Coatings

16 pages, 4495 KB

Open AccessEditor’s ChoiceReview

On Numerical Modelling and an Experimental Approach to Heterojunction Tandem Solar Cells Based on Si and Cu₂O/ZnO—Results and Perspectives

by Laurentiu Fara, Irinela Chilibon, Ileana Cristina Vasiliu, Dan Craciunescu, Alexandru Diaconu and Silvian Fara

Coatings 2024, 14(3), 244; https://doi.org/10.3390/coatings14030244 - 20 Feb 2024

Cited by 1 | Viewed by 1951

Abstract

A comparative analysis of three advanced architectures for tandem solar cells (SCs) is discussed, respectively: metal oxide, thin film, and perovskite. Plasmonic solar cells could further increase solar cell efficiency. Using this development, an innovative PV technology (an SHTSC based on metal oxides) [...] Read more.

A comparative analysis of three advanced architectures for tandem solar cells (SCs) is discussed, respectively: metal oxide, thin film, and perovskite. Plasmonic solar cells could further increase solar cell efficiency. Using this development, an innovative PV technology (an SHTSC based on metal oxides) represented by a four-terminal Cu₂O/c-Si tandem heterojunction solar cell is investigated. The experimental and numerical modelling study defines the main aim of this paper. The experimental approach to SHTSCs is analysed: (1) a Cu₂O layer is deposited using a magnetron sputtering system; (2) the morphological and optical characterization of Cu₂O thin films is studied. The electrical modelling of silicon heterojunction tandem solar cells (SHTSCs) is discussed based on five simulation tools for the optimized performance evaluation of solar devices. The main novelty of this paper is represented by the following results: (1) the analysis suggests that the incorporation of a buffer layer can improve the performance of a tandem heterojunction solar cell; (2) the effect of interface defects on the electrical characteristics of the AZO/Cu₂O heterojunction is discussed; (3) the stability of SHTSCs based on metal oxides is studied to highlight the degradation rate in order to define a reliable solar device. Perspectives on SHTSCs based on metal oxides, as well as Si perovskite tandem solar cells with metal oxides as carrier-selective contacts, are commented on. Full article

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

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11 pages, 23726 KB

Open AccessEditor’s ChoiceArticle

Microstructure, Wear Resistance and Corrosion Resistance of CrN Coating with Platinum-Iridium Co-Doping

by Di Yang, Feng Yan, Weilun Zhang and Zhiwen Xie

Coatings 2024, 14(2), 238; https://doi.org/10.3390/coatings14020238 - 18 Feb 2024

Cited by 4 | Viewed by 2665

Abstract

A novel Pt-Ir co-doping strategy was devised to enhance the corrosion resistance of CrN coating. The deposited CrN coating exhibits a coherent growth pattern, resulting in significant mechanical strength and large grain sizes. However, during the corrosion process, corrosive fluids infiltrate through growth [...] Read more.

A novel Pt-Ir co-doping strategy was devised to enhance the corrosion resistance of CrN coating. The deposited CrN coating exhibits a coherent growth pattern, resulting in significant mechanical strength and large grain sizes. However, during the corrosion process, corrosive fluids infiltrate through growth defects, leading to inadequate corrosion resistance of the coating. By incorporating Pt-Ir atoms as dopants, coherent grain growth is effectively hindered, yielding a uniformly smooth surface. Simultaneously, localized non-coherent lattice growth occurs due to co-doping in the coatings, impacting the mechanical properties of CrN-PtIr coatings and causing multidirectional fracture. Nevertheless, this dense coating surface impedes the penetration of corrosive fluids and enhances the corrosion resistance of the coating to some extent. Full article

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

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11 pages, 12013 KB

Open AccessEditor’s ChoiceCommunication

Interface Modulation of CoNi Alloy Decorated with Few-Layer Reduced Graphene Oxide for High-Efficiency Microwave Absorption

by Hai Xie, Jinmei Li, Yaoming Zhang, Juan Yang, Tingmei Wang and Qihua Wang

Coatings 2024, 14(2), 228; https://doi.org/10.3390/coatings14020228 - 15 Feb 2024

Cited by 5 | Viewed by 2191

Abstract

Metal-organic frameworks (MOFs)-derived microwave absorbers with tunable components and microstructures show great potential in microwave absorption. Herein, we report a facile thermal reduction approach for synthesizing CoNi alloy/reduced graphene oxide (CoNi/rGO) composites from bimetallic CoNi-MOFs. By tuning the ratio of graphene oxide (GO) [...] Read more.

Metal-organic frameworks (MOFs)-derived microwave absorbers with tunable components and microstructures show great potential in microwave absorption. Herein, we report a facile thermal reduction approach for synthesizing CoNi alloy/reduced graphene oxide (CoNi/rGO) composites from bimetallic CoNi-MOFs. By tuning the ratio of graphene oxide (GO) in the precursors, the resulting CoNi/rGO-2 composite demonstrates optimal microwave absorption performance with a minimum reflection loss (RL_min) of −66.2 dB at 7.6 GHz in the C band. Moreover, the CoNi/rGO-2 with 50 wt% filler loading achieves a maximum effective absorption bandwidth (EAB) of 6.8 GHz (10.6–17.4 GHz) at a thickness of 2.5 mm, almost spanning the entire Ku band and a portion of the X band. The outstanding performance of CoNi/rGO-2 is ascribed to the high magnetic loss from the CoNi alloy and the incorporation of rGO, which induces interfacial polarization to enhance the dielectric loss and improve the impedance matching of composite. These favorable findings highlight the considerable potential and superiority of the CoNi/rGO-2 composite as an electromagnetic wave absorption material. This work sets forth a viable strategy for designing high-efficiency alloy/rGO absorbers. Full article

(This article belongs to the Special Issue Functional Magnetic and Dielectric Composites: Fabrication, Properties and Applications)

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10 pages, 3330 KB

Open AccessEditor’s ChoiceArticle

Microstructure and Dry-Sliding Wear Resistance of CoCrFeNiMoTi_x High Entropy Alloy Coatings Produced by Laser Cladding

by Hui Liang, Jinxin Hou, Li Jiang and Zhiqiang Cao

Coatings 2024, 14(2), 221; https://doi.org/10.3390/coatings14020221 - 12 Feb 2024

Cited by 8 | Viewed by 3534

Abstract

The new-type CoCrFeNiMoTi_x high-entropy alloy coatings were successfully devised and prepared on Q235 steel using laser cladding. Influence of Ti content on their microstructure and wear-resistance was studied systematically; the relevant mechanisms were deeply revealed. The CoCrFeNiMoTi_x coatings consisted of NiTi, [...] Read more.

The new-type CoCrFeNiMoTi_x high-entropy alloy coatings were successfully devised and prepared on Q235 steel using laser cladding. Influence of Ti content on their microstructure and wear-resistance was studied systematically; the relevant mechanisms were deeply revealed. The CoCrFeNiMoTi_x coatings consisted of NiTi, FCC, and BCC phases, and with the increasing of Ti content, contents of BCC phase and FCC phase gradually increased and decreased, respectively. The CoCrFeNiMoTi₀.₇₅ coating had the highest hardness (950 HV), which was about 6.5 times higher than the substrate (Q235 steel, 150 HV). According to Archard law, metal materials’ wear resistance is generally proportional to hardness; thus, the CoCrFeNiMoTi₀.₇₅ high entropy alloy coating with the highest hardness showed the best wear resistance, exhibiting a wear mechanism of slight abrasive wear. Full article

(This article belongs to the Special Issue Advances in Wear-Resistant Coatings)

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17 pages, 9908 KB

Open AccessEditor’s ChoiceArticle

Enhanced Osteogenic Activity and Antibacterial Properties of Graphene Oxide-Poly(Lactic Acid) Films for the Repair of Cranial Defects in Rats

by Kai Liu, Wen Lai, Jianyong Wu and Yongjian Lu

Coatings 2024, 14(2), 223; https://doi.org/10.3390/coatings14020223 - 12 Feb 2024

Cited by 6 | Viewed by 2475

Abstract

The failure of bone defect repair caused by bacterial infection is a significant clinical challenge. However, the currently utilized bone graft materials lack antibacterial properties, necessitating the development of bone repair materials with both osteoinductive and antibacterial capabilities. Graphene oxide (GO) has garnered [...] Read more.

The failure of bone defect repair caused by bacterial infection is a significant clinical challenge. However, the currently utilized bone graft materials lack antibacterial properties, necessitating the development of bone repair materials with both osteoinductive and antibacterial capabilities. Graphene oxide (GO) has garnered considerable attention due to its distinctive physical, chemical, and biological characteristics. In this study, we prepared a graphene oxide-poly(lactic acid) (GO-PLA) film with exceptional biological properties. In vitro investigations demonstrated that the GO-PLA film substantially enhanced the adhesion and proliferation capacity of rat bone marrow mesenchymal stem cells (rBMSCs). Furthermore, we observed augmented alkaline phosphatase activity as well as increased expression levels of osteogenic genes in rBMSCs cultured on the GO-PLA film. Additionally, we evaluated the antibacterial activity of our samples using gram-positive Streptococcus mutans (Sm) and gram-negative Actinobacillus actinomycetemcomitans (Aa). Our findings revealed that GO doping significantly inhibited bacterial growth. Moreover, implantation experiments conducted on rat skull defects demonstrated excellent guided bone regeneration performance exhibited by the GO-PLA film. Overall, our results indicate that the GO-PLA film possesses outstanding osteogenic and antibacterial properties, making it a promising biomaterial for bone tissue regeneration. Full article

(This article belongs to the Section Thin Films)

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17 pages, 4918 KB

Open AccessEditor’s ChoiceArticle

The Antibacterial Properties of a Silver Multilayer Coating for the Prevention of Bacterial Biofilm Formation on Orthopedic Implants—An In Vitro Study

by Sanne W. G. van Hoogstraten, Janine Fechter, Rainer Bargon, Julia L. van Agtmaal, Laura C. W. Peeters, Jan Geurts and Jacobus J. C. Arts

Coatings 2024, 14(2), 216; https://doi.org/10.3390/coatings14020216 - 9 Feb 2024

Cited by 5 | Viewed by 4985

Abstract

The prevention of biofilm formation on orthopedic implants is essential, as biofilms are the main challenge in the effective treatment of periprosthetic joint infection (PJI). A silver multilayer (SML) coating was developed to prevent biofilm formation on the implant surface. Previous studies have [...] Read more.

The prevention of biofilm formation on orthopedic implants is essential, as biofilms are the main challenge in the effective treatment of periprosthetic joint infection (PJI). A silver multilayer (SML) coating was developed to prevent biofilm formation on the implant surface. Previous studies have already demonstrated its antibacterial properties without cytotoxic effects. However, the coating has not been previously tested when applied to common titanium surfaces used in total joint arthroplasty implants. These surfaces often have increased roughness and porosity in the case of cementless implants, which can alter the antibacterial effect of the coating. In this study, we assessed the antibacterial and anti-biofilm properties of the SML coating on corundum-blasted and plasma-sprayed microporous-coated titanium alloy surfaces, using S. aureus, S. epidermidis, and E. coli. An antibacterial activity test following the principles of ISO 22196, ASTM E2180-18, and JIS Z 2801 standards was performed, as well as a biofilm proliferation assay investigating bacterial adhesion and biofilm formation. The SML coating exhibited strong antibacterial effects for all bacterial strains. After 24 h biofilm culture, a >4-log reduction in CFU was induced by the SML coating for S. epidermidis and E. coli on the corundum-blasted and plasma-sprayed microporous-coated titanium surfaces, respectively, when compared to the uncoated surfaces. The coating showed bactericidal properties against Gram-positive bacteria on the corundum-blasted discs. The SML coating on two common titanium surfaces demonstrates significant potential as an effective strategy in combating PJI across a wide range of orthopedic implants. Full article

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

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34 pages, 17972 KB

Open AccessEditor’s ChoiceReview

Plasma Electrolytic Oxidation (PEO) as a Promising Technology for the Development of High-Performance Coatings on Cast Al-Si Alloys: A Review

by Patricia Fernández-López, Sofia A. Alves, Jose T. San-Jose, Eva Gutierrez-Berasategui and Raquel Bayón

Coatings 2024, 14(2), 217; https://doi.org/10.3390/coatings14020217 - 9 Feb 2024

Cited by 31 | Viewed by 9592

Abstract

Cast Al-Si alloys, recognized for their excellent mechanical properties, constitute one of the most widely employed non-ferrous substrates in several sectors, and are particularly relevant in the transport industry. Nevertheless, these alloys also display inherent limitations that significantly restrict their use in several [...] Read more.

Cast Al-Si alloys, recognized for their excellent mechanical properties, constitute one of the most widely employed non-ferrous substrates in several sectors, and are particularly relevant in the transport industry. Nevertheless, these alloys also display inherent limitations that significantly restrict their use in several applications. Among these limitations, their low hardness, low wear resistance, or limited anti-corrosion properties, which are often not enough when the component is subjected to more severe environments, are particularly relevant. In this context, surface modification and the development of coatings are essential for the application of cast Al-Si alloys. This review focuses on the development of coatings to overcome the complexities associated with improving the performance of cast Al-Si alloys. Against this background, plasma electrolytic oxidation (PEO), an advanced electrochemical treatment that has revolutionized the surface modification of several metallic alloys in recent years, emerges as a promising approach. Despite the growing recognition of PEO technology, the achievement of high-performance coatings on cast Al-Si is still a challenge nowadays, for which reason this review aims to provide an overview of the PEO treatment applied to these alloys. In particular, the impact of the electrolyte chemical composition on the properties of the coatings obtained on different alloys exposed to harsh environments has been analyzed and discussed. By addressing the existing gaps and challenges, this paper contributes to a better understanding of the intricacies associated with the development of robust PEO coatings on cast Al-Si alloys. Full article

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

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19 pages, 10825 KB

Open AccessEditor’s ChoiceArticle

The Influence of TiO₂ Nanoparticles on the Physico–Mechanical and Structural Characteristics of Cementitious Materials

by Carmen T. Florean, Horatiu Vermesan, Gyorgy Thalmaier, Bogdan V. Neamtu, Timea Gabor, Cristina Campian, Andreea Hegyi and Alexandra Csapai

Coatings 2024, 14(2), 218; https://doi.org/10.3390/coatings14020218 - 9 Feb 2024

Cited by 11 | Viewed by 2806

Abstract

The urgent need for sustainable construction that corresponds to the three pillars of sustainable development is obvious and continuously requires innovative solutions. Cementitious composites with TiO₂ nanoparticles (NT) addition show potential due to their improved durability, physico–mechanical characteristics, and self-cleaning capacity. This [...] Read more.

The urgent need for sustainable construction that corresponds to the three pillars of sustainable development is obvious and continuously requires innovative solutions. Cementitious composites with TiO₂ nanoparticles (NT) addition show potential due to their improved durability, physico–mechanical characteristics, and self-cleaning capacity. This study aimed to evaluate the influence of NT on cementitious composites by comparing those with 2%–5% nanoparticles with a similar control sample without nanoparticles, as well as an analysis of cost growth. The experimental results showed an increase in bulk density of the material (4.7%–7.4%), reduction in large pore sizes by min. 12.5%, together with an increase in cumulative volume and cumulative specific surface area of small pore sizes, indicating densification of the material, also supported by SEM, EDS, and XRD analyses indicating acceleration of cement hydration processes with formation of specific products. The changes at microstructural level support the experimental results obtained at macrostructural level, i.e., modest but existent increases in flexural strength (0.6%–7.9%) and compressive strength (0.2%–2.6%) or more significant improvements in abrasion resistance (8.2%–58%) and reduction in water absorption coefficient (37.5%–81.3%). Following the cost–benefit analysis, it was concluded that, for the example case considered of a pedestrian pavement with a surface area of 100 m², using 100 mm thick slabs, if these slabs were to be made with two layers, the lower layer made of cementitious composite as a reference and the upper layer with a thickness of 10 mm made of cementitious composite with 3% NT or 4% NT, the increase in cost would be acceptable, representing less than 15% compared to the cost for the exclusive use of cementitious composite without NT. Full article

(This article belongs to the Special Issue Development and Characterization of New Construction Materials and Coatings)

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19 pages, 9104 KB

Open AccessEditor’s ChoiceArticle

Silver Containing Antimicrobial Coatings on Innovative Ti-30Nb-5Mo β-Alloy Prepared by Micro-Arc Oxidation for Biomedical Implant Applications

by Giovana Collombaro Cardoso, Katia Barbaro, Pedro Akira Bazaglia Kuroda, Angela De Bonis, Roberto Teghil, Valentina Monteleone, Luca Imperatori, Marco Ortenzi, Iulian Antoniac, Carlos Roberto Grandini and Julietta V. Rau

Coatings 2024, 14(2), 214; https://doi.org/10.3390/coatings14020214 - 7 Feb 2024

Cited by 10 | Viewed by 2761

Abstract

Micro-arc oxidation (MAO) is a versatile surface-modification method that promotes higher wear and corrosion resistance, osseointegration, and biological activity to titanium alloys’ surfaces. This study aimed to modify the surface of a recently developed metastable β Ti alloy, which exhibits more favorable mechanical [...] Read more.

Micro-arc oxidation (MAO) is a versatile surface-modification method that promotes higher wear and corrosion resistance, osseointegration, and biological activity to titanium alloys’ surfaces. This study aimed to modify the surface of a recently developed metastable β Ti alloy, which exhibits more favorable mechanical properties for implant applications compared to some commercial Ti alloys, by incorporating Ag into the coatings to introduce a bactericidal function to the surface. The Ti-30Nb-5Mo alloy, with lower elastic modulus, was treated by the MAO method using electrolyte solutions containing calcium acetate, magnesium acetate, β-glycerol phosphate, and varied concentrations of silver nitrate (1.5 mM, 2.5 mM, and 3.5 mM). With an increase in the concentration of silver ions in the electrolyte, the galvanostatic period during the MAO process decreased from 1.7 s to 0.5 s. The Ca/P ratio increased from 0.72 up to 1.36. X-ray diffraction showed that the MAO coatings were formed by rutile and anatase TiO₂ main phases and calcium phosphates. X-ray photoelectron spectroscopy analysis detected the presence of amorphous Nb₂O₅, CaCO₃, and MgCO₃, and metallic and oxide forms of Ag. The increase in Ag in the electrolyte decreased the coating thickness (from 14.2 μm down to 10.0 μm), increased the contact angle (from 37.6° up to 57.4°), and slightly increased roughness (from 0.64 μm up to 0.79 μm). The maximum inhibition of Enterococcus faecalis, Pseudomonas aeruginosa, and Candida albicans strains growth was of 43%, 43%, and 61%, respectively. The Ag did not negatively affect the differentiation of adipose-tissue-derived mesenchymal stem cells. Therefore, the treatment of the surface of the innovative Ti-30Nb-5Mo alloy by the MAO method was effective in producing a noncytotoxic porous coating with bactericidal properties and improved osseointegration capabilities. Full article

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

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15 pages, 7136 KB

Open AccessEditor’s ChoiceArticle

Friction Evolution of Graphite Bearing Impregnated with Polymer Subjected to Vibration Fretting at High Temperature

by Hamid Zaïdi, Stéphane Tournis, Leila Deville, Caroline Richard, Mohamed Aissa and Kaouthar Bouguerra

Coatings 2024, 14(2), 207; https://doi.org/10.3390/coatings14020207 - 6 Feb 2024

Cited by 1 | Viewed by 2110

Abstract

To address friction and wear challenges in dry contacts, manufacturers often employ self-lubricating materials. Graphite and its derivatives stand out as particularly suitable due to their exceptional tribological properties. However, under intense friction conditions, graphite can experience a decline in lubricating efficiency due [...] Read more.

To address friction and wear challenges in dry contacts, manufacturers often employ self-lubricating materials. Graphite and its derivatives stand out as particularly suitable due to their exceptional tribological properties. However, under intense friction conditions, graphite can experience a decline in lubricating efficiency due to severe abrasive wear. This abrasive damage results in elevated activated carbon surfaces with increased surface energy, fostering greater adhesion between sliding surfaces. The low friction coefficient of graphite is not an inherent property but rather a consequence of water vapor adsorption by the material. Beyond 150 °C, desorption of the vapor occurs, leading to a transition in the friction coefficient from µ = 0.1 to µ = 0.6. To address this issue, impregnation solutions for self-lubricating materials have been developed, with various compositions tailored to specific objectives. Common types include molybdenum disulfide, soft metals and polymers. In this predominantly experimental study, the impact of polymer impregnation on the evolution of friction force and wear rate in graphite material bearings subjected to a dry fretting contact under severe thermal stresses at 270 °C was investigated. Additionally, the mechanical stresses in the bearings throughout different phases of our tests were analyzed using a numerical model. Full article

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

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10 pages, 2233 KB

Open AccessEditor’s ChoiceArticle

Coconut-Solid-Waste-Derived Hard-Carbon Anode Materials for Fast Potassium Ion Storage

by Yi Ma, Wenhao Liu, Wenhan Liu, Guangwan Zhang, Yu Wang, Haokai Wang, Wei Chen, Meng Huang and Xuanpeng Wang

Coatings 2024, 14(2), 208; https://doi.org/10.3390/coatings14020208 - 6 Feb 2024

Cited by 8 | Viewed by 3088

Abstract

Hard carbon, which features recyclability, low costs, and environmental friendliness, is an attractive anode material for K⁺ storage. Nevertheless, the state-of-the-art hard carbon is still unsatisfactory due to its poor multiplication performance and unclear energy storage mechanism. In this study, a one-pot [...] Read more.

Hard carbon, which features recyclability, low costs, and environmental friendliness, is an attractive anode material for K⁺ storage. Nevertheless, the state-of-the-art hard carbon is still unsatisfactory due to its poor multiplication performance and unclear energy storage mechanism. In this study, a one-pot carbonisation method using coconut solid waste biomass is applied to obtain high-performance hard-carbon (CHC) anode materials. The microstructure and electrochemical properties of the CHC are investigated at different carbonisation temperatures (1100–1500 °C). The CHC materials prepared at 1300 °C (CHC1300) have a high capacity of 265.8 mAh g⁻¹ at a current density of 25 mA g⁻¹ and a superior cyclability of 1000 cycles at 1.0 A g⁻¹ with a capacity retention of 96.6%. This approach, referred to as the “biomass-to-application” strategy, holds promise for advancing the development of cost-effective and sustainable KIBs. Full article

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

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17 pages, 3199 KB

Open AccessEditor’s ChoiceArticle

The Wavelet Transform for Feature Extraction and Surface Roughness Evaluation after Micromachining

by Daniel Grochała, Rafał Grzejda, Arkadiusz Parus and Stefan Berczyński

Coatings 2024, 14(2), 210; https://doi.org/10.3390/coatings14020210 - 6 Feb 2024

Cited by 16 | Viewed by 2875

Abstract

Miniaturization is a dominant trend in machine building which requires the use of advanced techniques of manufacturing and control. Apart from dimensional and shape precision of miniaturized components, surface geometry, particularly roughness and so-called microroughness that results from the use of advanced treatment [...] Read more.

Miniaturization is a dominant trend in machine building which requires the use of advanced techniques of manufacturing and control. Apart from dimensional and shape precision of miniaturized components, surface geometry, particularly roughness and so-called microroughness that results from the use of advanced treatment techniques, plays an important role in correct assembly, reliable operation and durability of the whole machine. The selection of filtration method in surface geometry of micro-objects can be a substantial problem. The authors of the paper propose to use wavelet filtration in digital processing of a point cloud to remove measurement noise and not to change the surface character of the measured object. Also, the authors propose, in this paper, some criteria for selecting the number of wavelet filtration levels based on minimalization of the RMS value. It is supposed to improve the efficiency of low-pass filtration of small areas of the surface, particularly compared to traditional λs Gaussian filtration. Full article

(This article belongs to the Special Issue Recent Trends in Precision Measurement of Metals and Alloys)

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44 pages, 6271 KB

Open AccessEditor’s ChoiceReview

Recent Advances in the Application of Metal Oxide Nanomaterials for the Conservation of Stone Artefacts, Ecotoxicological Impact and Preventive Measures

by Marwa Ben Chobba, Maduka L. Weththimuni, Mouna Messaoud, Clara Urzi and Maurizio Licchelli

Coatings 2024, 14(2), 203; https://doi.org/10.3390/coatings14020203 - 4 Feb 2024

Cited by 13 | Viewed by 4548

Abstract

Due to the ongoing threat of degradation of artefacts and monuments, the conservation of cultural heritage items has been gaining prominence on the global scale. Thus, finding suitable approaches that can preserve these materials while keeping their natural aspect of is crucial. In [...] Read more.

Due to the ongoing threat of degradation of artefacts and monuments, the conservation of cultural heritage items has been gaining prominence on the global scale. Thus, finding suitable approaches that can preserve these materials while keeping their natural aspect of is crucial. In particular, preventive conservation is an approach that aims to control deterioration before it happens in order to decrease the need for the intervention. Several techniques have been developed in this context. Notably, the application of coatings made of metal oxide nanomaterials dispersed in polymer matrix can be effectively address stone heritage deterioration issues. In particular, metal oxide nanomaterials (TiO₂, ZnO, CuO, and MgO) with self-cleaning and antimicrobial activity have been considered as possible cultural heritage conservative materials. Metal oxide nanomaterials have been used to strengthen heritage items in several studies. This review seeks to update the knowledge of different kinds of metal oxide nanomaterials, especially nanoparticles and nanocomposites, that have been employed in the preservation and consolidation of heritage items over the last 10 years. Notably, the transport of nanomaterials in diverse environments is undoubtedly not well understood. Therefore, controlling their effects on various neighbouring non-target organisms and ecological processes is crucial. Full article

(This article belongs to the Special Issue Heritage Conservation and Restoration: Surface Characterization, Cleaning and Treatments)

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18 pages, 5323 KB

Open AccessEditor’s ChoiceArticle

Interface Interaction between MoO₃ and Carbon Dots Derived from Chitosan Promoted the Photocurrent Extraction Ability of Carriers in a Wide Range of the Light Spectrum

by Xingfa Ma, Mingjun Gao, Xintao Zhang, You Wang and Guang Li

Coatings 2024, 14(2), 171; https://doi.org/10.3390/coatings14020171 - 29 Jan 2024

Cited by 4 | Viewed by 2358

Abstract

Due to the large number of defects at the grain boundaries of nanocomposites, defects have a significant effect on the physico-chemical properties of a material. Therefore, controlling the charging behaviour of functional nanocomposites in a non-contact manner with a light field can improve [...] Read more.

Due to the large number of defects at the grain boundaries of nanocomposites, defects have a significant effect on the physico-chemical properties of a material. Therefore, controlling the charging behaviour of functional nanocomposites in a non-contact manner with a light field can improve their physical and chemical properties. Chitosan-derived carbon dots were synthesised by exploiting the abundant N element in chitosan. In order to passivate the defects of chitosan-derived carbon dots, a MoO₃/carbon dot nanocomposite was constructed in this study to tailor the band gap and improve the extraction ability of carriers through light induction. The results showed that the strong interfacial interaction between MoO₃ and carbon dots enhanced the optical absorption and interfacial charge transfer in the visible and some near-infrared regions. The resulting MoO₃/carbon dot heterostructure was coated on A4 printing paper, and electrodes were integrated in the coating film. The photocurrent signals of the thick film were investigated using 405, 532, 650, 808, 980 and 1064 nm light sources. The results indicated that the phenomenon of photocurrent switching to the visible light and some near-infrared light regions was observed. The charge carrier extraction ability of the MoO₃/carbon dot nanocomposite through light triggering was much better than that of chitosan-derived carbon dots. The on/off ratio and response speed of the MoO₃/carbon dot nanocomposite were significantly improved. The physical mechanism was discussed based on the ordered and disordered structures of polymer-derived carbon nanomaterials. This material could be applicable to the development of broadband flexible photosensors, artificial vision or light-utilising interdisciplinary fields. Full article

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

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24 pages, 5414 KB

Open AccessEditor’s ChoiceArticle

Study of the Geochemical Decay and Environmental Causes of Granite Stone Surfaces in the Built Heritage of Barbanza Peninsula (Galicia, NW Spain)

by Ana C. Hernandez, Jorge Sanjurjo-Sánchez, Carlos Alves and Carlos A. M. Figueiredo

Coatings 2024, 14(2), 169; https://doi.org/10.3390/coatings14020169 - 28 Jan 2024

Cited by 7 | Viewed by 5024

Abstract

In Galicia (NW Spain), granite was the most used stone material in historical buildings. Despite the good properties of granite as a construction material, it overcomes several physical and chemical weathering processes that cause decay, resulting in a loss of value in building [...] Read more.

In Galicia (NW Spain), granite was the most used stone material in historical buildings. Despite the good properties of granite as a construction material, it overcomes several physical and chemical weathering processes that cause decay, resulting in a loss of value in building materials, architectural elements and details. This is caused by a range of processes, from aesthetic damage to stone erosion. The causes of such decay are well known from case studies of historical buildings, being correlated with atmospheric agents, air pollution and aggregate materials, among others. In this work, we studied 15 historical monuments built with granite blocks of the architectural Heritage of the Barbanza Peninsula (Galicia). Because of the geographic features of this area, there is a steep rainfall and sea spray gradient that allows us to study historical buildings exposed to different environmental conditions in a short distance from the shoreline to inland. We used geochemical, petrological and microscopic tools to assess the decay of the granites and compared the results with environmental factors to assess the role of humidity (rainfall) and sea spray on the decay. Both the observation of coatings and the assessment of weathering have shown that buildings close to the shoreline are more affected by sea salts, while buildings far from the coast are mostly affected by biological weathering. Surprisingly, chemical weathering is higher in a strip area some hundreds of meters away from the sea shore and at lower altitudes (between 10 and 30 m). Indeed, very good correlation is observed for weathering indices, such as CIA, MWPI, VR, Si-Ti index, Kr, CAN and AKN, with a distance to the shoreline from 0.5 km, with linear correlation values ranging from −0.91 to 0.80. Full article

(This article belongs to the Section Surface Characterization, Deposition and Modification)

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17 pages, 916 KB

Open AccessEditor’s ChoiceArticle

Temperature Coefficient of Electronic Polarizability in Thin Polymer Films Deposited on Si and SiO₂ Substrates Determined via Spectroscopic Ellipsometry

by Henryk Bednarski, Barbara Hajduk, Paweł Jarka and Pallavi Kumari

Coatings 2024, 14(2), 166; https://doi.org/10.3390/coatings14020166 - 27 Jan 2024

Cited by 2 | Viewed by 2203

Abstract

Ellipsometry is widely used to determine the thermo-optical properties of thin polymer films. However, if the thermo-optic coefficient (TOC) and the linear thermal expansion coefficient (LTEC) are to be used to determine the temperature coefficient of electronic polarizability (TCEP) in thin polymer films, [...] Read more.

Ellipsometry is widely used to determine the thermo-optical properties of thin polymer films. However, if the thermo-optic coefficient (TOC) and the linear thermal expansion coefficient (LTEC) are to be used to determine the temperature coefficient of electronic polarizability (TCEP) in thin polymer films, their values must be determined with the greatest possible accuracy, as both have the opposite effect. In this article, we analyze changes in ellipsometric parameters resulting from changes in the thin film temperature in order to develop a data analysis method for temperature-dependent spectroscopic ellipsometry that will facilitate the accurate determination of thermo-optical parameters, including the TCEP, in polymer thin films. As practical application examples, we identified optimal spectral windows to accurately determine the thermo-optical parameters of 50 to 150 nm-thick PMMA thin films deposited on Si and SiO₂ substrates. The influence of thin-film thickness on the accuracy of TOC and LTEC determination is discussed. Full article

(This article belongs to the Special Issue Thin-Film Synthesis, Characterization and Properties)

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12 pages, 5843 KB

Open AccessEditor’s ChoiceArticle

Influence of the Gas Flow Rate on the Crack Formation of AlCoCrNi High-Entropy Metallic Film Fabricated Using Magnetron Sputtering

by Young-Soon Kim, Hae-Jin Park, Young-Seok Kim, Sung-Hwan Hong and Ki-Buem Kim

Coatings 2024, 14(1), 144; https://doi.org/10.3390/coatings14010144 - 21 Jan 2024

Cited by 4 | Viewed by 2223

Abstract

In the present study, the AlCoCrNi high-entropy metallic film was deposited on a Si wafer using a magnetron sputtering system. To capture the effects of the sputtering parameters on the microstructure and mechanical properties of the film, the flow rate of Ar gas [...] Read more.

In the present study, the AlCoCrNi high-entropy metallic film was deposited on a Si wafer using a magnetron sputtering system. To capture the effects of the sputtering parameters on the microstructure and mechanical properties of the film, the flow rate of Ar gas injected into the chamber (5, 7, and 8 sccm) was controlled. All films were identified as being of BCC phase with compositions of near equiatomic proportions, regardless of the gas flow rates. Nano-scale clusters were observed on the surfaces of all films, and nano-cracks were found in the film deposited at the Ar gas flow rate of 8 sccm, unlike the films deposited at the gas flow rates of 5 and 7 sccm. Detailed microstructural analysis of film deposition at an Ar gas flow rate of 8 sccm indicated that the void boundaries contribute to the formation of nano-cracks. The nano-indentation results indicated that the Ar gas flow rate 5 sccm specimen, with the smallest cluster size at the topmost surface, showed the highest hardness (12.21 ± 1.05 GPa) and Young’s modulus (188.1 ± 11 GPa) values. Full article

(This article belongs to the Special Issue Advanced High-Entropy Materials and Coatings)

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17 pages, 4276 KB

Open AccessEditor’s ChoiceArticle

Revolutionizing Construction Safety with Geopolymer Composites: Unveiling Advanced Techniques in Manufacturing Sandwich Steel Structures Using Formwork-Free Spray Technology

by Van Su Le and Kinga Setlak

Coatings 2024, 14(1), 146; https://doi.org/10.3390/coatings14010146 - 21 Jan 2024

Cited by 2 | Viewed by 2412

Abstract

The article discusses the fabrication of sandwich steel and geopolymer structures using spray technology without the need for formwork. In the article, the effects of high temperatures on geopolymer materials are analyzed and their mechanical properties and durability are examined. The importance of [...] Read more.

The article discusses the fabrication of sandwich steel and geopolymer structures using spray technology without the need for formwork. In the article, the effects of high temperatures on geopolymer materials are analyzed and their mechanical properties and durability are examined. The importance of geopolymer coatings for steel protection is also highlighted, and specific features such as the setting time, application process, attachment strength, fire testing, and production costs are analyzed. The materials and methods used in the study are described, including the composition of geopolymer binders and the process of applying geopolymer coatings to steel plates. The research includes test methods such as strength tests, density tests, thermal conductivity tests, accelerated aging tests, microstructure analyses, pore size analyses, and fire resistance tests. The research section concludes with a summary of the chemical and phase composition of the materials and a discussion of the fire resistance of the geopolymer composites (GCs). The results show that GC foams offer excellent thermal insulation, providing up to 75 min of fire resistance with a 6 mm coating, reducing temperatures by 150 °C compared to uncoated steel. GC foams have a density of 670 kg/m³, a thermal conductivity of 0.153 W/m∙K, and a cost effectiveness of USD 250 per cubic meter. Full article

(This article belongs to the Section Surface Characterization, Deposition and Modification)

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13 pages, 3189 KB

Open AccessEditor’s ChoiceArticle

Exploring the Influence of the Deposition Parameters on the Properties of NiTi Shape Memory Alloy Films with High Nickel Content

by André V. Fontes, Patrícia Freitas Rodrigues, Daniela Santo and Ana Sofia Ramos

Coatings 2024, 14(1), 138; https://doi.org/10.3390/coatings14010138 - 20 Jan 2024

Cited by 4 | Viewed by 2672

Abstract

NiTi shape memory alloy films were prepared by magnetron sputtering using a compound NiTi target and varying deposition parameters, such as power density, pressure, and deposition time. To promote crystallization, the films were heat treated at a temperature of 400 °C for 1 [...] Read more.

NiTi shape memory alloy films were prepared by magnetron sputtering using a compound NiTi target and varying deposition parameters, such as power density, pressure, and deposition time. To promote crystallization, the films were heat treated at a temperature of 400 °C for 1 h. For the characterization, scanning electron microscopy, energy dispersive X-ray spectroscopy, atomic force microscopy, synchrotron X-ray diffraction, and nanoindentation techniques were used on both as-deposited and heat-treated films. Apart from the morphology and hardness of the as-deposited films that depend on the deposition pressure, the power applied to the target and the deposition pressure did not seem to significantly influence the characteristics of the NiTi films studied. After heat treatment, austenitic (B2) crystalline superelastic films with exceptionally high nickel content (~60 at.%) and vein-line cross-section morphology were produced. The crystallization of the films resulted in an increase in hardness, Young’s modulus, and elastic recovery. 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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11 pages, 3861 KB

Open AccessEditor’s ChoiceArticle

Preparation of Metal–Organic-Framework-Derived Fe-CN@CoCN Nanocomposites and Their Microwave Absorption Performance

by Shuning Ren, Pengfei Ju, Haojie Yu, Bohua Nan, Li Wang, Aizhen Lian, Xusheng Zang and Hongyu Liang

Coatings 2024, 14(1), 133; https://doi.org/10.3390/coatings14010133 - 19 Jan 2024

Cited by 8 | Viewed by 2152

Abstract

Microwave technology is commonly used in many fields such as wireless communication and medical treatment, which are closely related to social development. However, electromagnetic pollution caused by microwaves is gradually increasing and the demand for high-performance microwave absorption materials is also increasing. Porous [...] Read more.

Microwave technology is commonly used in many fields such as wireless communication and medical treatment, which are closely related to social development. However, electromagnetic pollution caused by microwaves is gradually increasing and the demand for high-performance microwave absorption materials is also increasing. Porous materials obtained by the pyrolysis of metal–organic frameworks (MOFs) at high temperatures exhibit good conductivity and magnetism, and the original skeleton structure of MOFs can be maintained; thus, MOF-derived materials can be considered viable candidates of microwave absorption materials. In this paper, Fe-CN@CoCN materials were prepared by pyrolyzing a ferrocene (Fc)-doped core–shell zeolite imidazole framework (Fc-ZIF-8@ZIF-67) at 700, 800, and 900 °C for 2 h in an Ar atmosphere. The obtained Fe-CN@CoCN-0.25-700 nanocomposite exhibited excellent microwave absorption (MA) performance with a minimum reflection loss (RL_min) of −42.27 dB at 5.68 GHz and an effective absorption bandwidth (EAB, RL < −10 dB) of 4.80 GHz at a thickness of 2.5 mm. The Fe-CN@CoCN-0.25-800 nanocomposite possessed optimized MA properties with an RL_min of −40.78 dB at 12.56 GHz and an EAB of 4.16 GHz at relatively low thickness of 2 mm. Fe-CN@CoCN nanocomposites are expected to be efficient materials for microwave absorption coatings. Full article

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

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11 pages, 3617 KB

Open AccessEditor’s ChoiceArticle

Improved Heat Dissipation of Dip-Coated Single-Walled Carbon Nanotube/Mesh Sheets with High Flexibility and Free-Standing Strength for Thermoelectric Generators

by Katsuma Miura, Takuya Amezawa, Saburo Tanaka and Masayuki Takashiri

Coatings 2024, 14(1), 126; https://doi.org/10.3390/coatings14010126 - 18 Jan 2024

Cited by 8 | Viewed by 2462

Abstract

Single-walled carbon nanotubes (SWCNTs) are promising thermoelectric materials used in thermoelectric generators (TEGs) to power sensors. However, the limitation of SWCNTs is their high thermal conductivity, which makes it difficult to create a sufficient temperature difference. In this study, we fabricated dip-coated SWCNT/mesh [...] Read more.

Single-walled carbon nanotubes (SWCNTs) are promising thermoelectric materials used in thermoelectric generators (TEGs) to power sensors. However, the limitation of SWCNTs is their high thermal conductivity, which makes it difficult to create a sufficient temperature difference. In this study, we fabricated dip-coated SWCNT/mesh sheets using an SWCNT dispersion. Several types of mesh materials were tested, and the most suitable material was polyphenylene sulfide (PPS). SWCNTs were uniformly deposited on the PPS mesh surface without filling the mesh openings. The SWCNT/PPS mesh sheets exhibited flexibility and free-standing strength. When the edge of the SWCNT/PPS mesh sheets were heated, a higher temperature gradient was produced compared with that of the conventional SWCNT film owing to the increase in heat dissipation. A flexible and free-standing TEG with an area of 1200 mm², fabricated using SWCNT/PPS mesh sheets, exhibited an output voltage of 31.5 mV and maximum power of 631 nW at a temperature difference of 60 K (T_low: 320 K). When the TEG was exposed to wind at 3 m/s, temperature difference further increased, and the performance of the TEG increased by a factor of 1.3 for output voltage and 1.6 for maximum power. Therefore, we demonstrated that the TEG’s performance could be improved using SWCNT/PPS mesh sheets. Full article

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

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28 pages, 17574 KB

Open AccessEditor’s ChoiceArticle

The Effect of Laser Shock Peening (LSP) on the Surface Roughness and Fatigue Behavior of Additively Manufactured Ti-6Al-4V Alloy

by Krista Dyer, Samira Ghadar, Sanin Zulić, Danijela Rostohar, Ebrahim Asadi and Reza Molaei

Coatings 2024, 14(1), 110; https://doi.org/10.3390/coatings14010110 - 15 Jan 2024

Cited by 10 | Viewed by 3898

Abstract

Laser shock peening (LSP) uses plasma shock waves to induce compressive residual stress at the surface of a component which has the potential to improve its fatigue properties. For AM parts, the existence of internal defects, surface roughness, and tensile residual stresses leads [...] Read more.

Laser shock peening (LSP) uses plasma shock waves to induce compressive residual stress at the surface of a component which has the potential to improve its fatigue properties. For AM parts, the existence of internal defects, surface roughness, and tensile residual stresses leads to noticeably lower fatigue strength compared to materials produced through conventional processes. Furthermore, there is a tendency for greater scatter in the fatigue behavior of these parts when compared to traditionally manufactured components. In this study, the effect of LSP on the roughness and fatigue behavior of Ti-6Al-4V alloy constructed through Laser Powder Bed Fusion (L-PBF) technique was investigated. Two types of samples were designed and tested: as-built surface air foil samples for four-point bending tests and machined surface straight gage samples for uniaxial fatigue testing. Two sets of process parameters, optimized and non-optimized, were also used for the fabrication of each sample type. It was found that LSP had negative effects on the smooth (i.e., machined) surface samples, whereas for as-built surfaces the roughness was enhanced by decreasing the sharpness of the deep valleys and partially remelting the loosely bonded particles on the peaks. It was found that the scatter of the fatigue data decreased for optimized machined samples, while no clear improvement was observed in their lives. However, all non-optimized samples showed improvements in fatigue lives after the LSP process. Full article

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

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12 pages, 11049 KB

Open AccessEditor’s ChoiceArticle

High-Temperature Heat Treatment of Plasma Sprayed Ti–Si–C–Mo Coatings

by Jining He, Jialin Liu, Hongjian Zhao, Yanfang Qin and Jiawei Fan

Coatings 2024, 14(1), 109; https://doi.org/10.3390/coatings14010109 - 15 Jan 2024

Cited by 2 | Viewed by 1811

Abstract

In this work, the effect of 800 °C and 1100 °C post-heat treatment on the plasma spraying of Ti–Si–C–xMo (x = 1.0, 1.5) composite coatings was investigated. The composite coatings were composed of TiC, Ti₃SiC₂, Ti₅Si₃ [...] Read more.

In this work, the effect of 800 °C and 1100 °C post-heat treatment on the plasma spraying of Ti–Si–C–xMo (x = 1.0, 1.5) composite coatings was investigated. The composite coatings were composed of TiC, Ti₃SiC₂, Ti₅Si₃ and Mo₅Si₃ reacted phases. After heat treatment, the Ti₃SiC₂ and Mo₅Si₃ phases increased. The coating microhardness decreased by 16% and 18% for Ti–Si–C–1.0Mo and Ti–Si–C–1.5Mo coatings, respectively, after heat treatment at 1100 °C. Fracture toughness increased by 16% for the Ti–Si–C–1.5Mo coating after heat treatment at 1100 °C, which was mainly due to the heat treatment promoting Ti₃SiC₂ formation, healing micro-cracks, reducing the internal stress and making the microstructure dense. The coating friction coefficient before and after heat -treatment was between 0.4 and 0.6. After heat treatment, the wear amount of the coating was first reduced and then increased, and the minimum wear loss occurred after heat treatment at 800 °C. The wear mechanism was mixed abrasive wear, adhesive wear and tribo-oxidation wear. Full article

(This article belongs to the Special Issue Advanced Materials and Surface Protection)

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14 pages, 12915 KB

Open AccessEditor’s ChoiceArticle

Decoration of a Glass Surface with AgNPs Using Thio-Derivates for Environmental Applications

by Cornelia-Ioana Ilie, Angela Spoială, Ludmila Motelica, Liliana Marinescu, Georgiana Dolete, Doina-Roxana Trușcă, Ovidiu-Cristian Oprea, Denisa Ficai and Anton Ficai

Coatings 2024, 14(1), 96; https://doi.org/10.3390/coatings14010096 - 11 Jan 2024

Cited by 5 | Viewed by 2895

Abstract

The aim of this study is to decorate a glass surface with silver nanoparticles (AgNPs) and further prove its efficiency in the removal of some thio-derivatives—potential pollutants from water. Therefore, grafting the surface of glass-based platforms with AgNPs will strongly influence their interaction [...] Read more.

The aim of this study is to decorate a glass surface with silver nanoparticles (AgNPs) and further prove its efficiency in the removal of some thio-derivatives—potential pollutants from water. Therefore, grafting the surface of glass-based platforms with AgNPs will strongly influence their interaction with other substances or molecules. The most commonly used molecules for glass-based platform functionalization/modification are organosilanes. In this case, the main interest is in thioalkyl organosilanes because, after silanization, the thio (-SH) functional groups that have a high affinity for AgNPs can intermediate their binding on the surface. By decorating the glass platforms with AgNPs, these surfaces become active for the adsorption of dyes from wastewater. Certainly, in this case, the dyes must bear -SH groups to ensure a high affinity for these surfaces. Therefore, the desired purpose of this study was to develop glass-based platforms decorated with AgNPs able to bind model molecules—dyes from aqueous media (dithizone—DIT and thioindigo—TIO), with these platforms being potentially used for environmental applications. Full article

(This article belongs to the Collection Feature Paper Collection in 'Surface Coatings for Biomedicine and Bioengineering')

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43 pages, 7178 KB

Open AccessEditor’s ChoiceReview

Coatings and Surface Modification of Alloys for Tribo-Corrosion Applications

by Robert J. K. Wood and Ping Lu

Coatings 2024, 14(1), 99; https://doi.org/10.3390/coatings14010099 - 11 Jan 2024

Cited by 33 | Viewed by 7506

Abstract

This review of the tribocorrosion of coatings and surface modifications covers nearly 195 papers and reviews that have been published in the past 15 years, as compared to only 37 works published up to 2007, which were the subject of a previous review [...] Read more.

This review of the tribocorrosion of coatings and surface modifications covers nearly 195 papers and reviews that have been published in the past 15 years, as compared to only 37 works published up to 2007, which were the subject of a previous review published in 2007. It shows that the research into the subject area is vibrant and growing, to cover emerging deposition, surface modification and testing techniques as well as environmental influences and modelling developments. This growth reflects the need for machines to operate in harsh environments coupled with requirements for increased service life, lower running costs and improved safety factors. Research has also reacted to the need for multifunctional coating surfaces as well as functionally graded systems with regard to depth. The review covers a range of coating types designed for a wide range of potential applications. The emerging technologies are seen to be molten-, solution-, PVD- and PEO-based coatings, with CVD coatings being a less popular solution. There is a growing research interest in duplex surface engineering and coating systems. Surface performance shows a strong playoff between wear, friction and corrosion rates, often with antagonistic relationships and complicated interactions between multiple mechanisms at different scale lengths within tribocorrosion contacts. The tribologically induced stresses are seen to drive damage propagation and accelerate corrosion either within the coating or at the coating coating–substrate interface. This places a focus on coating defect density. The environment (such as pH, DO₂, CO₂, salinity and temperature) is also shown to have a strong influence on tribocorrosion performance. Coating and surface modification solutions being developed for tribocorrosion applications include a whole range of electrodeposited coatings, hard and tough coatings and high-impedance coatings such as doped diamond-like carbon. Hybrid and multilayered coatings are also being used to control damage penetration into the coating (to increase toughness) and to manage stresses. A particular focus involves the combination of various treatment techniques. The review also shows the importance of the microstructure, the active phases that are dissolved and the critical role of surface films and their composition (oxide or passive) in tribocorrosion performance which, although discovered for bulk materials, is equally applicable to coating performance. New techniques show methods for revealing the response of surfaces to tribocorrosion (i.e., scanning electrochemical microscopy). Modelling tribocorrosion has yet to embrace the full range of coatings and the fact that some coatings/environments result in reduced wear and thus are antagonistic rather than synergistic. The actual synergistic/antagonistic mechanisms are not well understood, making them difficult to model. Full article

(This article belongs to the Special Issue Role of Coatings on Corrosion, Wear and Erosion Behavior)

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18 pages, 9818 KB

Open AccessEditor’s ChoiceArticle

Tensile Properties of Aircraft Coating Systems and Applied Strain Modeling

by Attilio Arcari, Rachel M. Anderson, Carlos M. Hangarter, Erick B. Iezzi and Steven A. Policastro

Coatings 2024, 14(1), 91; https://doi.org/10.3390/coatings14010091 - 10 Jan 2024

Cited by 5 | Viewed by 1987

Abstract

In this work, we develop a structural model for the fracturing of an aircraft coating system applied to a complex airframe structure that includes aluminum panels and stainless-steel fasteners. The mechanical properties of the coating system, which consisted of an MIL-PRF-85582E, Type II, [...] Read more.

In this work, we develop a structural model for the fracturing of an aircraft coating system applied to a complex airframe structure that includes aluminum panels and stainless-steel fasteners. The mechanical properties of the coating system, which consisted of an MIL-PRF-85582E, Type II, Class C1, two-part epoxy primer and an MIL-PRF-85285 Rev E, Type IV, Class H, two-part polyurethane topcoat, were measured before and after 8 months of atmospheric exposure. The loads applied to the coating occurred from local deformations of the fastener-panel system in response to flight stresses. Two types of flight stresses, compression dominated and tension dominated, were modeled. The degradation of the mechanical properties of the coating after atmospheric exposure increases the severity of cracking of the coating at a critical fastener–skin interface. Full article

(This article belongs to the Special Issue Research Progress on Coatings Degradation and Atmospheric Corrosion of Metal Surfaces)

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30 pages, 1508 KB

Open AccessEditor’s ChoiceSystematic Review

Antimicrobial Activity of Photocatalytic Coatings on Surfaces: A Systematic Review and Meta-Analysis

by Francesca Ubaldi, Federica Valeriani, Veronica Volpini, Giusy Lofrano and Vincenzo Romano Spica

Coatings 2024, 14(1), 92; https://doi.org/10.3390/coatings14010092 - 10 Jan 2024

Cited by 16 | Viewed by 6492

Abstract

Photocatalytic technologies represent an innovative method to reduce microbial load on surfaces, even considering recent public health emergencies involving coronaviruses and other microorganisms, whose presence has been detected on surfaces. In this review paper, the antimicrobial efficacy of various photocatalysts applied by different [...] Read more.

Photocatalytic technologies represent an innovative method to reduce microbial load on surfaces, even considering recent public health emergencies involving coronaviruses and other microorganisms, whose presence has been detected on surfaces. In this review paper, the antimicrobial efficacy of various photocatalysts applied by different coating methods on different surfaces has been compared and critically discussed. Publications reviewing the use of photocatalytic coatings on surfaces for antimicrobial effectiveness have been examined. Clear search parameters were employed to analyze the PubMed, Scopus, and WOS databases, resulting in 45 papers published between 2006 to 2023 that met the inclusion criteria. The paper assessed various types of photocatalytic coatings that targeted different microbial objectives. Based on the pooled data analysis, the TiO₂ coating exhibited a substantial effect in decreasing bacteria strains, both Gram-positive and -negative (99.4%). Although the diversity of these technologies poses significant obstacles to obtaining a comprehensive final assessment of their effectiveness and feasibility for surface application, subgroup analysis indicated significant variations in the removal efficiency of Gram-positive strains based on different surface types (p = 0.005) and time of exposure (p = 0.05). Photocatalytic coatings provide a promising approach to combating the spread of microorganisms on surfaces. Further “in-field” investigations are necessary in the foreseeable future to explore and optimize this novel and exciting health technology. Full article

(This article belongs to the Special Issue Nanostructured Materials and Interfaces: Biomedical and Healthcare Applications)

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14 pages, 7220 KB

Open AccessEditor’s ChoiceArticle

A One-Step Novel Method to Fabricate Multigrade Ti6Al4V/TiN Composites Using Laser Powder Bed Fusion

by Carmen Sánchez de Rojas Candela, Ainhoa Riquelme, Pilar Rodrigo, Victoria Bonache, Javier Bedmar, Belén Torres and Joaquín Rams

Coatings 2024, 14(1), 90; https://doi.org/10.3390/coatings14010090 - 9 Jan 2024

Cited by 2 | Viewed by 2230

Abstract

Ti6Al4V is the most used alloy for implants because of its excellent biocompatibility; however, its low wear resistance limits its use in the biomedical industry. The additive manufacturing (AM) of Ti6Al4V is a well-established technique that is being used in many fields. However, [...] Read more.

Ti6Al4V is the most used alloy for implants because of its excellent biocompatibility; however, its low wear resistance limits its use in the biomedical industry. The additive manufacturing (AM) of Ti6Al4V is a well-established technique that is being used in many fields. However, the AM of Ti6Al4V composites is currently under investigation, and its manufacture using laser powder bed fusion (L-PBF) would result in a great benefit for many industries. The one-step novel concept proposed uses a gas-controlled L-PBF system that enables the AM of layers with different compositions. Six millimeter-edged cubes of Ti6Al4V were manufactured in an Ar atmosphere and coated with in situ Ti6Al4V/TiN layers by using an Ar–N₂ mixture given the direct reaction between titanium and nitrogen. Unreinforced Ti6Al4V presented a martensitic microstructure, and TiN reinforcement dendrites and a minor Ti₂N phase were gradually introduced into an α + β basketweave titanium matrix. The composites’ microhardness, nanohardness, and elastic modulus were 2, 3, and 1.5 times higher, respectively, than those of the Ti6Al4V. Porosity levels (caused by a lack of fusion, trapping gases, and interdendritic porosity), ranged from 7 to 12% (most measured 20–40 µm) and increased with the reinforcement content (15 to 25%). A scaled-up, proof-of-concept design of a hip implant stem was 3D printed using this nitriding method. Since the neck of the stem (top part) is more susceptible to the fracture and fretting corrosion process, the resulting graded material part consisted of unreinforced Ti6Al4V at the bottom and Ti6Al4V/TiN at the top. This change was controlled by gradually adding nitrogen to the atmosphere; moreover, it was found that the more nitrogen in the chamber, the more TiN reinforcement formed in the part. A microhardness of ~450 HV_0.1 was measured at the bottom and gradually increased to ~900 HV_0.1, with the increment corresponding to the in situ TiN reinforcement amount. Full article

(This article belongs to the Special Issue Additive Manufacturing of Metallic Components for Hard Coatings)

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23 pages, 7194 KB

Open AccessEditor’s ChoiceArticle

Functionalization of Plasma Electrolytic Oxidation/Sol–Gel Coatings on AZ31 with Organic Corrosion Inhibitors

by Borja Pillado, Endzhe Matykina, Marie-Georges Olivier, Marta Mohedano and Raúl Arrabal

Coatings 2024, 14(1), 84; https://doi.org/10.3390/coatings14010084 - 7 Jan 2024

Cited by 9 | Viewed by 2686

Abstract

In this investigation, the sol–gel method is employed along with a corrosion inhibitor to seal a plasma electrolytic oxidation (PEO) coating, aiming to improve the long-term corrosion resistance of the AZ31 Mg alloy. Following an initial screening of corrosion inhibitors, 8-hydroxyquinoline (8HQ) is [...] Read more.

In this investigation, the sol–gel method is employed along with a corrosion inhibitor to seal a plasma electrolytic oxidation (PEO) coating, aiming to improve the long-term corrosion resistance of the AZ31 Mg alloy. Following an initial screening of corrosion inhibitors, 8-hydroxyquinoline (8HQ) is incorporated into the hybrid PEO/sol–gel system using two methods: (i) post-treatment of the PEO layer through immersion in an inhibitor-containing solution; (ii) loading the inhibitor into the sol–gel precursor. The characterization includes scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), ultraviolet-visible spectroscopy (UV-vis), and water drop contact angle measurements. The rheological properties of the inhibitor-loaded sol–gel precursors are assessed by measuring flow curves. The corrosion processes are evaluated in a saline solution through electrochemical impedance spectroscopy (EIS) and immersion tests with unscratched and scratched specimens, respectively. The results demonstrate the successful incorporation of the inhibitor for both loading strategies. Regardless of the loading approach, systems containing 8HQ exhibit the most favourable long-term corrosion resistance. Full article

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

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14 pages, 3660 KB

Open AccessEditor’s ChoiceArticle

Investigation of Polyelectrolyte Multilayers Deposited on Biodegradable Corona-Charged Substrates Used as Drug Delivery Systems

by Asya Viraneva, Maria Marudova, Sofia Milenkova, Aleksandar Grigorov and Temenuzhka Yovcheva

Coatings 2024, 14(1), 85; https://doi.org/10.3390/coatings14010085 - 7 Jan 2024

Cited by 4 | Viewed by 1984

Abstract

Polyelectrolyte multilayers (PEMs) deposited on porous composite polylactic acid/poly(ε-caprolactone) (PDLA/PEC) substrates were studied. The substrates were previously charged in a corona discharge. Time dependences of the normalized surface potential for positively and negatively charged electrets were investigated. The morphology of the obtained porous [...] Read more.

Polyelectrolyte multilayers (PEMs) deposited on porous composite polylactic acid/poly(ε-caprolactone) (PDLA/PEC) substrates were studied. The substrates were previously charged in a corona discharge. Time dependences of the normalized surface potential for positively and negatively charged electrets were investigated. The morphology of the obtained porous substrates was examined by means of scanning electron microscopy (SEM). The chitosan and the casein polyelectrolytes were deposited on the substrates using the layer-by-layer (LbL) technique. The drug loading efficiency and the release kinetics were determined spectrophotometrically. Full article

(This article belongs to the Section Surface Characterization, Deposition and Modification)

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17 pages, 5240 KB

Open AccessEditor’s ChoiceArticle

Tailoring the Silicon Cementation Applied to P265GH Grade Steel

by Mihai Branzei, Mihai Ovidiu Cojocaru, Mircea Dan Morariu and Leontin Nicolae Druga

Coatings 2024, 14(1), 74; https://doi.org/10.3390/coatings14010074 - 4 Jan 2024

Viewed by 1555

Abstract

Increasing the serviceability of industrial components intended for the petrochemical industry is possible through their superficial saturation with silicon (silicon cementation). Obtaining a silicon-rich surface coating results in a considerable increase in corrosion resistance, refractoriness, and wear resistance. One of the most economically [...] Read more.

Increasing the serviceability of industrial components intended for the petrochemical industry is possible through their superficial saturation with silicon (silicon cementation). Obtaining a silicon-rich surface coating results in a considerable increase in corrosion resistance, refractoriness, and wear resistance. One of the most economically convenient options for silicon cementation is pack siliconizing in powdery solid media. This paper presents the possibility of pack siliconizing that contains ferrosilicon (FeSi75C) and a thermite mixture (SiO₂ + Al) as active, silicon-providing components, in P265GH grade steel, which is frequently used in the petrochemical industry. The aim of the study was to determine the most suitable active component of the two that were analyzed and at the same time identify the processing conditions in which the siliconized coating has the greatest thickness, is free of porosity, and is in direct contact with the support. The use of experimental programming methods allowed the optimization of the operation to obtain the optimal solution. It was concluded that the thermite mixture is not compatible with pack siliconizing because it results in a superficial saturation predominantly composed of aluminum. When ferrosilicon is used as the active component, it determines the particularly intense formation kinetics of the non-porous siliconized coating with its maximum thickness being reached at high processing temperature values (over 1100 °C) with a proportion of 60% FeSi75 and, simultaneously, with the lowest possible proportion of ammonium chloride (max. 3%), which is the surface activation/cleaning component. Full article

(This article belongs to the Special Issue Advanced Coatings with Noble and Refractory Alloy Metals in Extreme Environments)

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13 pages, 19782 KB

Open AccessEditor’s ChoiceArticle

Effects of Heat Treatment and Erosion Particle Size on Erosion Resistance of a Hypereutectic High-Chromium Cast Iron

by Alessio Suman and Annalisa Fortini

Coatings 2024, 14(1), 66; https://doi.org/10.3390/coatings14010066 - 3 Jan 2024

Cited by 1 | Viewed by 1830

Abstract

This research addresses the erosive resistance of a hypereutectic high-chromium cast iron subjected to solid particle erosion. The study stems from a specific application of high-chromium cast iron, i.e., the critical surfaces of large industrial fans operating in a cement clinker grinding plant [...] Read more.

This research addresses the erosive resistance of a hypereutectic high-chromium cast iron subjected to solid particle erosion. The study stems from a specific application of high-chromium cast iron, i.e., the critical surfaces of large industrial fans operating in a cement clinker grinding plant where such damage is a limiting factor for the components’ lifespan. A dedicated experimental investigation on the impact of substrate microstructure and erodent particle size on erosion resistance was set. The experimental campaign, conducted on a dedicated test bench per the ASTM G76 standard, comprised the analysis of the as-received, tempered, and destabilized conditions for the cast iron. From a preliminary image analysis of the microstructural features, two diameters of the erodent powder for the erosion tests were defined. The observed erosion rate decreased with the increase in the mean particle diameter of the erodent, indicating more severe erosive conditions for smaller particles. From the analysis of the worn surfaces, it was possible to highlight the involved mechanisms concerning the considered test combinations. For the as-received condition, the erosion rate with the larger mean particle diameter of the erodent decreased three times compared to the smaller one. For the heat-treated conditions, the erosion rate was halved with the larger mean particle diameter of the erodent. The proposed analysis, intended to acquire more insight into the limiting factor for the components’ lifespan for erosive wear damage, proved that erosion resistance is not dependent on the material’s hardness. The contribution of the mean particle diameter of the erodent is predominant compared to the substrate conditions. Full article

(This article belongs to the Special Issue Wear-Resistance and Corrosion-Resistance Coatings)

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17 pages, 8339 KB

Open AccessEditor’s ChoiceArticle

Preparation and Characterization of Polymer-Based Electrospun Nanofibers for Flexible Electronic Applications

by Gopiraman Mayakrishnan, Ramkumar Vanaraj, Takayasu Kitauchi, Rajakumar Kanthapazham, Seong Cheol Kim and Ick Soo Kim

Coatings 2024, 14(1), 35; https://doi.org/10.3390/coatings14010035 - 27 Dec 2023

Cited by 2 | Viewed by 2450

Abstract

This study was undertaken to synthesize and characterize PVDF/CB (polyvinylidene fluoride/carbon block) nanofiber composites for flexible, wearable electronic applications. Nanofibers were produced by electrospinning method and used to produce thin films. Fiber surface morphologies were investigated by FE-SEM and HR-TEM, crystalline structures by [...] Read more.

This study was undertaken to synthesize and characterize PVDF/CB (polyvinylidene fluoride/carbon block) nanofiber composites for flexible, wearable electronic applications. Nanofibers were produced by electrospinning method and used to produce thin films. Fiber surface morphologies were investigated by FE-SEM and HR-TEM, crystalline structures by FT-IR and P-XRD, and thermal characteristics by TGA and DSC. The prepared materials are thermally stable up to 390 °C. Mechanical properties were ascertained using tensile characteristics, and results showed that the addition of carbon black (CB) powder to PVDF polymer solution decreased Young’s modulus values and reduced the dielectric constant of PVDF nanofiber films. The obtained dielectric constants of nanofibers loaded with various concentrations of CB were found from 1.4 to 2.0. Flexible electronics materials are essential for the production of wearable electronics and various biomedical engineering applications. The PVDF/CB nanofibers containing 1% showed maximum Young’s moduli of 101.29 ± 15.94. Nanofiber thin films offer various advantages, including simplicity of manufacture, low power consumption, flexibility, and exceptional stability, all of which are crucial for flexible, wearable device applications. Full article

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

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18 pages, 4613 KB

Open AccessEditor’s ChoiceArticle

Machine Learning Modeling and Run-to-Run Control of an Area-Selective Atomic Layer Deposition Spatial Reactor

by Matthew Tom, Henrik Wang, Feiyang Ou, Gerassimos Orkoulas and Panagiotis D. Christofides

Coatings 2024, 14(1), 38; https://doi.org/10.3390/coatings14010038 - 27 Dec 2023

Cited by 5 | Viewed by 2613

Abstract

Semiconducting materials require stringent design specifications that make their fabrication more difficult and prone to flaws that are costly and damaging to their computing and electrical properties. Area-selective atomic layer deposition is a process that addresses concerns associated with design imperfections but requires [...] Read more.

Semiconducting materials require stringent design specifications that make their fabrication more difficult and prone to flaws that are costly and damaging to their computing and electrical properties. Area-selective atomic layer deposition is a process that addresses concerns associated with design imperfections but requires substantial monitoring to ensure that process regulation is maintained. This work proposes a run-to-run controller with an exponentially weighted moving average method for an area-selective atomic layer deposition rotary reactor by adjusting the rotation speed of the substrate to control the growth per cycle of the wafer, which is calculated through a multiscale model with machine learning integration for pressure field generation and kinetic Monte Carlo simulations to increase computational efficiency. Results indicate that the run-to-run controller was able to bring the process to the setpoint when subjected to moderate pressure and kinetic shift disturbances. Full article

(This article belongs to the Special Issue Recent Advances in Chemical Vapor Deposition)

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9 pages, 2574 KB

Open AccessEditor’s ChoiceArticle

Atomic Layer Deposition for Tailoring Tamm Plasmon-Polariton with Ultra-High Accuracy

by Mantas Drazdys, Ernesta Bužavaitė-Vertelienė, Darija Astrauskytė and Zigmas Balevičius

Coatings 2024, 14(1), 33; https://doi.org/10.3390/coatings14010033 - 26 Dec 2023

Viewed by 1887

Abstract

In this study, we demonstrate the potential capability to control Tamm plasmon-polaritons (TPP) by applying atomic layer deposition (ALD) as a highly precise technique for plasmonic applications. Applications in plasmonics usually require tens of nanometers or less thick layers; thus, ALD is a [...] Read more.

In this study, we demonstrate the potential capability to control Tamm plasmon-polaritons (TPP) by applying atomic layer deposition (ALD) as a highly precise technique for plasmonic applications. Applications in plasmonics usually require tens of nanometers or less thick layers; thus, ALD is a very suitable technique with monolayer-by-monolayer growth of angstrom resolution. Spectroscopic ellipsometry and polarized reflection intensity identified the TPP resonances in the photonic band gap (PBG) formed by periodically alternating silicon oxide and tantalum oxide layers. The sub-nanometer control of the Al₂O₃ layer by ALD allows precise tailoring of TPP resonances within a few nanometers of spectral shift. The employing of the ALD method for the fabrication of thin layers with sub-nanometer thickness accuracy in more complex structures proves to be a versatile platform for practical applications where tunable plasmonic resonances of high quality are required. Full article

(This article belongs to the Special Issue Fabrication of Plasmonic Thin Films, Their Characterization and Applications)

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25 pages, 3792 KB

Open AccessEditor’s ChoiceReview

Structural Damage Detection Based on Static and Dynamic Flexibility: A Review and Comparative Study

by Xi Peng, Qiuwei Yang, Fengjiang Qin and Binxiang Sun

Coatings 2024, 14(1), 31; https://doi.org/10.3390/coatings14010031 - 26 Dec 2023

Cited by 4 | Viewed by 2853

Abstract

Material damage in structures must be detected in a timely manner to prevent engineering accidents. Damage detection based on structural flexibility has attracted widespread attention in recent years due to its simplicity and practicality. This article provides a detailed overview of damage detection [...] Read more.

Material damage in structures must be detected in a timely manner to prevent engineering accidents. Damage detection based on structural flexibility has attracted widespread attention in recent years due to its simplicity and practicality. This article provides a detailed overview of damage detection methods based on structural flexibility. Depending on the calculation method and data used, flexibility-based methods can be divided into the following categories: flexibility difference, flexibility derivative index, flexibility sensitivity, flexibility decomposition, static flexibility, and combinations of flexibility with other methods. The basic principles and main calculation formulas of various flexibility methods are explained, and their advantages and disadvantages are analyzed. For the method using flexibility difference, the advantage is that the calculation is very simple and does not require the construction of a finite element model of the structure. The disadvantage is that it requires the measurement of modal data of the intact structure, and this method cannot quantitatively assess the degree of damage. For the method using the flexibility derivative index, the advantage is that it only requires the modal data of the damaged structure to locate the damage, but this method is particularly sensitive to noise in the data and is prone to misjudgment. For methods based on flexibility sensitivity and flexibility decomposition, the advantage is that they can simultaneously obtain the location and degree of damage in the structure, but the disadvantage is that they require the establishment of accurate finite element models in advance. Static flexibility methods can compensate for the shortcomings of dynamic flexibility methods, but they usually affect the normal use of the structure during static testing. Combining flexibility-based methods with advanced intelligent algorithms and other methods can further improve their accuracy and efficiency in identifying structural damage. Finally, this article discusses the challenges that have not yet been solved among damage detection methods based on structural flexibility. Full article

(This article belongs to the Special Issue Development and Characterization of New Construction Materials and Coatings)

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14 pages, 3501 KB

Open AccessEditor’s ChoiceArticle

Physicomechanical Properties of Gypsum with Mineral Additions at Elevated Temperatures

by Junjie Wang and Engui Liu

Coatings 2023, 13(12), 2091; https://doi.org/10.3390/coatings13122091 - 15 Dec 2023

Cited by 1 | Viewed by 3810

Abstract

Gypsum, from either nature or industrial by-products, can be a lower-cost and cleaner alternative binder to Portland cement used in construction projects, such as affordable housing in developing countries. Although various building products have successfully used gypsum as the binder, some drawbacks of [...] Read more.

Gypsum, from either nature or industrial by-products, can be a lower-cost and cleaner alternative binder to Portland cement used in construction projects, such as affordable housing in developing countries. Although various building products have successfully used gypsum as the binder, some drawbacks of this material have still been claimed, for example, in the aspects of mechanical strength and some other physical properties. Using mineral additions to gypsum seems to be a possible solution to create composite gypsum with improved properties. This work has investigated the possibility of two common minerals (silica flour and talc powder) in modifying composite gypsum’s physical and mechanical performance at elevated temperatures (100–1100 °C), including hydration, strength, thermal conduction and stability, and microstructure. The results suggest that 10% gypsum replacement by silica flour or talc powder modifies gypsum’s physical and mechanical properties, with silica flour performing better than talc powder. The performance of composite gypsum at elevated temperatures depends on the treatment temperature and reflects the combined effects of gypsum phase change and the filler effects of silica flour or talc powder. Thermal treatment at ≤200 °C increased the thermal resistance of all gypsum boards but decreased their compressive strength. Thermal treatment at ≥300 °C significantly increased the compressive strength of gypsum with silica flour and talc powder but induced intensive microcracks and thus failed the thermal insulation. This investigation indicates that silica flour can potentially raise the mechanical performance of gypsum. At the same time, talc powder can hold water and lubricate, which may help with the continuous hydration of gypsum phases and the rheology of its mixtures. Full article

(This article belongs to the Special Issue Effective Coating Barriers for Protection of Reinforced Concrete)

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17 pages, 7792 KB

Open AccessEditor’s ChoiceArticle

The Effect of Plasma Spray Parameters on the Quality of Al-Ni Coatings

by Shenglian Wang, Shuang Chen, Ming Liu, Qinghua Huang, Zimo Liu, Xin Li and Shaofeng Xu

Coatings 2023, 13(12), 2063; https://doi.org/10.3390/coatings13122063 - 9 Dec 2023

Cited by 6 | Viewed by 3211

Abstract

The plasma spray method is widely utilized for enhancing wear, surface fatigue, and corrosion properties through coating. The mechanical and surface characteristics of the resulting coating are contingent upon various spraying parameters, including arc current, working current, spraying distance, and plasma gun traversing [...] Read more.

The plasma spray method is widely utilized for enhancing wear, surface fatigue, and corrosion properties through coating. The mechanical and surface characteristics of the resulting coating are contingent upon various spraying parameters, including arc current, working current, spraying distance, and plasma gun traversing speed. This study investigates the impact of these manufacturing parameters on the porosity, hardness, and bond strength of a coating produced from an Al-Ni alloy applied to a Q235 steel substrate. An extensive experimental program was conducted to analyze the influence of these parameters on the coating properties. Consequently, a preferred combination of parameters, identified through a comprehensive evaluation method, yielded greater performance benefits compared to the orthogonal experimental groups. Full article

(This article belongs to the Special Issue Application of Advanced Plasma Technology in Coatings, Films and Etching)

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27 pages, 4410 KB

Open AccessEditor’s ChoiceReview

Protecting Street Art from Outdoor Environmental Threats: What Are the Challenges?

by Laura Pagnin, Nicolò Guarnieri, Francesca Caterina Izzo, Sara Goidanich and Lucia Toniolo

Coatings 2023, 13(12), 2044; https://doi.org/10.3390/coatings13122044 - 5 Dec 2023

Cited by 15 | Viewed by 5453

Abstract

Street Art is an artistic expression in constant development, whose interest has grown in recent years among society, public administrations, conservators, and heritage scientists. This growing awareness has given rise to a series of debates between professionals with the intent to expand the [...] Read more.

Street Art is an artistic expression in constant development, whose interest has grown in recent years among society, public administrations, conservators, and heritage scientists. This growing awareness has given rise to a series of debates between professionals with the intent to expand the knowledge relating to conservation practices and possible protection solutions. Additionally, the paint materials used by contemporary artists are in constant development; therefore, difficulty has emerged in the identification of their degradation processes when exposed to environmental conditions and in the consequent selection of a specific protection system. This review presents an overview of the recent literature and experiences in the field of knowledge and preservation of Street Art, focusing on the type and nature of paint formulations, the main deterioration processes of painted artworks in outdoor conditions, and the most recent advances in materials and methods for the conservation and protection of Street Art. This review aims to emphasise how the approach to the challenge of preservation of Street Art is complex, aspiring to the need for optimised diagnostic protocols for the development of innovative and effective protective coatings. This paper is a starting point to provide suggestions and indications for the development of further research projects within the framework of preservation and protection of contemporary muralism. Full article

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

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16 pages, 5968 KB

Open AccessEditor’s ChoiceArticle

Self-Healing UV-Curable Urethane (Meth)acrylates with Various Soft Segment Chemistry

by Paulina Bednarczyk, Paula Ossowicz-Rupniewska, Joanna Klebeko, Joanna Rokicka, Yongping Bai and Zbigniew Czech

Coatings 2023, 13(12), 2045; https://doi.org/10.3390/coatings13122045 - 5 Dec 2023

Cited by 3 | Viewed by 3356

Abstract

This study explores the synthesis and evaluation of UV-curable urethane (meth)acrylates (UA) incorporating a Diels–Alder adduct (HODA), diisocyanate, poly(ethylene glycol), and hydroxy (meth)acrylate. Six UAs, distinguished by the soft segment of polymer chains, underwent comprehensive characterization using FTIR and NMR spectroscopy. Real-time monitoring [...] Read more.

This study explores the synthesis and evaluation of UV-curable urethane (meth)acrylates (UA) incorporating a Diels–Alder adduct (HODA), diisocyanate, poly(ethylene glycol), and hydroxy (meth)acrylate. Six UAs, distinguished by the soft segment of polymer chains, underwent comprehensive characterization using FTIR and NMR spectroscopy. Real-time monitoring of the UV-curing process and analysis of self-healing properties were performed. The research investigates the influence of various molecular weights of PEGs on the self-healing process, revealing dependencies on photopolymerization kinetics, microstructure, thermal properties, and thermoreversibility of urethane (meth)acrylates. This work provides valuable insights into the development of UV-curable coatings with tailored properties for potential applications in advanced materials. Full article

(This article belongs to the Special Issue Advanced Polymeric Materials and Coatings: Synthesis, Properties and Applications)

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62 pages, 10199 KB

Open AccessEditor’s ChoiceReview

Electrochemical Detection of Hormones Using Nanostructured Electrodes

by Naila Haroon and Keith J. Stine

Coatings 2023, 13(12), 2040; https://doi.org/10.3390/coatings13122040 - 4 Dec 2023

Cited by 29 | Viewed by 12316

Abstract

Hormones regulate several physiological processes in living organisms, and their detection requires accuracy and sensitivity. Recent advances in nanostructured electrodes for the electrochemical detection of hormones are described. Nanostructured electrodes’ high surface area, electrocatalytic activity, and sensitivity make them a strong hormone detection [...] Read more.

Hormones regulate several physiological processes in living organisms, and their detection requires accuracy and sensitivity. Recent advances in nanostructured electrodes for the electrochemical detection of hormones are described. Nanostructured electrodes’ high surface area, electrocatalytic activity, and sensitivity make them a strong hormone detection platform. This paper covers nanostructured electrode design and production using MOFs, zeolites, carbon nanotubes, metal nanoparticles, and 2D materials such as TMDs, Mxenes, graphene, and conducting polymers onto electrodes surfaces that have been used to confer distinct characteristics for the purpose of electrochemical hormone detection. The use of aptamers for hormone recognition is producing especially promising results, as is the use of carbon-based nanomaterials in composite electrodes. These materials are optimized for hormone detection, allowing trace-level quantification. Various electrochemical techniques such as SWV, CV, DPV, EIS, and amperometry are reviewed in depth for hormone detection, showing the ability for quick, selective, and quantitative evaluation. We also discuss hormone immobilization on nanostructured electrodes to improve detection stability and specificity. We focus on real-time monitoring and tailored healthcare with nanostructured electrode-based hormone detection in clinical diagnostics, wearable devices, and point-of-care testing. These nanostructured electrode-based assays are useful for endocrinology research and hormone-related disease diagnostics due to their sensitivity, selectivity, and repeatability. We conclude with nanotechnology–microfluidics integration and tiny portable hormone-detection devices. Nanostructured electrodes can improve hormone regulation and healthcare by facilitating early disease diagnosis and customized therapy. Full article

(This article belongs to the Special Issue Advances in the Preparation and Characterization Techniques for Developing Coating Materials and Applications)

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22 pages, 5029 KB

Open AccessFeature PaperEditor’s ChoiceArticle

Novel Method for Assessing the Protection Lifetime of Building Coatings against Fungi

by Justyna Szulc, Michał Komar, Iwona Kata, Krzysztof Szafran and Beata Gutarowska

Coatings 2023, 13(12), 2026; https://doi.org/10.3390/coatings13122026 - 30 Nov 2023

Cited by 5 | Viewed by 2391

Abstract

The aim of this study was to develop a novel method for evaluating the service life of building coatings. In Stage 1, we assessed existing methods for determining the degree of fungal overgrowth on building materials (visual assessment, culture method, luminometric ATP (adenosine-5’-triphosphate) [...] Read more.

The aim of this study was to develop a novel method for evaluating the service life of building coatings. In Stage 1, we assessed existing methods for determining the degree of fungal overgrowth on building materials (visual assessment, culture method, luminometric ATP (adenosine-5’-triphosphate) measurement, and spectrophotometric assessment of colour changes). Laboratory tests were carried out for 19 types of facade coating (mineral and silicone with/without primer, silicone paint, biocides) and 7 fungal strains (moulds Alternaria alternata, Aspergillus niger, Aureobasidium melanogenum, Cladosporium cladosporioides, Fusarium sp., Penicillium citrinum, and the yeast Rhodotorula mucilaginosa). The number of fungi on the facade coatings after 28 days of incubation was 1.7 × 10⁵–4.6 × 10⁵ CFUs (colony-forming units)/sample. The ATP content was 12 RLUs–30333 RLUs (relative light units). Colour change was ΔE > 5 depending on the coating type and fungal strain. A high or very high correlation was found between the ATP concentration (RLUs), colour change (ΔE), and the results of the culture method (CFUs/sample). In Stage 2, a new methodology for evaluating the protection lifetime of building coatings against fungi was developed, taking into account environmental conditions (impact of ultraviolet radiation, precipitation, presence of organic matter on the surface, quantitative and qualitative composition of bioaerosol). The developed method consists of one research cycle conducted in the laboratory, corresponding to one year under natural conditions. Preliminary verification showed the model to be compatible with long-term observations (3 years) of fungal growth on the facade coatings under real environmental conditions. The novel method could be used to design biodeterioration control and protection strategies for both new and cultural heritage buildings. Full article

(This article belongs to the Special Issue Biological Colonization of Cultural Heritage. Emerging Trends in the Protection of Cultural Properties—Novel Control Strategies and Preventive Approaches)

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17 pages, 6534 KB

Open AccessEditor’s ChoiceArticle

The Effect of CO₂ Laser Engraving on the Surface Structure and Properties of Spruce Wood

by Jozef Kúdela, Michal Andrejko and Ivan Kubovský

Coatings 2023, 13(12), 2006; https://doi.org/10.3390/coatings13122006 - 26 Nov 2023

Cited by 11 | Viewed by 2374

Abstract

This work appraises the influence of CO₂ laser irradiation on mass loss, morphology, chemical changes and discolouration of spruce wood surfaces. The amount of energy applied to the surface was expressed as the total irradiation dose, which was demonstrated to have a [...] Read more.

This work appraises the influence of CO₂ laser irradiation on mass loss, morphology, chemical changes and discolouration of spruce wood surfaces. The amount of energy applied to the surface was expressed as the total irradiation dose, which was demonstrated to have a strong impact on increasing wood weight loss. Along with increasing mass loss, surface roughness also increased, resulting from the differences in density between the early wood and late wood. The evaluated roughness parameters increased linearly with increasing irradiation dose and mass loss. At the maximum irradiation dose, the Ra parameter value parallel to the fibre direction showed a 6-fold increase; perpendicular to the grain, the increase was as much as 33.5-fold. Similar differences were also observed for the parameter Rz. At the lowest laser power and the lowest raster density, the engraved spruce wood surface exhibited some evidence of discolouration (ΔE* ≅ 9). An additional increase in the amount of supplied energy clearly resulted in a novel surface colour compared to the original (ΔE* = 12). The chemical analysis of the wood surface revealed that the discolouration was mainly caused by heat-induced cleavage of C=O groups in the lignin and hemicellulose structures. Part of these structures (so-called chromophores) are responsible for the natural colour of the wood as well as for colour changes caused by engraving. The detected dependences of the wood mass loss and colour values on the total radiation dose are the basis for achieving targeted modifications of spruce wood surfaces using a laser beam. Full article

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

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15 pages, 6706 KB

Open AccessEditor’s ChoiceArticle

Effect of the Solvent Type on the Colloidal Stability and the Degree of Condensation of Silica Sols Stabilized by Amphiphilic Urethane Acrylate and the Properties of Their Coating Films

by Hong Nhung Le, Choonho Lee, Woochul Jung and Juyoung Kim

Coatings 2023, 13(12), 1997; https://doi.org/10.3390/coatings13121997 - 24 Nov 2023

Cited by 2 | Viewed by 3299

Abstract

The colloidal stability of silica O-I hybrid sols that have a high degree of condensation could result in the formation of a hard coating film on a substrate, which could depend on the properties of solvents used in the sol-gel reaction. In this [...] Read more.

The colloidal stability of silica O-I hybrid sols that have a high degree of condensation could result in the formation of a hard coating film on a substrate, which could depend on the properties of solvents used in the sol-gel reaction. In this study, the effect of the solvent type on the colloidal stability and degree of condensation of the silica sols was investigated by preparing various silica O-I hybrid sols using different solvent mixtures composed of various aprotic and protic solvents in the presence of amphiphilic urethane acrylate. Silica sols prepared using the appropriate aprotic-protic solvent mixture showed a higher degree of condensation and long-term colloidal stability, which was confirmed using ²⁹Si-NMR and DLS. Furthermore, the coating film formed from these silica sols showed a remarkable hardness of 0.97 GPa, with a thickness of 4.76 µm confirmed using nanoindentation measurements. Full article

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

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28 pages, 11599 KB

Open AccessEditor’s ChoiceReview

A Review on Geothermal Heat Exchangers: Challenges, Coating Methods, and Coating Materials

by Arunima Bhuvanendran Nair Jayakumari, Nigar Gul Malik, Garima Mittal, David Martelo, Namrata Kale and Shiladitya Paul

Coatings 2023, 13(12), 1988; https://doi.org/10.3390/coatings13121988 - 23 Nov 2023

Cited by 10 | Viewed by 5816

Abstract

Geothermal energy is likely to be a significant contributor in achieving sustainable energy goals and net-zero emissions targets. Within geothermal power plants, heat exchangers play a critical role in harnessing this renewable energy source. However, these heat exchangers encounter significant challenges when exposed [...] Read more.

Geothermal energy is likely to be a significant contributor in achieving sustainable energy goals and net-zero emissions targets. Within geothermal power plants, heat exchangers play a critical role in harnessing this renewable energy source. However, these heat exchangers encounter significant challenges when exposed to geothermal fluids, including erosion, corrosion, and scaling, which adversely affects their performance and longevity. The current review focuses on surface engineering techniques, particularly coatings, as a highly effective and economically viable solution to address these challenges in geothermal heat exchangers. The review begins by providing an overview of geothermal energy, its significance in the context of sustainability and the important role played by heat exchangers in geothermal power generation, followed by the challenges and their impact on heat exchangers. The subsequent section focuses on surface engineering by coatings and its types employed to enhance the performance of heat exchangers. In the final part, the reader is presented with an overview of the challenges associated with the application of coatings in geothermal heat exchangers and potential future directions in this field. This review offers a detailed understanding of the critical role coatings play in improving the efficiency and service life of heat exchangers in geothermal power plants. Full article

(This article belongs to the Special Issue Recent Research in Coatings for Harsh Environments)

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16 pages, 4798 KB

Open AccessFeature PaperEditor’s ChoiceArticle

Calcium Hydroxyapatite Coatings: Low-Temperature Synthesis and Investigation of Antibacterial Properties

by Laura Lukaviciute, Justina Karciauskaite, Inga Grigoraviciute, Dovile Vasiliauskiene, Denis Sokol and Aivaras Kareiva

Coatings 2023, 13(12), 1991; https://doi.org/10.3390/coatings13121991 - 23 Nov 2023

Cited by 7 | Viewed by 2654

Abstract

In the present work, the low-temperature synthesis of substituted calcium hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂, HAP) with copper and zinc ions on titanium substrates was performed. Initially, CaCO₃ coatings were synthesised on titanium substrate using the sol-gel [...] Read more.

In the present work, the low-temperature synthesis of substituted calcium hydroxyapatite (Ca₁₀(PO₄)₆(OH)₂, HAP) with copper and zinc ions on titanium substrates was performed. Initially, CaCO₃ coatings were synthesised on titanium substrate using the sol-gel method at 550 °C in a CO₂ atmosphere. Crystalline calcium hydroxyapatite was then synthesised from these CaCO₃ coatings through the dissolution-precipitation method at low temperature (80 °C). X-ray diffraction (XRD) analysis, FTIR and Raman spectroscopies, and scanning electron microscopy (SEM) were employed to evaluate the phase composition, surface functional groups, crystallinity, and morphology of the coatings. The results showed the formation of hexagonal HAP particles with a size of 20 nm at low temperature, exhibiting high homogeneity in particle size distribution. In the calcium hydroxyapatite, some of the Ca²⁺ ions were replaced by Cu²⁺ ions. Heating the mixture of Ca(NO₃)₂ and Cu(NO₃)₂ solutions at 550 °C in a CO₂ atmosphere led to the formation of copper hydroxide carbonate (malachite, Cu₂(OH)₂CO₃) along with CaCO₃. The reaction between the sol-gel precursor obtained and Na₂HPO₄ resulted in the formation of copper-substituted hydroxyapatite (Cu-HAP). Different synthesis methods were tested with Zn²⁺ ions, and on the surface of the coating, Zn(OH)(NO₃)(H₂O), Zn₃(OH)₄(NO₃)₂, and unreacted CaCO₃ were formed. Antibacterial properties of the coatings were tested using the inhibition zone method. No inhibition zones were observed for HAP. However, in the Cu and Zn containing coatings, inhibition zones were observed in the presence of a colony of B. subtilis bacteria. However, no inhibition zones were detected in the presence of E. coli bacteria. Full article

(This article belongs to the Special Issue Advances in Surface Engineering and Biocompatible Coatings for Biomedical Applications)

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20 pages, 26455 KB

Open AccessEditor’s ChoiceArticle

Comparison of Various Conversion Layers for Improved Friction Performance of Railway Wheel-End Bearings

by Esteban Broitman, Arnaud Ruellan, Ralph Meeuwenoord, Daan Nijboer and Victor Brizmer

Coatings 2023, 13(12), 1980; https://doi.org/10.3390/coatings13121980 - 21 Nov 2023

Cited by 7 | Viewed by 2488

Abstract

With a growing global railway market which needs to reduce its energy consumption and emissions, railway wheel-end bearing units are being optimized to further reduce power losses with no compromise on reliability. One of the different solutions being evaluated is the selection of [...] Read more.

With a growing global railway market which needs to reduce its energy consumption and emissions, railway wheel-end bearing units are being optimized to further reduce power losses with no compromise on reliability. One of the different solutions being evaluated is the selection of the optimum surface engineering. Inner and outer rings of railway bearing units are currently coated with a zinc-calcium phosphate conversion coating designed for anti-corrosion, anti-fretting, and mounting properties. In this study, different conversion layers, like zinc-calcium phosphate, manganese-phosphate and tribological black oxide, have been compared in terms of friction performance using a single-contact tribometer and a grease-lubricated bearing friction test rig. Results demonstrate that an optimum tribological black oxide conversion layer can reduce the bearing torque by up to 30% in both low and intermediate speeds relevant to intercity trains. Full article

(This article belongs to the Special Issue Surface Engineering, Coatings and Tribology)

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18 pages, 4423 KB

Open AccessEditor’s ChoiceArticle

Effect of Electrodeposited Gold Coatings on Micro-Gaps, Surface Profile and Bacterial Leakage of Cast UCLA Abutments Attached to External Hexagon Dental Implants

by Terry R. Walton

Coatings 2023, 13(12), 1976; https://doi.org/10.3390/coatings13121976 - 21 Nov 2023

Cited by 1 | Viewed by 1799

Abstract

Purpose: The objective of the study was to qualitatively assess the micro-gap dimensions, connecting fitting surface profile, and bacterial leakage of cast high-gold-alloy UCLA abutments, with or without electrodeposited gold coatings attached to external hexagon implants. Materials and methods: Sixteen plastic [...] Read more.

Purpose: The objective of the study was to qualitatively assess the micro-gap dimensions, connecting fitting surface profile, and bacterial leakage of cast high-gold-alloy UCLA abutments, with or without electrodeposited gold coatings attached to external hexagon implants. Materials and methods: Sixteen plastic UCLAs (PUCLAs) were cast with a high-gold-content alloy. Eight were electrolytically gold plated. Five machined cast-to-UCLA (GUCLA) control abutments were cast with the same alloy. All abutments were attached to external hexagon implants, giving 21 implant-abutment combinations (IACs). External perimeter micro-gaps measured with SEM under shadow eliminating silhouette illumination and 2000× magnification were averaged over three regions. The IACs were examined for E. coli leakage following an initial sterility test. Disassembled combinations were examined with SEM, and surface profiles were qualitatively assessed. Results: External micro-gap measurements did not reflect the variable connecting surface profiles, but average values < 5.0 μm were observed for all IACs measured under the shadow eliminating silhouette illumination for both cast and pre-machined external hexagon abutments with and without Au plating. E. coli transfer was observed in 3 of 5 PUCLA-plated and 2 of 5 PUCLA-non-plated IACs. No transfer occurred in the 3 GUCLA-non-plated or 2 GUCLA-plated control IACs. Abutment connecting surfaces, both Au-plated and not Au-plated, showed plastic deformation (smearing) in variable mosaic patterns across the micro-gap. Conclusions: Micro-gap dimensions < 5μm were obtained with both the high noble metal cast and pre-machined control external hexagon abutments with and without Au electrodeposited on the abutment connecting surface. Regions of intimate contact due to plastic deformation (smearing) of these surfaces were observed. A continuous smeared region around the circumference of the surfaces can provide an effective barrier to the egress of E. coli bacteria from the internal regions of the implant under static loading. The sample size was insufficient to determine if the gold coating resulted in a superior bacterial barrier. Full article

(This article belongs to the Special Issue Advances in Surface Engineering and Biocompatible Coatings for Biomedical Applications)

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24 pages, 3488 KB

Open AccessEditor’s ChoiceReview

Strategies to Enhance Biomedical Device Performance and Safety: A Comprehensive Review

by Julia Sánchez-Bodón, Maria Diaz-Galbarriatu, Leyre Pérez-Álvarez, Isabel Moreno-Benítez and José Luis Vilas-Vilela

Coatings 2023, 13(12), 1981; https://doi.org/10.3390/coatings13121981 - 21 Nov 2023

Cited by 14 | Viewed by 4795

Abstract

This paper reviews different approaches to obtain biomaterials with tailored functionalities and explains their significant characteristics that influence their bioactivity. The main goal of this discussion underscores the significance of surface properties in materials, with a particular emphasis on their role in facilitating [...] Read more.

This paper reviews different approaches to obtain biomaterials with tailored functionalities and explains their significant characteristics that influence their bioactivity. The main goal of this discussion underscores the significance of surface properties in materials, with a particular emphasis on their role in facilitating cell adhesion in order to obtain good biocompatibility and biointegration, while preventing adverse effects, such as bacterial contamination and inflammation processes. Consequently, it is essential to design strategies and interventions that avoid bacterial infections, reducing inflammation and enhancing compatibility systems. Within this review, we elucidate the most prevalent techniques employed for surface modification, notably emphasizing surface chemical composition and coatings. In the case of surface chemical composition, we delve into four commonly applied approaches: hydrolysis, aminolysis, oxidation, and plasma treatment. On the other hand, coatings can be categorized based on their material composition, encompassing ceramic-based and polymer-based coatings. Both types of coatings have demonstrated efficacy in preventing bacterial contamination, promoting cell adhesion and improving biological properties of the surface. Furthermore, the addition of biological agents such as drugs, proteins, peptides, metallic ions plays a pivotal role in manifesting the prevention of bacterial infection, inflammatory responses, and coagulation mechanism. Full article

(This article belongs to the Special Issue Advanced Coatings for Biomedical Applications)

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13 pages, 1358 KB

Open AccessEditor’s ChoiceArticle

Paper Coatings Based on Polyvinyl Alcohol and Cellulose Nanocrystals Using Various Coating Techniques and Determination of Their Barrier Properties

by Alicja Tarnowiecka-Kuca, Roos Peeters, Bram Bamps, Magdalena Stobińska, Paulina Kamola, Artur Wierzchowski, Artur Bartkowiak and Małgorzata Mizielińska

Coatings 2023, 13(11), 1975; https://doi.org/10.3390/coatings13111975 - 20 Nov 2023

Cited by 5 | Viewed by 4368

Abstract

The goal of this work was to improve the barrier properties of selected papers against water, grease and oil or gases (water vapor and oxygen) by covering them with biodegradable commercial coating carriers based on cellulose nanocrystals (CNCs) and polyvinyl alcohol (PVOH). The [...] Read more.

The goal of this work was to improve the barrier properties of selected papers against water, grease and oil or gases (water vapor and oxygen) by covering them with biodegradable commercial coating carriers based on cellulose nanocrystals (CNCs) and polyvinyl alcohol (PVOH). The aim was also to obtain cellulose recyclable packaging materials with improved barrier characteristics. The properties of paper coatings based on CNCs and PVOH were characterized. Various paper coating techniques (flexographic printing, rotogravure printing and blade printing) were evaluated with respect to the final properties of the surface-modified paper with different starting grammages (40 g/m², 70 g/m², 100 g/m²). Functional properties, such as the barrier against oxygen, water vapor, water and grease; mechanical properties; and seal characterization of coated paper were examined. The results of this study demonstrated that the covering of the paper may improve the water, grease and oil barrier and that the best results were obtained for Gerstar 70 g/m² coated with J12 coatings using the flexographic technique. Full article

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

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