Coatings

29 pages, 897 KB

Open AccessEditor’s ChoiceArticle

Identification of Potential Migrants in Food Contact Materials Labeled as Bio-Based and/or Biodegradable by GC-MS

by Emma López Sanvicente, Letricia Barbosa-Pereira, Raquel Sendón, Ana Rodríguez Bernaldo de Quirós and Antía Lestido-Cardama

Coatings 2025, 15(7), 751; https://doi.org/10.3390/coatings15070751 - 25 Jun 2025

Viewed by 2955

Abstract

Bio-based and/or biodegradable food contact materials are being developed as alternatives to conventional petroleum-based materials. Like other food contact materials, these are subject to regulatory requirements. The characterization of these biomaterials enables the identification of chemical substances that could potentially migrate from these [...] Read more.

Bio-based and/or biodegradable food contact materials are being developed as alternatives to conventional petroleum-based materials. Like other food contact materials, these are subject to regulatory requirements. The characterization of these biomaterials enables the identification of chemical substances that could potentially migrate from these materials into food and may pose a risk to consumer health. In this work, commercial samples of food contact materials labeled as bio-based and/or biodegradable were analyzed. To tentatively identify compounds, two analytical methods were optimized: purge and trap (P&T) for volatile compounds and methanolic extract injection for the determination of semi-volatile compounds, both using gas chromatography coupled with mass spectrometry (GC-MS). Compound toxicity was estimated using an in silico methodology, namely Cramer’s rules. More than 200 compounds of different natures were tentatively identified, but only 29 are included in Regulation (EU) 10/2011 on plastic materials intended to come into contact with food, and 38 of them were classified as high-toxicity compounds. Full article

(This article belongs to the Special Issue Bio-Based and Biodegradable Packaging Materials for Food Contact)

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20 pages, 14981 KB

Open AccessEditor’s ChoiceArticle

Multi-Scale Modelling of Residual Stress on Arbitrary Substrate Geometry in Atmospheric Plasma Spray Process

by Jose Martínez-García, Venancio Martínez-García and Andreas Killinger

Coatings 2025, 15(6), 723; https://doi.org/10.3390/coatings15060723 - 17 Jun 2025

Viewed by 954

Abstract

This work presents an exhaustive parametric study of the multi-scale residual stress analysis on arbitrary substrate geometry based on a one-way-coupled thermo-mechanical model in an Atmospheric Plasma Spray process. It was carried out by modifying key process parameters, such as substrate surface geometry, [...] Read more.

This work presents an exhaustive parametric study of the multi-scale residual stress analysis on arbitrary substrate geometry based on a one-way-coupled thermo-mechanical model in an Atmospheric Plasma Spray process. It was carried out by modifying key process parameters, such as substrate surface geometry, substrate pre-heating temperature, and coating thickness, in an Al₂O₃ coating process on an aluminium substrate. The relationship of these parameters to the generation of quenching stress, thermal stress and residual stress was analysed at three different sub-modelling scales, from the macroscopic dimension of the substrate to the microscopic dimension of the splats. The thermo-mechanical phenomena occurring during the deposition process at the microscopic level were discussed in the proposed cases. Understanding these phenomena helps to optimise the parameters of the coating process by identifying the underlying mechanisms responsible for the generation of residual stresses. The simulated residual stresses of the 200 μm Al₂O₃ outer coated aluminium cylinder were experimental validated using the incremental high-speed micro-hole drilling and milling method. Full article

(This article belongs to the Special Issue Advances in Surface Coatings for Wear and Corrosion Protection)

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18 pages, 3833 KB

Open AccessEditor’s ChoiceArticle

Protective ALD Thin Films for Morphologically Diverse Types of Limestone

by Gillian P. Boyce, Suveena Sreenilayam, Eleonora Balliana, Elisabetta Zendri and Raymond J. Phaneuf

Coatings 2025, 15(6), 698; https://doi.org/10.3390/coatings15060698 - 10 Jun 2025

Viewed by 790

Abstract

We report on the results of investigations of atomic layer deposited (ALD) amorphous alumina (Al₂O₃) coatings for the protection of limestone with a wide range of porosity against acid-based dissolution. The protective effects of the ALD coatings were investigated [...] Read more.

We report on the results of investigations of atomic layer deposited (ALD) amorphous alumina (Al₂O₃) coatings for the protection of limestone with a wide range of porosity against acid-based dissolution. The protective effects of the ALD coatings were investigated by aqueous acid immersion. The solution pH was tracked over time for a constant volume of acetic acid solution with an initial pH of 4 with the stone samples immersed. We find the protective effect of ALD alumina coatings is extremely promising, with 90 nm thick coatings slowing the initial and total rate of substrate mass loss significantly by up to two orders of magnitude. The eventual failure of the ALD coatings during immersion was also investigated. Pitted areas on the substrate were discovered and were found to have an area fraction that correlates to the changing pH of the acid solution during immersion. The variation of the protective action of the films with thickness is consistent with kinetics, which are limited by diffusion within the pits rather than through the films. Our findings point to the dominant role of defects in the coatings in their eventual failure. We also show that the appearance of the stone does not change significantly for the thickest and most protective ALD films, making the treatment promising for cultural heritage applications. Full article

(This article belongs to the Special Issue Advanced Coating Material for Heritage Preservation, 2nd Edition)

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21 pages, 4658 KB

Open AccessEditor’s ChoiceArticle

Potentiostatic Plasma Electrolytic Oxidation (PEO) of Aluminum Alloy AA6082: Effect of Electrical Input on Coating Microstructure and Corrosion Resistance

by Alberto Berardi, Matteo Gamba, Luca Paterlini, Federica Ceriani and Marco Ormellese

Coatings 2025, 15(6), 653; https://doi.org/10.3390/coatings15060653 - 29 May 2025

Cited by 1 | Viewed by 1356

Abstract

Aluminum alloy AA6082 (Al-Si-Mg) is a lightweight alloy that requires thick barrier coatings to be protected from localized corrosion. Plasma Electrolytic Oxidation (PEO) coating is a common anodic surface treatment used for growing protective oxides; the main process variables of PEO are the [...] Read more.

Aluminum alloy AA6082 (Al-Si-Mg) is a lightweight alloy that requires thick barrier coatings to be protected from localized corrosion. Plasma Electrolytic Oxidation (PEO) coating is a common anodic surface treatment used for growing protective oxides; the main process variables of PEO are the composition of the electrolytic solution and the electrical input. This work focuses on the optimization of the electrical input by comparing different coatings produced by potentiostatic PEO at the effective potential of 350 V, applied by different combinations of voltage ramps with various slopes and maintenance times at the fixed potential. All processes lasted five minutes. The innovative character of this research work is the evaluation of the combined effect of the anodizing voltage and its different trends with time on the coating structure and morphology. The corrosion resistance of coated AA6082 is assessed in contact with chlorides, reproducing seawater. The resulting anodic coatings were compared in terms of structure, composition (thickness, XRD, SEM-EDS) and corrosion resistance (potentiodynamic polarization and electrochemical impedance spectroscopy), finding that longer maintenance at high anodizing potentials promotes localized high-energy plasma discharges, producing larger pores and thicker, but less protective coatings. Results show that the coating thickness increases with the maintenance time (maximum thickness value~17.6 μm). Shorter maintenance periods and longer voltage ramps lead to a lower surface porosity and enhanced corrosion performances of the oxide. The thinnest and least porous coating exhibits the best corrosion behavior (CR~1.1 μm/year). Full article

(This article belongs to the Special Issue Tribomechanical and Corrosion Tests for Advanced Surface Characterization)

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19 pages, 15431 KB

Open AccessEditor’s ChoiceArticle

Effect of Fe₂O₃@SiO₂ Core–Shell Nanoparticle Doping Ratio on Color Appearance of Synthetic Opal Films Inspired by Natural Fire Opal

by Bowen Li and Andy Hsitien Shen

Coatings 2025, 15(6), 646; https://doi.org/10.3390/coatings15060646 - 27 May 2025

Cited by 1 | Viewed by 1252

Abstract

Synthetic opal-based photonic materials with tunable optical properties not only exhibit significant application potential but also provide valuable models in terms of understanding color formation mechanisms in natural gemstones. Inspired by natural fire opals containing small amounts of Fe₂O₃ nanoparticle [...] Read more.

Synthetic opal-based photonic materials with tunable optical properties not only exhibit significant application potential but also provide valuable models in terms of understanding color formation mechanisms in natural gemstones. Inspired by natural fire opals containing small amounts of Fe₂O₃ nanoparticle inclusions (0 wt%~0.23 wt%), we fabricated short-range ordered opal films doped with low concentrations (0 wt%~2.00 wt%) of Fe₂O₃@SiO₂ core–shell nanoparticles using a modified vertical deposition method. The Fe₂O₃@SiO₂ nanoparticles were synthesized via a sol–gel process to encapsulate the Fe₂O₃ core with a 10-nm-thick SiO₂ shell, preventing agglomeration and enhancing the chemical stability. Experimental results show that even small amounts of doping significantly affect the reflection peak intensity of the films, leading to notable color appearance changes. Combined with numerical simulations, we attribute this modulation to both light absorption and backward scattering effects introduced by the doped nanoparticles. Moreover, the numerical simulation results for Fe₂O₃ nanoparticles and Fe₂O₃@SiO₂ nanoparticles (with a 10 nm silica shell and similar particle size) show comparable optical properties, suggesting that such inclusions may contribute similarly to the color formation mechanisms in natural fire opals. This work demonstrates that low-concentration Fe₂O₃@SiO₂ NP doping provides an effective strategy to tune the color appearance of opal films, with implications for both structural color material development and gemological research. Full article

(This article belongs to the Special Issue Modification and Technology of Nanoparticles and Thin Films)

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17 pages, 2733 KB

Open AccessEditor’s ChoiceArticle

Study on the Mechanism and Control Technology of Biodeterioration at the Sanyangzhuang Earthen Site

by Xiang Chang, Yu Ye, Qingwen Ma, Haitao Yan, Zhining Li and Fang Guo

Coatings 2025, 15(5), 617; https://doi.org/10.3390/coatings15050617 - 21 May 2025

Viewed by 737

Abstract

Biodeterioration poses a significant challenge in the conservation of cultural heritage, particularly for earthen sites in humid environments, which are highly susceptible due to their inherent material properties. To address the diverse biological threats affecting such sites, we developed a novel broad-spectrum biocide, [...] Read more.

Biodeterioration poses a significant challenge in the conservation of cultural heritage, particularly for earthen sites in humid environments, which are highly susceptible due to their inherent material properties. To address the diverse biological threats affecting such sites, we developed a novel broad-spectrum biocide, FACA, formulated by combining phenylcarbamoylthiazoles and isothiaquinolones to achieve triple efficacy: antimicrobial, anti-algal, and anti-lichen effects. Laboratory assessments demonstrated FACA’s rapid efficacy in eliminating molds, algae, and lichens. A 12-month field application at the Sanyangzhuang earthen site (Neihuang, Henan) yielded excellent results, confirming long-term protection against biological colonization without recurrence. Crucially, the treatment exhibited no adverse effects on the earthen sites, enabling sustainable coexistence between the heritage site and its surrounding ecosystem. These findings support the applicability of FACA for surface treatment across various humid earthen archeological sites. Full article

(This article belongs to the Section Environmental Aspects in Colloid and Interface Science)

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17 pages, 1888 KB

Open AccessEditor’s ChoiceArticle

Effects of Coating Thickness and Aggregate Size on the Damping Properties of Concrete: A Numerical Simulation Approach

by Yisihak Gebre Tarekegn, Tom Lahmer, Abrham Gebre Tarekegn and Esayas Gebreyouhannes Ftwi

Coatings 2025, 15(5), 610; https://doi.org/10.3390/coatings15050610 - 21 May 2025

Cited by 2 | Viewed by 782

Abstract

Concrete properties are investigated using intensive physical testing processes that require large amounts of labor and materials that are costly and time-consuming. Properly validated computer models can replace most of the existing physical testing procedures with computer simulations that are relatively quick and [...] Read more.

Concrete properties are investigated using intensive physical testing processes that require large amounts of labor and materials that are costly and time-consuming. Properly validated computer models can replace most of the existing physical testing procedures with computer simulations that are relatively quick and inexpensive. Therefore, in this study, the effects of coating thickness and aggregate size on the damping properties of concrete were investigated using numerical simulation with Abaqus/CAE 6.14-1 software. Two different groups of aggregates were used in the simulation, with maximum aggregate sizes of 25 mm and 32 mm. The coating thickness ranged from 0.4 mm to 5.0 mm, using epoxy, silicone, and rubber coatings. The results showed that coatings with smaller aggregate size led to an increase in the damping ratio compared to those with larger aggregate size. Moreover, replacing 20% of coarse aggregates with rubber-coated aggregates results in a damping ratio of 5.75% to 6.21%, reflecting an increase of 22.8% to 32.7%. This variation occurs with coating thicknesses ranging from 0.4 mm to 5.0 mm, with the optimal thickness of 5.0 mm leading to the maximum increase (32.7%) in the damping ratio of concrete. Full article

(This article belongs to the Section Environmental Aspects in Colloid and Interface Science)

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16 pages, 4581 KB

Open AccessEditor’s ChoiceArticle

PLA-Based Green Antimicrobial and Flame-Retardant Biocomposites Reinforced with Sida hermaphrodita Fibers

by Sandra Bischof, Tea Bušac, Tomislav Ivanković, Sabine Rolland du Roscoat, Bratislav Lukic and Zorana Kovačević

Coatings 2025, 15(5), 595; https://doi.org/10.3390/coatings15050595 - 17 May 2025

Cited by 2 | Viewed by 1127

Abstract

Enhanced demand for the development of sustainable materials has generated significant research interest in products containing biomass-derived fibers, such as the fibers extracted from the energy crop Sida hermaphrodita (SH). Green chemicals and green methods, such as microwave treatment, have been used for [...] Read more.

Enhanced demand for the development of sustainable materials has generated significant research interest in products containing biomass-derived fibers, such as the fibers extracted from the energy crop Sida hermaphrodita (SH). Green chemicals and green methods, such as microwave treatment, have been used for the isolation of fibers from biomass waste. In this study, long extracted fibers were used as a reinforcement of the PLA matrix to give them high strength, which is required for high-performance biocomposites. To enable composite usage in automotive industry, several additives were applied to enhance their mechanical, thermal, and antimicrobial properties. Therefore, vegetable drying oil, montmorillonite nanoclay (MMT), and milled cork were used to improve their mechanical and thermal properties. Zinc oxide (ZnO) was applied to enhance the biocomposite’s antimicrobial properties, which were confirmed through significant bacterial reduction across all tested biocomposite variants, particularly in samples functionalized with ZnO, cork, and montmorillonite. Additionally, X-ray microtomography provided detailed insight into fiber dispersion and internal structural heterogeneity, which is crucial for evaluating mechanical performance and flame-retardant behavior. All characterization methods, including mechanical ones, lead to the conclusion that green and sustainable biocomposites based on PLA and Sida hermaphrodita fibers treated with antimicrobial (AM) and flame-retardant (FR) agents can be successfully applied for a wide variety of antimicrobial and flame-retardant products. Full article

(This article belongs to the Special Issue Engineered Coatings for a Sustainable Future)

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35 pages, 9564 KB

Open AccessEditor’s ChoiceReview

Research Progress of the Coatings Fabricated onto Titanium and/or Titanium Alloy Surfaces in Biomaterials for Medical Applications for Anticorrosive Applications

by Qin Rao, Jinshuang Zhang, Yaqing Chen, Yujin Yang, Xu Chen, Donghao Liu, Ruilu Zhu, Ang Li, Yanping Lv and Shunli Zheng

Coatings 2025, 15(5), 599; https://doi.org/10.3390/coatings15050599 - 17 May 2025

Cited by 2 | Viewed by 1538

Abstract

Titanium (Ti) and its alloys have attracted more interest, as they are widely employed as biomaterials due to their great biocompatibility, excellent strength ratio, and lightweight. However, corrosion occurs slowly due to an electrochemical reaction once the Ti material has been placed in [...] Read more.

Titanium (Ti) and its alloys have attracted more interest, as they are widely employed as biomaterials due to their great biocompatibility, excellent strength ratio, and lightweight. However, corrosion occurs slowly due to an electrochemical reaction once the Ti material has been placed in the human body, contributing to infection and failure of implants in medical applications. Thus, the corrosion phenomenon has caused great concern in the biomedical field. It is desirable to make the surface modification to provide better corrosion resistance. The fabrication techniques of the coatings fabricated onto Ti and/or Ti alloy surfaces have been reported, including sol–gel, annealing, plasma spraying, plasma immersion ion implantation, physical vapor deposition, chemical vapor deposition, anodization, and micro-arc oxidation. This review first describes the corrosion types, including localized corrosion (both pitting and crevice corrosion), galvanic corrosion, selective leaching, stress corrosion cracking (SCC), corrosion fatigue (CF), and fretting corrosion. In the second part, the effects of corrosion on the human body were discussed, and the primary cause for clinical failure and allergies has been identified as the excessive release of poisonous and dangerous metal ions (Co, Ni, and Ti) from corroded implants into bodily fluids. The inclusion and exclusion criteria during the selection of literature are described in the third section. In the last section, we emphasized the current research progress of Ti alloy (particularly Ti6Al4V alloy) coatings in biomaterials for medical applications involving dental, orthopedic, and cardiovascular implants for anticorrosive applications. However, there are also several problems to explore and address in future studies, such as the release of excessive metal ions, etc. This review will draw attention to both researchers and clinicians, which could help to increase the coatings fabricated onto Ti and/or Ti alloy surfaces for anticorrosive applications in biomaterials for medical applications. Full article

(This article belongs to the Special Issue Innovative Coatings for Corrosion Protection of Alloy Surfaces)

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29 pages, 6857 KB

Open AccessEditor’s ChoiceArticle

Physicochemical and Preliminary Biological Properties of Thin Films Based on Fluoride-Doped Hydroxyapatite in a Dextran Matrix for Biomedical Applications

by Liliana Ghegoiu, Daniela Predoi, Simona Liliana Iconaru, Carmen Steluta Ciobanu, Krzysztof Rokosz, Steinar Raaen, Monica Luminita Badea and Mihai Valentin Predoi

Coatings 2025, 15(5), 565; https://doi.org/10.3390/coatings15050565 - 9 May 2025

Cited by 3 | Viewed by 1068

Abstract

A spin-coating technique was used to produce new thin films of fluoride-doped hydroxyapatite (HApF) and fluoride-doped hydroxyapatite in a dextran matrix (HApF-Dx) with the potential to be used as nanocoatings for various biomedical implants. The stability of the suspensions used in obtaining the [...] Read more.

A spin-coating technique was used to produce new thin films of fluoride-doped hydroxyapatite (HApF) and fluoride-doped hydroxyapatite in a dextran matrix (HApF-Dx) with the potential to be used as nanocoatings for various biomedical implants. The stability of the suspensions used in obtaining the thin films was confirmed by ultrasonic measurements with double-distilled water as a reference. The HApF and HApF-Dx thin films obtained by spin-coating showed diffraction patterns corresponding to hexagonal hydroxyapatite. The X-ray photoelectron spectroscopy studies confirmed the partial substitution of hydroxyl groups (-OH) by fluoride ions. The FTIR studies were conducted in order to highlight the presence of the functional group specific for the HAp in the samples and the influence of the dextran addition on the vibrational characteristics. The surface morphologies of the HApF and HApF-Dx thin films were explored using scanning electron microscopy (SEM), atomic force microscopy (AFM), and metallographic microscopy (MM). The surfaces of the HApF and HApF-Dx thin films were found to be smooth, homogenous, and nanostructured. The biocompatibility assays on HGF-1 cells confirmed that both coatings exhibited good cell viability for all the tested time intervals (24 and 48 h). The findings highlighted the potential of HApF and HApF-Dx coatings for biomedical applications. Additional information about the HGF-1 adherence and development on the surface of the HApF and HApF-Dx coatings was obtained using metallographic microscopy, scanning electron microscopy, and atomic force microscopy techniques. This research demonstrates that the spin-coating method can be successfully used to fabricate HApF and HApF-Dx nanocoatings for potential biomedical applications. Full article

(This article belongs to the Special Issue Films and Coatings with Biomedical Applications)

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12 pages, 3903 KB

Open AccessEditor’s ChoiceArticle

Microstructure and Electrical Properties of Scandium-Doped Aluminum Nitride Thin Film

by Jiaqiang Chen, Junxi Zhang, Zhiyang Fan and Ping Yu

Coatings 2025, 15(5), 549; https://doi.org/10.3390/coatings15050549 - 4 May 2025

Cited by 4 | Viewed by 2130

Abstract

Highly (0002)-oriented Al_1−xSc_xN thin films with different Sc doping concentrations (x = 0, 0.2, 0.25, 0.3, and 0.43) were prepared via a magnetron sputtering system. The effects of Sc doping on the crystal structure and electrical property [...] Read more.

Highly (0002)-oriented Al_1−xSc_xN thin films with different Sc doping concentrations (x = 0, 0.2, 0.25, 0.3, and 0.43) were prepared via a magnetron sputtering system. The effects of Sc doping on the crystal structure and electrical property of the as-prepared thin films were investigated experimentally. The results of synchrotron radiation grazing-incidence wide-angle X-ray scattering (GIWAXS) and X-ray diffraction (XRD) demonstrated that the Sc³⁺ substitution for Al³⁺ induced asymmetric lattice distortion: the a-axis exhibited monotonic expansion (reaching 3.46 Å at x = 0.43) due to the larger atomic radius of Sc (~0.87 Å), while the c-axis attained a maximum value of 5.14 Å at x = 0.2 and subsequently contracted as the bond angle reduction became dominant. The dielectric constant increased to 34.67 (225% enhancement) at x = 0.43, attributed to the enhanced polarization of Sc-N bonds and interfacial charge accumulation effects. Simultaneously, the dielectric loss increased from 0.15% (x = 0) to 6.7% (x = 0.43). Leakage current studies revealed that high Sc doping (x = 0.43) elevated the leakage current density to 10⁻⁶ A/cm² under an electric field of 0.2 MV/cm, accompanied by a transition from Ohmic conduction to space-charge-limited current (SCLC) at a low electric field strength (<0.072 MV/cm). Full article

(This article belongs to the Section Thin Films)

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24 pages, 28892 KB

Open AccessEditor’s ChoiceArticle

Mechanical and Tribological Behavior of TiAlSiN/AlSiN Coatings Depending on the High-Temperature Treatment

by Stefan Kolchev, Lilyana Kolaklieva, Daniela Kovacheva, Genoveva Atanasova, Tetiana Cholakova, Vasiliy Chitanov, Ekaterina Zlatareva, Roumen Kakanakov and Chavdar Pashinski

Coatings 2025, 15(5), 542; https://doi.org/10.3390/coatings15050542 - 30 Apr 2025

Cited by 1 | Viewed by 876

Abstract

TiAlSiN/AlSiN coatings, with 3 and 30 periods, were successfully deposited by cathodic-arc evaporation technology. The composition, structure, mechanical, and tribological properties were studied at thermal treatment from 700 °C to 900 °C. The SEM observation and EDS analysis verified the dense structure and [...] Read more.

TiAlSiN/AlSiN coatings, with 3 and 30 periods, were successfully deposited by cathodic-arc evaporation technology. The composition, structure, mechanical, and tribological properties were studied at thermal treatment from 700 °C to 900 °C. The SEM observation and EDS analysis verified the dense structure and stable element composition in the coating depth at increased temperatures. A limited surface oxidation was identified at 800 °C, which increased moderately at a higher temperature of 900 °C. The coating period displays a nanocomposite structure of TiAl(Si)N and AlN nanograins incorporated in an amorphous Si₃N₄ matrix obtained by XRD and XPS analyses. The coatings exhibit high hardness of 41.1 GPa and 36.4 GPa for the 3- and 30-period coatings, respectively. The coatings with higher modulation periods demonstrate an excellent high temperature hardness and resistance to elastic and plastic deformations up to 900 °C. The hardness of the coatings with a smaller modulation period reduces to 29.7 GPa at the same temperature, causing a decrease in the H/E and H³/E^*2 ratios. The tribological tests found that the high-temperature wear resistance depends strongly on the coating composition and architecture. An oxidation wear mechanism dominates the coatings with a large modulation period, and the wear rate decreases with a temperature increase. Abrasive wear is predominant in coatings with a lower modulation period, leading to an increasing wear rate. Wear rate values of 7.27 × 10⁻⁶ mm³/N·m and 8.53 × 10⁻⁶ mm³/N·m were determined after annealing at 900 °C for the 3- and 30-period coatings, respectively. Full article

(This article belongs to the Special Issue Tribological and Mechanical Properties of Coatings)

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12 pages, 3562 KB

Open AccessEditor’s ChoiceArticle

Stabilization of Epitaxial NiO(001) Ultra-Thin Films on Body-Centered-Cubic Ni(001)-p(1x1)O

by Andrea Picone, Franco Ciccacci, Lamberto Duò and Alberto Brambilla

Coatings 2025, 15(5), 507; https://doi.org/10.3390/coatings15050507 - 23 Apr 2025

Cited by 1 | Viewed by 819

Abstract

Ultrathin NiO films, ranging from 1 to 16 monolayers (ML) in thickness, have been stabilized via reactive molecular beam epitaxy on the (001) surface of a metastable body-centered cubic (BCC) Ni film. Low-energy electron diffraction (LEED) confirms that NiO grows as a crystalline [...] Read more.

Ultrathin NiO films, ranging from 1 to 16 monolayers (ML) in thickness, have been stabilized via reactive molecular beam epitaxy on the (001) surface of a metastable body-centered cubic (BCC) Ni film. Low-energy electron diffraction (LEED) confirms that NiO grows as a crystalline film, exposing the (001) surface. Auger electron spectroscopy (AES) reveals a slight oxygen excess compared to a perfectly stoichiometric NiO film. Scanning tunneling microscopy (STM) shows that at low coverages the film exhibits atomically flat terraces, while at higher coverage a “wedding cake” morphology emerges. Scanning tunneling spectroscopy (STS) reveals a thickness-dependent evolution of the electronic band gap, which increases from 0.8 eV at 3 ML to 3.5 eV at 16 ML. The center of the band gap is approximately 0.2 eV above the Fermi level, indicating that NiO is p-doped. Full article

(This article belongs to the Special Issue Accelerated Development of Nanomaterials, Coatings, and Thin Films for Optical and Electronic Applications)

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30 pages, 10226 KB

Open AccessEditor’s ChoiceArticle

Environmentally Friendly Solutions as Potential Alternatives to Chromium-Based Anodization and Chromate Sealing for Aeronautic Applications

by Norica Godja and Florentina-Daniela Munteanu

Coatings 2025, 15(4), 439; https://doi.org/10.3390/coatings15040439 - 8 Apr 2025

Cited by 3 | Viewed by 1837

Abstract

The adoption of chrome-free anodizing and sealing systems for aluminum alloys, particularly AA2024, is gaining prominence due to environmental and health concerns associated with traditional Cr(VI)-based processes. This study evaluates the environmental and economic impacts of sulfuric acid anodizing (SAA) combined with sealing [...] Read more.

The adoption of chrome-free anodizing and sealing systems for aluminum alloys, particularly AA2024, is gaining prominence due to environmental and health concerns associated with traditional Cr(VI)-based processes. This study evaluates the environmental and economic impacts of sulfuric acid anodizing (SAA) combined with sealing based on fluorozirconate, molybdate, and cerate. Comparative analyses were conducted against conventional Cr(VI) systems and SAA with Cr(III) sealing, focusing on corrosion resistance, energy consumption, washing steps and material flows. The entire anodizing process was examined, including pretreatment, anodization, and sealing. Electrochemical analyses and surface characterization through SEM/EDS, FIB, and XPS were conducted. The results demonstrate that the chromium-free system offers competitive corrosion resistance while significantly reducing environmental and economic costs. Furthermore, fluorozirconate, molybdate, and cerate-based post-treatments broaden its application spectrum in corrosion science and warrant further exploration. However, adopting new sealing technologies in aerospace requires extensive certification involving corrosion resistance, durability assessments, and stringent environmental simulations. Compliance with regulatory standards set by the FAA (Federal Aviation Administration) and EASA (European Union Aviation Safety Agency) necessitates thorough documentation, third-party validation, and testing to ensure safety and performance before industrial implementation. These challenges underscore the complexity of transitioning to more sustainable anodizing and sealing technologies in the aerospace industry. Full article

(This article belongs to the Special Issue Corrosion Protection of Metals and Alloys in Extreme Environments)

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13 pages, 14903 KB

Open AccessEditor’s ChoiceArticle

Al₂O₃/ZnO Multilayer Coatings for Improvement in Functional Properties of Surgical Scalpel Blades

by Magdalena Monika Szindler, Marek Szindler, Jakub Bicz and Krzysztof Matus

Coatings 2025, 15(4), 436; https://doi.org/10.3390/coatings15040436 - 7 Apr 2025

Cited by 4 | Viewed by 1119

Abstract

This work aimed to investigate the structure and corrosion resistance of Al₂O₃/ZnO multilayer coatings deposited by ALD on the standard surgical scalpel blades made of carbon steel. The surface topography of the coatings was examined using a scanning electron [...] Read more.

This work aimed to investigate the structure and corrosion resistance of Al₂O₃/ZnO multilayer coatings deposited by ALD on the standard surgical scalpel blades made of carbon steel. The surface topography of the coatings was examined using a scanning electron microscope (SEM), revealing the significant effect of the number of deposited Al₂O₃/ZnO bilayers on the morphology of the multilayer coatings. The XRD method was used for the phase analysis, allowing to confirm the presence of ZnO and ZnAl₂O₄ phases. The presence of the ZnAl₂O₄ structure was also confirmed using a Raman spectrometer. A qualitative analysis of the chemical composition of the obtained coatings was performed using the energy dispersive spectrometry (EDX) method. In order to determine the corrosion resistance, potentiodynamic tests were performed using Ringer’s solution at a temperature of 37 °C. The beneficial effect of increasing the number of deposited Al₂O₃/ZnO bilayers on the corrosion resistance was confirmed, with the lowest corrosion current density value of 2.05 μA/cm² and the highest polarization resistance of 12.15 kΩ obtained in the case of the N72 coating. Full article

(This article belongs to the Special Issue Advances in Corrosion Behaviors and Protection of Coatings)

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14 pages, 3801 KB

Open AccessEditor’s ChoiceArticle

Synthesis and Characterization of Silane-Coupled Sodium Silicate Composite Coatings for Enhanced Anticorrosive Performance

by Minghui Liu, Zhiwen Tan, Shengda Xu, Yuantao Zhao, Haoran Wang, Shitao Zhang, Rong Ma, Tao Jiang, Zhen Ma, Ning Zhong and Wenge Li

Coatings 2025, 15(4), 428; https://doi.org/10.3390/coatings15040428 - 4 Apr 2025

Cited by 4 | Viewed by 1628

Abstract

Ships and offshore equipment operating in marine environments often face issues such as seawater corrosion and biofouling, leading to significant economic losses. To address the corrosion problems of ships and offshore equipment, heavy-duty anticorrosive coatings are widely used for corrosion protection in marine [...] Read more.

Ships and offshore equipment operating in marine environments often face issues such as seawater corrosion and biofouling, leading to significant economic losses. To address the corrosion problems of ships and offshore equipment, heavy-duty anticorrosive coatings are widely used for corrosion protection in marine environments due to their long-term effectiveness, cost-efficiency, and excellent applicability. In this study, silane coupling agent (KH-560) was employed to modify sodium silicate, and the modified sodium silicate was then incorporated as a reinforcing phase into polyurethane to ultimately prepare a modified sodium silicate/polyurethane coating. The feasibility of the modified sodium silicate/polyurethane coating was investigated by characterizing its conventional physicochemical properties, weather resistance, acid and alkali resistance, and salt spray corrosion resistance. Experimental results indicate that the silane coupling agent acts as a bridge between the organic and inorganic interfaces through the hydrolysis and condensation reactions of its bifunctional groups, forming an interfacial layer connected by hydrogen bonds and covalent bonds, thereby improving the compatibility between the organic resin and inorganic sodium silicate. Comprehensive performance analysis revealed that when the content of modified sodium silicate was 60 wt%, the coating hardness reached 4H. Additionally, electrochemical tests demonstrated that the coating exhibited higher impedance (9.62 × 10⁴ Ω/cm²) and lower corrosion current density (5.82 × 10⁻⁷ A/cm²). This study provides a theoretical and experimental basis for the development of high-performance anticorrosive coatings for marine applications. Full article

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

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11 pages, 2921 KB

Open AccessEditor’s ChoiceArticle

Optical Coating Deposition on Submicron-Patterned Surfaces

by Lina Grineviciute, Simas Melnikas, Julianija Nikitina, Mantas Drazdys, Algirdas Selskis and Darija Astrauskytė

Coatings 2025, 15(4), 372; https://doi.org/10.3390/coatings15040372 - 22 Mar 2025

Cited by 3 | Viewed by 1414

Abstract

Periodically modulated optical coatings, fabricated by depositing conformal films on modulated substrates, offer unique capabilities for spectral and spatial filtering of light. However, conventional deposition methods often do not achieve required replication and conformality on submicron-size structured surfaces. In this paper, we compare [...] Read more.

Periodically modulated optical coatings, fabricated by depositing conformal films on modulated substrates, offer unique capabilities for spectral and spatial filtering of light. However, conventional deposition methods often do not achieve required replication and conformality on submicron-size structured surfaces. In this paper, we compare various thin film deposition techniques, including electron beam evaporation, atomic layer deposition, and ion beam sputtering, to evaluate their ability to control multilayer coating growth on periodically modulated substrates. Our study demonstrates that both single-layer and multilayer coatings produced by ion beam sputtering effectively replicate the initial geometry of structured surfaces, thereby enhancing optical performance. Full article

(This article belongs to the Special Issue Optical Coatings: From Materials to Applications)

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29 pages, 3266 KB

Open AccessEditor’s ChoiceReview

Pitfalls and Challenges in Specific Absorption Rate Evaluation for Functionalized and Coated Magnetic Nanoparticles Used in Magnetic Fluid Hyperthermia

by Nicusor Iacob

Coatings 2025, 15(3), 345; https://doi.org/10.3390/coatings15030345 - 17 Mar 2025

Cited by 2 | Viewed by 2216

Abstract

In recent decades, magnetic hyperthermia (MH) has gained considerable scientific interest in cancer treatment due to its ability to heat tumor tissues deeply localized inside the body. Functionalizing magnetic nanoparticles (MNPs) with vector molecules via specific organic molecules that coat the particle surface [...] Read more.

In recent decades, magnetic hyperthermia (MH) has gained considerable scientific interest in cancer treatment due to its ability to heat tumor tissues deeply localized inside the body. Functionalizing magnetic nanoparticles (MNPs) with vector molecules via specific organic molecules that coat the particle surface has enabled targeting particular tissues, thereby increasing the specificity of MH. MH relies on applying radiofrequency (RF) magnetic fields to a magnetic nanoparticle distribution injected in a tumor tissue. The RF field energy is converted into thermal energy through specific relaxation mechanisms and magnetic hysteresis-driven processes. This increases the tumor tissue temperature over the physiological threshold, triggering a series of cellular apoptosis processes. Additionally, the mechanical effects of low-frequency AC fields on anisotropic MNPs have been shown to be highly effective in disrupting the functional cellular components. From the macroscopic perspective, a crucial parameter measuring the efficiency of magnetic nanoparticle systems in MH is the specific absorption rate (SAR). This parameter is experimentally evaluated by different calorimetric and magnetic techniques and methodologies, which have specific drawbacks and may induce significant errors. From a microscopic perspective, MH relies on localized thermal and kinetic effects in the nanoparticle proximity environment. Studying MH at the cellular level has become a focused research topic in the last decade. In the context of these two perspectives, inevitable questions arise: could the thermal and kinetic effects exhibited at the cellular scale be linked by the macroscopic SAR parameter, or should we find new formulas for quantifying them? The present work offers a general perspective of MH, highlighting the experimental pitfalls encountered in SAR evaluation and motivating the necessity of standardizing the devices and protocols involved. It also discusses the challenges that arise in MH performance evaluation at the cellular level. Full article

(This article belongs to the Special Issue Advances of Nanoparticles and Thin Films)

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15 pages, 14089 KB

Open AccessEditor’s ChoiceArticle

The Effect of Warm Shot Peening on Microstructure Evolution and Residual Stress in Gradient Nanostructured Mg-8Gd-3Y-0.4Zr Alloys

by Huabing Liu, Xiang Zhang, Xiaoxiao Wei, Jin Gan and Chuanhai Jiang

Coatings 2025, 15(3), 316; https://doi.org/10.3390/coatings15030316 - 9 Mar 2025

Cited by 4 | Viewed by 1164

Abstract

This work systematically investigated the effects of warm shot peening (WSP) on the microstructure evolution, residual stress, and microhardness of the Mg-8Gd-3Y-0.4Zr (GW83) alloy by X-ray diffraction line profile analysis, transmission electron microscopy, and X-ray stress analyzer and hardness tester. The results indicated [...] Read more.

This work systematically investigated the effects of warm shot peening (WSP) on the microstructure evolution, residual stress, and microhardness of the Mg-8Gd-3Y-0.4Zr (GW83) alloy by X-ray diffraction line profile analysis, transmission electron microscopy, and X-ray stress analyzer and hardness tester. The results indicated that severe plastic deformation induced by WSP resulted in a gradient nanostructure in the GW83 alloy, accompanied by significant compressive residual stress. In contrast to conventional SP, WSP led to working softening due to the dynamic recrystallization behavior. The formation of nanograins in the GW83 alloy during WSP occurs in three steps: (i) at an early stage, the introduction of a high density of dislocations and a few deformation twins subdivide bulk grains into substructures; (ii) through the processes of dislocation gliding, accumulation, and rearrangement, these substructures undergo further refinement, gradually evolving into ultrafine grains; and (iii) the inhomogeneous ultrafine grains develop into nanograins through dislocation-assisted lattice rotation and dynamic recrystallization. Full article

(This article belongs to the Special Issue Advancement in Heat Treatment and Surface Modification for Metals)

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21 pages, 6643 KB

Open AccessEditor’s ChoiceArticle

Impact of Irradiation on Corrosion Performance of Hybrid Organic/Inorganic Coatings on Austenitic Stainless Steel

by Natalie Click, Andrew Knight, Brendan Nation, Makeila Maguire, Samay Verma, Gavin DeBrun, Tyler McCready, Adam Goff, Audrey Rotert, Don Hanson and Rebecca Filardo Schaller

Coatings 2025, 15(3), 312; https://doi.org/10.3390/coatings15030312 - 7 Mar 2025

Viewed by 1210

Abstract

The effects of gamma radiation on the performance of two corrosion-resistant coatings applied to stainless-steel 304L (SS304L) surfaces are presented. Specifically, the ability of the coatings to mitigate corrosion of SS304L surfaces as a function of the dose received (0–1300 Mrad) and dose [...] Read more.

The effects of gamma radiation on the performance of two corrosion-resistant coatings applied to stainless-steel 304L (SS304L) surfaces are presented. Specifically, the ability of the coatings to mitigate corrosion of SS304L surfaces as a function of the dose received (0–1300 Mrad) and dose rate (176 compared to 1054 rad/s) is evaluated using electrochemical methods, spectroscopy, and microscopy. Coating A, an organic/inorganic hybrid coating consisting of a two-part silica ceramic component and a polymer linker was evaluated in comparison to Coating B, which utilized Coating A as a topcoat for a commercial, off-the-shelf, Zn-rich primer. Post irradiation, Coating A demonstrated some corrosion protection following exposure to low levels of gamma radiation, but coating degradation occurred with an increased exposure dose and resulted in isolated regions of corrosion initiation. For Coating B, greater corrosion resistance was observed compared to Coating A due to the sacrificial nature of the Zn at elevated doses of gamma radiation. No effect of the dose rate (for the single dose examined) was observed for either coating. It is proposed for Coating B that as the polymer coating thermally degrades above 250 °C (bond scission of the polymer occurs), the remaining Zinc layer adhered to the SS304L post-irradiation enables enhanced corrosion resistance as compared to Coating A, which displays solely polymer degradation. The results presented herein establish an understanding of coating behavior with radiation exposure, specifically the relationship between corrosion coating performance and radiation dose, and can inform ageing and lifetime management for various applications. Full article

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

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26 pages, 3340 KB

Open AccessEditor’s ChoiceArticle

Antimicrobial Efficacy of Nanochitosan and Chitosan Edible Coatings: Application for Enhancing the Safety of Fresh-Cut Nectarines

by Virginia Prieto-Santiago, Marcela Miranda, Ingrid Aguiló-Aguayo, Neus Teixidó, Jordi Ortiz-Solà and Maribel Abadias

Coatings 2025, 15(3), 296; https://doi.org/10.3390/coatings15030296 - 3 Mar 2025

Cited by 3 | Viewed by 2926

Abstract

The growing demand for fresh foods, as well as the rise in ready-to-eat foods, is leading the food industry to study edible coatings to maintain the quality of fresh-cut fruit. The objective of this work was, first, to determine the antimicrobial activity of [...] Read more.

The growing demand for fresh foods, as well as the rise in ready-to-eat foods, is leading the food industry to study edible coatings to maintain the quality of fresh-cut fruit. The objective of this work was, first, to determine the antimicrobial activity of a commercial anti-browning solution (A), chitosan (CH), and nanochitosan (NCH) both in vitro and in vivo and, secondly, to assess the effects of those coatings on the quality of fresh-cut nectarines. Antimicrobial activity was studied against Listeria monocytogenes and Saccharomyces cerevisiae, which were used as models of a foodborne pathogen and a spoilage microorganism, respectively. After evaluating their effect against both microorganisms, including in nectarines (Prunus persica L. cv Nectagala), the fruit was treated with commercial anti-browning alone (A), anti-browning with chitosan (A + CH), and anti-browning with nanochitosan (A + NCH). The slices were then sealed in polyethylene plastic trays and stored at 5 °C for 6 days. pH, titratable acidity, soluble solids content, firmness, color, visual acceptance, and microbiological evolution were assessed. Total color difference (TCD) results demonstrated higher value in the fresh-cut fruit without coating. The chitosan coating controlled microbial growth during cold storage without causing significant alterations to the fruit’s quality, while it had the highest overall visual acceptance of the final product. Chitosan demonstrated clear advantages as an edible biocoating for fresh-cut nectarines, whereas nanochitosan did not perform as effectively as expected, indicating the need for further optimization to realize its potential benefits. The combination of chitosan and anti-browning agents presents a sustainable method for enhancing the quality and safety of fresh-cut nectarines, which may contribute to the extension of their shelf life Full article

(This article belongs to the Special Issue Chitosan and Other Edible Coatings with Antimicrobial Activity: Synthesis, Properties and Horticultural Applications II)

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14 pages, 10551 KB

Open AccessEditor’s ChoiceArticle

Micro- and Nanofibrillated Cellulose Coatings as Barriers Against Water and Oil in Food Packaging Paper: A Sustainable Alternative to Plastic Coatings

by Marcin Dubowik, Kamila Przybysz, Jacek Dańczak, Aneta Lipkiewicz, Marta Gajadhur, Beata Górska, Ewelina Pawłowska, Robert Drozd and Piotr Przybysz

Coatings 2025, 15(3), 270; https://doi.org/10.3390/coatings15030270 - 24 Feb 2025

Cited by 2 | Viewed by 3216

Abstract

This research investigates the effectiveness of micro- and nanofibrillated cellulose (M-NFC) coatings compared to traditional synthetic coatings in enhancing the barrier properties of paper. Papers were coated at various grammages (1.2, 1.8, and 2.9 g/m²) and tested for properties such as [...] Read more.

This research investigates the effectiveness of micro- and nanofibrillated cellulose (M-NFC) coatings compared to traditional synthetic coatings in enhancing the barrier properties of paper. Papers were coated at various grammages (1.2, 1.8, and 2.9 g/m²) and tested for properties such as hydrophobicity, lyophobicity, and surface smoothness. Paper coated with 2.9 g/m² M-NFC showed water absorbency of 10.5 g/m² and castor oil absorbency of 9.6 g/m², which were lower than for commercially available WBB-coated paper (respectively, 12.2 and 14.8 g/m²). The coatings were evaluated through microscopic analysis and physical testing methods including Cobb and Cobb–Unger absorbency tests and wettability measurements. The results indicate that M-NFC coatings provide a sustainable alternative with competitive barrier properties suitable for short-term use products, showcasing potential reductions in synthetic material usage, especially in food packaging. Full article

(This article belongs to the Special Issue Advanced Coatings and Films for Food Packing and Storage, 2nd Edition)

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27 pages, 12594 KB

Open AccessEditor’s ChoiceArticle

Chrome Doped Hydroxyapatite Enriched with Amoxicillin Layers for Biomedical Applications

by Carmen Steluta Ciobanu, Daniela Predoi, Simona Liliana Iconaru, Krzysztof Rokosz, Steinar Raaen, Catalin Constantin Negrila, Liliana Ghegoiu, Coralia Bleotu and Mihai Valentin Predoi

Coatings 2025, 15(2), 233; https://doi.org/10.3390/coatings15020233 - 15 Feb 2025

Cited by 6 | Viewed by 1227

Abstract

In the last decade, it has been observed that the field of biomaterials has gained the attention of the researchers. This study presents the physicochemical and biological properties of coatings based on chromium-doped hydroxyapatite (CrHAp) and chromium-doped hydroxyapatite enriched with amoxicillin (CrHApAx). The [...] Read more.

In the last decade, it has been observed that the field of biomaterials has gained the attention of the researchers. This study presents the physicochemical and biological properties of coatings based on chromium-doped hydroxyapatite (CrHAp) and chromium-doped hydroxyapatite enriched with amoxicillin (CrHApAx). The coatings were obtained for the first time using the dip coating technique, beginning from dense suspensions of CrHAp and CrHApAx. The obtained layers were then analyzed by various methods in order to have a comprehensive overview of their physicochemical properties. Stability studies performed using ultrasound measurements showed that the CrHAp suspension has very good stability (S = 6.86·10⁻⁶ s⁻¹) compared to double-distilled water. The CrHApAx suspension (S = 0.00025 s⁻¹) shows good but weaker stability compared to that of the CrHAp suspension. Following XRD studies, a single hydroxyapatite-specific phase was observed in the CrHAp sample, while in the case of the CrHApAx sample, an amoxicillin-specific peak was also observed. The AFM results showed that the CrHAp coatings had a surface topography of a homogenous and uniform layer, with no significant cracks and fissures, while the CrHApAx coatings exhibited a surface morphology of homogenous layers formed of particles conglomerates. The biocompatibility of CrHAp and CrHApAx coatings was assessed using the MG63 cell line. The cytotoxicity of the coatings was evaluated by measuring cell viability with the aid of an MTT assay after 24, 48, and 72 h of incubation with the CrHAp and CrHApAx coatings. The results demonstrated that both CrHAp and CrHApAx coatings exhibited good biocompatibility for all the tested time intervals. The in vitro antibacterial activity of the coatings was also assessed against Pseudomonas aeruginosa 27853 ATCC (P. aeruginosa) bacterial cells. The potential of P. aeruginosa bacterial cells to adhere and develop on the surfaces of CrHAp and CrHApAx coatings was also investigated using AFM analysis. The findings of the biological assays suggest that CrHAp and CrHApAx coatings could be considered as promising candidates for biomedical applications, including the development of novel antimicrobial materials. Full article

(This article belongs to the Special Issue Advanced Biomaterials and Coatings)

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47 pages, 12325 KB

Open AccessEditor’s ChoiceReview

Crack-Templated Patterns in Thin Films: Fabrication Techniques, Characterization, and Emerging Applications

by Eleonora Sofia Cama, Mariacecilia Pasini, Umberto Giovanella and Francesco Galeotti

Coatings 2025, 15(2), 189; https://doi.org/10.3390/coatings15020189 - 6 Feb 2025

Cited by 5 | Viewed by 4563

Abstract

Crack-templated thin films, inspired by naturally occurring patterns such as leaf venation, spider webs, and the networked structure of dried egg white, represent a paradigm shift in the design of functional materials. Traditionally, cracks in coatings are seen as defects to be avoided [...] Read more.

Crack-templated thin films, inspired by naturally occurring patterns such as leaf venation, spider webs, and the networked structure of dried egg white, represent a paradigm shift in the design of functional materials. Traditionally, cracks in coatings are seen as defects to be avoided due to their potential to compromise mechanical integrity and performance. However, in this context, cracks are deliberately induced and meticulously controlled to serve as templates for versatile applications. This review explores the latest advances in preparation techniques, including solvent evaporation and thermal stress induction, with a focus on the interplay between material properties (e.g., polymers and ceramics) and process parameters (e.g., drying rates and temperature, layer thickness, substrate interactions) that govern crack behavior. The resulting crack patterns offer tunable features, such as density, width, shape, and orientation, which can be harnessed for applications in semitransparent electrodes, flexible sensors, and wearable and energy storage devices. Our study aims to navigate the advancements in crack engineering in the last 10 years and underscores its importance as a purposeful and versatile strategy for next-generation thin-film technologies, offering a novel and affordable approach to transforming perceived defects into assets for cutting-edge thin-film technologies. Full article

(This article belongs to the Special Issue Accelerated Development of Nanomaterials, Coatings, and Thin Films for Optical and Electronic Applications)

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15 pages, 5737 KB

Open AccessEditor’s ChoiceArticle

Guidance of Osteoblast Migration Using Femtosecond Laser-Induced Hierarchical Structures

by Johannes Heitz, Simon Glachs, Lukas Wagner, Christoph Wolf, Cristina Plamadeala, Martina Muck, Karoline Seibert, Christian Maier, Romy Marek, Agnes Weth and Werner Baumgartner

Coatings 2025, 15(2), 127; https://doi.org/10.3390/coatings15020127 - 23 Jan 2025

Viewed by 1386

Abstract

The adhesion and alignment of osteoblasts and fibroblasts on titanium alloy (Ti-6Al-4V) surfaces can be adjusted over a wide range by femtosecond laser treatment and anodization. The great differences in cell behavior between different experimental conditions raised further questions about the role of [...] Read more.

The adhesion and alignment of osteoblasts and fibroblasts on titanium alloy (Ti-6Al-4V) surfaces can be adjusted over a wide range by femtosecond laser treatment and anodization. The great differences in cell behavior between different experimental conditions raised further questions about the role of cell migration, which will be addressed in this study. For that, Ti-6Al-4V surfaces were laser-structured to obtain a surface covered with ripples, i.e., laser-induced periodic surface structures (LIPSS), or micro-cones superimposed with ripples. Then, cells were seeded either directly onto the non-structured or laser-structured areas on the titanium alloy samples or beside such samples where they can reach the surface by cell migration. After two weeks in culture, the cell coverage of the samples was evaluated by scanning electron microscopy (SEM). The results showed that cells directly seeded onto the non-structured or laser-structured areas covered the surface nearly completely and eventually aligned along the ripple direction for the laser-structured areas. In contrast, for cell-seeding beside the samples, the laser-structured areas remain nearly cell-free while the non-structured areas were covered with cells in a similar non-oriented manner as for direct cell-seeding. These results on reduced osteoblast migration due to laser structuring are in line with the findings in animal experiments. There, the new bone formation of laser-processed samples was 26.1% ± 16.9% lower in comparison to untreated samples of the same type, which can be explained by hindered cell migration on the laser-processed areas of the screws. Full article

(This article belongs to the Special Issue Bioadhesion on Laser Functionalized Surfaces)

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25 pages, 19542 KB

Open AccessEditor’s ChoiceArticle

Preparation and Characterization of Mg-Based Biomaterials with Bioactive Surfaces Functionalized with EU/Gd NPs for Bone Tissue Regeneration Obtained via PEO Process

by Klaudia Kuźmiak, Łukasz Janus, Aleksandra Sierakowska-Byczek and Julia Radwan-Pragłowska

Coatings 2025, 15(2), 124; https://doi.org/10.3390/coatings15020124 - 21 Jan 2025

Viewed by 1660

Abstract

This study aimed to develop a novel type of biodegradable magnesium (Mg)-based implant with enhanced biological activity through surface modification using plasma electrolytic oxidation (PEO) combined with the incorporation of rare earth ions (Eu and Gd). Magnesium is recognized for its lightweight nature, [...] Read more.

This study aimed to develop a novel type of biodegradable magnesium (Mg)-based implant with enhanced biological activity through surface modification using plasma electrolytic oxidation (PEO) combined with the incorporation of rare earth ions (Eu and Gd). Magnesium is recognized for its lightweight nature, biocompatibility, and bone-like mechanical properties, making it a promising alternative to titanium implants. Unlike titanium, Mg-based biomaterials can be safely used in pediatric surgery due to their ability to degrade naturally within the body. However, pure magnesium is highly reactive in physiological fluids, necessitating surface modifications to mitigate biocorrosion prior to clinical application. To address this challenge, the PEO process was employed, resulting in surface passivation and the formation of a protective coating. Experimental evaluations demonstrated reduced biodegradation rates and magnesium ion release, confirming the beneficial role of rare earth elements in decreasing reactivity. Wettability tests indicated high hydrophilicity, while scanning electron microscopy (SEM) revealed appropriate surface morphology and element deposition conducive to bone regeneration. Electrochemical analyses further validated the protective efficacy of the magnesium oxide layers enhanced with rare earth ions. Finally, in vitro cytotoxicity tests on the MG-63 osteosarcoma cell line confirmed the biocompatibility of the modified magnesium implants. Overall, this study highlights the potential of Mg-based biomaterials, modified through PEO and rare earth ion incorporation, for use in medical implants. Full article

(This article belongs to the Section Surface Coatings for Biomedicine and Bioengineering)

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16 pages, 2152 KB

Open AccessEditor’s ChoiceArticle

The Effect of Ti(C,N)-Based Coating Composition on Ni-Cr Alloys on the Initial Adhesion of E. coli Bacteria and C. albicans Fungi

by Katarzyna Banaszek, Katarzyna Dąbrowska, Witold Jakubowski, Leszek Klimek and Zofia Kula

Coatings 2025, 15(2), 121; https://doi.org/10.3390/coatings15020121 - 21 Jan 2025

Cited by 1 | Viewed by 960

Abstract

Under natural physiological conditions, the oral cavity is colonized by a diverse range of microorganisms, which inhabit its anatomical structures as well as prosthetic restorations and the supragingival surfaces of implants. The metabolic activity of these microorganisms can contribute to microbiological corrosion, leading [...] Read more.

Under natural physiological conditions, the oral cavity is colonized by a diverse range of microorganisms, which inhabit its anatomical structures as well as prosthetic restorations and the supragingival surfaces of implants. The metabolic activity of these microorganisms can contribute to microbiological corrosion, leading to the degradation of metal prosthetic materials. No material used for prosthetic elements is entirely resistant to bacterial adhesion. However, the application of protective coatings, such as Ti(C,N) coatings, on prosthetic surfaces can significantly reduce microorganism adherence. This study aimed to evaluate the influence of carbon and nitrogen content in Ti(C,N) coatings on reducing microorganism adhesion. Tests were conducted on five groups of Ni-Cr alloy specimens, each coated with Ti(C,N) layers containing varying amounts of carbon and nitrogen. The adhesion of E. coli bacteria and C. albicans fungi was assessed under both stationary and dynamic flow conditions. Results demonstrated that all tested coatings significantly reduced microorganism adhesion compared to uncoated Ni-Cr alloy samples. Full article

(This article belongs to the Special Issue Ceramic and Metallic Biomaterials. Application in Medical Sciences)

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15 pages, 11178 KB

Open AccessEditor’s ChoiceArticle

Temperature Influence on the Deposition of Nitrogen-Doped Silicon Carbide Polycrystalline Films

by Michail Gavalas, Scott Greenhorn, Frédéric Mercier and Konstantinos Zekentes

Coatings 2025, 15(1), 106; https://doi.org/10.3390/coatings15010106 - 18 Jan 2025

Cited by 2 | Viewed by 3592

Abstract

Polycrystalline nitrogen-doped cubic silicon carbide (3C-SiC) thin films are grown on 2″ Si wafers by a low-pressure chemical vapor deposition (LPCVD) technique with the aim for them to be used as support and active materials in microelectronic devices for neural interfaces. The effect [...] Read more.

Polycrystalline nitrogen-doped cubic silicon carbide (3C-SiC) thin films are grown on 2″ Si wafers by a low-pressure chemical vapor deposition (LPCVD) technique with the aim for them to be used as support and active materials in microelectronic devices for neural interfaces. The effect of deposition temperature on the structural, mechanical, and electrical properties is investigated. The growth rate is varying, from 1 μm/h to 14 μm/h, along with the deposition temperature. We show that the structural and electrical properties of polycrystalline SiC are modified when changing the deposition temperature. Films with resistivity as low as (10.0 ± 0.5) mΩ·cm, a low residual stress of (−397 ± 158) MPa, and a low root mean square surface roughness of (53 ± 19) nm are achieved. Accelerated aging tests in heated phosphate buffer solution (PBS) show an etching rate of less than 1 nm/day and a steady low electrical resistivity for 77 days, indicating that the nitrogen-doped polycrystalline SiC is a chemically stable material, capable of chronic stability in a saline electrolyte. Full article

(This article belongs to the Section Thin Films)

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30 pages, 10906 KB

Open AccessEditor’s ChoiceArticle

Individual and Joint Effect of Oleic Acid Imidazoline and CeCl₃ on Carbon Steel Corrosion in CO₂-Saturated Brine Solution

by Tihomir Borko, Gordana Bilić, Katarina Žbulj and Helena Otmačić Ćurković

Coatings 2025, 15(1), 93; https://doi.org/10.3390/coatings15010093 - 15 Jan 2025

Cited by 2 | Viewed by 1833

Abstract

In production and transportation systems of the oil industry, brine solutions contain high concentrations of chloride and dissolved CO₂, which is a very corrosive medium to which carbon steel is exposed. Therefore, finding new effective and environmentally friendly corrosion inhibitors is [...] Read more.

In production and transportation systems of the oil industry, brine solutions contain high concentrations of chloride and dissolved CO₂, which is a very corrosive medium to which carbon steel is exposed. Therefore, finding new effective and environmentally friendly corrosion inhibitors is of great importance. The effect of CeCl₃ (in concentrations from 5 mg dm⁻³ to 20 mg dm⁻³) and oleic acid imidazoline (IOA) (in concentrations from 5 mg dm⁻³ to 20 mg dm⁻³) separately and their mixtures (in concentrations from 5 mg dm⁻³ to 15 mg dm⁻³ of CeCl₃ and from 5 mg dm⁻³ to 20 mg dm⁻³ of IOA) as corrosion inhibitors of AISI 1018 carbon steel corrosion in simulated brine solution saturated with CO₂ at 60 °C were examined by means of weight-loss testing, electrochemical measurements (polarization resistance, linear polarization with Tafel extrapolation, electrochemical impedance spectroscopy) and surface analyses (scanning electron microscopy with energy-dispersive X-ray spectroscopy analyses, Raman spectroscopy and X-ray diffraction). All test methods showed a higher efficiency of compounds′ mixtures (from 62.77% to 97.94%) and a higher degree of corrosion protection compared to the action of individual compounds (efficiency from 3.43% to 94.61% for IOA and from 57.58% to 96.27% for CeCl₃). Imidazoline, a common corrosion inhibitor in CO₂-saturated systems, most likely forms a surface film with voids via its adsorption on steel surface, while cerium carbonate tends to fill these voids by creating a more compact film. In this way, a denser and thicker surface film is formed. Full article

(This article belongs to the Special Issue Corrosion Resistance of Innovative Composite Coatings Based on Nanoparticles)

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24 pages, 44850 KB

Open AccessEditor’s ChoiceArticle

Evolution of Surface Integrity Characteristics and Mechanical Behavior of Diamond Burnished and Turned AISI 304 Steel Specimens After Prolonged Exposure to Natural Seawater

by Yaroslav Argirov, Jordan Maximov, Galya Duncheva, Angel Anchev, Vladimir Dunchev and Tatyana Mechkarova

Coatings 2025, 15(1), 31; https://doi.org/10.3390/coatings15010031 - 1 Jan 2025

Cited by 4 | Viewed by 1194

Abstract

This article presents results on the evolution of surface integrity, microstructure, mechanical characteristics, fatigue strength, and wear behavior of AISI 304 steel specimens after prolonged exposure (up to 746 days) to a natural seawater environment, specifically near the port of Varna, Bulgaria. The [...] Read more.

This article presents results on the evolution of surface integrity, microstructure, mechanical characteristics, fatigue strength, and wear behavior of AISI 304 steel specimens after prolonged exposure (up to 746 days) to a natural seawater environment, specifically near the port of Varna, Bulgaria. The samples, having different shapes and sizes according to the respective tests, were divided into two main groups based on the finishing process: fine turning (FT) and diamond burnishing (DB). Additionally, fatigue FT specimens were polished to meet the standard requirements. Some of the cylindrical samples from both groups were heat-treated to dissolve the car-bides. No significant improvement in the corrosion resistance of the heat-treated samples (FT and DB) was observed compared with untreated samples after 746 days of immersion in seawater. Overall, all types of DB specimens showed less mass loss (indicating a higher corrosion resistance), higher static and fatigue strength, greater plasticity, and greater wear resistance than the corresponding FT specimens. Notably, pitting corrosion was observed on all specimens, as well as trac-es of intergranular corrosion in some FT specimens. The hardening DB effects have a complex impact on corrosion activity. The increases in dislocation density and the surface and internal energy of the subsurface layers intensify the nucleation of corrosion centers in the surface layers; however, the refined fibrous structure and significant reduction in the roughness slow down the development of corrosion. Therefore, the implementation of DB as a smoothing process will re-duce the surface energy, and hence will lead to further increases in corrosion resistance. Full article

(This article belongs to the Special Issue Effects of Surface Layer Modification on Fatigue, Corrosion and Wear Behavior of Metallic Materials)

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9 pages, 956 KB

Open AccessEditor’s ChoiceArticle

Atomic Layer Deposition of Y₂O₃ Thin Films Using Y(MeCp)₂(iPr-nPrAMD) Precursor and H₂O, and Their Erosion Resistance in CF₄-Based Plasma

by Seong Lee, Hyunchang Kim and Sehun Kwon

Coatings 2025, 15(1), 22; https://doi.org/10.3390/coatings15010022 - 30 Dec 2024

Cited by 4 | Viewed by 2434

Abstract

Atomic layer deposition (ALD) of Y₂O₃ thin films was investigated using Y(MeCp)₂(iPr-nPrAMD) precursor and H₂O reactant. The self-limiting reaction mechanism of ALD-Y₂O₃ thin films was confirmed at a growth temperature of 260 °C. [...] Read more.

Atomic layer deposition (ALD) of Y₂O₃ thin films was investigated using Y(MeCp)₂(iPr-nPrAMD) precursor and H₂O reactant. The self-limiting reaction mechanism of ALD-Y₂O₃ thin films was confirmed at a growth temperature of 260 °C. And, the saturated growth rate was confirmed to be ~0.11 nm/cycle. Also, it was demonstrated that a wide ALD temperature window from 150 °C to 290 °C maintains a consistent growth rate. ALD-Y₂O₃ thin films were found to have a typical cubic polycrystalline structure, independent of growth temperature, which can be attributed to their stoichiometric composition of Y₂O₃, negligible carbon impurity, and high film density, analogous to the Y₂O₃ bulk. Even at a low growth temperature of 150 °C, ALD-Y₂O₃ exhibited a markedly lower plasma etching rate (~0.77 nm/min) than that (~4.6 nm/min) of ALD-Al₂O₃ when using RIE at a plasma power of 400 W with a mixed gas of Ar/CF₄/O₂. Furthermore, the growth temperature of Y₂O₃ thin films had minimal impact on the etching rate. Full article

(This article belongs to the Special Issue Anti-Corrosion and Anti-Wear Coatings: Fundamentals, Technologies, and Applications)

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20 pages, 17374 KB

Open AccessEditor’s ChoiceArticle

Tribological Behavior of Gas-Nitrided 42CrMo4 Steel at Elevated Temperatures

by Dominika Panfil-Pryka, Michal Kulka, Mateusz Kotkowiak, Jerzy Michalski and Karol Grochalski

Coatings 2025, 15(1), 18; https://doi.org/10.3390/coatings15010018 - 28 Dec 2024

Cited by 2 | Viewed by 1753

Abstract

Nitriding is a well-known thermochemical treatment improving the surface hardness and the wear resistance of steel. The phase composition and growth kinetics of the nitrided layer can be controlled using a gas nitriding with changeable nitriding potential. In this work, such a gas [...] Read more.

Nitriding is a well-known thermochemical treatment improving the surface hardness and the wear resistance of steel. The phase composition and growth kinetics of the nitrided layer can be controlled using a gas nitriding with changeable nitriding potential. In this work, such a gas nitriding was used to produce, on 42CrMo4 steel, the two nitrided layers differing in the thickness of compound zone and diffusion zone. The microstructure and nanohardness of these layers were studied. For the first time, the tribological behavior of gas nitrided layers at elevated temperatures (from 23 to 400 °C) was investigated. The compound zone consisted of ε + (ε + γ’) iron nitrides and, in the diffusion zone, the nitric sorbite with γ’ precipitates was observed. The highest nanohardness was measured in the ε + γ’ zone. The lowest values of friction coefficients were obtained if the contact surface of the friction pair entered the ε + γ’ zone. After the wear process, at a final temperature of 400 °C, worn surfaces showed only intensive abrasive wear, evidenced by shallow grooves. The increased oxygen content at the edges of wear tracks indicated possible oxidative wear. Full article

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

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24 pages, 6981 KB

Open AccessEditor’s ChoiceArticle

Machine-Learning-Driven Optimization of Cold Spray Process Parameters: Robust Inverse Analysis for Higher Deposition Efficiency

by Abderrachid Hamrani, Aditya Medarametla, Denny John and Arvind Agarwal

Coatings 2025, 15(1), 12; https://doi.org/10.3390/coatings15010012 - 26 Dec 2024

Cited by 5 | Viewed by 2896

Abstract

Cold spray technology has become essential for industries requiring efficient material deposition, yet achieving optimal deposition efficiency (DE) presents challenges due to complex interactions among process parameters. This study developed a two-stage machine learning (ML) framework incorporating Bayesian optimization to address these challenges. [...] Read more.

Cold spray technology has become essential for industries requiring efficient material deposition, yet achieving optimal deposition efficiency (DE) presents challenges due to complex interactions among process parameters. This study developed a two-stage machine learning (ML) framework incorporating Bayesian optimization to address these challenges. In the first stage, a classification model predicted the occurrence of deposition, while the second stage used a regression model to forecast DE values given deposition presence. The approach was validated on Aluminum 6061 data, demonstrating its capability to accurately predict DE and identify optimal process parameters for target efficiencies. Model interpretability was enhanced with SHAP analysis, which identified gas temperature and gas type as primary factors affecting DE. Scenario-based inverse analysis further validated the framework by comparing model-predicted parameters to literature data, revealing high accuracy in replicating real-world conditions. Notably, substituting hydrogen as the gas carrier reduced the required gas temperature and pressure for high DE values, suggesting economic and operational benefits over helium and nitrogen. This study demonstrates the effectiveness of AI-driven solutions in optimizing cold spray processes, contributing to more efficient and practical approaches in material deposition. Full article

(This article belongs to the Special Issue Functional Coatings: Microstructure, Mechanical Properties, and Wear Behaviour)

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19 pages, 14017 KB

Open AccessEditor’s ChoiceArticle

Multi-Step Simulations of Ionized Metal Physical Vapor Deposition to Enhance the Plasma Formation Uniformity

by Cheongbin Cheon, Min Young Hur, Ho Jun Kim and Hae June Lee

Coatings 2025, 15(1), 11; https://doi.org/10.3390/coatings15010011 - 25 Dec 2024

Viewed by 1735

Abstract

Ionized metal physical vapor deposition (IMPVD), which is operated at a very low pressure to take advantage of the metal sputtering effect on the target surface, has unique properties compared with conventional DC magnetron sputtering. In this study, we investigated the effect of [...] Read more.

Ionized metal physical vapor deposition (IMPVD), which is operated at a very low pressure to take advantage of the metal sputtering effect on the target surface, has unique properties compared with conventional DC magnetron sputtering. In this study, we investigated the effect of the rotating magnetic field on the plasma formation of IMPVD to enhance the deposition uniformity. This was accomplished through a multi-step simulation, which enabled plasma analysis, sputtered particle and chemical reaction analysis, and deposition profile analysis. A two-dimensional particle-in-cell Monte Carlo simulation utilizes the exact cross-section data of the Cu ion collisions and calculates the particle trajectories under specific magnetic field profiles. This new methodology gives guidance for the design of the magnetic field profiles of IMPVD and an understanding of the physical mechanism. Full article

(This article belongs to the Special Issue Advanced Coating Technology by Physical Vapor Deposition and Applications)

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18 pages, 1365 KB

Open AccessEditor’s ChoiceArticle

Increasing the Resistance of Steel and Austenitic Stainless Steels Against Pitting Corrosion by a γ-Irradiated Self-Assembled Amphiphilic Molecular Layer

by Éva Kocsisné Pfeifer, Zoltán May, Miklós Péter Mohai, János Mink, István Gábor Gyurika and Judit Telegdi

Coatings 2024, 14(12), 1601; https://doi.org/10.3390/coatings14121601 - 21 Dec 2024

Cited by 1 | Viewed by 1264

Abstract

This study, based on our previous research, aims to quantitatively determine the enhanced protection of austenitic stainless steels against pitting corrosion in NaCl solution by self-assembled molecular (SAM) layers, in their original form and after γ-irradiation. This study focuses on four stainless steels [...] Read more.

This study, based on our previous research, aims to quantitatively determine the enhanced protection of austenitic stainless steels against pitting corrosion in NaCl solution by self-assembled molecular (SAM) layers, in their original form and after γ-irradiation. This study focuses on four stainless steels of varying compositions, covered by self-assembled undecenyl phosphonic acid layers. The metal dissolution in corrosion experiments was measured by a special, highly sensitive analytical technique using the inductively coupled plasma–optical emission spectrometry (ICP-OES). The comparison of the dissolved metal ion concentrations measured in the presence of different metals with and without nanocoatings allowed the evaluation of the anticorrosion effectiveness of nanofilms as well as the importance of the alloying elements. The ICP-OES results demonstrated that the quality of layers have a significant impact on anticorrosion efficacy. The γ-irradiated self-assembled layers were the most effective in controlling the dissolution of stainless steels. The mechanisms of the inhibition in the presence of these nanolayers were elucidated by infrared spectroscopy. First of all, it revealed the differences in the adsorption of the undecenyl phosphonic acid self-assembled layer, both with and without γ-irradiation. The other important observation that confirmed the increased anticorrosion efficiency after γ-irradiation proved the formation of a more compact, polymer-like layer over the metal surface. The increased anticorrosion efficacy, defined as the enhancement in Pitting Resistance Equivalent Numbers (PRENs) in the presence of self-assembled layers (either pre- or post-γ-irradiation), can be documented. Full article

(This article belongs to the Special Issue Anticorrosion Coatings: From Materials to Applications)

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17 pages, 13353 KB

Open AccessEditor’s ChoiceArticle

Microstructural, Nanomechanical, and Tribological Properties of Thin Dense Chromium Coatings

by E. Broitman, A. Jahagirdar, E. Rahimi, R. Meeuwenoord and J. M. C. Mol

Coatings 2024, 14(12), 1597; https://doi.org/10.3390/coatings14121597 - 20 Dec 2024

Cited by 4 | Viewed by 1638

Abstract

Nowadays, Thin Dense Chromium (TDC) coatings are being industrially used in rolling bearings applications due to their claimed advantages such as high hardness, low wear, and good corrosion resistance. However, despite their broad commercial use, very little has been published in the open [...] Read more.

Nowadays, Thin Dense Chromium (TDC) coatings are being industrially used in rolling bearings applications due to their claimed advantages such as high hardness, low wear, and good corrosion resistance. However, despite their broad commercial use, very little has been published in the open scientific literature regarding their microstructure, nanomechanical, and tribological properties. In this paper, TDC coatings with a thickness of about 5 µm were deposited by a customized electrochemical process on ASTM 52100 bearing steel substrates. Surface microstructure and chemical composition analysis of the TDC coatings was carried out by scanning electron microscopy and atomic force microscopy. The results revealed a coating with a dense, nodular, and polycrystalline microstructure. Unlike standard electrodeposited “Hard Chromium” coatings, TDC coatings show no presence of micro/nano-cracks, likely contributing to their superior corrosion resistance. The nanomechanical behavior, studied by nanoindentation as a function of penetration depths, exhibits a pronounced size effect near the coating surface that can be linked to the nodular microstructure. A hard surface with hardness H_IT 14.9 ± 0.5 GPa and reduced elastic modulus E_r = 216.8 ± 3.9 GPa was observed. Tribological characterization under the presence of lubricants was performed by two single-contact tribometers using coated and uncoated steel balls against flat steel substrates. An in-house fretting wear rig was used to measure the lubricated friction coefficient in pure sliding conditions, whilst the friction performance in rolling/sliding lubricated conditions was evaluated using a WAM test rig. In pure sliding, TDC/TDC contacts show ~13% lower friction than for steel. Under rolling/sliding conditions with 5% sliding, the traction coefficient of TDC/TDC coating contact was at least 20% lower than that for steel/steel contact. The tribological results obtained in various contact conditions demonstrate the benefits of applying TDC coatings to reduce bearing friction. Full article

(This article belongs to the Special Issue Advanced Tribological Coatings: Fabrication and Application)

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11 pages, 3079 KB

Open AccessEditor’s ChoiceArticle

Controlled Aggregation of Cobalt and Platinum Atoms via Plasma Treatment for Exceptional Hydrogen Evolution Reaction Activity

by Guoqing Zhang, Jiankun Li, Yixing Wang, Linfeng Lei and Linzhou Zhuang

Coatings 2024, 14(12), 1569; https://doi.org/10.3390/coatings14121569 - 15 Dec 2024

Cited by 2 | Viewed by 1228

Abstract

Designing and developing highly active, stable, and cost-effective hydrogen evolution reaction (HER) catalysts is crucial in the field of water electrolysis. In this study, we utilize N-doped porous carbon (CoNC) derived from zeolite imidazole metal–organic frameworks (ZIF-67) as support and prepare CoNC-Pt-IM-P via [...] Read more.

Designing and developing highly active, stable, and cost-effective hydrogen evolution reaction (HER) catalysts is crucial in the field of water electrolysis. In this study, we utilize N-doped porous carbon (CoNC) derived from zeolite imidazole metal–organic frameworks (ZIF-67) as support and prepare CoNC-Pt-IM-P via chemical impregnation (CoNC-Pt-IM) and plasma treatment. Systematic analyses reveal that calcined CoNC with pyridinic nitrogen could serve as a robust support to strongly anchor PtCo nanoclusters, while argon plasma treatment could lead to a noticeable aggregation of Co and Pt atoms so as to alter the electronic environment and enhance intrinsic HER catalytic activity. CoNC-Pt-IM-P could exhibit outstanding catalytic activity toward HER, achieving an exceptionally low overpotential of 31 mV at the current density of −10 mA cm⁻² and a Tafel slope of 36 mV dec⁻¹. At an overpotential of 50 mV, its mass activity reaches 4.90 A mg_Pt⁻¹, representing enhancements of 1.5 times compared to CoNC-Pt-IM and 12.3 times compared to commercial 20 wt% Pt/C. Furthermore, it could operate stably for over 110 h at a current density of −10 mA cm⁻², demonstrating its exceptional durability. This work uses plasma treatment to achieve the controllable aggregation of Co and Pt atoms to enhance their catalytic activity, which has the advantage of avoiding excessive particle aggregation compared to the commonly used method of high-temperature calcination. Full article

(This article belongs to the Special Issue Coatings as Key Materials in Catalytic Applications)

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15 pages, 2546 KB

Open AccessEditor’s ChoiceArticle

Essential Oils and Essential Oil-Based Products Compared to Chemical Biocides Against Microbial Patinas on Stone Cultural Heritage

by Federica Antonelli, Sara Iovine, Carlotta Sacco Perasso, Natalia Macro, Eleonora Gioventù, Filippo Edoardo Capasso and Marco Bartolini

Coatings 2024, 14(12), 1546; https://doi.org/10.3390/coatings14121546 - 11 Dec 2024

Cited by 3 | Viewed by 1638

Abstract

In recent years, attention has been paid to finding eco-friendly products that could represent an alternative for the chemicals usually used during conservation procedures. In the field of the devitalization of biological patinas, the most studied products are essential oils (EOs). Several works [...] Read more.

In recent years, attention has been paid to finding eco-friendly products that could represent an alternative for the chemicals usually used during conservation procedures. In the field of the devitalization of biological patinas, the most studied products are essential oils (EOs). Several works tested EOs in vitro on microorganisms isolated from stone artifacts but few applied these products on real artworks colonized by a complex patina. In the present work, the biocidal effect of two EOs (cinnamon bark and oregano) and two EO-based products (Biotersus and Essenzio) was compared to that of three chemical biocides commonly used in the conservation of stone artifacts (Biotin R1+R2, NewDes50, and Preventol RI50). The products were applied by brush in situ on a marble slab characterized by a green patina. The biocidal activity was evaluated by analyzing the chlorophyll fluorescence and quantifying ATP through biochemical tests. Furthermore, the products’ interference with stone was evaluated by colorimetric measures on sedimentary rock samples. The results indicate that chemical biocides exhibited biocidal activity of greater than 99.5% with a single application, while cinnamon oil (at a 1% concentration) and Essenzio required two applications to achieve the same level of efficacy. Conversely, oregano oil and Biotersus were not able to effectively reduce microorganism vitality, even with repeated applications. Full article

(This article belongs to the Special Issue Coatings for Cultural Heritage: Cleaning, Protection and Restoration)

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19 pages, 4428 KB

Open AccessEditor’s ChoiceArticle

Machine Learning-Driven Optimization of Micro-Textured Surfaces for Enhanced Tribological Performance: A Comparative Analysis of Predictive Models

by Zhenghui Ge, Qifan Hu, Rui Wang, Haolin Fei, Yongwei Zhu and Ziwei Wang

Coatings 2024, 14(12), 1539; https://doi.org/10.3390/coatings14121539 - 8 Dec 2024

Cited by 2 | Viewed by 1858

Abstract

Micro-textured surfaces show promise in improving tribological properties, but predicting their performance remains challenging due to complex relationships between surface features and frictional behavior. This study evaluates five algorithms—linear regression, decision tree, gradient boosting, support vector machine, and neural network—for their ability to [...] Read more.

Micro-textured surfaces show promise in improving tribological properties, but predicting their performance remains challenging due to complex relationships between surface features and frictional behavior. This study evaluates five algorithms—linear regression, decision tree, gradient boosting, support vector machine, and neural network—for their ability to predict load-carrying capacity and friction force based on texture parameters including depth, side length, surface ratio, and shape. The neural network model demonstrated superior performance, achieving the lowest MAE (24.01) and highest R-squared value (0.99) for friction force prediction. The results highlight the potential of machine learning techniques to enhance the understanding and prediction of friction-reducing micro-textures, contributing to the development of more efficient and durable tribological systems in industrial applications. Full article

(This article belongs to the Special Issue Advances in Measurement and Data Analysis of Surfaces with Functionalized Coatings)

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12 pages, 1561 KB

Open AccessEditor’s ChoiceArticle

Silver Linings: Electrochemical Characterization of TiO₂ Sol-Gel Coating on Ti6Al4V with AgNO₃ for Antibacterial Excellence

by Julia Both, Gabriella Stefania Szabó, Alexandra Ciorîță and Liana Maria Mureșan

Coatings 2024, 14(12), 1532; https://doi.org/10.3390/coatings14121532 - 4 Dec 2024

Viewed by 1585

Abstract

This study aimed to synthesize TiO₂ and silver-containing TiO₂ layers on Ti6Al4V titanium alloy substrates, also known as titanium grade 5 (TiGr5), to provide corrosion resistance and antibacterial activity. The TiO₂ layers were prepared through the sol-gel method and dip-coating [...] Read more.

This study aimed to synthesize TiO₂ and silver-containing TiO₂ layers on Ti6Al4V titanium alloy substrates, also known as titanium grade 5 (TiGr5), to provide corrosion resistance and antibacterial activity. The TiO₂ layers were prepared through the sol-gel method and dip-coating technique. Silver introduction into the layers was performed in two different ways. One was the impregnation method by dipping the TiO₂ layer-covered metal in aqueous AgNO₃ solutions of various concentrations (TiO₂/AgNO₃), and the other was by direct introduction of AgNO₃ into the precursor sol (Ag-TiO₂). The two methods for incorporating AgNO₃ into the coating matrix are novel, as they preserve silver in its ionic form rather than reducing it to metallic silver. The samples were put through electrochemical characterization, namely potentiodynamic polarization and electrochemical impedance spectroscopy (EIS), and were tested in Hank’s solution, simulating a physiological environment. The behavior of the layers was monitored over time. Also, the thin layers’ thickness and adhesion to the substrate were determined. Microbiological evaluation of the Ag-doped coatings on glass substrates confirmed their significant bactericidal activity against Gram-negative Escherichia coli. Among the two types of coatings, the impregnated coatings demonstrated the most promising electrochemical performance, as evidenced by both EIS and potentiodynamic polarization analyses. Full article

(This article belongs to the Special Issue Advances in Nanostructured Thin Films and Coatings, 2nd Edition)

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20 pages, 20891 KB

Open AccessEditor’s ChoiceArticle

Efficient Photocatalytic Reduction of Hexavalent Chromium by NiCo₂S₄/BiOBr Heterogeneous Photocatalysts

by Shumeng Qin, Ruofan Xu, Qiu Jin, Sen Wang, Yi Ren, Yulin Huang, Ziye Zheng, Lihui Xiao, Dong Zhai, Shuguang Wang and Zuoli He

Coatings 2024, 14(12), 1492; https://doi.org/10.3390/coatings14121492 - 27 Nov 2024

Cited by 6 | Viewed by 1449

Abstract

For typical Cr(VI)-containing industrial wastewater, more efficient water treatment technologies need to be used to ensure that Cr(VI) concentrations are reduced to safe levels before discharge. Photocatalytic technology is highly efficient, environmentally friendly, and has been extensively used to address this demand. Herein, [...] Read more.

For typical Cr(VI)-containing industrial wastewater, more efficient water treatment technologies need to be used to ensure that Cr(VI) concentrations are reduced to safe levels before discharge. Photocatalytic technology is highly efficient, environmentally friendly, and has been extensively used to address this demand. Herein, heterogeneous NiCo₂S₄/BiOBr photocatalysts with different ratios were prepared using a solvothermal method. When compared with pure NiCo₂S₄ and BiOBr, the NiCo₂S₄/BiOBr-30 had significantly increased adsorption capacity and visible-light-driven photocatalytic reduction activity for Cr(VI) removal. The improved adsorption performance of the NiCo₂S₄/BiOBr-30 was mainly due to its increased specific surface area, and the enhanced photocatalytic performance of the NiCo₂S₄/BiOBr-30 could be attributed to the improved separation and transfer of photogenerated carriers at the interface. Lastly, a possible enhanced photocatalytic Cr(VI) reduction mechanism of the NiCo₂S₄/BiOBr heterostructure was developed. Full article

(This article belongs to the Special Issue Advanced Materials and Coatings for Photocatalytic Applications)

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19 pages, 6285 KB

Open AccessEditor’s ChoiceArticle

Improving Prediction Model for Colorimetric Changes Due to Coating Processes with Oil-Based and UV Coatings

by Igor Zjakić, Eduard Galić, Ivana Ljevak and Mile Matijević

Coatings 2024, 14(12), 1488; https://doi.org/10.3390/coatings14121488 - 26 Nov 2024

Cited by 1 | Viewed by 1322

Abstract

The measurability and predictability of the printing process are influenced by the impact of various coating methods. Besides enhancing and protecting the printed product, these methods can alter the colorimetric properties of spot colors across different wavelengths. Prediction models based on ink trapping [...] Read more.

The measurability and predictability of the printing process are influenced by the impact of various coating methods. Besides enhancing and protecting the printed product, these methods can alter the colorimetric properties of spot colors across different wavelengths. Prediction models based on ink trapping formulas were analyzed, particularly those from Deshpande, Green, and Hoffstadt, designed to forecast colorimetric values in overprinted spot color scenarios. This study examined the influence of coating methods on the colorimetric properties of spot colors and evaluated the applicability of the prediction model for these conditions. Spectrophotometric and densitometric methods, combined with mathematical analysis, were used to quantify the degree of color change induced by different coatings. The findings clearly indicate the extent of colorimetric changes in spot colors resulting from various coating applications. They also highlight the potential, albeit limited, application of this model in predicting color changes for improved process repeatability and predictability. While the prediction method analyzed in this study proved inadequate for coating-over-spot-color scenarios, it remains useful for predicting colorimetric shifts in spot-on-spot-color overprinting. The model demonstrated that it is not entirely accurate, as some coatings show ∆E₀₀ deviations of up to 10. To improve the model’s applicability, a varnishing coefficient, V, should be introduced, which can reduce ∆E₀₀ variation for each color and substrate. The research showed that a coefficient range from 0.8 to 1.2 yields acceptable results, bringing ∆E₀₀ below 2, thus making the model suitable for coating processes with oil-based and UV coatings. Full article

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

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16 pages, 5245 KB

Open AccessEditor’s ChoiceArticle

Ball-on-Disk Wear Maps for Bearing Steel–Hard Anodized EN AW-6082 Aluminum Alloy Tribocouple in Dry Sliding Conditions

by Enrico Baroni, Annalisa Fortini, Lorenzo Meo, Chiara Soffritti, Mattia Merlin and Gian Luca Garagnani

Coatings 2024, 14(11), 1469; https://doi.org/10.3390/coatings14111469 - 19 Nov 2024

Cited by 2 | Viewed by 1934

Abstract

In recent years, Golden Hard Anodizing (G.H.A.^®) has been developed as a variant of the traditional hard anodizing process with the addition of Ag⁺ ions in the nanoporous structure. The tribological properties of this innovative surface treatment are still not [...] Read more.

In recent years, Golden Hard Anodizing (G.H.A.^®) has been developed as a variant of the traditional hard anodizing process with the addition of Ag⁺ ions in the nanoporous structure. The tribological properties of this innovative surface treatment are still not well understood. In this study, ball-on-disk tests were conducted in dry sliding conditions using 100Cr6 (AISI 52100) bearing steel balls as a counterbody and GHA^®-anodized EN AW-6082 aluminum alloy disks. The novelty of this work lies in the mapping of the wear properties of the tribocouple under different test conditions for a better comparison of the results. Three different normal loads (equal to 5, 10, and 15 N) and three different reciprocating frequencies (equal to 2, 3, and 4 Hz) were selected to investigate a spectrum of operating conditions for polished and unpolished G.H.A.^®-anodized EN AW-6082 aluminum alloy. Quantitative wear maps were built based on the resulting wear rate values to define the critical operating limits of the considered tribocouple. The results suggest that the coefficient of friction (COF) was independent of test conditions, while different wear maps were found for polished and non-polished surfaces. Polishing before anodizing permitted the acquisition of lower wear for the anodized disks and the steel balls. Full article

(This article belongs to the Special Issue Mechanical Properties and Tribological Behavior of Alloy/Coatings, 2nd Edition)

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13 pages, 7529 KB

Open AccessEditor’s ChoiceArticle

Ammonia Plasma Surface Treatment for Enhanced Cu–Cu Bonding Reliability for Advanced Packaging Interconnection

by Ho Jeong Jeon and Sang Jeen Hong

Coatings 2024, 14(11), 1449; https://doi.org/10.3390/coatings14111449 - 14 Nov 2024

Cited by 5 | Viewed by 2878

Abstract

With the emergence of 3D stacked semiconductor products, such as high-bandwidth memory, bonding-interface reliability cannot be overemphasized. The condition of the surface interface before bonding is important and can substantially affect product reliability. Plasma technology can be used to control the state of [...] Read more.

With the emergence of 3D stacked semiconductor products, such as high-bandwidth memory, bonding-interface reliability cannot be overemphasized. The condition of the surface interface before bonding is important and can substantially affect product reliability. Plasma technology can be used to control the state of a bonding interface, but various factors of interest, such as surface roughness, chemical bonding state, and surface cleanliness, may depend on the type of gaseous plasma. These factors may increase voids at the interface, which can jeopardize the product reliability. In this study, NH₃ plasma surface treatment is investigated and compared with the conventionally preferred surface treatment under Ar plasma. Under the latter method, specific anomalies occurred and led to void formation at the interface during bonding. By contrast, NH₃ plasma treatment maintained higher uniformity, higher overall surface conditions, and a smooth reduction process. Furthermore, the formation of a nitride passivation layer effectively inhibited the oxidation of the metal surface, and the flat surface resulted in the decrease in voids compared with the Ar plasma treatment after the copper–copper bonding. From the experimental analysis, we achieved a 12% reduction in resistance in the samples treated with NH₃ plasma treatment due to the suppression of surface oxidation. However, it is unfortunate that the shear strength in the experimental samples treated with NH₃ plasma treatment needs to be further improved. Full article

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

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13 pages, 6719 KB

Open AccessEditor’s ChoiceArticle

Fatigue Crack Growth Behavior of Additively Manufactured Ti Metal Matrix Composite with TiB Particles

by Thevika Balakumar, Afsaneh Edrisy and Reza A. Riahi

Coatings 2024, 14(11), 1447; https://doi.org/10.3390/coatings14111447 - 13 Nov 2024

Viewed by 1584

Abstract

Fatigue crack growth behavior of additively manufactured Ti metal matrix composite with TiB particles at room temperature was studied using a compact tension specimen and at the stress ratio of 0.1 (R = 0.1). The composite studied in this work was manufactured with [...] Read more.

Fatigue crack growth behavior of additively manufactured Ti metal matrix composite with TiB particles at room temperature was studied using a compact tension specimen and at the stress ratio of 0.1 (R = 0.1). The composite studied in this work was manufactured with a unique additive technique called plasma transferred arc solid free-form fabrication, which was designed to manufacture low-cost near-net-shaped components for aerospace and automotive industries. The fatigue crack growth rate experiments were carried perpendicular and parallel to the additive material build, aiming to find any fatigue anisotropies at room temperature. The findings reveal that additively manufactured Ti-TiB composite shows isotropic fatigue properties with respect to fatigue crack growth. Furthermore, the fatigue crack growth mechanisms in this additive composite material were identified as void nucleation/coalescence and the bypassing of particles and matrix, depending on the interparticle distance. Full article

(This article belongs to the Special Issue Latest Insights in Metal Fatigue, Failure, and Fracture)

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29 pages, 4458 KB

Open AccessEditor’s ChoiceReview

The Preparation of Biomass-Derived Carbon Dots and Its Application Prospect in the Field of Vascular Stent Coating

by Huimin Duan, Yanchao Wang, Zhongna Zhang, Ambreen Akram, Lan Chen and Jingan Li

Coatings 2024, 14(11), 1432; https://doi.org/10.3390/coatings14111432 - 11 Nov 2024

Cited by 4 | Viewed by 2998

Abstract

Biomass material serves as one of the most advantageous carbon sources for the synthesis of carbon dots (CDs) due to its abundant availability, cost-effectiveness, and environmental sustainability. Biomass-derived carbon dots (B-CDs), which are new zero-dimensional carbon nanomaterials, have presented broad application prospects in [...] Read more.

Biomass material serves as one of the most advantageous carbon sources for the synthesis of carbon dots (CDs) due to its abundant availability, cost-effectiveness, and environmental sustainability. Biomass-derived carbon dots (B-CDs), which are new zero-dimensional carbon nanomaterials, have presented broad application prospects in the medical field and have become a research focus. In recent years, the death rate caused by vascular diseases has been high, and interventional therapy is one of the important means to treat vascular stenosis. As a material with excellent biocompatibility and fluorescence properties, B-CDs have shown great potential in the field of vascular stents, and their unique properties provide new ideas and possibilities for improving the biocompatibility of vascular stents and realizing real-time tracer diagnosis. This paper reviews the preparation methods, modification techniques, and application prospects of B-CDs in the coating of vascular stents. It discusses current challenges and potential solutions while forecasting future development directions, thereby providing innovative insights and pathways for the research and development of a new generation of vascular stents. Full article

(This article belongs to the Special Issue Advanced Alloy Degradation and Implants, 2nd Edition)

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17 pages, 7142 KB

Open AccessEditor’s ChoiceArticle

Wear and Corrosion Resistance of ZrN Coatings Deposited on Ti6Al4V Alloy for Biomedical Applications

by Stanislava Rabadzhiyska, Dimitar Dechev, Nikolay Ivanov, Tatyana Ivanova, Velichka Strijkova, Vesela Katrova, Velko Rupetsov, Nina Dimcheva and Stefan Valkov

Coatings 2024, 14(11), 1434; https://doi.org/10.3390/coatings14111434 - 11 Nov 2024

Cited by 10 | Viewed by 2347

Abstract

Zirconium nitrides films were synthesized on Ti6Al4V substrates at a bias voltage of −50 V, −80 V, −110 V and −150 V by the direct current (DC) reactive magnetron sputtering technique. The as-deposited coatings were characterized by X-ray diffraction (XRD), Fourier-transform infrared (FTIR) [...] Read more.

Zirconium nitrides films were synthesized on Ti6Al4V substrates at a bias voltage of −50 V, −80 V, −110 V and −150 V by the direct current (DC) reactive magnetron sputtering technique. The as-deposited coatings were characterized by X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM) and atomic force microscopy (AFM). The wear and corrosion resistance of the obtained ZrN coatings were evaluated to determine the possibility for their implementation in modern biomedical applications. It was found that the intensity of the diffraction peak of the Zr-N phase corresponding to the (1 1 1) crystallographic plane rose as the bias voltage increased, while the ZrN coatings’ thickness reduced from 1.21 µm to 250 nm. The ZrN films’ surface roughness rose up to 75 nm at −150 V. Wear tests showed an increase in the wear rate and wear intensity as the bias voltage increased. Corrosion studies of the ZrN coatings were carried out by three electrochemical methods: open circuit potential (OCP), cyclic voltammetry (polarization measurements) and electrochemical impedance spectroscopy (EIS). All electrochemical measurements confirmed that the highest protection to corrosion is the ZrN coating, which was deposited on the Ti6Al4V substrate at a bias voltage of −150 V. Full article

(This article belongs to the Special Issue Anti-corrosion Coatings of Metals and Alloys—New Perspectives)

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17 pages, 4223 KB

Open AccessEditor’s ChoiceArticle

Stainless Steel Deposits on an Aluminum Support Used in the Construction of Packaging and Food Transport Containers

by Steluța Radu and Stefan Lucian Toma

Coatings 2024, 14(11), 1431; https://doi.org/10.3390/coatings14111431 - 11 Nov 2024

Cited by 1 | Viewed by 1740

Abstract

A series of chemical elements from the chemical composition of the packs of liquid food products migrate inside them or they combine with other chemical elements existing in the food, resulting in chemical compounds that worsen the quality of the food. In the [...] Read more.

A series of chemical elements from the chemical composition of the packs of liquid food products migrate inside them or they combine with other chemical elements existing in the food, resulting in chemical compounds that worsen the quality of the food. In the present paper, layers of food stainless steel were deposited using thermal arc spraying on an aluminum alloy substrate to stop the migration of aluminum ions inside liquid food products. The physical-chemical and mechanical properties of the protection system: stainless steel layer used in the food industry (suggestively called: food-grade stainless steel)—aluminum substrate were investigated, and then the organoleptic properties of the food liquids that came into contact with the deposit were evaluated. It was found that food-gradestainless steel deposits have low porosity (3.8%) and relatively high adhesion and hardness, which allows complete isolation of the substrate material. The investigations carried out on the properties of food liquids that come into contact with the stainless steel deposit revealed the fact that it perfectly seals the aluminum start. The food-grade stainless steel coating (80T) was much better and safer for preserving dairy products maintaining a constant acidity up to 17 degrees Thorner, wines (with an average acidity of 3.5–4 degrees), juices (with natural pigments), and oils (with a good absorbance level correlated with clarity). This aspect suggests that the created system can be successfully used to manufacture containers for the transport of liquid products. Full article

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

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23 pages, 16310 KB

Open AccessEditor’s ChoiceArticle

Coupling APS/SPS Techniques for Cu-TiO₂ Antibacterial Coating Deposition: Application to Water Treatment

by Laurène Youssef, Audrey Prorot, Laurène Gnodé, Pierre Th’Madiou Verdieu, Armelle Vardelle, Vincent Rat and Alain Denoirjean

Coatings 2024, 14(11), 1426; https://doi.org/10.3390/coatings14111426 - 9 Nov 2024

Viewed by 2101

Abstract

Since the COVID-19 pandemic, efforts in the field of surface decontamination have been redoubled. Finding innovative self-cleaning devices has become a challenge, and several solutions have been proposed in the market in recent years. In this work, an optimized powder/suspension plasma spray process [...] Read more.

Since the COVID-19 pandemic, efforts in the field of surface decontamination have been redoubled. Finding innovative self-cleaning devices has become a challenge, and several solutions have been proposed in the market in recent years. In this work, an optimized powder/suspension plasma spray process at atmospheric pressure, using a Triplex Pro 210^TM torch, is implemented to produce Cu-TiO₂ surface coatings on stainless steel. The purpose is to investigate the potential improvement of antibacterial efficacy by the reactive surface species generated from TiO₂ photoactivity under irradiation. A water-based suspension, prepared with AnalaR NORMAPUR^TM TiO₂, is used as a precursor to incorporate the photocatalyst into an antibacterial copper matrix. Surface antibacterial tests according to ASTM 2180 standards were performed, and experiments were performed in treated contaminated water. Sub-stoichiometric blue TiO₂ coatings showed complete bacterial elimination after 90 min of visible light irradiation, and Cu-TiO₂ surface coatings were even able to disinfect the surfaces under white light, making the application interesting for bacterial destruction under natural illumination. These materials are also intended for application in water treatment, including both pathogens and chemical micropollutants, which is a pressing issue facing many countries today. Full article

(This article belongs to the Special Issue Advances in Thermal Spray Coatings: Technologies and Applications)

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13 pages, 4685 KB

Open AccessEditor’s ChoiceArticle

High-Performance SAW-Based Microfluidic Actuators Composed of Sputtered Al–Cu IDT Electrodes

by Hwansun Kim, Youngjin Lee, Peddathimula Puneetha, Sung Jin An, Jae-Cheol Park and Siva Pratap Reddy Mallem

Coatings 2024, 14(11), 1420; https://doi.org/10.3390/coatings14111420 - 8 Nov 2024

Viewed by 2565

Abstract

To realize highly sensitive SAW devices, novel Al–Cu thin films were developed using a combinatorial sputtering system. The Al–Cu sample library exhibited a wide range of chemical compositions and electrical resistivities, providing valuable insights for selecting optimal materials for SAW devices. Considering the [...] Read more.

To realize highly sensitive SAW devices, novel Al–Cu thin films were developed using a combinatorial sputtering system. The Al–Cu sample library exhibited a wide range of chemical compositions and electrical resistivities, providing valuable insights for selecting optimal materials for SAW devices. Considering the significant influence of electrode resistivity and density on acoustic wave propagation, an Al–Cu film with 65 at% Al was selected as the IDT electrode material. The selected Al–Cu film demonstrated a resistivity of 6.0 × 10⁻⁵ Ω-cm and a density of 4.4 g/cm³, making it suitable for SAW-based microfluidic actuator applications. XRD analysis revealed that the Al–Cu film consisted of a physical mixture of Al and Cu without the formation of Al–Cu alloy phases. The film exhibited a fine-grained microstructure with an average crystallite size of 7.5 nm and surface roughness of approximately 6 nm. The SAW device fabricated with Al–Cu IDT electrodes exhibited excellent acoustic performance, resonating at 143 MHz without frequency shift and achieving an insertion loss of −13.68 dB and a FWHM of 0.41 dB. In contrast, the Au electrode-based SAW device showed significantly degraded acoustic characteristics. Moreover, the SAW-based microfluidic module equipped with optimized Al–Cu IDT electrodes successfully separated 5 μm polystyrene (PS) particles even at high flow rates, outperforming devices with Au IDT electrodes. This enhanced performance can be attributed to the improved resonance characteristics of the SAW device, which resulted in a stronger acoustic radiation force exerted on the PS particles. Full article

(This article belongs to the Special Issue Thin Films and Nanostructures for Electronics)

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