Evaluation of the Cleaning Effect of Natural-Based Biocides: Application on Different Phototropic Biofilms Colonizing the Same Granite Wall
Dynamic Impact Resistance and Scratch Adhesion of AlCrN Coatings Sputtered Using Cathodic Arc Glow Discharge
Multifunctionalization and Increased Lifespan of a Worsted Wool Fabric
The Influence of Galvanizing on the Surface Quality and Part Precision of S235J0 Alloy Machined by Turning

Journal Description

Coatings

Coatings is a peer-reviewed journal of coatings and surface engineering published monthly online by MDPI. The Korean Tribology Society (KTS) is affiliated with Coatings and its members receive discounts on the article processing charges.

Open Access— free for readers, with article processing charges (APC) paid by authors or their institutions.
High Visibility: indexed within Scopus, SCIE (Web of Science), Inspec, CAPlus / SciFinder, and other databases.
Journal Rank: JCR - Q2 (Materials Science, Coatings & Films) / CiteScore - Q2 (Surfaces and Interfaces)
Rapid Publication: manuscripts are peer-reviewed and a first decision is provided to authors approximately 13.5 days after submission; acceptance to publication is undertaken in 3.5 days (median values for papers published in this journal in the second half of 2022).
Recognition of Reviewers: reviewers who provide timely, thorough peer-review reports receive vouchers entitling them to a discount on the APC of their next publication in any MDPI journal, in appreciation of the work done.
Sections: published in 15 topical sections.
Testimonials: See what our editors and authors say about Coatings.

Impact Factor: 3.236 (2021); 5-Year Impact Factor: 3.312 (2021)

Imprint Information Journal Flyer Open Access ISSN: 2079-6412

Latest Articles

Open AccessArticle

Rheological Properties of Composite Inorganic Micropowder Asphalt Mastic

and

Coatings 2023, 13(6), 1068; https://doi.org/10.3390/coatings13061068 (registering DOI) - 08 Jun 2023

Abstract

Graphene Tourmaline Composite Micropowder (hereinafter referred to as GTCM) modified asphalt was prepared by the ball milling method. The effects of different temperatures and different frequencies on the high-temperature performance of composite-modified asphalt were evaluated by dynamic shear rheological test, and the viscoelastic properties of composite-modified asphalt under different stresses and different temperatures were analyzed. The low-temperature rheological properties of GTCM-modified asphalt were analyzed by bending beam rheological test, and its mechanism was analyzed by Fourier transform infrared spectroscopy (FTIR) test. The results show that the temperature sensitivity and anti-aging resistance of GTCM-modified asphalt are significantly higher than that of tourmaline-modified asphalt. The improvement effect gradually increases with the increase in graphene powder content, and its addition does not change the viscoelastic properties of asphalt. The complex shear modulus and phase angle of GTCM-modified asphalt at appropriate temperatures are more conducive to tourmaline-modified asphalt and matrix asphalt, which can improve the rutting resistance of asphalt. In the same type, with the increase in composite modified micropowder content, the rutting resistance of modified asphalt is better. The improvement of rutting resistance of GTCM-0.5, GTCM-1.0 and GTCM-1.5-modified asphalt can reach 12.95%, 10.12% and 24.25%, respectively; the improvement range is more complicated due to temperature and frequency changes. The GTCM-modified asphalt has good low-temperature crack resistance. The creep stiffness modulus of GTCM-modified asphalt decreases with the increase in load time under different types and dosages, and its stiffness modulus is smaller than that of tourmaline-modified asphalt and mineral powder asphalt mastic. The creep rate increases with the extension of load time, which is greater than that of tourmaline-modified asphalt and mineral powder asphalt mastic. When the load was 60 s, the creep stiffness modulus of GTCM-0.5, GTCM-1.0 and GTCM-1.5-modified asphalt decreased by 5.75%, 6.97% and 13.73%, respectively, and the creep rate increased by 1.37%, 2.52% and 4.35%, respectively. After adding GTCM or tourmaline to the matrix asphalt, no new functional groups were produced due to the chemical reaction with the asphalt. Full article

(This article belongs to the Special Issue Recent Development in Novel Green Asphalt Materials for Pavement)

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Open AccessArticle

Extrusion-Based Additive Manufacturing of the Ti6Al4V Alloy Parts

and

Coatings 2023, 13(6), 1067; https://doi.org/10.3390/coatings13061067 (registering DOI) - 08 Jun 2023

Abstract

The paper shows the possibility of synthesizing microparticles coated with nanoparticles by electric explosion of a wire made of Ti-6Al-4V alloy. Particles in which the core is a microparticle and the shell of a nanoparticle can provide effective sliding of the microparticles relative to each other and are promising for obtaining flowable metal-polymer compositions filled with powder up to 70 vol.%. Such compositions are promising feedstocks for the additive molding of complex metal parts, for example, customized implants from the Ti-6Al-4V alloy, by material extrusion. The article describes the properties of feedstock based on micro- and nanoparticles of the Ti-6Al-4V alloy, the microstructure and some mechanical properties of sintered samples. The structure, bending strength and Vickers hardness of additively formed samples sintered at a temperature of 1200 °C was investigated. Full article

(This article belongs to the Special Issue Protective Composite Coatings: Implementation, Structure, Properties)

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Open AccessArticle

Prediction of Deposition Layer Morphology Dimensions Based on PSO-SVR for Laser–arc Hybrid Additive Manufacturing

and

Coatings 2023, 13(6), 1066; https://doi.org/10.3390/coatings13061066 - 08 Jun 2023

Abstract

Laser–arc composite additive manufacturing holds significant potential for a wide range of industrial applications, and the control of morphological dimensions in the deposited layer is a critical aspect of this technology. The width and height dimensions within the deposited layer of laser–arc hybrid additive manufacturing serve as essential indicators of its morphological characteristics, directly influencing the shape quality of the deposited layer. Accurate prediction of the shape dimensions becomes crucial in providing effective guidance for size control. To achieve precise prediction of shape dimensions in laser–arc composite additive manufacturing and ensure effective regulation of the deposited layer’s shape quality, this study introduces a novel approach that combines a particle swarm algorithm (PSO) with an optimized support vector regression (SVR) technique. By optimizing the SVR parameters through the PSO algorithm, the SVR model is enhanced and fine-tuned to accurately predict the shape dimensions of the deposited layers. In this study, a series of 25 laser–arc hybrid additive manufacturing experiments were conducted to compare different approaches. Specifically, the SVR model was built using selected radial basis function (rbf) kernel functions. Furthermore, the penalty factors and kernel parameters of the SVR model were optimized using the particle swarm optimization (PSO) algorithm, leading to the development of a PSO-SVR prediction model for the morphological dimensions of the deposited layers. The performance of the PSO-SVR model was compared with that of the SVR, BPNN, and LightGBM models. Model accuracy was evaluated using a test set, revealing average relative errors of 2.39%, 7.719%, 9.46%, and 5.356% for the PSO-SVR, SVR, BPNN, and LightGBM models, respectively. The PSO-SVR model exhibited excellent prediction accuracy with minimal fluctuations in prediction error. This performance demonstrates the model’s ability to effectively capture the intricate and non-linear relationship between process parameters and deposition layer dimensions. Consequently, the PSO-SVR model can provide a foundation for the control of morphological dimensions in the deposition layer, offering an effective guide for deposition layer morphology dimension control in laser–arc composite additive manufacturing. Full article

(This article belongs to the Special Issue Laser Surface Treatments and Additive Manufacturing)

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Open AccessFeature PaperArticle

Influence of Feedstock in the Formation Mechanism of Cold-Sprayed Copper Coatings

and

Coatings 2023, 13(6), 1065; https://doi.org/10.3390/coatings13061065 - 08 Jun 2023

Abstract

The aim of this article is to investigate the characterizations and formation mechanisms of cold-sprayed coatings using gas-atomized and electrolytic powders. The study highlights the importance of reaching the particles’ critical velocity for optimal deposition. The main findings reveal that the morphology and stacking conditions of the coatings have a significant impact on their mechanical properties. Coatings made with gas-atomized powders exhibited noticeable pores and higher plastic deformation, while electrolytic powder coatings had greater density and smoother interfaces with the substrate. Adhesion strength relied on the physical bonding resulting from the plastic deformation energy between the spraying powders and the substrate. Gas-atomized powders showed higher adhesion compared to electrolytic powders, with dendritic powders resulting in lower adhesion due to dispersed impact force. The interaction between thermal and kinetic energy during the cold spraying process facilitated plastic deformation and particle deposition by softening and eroding the substrate surface. Insufficient plastic deformation with dendritic powders led to incomplete overlap, pore formation at the interface, and the persistence of the oxide layer along powder boundaries. Overall, these findings provide valuable insights into the influence of powder properties on coating morphology, adhesion strength, and overall performance, contributing to the understanding and optimization of cold spray processes. Full article

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

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Open AccessArticle

Can Sodium Ascorbate Increase the In Vitro Bond Strength of the Interface between a Composite and Bleached Enamel?

Louis Hardan

Rim Bourgi

Carlos Enrique Cuevas-Suárez

and

Monika Lukomska-Szymanska

Coatings 2023, 13(6), 1064; https://doi.org/10.3390/coatings13061064 - 08 Jun 2023

Abstract

Recently, the use of antioxidants before the bonding of bleached enamel was considered effective for reversing the reduction in the bond strength. This article aimed to assess the influence of different sodium ascorbate (SA) presentations (liquid, gel, and semi-gel) on the composite resin–enamel bond strength after a bleaching protocol. Sound human anterior teeth were collected, cleaned, prepared for a bond strength test, and randomly allocated into groups according to the bonding procedure. Group 1 acted as a control, without bleaching treatment, and without applying an antioxidant agent. In groups 2–6, specimens were bleached using 10% carbamide peroxide. In groups 3, 4 and 5, 10% wt% SA was applied for 10 min as an antioxidant in the form of a liquid, gel, and semi-gel, respectively. In group 6, samples were bleached and immersed in fresh human saliva for 14 days. After the bleaching process, the materials were restored by means of an adhesive system and a resin composite material. The analysis revealed that the differences between the shear bond strength (SBS) between the different groups were statistically significant (p = 0.0469). The highest SBS was achieved for the group where the 10 wt% SA liquid was applied before the bonding procedures. The application of liquid 10 wt% SA might reverse the negative impact that bleaching has on the bond strength of a resin composite and enamel. Full article

(This article belongs to the Special Issue Surface Properties of Dental Materials and Instruments II)

Open AccessArticle

Effect of Sealing Treatment on Corrosion Resistance of Arc-Sprayed Zn and Zn85-Al15 Coatings

and

Coatings 2023, 13(6), 1063; https://doi.org/10.3390/coatings13061063 - 08 Jun 2023

Abstract

This study investigated the corrosion morphology of arc-sprayed Zn and Zn85-Al15 coatings with and without sealing treatment under simulated defect conditions. The hole sealing treatment was carried out by Conventional Impregnation Sealing (CIS). The performance of two coatings was assessed by employing morphological analysis, chemical composition, and electrochemical studies. The results showed that the corrosion performance of two coatings with sealing treatments was better than that of the un-sealing coating. Through the double protection of coating and sealing treatment, the defect-free material has excellent anti-corrosion performance in the salt spray experiment. In the simulated defect environment, the Zn-Al coating has better corrosion resistance, and the corrosion products are denser and more stable near the defects, which reduces the overall corrosion rate of the coating. The electrochemical experiment results demonstrated that the Zn-Al coating exhibited a three times lower corrosion rate compared to the Zn coating in the immersion experiment, and the corrosion rate did not change with the thickness of the coating. The average adhesion values of the two different methods (chilled iron and alumina) were similar (~8 MPa), but after the salt spray test, the adhesion strength increased. The corrosion mechanisms of Zn coating and Zn-Al coating are analyzed and compared. In general, it was indicated that the Zn85/Al15 coating prepared by sealing treatment has better corrosion resistance than the matrix steel. This study can provide some reference for corrosion behavior in defect environments. Full article

(This article belongs to the Special Issue Durability of Transmission Lines)

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Open AccessFeature PaperArticle

Highly Efficient and Stable CsPbBr₃-Alginic Acid Composites for White Light-Emitting Diodes

and

Coatings 2023, 13(6), 1062; https://doi.org/10.3390/coatings13061062 - 07 Jun 2023

Abstract

All-inorganic perovskite nanocrystals (NCs) have attractive potential for applications in display and lighting fields due to their special optoelectronic properties. However, they still suffer from poor water and thermal stability. In this work, green CsPbBr₃-alginic acid (CsPbBr₃-AA) perovskite composites were synthesized by an in situ hot-injection process which showed a high photoluminescence quantum yield (PLQY) of 86.43% and improved moisture and thermal stability. Finally, white light-emitting diodes (WLEDs) were fabricated by combining the green CsPbBr₃-AA perovskite composites with red K₂SiF₆:Mn⁴⁺ phosphors and blue InGaN LED chips. The WLEDs show a relatively high luminous efficacy of 36.4 lm/W and a wide color gamut (124% of the National Television System Committee). These results indicate that the green CsPbBr₃-AA perovskite composites have great potential applications in backlight displays. Full article

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

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Open AccessFeature PaperArticle

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

and

Coatings 2023, 13(6), 1061; https://doi.org/10.3390/coatings13061061 - 07 Jun 2023

Abstract

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

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

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Open AccessArticle

Data-Driven Method for Porosity Measurement of Thermal Barrier Coatings Using Terahertz Time-Domain Spectroscopy

and

Coatings 2023, 13(6), 1060; https://doi.org/10.3390/coatings13061060 - 07 Jun 2023

Abstract

Accurate measurement of porosity is crucial for comprehensive performance evaluation of thermal barrier coatings (TBCs) on aero-engine blades. In this study, a novel data-driven predictive method based on terahertz time-domain spectroscopy (THz-TDS) was proposed. By processing and extracting features from terahertz signals, multivariate parameters were composed to characterize the porosity. Principal component analysis, which enabled effective representation of the complex signal information, was introduced to downscale the dimensionality of the time-domain data. Additionally, the average power spectral density of the frequency spectrum and the extreme points of the first-order derivative of the phase spectrum were extracted. These extracted parameters collectively form a comprehensive set of multivariate parameters that accurately characterize porosity. Subsequently, the multivariate parameters were used as inputs to construct an extreme learning machine (ELM) model optimized by the sparrow search algorithm (SSA) for predicting porosity. Based on the experimental results, it was evident that the predictive accuracy of SSA-ELM was significantly higher than the basic ELM. Furthermore, the robustness of the model was evaluated through K-fold cross-validation and the final model regression coefficient was 0.92, which indicates excellent predictive performance of the data-driven model. By introducing the use of THz-TDS and employing advanced signal processing techniques, the data-driven model provided a novel and effective solution for the rapid and accurate detection of porosity in TBCs. The findings of this study offer valuable references for researchers and practitioners in the field of TBCs inspection, opening up new avenues for improving the overall assessment and performance evaluation of these coatings. Full article

(This article belongs to the Special Issue Nondestructive Evaluation of Material Surfaces: Theory, Techniques and Applications)

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Open AccessArticle

Hybrid Coating of Polystyrene–

{ZrO}_{2}

for Corrosion Protection of AM Magnesium Alloys

Luis Chávez

Lucien Veleva

Diana Sánchez-Ahumada

and

Rafael Ramírez-Bon

Coatings 2023, 13(6), 1059; https://doi.org/10.3390/coatings13061059 - 07 Jun 2023

Abstract

A hybrid material of polystyrene (PS)–

{ZrO}_{2}

was developed by the sol–gel technique and deposited by spin-coating on AM60 and AM60–AlN nanocomposite surfaces to enhance corrosion resistance in marine environments.

{PS - ZrO}_{2}

with an average thickness of ≈ [...] Read more.

A hybrid material of polystyrene (PS)–

{ZrO}_{2}

was developed by the sol–gel technique and deposited by spin-coating on AM60 and AM60–AlN nanocomposite surfaces to enhance corrosion resistance in marine environments.

{PS - ZrO}_{2}

with an average thickness of ≈

305 \pm 20 nm

was dispersed homogeneously, presenting isolated micro–nano-structure defects with air trapped inside, which led to an increase in roughness (≈4 times). The wettability of the coated substrates was close to the hydrophobic border (

θ_{CA} = 90 ° - 94 °) .

The coated samples were exposed for 30 days to SME solution, simulating the marine–coastal ambience. The initial pH = 7.94 of the SME shifted to more alkaline pH ≈ 8.54, suggesting the corrosion of the Mg matrix through the coating defects. In the meantime, the release of

{Mg}^{2 +}

from the

{PS - ZrO}_{2}

-coated alloy surfaces was reduced by ≈90% compared to that of non-coated. Localized pitting attacks occurred in the vicinity of Al–Mn and

{β - Mg}_{17} {Al}_{12}

cathodic particles characteristic of the Mg matrix. The depth of penetration (≈23 µm) was reduced by ≈85% compared to that of non-coated substrates. The protective effect against Cl ions, attributed to the hybrid PS–ZrO₂-coated AM60 and AM60–AlN surfaces, was confirmed by the increase in their polarization resistance (Rp) in 37% and 22%, respectively, calculated from EIS data. Full article

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

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Open AccessArticle

Correlation between the Rheological Properties of Asphalt Mortar and the High-Temperature Performance of Asphalt Mixture

and

Coatings 2023, 13(6), 1058; https://doi.org/10.3390/coatings13061058 - 07 Jun 2023

Abstract

The performance of an asphalt mixture is significantly affected by the properties of its asphalt mortar, which consists of an asphalt binder, mineral fillers, fine aggregates and air voids. The aim of this work was to evaluate the correlations between the high-temperature performance of an asphalt mixture and the rheological properties of its corresponding asphalt mortar. The multisequence repeated loading (MSRL) test was used to estimate the high-temperature performance of the asphalt mixture. Six different gradations, AC-13, SMA-13, SUP-13, AC-20, SUP-20 and AC-25, and two styrene–butadiene–styrene (SBS)-modified asphalt binders were considered and used to prepare the asphalt mixture specimens. The gradations and asphalt types of asphalt mortars were consistent with their asphalt mixtures. A modified multiple-stress creep–recovery (MSCR) test was proposed for evaluating the rheological properties of asphalt mortar with a dynamic shear rheometer (DSR). Based on the basic form of the Hirsh model, a multiple regression model was established, and its coefficient of determination (R-square) was 0.96. The rheological response of the asphalt mortar presented great correlation with the high-temperature behaviour of the asphalt mixture. In addition, the MSCR indicators (nonrecoverable compliance and percent recovery) obtained at 12.8 kPa creep stress represented the rheological status of asphalt mortar in asphalt mixture well. Therefore, the mechanical behaviours of asphalt mixture at high temperature could be accurately predicted by the MSCR indicators of asphalt mortar and its coarse aggregate parameters. Full article

(This article belongs to the Special Issue Asphalt Pavement: Materials, Design and Characterization)

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Open AccessArticle

Inhibition of Surface Corrosion Behavior of Zinc-Iron Alloy by Silicate Passivation

and

Coatings 2023, 13(6), 1057; https://doi.org/10.3390/coatings13061057 - 07 Jun 2023

Abstract

The passivation of zinc alloy coating was achieved through the utilization of both silicate and trivalent chromium passivation systems, employing a specific process formula consisting of Co(NO₃)₂ at a concentration of 2.5 g/L, C₇₆H₅₂O₄₆ at 3 mL/L, Na₂SiO₃ at 25 g/L, C₆H₅Na₃O₇ at 15 g/L, and an appropriate amount of organic accelerator. The composite passivation of silicate and tannic acid was found to be more effective than the trivalent chromium passivation film, as it successfully eliminated the dendrite structure on the coating surface and reduced surface defects. The coordination between negatively charged SiO²⁻ or SiO₂ micelles and Zn²⁺ results in the formation of a passivation film that exhibits lower corrosion current and higher corrosion potential compared to the trivalent chromium passivation film. Additionally, the impedance test fitting results indicate that the silicate passivation film possesses a higher resistance value. Overall, the proposed silicate passivation system presents a viable alternative to the toxic chromate passivation system, offering non-toxicity and superior protective performance relative to the trivalent chromium passivation system. Full article

(This article belongs to the Special Issue Advanced Corrosion Protection through Coatings and Surface Rebuilding)

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Open AccessArticle

Effect of Hot Spot within Combustion Liner on YSZ Crack Propagation Mode

and

Coatings 2023, 13(6), 1056; https://doi.org/10.3390/coatings13061056 - 07 Jun 2023

Abstract

On the aero-engine combustor liner, a phenomenon of overheating resembling a hot spot exists, accompanied by a preferential peeling of the YSZ thermal barrier coating that will negatively affect the service life of the component. The hot spot temperatures will affect the ineffectiveness of YSZ, so in this paper, the morphological and property changes of YSZ sintering is investigated experimentally, and a coupled analysis of the YSZ crack propagation mode under the hot spot is performed using ABAQUS. The results show that the pore fractal size D of YSZ increases by 15%. Inside the hot spot region, the coating has a shear stress of 75 MPa. By inserting cohesive units globally in the FEM to simulate the random crack initiation and propagation, unlike the thinning of YSZ layered peeling caused by uniform superheating, the hot spot will cause the crack initiation at the tip of the pores inside the coating and the oblique propagation, eventually forming an oblique crack connection through the pores. When the temperature gradient reaches 30 K/mm, the crack propagation is 40% greater than in a uniform temperature field; consequently, the YSZ in the hot spot boundary region with a greater temperature gradient results in more severe bulk peeling. Full article

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Open AccessCommunication

Beyond Cultivation: Combining Culture-Dependent and Culture-Independent Techniques to Identify Bacteria Involved in Paint Spoilage

and

Coatings 2023, 13(6), 1055; https://doi.org/10.3390/coatings13061055 - 07 Jun 2023

Abstract

Due to globally increasing problems concerning biodeterioration of paints, it is worthwhile to enhance the determination of colony forming units (CFU) as a gold standard method via more rapid and culture-independent techniques. Here, we combined traditional culture-dependent techniques with subsequent sequencing, quantitative qPCR, and a serial quantification method (most probable number; MPN) to detect paint degrading bacteria in general and sulfate-reducing bacteria (SRB) in particular. During our investigation of three water-based paints that showed visible contamination, we found high bacterial counts of up to 10⁷ CFU mL⁻¹. Subsequent sequencing allowed the identification of common paint degraders including Bacillus sp. and Pseudomonas sp., but less frequently detected bacteria such as Rhodococcus sp. and Delftia spp. were also found to be present. MPN, as well as dsrA-targeted qPCR to detect SRB, only showed positive results for two out of three samples. These results coincided with the inherent physicochemical properties of the paints offering suitable conditions for microbial growth or not. The MPN method can be used for a diversity of aerobic and anaerobic bacteria and is rapid and reproducible. A combination of culture-independent techniques such as qPCR or NGS can help to fully elucidate the bacterial diversity in spoiled paint by also recovering anaerobic and unculturable ones. Full article

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Open AccessArticle

Research on the Influence of Coating Technologies on Adhesion Anti-Corrosion Layers in the Case of Al7175 Aluminum Alloy

Aurel Mihail Titu

Sandor Ravai-Nagy

and

Alina Bianca Pop

Coatings 2023, 13(6), 1054; https://doi.org/10.3390/coatings13061054 - 06 Jun 2023

Abstract

A key element in ensuring the service life and strength of aluminum alloys in many industrial applications is the adhesion of anti-corrosion coatings. The aim of this study is to analyze how coating processes affect the adhesion of anti-corrosion coatings on aluminum alloy 7175. In other words, the influence of the nature of the elementary layers that form the anti-corrosion coating was studied for the following: the anodic layer, the primer, and the topcoat. To learn more about the different coating technologies and how they affect adhesion, a thorough literature review was carried out. In addition, a case study using electrocoating and thermal spraying was conducted to show the impact of coating processes on adhesion. The results showed that electrodeposition, as opposed to thermal spraying, improved the adhesion of anti-corrosion coatings. In the case of the aluminum alloy analyzed, there is a significant difference in terms of the adhesion strength of the anti-corrosion coatings. This resistance is influenced by both the anodic coating (BSA TSA SAA) and the type of primer and topcoat used (water-based or solvent-based). The correct choice of anode coat and primer and topcoat can lead to an increase (or decrease) in the adhesion strength of the paint coat by 20%. In conclusion, this study highlights how crucial it is to select the best coating process to maximize the adhesion and durability of aluminum alloys under corrosion conditions. Full article

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

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Open AccessArticle

Electrophoretic Deposition and Characterization of Er-Doped Bi₂O₃ Cathode Barrier Coatings on Non-Conductive Ce_0.8Sm_0.2O_1.9 Electrolyte Substrates

Elena Kalinina

Larisa Ermakova

and

Elena Pikalova

Coatings 2023, 13(6), 1053; https://doi.org/10.3390/coatings13061053 - 06 Jun 2023

Abstract

In this study, the formation of thin-film barrier coatings based on a highly conductive Bi_1.60Er_0.4O₃ (EDB) solid electrolyte on supporting Ce_0.8Sm_0.2O_1.9 (SDC) electrolyte substrates was implemented for the first time using electrophoretic deposition (EPD). The electrokinetic properties of EDB-based suspensions in a non-aqueous dispersion medium of isopropanol modified with small additions of polyethyleneimine (PEI, 0.26 g/L) and acetylacetone (0.15 g/L), as well as in a mixed isopropanol/acetylacetone (70/30 vol.%) medium, were studied. The dependences of the thickness of the EDB coatings on voltage and deposition time were obtained using deposition on a model Ni foil electrode. Preliminary synthesis of a conductive polypyrrole (PPy) polymer film was used to create surface conductivity on non-conductive SDC substrates. The efficiency of using a modified dispersion medium based on isopropanol to obtain a continuous EDB coating 12 μm thick, sintered at a temperature of 850 °C for 5 h, is shown. The microstructure and morphology of the surface of the EDB coating were studied. A Pt/SDC/EDB/Pt cell was used to characterize the coating’s conductivity. The EPD method is shown to be promising for the formation of barrier coatings based on doped bismuth oxide. The developed method can be used for creating cathode barrier layers in SOFC technology. Full article

(This article belongs to the Special Issue Electrochemical Deposition: Properties and Applications)

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Graphical abstract

Open AccessArticle

Metal-Free Catalytic Preparation of Graphene Films on a Silicon Surface Using CO as a Carbon Source in Chemical Vapor Deposition

and

Coatings 2023, 13(6), 1052; https://doi.org/10.3390/coatings13061052 - 06 Jun 2023

Abstract

The metal-free synthesis of graphene films on Si substrates, the most common commercial semiconductors, is of paramount significance for graphene application on semiconductors and in the field of electronics. However, since current research mainly uses C-H gas as the carbon source in chemical vapor deposition (CVD), and Si does not have a catalytic effect on the decomposition and adsorption of C-H gas, it is challenging to prepare high-quality graphene on the Si surface directly. In this work, we report the growth of graphene directly on Si without metal catalysis by CVD using CO was selected as the carbon source. By controlling the growth temperature (1000–1150 °C), a process of 2–5 layers of graphene growth on silicon was developed. The electrical performance results showed that the graphene film had a sheet resistance of 79 Ω/sq, a resistivity of 7.06 × 10⁻⁷ Ω·m, and a carrier migration rate of up to 1473.1 cm² V⁻¹·S⁻¹. This work would be a significant step toward the growth of graphene on silicon substrates with CO as the carbon source. Full article

(This article belongs to the Special Issue Graphite/Carbon: Surface Modification and Application)

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Open AccessArticle

Nonuniform Distribution of Crystalline Phases and Grain Sizes in the Surface Layers of WC Ceramics Produced by Spark Plasma Sintering

Yury V. Blagoveshchensky

Maksim S. Boldin

and

Vladimir N. Chuvil’deev

Coatings 2023, 13(6), 1051; https://doi.org/10.3390/coatings13061051 - 06 Jun 2023

Abstract

The research results conducted on binderless tungsten carbide (WC) ceramics obtained by spark plasma sintering (SPS) of WC powders with different average particle sizes (95, 800, 3000 nm) are presented. Nonuniform distribution of crystalline phases and microstructure of the WC ceramics was studied using layer-by-layer X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM). Surface layers of the WC-based ceramics are characterized by nonuniform distribution of W₂C crystalline phase and grain sizes, including the appearance of abnormally large grains. Thickness of the nonuniform layer was at least 50 μm. The effect under study is associated with an intense carbon diffusion from graphite foil. On the one hand, this contributed to a decrease in the intensity of W₂C phase particle formation, which is transformed into α-WC phase due to the carbon. On the other hand, it caused abnormal grain growth in the layer where the carbon diffused. The obtained value of the carbon diffusion depth (50 μm) exceeds the values known from the literature (up to 1 μm in the case of volume diffusion even at temperature of 2370 °C and exposure time of ~60 h). The use of boron nitride (BN) as a protective coating on graphite mold parts did not prevent the formation of nonuniform layer on the ceramic surface. Full article

(This article belongs to the Special Issue Trends in Spark Plasma Sintering of Advanced Materials)

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Open AccessArticle

Sunlight-Activated Long Persistent Luminescent Coating for Smart Highways

and

Coatings 2023, 13(6), 1050; https://doi.org/10.3390/coatings13061050 - 06 Jun 2023

Abstract

With the whole society’s demand for intelligence, the smart highway has become the inevitable trend of road development. Luminescent road marking made of long persistent luminescent coating is a new type of functional marking that is designed with long afterglow luminescent material as the raw material and has many features such as safety, beauty and energy saving. Here, SrA1₂O₄:Eu²⁺,Dy³⁺ green long afterglow phosphors were prepared using a high-temperature solid state method. The green phosphors obtained at 1350 °C have two traps with a shallow trap depth of 0.66 eV and a deep trap depth of 0.8 eV. The green afterglow can be seen in the dark for more than 8 h after sunlight excitation for 2 h. The green long persistent luminescent coatings were synthesized using the blending method. The uniformity of each component can be improved by adding 1.25% SiO₂ into the luminescent coatings. The addition of 3.5% CaCO₃ will improve the compactness of the coatings and reduce water absorption. After soaking in water for 120 h, the afterglow intensity of the coating decreases to 76% of the original, showing good water resistance. After daylight excitation in different weather conditions (cloudy, sunny, rainy), the afterglow can reach more than 5 h; therefore, it can be applied to a smart highway. Full article

(This article belongs to the Special Issue Ceramic Films and Coatings: Properties and Applications)

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Ice Adhesion Evaluation of PTFE Solid Lubricant Film Applied on TiO₂ Coatings

and

Coatings 2023, 13(6), 1049; https://doi.org/10.3390/coatings13061049 - 06 Jun 2023

Abstract

Ice formation affects the performance of many industrial components, including aircraft wings, spacecraft, and power transmission cables. In particular, ice build-up on airplane components increases drag and fuel consumption. A large number of studies have been carried out to reduce ice adhesion by developing passive methods such as icephobic coatings and active ice removal approaches such as mechanical vibrations or chemical-based solutions. Despite remarkable recent breakthroughs in the fabrication of icephobic coatings, passive ice removal solutions require higher durability to resist cyclical mechanical ice detachment treatments. Functionalized TiO₂ coatings, applied using the suspension plasma spray (SPS) technique, have been shown to be robust and to have dual-scale characteristics in an ice accretion analysis. In this study, the icephobicity and mechanical durability of a novel duplex coating consisting of polytetrafluoroethylene (PTFE) solid lubricant films on TiO₂-coated substrates were evaluated. Notably, various amounts of PTFE were applied on top of the TiO₂ coating to identify the ideal quantity required to obtain optimal icephobic properties. Ice was generated in an icing wind tunnel, and the amount of accreted ice was evaluated to assess the anti-icing properties. Wettability parameters, including static water contact angle and contact angle hysteresis, were measured to determine the water mobility and surface energy. Ice shear adhesion to the PTFE-TiO₂ duplex coating was measured using a custom-built test rig. The mechanical durability was assessed by measuring the ice shear strength for almost twenty icing–deicing cycles, and after five cycles, the roughness parameters and images taken from the surface of the samples were compared. The combination of PTFE solid lubricant film and TiO₂ coating reduced ice adhesion by 70%–90% compared to that of a bare aluminum substrate (reference material). Additionally, the results showed that the application of a uniform layer of PTFE solid lubricant film on dual-scale TiO₂ coating significantly reduced ice adhesion and maintained mechanical durability for 25 deicing cycles, making this combination a promising candidate for deicing approaches. Full article

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