacts. For the detrimental operating condition of mixed friction, wear is induced by the solid contact. In this study, a methodology for wear calculation in textured, lubricated contacts is [...] Read more.

Specific surface textures may reduce the friction and increase the lifting forces in lubricated contacts. For the detrimental operating condition of mixed friction, wear is induced by the solid contact. In this study, a methodology for wear calculation in textured, lubricated contacts is presented that considers the wear-induced surface topography evolution. Based on the Reynolds differential equation, the mass-conserving cavitation model according to Jakobsson, Floberg, and Olsson (JFO), a wear-dependent asperity contact pressure curve and the wear equation according to Archard, wear in a wedge-shaped, textured lubrication gap was calculated. The results show the wear behavior of textured lubrication gaps. Based on the wear simulations, the tribological behavior of the textured surfaces compared to smooth surfaces is discussed. It is evident that textures, which improve the tribological performance in the hydrodynamic lubrication regime, are not necessarily associated with low wear values in a lubrication condition in the mixed friction regime. The analysis of the wear-dependent parameters initially showed a ‘recovery’ of the tribological system with increasing wear until the performance decreased again after a specific reversal point. This behavior is attributed to the relative position of the surface textures in the lubrication gap. Full article

(This article belongs to the Special Issue Friction, Wear, Lubrication and Mechanics of Surfaces and Interfaces)

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12 pages, 5384 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Thermoelectric and Structural Properties of Sputtered AZO Thin Films with Varying Al Doping Ratios

by Muhammad Isram, Riccardo Magrin Maffei, Valeria Demontis, Leonardo Martini, Stiven Forti, Camilla Coletti, Vittorio Bellani, Andrea Mescola, Guido Paolicelli, Alberto Rota, Stefania Benedetti, Alessandro di Bona, Joana M. Ribeiro, Carlos J. Tavares and Francesco Rossella

Coatings 2023, 13(4), 691; https://doi.org/10.3390/coatings13040691 - 28 Mar 2023

Cited by 3 | Viewed by 2366

Abstract

Nanomaterials can be game-changers in the arena of sustainable energy production because they may enable highly efficient thermoelectric energy conversion and harvesting. For this purpose, doped thin film oxides have been proven to be promising systems for achieving high thermoelectric performances. In this [...] Read more.

Nanomaterials can be game-changers in the arena of sustainable energy production because they may enable highly efficient thermoelectric energy conversion and harvesting. For this purpose, doped thin film oxides have been proven to be promising systems for achieving high thermoelectric performances. In this work, the design, realization, and experimental investigation of the thermoelectric properties exhibited by a set of five Al:ZnO thin films with thicknesses of 300 nm and Al doping levels ranging from 2 to 8 at.% are described. Using a multi-technique approach, the main structural and morphological features of the grown thin films are addressed, as well as the electrical and thermoelectrical transport properties. The results show that the samples exhibited a Seebeck coefficient absolute value in the range of 22–33 μV/K, assuming their maximum doping level was 8 at.%, while the samples’ resistivity was decreased below 2 × 10⁻³ Ohm·cm with a doping level of 3 at.%. The findings shine light on the perspectives of the applications of the metal ZnO thin film technology for thermoelectrics. Full article

(This article belongs to the Special Issue Thermoelectric Thin Films for Thermal Energy Harvesting)

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11 pages, 4272 KiB

Open AccessEditor’s ChoiceArticle

Inkjet Printing of High Aspect Ratio Silver Lines via Laser-Induced Selective Surface Wetting Technique

by Iseok Sim, Seongju Park, Kwon-Yong Shin, Chanwoo Yang, Heuiseok Kang, Jun Young Hwang and Seung-Jae Moon

Coatings 2023, 13(4), 683; https://doi.org/10.3390/coatings13040683 - 27 Mar 2023

Cited by 4 | Viewed by 2240

Abstract

The field of printed electronics for highly integrated circuits and energy devices demands very fine and highly conductive electric interconnections. In this study, conductive lines having a high cross-sectional aspect ratio were printed via the inkjet printing of Ag nanoparticle inks assisted by [...] Read more.

The field of printed electronics for highly integrated circuits and energy devices demands very fine and highly conductive electric interconnections. In this study, conductive lines having a high cross-sectional aspect ratio were printed via the inkjet printing of Ag nanoparticle inks assisted by a laser-induced selective surface wetting technique: a hydrophobic layer of self-assembled monolayer-treated ZnO nanorods was coated on a glass substrate and selectively ablated by a laser to form micro-channels for the inkjet, whose surface energy changed from 36.3 mJ/m² to 51.5 mJ/m² before and after the laser irradiation. With the varying width of the laser-ablated channels and pitch of jetted ink drops, the 3D shapes of the printed silver lines were measured to investigate their effects on the widths, heights, and uniformities of the printed patterns. The results showed that the present technique realized a uniform line of 35 μm width and 0.46 μm average thickness, having an aspect ratio of 0.013, which is 7.6 times higher than that printed on bare glass. Full article

(This article belongs to the Special Issue Printed Functional Thin Films for Electronic, Optoelectronic and Sensing Applications)

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19 pages, 5421 KiB

Open AccessEditor’s ChoiceArticle

The Effect of Curing Temperature and Thickness of Polybutyl Methacrylate Siloxane Coatings on the Corrosion Protection of Structural Steel S355

by Damir Hamulić, Gregor Medoš, Dorota Korte, Peter Rodič and Ingrid Milošev

Coatings 2023, 13(4), 675; https://doi.org/10.3390/coatings13040675 - 26 Mar 2023

Cited by 4 | Viewed by 1994

Abstract

This study aimed to determine the effects of coating thickness and curing temperature on the properties of a polybutyl methacrylate-siloxane coating deposited on structural steel S355. First, the thermal properties of the sol as a function of temperature were investigated using thermogravimetric analysis [...] Read more.

This study aimed to determine the effects of coating thickness and curing temperature on the properties of a polybutyl methacrylate-siloxane coating deposited on structural steel S355. First, the thermal properties of the sol as a function of temperature were investigated using thermogravimetric analysis coupled with mass spectrometry and differential scanning calorimetry. After coating deposition on structural steel S355 using a dip-coating process, the coating composition and porosity were evaluated using Fourier transform infrared spectroscopy and photothermal beam deflection spectroscopy. In the second part, coating thickness, topography, and corrosion properties were studied as functions of withdrawal rate during deposition. The corrosion properties of variously prepared coatings were evaluated using electrochemical impedance measurements in 3.5 wt.% NaCl and salt spray testing according to the ASTM B117 standard. An elevated curing temperature (at 150 °C) of the polybutyl methacrylate siloxane sol-gel coating impairs greater crosslinking and lower porosity, while the optimal thickness of 4 μm is achieved with the appropriate withdrawal rate to obtain a homogeneous, defect-free surface. Under these optimal conditions, the protection of structural steel against corrosion in a chloride environment lasting for more than 6 months can be achieved. Full article

(This article belongs to the Special Issue New Developments of Protective Coatings, Organic Polymers, and Surface Analysis)

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17 pages, 11204 KiB

Open AccessEditor’s ChoiceArticle

Characterization and Control of Residual Stress in Plasma-Sprayed Silicon Coatings on SiC/SiC Composites

by Mengqiu Guo, Yongjing Cui, Changliang Wang, Jian Jiao, Xiaofang Bi and Chunhu Tao

Coatings 2023, 13(4), 674; https://doi.org/10.3390/coatings13040674 - 26 Mar 2023

Cited by 5 | Viewed by 1911

Abstract

In order to reveal the relationship between residual stress in Si layers of SiC/SiC composites and the different parameters used in their preparation, the residual stress of the coating surface was tested using X-ray sin²ψ technology and laser Raman spectroscopy. Then, [...] Read more.

In order to reveal the relationship between residual stress in Si layers of SiC/SiC composites and the different parameters used in their preparation, the residual stress of the coating surface was tested using X-ray sin²ψ technology and laser Raman spectroscopy. Then, the Raman shift–stress coefficient (P) and the Raman shift with free stress (ω₀) were calculated as −201.41 MPa/cm⁻¹ and 520.591 cm⁻¹ via linear fitting with the least squares method. The results showed that all the as-sprayed Si coatings exhibited tensile stress on the surface, ranging from 53.5 to 65.9 MPa. The parameters of the spraying distance and second gas (H₂) flow rate were considered to be the most important for controlling the residual stress on the coating surface. Additionally, the surface tensile stress of the Si layers could be eliminated and even changed into compressive stress by annealing above 800 °C. Furthermore, the residual stress distribution in the cross-section of the Si layers was evaluated using laser Raman spectroscopy. Additionally, the particle characteristics, such as in-flight velocity and temperature, were investigated using a diagnostic system. The results of this research contribute to increasing the understanding and control of residual stress in APS Si bond layers. Full article

(This article belongs to the Special Issue Thermal Spray Coatings)

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16 pages, 5935 KiB

Open AccessEditor’s ChoiceArticle

Tailored Biobased Resins from Acrylated Vegetable Oils for Application in Wood Coatings

by Sabine Briede, Oskars Platnieks, Anda Barkane, Igors Sivacovs, Armands Leitans, Janis Lungevics and Sergejs Gaidukovs

Coatings 2023, 13(3), 657; https://doi.org/10.3390/coatings13030657 - 20 Mar 2023

Cited by 4 | Viewed by 3018

Abstract

The modern coating market is dominated by acrylic, polyurethane, and polyester polymer resins produced from unsustainable fossil resources. Herein, we propose the preparation of resins from biobased components to produce functional and solvent-free wood coatings with enhanced performance properties. Acrylated rapeseed, linseed, and [...] Read more.

The modern coating market is dominated by acrylic, polyurethane, and polyester polymer resins produced from unsustainable fossil resources. Herein, we propose the preparation of resins from biobased components to produce functional and solvent-free wood coatings with enhanced performance properties. Acrylated rapeseed, linseed, and grapeseed oils were prepared via a one-step synthesis and used as a basis for the control of resin viscosity and fatty acid content. A combination of vegetable oil acrylates was used as a matrix and the biobased monomer propoxylated glycerol triacrylate (GPT) was selected to tailor the properties of the UV crosslinked network. During polymerization, the GPT monomer induced a two-phase microstructure as indicated by an SEM analysis. The possibility of generating a tailored microstructure in the final material was examined in this study. The addition of GPT increased the storage modulus by up to five-fold, crosslink density by up to two-fold at 20 °C, and glass transition temperature by up to 10.2 °C. Pull-off adhesion tests showed a strength of 1.21 MPa. In addition, the photo-oxidation effect on samples, i.e., aging, was assessed with microhardness, sliding friction, and optical microscopy. Coatings showed a microhardness value up to 250 MPa, while a coefficient of friction (μ) was in the range of 0.21 to 0.88. Full article

(This article belongs to the Special Issue Bio-Based and Bio-Inspired Polymers and Composites)

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14 pages, 4498 KiB

Open AccessEditor’s ChoiceArticle

Behaviour of Thermochromic Coatings under Thermal Exposure

by Zuzana Tatíčková, Jan Kudláček, Michal Zoubek and Jiří Kuchař

Coatings 2023, 13(3), 642; https://doi.org/10.3390/coatings13030642 - 18 Mar 2023

Cited by 4 | Viewed by 1874

Abstract

Interactive thermochromic coatings based on Leuco dye are most commonly used in research for building cooling applications. The coatings developed by the authors are primarily aimed at industrial applications on metal substrates, mainly for safety reasons. Thanks to a higher transition temperature associated [...] Read more.

Interactive thermochromic coatings based on Leuco dye are most commonly used in research for building cooling applications. The coatings developed by the authors are primarily aimed at industrial applications on metal substrates, mainly for safety reasons. Thanks to a higher transition temperature associated with a significant change in shade, they have the potential to prevent burns and can be used as an element of active protection in exposed areas. Interactive thermochromic materials with different base matrices and two dispersion methods have been monitored and tested over the long term to gain an overall impression of their behaviour and applicability. The monitoring of colour characteristics helps to understand the behaviour of the thermochromic pigment in different primer matrices. The values of L*, a*, and b* and the spectral curves measured by a spectrophotometer were compared. Colour differences between the cold and heated conditions were also evaluated. ΔE* values for acrylate polyol reached up to 39. For waterborne paint, they varied according to the method of dispersion—when using a saw tooth stirrer, ΔE* was 23, and when mixing with a rotor-stator device, up to 56. Similarly, for the polyurethane matrix: ΔE* went up to 39 for stirring with a saw tooth stirrer while ΔE* was 64 for the rotor-stator. From the measurement of the behaviour of the coatings during temperature exposure, it can be concluded that most of the samples show a decrease in the transition temperature. Monitoring the behaviour of coatings during cooling is important for choosing a suitable base matrix that will ensure the long-term functionality of the coating and declare the temperature range of its use for safety applications. Full article

(This article belongs to the Section Functional Polymer Coatings and Films)

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18 pages, 3309 KiB

Open AccessEditor’s ChoiceArticle

Titanium Implant Alloy Modified by Electrochemically Deposited Functional Bioactive Calcium Phosphate Coatings

by Jozefina Katić, Sara Krivačić, Željka Petrović, Dajana Mikić and Marijan Marciuš

Coatings 2023, 13(3), 640; https://doi.org/10.3390/coatings13030640 - 17 Mar 2023

Cited by 10 | Viewed by 2893

Abstract

Calcium phosphate-based (CaP) bioceramic materials are widely used in the field of bone regeneration, both in orthopaedics and in dentistry, due to their good biocompatibility, osseointegration and osteoconduction. The formation of CaP coatings on high-strength implant materials such as titanium alloys combines the [...] Read more.

Calcium phosphate-based (CaP) bioceramic materials are widely used in the field of bone regeneration, both in orthopaedics and in dentistry, due to their good biocompatibility, osseointegration and osteoconduction. The formation of CaP coatings on high-strength implant materials such as titanium alloys combines the superior mechanical properties of metals with the osteoconductive properties of CaP materials. In this work, the electrochemically assisted deposition of CaP coatings on the titanium alloy, TiAlNb, which is commonly used commercially as an implant material in orthopaedic devices, was examined. The barrier properties (electronic properties) of unmodified and CaP-modified titanium alloy were tested in situ in a simulated physiological solution, Hanks’ solution, under in vitro conditions of real implant applications using electrochemical impedance spectroscopy (EIS). The morphology and microstructure of the obtained CaP deposit were characterised by scanning electron microscopy (SEM) and chemical composition was assessed by energy dispersive X-ray spectroscopy (EDS) and attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR). The aim was to investigate the effect of calcium phosphate CaP coating on the corrosion resistance of the titanium TiAlNb alloy and to understand better the deposition process in the production of bioactive functional coatings on metallic implant materials. Full article

(This article belongs to the Special Issue Biomimetic Approaches in Coatings Synthesis)

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18 pages, 3372 KiB

Open AccessEditor’s ChoiceArticle

Direct Liquid Reactor-Injector of Nanoparticles: A Safer-by-Design Aerosol Injection for Nanocomposite Thin-Film Deposition Adapted to Various Plasma-Assisted Processes

by Guillaume Carnide, Laura Cacot, Yohan Champouret, Vincent Pozsgay, Thomas Verdier, Adèle Girardeau, Marjorie Cavarroc, Andranik Sarkissian, Anne-Françoise Mingotaud, Constantin Vahlas, Myrtil Louise Kahn, Nicolas Naudé, Luc Stafford and Richard Clergereaux

Coatings 2023, 13(3), 630; https://doi.org/10.3390/coatings13030630 - 16 Mar 2023

Cited by 3 | Viewed by 2023

Abstract

The requirements of nanocomposite thin films, having non-aggregated nanoparticles homogeneously dispersed in the matrix, have been realized using a new method of Direct Liquid Reactor-Injector (DLRI) of nanoparticles. In this approach, unlike conventional aerosol-assisted plasma deposition, the nanoparticles are synthesized before their injection [...] Read more.

The requirements of nanocomposite thin films, having non-aggregated nanoparticles homogeneously dispersed in the matrix, have been realized using a new method of Direct Liquid Reactor-Injector (DLRI) of nanoparticles. In this approach, unlike conventional aerosol-assisted plasma deposition, the nanoparticles are synthesized before their injection as an aerosol into plasma. In our experiments, we have used two different plasma reactors, namely an asymmetric low-pressure RF plasma reactor and a parallel plate dielectric barrier discharge at atmospheric pressure. Our results have shown that DLRI can be easily coupled with various plasma processes as this approach allows the deposition of high-quality multifunctional nanocomposite thin films, with embedded nanoparticles of less than 10 nm in diameter. Hence, DLRI coupled with plasma processes meets the specifications for the deposition of multifunctional coatings. Full article

(This article belongs to the Special Issue Functionalities of Polymer-Based Nanocomposite Films and Coatings)

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13 pages, 2496 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Development of a Surface Treatment to Achieve Long-Lasting Antimicrobial Properties and Non-Cytotoxicity through Simultaneous Incorporation of Ag and Zn via Two-Step Micro-Arc Oxidation

by Yusuke Tsutsumi, Harumi Tsutsumi, Tomoyo Manaka, Peng Chen, Maki Ashida, Hideki Katayama and Takao Hanawa

Coatings 2023, 13(3), 627; https://doi.org/10.3390/coatings13030627 - 16 Mar 2023

Cited by 1 | Viewed by 1823

Abstract

A customized micro-arc oxidation (MAO) treatment technique was developed to obtain antibacterial properties with no toxicity on Ti surfaces. A two-step MAO treatment was used to fabricate a specimen containing both Ag and Zn in its surface oxide layer, and the optimal incorporation [...] Read more.

A customized micro-arc oxidation (MAO) treatment technique was developed to obtain antibacterial properties with no toxicity on Ti surfaces. A two-step MAO treatment was used to fabricate a specimen containing both Ag and Zn in its surface oxide layer, and the optimal incorporation conditions were determined. Surface characterization by EDS was performed followed by the antibacterial properties against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) and osteogenic cell compatibility evaluations. In addition, metal ion release tests were performed to evaluate the contents of Ag and Zn and the ion release behavior in order to simulate practical usage. MAO-treated specimens prepared using proper concentrations of Ag and Zn (0.5Ag-5Zn: 0.5 mM AgNO₃ and 5.0 mM ZnCl, respectively) exhibited excellent antibacterial properties against E. coli and S. aureus and no toxicity to MC3T3-E1 in antibacterial and cytotoxic evaluations, respectively. The antibacterial property of 0.5Ag-5Zn against S. aureus was sustained even after two months of immersion in physiological saline, simulating the in vivo environment. Full article

(This article belongs to the Special Issue Biomimetic Approaches in Coatings Synthesis)

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16 pages, 7047 KiB

Open AccessEditor’s ChoiceArticle

Microstructure, Mechanical Properties, Wear and Erosion Performance of a Novel High Entropy Nitride (AlCrTiMoV)N Coating Produced by Cathodic Arc Evaporation

by Alex Lothrop, Qi Yang and Xiao Huang

Coatings 2023, 13(3), 619; https://doi.org/10.3390/coatings13030619 - 14 Mar 2023

Cited by 1 | Viewed by 1608

Abstract

(AlCrTiMoV)N high entropy nitride film was prepared on 17-4PH stainless steel substrate using cathodic arc evaporation (CAE). The composition, microstructure, and thermal stability were investigated using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). Mechanical properties such as hardness [...] Read more.

(AlCrTiMoV)N high entropy nitride film was prepared on 17-4PH stainless steel substrate using cathodic arc evaporation (CAE). The composition, microstructure, and thermal stability were investigated using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). Mechanical properties such as hardness and Young’s modulus and coating performance against wear and erosion were also evaluated. The results show that the (AlCrTiMoV)N coating assumes a single-phased solid solution B1 FCC structure. It has excellent thermal stability and retains its structure with no decomposition observed up to a temperature of 1000 °C. The hardness and elastic modulus are measured as 21.3 GPa and 304 GPa, respectively. The coating contains some metallic droplets. As a potential protective coating, the (AlCrTiMoV)N coating has a lower wear rate but a higher erosion rate when compared to the TiN baseline coating. Full article

(This article belongs to the Special Issue Chemical/Physical Vapor Deposition Coatings on Metallic Substrates)

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15 pages, 6721 KiB

Open AccessEditor’s ChoiceArticle

Coating of Leather with Dye-Containing Antibacterial and Conducting Polypyrrole

by Fahanwi Asabuwa Ngwabebhoh, Oyunchimeg Zandraa, Tomáš Sáha, Jaroslav Stejskal, Dušan Kopecký, Miroslava Trchová and Jiří Pfleger

Coatings 2023, 13(3), 608; https://doi.org/10.3390/coatings13030608 - 13 Mar 2023

Cited by 4 | Viewed by 1991

Abstract

In the search for functional organic biomaterials, leather constituted by collagen fibers was coated with a conducting polymer, polypyrrole. The coating was carried out during the oxidation of pyrrole in an aqueous solution of poly(N-vinylpyrrolidone) in the presence of five organic [...] Read more.

In the search for functional organic biomaterials, leather constituted by collagen fibers was coated with a conducting polymer, polypyrrole. The coating was carried out during the oxidation of pyrrole in an aqueous solution of poly(N-vinylpyrrolidone) in the presence of five organic dyes: crystal violet, neutral red, methyl orange, acriflavine, and methylene blue. This technique ensures the uniform coating of collagen fibers with polypyrrole and incorporation of organic dyes. The surface morphology was observed with scanning electron microscopy and the transverse profile, reflecting the penetration of the conducting phase into the leather body with optical microscopy. While the polypyrrole coating endows leather with electrical conductivity, organic dyes are expected to affect the polymer morphology and to provide an antibacterial effect. The lowest sheet resistance and antibacterial activity were obtained with crystal violet. This type of coating was characterized in more detail. Infrared spectroscopy confirmed the coating of collagen fibers with polypyrrole and dye incorporation. Mechanical properties were extended to the cyclic bending of the leather at various angles over 5000 cycles. The relative resistance changes were a few percent, indicating good electrical stability during repeated mechanical stress. Full article

(This article belongs to the Special Issue Functional Polymer Films and Their Applications)

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11 pages, 2835 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Physico-Mechanical Properties of a Newly Developed Base Material Containing Mineral Trioxide Aggregate

by Keigo Nakamura, Noriko Horasawa, Toshiyuki Okuse, Ryutaro Uchikawa, Katsumitsu Shimada, Akihiro Kuroiwa, Satoshi Murakami, Hiromasa Hasegawa and Atsushi Kameyama

Coatings 2023, 13(3), 597; https://doi.org/10.3390/coatings13030597 - 11 Mar 2023

Cited by 1 | Viewed by 1887

Abstract

The aim of this study was to evaluate the physico-mechanical properties of a new cavity base material containing mineral trioxide aggregate, LA-T1, prototyped by Neo Dental Chemical Products for indirect restoration. Three base materials, LA-T1, Cavios (CAV, Neo Dental Chemical Products), and Bulk [...] Read more.

The aim of this study was to evaluate the physico-mechanical properties of a new cavity base material containing mineral trioxide aggregate, LA-T1, prototyped by Neo Dental Chemical Products for indirect restoration. Three base materials, LA-T1, Cavios (CAV, Neo Dental Chemical Products), and Bulk Base Hard (BBH, Sun Medical), were examined. The depth of cure, microshear bond strength with a resin-based luting cement, and the compressive strength of these materials were investigated. The depth of cure of LA-T1 was similar to that of CAV, while the depth of cure of BBH was above the measurement limit. The distance from the base material to the light source, 0 mm and 4 mm, did not significantly affect the depth of cure of all materials. The microshear bond strength of LA-T1 bonded to a resin-based luting cement was slightly higher than that of CAV and similar to that of BBH, both of which were bonded to the same luting cement under the same conditions. The compressive strength of LA-T1 was similar to that of CAV but less than that of BBH. The results of this study indicate that LA-T1 has properties that are similar to those of CAV and thus can be clinically applied. Full article

(This article belongs to the Special Issue Biomimetic Approaches in Coatings Synthesis)

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18 pages, 4459 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Effect of Deposition Temperature on the Structure, Mechanical, Electrochemical Evaluation, Degradation Rate and Peptides Adhesion of Mg and Si-Doped Hydroxyapatite Deposited on AZ31B Alloy

by Anca Constantina Parau, Mihaela Dinu, Cosmin Mihai Cotrut, Iulian Pana, Diana Maria Vranceanu, Lidia Ruxandra Constantin, Giuseppe Serratore, Ioana Maria Marinescu, Catalin Vitelaru, Giuseppina Ambrogio, Dennis Alexander Böhner, Annette G. Beck-Sickinger and Alina Vladescu (Dragomir)

Coatings 2023, 13(3), 591; https://doi.org/10.3390/coatings13030591 - 9 Mar 2023

Cited by 5 | Viewed by 1698

Abstract

Degradable and non-degradable biomaterials are two categories that can be used to classify the existing biomaterials, being a solution for eliminating a second surgical intervention of the implant when the tissue has properly recovered. In the present paper, the effect of deposition temperature [...] Read more.

Degradable and non-degradable biomaterials are two categories that can be used to classify the existing biomaterials, being a solution for eliminating a second surgical intervention of the implant when the tissue has properly recovered. In the present paper, the effect of deposition temperature on the structure, morphology, hardness, electrochemical evaluation, degradation properties and functional peptides adhesion of Mg and Si-doped hydroxyapatite was investigated. The coatings were obtained by RF magnetron sputtering technique at room temperature (RT) and 200 °C on AZ31B alloy substrate. Results showed that an increase in deposition temperature led to an improvement in hardness and reduced modulus of about 47%. From an electrochemical point of view, a comparative assessment of corrosion resistance was made as a function of the immersion medium used, highlighting the superior behaviour revealed by the coating deposited at elevated temperature when immersed in DMEM medium (i_corr~12 µA/cm², R_coat = 705 Ω cm², R_ct = 7624 Ω cm²). By increasing the deposition temperature up to 200 °C, the degradation rate of the coatings was slowed, more visible in the case of DMEM, which had a less aggressive effect after 14 days of immersion. Both deposition temperatures are equally suitable for further bio-inspired coating with a mussel-derived peptide, to facilitate biointegration. Full article

(This article belongs to the Special Issue Synthetic and Biological-Derived Hydroxyapatite Implant Coatings)

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13 pages, 1983 KiB

Open AccessEditor’s ChoiceArticle

Fabrication of Nano-Silver–Silver Ion Composite Antibacterial Agents for Green Powder Coatings

by Haiping Zhang, Jixing Cui, Jesse Zhu, Yuanyuan Shao and Hui Zhang

Coatings 2023, 13(3), 575; https://doi.org/10.3390/coatings13030575 - 7 Mar 2023

Cited by 2 | Viewed by 2443

Abstract

Nano-silver is characterized by broad-spectral, strong and stable antibacterial properties, which make it a promising material in coating applications. However, the efficiency of nano-silver is generally low in the coating of films. Here, we developed a series of highly active and durable silver [...] Read more.

Nano-silver is characterized by broad-spectral, strong and stable antibacterial properties, which make it a promising material in coating applications. However, the efficiency of nano-silver is generally low in the coating of films. Here, we developed a series of highly active and durable silver ions–nano-silver antimicrobial agents for powder coatings. To optimize antimicrobial activity and durability, two different nano-silver generation methods, i.e., in situ and ex situ methods combined with different carrier materials, i.e., zeolite with high ion-exchange ability and montmorillonite of layered structure were adopted and investigated. All four antibacterial additives show high activity with a reduction rate of over 99.99% and R value of over 5. The ex situ generated nano-silver antibacterial agents with both carriers exhibit higher activity in the initial antibacterial property and antibacterial durability that the coating films are able to maintain over 99% antimicrobial reduction after 20 cycles (1200 times) of soap solution wiping. They also show a lower yellowish color difference of less than three compared to the films with in situ generation method. The one with montmorillonite as carrier shows the stronger antibacterial property with an R value of 5.88 and slightly better film appearance of lower color difference, smaller reduction in gloss and increase in haze as compared to zeolite carrier due to the layered structure. Full article

(This article belongs to the Section Functional Polymer Coatings and Films)

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13 pages, 13057 KiB

Open AccessEditor’s ChoiceArticle

NiCo Prussian-Blue-Derived Cobalt–Nickel-Layered Double Hydroxide with High Electrochemical Performance for Supercapacitor Electrodes

by Qihao Yin, Bo Gao, Haiyang Fu and Liang Hu

Coatings 2023, 13(3), 554; https://doi.org/10.3390/coatings13030554 - 4 Mar 2023

Cited by 4 | Viewed by 2213

Abstract

High-performance electrode materials are crucial to the improvement of the supercapacitor performance index. Ni₂Co₁HCF@CoNi-LDH composites with a core–shell structure were prepared by a combination of coprecipitation and constant potential electrodeposition, and the microscopic morphology and phase composition of the [...] Read more.

High-performance electrode materials are crucial to the improvement of the supercapacitor performance index. Ni₂Co₁HCF@CoNi-LDH composites with a core–shell structure were prepared by a combination of coprecipitation and constant potential electrodeposition, and the microscopic morphology and phase composition of the composites were characterized by XRD, SEM, FTIR and XPS. The results showed that the NiCo Prussian blue (Ni₂Co₁HCF) was grown on the nickel foam (NF) substrate by in situ etching, while the nickel–cobalt double hydroxide (CoNi-LDH) was covered on the NiCo Prussian blue surface by electrodeposition, and the composite still retained the cubic skeleton morphology of the NiCo Prussian blue. The electrochemical properties of the composites were investigated using a three-electrode system in 2 M KOH. The results showed that their discharge specific capacity was as high as 1937 F·g⁻¹ at a current density of 1 A·g⁻¹ and still had 81.3% capacity retention at 10 A·g⁻¹, and they exhibited an excellent rate capability. The capacity retention rate was 87.1% after 1000 cycles at 5 A·g⁻¹ and, thus, the composite material has good application prospects as a supercapacitor electrode material. Full article

(This article belongs to the Special Issue Coating Electrode Materials for Next-Generation Energy Storage)

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21 pages, 43488 KiB

Open AccessEditor’s ChoiceReview

Metallizing the Surface of Halloysite Nanotubes—A Review

by Abdul-Razak Masoud, Femi Alakija, Mohammad Jabed Perves Bappy, Patrick A. S. Mills and David K. Mills

Coatings 2023, 13(3), 542; https://doi.org/10.3390/coatings13030542 - 2 Mar 2023

Cited by 9 | Viewed by 4388

Abstract

Halloysite nanotubes (HNTs) have been shown to be ideal nanoparticles for polymer reinforcement, sustained drug release, nano-reactor synthesis, toxic material removal, regenerative medicine, and as a substrate material for nanostructured coatings. Metal and metal oxide nanoparticles have been used for centuries in various [...] Read more.

Halloysite nanotubes (HNTs) have been shown to be ideal nanoparticles for polymer reinforcement, sustained drug release, nano-reactor synthesis, toxic material removal, regenerative medicine, and as a substrate material for nanostructured coatings. Metal and metal oxide nanoparticles have been used for centuries in various medical applications, primarily for their antimicrobial, antifungal, and antiviral properties. The focus of this review is the metallization of HNT surfaces. Different technologies use specific metal compounds and multi-step chemical reactions to metalize the HNT surface. This review begins with a brief overview of the current methods for metallizing the HNT surface. Our focus then provides a detailed study on specific applications of metal-coated HNTs (mHNTs) in the field of nanomedicine. The focus is on using mHNTs and Mhnt polymer composites in anti-infective therapy, immunotherapy, dentistry, regenerative medicine, and wound healing. The importance of HNTs in aerospace, defense, and industry has emerged, and the application potential and enormous market value for metal oxide nanoparticles is apparent. The commercialization potential of metal-coated HNTs is also discussed. Full article

(This article belongs to the Special Issue Fabrication and Biomedical Applications of Multifunctional Bio-Interfaces)

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