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12 pages, 2576 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Influence of Deposition Conditions and Thermal Treatments on Morphological and Chemical Characteristics of Li_6.75La₃Zr_1.75Ta_0.25O₁₂ Thin Films Deposited by Nanosecond PLD

by Mariangela Curcio, Sergio Brutti, Arcangelo Celeste, Agostino Galasso, Angela De Bonis and Roberto Teghil

Coatings 2023, 13(9), 1496; https://doi.org/10.3390/coatings13091496 - 24 Aug 2023

Cited by 1 | Viewed by 1753

Abstract

The production of thin films has been extensively studied due to their unique properties that make them highly useful in a wide range of scientific and technological applications. Obtaining thin films with well-defined stoichiometry and crystallinity is a challenging task, especially when dealing [...] Read more.

The production of thin films has been extensively studied due to their unique properties that make them highly useful in a wide range of scientific and technological applications. Obtaining thin films with well-defined stoichiometry and crystallinity is a challenging task, especially when dealing with materials of complex stoichiometry. Among diverse methodologies for the manufacture of thin films, pulsed laser deposition (PLD) stands out as a versatile technique for producing crystalline films with complex chemical compositions. In this study, nanosecond PLD was employed to manufacture thin films of Ta-doped Li₇La₃Zr₂O₁₂ (LLZTO), a garnet-like oxide that has been proposed as solid electrolyte for Li-ion solid state batteries. Two distinct deposition atmospheres were investigated: vacuum conditions at 10⁻³ Pa and an oxygen-enriched environment with 10 Pa of O₂ gas buffer. To mitigate lithium losses during deposition, a minor addition of lithium oxide was incorporated into the target. The effects of deposition atmosphere and the impact of post-deposition annealing on the structural, compositional, and morphological properties of LLZTO thin films were analysed through a multi-technique approach. The results suggest deposition under oxygen pressure led to the growth of compact, crystalline films characterized by homogenous elemental distribution across the surface and throughout the film’s depth. These films closely resemble the composition of the target LLZTO material, offering valuable insights for the fabrication of high-quality complex oxide thin films. Full article

(This article belongs to the Special Issue Advances and Challenges in Pulsed Laser Deposition for Complex Material Applications)

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24 pages, 7460 KiB

Open AccessEditor’s ChoiceArticle

Evaluation of Antimicrobial and Antioxidant Activities of Alginate Edible Coatings Incorporated with Plant Extracts

by Ana I. Lopes, Adma Melo, Cristina Caleja, Eliana Pereira, Tiane C. Finimundy, Tiago B. Afonso, Sara Silva, Marija Ivanov, Marina Soković, Freni K. Tavaria, Lillian Barros and Manuela Pintado

Coatings 2023, 13(9), 1487; https://doi.org/10.3390/coatings13091487 - 23 Aug 2023

Cited by 9 | Viewed by 3223

Abstract

Plant extracts (PEs) are natural substances that perform interesting bioactivities. However, they have some limitations. In this work, PEs from licorice, eucalyptus, sage, and thyme were produced and characterized. These extracts showed good bioactive properties. Alginate-based edible coatings and films incorporated with the [...] Read more.

Plant extracts (PEs) are natural substances that perform interesting bioactivities. However, they have some limitations. In this work, PEs from licorice, eucalyptus, sage, and thyme were produced and characterized. These extracts showed good bioactive properties. Alginate-based edible coatings and films incorporated with the extracts were produced and their antimicrobial and antioxidant properties were determined. The results showed that the coatings completely inhibited or reduced the growth of all bacteria (E. coli, P. aeruginosa, B. cereus, L. monocytogenes, and S. aureus), except the coating with sage extract. However, only the films incorporated with licorice and eucalyptus could inhibit the growth of Gram-positive bacteria and none of the films were able to inhibit Gram-negative bacteria. The film incorporated with sage extract was the one with the best antifungal property. All films possess a good antioxidant property (ABTS: 942.52–5654.62; DPPH: 1040.67–5162.93 Trolox equivalents (µM)/mg film). Based on the results, it is possible to conclude that alginate coatings and films with PEs present good bioactive properties and can potentially be used as new, biodegradable packages. However, further experiments need to be performed to assess their safety profile, and to prove that they can be a real alternative to traditional food packaging. Full article

(This article belongs to the Section Coatings for Food Technology and System)

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18 pages, 2633 KiB

Open AccessEditor’s ChoiceArticle

Temperature Dependent Anti-Icing Performance of the Microstructure Surface: Wettability Change and Ice Nucleation

by Yi Lu

Coatings 2023, 13(9), 1485; https://doi.org/10.3390/coatings13091485 - 22 Aug 2023

Cited by 2 | Viewed by 1669

Abstract

Icing has caused much inconvenience to daily production and life. A microstructure surface possessing a hydrophobic property is an effective countermeasure to impede or delay ice formation for anti-icing purposes. However, surface wettability is sensitive to environmental conditions such as temperature and humidity. [...] Read more.

Icing has caused much inconvenience to daily production and life. A microstructure surface possessing a hydrophobic property is an effective countermeasure to impede or delay ice formation for anti-icing purposes. However, surface wettability is sensitive to environmental conditions such as temperature and humidity. In the worst-case scenario, a Wenzel state drop forms and causes degradation of surface anti-icing performance. In this study, a copper alloy was used as the testing sample, and the surface was fabricated using mechanical polishing, micro-milling machining and ultrafast laser etching to form the desired topology and microstructures. The hydrophobicity and icephobicity of four types of surfaces including smooth flat, rough flat, rough microstructure and smooth microstructure were tested by depositing droplets from room temperature to an ultralow subzero temperature condition (below −30 °C). At −10 °C, the icephobicity of the surface was consistent with the surface wettability at room temperature. However, the hydrophobicity of the surface slightly decreased, and a Wenzel state drop formed on the microstructure surface. At −30 °C, the apparent contact angle and the ice–substrate contact area were mainly affected by ice nucleation rather than surface wettability. The bottom layer of the droplet froze after immediate contact with the substrate due to a higher degree of supercooling. The formation of a Cassie state drop reduced the ice–substrate contact area and created more air cushions, which facilitated the extension of the icing process of the drop. The enhancement in the anti-icing performance of the microstructure surface was analyzed from a theoretical basis. Full article

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

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30 pages, 15807 KiB

Open AccessEditor’s ChoiceArticle

Characterization and Corrosion Behavior of Zinc Coatings for Two Anti-Corrosive Protections: A Detailed Study

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

Coatings 2023, 13(8), 1460; https://doi.org/10.3390/coatings13081460 - 19 Aug 2023

Viewed by 3350

Abstract

The purpose of this research is to characterize and evaluate the corrosion behavior of zinc coatings used for corrosion protection, with a special focus on the S235 steel material. The introduction highlights the need for corrosion protection in industrial settings, as well as [...] Read more.

The purpose of this research is to characterize and evaluate the corrosion behavior of zinc coatings used for corrosion protection, with a special focus on the S235 steel material. The introduction highlights the need for corrosion protection in industrial settings, as well as the importance of understanding corrosion processes and the development of corrosion products to develop more effective solutions. The study’s goals are to undertake an extensive analysis of corrosion products formed on the zinc coating’s surface, to evaluate the performance of these coatings under atmospheric circumstances, and to investigate the effect of deposition parameters on coating quality. The essential message provided to readers is the critical significance of knowing corrosion product formation mechanisms and zinc coating corrosion behavior in developing long-lasting and effective protection measures. The study methodology includes cycle testing, morphological and chemical examination of corrosion products, as well as optical and electron microscopy and energy-dispersive spectroscopy. Corrosion resistance is assessed using accurate measurements. The results show that zinc coatings have exceptional corrosion resistance under air settings, with the produced corrosion products offering further protection to the underlying material. Furthermore, the study demonstrates that the surface roughness of S235 steel has a substantial impact on the quality and corrosion behavior of hot-dip galvanized coatings. The findings emphasize the necessity of detailed characterization of corrosion products, the effect of depositional factors on zinc coating performance, and the need for novel corrosion protection methods. These discoveries have significant implications for the corrosion protection sector, providing the potential to improve the longevity and efficiency of protective systems used in industrial applications. Full article

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

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20 pages, 7439 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Effect of Post-Fabrication Heat Treatments on the Microstructure of WC-12Co Direct Energy Depositions

by Cindy Morales, Annalisa Fortini, Chiara Soffritti and Mattia Merlin

Coatings 2023, 13(8), 1459; https://doi.org/10.3390/coatings13081459 - 19 Aug 2023

Cited by 2 | Viewed by 2862

Abstract

Laser-Directed Energy Deposition (L-DED) is an additive manufacturing technique that has lately been employed to deposit coatings of cemented carbides, such as WC-Co. During deposition, complex microstructural phenomena usually occur, strongly affecting the microstructural and mechanical behavior of the coatings. Post-fabrication heat treatments [...] Read more.

Laser-Directed Energy Deposition (L-DED) is an additive manufacturing technique that has lately been employed to deposit coatings of cemented carbides, such as WC-Co. During deposition, complex microstructural phenomena usually occur, strongly affecting the microstructural and mechanical behavior of the coatings. Post-fabrication heat treatments (PFHTs) may be applied to homogenize and strengthen the microstructure; nevertheless, to the best of the authors’ knowledge, just a few papers deepened the effect of these treatments on cemented carbides fabricated by additive manufacturing. This work evaluates the influence of four PFHTs on the microstructural evolution and hardness of L-DED WC-12Co. For each treatment, different combinations of solubilization time and temperature (between 30 and 180 min and from 400 °C to 700 °C, respectively) were adopted. The microstructure was investigated by optical and scanning electron microscopy equipped with energy-dispersive spectroscopy, whereas the mechanical properties were determined by Vickers hardness measurements. Based on the results, high microstructural heterogeneity in terms of WC particles, η-phase structures, and Co distribution was observed in the sample in the as-built condition. Some cracking defects were also observed in the samples, irrespective of the heat treatment conditions. Finally, a finer microstructure and a lower amount of brittle ternary η-phase, together with an increase in hardness (1030 ± 95 HV10), were found for the highest dwelling times (180 min) and for solubilization temperatures in the range of 500–600 °C. Full article

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

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14 pages, 3280 KiB

Open AccessEditor’s ChoiceArticle

Green Synthesis and Antibacterial Activity of Silver Nanoparticles Obtained from Moringa oleifera Seed Cake

by Nuno Coelho, João P. Jacinto, Rodrigo Silva, Jéssica C. Soares, Alice S. Pereira and Pedro Tavares

Coatings 2023, 13(8), 1439; https://doi.org/10.3390/coatings13081439 - 16 Aug 2023

Cited by 2 | Viewed by 1775

Abstract

In the present work, we report a simple, cost-efficient, and eco-friendly green method to synthesize silver nanoparticles with antimicrobial activity. An ethanolic extract from Moringa oleifera seed residue was used as a reducing and stabilizing agent in an aqueous solution of silver nitrate. [...] Read more.

In the present work, we report a simple, cost-efficient, and eco-friendly green method to synthesize silver nanoparticles with antimicrobial activity. An ethanolic extract from Moringa oleifera seed residue was used as a reducing and stabilizing agent in an aqueous solution of silver nitrate. The synthesized silver nanoparticles’ hydrodynamic radius, polydispersity index, and zeta-potential were evaluated by Dynamic Light Scattering. Scanning Electron Microscopy was employed to confirm the size and morphology of the nanoparticles. Synthesis of spherical particles with 127 ± 24 nm was confirmed. After sintering, the product of the synthesis was analyzed by X-ray diffraction. The X-ray diffraction pattern attributed to reflections of the (111), (200), (220), and (311) planes, which are characteristic of silver nanoparticles, confirms the successful synthesis of crystalline face-centered cubic nanoparticles. The antimicrobial activity of the bionanoparticles was tested against Escherichia coli BL21(DE3) cells and compared with the effect of a Moringa oleifera seed cake extract. Herein, we show that the growth of Escherichia coli is significantly affected by the addition of the synthesized bionanoparticles. Addition of the bionanoparticles inhibited the growth and lengthened the lag phase of the bacterial culture. Full article

(This article belongs to the Section Bioactive Coatings and Biointerfaces)

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20 pages, 19407 KiB

Open AccessEditor’s ChoiceArticle

Fe/TaC Coatings Produced on 145Cr6 Steel by Laser Alloying—Manufacturing Parameters and Material Characterization

by Dariusz Bartkowski and Aneta Bartkowska

Coatings 2023, 13(8), 1432; https://doi.org/10.3390/coatings13081432 - 15 Aug 2023

Viewed by 2132

Abstract

This paper focuses on Fe/TaC composite coatings produced on 145Cr6 steel by laser alloying a TaC precoat in paste form. Fe/TaC coatings were produced in two consecutive steps. The first stage was the application of a precoat in paste form made from tantalum [...] Read more.

This paper focuses on Fe/TaC composite coatings produced on 145Cr6 steel by laser alloying a TaC precoat in paste form. Fe/TaC coatings were produced in two consecutive steps. The first stage was the application of a precoat in paste form made from tantalum carbide and water glass on a steel substrate. Three TaC precoat thicknesses were produced: 30 µm, 60 µm and 90 µm. In the second step, the TaC precoat was remelted on a steel substrate using a 3 kW rated diode laser beam. A constant laser beam scanning speed of 3 m/min and three laser beam powers were used: 500 W, 800 W and 1100 W. In the study, microstructure, microhardness, chemical and phase composition and wear resistance were tested. The aim of the research was to check the possibility of producing composite coatings in which the reinforcing phase will be TaC, and the role of the matrix will be played by the material from the substrate. It was found that it is possible to produce the continuous composite coatings by remelting the TaC precoat with steel substrate. As microhardness increased, so did wear resistance. The coating microhardness obtained ranged from about 750 to 850 HV0.05 depending on the parameters used. Full article

(This article belongs to the Special Issue Advances in Metal Matrix Composite Coatings and Layers: Microstructure, Physicochemical and Mechanical Properties)

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10 pages, 2672 KiB

Open AccessEditor’s ChoiceArticle

Coating of Carbonized Leather Waste with the Conducting Polymer Polyaniline: Bicontinuous Composites for Dye Adsorption

by Jaroslav Stejskal, Fahanwi Asabuwa Ngwabebhoh, Tomáš Sáha and Jan Prokeš

Coatings 2023, 13(8), 1419; https://doi.org/10.3390/coatings13081419 - 13 Aug 2023

Cited by 2 | Viewed by 2280

Abstract

Leather waste carbonized at 800 °C in an inert atmosphere was coated in situ with the conducting polymer polyaniline. The composition of composites varied from neat carbonaceous to polyaniline. Due to the fibrous collagen structure of the original leather after carbonization, the composites [...] Read more.

Leather waste carbonized at 800 °C in an inert atmosphere was coated in situ with the conducting polymer polyaniline. The composition of composites varied from neat carbonaceous to polyaniline. Due to the fibrous collagen structure of the original leather after carbonization, the composites had a bicontinuous conducting morphology. The resistivity of composites determined as a function of applied pressure from 0.1 to 10 MPa fell mainly into the range of units to tens of Ω cm. In contrast to neat polyaniline, the composites maintained a good level of conductivity even under alkaline conditions. The application of a composite as an adsorbent of organic-dye pollutants in water treatment was illustrated using methylene blue and methyl orange with an eye to future functional adsorbents controllable by applied electrical potential. Full article

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

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15 pages, 3824 KiB

Open AccessEditor’s ChoiceArticle

Assessing the Bioreceptivity of Biobased Cladding Materials

by Karen Butina Ogorelec, Ana Gubenšek, Faksawat Poohphajai and Anna Sandak

Coatings 2023, 13(8), 1413; https://doi.org/10.3390/coatings13081413 - 11 Aug 2023

Cited by 2 | Viewed by 1764

Abstract

Materials exposed to the outdoors are prone to various deterioration processes. Architectural coatings are designed to protect surfaces against environmental and biotic degradation and to provide a decorative layer. The objective of this work was to examine the early colonisers on a diverse [...] Read more.

Materials exposed to the outdoors are prone to various deterioration processes. Architectural coatings are designed to protect surfaces against environmental and biotic degradation and to provide a decorative layer. The objective of this work was to examine the early colonisers on a diverse set of coated and non-coated biobased façade materials. A set of 33 wood-based cladding materials were exposed to four cardinal directions and monitored in outdoor conditions. The surfaces were sampled using a wet swab and plated on DG-18 agar, which prevents the growth of bacteria and limits the growth of fast-growing fungi. Pure cultures were then isolated and identified through PCR amplification and Sanger sequencing of specific DNA regions/genes. The response of cladding materials to weathering and fungal infestation was assessed. The proposed techniques enabled the identification of features that promote/inhibit fungal colonisation and revealed the preference of certain fungi for specific materials. Both the material type and the climate condition at the exposure site influence fungal colonisation. This study is a starting point for more exhaustive assays that aim to develop a novel coating system based on controlled and optimized fungal biofilm formation, and is proposed as a nature-inspired alternative for the protection of architectonic surfaces. Full article

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

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17 pages, 2753 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Effect of Mucilage-Based Edible Coating Enriched with Oregano Essential Oil on Postharvest Quality and Sensorial Attributes of Fresh-Cut Loquat

by Giorgia Liguori, Giuseppe Greco, Francesco Gargano, Raimondo Gaglio, Luca Settanni and Paolo Inglese

Coatings 2023, 13(8), 1387; https://doi.org/10.3390/coatings13081387 - 7 Aug 2023

Cited by 5 | Viewed by 2040

Abstract

Due to pulp browning, weight loss, firmness loss, and decay, loquat fruits, and even more minimally processed fruits have a very short post-harvest life. The aim of our study was to evaluate the effect of Opuntia ficus-indica mucilage-based edible coating enriched with oregano [...] Read more.

Due to pulp browning, weight loss, firmness loss, and decay, loquat fruits, and even more minimally processed fruits have a very short post-harvest life. The aim of our study was to evaluate the effect of Opuntia ficus-indica mucilage-based edible coating enriched with oregano oil on postharvest quality, microbial growth, and sensorial attributes of fresh-cut cv Martorana loquat fruit during cold storage. Fresh-cut loquat fruits were dipped in the mucilage-based solution enriched with oregano essential oil (MO-EC) and in distilled water used as control (CTR). According to our results, the mucilage-based edible coating enriched with oregano oil significantly improved the postharvest life of minimally processed loquat fruits by preserving quality, nutraceutical value, and sensory aspects. MO-EC had a barrier effect on fresh-cut loquat fruit, reducing weight and firmness losses, inhibiting TSS, TA, ascorbic acid content decrease, and enhancing the antioxidant activity until the end of the cold storage period (11 days at 5 °C). Microbiological analysis revealed that coated loquat fruits were characterized by a cell density of spoilage microorganisms 1 Log cycle lower than control fruits. The mucilage-based coating enriched with OEO positively affects the visual appearance of fresh-cut loquat fruits, at the end of the cold storage period, MO-EC samples did indeed report visual ratings that were five times greater than CTR samples. Our research suggests that applying mucilage-based coating enriched with OEO improves peeled loquat fruit shelf-life and allows the producers to sell products that are usually considered unmarketable (fruit with epicarp with large spot areas) to the market. Full article

(This article belongs to the Special Issue Innovations in Active Food Packaging during the Pandemic and into the 'New Normal')

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16 pages, 11179 KiB

Open AccessEditor’s ChoiceArticle

Development of a Transparent Thermal Reflective Thin Film Coating for Accurate Separation of Food-Grade Plastics in Recycling Process via AI-Based Thermal Image Processing

by Ali Salimian and Uchechukwu Onwukwe

Coatings 2023, 13(8), 1332; https://doi.org/10.3390/coatings13081332 - 28 Jul 2023

Viewed by 3007

Abstract

This paper presents the development of a specific thin film coating designed to address the challenge of accurately separating food-grade plastics in the recycling process. The coating, created using a plasma sputtering process, is transparent to the visible spectrum of light while effectively [...] Read more.

This paper presents the development of a specific thin film coating designed to address the challenge of accurately separating food-grade plastics in the recycling process. The coating, created using a plasma sputtering process, is transparent to the visible spectrum of light while effectively reflecting infrared emissions above 1500 nm. Composed of a safe metal oxide formulation with a proprietary composition, the coating is applied to packaging labels. By employing thermal imaging and a computer vision AI model, the coated labels enable precise differentiation of plastics associated with food packaging in the initial stage of plastic recycling. The proposed system achieved a remarkable 100% accuracy in separating food-grade plastics from other types of plastics. This innovative approach holds great potential for enhancing the efficiency and effectiveness of plastic recycling processes, ensuring the recovery of food-grade plastics for future use. Full article

(This article belongs to the Special Issue Advanced Coatings and Films for Food Packing and Storage)

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17 pages, 8388 KiB

Open AccessEditor’s ChoiceArticle

Production and Characterization of Graphene Oxide Surfaces against Uropathogens

by Samuel Belo, Francisca Sousa-Cardoso, Rita Teixeira-Santos, Luciana C. Gomes, Rita Vieira, Jelmer Sjollema, Olívia S. G. P. Soares and Filipe J. Mergulhão

Coatings 2023, 13(8), 1324; https://doi.org/10.3390/coatings13081324 - 28 Jul 2023

Cited by 3 | Viewed by 2114

Abstract

Graphene and its functionalized derivatives have been increasingly applied in the biomedical field, particularly in the production of antimicrobial and anti-adhesive surfaces. This study aimed to evaluate the performance of graphene oxide (GO)/polydimethylsiloxane (PDMS) composites against Staphylococcus aureus and Pseudomonas aeruginosa biofilms. GO/PDMS [...] Read more.

Graphene and its functionalized derivatives have been increasingly applied in the biomedical field, particularly in the production of antimicrobial and anti-adhesive surfaces. This study aimed to evaluate the performance of graphene oxide (GO)/polydimethylsiloxane (PDMS) composites against Staphylococcus aureus and Pseudomonas aeruginosa biofilms. GO/PDMS composites containing different GO loadings (1, 3, and 5 wt.%) were synthesized and characterized regarding their morphology, roughness, and hydrophobicity, and tested for their ability to inhibit biofilm formation under conditions that mimic urinary tract environments. Biofilm formation was assessed by determining the number of total and culturable cells. Additionally, the antibacterial mechanisms of action of GO were investigated for the tested uropathogens. Results indicated that the surfaces containing GO had greater roughness and increased hydrophobicity than PDMS. Biofilm analysis showed that the 1 wt.% GO/PDMS composite was the most effective in reducing S. aureus biofilm formation. In opposition, P. aeruginosa biofilms were not inhibited by any of the synthesized composites. Furthermore, 1% (w/v) GO increased the membrane permeability, metabolic activity, and endogenous reactive oxygen species (ROS) synthesis in S. aureus. Altogether, these results suggest that GO/PDMS composites are promising materials for application in urinary catheters, although further investigation is required. Full article

(This article belongs to the Special Issue Advances in Antibacterial and Antivirus Materials and Coatings: From Fundamentals to Application)

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15 pages, 4909 KiB

Open AccessEditor’s ChoiceArticle

Improving the Technical Characteristics of Untreated and Heat-Treated Ayous Wood against Accelerating Ageing by Testing Two Application Modalities of an Innovative Polyurethane Coating for Outdoor Uses

by Gianluca Rubino, Angela Lo Monaco, Luca Lanteri and Claudia Pelosi

Coatings 2023, 13(8), 1312; https://doi.org/10.3390/coatings13081312 - 26 Jul 2023

Cited by 1 | Viewed by 1378

Abstract

This paper presents the results of tests of a new mono-component polyurethane coating for wood with the aim of evaluating its effect on Ayous (Triplochiton scleroxylon K. Schum), which is a wood species used in Europe for various applications, especially outdoors, after [...] Read more.

This paper presents the results of tests of a new mono-component polyurethane coating for wood with the aim of evaluating its effect on Ayous (Triplochiton scleroxylon K. Schum), which is a wood species used in Europe for various applications, especially outdoors, after being heat treated. The coating was tested on both untreated and thermally treated samples, as the latter procedure is commonly used in the wood industry to modify the material’s characteristics. Moreover, two kinds of coating application were tested: coatings applied via brushing and coatings applied via spraying; in this test, we also verified the most suitable and effective modality. Samples were investigated using the following techniques: colour measurement, roughness mapping, contact angle measurement, surface micro-hardness and the wearing test; these techniques were applied before and after a period of artificial ageing under simulated solar irradiation. Upon synthesizing the main results, we identified the following results: (i) the polyurethane coating reduced the colour variation as a result of artificial aging of the untreated Ayous wood; in contrast, heat-treated wood underwent large colour changes; (ii) the coating acted effectively as a hydrophobic agent on the surface of the wood in each case examined, though even a short aging time altered the initial wettability characteristics; and (iii) the application of the coating caused a decrease in the roughness of both untreated and heat-treated surfaces, though this trend was much more evident in the case of the spray modality of application; however, aging always induced an increase in roughness, which was mainly observed in uncoated wood samples. Full article

(This article belongs to the Special Issue Advances in Surface Modification and Coatings of Wood and Wood Composites)

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11 pages, 3606 KiB

Open AccessEditor’s ChoiceArticle

Influence of Surface Roughness on Nanocrystalline Diamond Films Deposited by Distributed Antenna Array Microwave System on TA6V Substrates

by Azadeh Valinattaj Omran, Chaimaa Mahi, Romain Vayron, Céline Falentin-Daudré and Fabien Bénédic

Coatings 2023, 13(7), 1300; https://doi.org/10.3390/coatings13071300 - 24 Jul 2023

Cited by 1 | Viewed by 2514

Abstract

In this study, the characteristics of nanocrystalline diamond films synthesized at low surface temperature on Ti-6Al-4V (TA6V) substrates using a distributed antenna array microwave reactor aiming at biomedical applications were investigated. The surface roughness of the TA6V substrates is varied by scratching with [...] Read more.

In this study, the characteristics of nanocrystalline diamond films synthesized at low surface temperature on Ti-6Al-4V (TA6V) substrates using a distributed antenna array microwave reactor aiming at biomedical applications were investigated. The surface roughness of the TA6V substrates is varied by scratching with emery paper of 1200, 2400, 4000 polishing grit. Nanocrystalline diamond (NCD) coatings with morphology, purity, and microstructure comparable to those obtained on silicon substrates usually employed in the same reactor and growth conditions are successfully achieved whatever the polishing protocol. However, the latter has a significant effect on the roughness parameters and hardness of the NCD films. The use of the finest polishing grit thus permits us to enhance the hardness value, which can be related to the work-hardening phenomenon arising from the polishing process. Full article

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

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21 pages, 10324 KiB

Open AccessEditor’s ChoiceArticle

Effect of Zn on Phase Evolution and Shear Resistance of Stainless Steel and Aluminum Alloy Interface by Laser Cladding

by Keyan Wang, Xianqing Yin, Chengxin Li and Kaiping Du

Coatings 2023, 13(7), 1267; https://doi.org/10.3390/coatings13071267 - 19 Jul 2023

Cited by 1 | Viewed by 1152

Abstract

The connection between aluminum and iron alloys is of immense significance in the pursuit of lightweight industrial products. However, the Fe-Al interface’s inherent weakness restricts its widespread application. This study investigates the impact of Zn at the interface of Al-Fe laser cladding on [...] Read more.

The connection between aluminum and iron alloys is of immense significance in the pursuit of lightweight industrial products. However, the Fe-Al interface’s inherent weakness restricts its widespread application. This study investigates the impact of Zn at the interface of Al-Fe laser cladding on the phase and mechanical properties of the interface. Specifically, we examine the influence of the applied Zn powder layer and alloying Zn layer on the morphology of the Fe-based cladding layer. The inclusion of Zn enhances the spreadability of the Fe-based cladding layer. Additionally, we elucidate the effect of Zn on the composition and phase of the Fe-Al laser cladding interface. Notably, the affinity between Zn and the η phase surpasses that of the θ phase, and an increased Zn content significantly thickens the η phase. Shear tests reveal that the failure mode of shear fracture encompasses both brittle and ductile fractures. Density functional theory (DFT) calculations indicate that Zn has a limited effect on the strength of the η phase but reduces the enthalpy of formation of the η phase. Our findings demonstrate that the alloyed Zn layer initially facilitates the formation of a continuous and uniform η layer, while an increased Zn content enhances and stabilizes the shear strength of the interface. Full article

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

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11 pages, 12980 KiB

Open AccessEditor’s ChoiceArticle

Quasi Non-Destructive Quality Assessment of Thermally Sprayed AISI 316L Coatings Using Polarization Measurements in 3.5% NaCl Gel Electrolyte

by Maximilian Grimm, Pia Kutschmann, Christian Pluta, Olga Schwabe, Thomas Lindner and Thomas Lampke

Coatings 2023, 13(7), 1256; https://doi.org/10.3390/coatings13071256 - 16 Jul 2023

Viewed by 1165

Abstract

There is currently a lack of suitable methods of non-destructive quality assessment of thermally sprayed coatings. Therefore, this study investigates the suitability of polarization measurements that are adapted to the special needs of thermally sprayed coatings for non-destructive quality testing. For this purpose, [...] Read more.

There is currently a lack of suitable methods of non-destructive quality assessment of thermally sprayed coatings. Therefore, this study investigates the suitability of polarization measurements that are adapted to the special needs of thermally sprayed coatings for non-destructive quality testing. For this purpose, a gel electrolyte containing 3.5% NaCl and a measuring cell based on the three-electrode arrangement were developed to prevent the corrosion medium from infiltrating the typical microstructure of thermally sprayed coatings (pores and microcracks). The newly developed method was evaluated on AISI 316L coatings deposited by high velocity air fuel (HVAF) and atmospheric plasma spraying (APS). The polarization curves showed significant differences as a result of spraying process-related changes in the coating microstructure. Even slight differences in oxide content within the AISI 316L coating produced by APS can be detected by the new method. In order to verify the new findings, the coatings were analyzed regarding their microstructure by optical microscope, scanning electron microscope and energy dispersive X-ray spectroscopy. The measuring cell and gel electrolyte developed offer a promising opportunity to evaluate the quality of thermally sprayed coatings in a largely non-destructive manner using polarization curves. Full article

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

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9 pages, 5005 KiB

Open AccessEditor’s ChoiceArticle

Optoelectronic Properties of Ferroelectric Composites of Bi_3.25La_0.75Ti₃O₁₂ (BLT) and Co-Doped BLT Thin Films Modified by FeCo-Doped BLT

by Rui Tang, Rui He, Sangmo Kim and Chung Wung Bark

Coatings 2023, 13(7), 1223; https://doi.org/10.3390/coatings13071223 - 8 Jul 2023

Viewed by 1019

Abstract

Driven by the growing demand for renewable and clean energy, the photovoltaic effect of various solar cells and materials was investigated for the conversion of light energy into electricity. We modified the Bi_3.25La_0.75Ti₃O₁₂ (BLT) and Co-doped [...] Read more.

Driven by the growing demand for renewable and clean energy, the photovoltaic effect of various solar cells and materials was investigated for the conversion of light energy into electricity. We modified the Bi_3.25La_0.75Ti₃O₁₂ (BLT) and Co-doped BLT (Co–BLT) composites with Fe and Co-doped BLT (FeCo–BLT) films to narrow the bandgap and increase visible light absorption, thereby improving the efficiency of the photovoltaic reaction. In this study, BLT and Co–BLT thin films were fabricated by off-axis sputtering and then modified with FeCo–BLT thin films to produce dual-ferroelectric, thin-film composite materials that improved the photovoltaic power generation performance. Photoelectric test results showed that the modified double-ferroelectric, thin-film composites had superior optoelectronic properties. The current density was significantly enhanced by modifying the BLT films with doped Fe and Co. Therefore, this modification improved the efficiency of ferroelectric thin-film photovoltaic reactions. Full article

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

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14 pages, 5148 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

High-Entropy Composite Coating Based on AlCrFeCoNi as an Anode Material for Li-Ion Batteries

by Dávid Csík, Gabriela Baranová, Róbert Džunda, Dóra Zalka, Ben Breitung, Mária Hagarová and Karel Saksl

Coatings 2023, 13(7), 1219; https://doi.org/10.3390/coatings13071219 - 7 Jul 2023

Cited by 4 | Viewed by 3555

Abstract

In this study, a high entropy composite coating was synthesized by oxidizing a high entropy alloy, AlCrFeCoNi, at elevated temperatures in a pure oxygen atmosphere. X-Ray diffraction (XRD) analysis revealed that the prepared material was a dual-phase composite material consisting of a spinel-structured [...] Read more.

In this study, a high entropy composite coating was synthesized by oxidizing a high entropy alloy, AlCrFeCoNi, at elevated temperatures in a pure oxygen atmosphere. X-Ray diffraction (XRD) analysis revealed that the prepared material was a dual-phase composite material consisting of a spinel-structured high entropy oxide and a metallic phase with a face-centered cubic structure. The metallic phase can improve the electrical conductivity of the oxide phase, resulting in improved electrochemical performance. Scanning electron microscopy with energy dispersive spectroscopy (SEM/EDS) analysis unveiled the compositional homogeneity of the composite material. The prepared material was utilized as an anode active material in lithium-ion batteries. Cyclic voltammetry (CV) revealed the oxidation and reduction regions, while the electrochemical impedance spectroscopy (EIS) measurements showed a decrease in the charge transfer resistance during the cycling process. A long-term rate capability test was conducted at various current densities: 100, 200, 500, 1000, and 2000 mA g⁻¹. During this test, a notable phenomenon was observed in the regeneration process, where the capacity approached the initial discharge capacity. Remarkably, a high regeneration efficiency of 98% was achieved compared with the initial discharge capacity. This phenomenon is typically observed in composite nanomaterials. At a medium current density of 500 mA g⁻¹, an incredible discharge capacity of 543 mAh g⁻¹ was obtained after 1000 cycles. Based on the results, the prepared material shows great potential for use as an anode active material in lithium-ion batteries. Full article

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

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16 pages, 20266 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Thin 1,2,4-Triazole Films for the Inhibition of Carbon Steel Corrosion in Sulfuric Acid Solution

by Yaroslav G. Avdeev, Tatyana A. Nenasheva, Andrey Yu. Luchkin, Andrey I. Marshakov and Yurii I. Kuznetsov

Coatings 2023, 13(7), 1221; https://doi.org/10.3390/coatings13071221 - 7 Jul 2023

Cited by 5 | Viewed by 1125

Abstract

Etching of steel items in sulfuric acid solution is used in various human activities (oil and gas industry, metal production, utilities, transport, etc.). This operation is associated with significant material costs due to corrosion losses of the metal. It has been found that [...] Read more.

Etching of steel items in sulfuric acid solution is used in various human activities (oil and gas industry, metal production, utilities, transport, etc.). This operation is associated with significant material costs due to corrosion losses of the metal. It has been found that an efficient way to prevent corrosion of steel in sulfuric acid solution involves the formation of thin protective films consisting of corrosion inhibitor molecules of triazole class on its surface. It has been shown that the protection of steels with a 3-substituted 1,2,4-triazole (3ST) in H₂SO₄ solution is accompanied by the formation of a polymolecular layer up to 4 nm thick. The 3ST layer immediately adjacent to the steel surface is chemisorbed on it. The efficiency of this compound as an inhibitor of corrosion and hydrogen absorption by steel is determined by its ability to form a protective organic layer, as experimentally confirmed by XPS and AFM data. The kinetic constants of the main stages of hydrogen evolution and permeation into steel in the H₂SO₄ solution were determined. A significant decrease in both the reaction rate of cathodic hydrogen evolution and the rate of hydrogen permeation into steel by the triazole in question was noted. It has been shown that the preservation of the metal plasticity in the acid medium containing the triazole under study is due to a decrease in the hydrogen concentration in the metal bulk. Full article

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

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12 pages, 5771 KiB

Open AccessEditor’s ChoiceArticle

Stoichiometric and Nonstoichiometric Surface Structures of Pyrochlore Y₂Zr₂O₇ and Their Relative Stabilities: A First-Principles Investigation

by Huajian Wu, Jianning Zhang, Yiren Wang, Jiacheng Shang and Yong Jiang

Coatings 2023, 13(7), 1203; https://doi.org/10.3390/coatings13071203 - 5 Jul 2023

Viewed by 938

Abstract

First-principle total energy calculations were performed to investigate the atomic structures and relative stabilities of two low miller-index surfaces of pyrochlore Y₂Zr₂O₇. The stoichiometric Y₂Zr₂O₇ (110) and (100) surfaces were predicted, with [...] Read more.

First-principle total energy calculations were performed to investigate the atomic structures and relative stabilities of two low miller-index surfaces of pyrochlore Y₂Zr₂O₇. The stoichiometric Y₂Zr₂O₇ (110) and (100) surfaces were predicted, with lowest formation energies of 1.20 and 1.47 J/m², respectively. Based on a thermodynamic defect model, non-stoichiometric Y₂Zr₂O₇ surface energies were further evaluated as a function of environmental oxygen partial pressure (p_O2) and temperature (T). With all of the results, we were able to construct the surface phase diagrams for T = 300 and 1400 K. The strong correlation between the structural stabilities and the surface stoichiometry was revealed as varying T and p_O2. At a given T, the most stable termination of the (110) surfaces would change from a (Y,Zr)−rich (ns−2Y2Zr6O) to O−rich ones (ns−4O_2 and ns−4O_1) as increasing p_O2, while that of the (100) surfaces would change from the stoichiometric (stoi−1Y1Zr_1) to the O−rich one (ns−5O). The critical p_O2 value for termination transition moves to its higher end as increasing T. Full article

(This article belongs to the Special Issue Nanostructured Materials and Interfaces: Energy and Environmental Applications)

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15 pages, 3658 KiB

Open AccessEditor’s ChoiceArticle

Epoxy Coating Modification with Metal Nanoparticles to Improve the Anticorrosion, Migration, and Antibacterial Properties

by Marina Samardžija, Ivan Stojanović, Marija Vuković Domanovac and Vesna Alar

Coatings 2023, 13(7), 1201; https://doi.org/10.3390/coatings13071201 - 4 Jul 2023

Cited by 2 | Viewed by 4004

Abstract

Nanoparticles are capable of making more durable and stronger materials with better chemical resistance. They are used for a wide range of applications. Likewise, the potential of metal nanoparticles as antimicrobial agents has been widely studied. In this work, we investigate various nanoparticles [...] Read more.

Nanoparticles are capable of making more durable and stronger materials with better chemical resistance. They are used for a wide range of applications. Likewise, the potential of metal nanoparticles as antimicrobial agents has been widely studied. In this work, we investigate various nanoparticles (Al, Ni, Ag) incorporated into epoxy coating. The anticorrosion and antibacterial properties of the unmodified and modified coatings were evaluated. According to the SEM and EDS analyses, the coating did not contain agglomerates, which confirms the quality of the dispersion of inorganic nanoparticles in the coating. After 24 h and 10days immersions in a 3.5 wt.% NaCl solution, the corrosion behaviour for all nanocomposite was studied by means of EIS investigations. The study included the evaluation of the inhibition zone of the nanoparticles and the antimicrobial properties of the nanocomposite. It was found that the nanoparticles of Al and Ag provide excellent antibacterial properties. The epoxy nanocomposite with Al NP showed the migration of ions in the range from 0.75 to 1 mg/L in a wastewater solution for 30 days, indicating a potential for antimicrobe activity. The 1% Al NP epoxy nanocomposite showed good anticorrosion and antibacterial properties and demonstrated great potential for applications in pipelines. Full article

(This article belongs to the Special Issue Investigation on Corrosion Behaviour of Metallic Materials)

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23 pages, 5911 KiB

Open AccessEditor’s ChoiceArticle

Hybrid Materials Based on ZnO Nanoparticles and Organo-Modified Silica Coatings as Eco-Friendly Anticorrosive Protection for Metallic Historic Artifacts

by Mihaela Ioan, Dan Florin Anghel, Mihai Anastasescu, Ioana Catalina Gifu, Elvira Alexandrescu, Roxana Ioana Matei, Cristian Petcu, Ioana Stanculescu, Georgiana Alexandra Sanda, Daniela Bala and Ludmila Otilia Cinteza

Coatings 2023, 13(7), 1193; https://doi.org/10.3390/coatings13071193 - 3 Jul 2023

Cited by 2 | Viewed by 2826

Abstract

Cultural heritage metallic artifacts are often subjected to environmental factors that promote degradation through corrosion processes. Anticorrosion protection is needed both for the long-term preservation of outdoor monuments and the short-term conservation of archaeological artifacts. In this work, functional nanocoatings based on ZnO [...] Read more.

Cultural heritage metallic artifacts are often subjected to environmental factors that promote degradation through corrosion processes. Anticorrosion protection is needed both for the long-term preservation of outdoor monuments and the short-term conservation of archaeological artifacts. In this work, functional nanocoatings based on ZnO nanoparticles (NPs) in a silica matrix are prepared as a replacement for a commercial Incralac lacquer. Facile sol–gel synthesis is employed for obtaining silica filmogenic materials, using tetraethoxysilane (TEOS) and 3-glycidyloxypropyl trimethoxysilane (GPTMS). Silica-based nanocomposite coatings, with and without ZnO NPs and benzotriazole (BTA) as anticorrosion agents, applied on copper coupons by brushing are characterized by using VIS and FTIR spectroscopy, SEM and AFM and compared to Incralac lacquer as reference materials. The optical and morphological properties of the proposed silica coatings are similar to the Incralac specimens. The protective effect against corrosion is investigated on the copper coupons as model metallic objects subjected to a corrosion test by using potentiodynamic polarization in a 3.5% NaCl solution at ambient temperature. The influence of the presence of BTA and ZnO NPs in both silica and Incralac coatings is studied, and the variations in the anticorrosive, morphological and optical properties with the concentration of ZnO NPs are evidenced. The presence of moderate concentrations of ZnO in both nanomaterials leads to changes in the color parameters slightly above the limit accepted in the field of cultural heritage (ΔE* 5.09 and 6.13), while a high ZnO concentration of 3% leads to higher values (ΔE* > 10). Regarding the anticorrosive effect, the silica-based coatings with ZnO and BTA present similar efficiencies to that of the Incralac reference material (corrosion rates in the range of 0.044–0.067 mm/year for silica coatings compared to 0.055 mm/year for Incralac). Full article

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

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12 pages, 3861 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Lignin and Starch Derivatives with Selenium Nanoparticles for the Efficient Reduction of Dyes and as Polymer Fillers

by Anna Modrzejewska-Sikorska, Mariola Robakowska, Emilia Konował, Hubert Gojzewski, Łukasz Gierz, Bartosz Wieczorek, Łukasz Warguła and Wiktor Łykowski

Coatings 2023, 13(7), 1185; https://doi.org/10.3390/coatings13071185 - 30 Jun 2023

Cited by 1 | Viewed by 2520

Abstract

Selenium nanoparticles (SeNPs) were synthesized and stabilized by biopolymers, namely, sodium lignosulfonate (LS) and starch sodium octenyl succinate (OSA). The obtained selenium nanoparticles were studied for their catalytic activity in the reduction of a dye (C.I. Basic Blue 9, methylene blue) by sodium [...] Read more.

Selenium nanoparticles (SeNPs) were synthesized and stabilized by biopolymers, namely, sodium lignosulfonate (LS) and starch sodium octenyl succinate (OSA). The obtained selenium nanoparticles were studied for their catalytic activity in the reduction of a dye (C.I. Basic Blue 9, methylene blue) by sodium borohydride. The SeNPs-OSA and SeNPs-LS nanoparticles were also dispersed in a photosensitive matrix and studied as polymer composites. The research confirmed the catalytic abilities of the prepared SeNPs in the reduction of the organic dye. Mechanical tests on the polymers and their composites showed an improvement in the composites’ strength in all tested cases. An increase in hardness and Young’s modulus values of the filled materials compared to the pure matrix was found as well. Full article

(This article belongs to the Special Issue Advanced Technology in Environmental Remediation and Resource Utilization)

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13 pages, 12441 KiB

Open AccessEditor’s ChoiceCommunication

The Microstructure, Hardness, Phase Transformation and Mechanical Properties of a NiTi Coating Applied to Graphite Substrate via a Plasma Spraying Process

by Sneha Samal, Jakub Zeman, Jaromír Kopeček and Petr Šittner

Coatings 2023, 13(7), 1174; https://doi.org/10.3390/coatings13071174 - 29 Jun 2023

Cited by 3 | Viewed by 1510

Abstract

In this study, Ni₅₀Ti₅₀ powder was coated on the surface of graphite substrate (C) via a plasma spraying process using a radio frequency inductively coupled plasma reactor. The coating was carried out using 12- and 9-kW power under Ar atmosphere. [...] Read more.

In this study, Ni₅₀Ti₅₀ powder was coated on the surface of graphite substrate (C) via a plasma spraying process using a radio frequency inductively coupled plasma reactor. The coating was carried out using 12- and 9-kW power under Ar atmosphere. The cross-section of coating layers and the surface were examined with Scanning Electron Microscope (SEM), Energy Dispersive X-ray Spectrum (EDX), and X-ray Diffractometer (XRD) analyses and microhardness test. The thickness and quality of the coating increased with the input power. Many pores were detected in the cross-sectional surface areas. Higher input power caused a better coating layer of NiTi alloy. The hardness of the coating layer decreases with higher input power. Full article

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

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11 pages, 7764 KiB

Open AccessEditor’s ChoiceArticle

Optimization of Crystalline Diamond Coating Structure Architecture for Improving Adhesion and Cutting Performance in Milling with Cemented Carbide Inserts

by Georgios Skordaris, Konstantinos-Dionysios Bouzakis, Antonios Bouzakis, Dimitrios Tsakalidis, Apostolos Boumpakis, Spyridon Kompogiannis, Emmanouil Bouzakis, Oliver Lemmer, Werner Kölker and Michael Woda

Coatings 2023, 13(7), 1170; https://doi.org/10.3390/coatings13071170 - 28 Jun 2023

Cited by 1 | Viewed by 2629

Abstract

The adhesion, structure architecture, and residual stresses of crystalline diamond coatings (CDCs) on cemented carbide inserts are the factors that significantly affect tool life. The influence of these factors on cutting performance cannot be investigated separately since interactions among them exist. The paper [...] Read more.

The adhesion, structure architecture, and residual stresses of crystalline diamond coatings (CDCs) on cemented carbide inserts are the factors that significantly affect tool life. The influence of these factors on cutting performance cannot be investigated separately since interactions among them exist. The paper elucidates such dependencies to optimize the CDC architecture and improve cutting performance. In this context, diamond coatings possessing different architectures were deposited on cemented carbide tools. The fatigue endurance and the milling performance of the coated tools were investigated using impact and milling tests, respectively. The residual stresses in the film structures were determined through impact tests and appropriate (Finite Element Analysis) FEA evaluation of the corresponding results. According to the obtained results, the application of a bottom micro-structured CDC prior to the deposition of an upper nanolayered one with inferior thickness improves the coated tools’ cutting performance. An optimum coating architecture is associated with a thickness ratio between the micro-structured bonding to the upper nanolayered CDCs of 2/1. Hereupon, the augmentation of coated tool life via the application of an optimum diamond coating architecture compensates for the high tool cost and improves milling productivity. The latter is further enhanced as the number of tool replacements decreases. Full article

(This article belongs to the Special Issue New Cutting Techniques for Improved Machining)

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59 pages, 9745 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Principles of Machine Learning and Its Application to Thermal Barrier Coatings

by Yuan Liu, Kuiying Chen, Amarnath Kumar and Prakash Patnaik

Coatings 2023, 13(7), 1140; https://doi.org/10.3390/coatings13071140 - 23 Jun 2023

Cited by 5 | Viewed by 2953

Abstract

Artificial intelligence (AI), machine learning (ML) and deep learning (DL) along with big data (BD) management are currently viable approaches that can significantly help gas turbine components’ design and development. Optimizing microstructures of hot section components such as thermal barrier coatings (TBCs) to [...] Read more.

Artificial intelligence (AI), machine learning (ML) and deep learning (DL) along with big data (BD) management are currently viable approaches that can significantly help gas turbine components’ design and development. Optimizing microstructures of hot section components such as thermal barrier coatings (TBCs) to improve their durability has long been a challenging task in the gas turbine industry. In this paper, a literature review on ML principles and its various associated algorithms was presented first and then followed by its application to investigate thermal conductivity of TBCs. This combined approach can help better understand the physics behind thermal conductivity, and on the other hand, can also boost the design of low thermal conductivity of the TBCs system in terms of microstructure–property relationships. Several ML models and algorithms such as support vector regression (SVR), Gaussian process regression (GPR) and convolution neural network and regression algorithms were used via Python. A large volume of thermal conductivity data was compiled and extracted from the literature for TBCs using PlotDigitizer software and then used to test and validate ML models. It was found that the test data were strongly associated with five key factors as identifiers. The prediction of thermal conductivity was performed using three approaches: polynomial regression, neural network (NN) and gradient boosting regression (GBR). The results suggest that NN using the BR model and GBR have better prediction capability. Full article

(This article belongs to the Special Issue Advances in Thermal Barrier Coatings (TBCs): Materials, Fabrication, Corrosion and Applications)

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10 pages, 13583 KiB

Open AccessEditor’s ChoiceArticle

Seeking the Oxidation Mechanism of Debris in the Fretting Wear of Titanium Functionalized by Surface Laser Treatments

by María del Carmen Marco de Lucas, Franck Torrent, Gianni-Paolo Pillon, Pascal Berger and Luc Lavisse

Coatings 2023, 13(6), 1110; https://doi.org/10.3390/coatings13061110 - 16 Jun 2023

Viewed by 1692

Abstract

Surface laser treatment (SLT) using nanosecond IR lasers has been shown to improve the tribological behaviour of titanium. Here, we studied the fretting wear of SLT-functionalized pure titanium in a mixture of reactive gases O

_{2}

(20 vol.%) + N

_{2}

(80 vol.%). [...] Read more.

Surface laser treatment (SLT) using nanosecond IR lasers has been shown to improve the tribological behaviour of titanium. Here, we studied the fretting wear of SLT-functionalized pure titanium in a mixture of reactive gases O

_{2}

(20 vol.%) + N

_{2}

(80 vol.%). The contact geometry was a ball on a plane and the ball was made of bearing steel. The very small amplitude of relative displacement between reciprocating parts in fretting wear makes the evacuation of wear particles difficult. Moreover, the oxidation mechanism of the debris depends on the accessibility of the surrounding atmosphere to the tribological contact. This work focused in the analysis of debris generation and oxidation mechanisms, and sought to differentiate the role of oxygen forming part of the ambient O

_{2}

+ N

_{2}

gas mixture from oxygen present in the surface layer of the SL-treated titanium. Before the fretting test, the surface of the commercially pure titanium plates was treated with a laser under a mixture of O

_{2}

+ N

_{2}

gases with oxygen enriched in the

^{18}

O isotope. Then, the fretting tests were performed in regular air containing natural oxygen. Micro-Raman spectroscopy and ion beam analysis (IBA) techniques were used to analyse the TiO

_{2}

surface layers and fretting scars. Iron oxide particles were identified by Raman spectroscopy and IBA as the third body in the tribological contact. The spatial distribution of

^{18}

O, Ti,

^{16}

O and Fe in the fretting scars was studied by IBA. The analysis showed that the areas containing high concentrations of Fe displayed also high concentrations of

^{16}

O, but smaller concentrations of

^{18}

O and Ti. Therefore, it was concluded that tribological contact allows the oxidation of iron debris by its reaction with ambient air. Full article

(This article belongs to the Section Laser Coatings)

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19 pages, 3299 KiB

Open AccessEditor’s ChoiceArticle

Bimetallic 3D Nickel-Manganese/Titanium Bifunctional Electrocatalysts for Efficient Hydrogen and Oxygen Evolution Reaction in Alkaline and Acidic Media

by Sukomol Barua, Aldona Balčiūnaitė, Jūrate Vaičiūnienė, Loreta Tamašauskaitė-Tamašiūnaitė and Eugenijus Norkus

Coatings 2023, 13(6), 1102; https://doi.org/10.3390/coatings13061102 - 15 Jun 2023

Cited by 4 | Viewed by 1901

Abstract

In this work, 3D nickel-manganese (NiMn) bimetallic coatings have been studied as electrocatalysts for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline (1.0 M KOH) media and the HER in acidic (0.5 M H₂SO₄) media. [...] Read more.

In this work, 3D nickel-manganese (NiMn) bimetallic coatings have been studied as electrocatalysts for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline (1.0 M KOH) media and the HER in acidic (0.5 M H₂SO₄) media. The catalysts have been deposited on a titanium substrate (1 × 1 cm²) using low-cost and facile electrochemical deposition method through a dynamic hydrogen bubble template technique. The electrocatalytic performance of these fabricated catalysts was investigated by using Linear Sweep Voltammetry (LSV) for HER and OER at different temperatures ranging from 25 up to 75 °C and also was characterized by scanning electron microscopy (SEM) and inductively coupled plasma optical emission spectroscopy (ICP-OES). It was found that fabricated NiMn/Ti-5 electrocatalyst with Ni²⁺/Mn²⁺ molar ratio of 1:5 exhibits excellent HER activity in alkaline media with overpotential of 127.1 mV to reach current density of 10 mA cm⁻². On the contrary, NiMn/Ti-1 electrocatalyst that fabricated with Ni²⁺/Mn²⁺ molar proportion of 1:1 and lowest Mn-loading of 13.43 µgcm⁻² demonstrates exceptional OER activity with minimum overpotential of 356.3 mV to reach current density of 10 mA cm⁻². The current densities increase ca. 1.8–2.2 times with an increase in temperature from 25 °C to 75 °C for both HER and OER investigation. Both catalysts also have exhibited excellent long-term stability for 10 h at constant potentials as well as constant current density of 10 mA cm⁻² that assure their robustness and higher durability regarding alkaline water splitting. Full article

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

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14 pages, 4667 KiB

Open AccessEditor’s ChoiceArticle

Characterization of Two Types of Polylactic Acid Coating Loaded with Gentamicin Sulphate Deposed on AZ31 Alloy

by Manuela Elena Voicu, Daniela Ionita, George-Octavian Buica, Doina Draganescu, Valentina Anuta, Florentina Monica Raduly and Ioana Demetrescu

Coatings 2023, 13(6), 1105; https://doi.org/10.3390/coatings13061105 - 15 Jun 2023

Cited by 1 | Viewed by 1309

Abstract

This paper compares two types of polylactic acid (PLA) coating on AZ31 alloy obtained by dip coating and electrospinning. Both types of coating were loaded with gentamicin sulphate (GS) and the drug-loading efficiency and release were assessed. A higher encapsulation and release efficiency [...] Read more.

This paper compares two types of polylactic acid (PLA) coating on AZ31 alloy obtained by dip coating and electrospinning. Both types of coating were loaded with gentamicin sulphate (GS) and the drug-loading efficiency and release were assessed. A higher encapsulation and release efficiency of GS was seen for dip coating (73% and 49.53%, respectively) compared to nanofiber coating (65% and 12.37%, respectively). Furthermore, the antibacterial effect of the samples with and without GS was assessed using Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) bacteria, showing that the samples with the drug encapsulated are more resistant to bacteria than the other samples. The electrochemical data reveal a higher stability in the SBF of the surface obtained by dipping than that obtained by electrospinning. The PLA coating shows a porosity of 46% for the sample obtained through dip coating and 32% for nanofibers, which is in accordance with the BET analysis results. Moreover, a higher adhesion strength was obtained for AZ31-PLA-dip (4.99 MPa) than for the AZ31-PLA-nanofibers (1.66 MPa). All samples were structurally, morphologically, and topographically characterized. Full article

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

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17 pages, 3867 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Copper Nitride: A Versatile Semiconductor with Great Potential for Next-Generation Photovoltaics

by M. I. Rodríguez-Tapiador, J. M. Asensi, M. Roldán, J. Merino, J. Bertomeu and S. Fernández

Coatings 2023, 13(6), 1094; https://doi.org/10.3390/coatings13061094 - 13 Jun 2023

Cited by 6 | Viewed by 4188

Abstract

Copper nitride (Cu₃N) has gained significant attention recently due to its potential in several scientific and technological applications. This study focuses on using Cu₃N as a solar absorber in photovoltaic technology. Cu₃N thin films were deposited on [...] Read more.

Copper nitride (Cu₃N) has gained significant attention recently due to its potential in several scientific and technological applications. This study focuses on using Cu₃N as a solar absorber in photovoltaic technology. Cu₃N thin films were deposited on glass substrates and silicon wafers via radio-frequency magnetron sputtering at different nitrogen flow ratios with total pressures ranging from 1.0 to 5.0 Pa. The thin films’ structural, morphology, and chemical properties were determined using XRD, Raman, AFM, and SEM/EDS techniques. The results revealed that the Cu₃N films exhibited a polycrystalline structure, with the preferred orientation varying from 100 to 111 depending on the working pressure employed. Raman spectroscopy confirmed the presence of Cu-N bonds in characteristic peaks observed in the 618–627 cm⁻¹ range, while SEM and AFM images confirmed the presence of uniform and smooth surface morphologies. The optical properties of the films were investigated using UV-VIS-NIR spectroscopy and photothermal deflection spectroscopy (PDS). The obtained band gap, refractive index, and Urbach energy values demonstrated promising optical properties for Cu₃N films, indicating their potential as solar absorbers in photovoltaic technology. This study highlights the favourable properties of Cu₃N films deposited using the RF sputtering method, paving the way for their implementation in thin-film photovoltaic technologies. These findings contribute to the progress and optimisation of Cu₃N-based materials for efficient solar energy conversion. Full article

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

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13 pages, 5802 KiB

Open AccessEditor’s ChoiceArticle

Electrophoretic Deposition of Rochelle Salt Nanocrystals on Aluminum Plate

by Rostislav Rusev, Boriana Tzaneva and George Angelov

Coatings 2023, 13(6), 1074; https://doi.org/10.3390/coatings13061074 - 10 Jun 2023

Cited by 1 | Viewed by 3031

Abstract

A straightforward and inexpensive electrophoretic method for obtaining environment-friendly nanocrystalline piezo layers from Rochelle salt (RS) is presented here. The electrophoretic deposition process includes the formation of nanocrystals by precipitation of Rochelle salt/water solutions in ethanol (anti-solvent method) under the influence of a [...] Read more.

A straightforward and inexpensive electrophoretic method for obtaining environment-friendly nanocrystalline piezo layers from Rochelle salt (RS) is presented here. The electrophoretic deposition process includes the formation of nanocrystals by precipitation of Rochelle salt/water solutions in ethanol (anti-solvent method) under the influence of a high electric field. A nanoporous anodic aluminum oxide membrane is used to separate the electrochemical cell into two chambers. The composition of the RS:H₂O:EtOH mixture and the spatial separation of the process of precipitation from electrophoretic deposition allow control of the nanocrystal size and the uniformity of the layer. The reaction kinetics, the morphology, and the piezo response to the resulting layers are all investigated. The best samples were obtained at RS:H₂O:EtOH ratio 1:22.5:37.5. Under these conditions, the nanocrystals are preferentially oriented on the aluminum substrate and form a dense and homogeneous layer. Although the obtained structure is polycrystalline, the resulting piezo effect is 1120 pC/N, which is comparable to inorganic monocrystals and piezoceramics. This allows the use of electrophoretically deposited polycrystalline piezo layers in applications such as energy harvesting. Full article

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

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16 pages, 3643 KiB

Open AccessEditor’s ChoiceArticle

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

by Jaehui Bang and Eunkyung Lee

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

Cited by 2 | Viewed by 1373

Abstract

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

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

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

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10 pages, 4936 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

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

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

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

Viewed by 1521

Abstract

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

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

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

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12 pages, 7543 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

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

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

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

Viewed by 1403

Abstract

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

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

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

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18 pages, 5917 KiB

Open AccessEditor’s ChoiceArticle

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

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

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

Cited by 9 | Viewed by 3060

Abstract

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

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

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

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12 pages, 6196 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

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

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

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

Cited by 2 | Viewed by 2143

Abstract

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

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

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

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13 pages, 3344 KiB

Open AccessEditor’s ChoiceArticle

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

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

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

Cited by 2 | Viewed by 1561

Abstract

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

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

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

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18 pages, 13890 KiB

Open AccessEditor’s ChoiceArticle

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

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

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

Cited by 10 | Viewed by 1834

Abstract

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

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

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

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15 pages, 8013 KiB

Open AccessEditor’s ChoiceArticle

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

by Daibin Tang and Enzhou Liu

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

Cited by 7 | Viewed by 1857

Abstract

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

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

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

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26 pages, 11891 KiB

Open AccessEditor’s ChoiceArticle

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

by Florina Branzoi and Simona Petrescu

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

Cited by 1 | Viewed by 1411

Abstract

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

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

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

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13 pages, 5486 KiB

Open AccessEditor’s ChoiceArticle

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

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

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

Cited by 2 | Viewed by 2343

Abstract

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

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

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

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17 pages, 2552 KiB

Open AccessEditor’s ChoiceArticle

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

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

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

Cited by 3 | Viewed by 1983

Abstract

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

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

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

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16 pages, 5107 KiB

Open AccessEditor’s ChoiceArticle

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

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

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

Cited by 2 | Viewed by 2428

Abstract

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

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

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

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16 pages, 4588 KiB

Open AccessEditor’s ChoiceArticle

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

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

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

Cited by 3 | Viewed by 3226

Abstract

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

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

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

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17 pages, 9111 KiB

Open AccessEditor’s ChoiceArticle

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

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

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

Cited by 4 | Viewed by 2375

Abstract

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

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

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

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18 pages, 4956 KiB

Open AccessEditor’s ChoiceArticle

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

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

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

Cited by 2 | Viewed by 1675

Abstract

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

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

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

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16 pages, 5640 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

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

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

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

Cited by 2 | Viewed by 2334

Abstract

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

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

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

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16 pages, 749 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

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

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

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

Cited by 1 | Viewed by 2342

Abstract

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

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

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

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17 pages, 8974 KiB

Open AccessEditor’s ChoiceArticle

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

by Liu Yang and Yinghua Wei

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

Cited by 1 | Viewed by 1764

Abstract

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

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

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

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10 pages, 6646 KiB

Open AccessEditor’s ChoiceArticle

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

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

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

Viewed by 1352

Abstract

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

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

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

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