Coatings

22 pages, 14327 KB

Open AccessEditor’s ChoiceReview

High Entropy Alloys Coatings Deposited by Laser Cladding: A Review of Grain Boundary Wetting Phenomena

by Boris B. Straumal, Leonid Klinger, Alexei Kuzmin, Gabriel A. Lopez, Anna Korneva, Alexander B. Straumal, Nikolai Vershinin and Alena S. Gornakova

Coatings 2022, 12(3), 343; https://doi.org/10.3390/coatings12030343 - 6 Mar 2022

Cited by 41 | Viewed by 5804

Abstract

High-entropy alloys (HEAs) are called also alloys without a main component or multiprincipal alloys. They consist of five, six or more components in more or less equal proportions and possess unique properties. Several dozens of thousands of publications have already been devoted to [...] Read more.

High-entropy alloys (HEAs) are called also alloys without a main component or multiprincipal alloys. They consist of five, six or more components in more or less equal proportions and possess unique properties. Several dozens of thousands of publications have already been devoted to bulk HEAs, while HEA coatings are just beginning to develop. More than half of the works on the deposition of HEA coatings are devoted to laser cladding. In the laser cladding process, a mixture of powders on a substrate is melted in a focused laser beam, which sequentially scans the substrate. In the heated zone, the powder mixture melts. At the end of the crystallization process, a solidified polycrystal and a small amount of residual melt are found in the heated zone. It is possible that the grain boundaries (GBs) in the solidified polycrystal are incompletely or fully wetted by this liquid phase. In this way, the GB wetting with a melt determines the morphology and microstructure of HEAs coatings. This review analyzes GB wetting in single-phase HEAs, as well as in HEAs containing two or more phases. We analyze how the HEAs’ composition, laser scanning speed, laser beam power, external magnetic field or ultrasonic impact affect the microstructure and GB wetting. It is also shown how the microstructure and GB wetting change over the thickness of the rather thick as well as multilayer coatings deposited using a laser cladding. Full article

(This article belongs to the Special Issue Laser Processing Effects on Special Steels and High Entropy Alloys)

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16 pages, 4409 KB

Open AccessEditor’s ChoiceArticle

Relationship between the Void and Sound Absorption Characteristics of Epoxy Porous Asphalt Mixture Based on CT

by Xiaolong Li, Junfeng Gao, Hui Du, Jingpeng Jia, Xiaojie Zhao and Tianqing Ling

Coatings 2022, 12(3), 328; https://doi.org/10.3390/coatings12030328 - 1 Mar 2022

Cited by 10 | Viewed by 3124

Abstract

This study investigates the relationship between the void characteristics and sound absorption characteristics of an epoxy porous asphalt mixture. The specimens are scanned and reconstructed under different void fractions using X-ray computed tomography (CT) technology and digital image processing, and the sound absorption [...] Read more.

This study investigates the relationship between the void characteristics and sound absorption characteristics of an epoxy porous asphalt mixture. The specimens are scanned and reconstructed under different void fractions using X-ray computed tomography (CT) technology and digital image processing, and the sound absorption coefficients at different frequencies are obtained using an acoustic impedance tube. The relationship between void characteristics and sound absorption characteristics is analyzed using gray correlation. The test results exhibited a good correlation between the void characteristics of the epoxy porous asphalt mixture obtained by CT scanning (mesoscale) and the measured values (macroscale). The difference between the void fraction and connected void fraction gradually decreased with an increase in the void fraction. The relationship curve between the sound absorption coefficient and frequency exhibited a bimodal trend, and the peak value of the sound absorption coefficient increased with an increase in the void fraction. The order of the gray correlation degree between the peak and average values of the sound absorption coefficient and the void characteristic parameters is as follows: connected void fraction > void fraction > equivalent diameter of connected void > surface area of connected void > curvature. Full article

(This article belongs to the Special Issue Surface Characterization and Treatments in Transportation Infrastructure)

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20 pages, 5239 KB

Open AccessEditor’s ChoiceArticle

Verification of the Influence of Particle Shape on the Chemical Resistance of Epoxy Coating and Use of Waste Glass as the Filler

by Jana Hodná, Jakub Hodul, Rostislav Drochytka and Michaela Seidlová

Coatings 2022, 12(3), 309; https://doi.org/10.3390/coatings12030309 - 24 Feb 2022

Cited by 7 | Viewed by 3778

Abstract

The use of suitable secondary raw materials as fillers in progressive, protective agents primarily intended for horizontal concrete construction is very effective not only from the ecological but also from the economic point of view. The impact of using various types of waste [...] Read more.

The use of suitable secondary raw materials as fillers in progressive, protective agents primarily intended for horizontal concrete construction is very effective not only from the ecological but also from the economic point of view. The impact of using various types of waste glass as fillers on the mechanical parameters of epoxy coatings was experimentally verified. Assessing the dependency of the coating’s chemical resistance on the shape of the used filler’s particles was the main aim of the performed research. A solvent-free epoxy suitable for a chemically aggressive environment was selected for the experiment. These were epoxy coatings filled with a micro filler based on raw materials such as glass flakes and silica flour. Three tested formulations containing fillers with different particle shapes and characteristics were exposed to H₂SO₄, HCl, CH₂O₂ and NaOH at concentrations of 5% and 30% and evaluated after 60, 90 and 120 days. The chemical resistance assessment was carried out not only visually but also using a scanning electron microscope (SEM). Thanks to the use of the waste glass as a coating filler, tensile properties and hardness improved, and its use did not negatively affect the chemical resistance and adhesion of the epoxy coatings. It was found that the shape of the filler particles influences the resistance of the coating against a chemically aggressive environment. The epoxy coating containing pre-treated waste windshield glass (shards) showed even better properties than the reference coating. Full article

(This article belongs to the Collection Feature Paper Collection for Topic Editors and Invited Scholars in Coatings)

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34 pages, 80589 KB

Open AccessEditor’s ChoiceReview

A Review on In Situ Mechanical Testing of Coatings

by Mohamed Amer, Qamar Hayat, Vit Janik, Nigel Jennett, Jon Nottingham and Mingwen Bai

Coatings 2022, 12(3), 299; https://doi.org/10.3390/coatings12030299 - 23 Feb 2022

Cited by 23 | Viewed by 8963

Abstract

Real-time evaluation of materials’ mechanical response is crucial to further improve the performance of surfaces and coatings because the widely used post-processing evaluation techniques (e.g., fractography analysis) cannot provide deep insight into the deformation and damage mechanisms that occur and changes in coatings’ [...] Read more.

Real-time evaluation of materials’ mechanical response is crucial to further improve the performance of surfaces and coatings because the widely used post-processing evaluation techniques (e.g., fractography analysis) cannot provide deep insight into the deformation and damage mechanisms that occur and changes in coatings’ material corresponding to the dynamic thermomechanical loading conditions. The advanced in situ examination methods offer deep insight into mechanical behavior and material failure with remarkable range and resolution of length scales, microstructure, and loading conditions. This article presents a review on the in situ mechanical testing of coatings under tensile and bending examinations, highlighting the commonly used in situ monitoring techniques in coating testing and challenges related to such techniques. Full article

(This article belongs to the Special Issue Micro- and Nano- Mechanical Testing of Coatings and Surfaces)

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13 pages, 2847 KB

Open AccessEditor’s ChoiceArticle

Thin Film Fabrication by Pulsed Laser Deposition from TiO₂ Targets in O₂, N₂, He, or Ar for Dye-Sensitized Solar Cells

by Dorel F. Albu, Jeanina Lungu, Gianina Popescu-Pelin, Cristian N. Mihăilescu, Gabriel Socol, Adrian Georgescu, Marcela Socol, Alexandra Bănică, Victor Ciupina and Ion N. Mihailescu

Coatings 2022, 12(3), 293; https://doi.org/10.3390/coatings12030293 - 22 Feb 2022

Cited by 17 | Viewed by 4386

Abstract

Active semiconductor layers of TiO₂ were synthesized via pulsed laser deposition in He, N₂, O₂, or Ar to manufacture DSSC structures. As-prepared nanostructured TiO₂ coatings grown on FTO were photosensitized by the natural absorption of the N719 [...] Read more.

Active semiconductor layers of TiO₂ were synthesized via pulsed laser deposition in He, N₂, O₂, or Ar to manufacture DSSC structures. As-prepared nanostructured TiO₂ coatings grown on FTO were photosensitized by the natural absorption of the N719 (Ruthenium 535-bis TBA) dye to fabricate photovoltaic structures. TiO₂ photoanode nanostructures with increased adsorption areas of the photosensitizer (a combination with voluminous media) were grown under different deposition conditions. Systematic SEM, AFM, and XRD investigations were carried out to study the morphological and structural characteristics of the TiO₂ nanostructures. It was shown that the gas nature acts as a key parameter of the architecture and the overall performance of the deposited films. The best electro-optical performance was reached for photovoltaic structures based on TiO₂ coatings grown in He, as was demonstrated by the short-circuit current (Isc) of 5.40 mA, which corresponds to the higher recorded roughness (of 44 ± 2.9 nm RMS). The higher roughness is thus reflected in a more efficient and deeper penetration of the dye inside the nanostructured TiO₂ coatings. The photovoltaic conversion efficiency (η) was 1.18 and 2.32% for the DSSCs when the TiO₂ coatings were deposited in O₂ and He, respectively. The results point to a direct correlation between the electro-optical performance of the prepared PV cells, the morphology of the TiO₂ deposited layers, and the crystallinity features, respectively. Full article

(This article belongs to the Collection Pulsed Laser Deposition of Thin Films: Recent Advances and Challenges)

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16 pages, 5736 KB

Open AccessEditor’s ChoiceArticle

Impact of Remelting in the Microstructure and Corrosion Properties of the Ti6Al4V Fabricated by Selective Laser Melting

by Javier Bedmar, Jorge de la Pezuela, Ainhoa Riquelme, Belén Torres and Joaquín Rams

Coatings 2022, 12(2), 284; https://doi.org/10.3390/coatings12020284 - 21 Feb 2022

Cited by 15 | Viewed by 4989

Abstract

The presence of defects like porosity and lack of fusion can negatively affect the properties of the materials manufactured by Selective Laser Melting (SLM). The optimization of the manufacturing conditions allows reducing the number of defects, but there is a limit for each [...] Read more.

The presence of defects like porosity and lack of fusion can negatively affect the properties of the materials manufactured by Selective Laser Melting (SLM). The optimization of the manufacturing conditions allows reducing the number of defects, but there is a limit for each manufacturing material and process. To expand the manufacturing envelope, a remelting after every layer of the SLM process has been used to manufacture Ti6Al4V alloy samples using an SLM with a CO₂ laser. The effect of this processing method on the microstructure, defects, hardness, and, especially, the corrosion properties was studied. It was concluded that the laser remelting strategy causes an increment of the α and β phases from the dissolution of metastable α’. This technique also provokes a decrease in the number of defects and a reduction of the hardness, which are also reduced with lower scanning speeds. On the other hand, all the corrosion tests show that a low scanning speed and the laser remelting strategy improve the corrosion resistance of the Ti6Al4V alloy since parameters like the Open Circuit Potential (OCP) and the Polarization Resistance (Rp) are nobler and the mass gain is lower. Full article

(This article belongs to the Special Issue The Applications of Laser Processing and Additive Manufacturing)

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24 pages, 64298 KB

Open AccessEditor’s ChoiceArticle

Novel Hydrophobic Nanostructured Antibacterial Coatings for Metallic Surface Protection

by Cristina Lavinia Nistor, Catalin Ionut Mihaescu, Daniela Bala, Ioana Catalina Gifu, Claudia Mihaela Ninciuleanu, Sabina Georgiana Burlacu, Cristian Petcu, Mariana-Gratiela Vladu, Adi Ghebaur, Lenuta Stroea and Ludmila Otilia Cinteza

Coatings 2022, 12(2), 253; https://doi.org/10.3390/coatings12020253 - 15 Feb 2022

Cited by 15 | Viewed by 5509

Abstract

A simple and cost-efficient method to modify different surfaces in order to improve their bioactivity, corrosion and wear resistance proved to be sol-gel coatings. The silane layers have been shown to be effective in the protection of steel, aluminum or magnesium alloys and [...] Read more.

A simple and cost-efficient method to modify different surfaces in order to improve their bioactivity, corrosion and wear resistance proved to be sol-gel coatings. The silane layers have been shown to be effective in the protection of steel, aluminum or magnesium alloys and copper and copper alloys. Moreover, it has been found that the adding of different inorganic nanoparticles into silica films leads to increasing their performance regarding corrosion protection. In this study, we fabricated, a simple sol-gel method, transparent mono- and bi-layered hydrophobic coatings with simultaneous antibacterial, hydrophobic and anti-corrosive properties for the protection of metallic surfaces against the action of air pollutants or from biological attacks of pathogens. The first layer (the base) of the coating contains silver (Ag) or zinc oxide (ZnO) nanoparticles with an antibacterial effect. The second layer includes zinc oxide nanoparticles with flower-like morphology to increase the hydrophobicity of the coating and to improve corrosion-resistant properties. The second layer of the coating contains a fluorinated silica derivative, 1H,1H,2H,2H-perfluorooctyl triethoxysilane (PFOTES), which contributes to the hydrophobic properties of the final coating by means of its hydrophobic groups. The mono- and bi-layered coatings with micro/nano rough structures have been applied by brushing on various substrates, including metallic surfaces (copper, brass and mild steel) and glass (microscope slides). The as-prepared coatings showed improved hydrophobic properties (water CA > 90°) when compared with the untreated substrates while maintaining the transparent aspect. The corrosion resistance tests revealed significantly lower values of the corrosion rates recorded for all the protected metallic surfaces, with the lowest values being measured for the bi-layered coatings containing ZnO particles, both in the first and in the second layers of the coating. Considering the antibacterial activity, the most effective were the AOAg-II and AOZnO-II coatings, which exhibited the highest reduction of microbial growth. Full article

(This article belongs to the Special Issue Coatings against Corrosion, Microbial Adhesion, and Biofouling)

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13 pages, 9551 KB

Open AccessEditor’s ChoiceArticle

SEM-EDX Analysis of Metal Particles Deposition from Surgical Burs after Implant Guided Surgery Procedures

by Giovanni Falisi, Giordano Foffo, Marco Severino, Carlo Di Paolo, Serena Bianchi, Sara Bernardi, Davide Pietropaoli, Sofia Rastelli, Roberto Gatto and Gianluca Botticelli

Coatings 2022, 12(2), 240; https://doi.org/10.3390/coatings12020240 - 12 Feb 2022

Cited by 19 | Viewed by 4375

Abstract

The preparation of the implant site in guided surgery procedure takes place without irrigation, which could lead to increased friction of the drills with the formation and release of debris or metal particles. The presence of metal particles in the peri-implant tissue could [...] Read more.

The preparation of the implant site in guided surgery procedure takes place without irrigation, which could lead to increased friction of the drills with the formation and release of debris or metal particles. The presence of metal particles in the peri-implant tissue could represent a trigger for macrophage activity, bone resorption processes, and consequent implant loss. According to the guided surgical protocol, the study aimed to evaluate the presence of metal particles deposited during implant site preparation. Twenty-five adult porcine ribs from the same adult individual were chosen due to their trabecular bone structure, similar to facial bones. The samples were all 8 cm (length) × 3 cm (depth) × 2 cm (width) and were further subdivided to obtain 50 elements of 4 cm × 3 cm × 2 cm. Plexiglass was used to create structures such as surgical guides so that their function could be mimicked, and the guided implant site preparation sequence could be performed with them. The drill kit used in this study is a guided surgery drill kit characterized by high wear resistance, high yield strength, and good corrosion resistance. This same kit was used 50 times in this way to prepare 50 different implant sites and evaluated at different edges and number of preparation (T0-neutral edge, T1-1 full preparation, T2-10, T3-20, T4-30, T5-40, and T6-50) by SEM-EDX to assess the presence of any metal deposition. The presence of metal residues in the implant site increased according to the cycles of use of the drills. We have observed that in the first three groups, there is no presence of metals. This is evident in groups T3 and T4. Finally, the presence of metal residues becomes significant in the study’s last two groups of samples. The study highlighted how the lack of irrigation in the work site leads the deposition of metal particles and in addition to a reduction in the efficiency of the drills, resulting in less precise cutting, altering the shape of the prepared site, and, lastly, reducing the primary stability of the implants. Full article

(This article belongs to the Collection Advanced Surface Coating of Nanoparticles)

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13 pages, 5221 KB

Open AccessEditor’s ChoiceArticle

The Laser Alloying Process of Ductile Cast Iron Surface with Titanium Powder in Nitrogen Atmosphere

by Aleksandra Lont, Jacek Górka, Damian Janicki and Krzysztof Matus

Coatings 2022, 12(2), 227; https://doi.org/10.3390/coatings12020227 - 10 Feb 2022

Cited by 12 | Viewed by 2632

Abstract

The article presents the results of the laser alloying process of a ductile cast iron EN-GJS 350-22 surface with titanium powder in nitrogen atmosphere. The aim of this research was to test the influence of nitrogen atmosphere on the structure and properties of [...] Read more.

The article presents the results of the laser alloying process of a ductile cast iron EN-GJS 350-22 surface with titanium powder in nitrogen atmosphere. The aim of this research was to test the influence of nitrogen atmosphere on the structure and properties of the ductile cast iron surface layer produced by a laser alloying process with titanium. The laser alloying process was conducted using a Rofin Sinar DL020 2 kW high-power diode laser (HPDDL) with rectangular focus and uniform power density distribution in the focus axis. The tests of the produced surface layers included macrostructure and microstructure observations, X-ray diffraction (XRD) analysis, energy-dispersive spectroscopy (EDS) on scanning electron microscope (SEM) and transmission electron microscope (TEM), Vickers hardness and solid particle erosion according to ASTM G76-04 standard. As a result of the laser alloying process in nitrogen atmosphere with titanium powder, the in situ metal matrix composite structure reinforced by TiCN particles was formed. The laser alloying process of ductile cast iron caused the increased hardness and erosion resistance of the surface. Full article

(This article belongs to the Special Issue Progress in Coatings Deposition by Advanced Welding and Welding-Related Processes)

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13 pages, 3867 KB

Open AccessEditor’s ChoiceArticle

Effect of the Nature of the Particles Released from Bone Level Dental Implants: Physicochemical and Biological Characterization

by Juan Carlos Vara, Juan Delgado, Alejandro Estrada-Martínez, Esteban Pérez-Pevida, Aritza Brizuela, Begoña Bosch, Román Pérez and Javier Gil

Coatings 2022, 12(2), 219; https://doi.org/10.3390/coatings12020219 - 8 Feb 2022

Cited by 7 | Viewed by 3139

Abstract

The placement of bone–level dental implants can lead to the detachment of particles in the surrounding tissues due to friction with the cortical bone. In this study, 60 bone–level dental implants were placed with the same design: 30 made of commercially pure grade [...] Read more.

The placement of bone–level dental implants can lead to the detachment of particles in the surrounding tissues due to friction with the cortical bone. In this study, 60 bone–level dental implants were placed with the same design: 30 made of commercially pure grade 4 titanium and 30 made of Ti6Al4V alloy. These implants were placed in cow ribs following the company’s placement protocols. Particles detached from the dental implants were isolated and their size and specific surface area were characterized. The irregular morphology was observed by scanning electron microscopy. Ion release to the medium was determined at different immersion times in physiological medium. Cytocompatibility studies were performed with fibroblastic and osteoblastic cells. Gene expression and cytokine release were analysed to determine the action of inflammatory cells. Particle sizes of around 15 μM were obtained in both cases. The Ti6Al4V alloy particles showed significant levels of vanadium ion release and the cytocompatibility of these particles is lower than that of commercially pure titanium. Ti6Al4V alloy presents higher levels of inflammation markers (TNFα and Il–1β) compared to that of only titanium. Therefore, there is a trend that with the alloy there is a greater toxicity and a greater pro-inflammatory response. Full article

(This article belongs to the Special Issue Recent Advanced in Titanium-Based Coatings)

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21 pages, 10045 KB

Open AccessEditor’s ChoiceArticle

Evolution in Wear and High-Temperature Oxidation Resistance of Laser-Clad Al_xMoNbTa Refractory High-Entropy Alloys Coatings with Al Addition Content

by Sichun Hong, Jun Li, Peng Zhao, Yinsi Xu and Wanggen Li

Coatings 2022, 12(2), 121; https://doi.org/10.3390/coatings12020121 - 21 Jan 2022

Cited by 27 | Viewed by 4255

Abstract

AlxMoNbTa (x = 0.5, 1.0 and 1.5) refractory high-entropy alloy (RHEAs) coatings were produced on Ti6Al4V by laser cladding. Ti₂AlNb as the second phase and the solid solutions with the body center cubic structure (BCC) as the matrix were synthesized in [...] Read more.

AlxMoNbTa (x = 0.5, 1.0 and 1.5) refractory high-entropy alloy (RHEAs) coatings were produced on Ti6Al4V by laser cladding. Ti₂AlNb as the second phase and the solid solutions with the body center cubic structure (BCC) as the matrix were synthesized in the coatings. The average microhardness of the coatings was increased with the increase in x, along with which the fracture toughness was decreased. Wear resistance of the coatings was investigated by the dry-sliding reciprocating wear tests at room temperature in air (Si₃N₄ as the counterparts, the 10 N load for 30 min, and the 3 mm/s sliding speed). The wear rate of the coatings was decreased with x enhanced from 0.5 (6.34 × 10⁻⁵ mm³/N·m) to 1.0 (5.90 × 10⁻⁵ mm³/N·m), then slightly increased with x enhanced to 1.5 (6.18 × 10⁻⁵ mm³/N·m). Oxidation resistance was evaluated by the high-temperature oxidation tests at 1000 °C in air for 120 h. The whole mass gain of the coatings showed a slight downward tendency (61.8 mg/cm² for x = 0.5, 57.8 mg/cm² for x = 1.0 and 56.3 mg/cm² for x = 1.5). The change in wear and oxidation mechanism with x was revealed in detail. Full article

(This article belongs to the Special Issue Friction, Wear Properties and Applications of Coatings)

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24 pages, 6768 KB

Open AccessEditor’s ChoiceArticle

Preparation of Very Thin Zinc Oxide Films by Liquid Deposition Process: Review of Key Processing Parameters

by Mouna Khiari, Mickaël Gilliot, Michaël Lejeune, Florica Lazar and Aomar Hadjadj

Coatings 2022, 12(1), 65; https://doi.org/10.3390/coatings12010065 - 6 Jan 2022

Cited by 12 | Viewed by 6394

Abstract

We used sol-gel and spin-coating in the original configuration of a liquid deposition process to synthesize particularly thin ZnO films (<100 nm) with nano-granular morphology, high grain orientation and variable optical properties. The concentration of the zinc salt, the concentration of the chelating [...] Read more.

We used sol-gel and spin-coating in the original configuration of a liquid deposition process to synthesize particularly thin ZnO films (<100 nm) with nano-granular morphology, high grain orientation and variable optical properties. The concentration of the zinc salt, the concentration of the chelating agent, the nature of the solvent and the substrate material have been identified as key parameters that determine the microstructure of the deposited layer and thus its final properties. The thorough and practical examination of the effects of the synthesis parameters evidenced a three-step growth mechanism for these ZnO thin films: (i) a reaction of precursors, (ii) a formation of nuclei, and (iii) a coalescence of nanoparticles under thermal annealing. The growth of these very thin films is thus conditioned by the interaction between the liquid phase and the substrate especially during the initial steps of the spin coating process. Such thin ZnO films with such nano-granular morphology may be of great interest in various applications, especially those requiring a large active surface area. Full article

(This article belongs to the Collection Feature Paper Collection in Thin Films)

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13 pages, 5352 KB

Open AccessFeature PaperEditor’s ChoiceArticle

Sol–Gel Encapsulation of ZnAl Alloy Powder with Alumina Shell

by David Svetlizky and Noam Eliaz

Coatings 2021, 11(11), 1389; https://doi.org/10.3390/coatings11111389 - 14 Nov 2021

Cited by 6 | Viewed by 4861

Abstract

Additive manufacturing (AM), for example, directed energy deposition (DED), may allow the processing of self-healing metal–matrix composites (SHMMCs). The sealing of cracks in these SHMMCs would be achieved via the melting of micro-encapsulated low melting point particulates (LMPPs), incorporated into the material during [...] Read more.

Additive manufacturing (AM), for example, directed energy deposition (DED), may allow the processing of self-healing metal–matrix composites (SHMMCs). The sealing of cracks in these SHMMCs would be achieved via the melting of micro-encapsulated low melting point particulates (LMPPs), incorporated into the material during AM, by heat treatment of the part during service. Zn-Al alloys are good candidates to serve as LMPPs, for example, when the matrix of the MMC is made of an aluminum alloy. However, such powders should first be encapsulated by a thermal and diffusion barrier. Here, we propose a sol–gel process for encapsulation of a custom-made ZA-8 (Zn92Al8, wt.%) core powder in a ceramic alumina (Al₂O₃) shell. We first modify the surface of the ZA-8 powder with (12-phosphonododecyl)phosphonic acid (Di-PA) hydrophobic self-assembled monolayer (SAM) in order to prevent extensive hydrogen evolution and formation of non-uniform and porous oxide/hydroxide surface layers during the sol–gel process. Calcination for 1 h at 500 °C is found to be insufficient for complete boehmite-to-γ(Al₂O₃) phase transformation. Thermal stability tests in an air-atmosphere furnace at 600 °C for 1 h result in melting, distortion, and sintering into a brittle sponge (aggregate) of the as-atomized powder. In contrast, the core/shell powder is not sintered and preserves its spherical morphology, with no apparent “leaks” of the ZA-8 core alloy out of the ceramic encapsulation. Full article

(This article belongs to the Special Issue Recent Developments of Electrodeposition Coatings II)

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31 pages, 13812 KB

Open AccessFeature PaperEditor’s ChoiceArticle

Surface Topography of PVD Hard Coatings

by Peter Panjan, Aljaž Drnovšek, Nastja Mahne, Miha Čekada and Matjaž Panjan

Coatings 2021, 11(11), 1387; https://doi.org/10.3390/coatings11111387 - 13 Nov 2021

Cited by 40 | Viewed by 10247

Abstract

The primary objective of this study was to investigate and compare the surface topography of hard coatings deposited by three different physical vapor deposition methods (PVD): low-voltage electron beam evaporation, unbalanced magnetron sputtering and cathodic arc evaporation. In these deposition systems, various ion [...] Read more.

The primary objective of this study was to investigate and compare the surface topography of hard coatings deposited by three different physical vapor deposition methods (PVD): low-voltage electron beam evaporation, unbalanced magnetron sputtering and cathodic arc evaporation. In these deposition systems, various ion etching techniques were applied for substrate cleaning. The paper summarizes our experience and the expertise gained during many years of development of PVD hard coatings for the protection of tools and machine components. Surface topography was investigated using scanning electron microscopy (SEM), atomic force microscopy (AFM), scanning transmission electron microscopy (STEM) and 3D stylus profilometry. Observed similarities and differences among samples deposited by various deposition methods are discussed and correlated with substrate material selection, substrate pretreatment and deposition conditions. Large variations in the surface topography were observed between selected deposition techniques, both after ion etching and deposition processes. The main features and implications of surface cleaning by ion etching are discussed and the physical phenomena involved in this process are reviewed. During a given deposition run as well as from one run to another, a large spatial variation of etching rates was observed due to the difference in substrate geometry and batching configurations. Variations related to the specific substrate rotation (i.e., temporal variations in the etching and deposition) were also observed. The etching efficiency can be explained by the influence of different process parameters, such as substrate-to-source orientation and distance, shadowing and electric field effects. The surface roughness of PVD coatings mainly originates from growth defects (droplets, nodular defects, pinholes, craters, etc.). We briefly describe the causes of their formation. Full article

(This article belongs to the Special Issue Surface Topography Effects on Functional Properties of PVD Coatings)

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12 pages, 2918 KB

Open AccessFeature PaperEditor’s ChoiceArticle

Physicochemical and Antimicrobial Properties of Whey Protein-Based Films Functionalized with Palestinian Satureja capitata Essential Oil

by Manar Abdalrazeq, Nidal Jaradat, Mohammad Qadi, C. Valeria L. Giosafatto, Eliana Dell’Olmo, Rosa Gaglione, Angela Arciello and Raffaele Porta

Coatings 2021, 11(11), 1364; https://doi.org/10.3390/coatings11111364 - 6 Nov 2021

Cited by 15 | Viewed by 4484

Abstract

The present study aimed to produce bio-active packaging materials made of whey proteins (WPs) and essential oil (EO) extracted from Thymbra (Satureja capitata, L.), one of the most popular Palestinian wild plants. In this study, two different Thymbra leaves from Nablus [...] Read more.

The present study aimed to produce bio-active packaging materials made of whey proteins (WPs) and essential oil (EO) extracted from Thymbra (Satureja capitata, L.), one of the most popular Palestinian wild plants. In this study, two different Thymbra leaves from Nablus and Qabatiya in Palestine were collected and analyzed for EOs by gas chromatography and mass spectrometry. Based on the analysis, two EOs, namely, TEO1 and TEO2, were extracted, and it was found that both samples primarily contain γ-terpinene and carvacrol, whereas p-cymene was detected only in TEO1. The antimicrobial activity of TEO1 and TEO2 was evaluated by microbroth microdilution assays against pathogenic bacteria and yeast. Based on the results, TEO1 exhibited potent antimicrobial activity against the test strains. Besides, TEO1 was chosen to functionalize WP-based films at different concentrations (0.1%, 0.4%, and 0.8% v/v of Film Forming Solutions). Film mechanical property investigation showed a marked reduction in the tensile strength and Young’s modulus at 0.8% TEO1. In contrast, its elongation at break value was significantly (p < 0.05) increased due to the plasticizing effect of the EO. Moreover, the film transparency was found to be significantly (p < 0.05) reduced by increasing TEO1 concentrations. Finally, microbiological investigations indicated that film antimicrobial activity against both gram-positive and gram-negative bacteria increased dose-dependently. The overall results open interesting perspectives for employing these films as preservative materials in food packaging. Full article

(This article belongs to the Special Issue Bio-Based Active Packaging for Shelf Life Extension)

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17 pages, 90411 KB

Open AccessFeature PaperEditor’s ChoiceArticle

Er:YAG Laser Cleaning of Painted Surfaces: Functional Considerations to Improve Efficacy and Reduce Side Effects

by Cong Wang, Yijian Cao, Fude Tie and Mara Camaiti

Coatings 2021, 11(11), 1315; https://doi.org/10.3390/coatings11111315 - 28 Oct 2021

Cited by 7 | Viewed by 4828

Abstract

The restoration of paintings always involves the removal of darkened superficial layers, which are mainly due to dust deposition and aged varnishes. As cleaning is an irreversible and invasive treatment, physical methods (i.e., laser cleaning) instead of chemical ones are frequently suggested to [...] Read more.

The restoration of paintings always involves the removal of darkened superficial layers, which are mainly due to dust deposition and aged varnishes. As cleaning is an irreversible and invasive treatment, physical methods (i.e., laser cleaning) instead of chemical ones are frequently suggested to reduce side effects on pictorial layers. Among the most employed laser systems, the free-running Er:YAG laser is considered very suitable for fine arts cleaning. This laser works at 2.94 μm, at which only –OH and –NH bonds in molecules are excited. This character can become a disadvantage when pigments with these functional groups are present. To understand the potential of the Er:YAG laser in such situations or in the presence of degradable pigments, the effectiveness of varnish removal from paintings prepared with egg yolk as the binder and cinnabar and lead white as the pigments were systematically investigated. Different cleaning conditions were used, and a hyperspectral sensor was innovatively used as a rapid, in situ and non-destructive technique to assess the effects of laser ablation, besides microscopic analysis. Though results obtained show all these pigments are sensitive to this laser radiation, satisfactory cleaning can be achieved without damaging the pictorial layer. The best cleaning conditions were 0.5 W of power (50 mJ and 10 Hz for energy and frequency), with 2-propanol as the wetting agent. Full article

(This article belongs to the Special Issue Conservation Tools, Protocols and Treatments on Painted Surfaces, Metal Leaves and Finishes in Cultural Heritage)

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10 pages, 2748 KB

Open AccessFeature PaperEditor’s ChoiceArticle

Design and Preparation of Nanoporous Cu/Ag Multilayer Films

by Yufei Wang, Shuangle Zhang, Zefeng Wu, Yong Fan, Huaqiang Chen, Qingning Meng, Yang Yan, Zhaoyi Hu, Jing Wang and Engang Fu

Coatings 2021, 11(10), 1187; https://doi.org/10.3390/coatings11101187 - 29 Sep 2021

Cited by 4 | Viewed by 3828

Abstract

Cu₃₀Al₇₀ and Ag₃₀Al₇₀ multilayer precursor films were prepared by magnetron sputtering, respectively. Then the nanoporous Cu/Ag multilayer composite films were successfully prepared by selecting the appropriate H₂SO₄ solution as the dealloying solution. It was [...] Read more.

Cu₃₀Al₇₀ and Ag₃₀Al₇₀ multilayer precursor films were prepared by magnetron sputtering, respectively. Then the nanoporous Cu/Ag multilayer composite films were successfully prepared by selecting the appropriate H₂SO₄ solution as the dealloying solution. It was found that the nanoporous structure was stable in the dealloying solution. The morphology and structure of nanoporous multilayer films are mainly related to the phase composition of precursors. The structure of nanoporous multilayers can be simply regarded as the superposition of single-layer structures. Our work shows that nanoporous multilayers can be well-prepared by magnetron sputtering combined with dealloying. Full article

(This article belongs to the Special Issue Nanoporous Films)

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20 pages, 9112 KB

Open AccessFeature PaperEditor’s ChoiceReview

Rare Earth Elements Enhanced the Oxidation Resistance of Mo-Si-Based Alloys for High Temperature Application: A Review

by Laihao Yu, Yingyi Zhang, Tao Fu, Jie Wang, Kunkun Cui and Fuqiang Shen

Coatings 2021, 11(9), 1144; https://doi.org/10.3390/coatings11091144 - 21 Sep 2021

Cited by 36 | Viewed by 5388

Abstract

Traditional refractory materials such as nickel-based superalloys have been gradually unable to meet the performance requirements of advanced materials. The Mo-Si-based alloy, as a new type of high temperature structural material, has entered the vision of researchers due to its charming high temperature [...] Read more.

Traditional refractory materials such as nickel-based superalloys have been gradually unable to meet the performance requirements of advanced materials. The Mo-Si-based alloy, as a new type of high temperature structural material, has entered the vision of researchers due to its charming high temperature performance characteristics. However, its easy oxidation and even “pesting oxidation” at medium temperatures limit its further applications. In order to solve this problem, researchers have conducted large numbers of experiments and made breakthrough achievements. Based on these research results, the effects of rare earth elements like La, Hf, Ce and Y on the microstructure and oxidation behavior of Mo-Si-based alloys were systematically reviewed in the current work. Meanwhile, this paper also provided an analysis about the strengthening mechanism of rare earth elements on the oxidation behavior for Mo-Si-based alloys after discussing the oxidation process. It is shown that adding rare earth elements, on the one hand, can optimize the microstructure of the alloy, thus promoting the rapid formation of protective SiO₂ scale. On the other hand, it can act as a diffusion barrier by producing stable rare earth oxides or additional protective films, which significantly enhances the oxidation resistance of the alloy. Furthermore, the research focus about the oxidation protection of Mo-Si-based alloys in the future was prospected to expand the application field. Full article

(This article belongs to the Special Issue Strengthening, Corrosion and Protection of High Temperature Structural Materials)

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11 pages, 3431 KB

Open AccessFeature PaperEditor’s ChoiceArticle

Three-Dimensional Carbon-Coated LiFePO₄ Cathode with Improved Li-Ion Battery Performance

by Can Wang, Xunlong Yuan, Huiyun Tan, Shuofeng Jian, Ziting Ma, Junjie Zhao, Xuewen Wang, Dapeng Chen and Yifan Dong

Coatings 2021, 11(9), 1137; https://doi.org/10.3390/coatings11091137 - 18 Sep 2021

Cited by 19 | Viewed by 6946

Abstract

LiFePO₄ (LFPO)has great potential as the cathode material for lithium-ion batteries; it has a high theoretical capacity (170 m·A·h·g⁻¹), high safety, low toxicity and good economic benefits. However, low conductivity and a low diffusion rate inhibit its future development. To [...] Read more.

LiFePO₄ (LFPO)has great potential as the cathode material for lithium-ion batteries; it has a high theoretical capacity (170 m·A·h·g⁻¹), high safety, low toxicity and good economic benefits. However, low conductivity and a low diffusion rate inhibit its future development. To overcome these weaknesses, three-dimensional carbon-coated LiFePO₄ that incorporates a high capacity, superior conductivity and low volume expansion enables faster electron transport channels. The use of Cetyltrimethyl Ammonium Bromid (CTAB) modification only requires a simple water bath and sintering, without the need to add a carbon source in the LFPO synthesis process. In this way, the electrode shows excellent reversible capacity, as high as 159.8 m·A·h·g⁻¹ at 2 C, superior rate capability with 97.3 m·A·h·g⁻¹ at 5 C and good cycling ability, preserving ~84.2% capacity after 500 cycles. By increasing the ion transport rate and enhancing the structural stability of LFPO nanoparticles, the LFPO-positive electrode achieves excellent initial capacity and cycle life through cost-effective and easy-to-implement carbon coating. This simple three-dimensional carbon-coated LiFePO₄ provides a new and simple idea for obtaining comprehensive and high-performance electrode materials in the field of lithium cathode materials. Full article

(This article belongs to the Special Issue Surface Coating in Advanced Energy Storage Devices)

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22 pages, 3743 KB

Open AccessFeature PaperEditor’s ChoiceReview

Synthesis, Microstructure and Properties of Magnetron Sputtered Lead Zirconate Titanate (PZT) Thin Film Coatings

by Youcao Ma, Jian Song, Xubo Wang, Yue Liu and Jia Zhou

Coatings 2021, 11(8), 944; https://doi.org/10.3390/coatings11080944 - 7 Aug 2021

Cited by 44 | Viewed by 7377

Abstract

Compared to aluminum nitride (AlN) with simple stoichiometry, lead zirconate titanate thin films (PZT) are the other promising candidate in advanced micro-electro-mechanical system (MEMS) devices due to their excellent piezoelectric and dielectric properties. The fabrication of PZT thin films with a large area [...] Read more.

Compared to aluminum nitride (AlN) with simple stoichiometry, lead zirconate titanate thin films (PZT) are the other promising candidate in advanced micro-electro-mechanical system (MEMS) devices due to their excellent piezoelectric and dielectric properties. The fabrication of PZT thin films with a large area is challenging but in urgent demand. Therefore, it is necessary to establish the relationships between synthesis parameters and specific properties. Compared to sol-gel and pulsed laser deposition techniques, this review highlights a magnetron sputtering technique owing to its high feasibility and controllability. In this review, we survey the microstructural characteristics of PZT thin films, as well as synthesis parameters (such as substrate, deposition temperature, gas atmosphere, and annealing temperature, etc.) and functional proper-ties (such as dielectric, piezoelectric, and ferroelectric, etc). The dependence of these influential factors is particularly emphasized in this review, which could provide experimental guidance for researchers to acquire PZT thin films with expected properties by a magnetron sputtering technique. Full article

(This article belongs to the Special Issue Nanocomposite Thin Film and Multilayers)

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23 pages, 6362 KB

Open AccessFeature PaperEditor’s ChoiceReview

TiO₂ Nanotubes Architectures for Solar Energy Conversion

by Yin Xu and Giovanni Zangari

Coatings 2021, 11(8), 931; https://doi.org/10.3390/coatings11080931 - 4 Aug 2021

Cited by 23 | Viewed by 4599

Abstract

Electromagnetic light from the Sun is the largest source, and the cleanest energy available to us; extensive efforts have been dedicated to developing science and engineering solutions in order to avoid the use of fossil fuels. Solar energy transforms photons into electricity via [...] Read more.

Electromagnetic light from the Sun is the largest source, and the cleanest energy available to us; extensive efforts have been dedicated to developing science and engineering solutions in order to avoid the use of fossil fuels. Solar energy transforms photons into electricity via the photovoltaic effect, generating about 20 GW of energy in the USA in 2020, sufficient to power about 17 million households. However, sunlight is erratic, and technologies to store electric energy storage are unwieldy and relatively expensive. A better solution to store energy and to deliver this energy on demand is storage in chemical bonds: synthesizing fuels such as H₂, methane, ethanol, and other chemical species. In this review paper we focus on titania (TiO₂) nanotubes grown through electrochemical anodization and various modifications made to them to enhance conversion efficiency; these semiconductors will be used to implement the synthesis of H₂ through water splitting. This document reviews selected research efforts on TiO₂ that are ongoing in our group in the context of the current efforts worldwide. In addition, this manuscript is enriched by discussing the latest novelties in this field. Full article

(This article belongs to the Special Issue Smart Coatings for Energy Saving Applications)

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22 pages, 996 KB

Open AccessFeature PaperEditor’s ChoiceReview

Structure and Applications of Pectin in Food, Biomedical, and Pharmaceutical Industry: A Review

by Cariny Maria Polesca Freitas, Jane Sélia Reis Coimbra, Victor Gomes Lauriano Souza and Rita Cássia Superbi Sousa

Coatings 2021, 11(8), 922; https://doi.org/10.3390/coatings11080922 - 1 Aug 2021

Cited by 248 | Viewed by 38250

Abstract

Pectin is a biocompatible polysaccharide with intrinsic biological activity, which may exhibit different structures depending on its source or extraction method. The extraction of pectin from various industrial by-products presents itself as a green option for the valorization of agro-industrial residues by producing [...] Read more.

Pectin is a biocompatible polysaccharide with intrinsic biological activity, which may exhibit different structures depending on its source or extraction method. The extraction of pectin from various industrial by-products presents itself as a green option for the valorization of agro-industrial residues by producing a high commercial value product. Pectin is susceptible to physical, chemical, and/or enzymatic changes. The numerous functional groups present in its structure can stimulate different functionalities, and certain modifications can enable pectin for countless applications in food, agriculture, drugs, and biomedicine. It is currently a trend to use pectin to produce edible coating to protect foodstuff, antimicrobial bio-based films, nanoparticles, healing agents, and cancer treatment. Advances in methodology, use of different sources of extraction, and knowledge about structural modification have significantly expanded the properties, yields, and applications of this polysaccharide. Recently, structurally modified pectin has shown better functional properties and bioactivities than the native one. In addition, pectin can be used in conjunction with a wide variety of biopolymers with differentiated properties and specific functionalities. In this context, this review presents the structural characteristics and properties of pectin and information on the modification of this polysaccharide, its respective applications, perspectives, and future challenges. Full article

(This article belongs to the Special Issue Recent Advances in Food Bio-Preservation Films)

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19 pages, 1332 KB

Open AccessFeature PaperEditor’s ChoiceReview

Active Casein Coatings and Films for Perishable Foods: Structural Properties and Shelf-Life Extension

by Muhammad Rehan Khan, Stefania Volpe, Marika Valentino, Nicoletta Antonella Miele, Silvana Cavella and Elena Torrieri

Coatings 2021, 11(8), 899; https://doi.org/10.3390/coatings11080899 - 28 Jul 2021

Cited by 64 | Viewed by 9320

Abstract

There is an urgent need to increase the food supplies to fulfil the demands of future generations as the population of the world is expected to grow beyond 10 billion by 2050. An essential component for ensuring global food security is to reduce [...] Read more.

There is an urgent need to increase the food supplies to fulfil the demands of future generations as the population of the world is expected to grow beyond 10 billion by 2050. An essential component for ensuring global food security is to reduce food losses during the post-harvest stage. Active edible coatings and films are a promising sustainable preservation technology for shelf-life extension of food products by hindering decay kinetics of minimally processed fruits and vegetables (F&V), by restricting the mass transfer of moisture, aroma, or gases and carrying an active compound, such as an antioxidant or antimicrobial. Active protein-based coatings and films have the potential to extend the shelf-life of food products by decreasing their respiration rates, as they exhibit an excellent gas barrier and good mechanical properties as compared to other biopolymeric packaging. Among protein-based biopolymers, casein and its derivatives as packaging films have been extensively studied due to their low cost, complete biodegradability, and availability. Currently, there is no review study focusing on caseinate-based active coating and film, thus, this review aims to give insights on the composition, rheology, structure, and properties of caseinate-based formulations by critically discussing the results presented in the literature. A methodological approach was followed to obtain relevant literature to discuss the influence of additives on the shelf-life of F&V. Furthermore, changes in secondary structure of casein were observed after incorporation of bioactive compounds (i.e., phenolic acids). Likewise, there is a need to explore chemical interactions among bioactive compounds and biopolymer material by using in silico and laboratory trials as food additives have shown to influence the physicochemical properties of film and shelf-life of food products. Full article

(This article belongs to the Special Issue Biopolymer Coatings for Food Packaging Applications)

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12 pages, 4428 KB

Open AccessEditor’s ChoiceArticle

Based on Ultrathin PEDOT:PSS/c-Ge Solar Cells Design and Their Photoelectric Performance

by Ju Su, Hua Yang, Yan Xu, Yijun Tang, Zao Yi, Fusheng Zheng, Fei Zhao, Li Liu, Pinghui Wu and Hailiang Li

Coatings 2021, 11(7), 748; https://doi.org/10.3390/coatings11070748 - 22 Jun 2021

Cited by 29 | Viewed by 4556

Abstract

In recent years, nanostructures have improved the performance of solar cells and are regarded as the most promising microstructures. The optical properties of PEDOT:PSS/c-Ge hybrid solar cells (HSCs) based on the octagon germanium nanoparticles (O-GNPs) were numerically analyzed using the finite-difference time-domain (FDTD) [...] Read more.

In recent years, nanostructures have improved the performance of solar cells and are regarded as the most promising microstructures. The optical properties of PEDOT:PSS/c-Ge hybrid solar cells (HSCs) based on the octagon germanium nanoparticles (O-GNPs) were numerically analyzed using the finite-difference time-domain (FDTD) method. The optimal structure of the hybrid solar cell is determined by changing the thickness of the organic layer and structural parameters of nanoparticles to enhance the optical absorption and eventually achieve high broadband absorption. By changing the structure parameter of O-GNPs, we studied its effect on solar cells. The optimization of geometric parameters is based on maximum absorption. The light absorption of our optimized HSCs is basically above 90% between 200 and 1500 nm. PEDOT:PSS is placed on top of O-GNPs to transmit the holes better, allowing O-GNPs to capture a lot of photons, to increase absorbance value properties in the AM1.5 solar spectral irradiated region. The transmittance is increased by adding poly-methyl methacrylate (PMMA). At the same time, the electrical characteristics of Ge solar cells were simulated by DEVICE, and short-circuit current (Jsc), open-circuit voltage (Voc), maximum power (Pmax), filling coefficient (FF) and photoelectric conversion efficiency (PCE) were obtained. According to the optimization results after adjusting the structural parameters, the maximum short-circuit current is 44.32 mA/cm²; PCE is 7.84 mW/cm²; FF is 69%. The results show that the O-GNPs have a good light trapping effect, and the structure design has great potential for the absorption of HSCs; it is believed that the conversion efficiency will be further improved through further research. Full article

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

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12 pages, 5635 KB

Open AccessEditor’s ChoiceArticle

Facile Synthesis of Copper(I) Oxide Nanochains and the Photo-Thermal Conversion Performance of Its Nanofluids

by Zhongjin Ni, Xiaohai Cao, Xinyi Wang, Shiyu Zhou, Caixia Zhang, Bin Xu and Yihua Ni

Coatings 2021, 11(7), 749; https://doi.org/10.3390/coatings11070749 - 22 Jun 2021

Cited by 71 | Viewed by 4523

Abstract

In this thesis, Cu₂O nanochains were synthesized by thermal decomposition with copper formate-octylamine as the precursor, oleic acid and oleylamine as the catalyst stabilizer agent and paraffin as the solvent. The phase structure and micromorphology of Cu₂O nanochains were [...] Read more.

In this thesis, Cu₂O nanochains were synthesized by thermal decomposition with copper formate-octylamine as the precursor, oleic acid and oleylamine as the catalyst stabilizer agent and paraffin as the solvent. The phase structure and micromorphology of Cu₂O nanochains were characterized by X-ray diffraction and transmission electron microscopy. The effect of reaction time and concentration of the precursor on the Cu₂O nanochains were discussed, and the formation mechanism of the Cu₂O nanochains was analyzed. The results show that Cu₂O nanochains were self-assembled by Cu₂O nanocrystals; with the extension of the reaction time, Cu₂O nanochains gradually become granular; increasing the concentration of the precursor will increase the entanglement degree of the nanochains. Oleic acid contributes to the formation of Cu₂O, and oleylamine plays a directional role in the formation of nanochains. On the basis of those phenomenon, a comparison of the Cu₂O nanochain-water nanofluids with that of a water-based liquid showed that after irradiating for 3000 s, the temperature of nanofluids reached 91.1 °C while the water was only 75.7 °C. This demonstrates the better performance of the Cu₂O nanochain-water nanofluid in the ability of light absorption, thermal conductivity and photothermal conversion. Full article

(This article belongs to the Special Issue Corrosion and Degradation of Materials)

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19 pages, 2875 KB

Open AccessFeature PaperEditor’s ChoiceReview

High Pressure X-ray Diffraction as a Tool for Designing Doped Ceria Thin Films Electrolytes

by Sara Massardo, Alessandro Cingolani and Cristina Artini

Coatings 2021, 11(6), 724; https://doi.org/10.3390/coatings11060724 - 16 Jun 2021

Cited by 3 | Viewed by 3417

Abstract

Rare earth-doped ceria thin films are currently thoroughly studied to be used in miniaturized solid oxide cells, memristive devices and gas sensors. The employment in such different application fields derives from the most remarkable property of this material, namely ionic conductivity, occurring through [...] Read more.

Rare earth-doped ceria thin films are currently thoroughly studied to be used in miniaturized solid oxide cells, memristive devices and gas sensors. The employment in such different application fields derives from the most remarkable property of this material, namely ionic conductivity, occurring through the mobility of oxygen ions above a certain threshold temperature. This feature is in turn limited by the association of defects, which hinders the movement of ions through the lattice. In addition to these issues, ionic conductivity in thin films is dominated by the presence of the film/substrate interface, where a strain can arise as a consequence of lattice mismatch. A tensile strain, in particular, when not released through the occurrence of dislocations, enhances ionic conduction through the reduction of activation energy. Within this complex framework, high pressure X-ray diffraction investigations performed on the bulk material are of great help in estimating the bulk modulus of the material, and hence its compressibility, namely its tolerance toward the application of a compressive/tensile stress. In this review, an overview is given about the correlation between structure and transport properties in rare earth-doped ceria films, and the role of high pressure X-ray diffraction studies in the selection of the most proper compositions for the design of thin films. Full article

(This article belongs to the Special Issue Functional Oxide Thin Films and Nanostructures: Growth, Properties, and Applications)

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12 pages, 2377 KB

Open AccessFeature PaperEditor’s ChoiceArticle

Plasma Enhanced-Chemical Vapor Deposition of 2-Isopropenyl-2-Oxazoline to Promote the Adhesion between a Polyethylene Terephthalate Monofilament and the Rubber in a Tire

by Carlo Maria Gaifami, Stefano Zanini, Luca Zoia and Claudia Riccardi

Coatings 2021, 11(6), 708; https://doi.org/10.3390/coatings11060708 - 12 Jun 2021

Cited by 3 | Viewed by 3601

Abstract

A Plasma-Enhanced Chemical Vapor Deposition was chosen in order to deposit an organic thin film on polyethylene terephthalate monofilament to increase its adhesion with the rubber compound in a tire. The aim of the work is to find an alternative “green” method to [...] Read more.

A Plasma-Enhanced Chemical Vapor Deposition was chosen in order to deposit an organic thin film on polyethylene terephthalate monofilament to increase its adhesion with the rubber compound in a tire. The aim of the work is to find an alternative “green” method to the classical chemical dipping with Resorcinol Formaldehyde Latex: plasma treatments are environmentally friendly and easy to use. 2-isoprepenyl-2-oxazoline (2-iox) was employed as precursor and the treatments were performed in a vacuum system, both in a continuous regime and a pulsed regime. Initially, the coatings were deposited on polyethylene terephthalate sheets to study the wettability (by the measurement of contact angle) and the thickness (by profilometer) of the plasma polymer. The chemical characterization was investigated by Infrared and X-ray Photoelectron spectroscopies. Finally, the adhesion of the polyethylene terephthalate sheets was measured by Peel Test, using the coating as adhesive and as a pre-dip. The measurement of the peel force made it possible to optimize the plasma parameters that were applied on the monofilament. The adhesion was estimated by the measure of the extraction force and the evaluation of the coverage compared with those of the classical chemical treatment Resorcinol Formaldehyde Latex. Full article

(This article belongs to the Special Issue Surface Plasma Treatments)

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11 pages, 2048 KB

Open AccessEditor’s ChoiceArticle

Influence of the Bottom Color Modification and Material Color Modification Process on the Performance of Modified Poplar

by Qingqing Liu, Di Gao and Wei Xu

Coatings 2021, 11(6), 660; https://doi.org/10.3390/coatings11060660 - 31 May 2021

Cited by 44 | Viewed by 3845

Abstract

According to the old surface coating process of European and American furniture, the surface of modified poplar is first differentiated pre-treatment, and then the bottom color modification and material color modification are respectively applied to the modified poplar after the surface differentiation treatment. [...] Read more.

According to the old surface coating process of European and American furniture, the surface of modified poplar is first differentiated pre-treatment, and then the bottom color modification and material color modification are respectively applied to the modified poplar after the surface differentiation treatment. The visual physical quantity and physical and chemical properties were measured and compared with mahogany, which is commonly used in old furniture in Europe and America to explore the effect of colorants and coloring steps, as well as different surface pretreatments on the coloring effect. Finally, it is concluded that continuous coloring operations can narrow the difference in brightness and red color value in the coloring layer of modified poplar and mahogany. Continuous coloring operations increase the difference between the yellow-green color values of modified poplar and mahogany. Therefore, the coloring difference between modified poplar and mahogany was affected by the colorant and coloring steps. Through color accumulation, the gap between the two in the target color coloring effect can be reduced, thereby reducing the difference between the coloring effect of modified poplar and mahogany. Full article

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8 pages, 3121 KB

Open AccessFeature PaperEditor’s ChoiceArticle

N⁺ Irradiation and Substrate-Induced Variability in the Metamagnetic Phase Transition of FeRh Films

by Steven P. Bennett, Samuel W. LaGasse, Marc Currie, Olaf Van’t Erve, Joseph C. Prestigiacomo, Cory D. Cress and Syed B. Qadri

Coatings 2021, 11(6), 661; https://doi.org/10.3390/coatings11060661 - 31 May 2021

Cited by 5 | Viewed by 4363

Abstract

Metamagnetic FeRh has been the focus of numerous studies for its highly unique antiferromagnetic (AF) to ferromagnetic (FM) metamagnetic transition. While this phase transition usually occurs above room temperature (often T_c > 400 K), both ion irradiation and strained epitaxial growth have [...] Read more.

Metamagnetic FeRh has been the focus of numerous studies for its highly unique antiferromagnetic (AF) to ferromagnetic (FM) metamagnetic transition. While this phase transition usually occurs above room temperature (often T_c > 400 K), both ion irradiation and strained epitaxial growth have been used to bring it to applicable temperatures. Nevertheless, cross sample variability is pervasive in these studies. Here we explore the optical and magnetic properties of 35 nm thick FeRh grown by magnetron sputter deposition simultaneously on two different single crystal substrates: epitaxially on MgO (001) and highly strained with large lattice mismatch on Al₂O₃ (1000). We then irradiate the epitaxial film with 5 keV N⁺ ions to introduce disorder (and to a lesser extent, modify chemical composition) without effecting the surface morphology. We find that the phase-transitional properties of both films are strikingly different due to the large lattice mismatch, despite being grown in tandem with nominally identical growth conditions including Fe/Rh stoichiometry, pressure, and temperature. We observe that N⁺ implantation lowers T_c by ~60 K, yielding a sample with nominally the same transition temperature as the non-epitaxial film on sapphire, yet with a significantly increased magnetic moment, a larger magnetization change and a more abrupt transition profile. We attribute these differences to the Volmer-Weber type growth mode induced by the sapphire substrate and the resulting rougher surface morphology. Full article

(This article belongs to the Special Issue Epitaxial Thin Films: Properties and Applications)

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14 pages, 4052 KB

Open AccessFeature PaperEditor’s ChoiceArticle

Effects of Polysilane Addition to Chlorobenzene and High Temperature Annealing on CH₃NH₃PbI₃ Perovskite Photovoltaic Devices

by Takeo Oku, Masaya Taguchi, Atsushi Suzuki, Kaede Kitagawa, Yugo Asakawa, Satoshi Yoshida, Masanobu Okita, Satoshi Minami, Sakiko Fukunishi and Tomoharu Tachikawa

Coatings 2021, 11(6), 665; https://doi.org/10.3390/coatings11060665 - 31 May 2021

Cited by 35 | Viewed by 4372

Abstract

CH₃NH₃PbI₃ perovskite photovoltaic devices treated with a polysilane layer were fabricated and characterized. Decaphenylcyclopentasilane (DPPS) in chlorobenzene solution was deposited at the surface of the perovskite layer, and the resulting device was annealed at 140–260 °C. The photoconversion [...] Read more.

CH₃NH₃PbI₃ perovskite photovoltaic devices treated with a polysilane layer were fabricated and characterized. Decaphenylcyclopentasilane (DPPS) in chlorobenzene solution was deposited at the surface of the perovskite layer, and the resulting device was annealed at 140–260 °C. The photoconversion efficiencies of the DPPS-treated device remained high even after 255 days in ambient air. Raman scattering spectroscopy and ab initio molecular orbital calculations of DPPS suggested that it increased hole transport efficiency in the treated devices, which was confirmed from the high shunt resistances of the DPPS-treated devices. Full article

(This article belongs to the Special Issue Synthesis, Chracterization and Applications of Coated Composite Materials for Energy Applications)

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18 pages, 34718 KB

Open AccessFeature PaperEditor’s ChoiceArticle

Consolidation and Adhesion of Pictorial Layers on a Stone Substrate. The Study Case of the Virgin with the Child from Palazzo Madama, in Turin

by Anita Negri, Marco Nervo, Stefania Di Marcello and Daniele Castelli

Coatings 2021, 11(6), 624; https://doi.org/10.3390/coatings11060624 - 23 May 2021

Cited by 8 | Viewed by 4814

Abstract

The study and the restoration of a polychrome limestone statue representing the Virgin with the Child, from Palazzo Madama in Turin (NW Italy) offered interesting conservation issue related to the polychromy on stone. To preserve the pictorial layers, it was necessary to re-establish [...] Read more.

The study and the restoration of a polychrome limestone statue representing the Virgin with the Child, from Palazzo Madama in Turin (NW Italy) offered interesting conservation issue related to the polychromy on stone. To preserve the pictorial layers, it was necessary to re-establish the cohesion among the different polychrome layers (original and repainted) and the adhesion between polychrome film and the stone substrate. Particular attention was paid to the choice of intervention materials, selected through a preliminary survey of the scientific literature, and then verified by laboratory tests (tape test, colorimetric test, and permeability test). The most suitable product should to be able to penetrate porosity, to consolidate the layers, to make the pictorial film adhere with the stone surface, and to avoid changes in the colour and in the permeability. The material chosen also had to ensure compatibility with the cleaning method that could only take place after the consolidation of the pictorial layers due to the problematic state of preservation. A range of products, characterised by their small particle size and low viscosity, was tested, and a micro-acrylic resin was selected and successfully applied on the polychromy of the sculpture. Full article

(This article belongs to the Special Issue Conservation Tools, Protocols and Treatments on Painted Surfaces, Metal Leaves and Finishes in Cultural Heritage)

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16 pages, 6577 KB

Open AccessFeature PaperEditor’s ChoiceArticle

Fabrication of Thermal Plasma Sprayed NiTi Coatings Possessing Functional Properties

by Sneha Samal, Ondřej Tyc, Jan Cizek, Jakub Klecka, František Lukáč, Orsolya Molnárová, Esther de Prado, Zdeněk Weiss, Jaromír Kopeček, Luděk Heller, Petr Šittner and Tomáš Chráska

Coatings 2021, 11(5), 610; https://doi.org/10.3390/coatings11050610 - 20 May 2021

Cited by 26 | Viewed by 4938

Abstract

Thick NiTi shape memory alloy coatings (300–500 µm) were produced on graphite and AISI 304 substrates by radio frequency inductively-coupled plasma spray technology (RF-ICP) from feedstock NiTi powders. Their microstructure as well as chemical and phase composition were characterized and a methodology for [...] Read more.

Thick NiTi shape memory alloy coatings (300–500 µm) were produced on graphite and AISI 304 substrates by radio frequency inductively-coupled plasma spray technology (RF-ICP) from feedstock NiTi powders. Their microstructure as well as chemical and phase composition were characterized and a methodology for the characterization of functional shape memory properties of the thick coatings was developed. The coatings exhibited cubic to monoclinic martensitic transformation and shape memory effect. The presented results prove that NiTi coatings with functional thermomechanical properties can be easily produced on structural materials by RF-ICP. Further optimization will be needed to prepare NiTi coatings with better microstructural and chemical homogeneity. Full article

(This article belongs to the Special Issue Thermal Plasma Processing for Coating: Structural, Functional Properties of Thick Films)

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16 pages, 2320 KB

Open AccessFeature PaperEditor’s ChoiceArticle

Pseudo-Planar Organic Heterojunctions by Sequential Printing of Quasi-Miscible Inks

by Ana-Gianina Gereanu, Camillo Sartorio, Aurelio Bonasera, Giuliana Giuliano, Sebastiano Cataldo, Michelangelo Scopelliti, Giuseppe Arrabito and Bruno Pignataro

Coatings 2021, 11(5), 586; https://doi.org/10.3390/coatings11050586 - 17 May 2021

Cited by 5 | Viewed by 4063

Abstract

This work deals with the interfacial mixing mechanism of picoliter (pL)-scale droplets produced by sequential inkjet printing of organic-based inks onto ITO/PET surfaces at a moderately high Weber number (~10¹). Differently from solution dispensing processes at a high Bond number such [...] Read more.

This work deals with the interfacial mixing mechanism of picoliter (pL)-scale droplets produced by sequential inkjet printing of organic-based inks onto ITO/PET surfaces at a moderately high Weber number (~10¹). Differently from solution dispensing processes at a high Bond number such as spin coating, the deposition by inkjet printing is strictly controlled by droplet velocity, ink viscosity, and surface tension. In particular, this study considers the interfacial mixing of droplets containing the most investigated donor/acceptor couple for organic solar cells, i.e., poly(3-hexylthiophene) (P3HT) and (6,6)-phenyl-C₆₁-butyric acid methyl ester (PCBM), showing how low-viscosity and low-surface energy inks can be leveraged for the fabrication of an interface suitable for a pseudo-planar heterojunction (pseudo-PHJ) organic solar cell (OSC) that is a convenient alternative to a bulk heterojunction (BHJ) OSC. The resulting thin-film morphology and molecular organization at the P3HT/PCBM interface are investigated, highlighting the roles of dissolution-driven molecular recirculation. This report represents a first step toward the sequential inkjet printing fabrication of pseudo-PHJ OSCs at low consumption of solvents/chemicals. Full article

(This article belongs to the Special Issue Application of Graphene and Two-Dimensional Materials in Thin Films)

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15 pages, 2753 KB

Open AccessFeature PaperEditor’s ChoiceArticle

Impact of Water-Repellent Products on the Moisture Transport Properties and Mould Susceptibility of External Thermal Insulation Composite Systems

by Renata Roncon, Giovanni Borsoi, João L. Parracha, Inês Flores-Colen, Rosário Veiga and Lina Nunes

Coatings 2021, 11(5), 554; https://doi.org/10.3390/coatings11050554 - 8 May 2021

Cited by 14 | Viewed by 4672

Abstract

External Thermal Insulation Composite Systems (ETICS) are constructive solutions widely used to increase the thermal insulation in new and retrofitted buildings. However, these systems can present several anomalies due to their constant exposure to weathering agents and anthropic factors. Water is generally the [...] Read more.

External Thermal Insulation Composite Systems (ETICS) are constructive solutions widely used to increase the thermal insulation in new and retrofitted buildings. However, these systems can present several anomalies due to their constant exposure to weathering agents and anthropic factors. Water is generally the major cause of degradation. Thus, the application of water-repellent products can minimize the appearance of anomalies and increase the durability of the systems. In this paper, acrylic-based and siloxane-based hydrophobic products were applied to ETICS, with the aim of assessing the compatibility, effectiveness, and durability of these products. The moisture transport properties and mould susceptibility were assessed through laboratory tests on untreated and treated specimens. The durability of the hydrophobic treatments was also evaluated through artificial aging tests (heat-cold and freeze-thaw cycles). Results show that the protection products generally decreased water absorption, slightly decreased the drying rate, and presented adequate water vapor permeability. After aging, the products still had reasonable effectiveness and, with one exception, improved the water vapor diffusion of the systems. Additionally, ETICS underwent an alteration in the finishing coat (possible modification of the porosity) due to the aging cycles. No clear linear correlation was found between the contact angle values and water absorption results, evidencing the influence of other factors related to the composition of the water-repellent products. Full article

(This article belongs to the Special Issue Advanced Coatings for Buildings - Challenges and Opportunities)

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15 pages, 6030 KB

Open AccessFeature PaperEditor’s ChoiceArticle

Hydrogen and Deuterium Incorporation in ZnO Films Grown by Atomic Layer Deposition

by Sami Kinnunen, Manu Lahtinen, Kai Arstila and Timo Sajavaara

Coatings 2021, 11(5), 542; https://doi.org/10.3390/coatings11050542 - 3 May 2021

Cited by 6 | Viewed by 7998

Abstract

Zinc oxide (ZnO) thin films were grown by atomic layer deposition using diethylzinc (DEZ) and water. In addition to depositions with normal water, heavy water (²H₂O) was used in order to study the reaction mechanisms and the hydrogen incorporation [...] Read more.

Zinc oxide (ZnO) thin films were grown by atomic layer deposition using diethylzinc (DEZ) and water. In addition to depositions with normal water, heavy water (²H₂O) was used in order to study the reaction mechanisms and the hydrogen incorporation at different deposition temperatures from 30 to 200 °C. The total hydrogen concentration in the films was found to increase as the deposition temperature decreased. When the deposition temperature decreased close to room temperature, the main source of impurity in hydrogen changed from ¹H to ²H. A sufficiently long purging time changed the main hydrogen isotope incorporated in the film back to ¹H. A multiple short pulse scheme was used to study the transient steric hindrance. In addition, the effect of the storage of the samples in ambient conditions was studied. During the storage, the deuterium concentration decreased while the hydrogen concentration increased an equal amount, indicating that there was an isotope exchange reaction with ambient H₂ and/or H₂O. Full article

(This article belongs to the Special Issue Coatings and Thin Film for Chemical Vapor Deposition (CVD) Application)

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27 pages, 8793 KB

Open AccessFeature PaperEditor’s ChoiceArticle

Development of DLC-Coated Solid SiAlON/TiN Ceramic End Mills for Nickel Alloy Machining: Problems and Prospects

by Sergey N. Grigoriev, Marina A. Volosova, Sergey V. Fedorov, Anna A. Okunkova, Petr M. Pivkin, Pavel Y. Peretyagin and Artem Ershov

Coatings 2021, 11(5), 532; https://doi.org/10.3390/coatings11050532 - 29 Apr 2021

Cited by 83 | Viewed by 7239

Abstract

The study is devoted to the development and testing of technological principles for the manufacture of solid end mills from ceramics based on a powder composition of α-SiAlON, β-SiAlON, and TiN additives, including spark plasma sintering powder composition, diamond sharpening of sintered ceramic [...] Read more.

The study is devoted to the development and testing of technological principles for the manufacture of solid end mills from ceramics based on a powder composition of α-SiAlON, β-SiAlON, and TiN additives, including spark plasma sintering powder composition, diamond sharpening of sintered ceramic blanks for shaping the cutting part of mills and deposition of anti-friction Si-containing diamond-like carbon (DLC) coatings in the final stage. A rational relationship between the components of the powder composition at spark plasma sintering was established. The influence of optimum temperature, which is the most critical sintering parameter, on ceramic samples’ basic physical and mechanical properties was investigated. DLC coatings’ role in changing the surface properties of ceramics based on SiAlON, such as microrelief, friction coefficient, et cetera, was studied. A comparative analysis of the efficiency of two tool options, such as developed samples of experimental mills made of SiAlON/TiN and commercial samples ceramic mills based on SiAlON, doped with stabilizing additives containing Yb when processing nickel alloys (NiCr20TiAl alloy was used as an example). DLC coatings’ contribution to the quantitative indicators of the durability of ceramic mills and the surface quality of machined products made of nickel alloy is shown. Full article

(This article belongs to the Special Issue Technologies of Coatings and Surface Hardening for Tool Industry)

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22 pages, 2819 KB

Open AccessFeature PaperEditor’s ChoiceReview

Curcumin: Modern Applications for a Versatile Additive

by Florentina Monica Raduly, Valentin Raditoiu, Alina Raditoiu and Violeta Purcar

Coatings 2021, 11(5), 519; https://doi.org/10.3390/coatings11050519 - 28 Apr 2021

Cited by 48 | Viewed by 8845

Abstract

The recent development of several methods for extracting curcumin from the root of the plant Curcuma longa has led to intensified research on the properties of curcumin and its fields of application. Following the studies and the accreditation of curcumin as a natural [...] Read more.

The recent development of several methods for extracting curcumin from the root of the plant Curcuma longa has led to intensified research on the properties of curcumin and its fields of application. Following the studies and the accreditation of curcumin as a natural compound with antifungal, antiviral, and antibacterial properties, new fields of application have been developed in two main directions—food and medical, respectively. This review paper aims to synthesize the fields of application of curcumin as an additive for the prevention of spoilage, safety, and quality of food. Simultaneously, it aims to present curcumin as an additive in products for the prevention of bacterial infections and health care. In both cases, the types of curcumin formulations in the form of (nano)emulsions, (nano)particles, or (nano)composites are presented, depending on the field and conditions of exploitation or their properties to be used. The diversity of composite materials that can be designed, depending on the purpose of use, leaves open the field of research on the conditioning of curcumin. Various biomaterials active from the antibacterial and antibiofilm point of view can be intuited in which curcumin acts as an additive that potentiates the activities of other compounds or has a synergistic activity with them. Full article

(This article belongs to the Special Issue Natural Materials in Functional Coatings)

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15 pages, 14616 KB

Open AccessFeature PaperEditor’s ChoiceArticle

Thermal Atomic Layer Deposition of Yttrium Oxide Films and Their Properties in Anticorrosion and Water Repellent Coating Applications

by Christian Dussarrat, Nicolas Blasco, Wontae Noh, Jooho Lee, Jamie Greer, Takashi Teramoto, Sunao Kamimura, Nicolas Gosset and Takashi Ono

Coatings 2021, 11(5), 497; https://doi.org/10.3390/coatings11050497 - 23 Apr 2021

Cited by 13 | Viewed by 7978

Abstract

The thermal atomic layer deposition (ThALD) of yttrium oxide (Y₂O₃) was developed using the newly designed, liquid precursor, Y(EtCp)₂(ⁱPr₂-amd), as the yttrium source in combination with different oxygen sources, such as ozone, water [...] Read more.

The thermal atomic layer deposition (ThALD) of yttrium oxide (Y₂O₃) was developed using the newly designed, liquid precursor, Y(EtCp)₂(ⁱPr₂-amd), as the yttrium source in combination with different oxygen sources, such as ozone, water and even molecular oxygen. Saturation was observed for the growth of the Y₂O₃ films within an ALD window of 300 to 450 °C and a growth per cycle (GPC) up to 1.1 Å. The resulting Y₂O₃ films possess a smooth and crystalline structure, while avoiding any carbon and nitrogen contamination, as observed by X-ray photoelectron spectroscopy (XPS). The films showed strong resistance to fluorine-containing plasma, outperforming other resistant materials, such as silicon oxide, silicon nitride and alumina. Interestingly, the hydrophilic character exhibited by the film could be switched to hydrophobic after exposure to air, with water contact angles exceeding 90°. After annealing under N₂ flow at 600 °C for 4 min, the hydrophobicity was lost, but proved recoverable after prolonged air exposure or intentional hydrocarbon exposure. The origin of these changes in hydrophobicity was examined. Full article

(This article belongs to the Special Issue Thin and Thick Films: Deposition, Characterization and Applications)

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16 pages, 5413 KB

Open AccessFeature PaperEditor’s ChoiceArticle

High Transmittance Superhydrophobic Coatings with Durable Self-Cleaning Properties

by Michele Ferrari, Paolo Piccardo, Justine Vernet and Francesca Cirisano

Coatings 2021, 11(5), 493; https://doi.org/10.3390/coatings11050493 - 22 Apr 2021

Cited by 25 | Viewed by 5928

Abstract

One of the most important factors determining a significant reduction in optical devices’ efficiency is the accumulation of soiling substances such as dust, which, especially in solar power plants, implies higher costs and materials ageing. The use of superhydrophobic (SH) coatings, water contact [...] Read more.

One of the most important factors determining a significant reduction in optical devices’ efficiency is the accumulation of soiling substances such as dust, which, especially in solar power plants, implies higher costs and materials ageing. The use of superhydrophobic (SH) coatings, water contact angle (CA) greater than 150°, represents a suitable solution to improve the self-cleaning action while at the same time providing high transmittance for energy conversion. A mixed organic–inorganic SH coating with surface roughness below 100 nm was prepared by an easily scalable spray method and employed, allowing us to modulate the covered area and transparency. The coating has been also investigated while simulating pollution agents like acid rain, harsh environments, and the impact of continuous water droplets and dust particles with different physicochemical properties. The spray coating method allows us to obtain a modulated SH and self-cleaning surface showing CA > 170°, high transmittance in UV-Vis range and the ability to completely restore its initial properties in terms of wettability and transmittance after durability and soiling tests. Full article

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

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32 pages, 6627 KB

Open AccessFeature PaperEditor’s ChoiceReview

Passive Layers and Corrosion Resistance of Biomedical Ti-6Al-4V and β-Ti Alloys

by Patrizia Bocchetta, Liang-Yu Chen, Juliana Dias Corpa Tardelli, Andréa Cândido dos Reis, Facundo Almeraya-Calderón and Paola Leo

Coatings 2021, 11(5), 487; https://doi.org/10.3390/coatings11050487 - 21 Apr 2021

Cited by 225 | Viewed by 21994

Abstract

The high specific strength, good corrosion resistance, and great biocompatibility make titanium and its alloys the ideal materials for biomedical metallic implants. Ti-6Al-4V alloy is the most employed in practical biomedical applications because of the excellent combination of strength, fracture toughness, and corrosion [...] Read more.

The high specific strength, good corrosion resistance, and great biocompatibility make titanium and its alloys the ideal materials for biomedical metallic implants. Ti-6Al-4V alloy is the most employed in practical biomedical applications because of the excellent combination of strength, fracture toughness, and corrosion resistance. However, recent studies have demonstrated some limits in biocompatibility due to the presence of toxic Al and V. Consequently, scientific literature has reported novel biomedical β-Ti alloys containing biocompatible β-stabilizers (such as Mo, Ta, and Zr) studying the possibility to obtain similar performances to the Ti-6Al-4V alloys. The aim of this review is to highlight the corrosion resistance of the passive layers on biomedical Ti-6Al-4V and β-type Ti alloys in the human body environment by reviewing relevant literature research contributions. The discussion is focused on all those factors that influence the performance of the passive layer at the surface of the alloy subjected to electrochemical corrosion, among which the alloy composition, the method selected to grow the oxide coating, and the physicochemical conditions of the body fluid are the most significant. Full article

(This article belongs to the Special Issue Anodizing Processes for the Production of Advanced Functional Coatings)

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32 pages, 535 KB

Open AccessFeature PaperEditor’s ChoiceReview

Enhancing Lithium Manganese Oxide Electrochemical Behavior by Doping and Surface Modifications

by Alexandru-Horaţiu Marincaş and Petru Ilea

Coatings 2021, 11(4), 456; https://doi.org/10.3390/coatings11040456 - 15 Apr 2021

Cited by 33 | Viewed by 8946

Abstract

Lithium manganese oxide is regarded as a capable cathode material for lithium-ion batteries, but it suffers from relative low conductivity, manganese dissolution in electrolyte and structural distortion from cubic to tetragonal during elevated temperature tests. This review covers a comprehensive study about the [...] Read more.

Lithium manganese oxide is regarded as a capable cathode material for lithium-ion batteries, but it suffers from relative low conductivity, manganese dissolution in electrolyte and structural distortion from cubic to tetragonal during elevated temperature tests. This review covers a comprehensive study about the main directions taken into consideration to supress the drawbacks of lithium manganese oxide: structure doping and surface modification by coating. Regarding the doping of LiMn₂O₄, several perspectives are studied, which include doping with single or multiple cations, only anions and combined doping with cations and anions. Surface modification approach consists in coating with different materials like carbonaceous compounds, oxides, phosphates and solid electrolyte solutions. The modified lithium manganese oxide performs better than pristine samples, showing improved cyclability, better behaviour at high discharge c-rates and elevated temperate and improves lithium ions diffusion coefficient. Full article

(This article belongs to the Special Issue Electrodeposition of Thin Films for Energy Applications)

13 pages, 2972 KB

Open AccessFeature PaperEditor’s ChoiceArticle

Synthesis and Properties of p-Si/n-Cd_1−xAg_xO Heterostructure for Transparent Photodiode Devices

by Mannarsamy Anitha, Karuppiah Deva Arun Kumar, Paolo Mele, Nagarajan Anitha, Karunamoorthy Saravanakumar, Mahmoud Ahmed Sayed, Atif Mossad Ali and Lourdusamy Amalraj

Coatings 2021, 11(4), 425; https://doi.org/10.3390/coatings11040425 - 7 Apr 2021

Cited by 8 | Viewed by 3566

Abstract

We developed silver-doped Cd₁–_xAg_xO thin films (where x = 0, 0.01, 0.02, 0.03 and 0.04) on amorphous glass substrate by an automated nebulizer spray pyrolysis set-up. The XRD patterns show rock salt cubic crystal structures, and the [...] Read more.

We developed silver-doped Cd₁–_xAg_xO thin films (where x = 0, 0.01, 0.02, 0.03 and 0.04) on amorphous glass substrate by an automated nebulizer spray pyrolysis set-up. The XRD patterns show rock salt cubic crystal structures, and the crystallite sizes vary with respect to Ag doping concentrations. SEM images exhibited a uniform distribution of grains with the addition of Ag; this feature could support the enhancement of electron mobility. The transmittance spectra reveal that all films show high transmittance in the visible region with the observed bandgap of about 2.40 eV. The room temperature photoluminescence (PL) studies show the increase of near-band-edge (NBE) emission of the films prepared by different Ag doping levels, resulting in respective decreases in the bandgaps. The photodiode performance was analyzed for the fabricated p-Si/n-Cd₁–_xAg_xO devices. The responsivity, external quantum efficiency and detectivity of the prepared p-Si/n-Cd₁–_xAg_xO device were investigated. The repeatability of the optimum (3 at.% Ag) photodiode was also studied. The present investigation suggests that Cd₁–_xAg_xO thin films are the potential candidates for various industrial and photodetector applications. Full article

(This article belongs to the Special Issue Functional Oxide Thin Films and Nanostructures: Growth, Properties, and Applications)

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23 pages, 1534 KB

Open AccessFeature PaperEditor’s ChoiceReview

Natural Ingredients in Functional Coatings—Recent Advances and Future Challenges

by Radu Claudiu Fierascu, Irina Fierascu and Irina Elena Chican

Coatings 2021, 11(4), 429; https://doi.org/10.3390/coatings11040429 - 7 Apr 2021

Cited by 9 | Viewed by 5811

Abstract

In recent decades, coating materials have gained researchers’ interest, finding applications in different areas such as antimicrobial coatings for biomedical applications, coatings for increasing the shelf-life of commercial products, or coatings for the conservation of cultural heritage artifacts. The use of new types [...] Read more.

In recent decades, coating materials have gained researchers’ interest, finding applications in different areas such as antimicrobial coatings for biomedical applications, coatings for increasing the shelf-life of commercial products, or coatings for the conservation of cultural heritage artifacts. The use of new types of coating materials based on natural ingredients can lead to the removal of harmful chemicals and contribute to the development of materials having different and promising properties. New challenges can appear both in the production process, as well as in the case of final application, when coating materials must be applied on various supports. The present review paper aims to be a critical discussion regarding the possibility of using natural ingredients as functional coatings, and to prove that the same material can be used in different fields, from the biomedical to environmental, or from cultural heritage protection to the food and cosmetic industries. The paper is based on the newest published studies, and its main goal is to be an inspiration source for researchers, in order to create more functional and applicable composite coatings in specific fields. Full article

(This article belongs to the Special Issue Natural Materials in Functional Coatings)

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18 pages, 33167 KB

Open AccessFeature PaperEditor’s ChoiceArticle

Improving the Protective Properties of Shellac-Based Varnishes by Functionalized Nanoparticles

by Maduka L. Weththimuni, Chiara Milanese, Maurizio Licchelli and Marco Malagodi

Coatings 2021, 11(4), 419; https://doi.org/10.3390/coatings11040419 - 4 Apr 2021

Cited by 25 | Viewed by 5513

Abstract

Shellac is a natural varnish still known as one of the most elegant finishes for furniture and musical instruments, and currently used for restoration and refinishing of wooden antiques. However, it displays some limitations such as (i) sensitivity to alcoholic solvents (ii) softness [...] Read more.

Shellac is a natural varnish still known as one of the most elegant finishes for furniture and musical instruments, and currently used for restoration and refinishing of wooden antiques. However, it displays some limitations such as (i) sensitivity to alcoholic solvents (ii) softness of the coating, and (iii) considerable weathering due to photo- and bio-degradation. Hence, the main aim of this study was to improve the properties of shellac-based finish by introducing functionalized nanoparticles. Two inorganic nano-sized materials were considered: ZnO that was expected to reduce photo- and bio-degradation problems, and ZrO₂ that was expected to improve the hardness of the varnish. Nanoparticles were synthesized and treated with a bifunctional silane coupling agent. Both plain and functionalized nanoparticles were extensively characterized using different experimental techniques. Functionalized nanoparticles were grafted on shellac through a reaction involving the epoxy-rings introduced on their surface. The resulting modified varnishes were applied on maple wood specimens according to traditional procedures. Different instrumental techniques and testing methods were used to characterize both nano-sized materials and the corresponding nanocomposites, as well as to evaluate the performance of the new coatings. The investigated composite materials display the same aesthetic appearance as plain shellac, while some other properties were improved. In particular, both nanocomposites are distinctly less soluble in alcohols than plain shellac and display antifungal properties. Moreover, coating containing functionalized ZnO nanoparticles displays photo-protection behavior, while shellac modified with ZrO₂ nanoparticles exhibits a higher hardness when compared to the traditional varnish. Full article

(This article belongs to the Special Issue Advanced Coatings for Cultural Heritage Preservation)

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19 pages, 4826 KB

Open AccessFeature PaperEditor’s ChoiceArticle

Surface Chemistry, Crystal Structure, Size and Topography Role in the Albumin Adsorption Process on TiO₂ Anatase Crystallographic Faces and Its 3D-Nanocrystal: A Molecular Dynamics Study

by Giuseppina Raffaini

Coatings 2021, 11(4), 420; https://doi.org/10.3390/coatings11040420 - 4 Apr 2021

Cited by 11 | Viewed by 5664

Abstract

TiO₂ is widely used in biomaterial implants. The topography, chemical and structural properties of titania surfaces are an important aspect to study. The size of TiO₂ nanoparticles synthetized by sol–gel method can influence the responses in the biological environment, and by [...] Read more.

TiO₂ is widely used in biomaterial implants. The topography, chemical and structural properties of titania surfaces are an important aspect to study. The size of TiO₂ nanoparticles synthetized by sol–gel method can influence the responses in the biological environment, and by using appropriate heat treatments different contents of different polymorphs can be formed. Protein adsorption is a crucial step for the biological responses, involving, in particular, albumin, the most abundant blood protein. In this theoretical work, using molecular mechanics and molecular dynamics methods, the adsorption process of an albumin subdomain is reported both onto specific different crystallographic faces of TiO₂ anatase and also on its ideal three-dimensional nanosized crystal, using the simulation protocol proposed in my previous theoretical studies about the adsorption process on hydrophobic ordered graphene-like or hydrophilic amorphous polymeric surfaces. The different surface chemistry of anatase crystalline faces and the nanocrystal topography influence the adsorption process, in particular the interaction strength and protein fragment conformation, then its biological activity. This theoretical study can be a useful tool to better understand how the surface chemistry, crystal structure, size and topography play a key role in protein adsorption process onto anatase surface so widely used as biomaterial. Full article

(This article belongs to the Special Issue Thin Films and Coatings by Sol-Gel Chemistry: Synthesis, Characterization and Applications)

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19 pages, 9272 KB

Open AccessFeature PaperEditor’s ChoiceArticle

Diffusion Aluminide Coatings for Hot Corrosion and Oxidation Protection of Nickel-Based Superalloys: Effect of Fluoride-Based Activator Salts

by Virgilio Genova, Laura Paglia, Giovanni Pulci, Cecilia Bartuli and Francesco Marra

Coatings 2021, 11(4), 412; https://doi.org/10.3390/coatings11040412 - 1 Apr 2021

Cited by 24 | Viewed by 6800

Abstract

The influence of two different fluoride-based activator salts (NH₄F and AlF₃) was studied for diffusion aluminide coatings obtained via pack cementation on a Ni-based superalloy (René 108DS). The resistance to oxidation and hot corrosion was assessed as a function [...] Read more.

The influence of two different fluoride-based activator salts (NH₄F and AlF₃) was studied for diffusion aluminide coatings obtained via pack cementation on a Ni-based superalloy (René 108DS). The resistance to oxidation and hot corrosion was assessed as a function of the concentration of activator salts used during the synthesis process by means of pack cementation. Two different concentrations were selected for activator salts (respecting the equimolarity of fluoride in the synthesis) and the obtained diffusion coatings were compared in terms of morphology, thickness and composition, as well as in terms of microstructural evolution after high temperature exposure. Isothermal oxidation tests were conducted at 1050 °C in air for 100 h in a tubular furnace. The oxidation kinetics were evaluated by measuring the weight variation with exposure time. The microstructural evolution induced by the high temperature exposure was investigated by SEM microscopy, EDS analysis and X-ray diffraction. Results showed that the coatings obtained with AlF₃ activator salt are thicker than those obtained using NH₄F as a consequence of different growth mechanism during pack-cementation. Despite this evidence, it was found that the NH₄F coatings show a better oxidation resistance, both in terms of total mass gain and of quality of the microstructure of the thermally grown oxide. On the other hand, coatings produced with high concentration of AlF₃ exhibited a better resistance in hot corrosion conditions, showing negligible mass variations after 200 h of high temperature exposure to aggressive NaCl and Na₂SO₄ salts. Full article

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

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42 pages, 9689 KB

Open AccessFeature PaperEditor’s ChoiceReview

Extrusion-Based 3D Printing Applications of PLA Composites: A Review

by Eda Hazal Tümer and Husnu Yildirim Erbil

Coatings 2021, 11(4), 390; https://doi.org/10.3390/coatings11040390 - 29 Mar 2021

Cited by 318 | Viewed by 33686

Abstract

Polylactic acid (PLA) is the most widely used raw material in extrusion-based three-dimensional (3D) printing (fused deposition modeling, FDM approach) in many areas since it is biodegradable and environmentally friendly, however its utilization is limited due to some of its disadvantages such as [...] Read more.

Polylactic acid (PLA) is the most widely used raw material in extrusion-based three-dimensional (3D) printing (fused deposition modeling, FDM approach) in many areas since it is biodegradable and environmentally friendly, however its utilization is limited due to some of its disadvantages such as mechanical weakness, water solubility rate, etc. FDM is a simple and more cost-effective fabrication process compared to other 3D printing techniques. Unfortunately, there are deficiencies of the FDM approach, such as mechanical weakness of the FDM parts compared to the parts produced by the conventional injection and compression molding methods. Preparation of PLA composites with suitable additives is the most useful technique to improve the properties of the 3D-printed PLA parts obtained by the FDM method. In the last decade, newly developed PLA composites find large usage areas both in academic and industrial circles. This review focuses on the chemistry and properties of pure PLA and also the preparation methods of the PLA composites which will be used as a raw material in 3D printers. The main drawbacks of the pure PLA filaments and the necessity for the preparation of PLA composites which will be employed in the FDM-based 3D printing applications is also discussed in the first part. The current methods to obtain PLA composites as raw materials to be used as filaments in the extrusion-based 3D printing are given in the second part. The applications of the novel PLA composites by utilizing the FDM-based 3D printing technology in the fields of biomedical, tissue engineering, human bone repair, antibacterial, bioprinting, electrical conductivity, electromagnetic, sensor, battery, automotive, aviation, four-dimensional (4D) printing, smart textile, environmental, and luminescence applications are presented and critically discussed in the third part of this review. Full article

(This article belongs to the Special Issue Surface Modification for Additive Manufacturing: Materials, Processing, Applications and Future Challenges)

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23 pages, 3256 KB

Open AccessEditor’s ChoiceReview

Migration of Silver and Copper Nanoparticles from Food Coating

by Hamed Ahari and Leila Khoshboui Lahijani

Coatings 2021, 11(4), 380; https://doi.org/10.3390/coatings11040380 - 26 Mar 2021

Cited by 62 | Viewed by 9680

Abstract

Packaging containing nanoparticles (NPs) can increase the shelf life of products, but the presence of NPs may hazards human life. In this regard, there are reports regarding the side effect and cytotoxicity of nanoparticles. The main aim of this research was to study [...] Read more.

Packaging containing nanoparticles (NPs) can increase the shelf life of products, but the presence of NPs may hazards human life. In this regard, there are reports regarding the side effect and cytotoxicity of nanoparticles. The main aim of this research was to study the migration of silver and copper nanoparticles from the packaging to the food matrix as well as the assessment techniques. The diffusion and migration of nanoparticles can be analyzed by analytical techniques including atomic absorption, inductively coupled plasma mass spectrometry, inductively coupled plasma atomic emission, and inductively coupled plasma optical emission spectroscopy, as well as X-ray diffraction, spectroscopy, migration, and titration. Inductively coupled plasma-based techniques demonstrated the best results. Reports indicated that studies on the migration of Ag/Cu nanoparticles do not agree with each other, but almost all studies agree that the migration of these nanoparticles is higher in acidic environments. There are widespread ambiguities about the mechanism of nanoparticle toxicity, so understanding these nanoparticles and their toxic effects are essential. Nanomaterials that enter the body in a variety of ways can be distributed throughout the body and damage human cells by altering mitochondrial function, producing reactive oxygen, and increasing membrane permeability, leading to toxic effects and chronic disease. Therefore, more research needs to be done on the development of food packaging coatings with consideration given to the main parameters affecting nanoparticles migration. Full article

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15 pages, 1870 KB

Open AccessFeature PaperEditor’s ChoiceArticle

Environmental Impact of Wood Modification

by Callum Hill, Mark Hughes and Daniel Gudsell

Coatings 2021, 11(3), 366; https://doi.org/10.3390/coatings11030366 - 23 Mar 2021

Cited by 26 | Viewed by 6211

Abstract

The modification of wood involves extra processing over and above what is associated with un-modified material and this will involve an associated environmental impact. There is now a body of information on this due to the presence in the public domain of a [...] Read more.

The modification of wood involves extra processing over and above what is associated with un-modified material and this will involve an associated environmental impact. There is now a body of information on this due to the presence in the public domain of a number of environmental product declarations (EPDs). Using these data, it is possible to determine what the extra impact associated with the modification is. The process of modification results in a life extension of the product, which has implications regarding the storage of sequestered atmospheric carbon in the harvested wood products (HWP) materials’ pool and also extended maintenance cycles (e.g., longer periods between applying coatings). Furthermore, the life extension benefits imparted by wood modification need to be compared with the use of other technologies, such as conventional wood preservatives. This paper analysed the published data from a number of sources (peer-reviewed literature, published EPDs, databases) to compare the impacts associated with different modification technologies. The effect of life extension was examined by modelling the carbon flow dynamics of the HWP pool and determining the effect of different life extension scenarios. Finally, the paper examined the impact of different coating periods, and the extensions thereof, imparted by the use of different modified wood substrates. Full article

(This article belongs to the Special Issue Wood Modification: Characterization, Modelling and Applications)

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Open AccessFeature PaperEditor’s ChoiceArticle

Improving the Laser Texture Strategy to Get Superhydrophobic Aluminum Alloy Surfaces

by Annalisa Volpe, Sara Covella, Caterina Gaudiuso and Antonio Ancona

Coatings 2021, 11(3), 369; https://doi.org/10.3390/coatings11030369 - 23 Mar 2021

Cited by 39 | Viewed by 5770

Abstract

Changing the wetting properties of surfaces is attracting great interest in many fields, in particular to achieve a surface with a superhydrophobic behavior. Laser machining is an emerging technique to functionalize materials with high precision and flexibility without any chemical treatment. However, when [...] Read more.

Changing the wetting properties of surfaces is attracting great interest in many fields, in particular to achieve a surface with a superhydrophobic behavior. Laser machining is an emerging technique to functionalize materials with high precision and flexibility without any chemical treatment. However, when it is necessary to treat large area surfaces laser-based methods are still too slow to be exploited in industrial productions. In this work, we show that by improving the laser texture strategy it is possible to reduce the laser processing time to produce superhydrophobic aluminum alloy surfaces. Three different surface texture geometries were micromachined; namely, square, circular and triangular lattice grooves. We found that if the spacing between the grooves is narrow, i.e., when the percentage of the textured surface is high, the volume of air trapped inside the micromachined structures plays an important role in the wetting behavior. Meanwhile, when the groove spacing approaches the droplet dimensions, the texture geometry has a preponderant influence. Based on these findings an appropriate choice of the laser texture strategy allowed the fabrication of superhydrophobic aluminum alloy surfaces with a 10% reduction of processing time. Full article

(This article belongs to the Special Issue Laser Surface Engineering)

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