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Editor’s Choice Articles

Editor’s Choice articles are based on recommendations by the scientific editors of MDPI journals from around the world. Editors select a small number of articles recently published in the journal that they believe will be particularly interesting to readers, or important in the respective research area. The aim is to provide a snapshot of some of the most exciting work published in the various research areas of the journal.

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10 pages, 5124 KB  
Article
Thick Columnar-Structured Thermal Barrier Coatings Using the Suspension Plasma Spray Process
by Dianying Chen and Christopher Dambra
Coatings 2024, 14(8), 996; https://doi.org/10.3390/coatings14080996 - 7 Aug 2024
Cited by 6 | Viewed by 2385
Abstract
Higher operating temperatures for gas turbine engines require highly durable thermal barrier coatings (TBCs) with improved insulation properties. A suspension plasma spray process (SPS) had been developed for the deposition of columnar-structured TBCs. SPS columnar TBCs are normally achieved at a short standoff [...] Read more.
Higher operating temperatures for gas turbine engines require highly durable thermal barrier coatings (TBCs) with improved insulation properties. A suspension plasma spray process (SPS) had been developed for the deposition of columnar-structured TBCs. SPS columnar TBCs are normally achieved at a short standoff distance (50.0 mm–75.0 mm), which is not practical when coating complex-shaped engine hardware since the plasma torch may collide with the components being sprayed. Therefore, it is critical to develop SPS columnar TBCs at longer standoff distances. In this work, a commercially available pressure-based suspension delivery system was used to deliver the suspension to the plasma jet, and a high-enthalpy TriplexPro-210 plasma torch was used for the SPS coating deposition. Suspension injection pressure was optimized to maximize the number of droplets injected into the hot plasma core and achieving the best particle-melting states and deposition efficiency. The highest deposition efficiency of 51% was achieved at 0.34 MPa injection pressure with a suspension flow rate of 31.0 g/min. With the optimized process parameters, 1000 μm thick columnar-structured SPS 8 wt% Y2O3-stabilized ZrO2 (8YSZ) TBCs were successfully developed at a standoff distance of 100.0 mm. The SPS TBCs have a columnar width between 100 μm and 300 μm with a porosity of ~22%. Furnace cycling tests at 1125 °C showed the SPS columnar TBCs had an average life of 1012 cycles, which is ~2.5 times that of reference air-plasma-sprayed dense vertically cracked TBCs with the same coating thickness. The superior durability of the SPS columnar TBCs can be attributed to the high-strain-tolerant microstructure. SEM cross-section characterization indicated the failure of the SPS TBCs occurred at the ceramic top coat and thermally grown oxide (TGO) interface. Full article
(This article belongs to the Special Issue Functional Coatings and Surface Science for Precision Engineering)
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12 pages, 2175 KB  
Article
Protection against Atmospheric Corrosion of Zinc in Marine Environment Rich in H2S Using Self-Assembled Monolayers Based on Sargassum fluitans III Extract
by Prescilla Lambert, Mahado Said-Ahmed, Benoit Lescop, Stéphane Rioual and Mounim Lebrini
Coatings 2024, 14(8), 988; https://doi.org/10.3390/coatings14080988 - 5 Aug 2024
Viewed by 1373
Abstract
The self-assembled monolayers (SAMs) process is one of the techniques used for the production of ultra-thin layers. The present work is therefore devoted to the study of the inhibition of zinc corrosion in a marine environment rich in H2S by SAMs [...] Read more.
The self-assembled monolayers (SAMs) process is one of the techniques used for the production of ultra-thin layers. The present work is therefore devoted to the study of the inhibition of zinc corrosion in a marine environment rich in H2S by SAMs based on Sargassum fluitans III. The protective effect of crude extracts of Sargassum fluitans on the surface of zinc using the SAMs process was evaluated by gravimetry and impedance on two different sites after three months of exposure. The formation of SAMs was characterized by FTIR, and the corrosion products formed on the surfaces were analyzed by XRD. The results obtained show that SAMs based on Sargassum fluitans III effectively inhibit zinc corrosion. Full article
(This article belongs to the Section Corrosion, Wear and Erosion)
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16 pages, 3022 KB  
Article
Data-Driven Optimization of Plasma Electrolytic Oxidation (PEO) Coatings with Explainable Artificial Intelligence Insights
by Patricia Fernández-López, Sofia A. Alves, Aleksey Rogov, Aleksey Yerokhin, Iban Quintana, Aitor Duo and Aitor Aguirre-Ortuzar
Coatings 2024, 14(8), 979; https://doi.org/10.3390/coatings14080979 - 3 Aug 2024
Cited by 2 | Viewed by 2529
Abstract
PEO constitutes a promising surface technology for the development of protective and functional ceramic coatings on lightweight alloys. Despite its interesting advantages, including enhanced wear and corrosion resistances and eco-friendliness, the industrial implementation of PEO technology is limited by its relatively high energy [...] Read more.
PEO constitutes a promising surface technology for the development of protective and functional ceramic coatings on lightweight alloys. Despite its interesting advantages, including enhanced wear and corrosion resistances and eco-friendliness, the industrial implementation of PEO technology is limited by its relatively high energy consumption. This study explores the development and optimization of novel PEO processes by means of machine learning (ML) to improve the coating thickness. For this purpose, ML models random forest and XGBoost were employed to predict the thickness of the developed PEO coatings based on the key process variables (frequency, current density, and electrolyte composition). The predictive performance was significantly improved by including the composition of the used electrolyte in the models. Furthermore, Shapley values identified the pulse frequency and the TiO2 concentration in the electrolyte as the most influential variables, with higher values leading to increased coating thickness. The residual analysis revealed a certain heteroscedasticity, which suggests the need for additional samples with high thickness to improve the accuracy of the model. This study reveals the potential of artificial intelligence (AI)-driven optimization in PEO processes, which could pave the way for more efficient and cost-effective industrial applications. The findings achieved further emphasize the significance of integrating interactions between variables, such as frequency and TiO2 concentration, into the design of processing operations. Full article
(This article belongs to the Special Issue Functional Films/Coatings Processing Technologies: Deposition and Process)
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18 pages, 12340 KB  
Article
High-Temperature Mechanical and Tribological Performance of W-DLC Coating with Cr interlayer on X40CrMoV5-1 Hot Work Tool Steel
by Mária Hagarová, Gabriela Baranová, Mária Heželová, Martin Truchlý, Marek Vojtko, Ondrej Petruš and Dávid Csík
Coatings 2024, 14(8), 971; https://doi.org/10.3390/coatings14080971 - 2 Aug 2024
Cited by 5 | Viewed by 2081
Abstract
Diamond-like carbon (DLC) coatings enhance tool wear resistance across various temperatures. The sp3/sp2 bond ratio within DLC significantly impacts its properties and thermal stability. Elevated temperatures can alter DLC’s structure, while metallic elements and interlayers like chromium can modify its [...] Read more.
Diamond-like carbon (DLC) coatings enhance tool wear resistance across various temperatures. The sp3/sp2 bond ratio within DLC significantly impacts its properties and thermal stability. Elevated temperatures can alter DLC’s structure, while metallic elements and interlayers like chromium can modify its microstructure and performance. To evaluate the potential of W-DLC coatings with a chromium interlayer on 40CrMoV5-1 hot work tool steel under elevated temperatures, mechanical and tribological properties were assessed at room temperature and at temperatures of 100, 200, 300, 400, and 500 °C. Nanoindentation revealed a maximum hardness of 14.1 ± 1.3 GPa for the coating deposited at room temperature, attributed to a high sp3 content confirmed by Raman spectroscopy. Hardness decreased to 9.3 ± 1.0 GPa at 400 °C due to graphitization. The elastic modulus remained relatively constant across all temperatures. Tribological tests indicated a low coefficient of friction (CoF) of 0.15 at room temperature, increasing to 0.35 at 100 °C. The CoF further rose to 0.5 at 200 °C, coinciding with increased graphitization. However, the CoF reduced to 0.45 and 0.35 at 400 °C and 500 °C, respectively, likely due to the formation of a WO3 tribo-film and the protective effect of the chromium interlayer. Full article
(This article belongs to the Special Issue Oxidation, Wear, Corrosion Behaviors and Activated Bonding Properties of Coatings Deposited on Metals)
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13 pages, 8603 KB  
Article
Natural Tannin Layers for the Corrosion Protection of Steel in Contact with Water-Based Media
by Rossella Sesia, Silvia Spriano, Marco Sangermano, Massimo Calovi, Stefano Rossi and Sara Ferraris
Coatings 2024, 14(8), 965; https://doi.org/10.3390/coatings14080965 - 2 Aug 2024
Cited by 3 | Viewed by 3098
Abstract
Numerous strategies have been developed for the corrosion protection of steel; however, most of them have a significant environmental impact and employ toxic compounds. Tannins are a green and promising solution for sustainable corrosion protection strategies. In this context, this work was focused [...] Read more.
Numerous strategies have been developed for the corrosion protection of steel; however, most of them have a significant environmental impact and employ toxic compounds. Tannins are a green and promising solution for sustainable corrosion protection strategies. In this context, this work was focused on natural (condensed and hydrolysable) tannin layers as a possible corrosion protection strategy for carbon steel. The impact of the tannins’ dissolution medium (ultrapure water or Phosphate-Buffered Saline), surface pre-treatment (acid pickling or plasma), and deposition technology (dipping or spin coating) on layer homogeneity and adhesion has been evaluated. The effects of these parameters on coating formation, homogeneity, and adhesion have been investigated by means of visual inspections, swabbing, Fourier Transformed Infrared spectroscopy (FTIR), Scanning Electron Microscopy equipped with Energy Dispersive Spectroscopy (SEM-EDS) and tape adhesion tests. Preliminary electrochemical corrosion tests have been performed on the most promising material (carbon steel acid pickled and coated with a hydrolysable tannin solved in water by spin coating) to estimate the protective ability of the developed layers and highlight the main criticisms to be overcome. Full article
(This article belongs to the Special Issue Advanced Anticorrosion Coatings and Coating Testing)
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14 pages, 11328 KB  
Article
High-Temperature Zn-5Al Hot Dip Galvanizing of Reinforcement Steel
by Anżelina Marek, Veronika Steinerová, Petr Pokorný, Henryk Kania and Franciszek Berger
Coatings 2024, 14(8), 959; https://doi.org/10.3390/coatings14080959 - 1 Aug 2024
Cited by 2 | Viewed by 2086
Abstract
This article presents the results of research on the growth kinetics, microstructure (SEM/EDS/XRD), and corrosion behavior of Zn-5Al coatings obtained using a high-temperature hot dip process on B500B reinforcing steel. The corrosion resistance of the coatings was determined using the neutral salt spray [...] Read more.
This article presents the results of research on the growth kinetics, microstructure (SEM/EDS/XRD), and corrosion behavior of Zn-5Al coatings obtained using a high-temperature hot dip process on B500B reinforcing steel. The corrosion resistance of the coatings was determined using the neutral salt spray (NSS) test (EN ISO 9227). Based on chemical composition tests in micro-areas (EDS) and phase composition tests (XRD), corrosion products formed on the coating surface after exposure to a corrosive environment containing chlorides were identified. In the outer layer of the coating, areas rich in Zn and Al were found, which were solid solutions of Al in Zn (α), while the diffusion layer was formed by a layer of Fe(Al,Zn)3 intermetallics. The growth kinetics of the coatings indicate the sequential growth of the diffusion layer, controlled by diffusion in the initial phase of growth, and the formation of a periodic layered structure with a longer immersion time. The NSS test showed an improved corrosion resistance of reinforcing bars with Zn-5Al coatings compared to a conventional hot-dip-galvanized zinc coating. The increase in corrosion resistance was caused by the formation of beneficial corrosion products: layered double hydroxides (LDH) based on Zn2+ and Al3+ cations and Cl− anions and simonkolleite—Zn5(OH)8Cl2·H2O. Full article
(This article belongs to the Special Issue High-Temperature Corrosion and Oxidation of Metals and Alloys)
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22 pages, 78862 KB  
Article
Fatigue Behaviour and Life Prediction of YSZ Thermal Barrier Coatings at Elevated Temperature under Cyclic Loads
by Qiannan Tao, Yanrong Wang and Yu Zheng
Coatings 2024, 14(8), 960; https://doi.org/10.3390/coatings14080960 - 1 Aug 2024
Cited by 5 | Viewed by 2085
Abstract
The concentration of interfacial normal stress at the free edges of thermal barrier coatings (TBCs) can result in coating spallation. Fatigue cracking is one of the main reasons for creating free edges under complex loads. It is crucial to investigate the fatigue cracking [...] Read more.
The concentration of interfacial normal stress at the free edges of thermal barrier coatings (TBCs) can result in coating spallation. Fatigue cracking is one of the main reasons for creating free edges under complex loads. It is crucial to investigate the fatigue cracking of coatings under cyclic loads to assess potential coating failure. To address this issue, a novel model was proposed to predict the fatigue life of the YSZ topcoat under stress parallel to the interface. Firstly, this study conducted uniaxial and tensile-torsional fatigue tests at elevated temperatures on specimens with atmospheric plasma-sprayed TBCs. The test results revealed that fatigue cracks appeared in the topcoat under cyclic loads, but these cracks did not propagate into the bondcoat or substrate immediately. The number of cycles before the topcoat cracked was found to be associated with the magnitude of the cyclic load. Secondly, this study analyzed the test conditions using the finite element method. Simulations indicated that the crack direction in the topcoat under complex loading conditions was aligned with the first principal stress direction. Finally, the fatigue life prediction model of the topcoat was established based on experiments and simulations. The predicted results fell within a fourfold scatter band. Full article
(This article belongs to the Section Surface Characterization, Deposition and Modification)
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14 pages, 9409 KB  
Article
The Effects of Nitrogen Content on the Mechanical and Tribological Properties of CrTaWNx Thin Films
by Li-Chun Chang, Li-Zhu Wang and Yung-I Chen
Coatings 2024, 14(8), 939; https://doi.org/10.3390/coatings14080939 - 26 Jul 2024
Cited by 2 | Viewed by 1212
Abstract
In the study described herein, CrTaWNx thin films were deposited on Si and 304 stainless-steel (SUS304) substrates through magnetron co-sputtering using CrW and Ta targets. The nitrogen flow ratio (fN2 = [N2/(N2 + Ar)]) was adjusted to [...] Read more.
In the study described herein, CrTaWNx thin films were deposited on Si and 304 stainless-steel (SUS304) substrates through magnetron co-sputtering using CrW and Ta targets. The nitrogen flow ratio (fN2 = [N2/(N2 + Ar)]) was adjusted to 0.05, 0.2, 0.4, and 0.5 to fabricate CrTaWNx films with various N contents. The CrTaWNx films prepared at a low fN2 of 0.05 exhibited a low stoichiometric ratio x of 0.16 and a nanocrystalline structure. In contrast, the CrTaWNx films fabricated at an fN2 of 0.2–0.5 exhibited x values of 0.42–0.62 and formed a face-centered cubic phase. The nanocrystalline (Cr0.34Ta0.20W0.46)N0.16 film exhibited mechanical properties and wear resistances that were inferior to those of the crystalline CrTaWNx thin films. A (Cr0.38Ta0.15W0.47)N0.55 film exhibited a hardness of 25.2 GPa, an elastic modulus of 289 GPa, and a low wear rate of 0.51 × 10−5 mm3/Nm. Full article
(This article belongs to the Special Issue Thin-Film Synthesis, Characterization and Properties)
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10 pages, 9460 KB  
Article
Influence of Oxygen Flow Rate on the Phase Structures and Properties for Copper Oxide Thin Films Deposited by RF Magnetron Sputtering
by Junghwan Park, Young-Guk Son, Chang-Sik Son and Donghyun Hwang
Coatings 2024, 14(8), 930; https://doi.org/10.3390/coatings14080930 - 25 Jul 2024
Cited by 2 | Viewed by 2191
Abstract
This study examines the impact of varying oxygen flow rates on the properties of Cu2O thin films deposited via radio frequency (RF) magnetron sputtering. X-ray diffraction (XRD) analysis showed a phase transition from cubic Cu2O to a mixed Cu [...] Read more.
This study examines the impact of varying oxygen flow rates on the properties of Cu2O thin films deposited via radio frequency (RF) magnetron sputtering. X-ray diffraction (XRD) analysis showed a phase transition from cubic Cu2O to a mixed Cu2O and CuO phase, eventually forming a Cu4O3 tetragonal structure as oxygen content increased. The surface morphology and cross-sectional structure of Cu2O thin films observed through field emission scanning electron microscopy (FE-SEM) were found to vary significantly depending on the oxygen flow rate. X-ray photoelectron spectroscopy (XPS) indicated notable variations in the chemical states of copper and oxygen. The Cu 2p spectra revealed peaks around 933 eV and 953 eV for all samples, with the S01 sample (deposited with only argon gas) exhibiting the lowest intensity. The S02 sample showed the highest peak intensity, which then gradually decreased from S03 to S06. The O 1s spectra followed a trend with peak intensity being highest in S02 and decreasing with further oxygen flow rates, indicating the formation of complex oxides such as Cu4O3. UV-Vis-NIR spectroscopy results demonstrated a decrease in transmittance and optical band gap energy with increasing oxygen content, suggesting a decline in crystallinity and an increase in defects and impurities. These findings underscore the critical role of precise oxygen flow rate control in tailoring the structural, morphological, compositional, and optical properties of Cu2O thin films for specific electronic and optical applications. Full article
(This article belongs to the Special Issue Magnetron Sputtering Coatings: From Materials to Applications)
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19 pages, 15991 KB  
Article
Amorphous Alumina ALD Coatings for the Protection of Limestone Cultural Heritage Objects
by Gillian P. Boyce, Suveena Sreenilayam, Eleonora Balliana, Elisabetta Zendri and Raymond J. Phaneuf
Coatings 2024, 14(8), 931; https://doi.org/10.3390/coatings14080931 - 25 Jul 2024
Cited by 1 | Viewed by 1977
Abstract
From natural erosion to pollution-accelerated decay, stone cultural heritage deteriorates constantly through interactions with the environment. Common protective treatments such as acrylic polymers are generally prone to degradation and loss of performance, and they are often limited in their ability to achieve uniform [...] Read more.
From natural erosion to pollution-accelerated decay, stone cultural heritage deteriorates constantly through interactions with the environment. Common protective treatments such as acrylic polymers are generally prone to degradation and loss of performance, and they are often limited in their ability to achieve uniform and conformal coverage across a stone’s topographical features. In this work, atomic layer deposition (ALD) was explored to address these issues by growing protective amorphous alumina coatings on compact carbonate (Istria) stone. ALD protective coatings, unlike coatings produced by traditional methods, do not significantly alter morphology by filling open pores or accumulating on the surface in more compact areas. Our morphological and spectroscopic investigations revealed that the ALD alumina films deposited uniformly over the surfaces of Istria stone, without significantly altering the topography or appearance. The protective effects of the ALD coatings were investigated by aqueous acid immersion. The solution pH, along with the Ca2+ concentration, was tracked over time for a constant volume of acetic acid solution with an initial pH of 4 with the stone samples immersed. We found that the protective effects of ALD alumina coatings were extremely promising, slowing the average rate of pH evolution significantly. The eventual failure of the ALD coatings during immersion was also investigated, with interesting morphological findings that point to the role of defects in the coatings, suggesting new directions for improving the use of ALD coatings in future research and applications. Full article
(This article belongs to the Special Issue Recent Advances in Chemical Vapor Deposition)
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18 pages, 6306 KB  
Article
Self-Assembled Pd Nanocomposites into a Monolayer for Enhanced Sensing Performance
by Mohammad Navvabpour, Pierre-Michel Adam, Safi Jradi and Suzanna Akil
Coatings 2024, 14(8), 934; https://doi.org/10.3390/coatings14080934 - 25 Jul 2024
Cited by 4 | Viewed by 1319
Abstract
To date, the advanced synthetic approaches for palladium nanoparticle-based catalysts involve multistep, toxic, and high-cost fabrication routes with low catalytic and sensing performance. In this work, we introduce a new one-shot approach to produce highly sensitive Pd nanocomposites using a large-area polymer self-assembly [...] Read more.
To date, the advanced synthetic approaches for palladium nanoparticle-based catalysts involve multistep, toxic, and high-cost fabrication routes with low catalytic and sensing performance. In this work, we introduce a new one-shot approach to produce highly sensitive Pd nanocomposites using a large-area polymer self-assembly strategy. This synthesis method allowed us to control the Pd nanoparticle shape and to tailor their plasmonic band positions in a wide light spectral range from ~350 to ~800 nm. We thus determined the critical synthesis conditions that give rise to a ringlike morphology in a reproducible manner. No need for a reducing agent and preliminary functionalization of the surface supporting the nanoparticles upon synthesis. To the best of our knowledge, few works have demonstrated the good performance of PdNPs in sensing. Here, we have demonstrated a robust SERS response for 4-mercaptopyridine with an enhancement factor of 4.2 × 105. We were able to exceed this high value, which matches the current maximum found in the literature, by decreasing the gap distances between Pd nanorings due to the high density of hotspots and the exacerbation of the coupling effect between PdNPs. These tailored products provide new insights for the use of Pd nanomaterials in photocatalysis applications, according to the well-established catalytic performance of Pd materials obtained in this work. Full article
(This article belongs to the Section Surface Engineering for Energy Harvesting, Conversion, and Storage)
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24 pages, 5687 KB  
Article
CMAS Corrosion Resistance of Plasma-Sprayed YSZ and Yb2O3-Y2O3-Co-Stabilized ZrO2 Coatings under 39–40 KW Spraying Power
by Wenkang Zhang, Wei Liu, Yangguang Liu, Weize Wang, Ting Yang, Kaibin Li, Junhao Wang, Xiaoqin Zhang, Shilong Yang, Pengpeng Liu and Chengcheng Zhang
Coatings 2024, 14(8), 928; https://doi.org/10.3390/coatings14080928 - 24 Jul 2024
Cited by 1 | Viewed by 1725
Abstract
This study uses atmospheric plasma spraying (APS) technology to prepare thermal barrier coatings (TBCs) with yttrium-stabilized zirconia (YSZ) and Yb2O3-Y2O3-co-stabilized ZrO2 (YbYSZ) materials at different spraying powers. It analyzes the differences and changes in [...] Read more.
This study uses atmospheric plasma spraying (APS) technology to prepare thermal barrier coatings (TBCs) with yttrium-stabilized zirconia (YSZ) and Yb2O3-Y2O3-co-stabilized ZrO2 (YbYSZ) materials at different spraying powers. It analyzes the differences and changes in the microstructure, thermodynamic properties, and mechanical properties of the TBCs. The CaO-MgO-Al2O3-SiO2 (CMAS) resistance of coatings was tested using thermal cycling-CMAS experiments and isothermal corrosion experiments. Compared to YSZ coatings, YbYSZ coatings have lower thermal conductivity, a higher hardness and elastic modulus, a longer lifetime under thermal cycling-CMAS conditions, and lower penetration and degradation depths. Under thermal cycling-CMAS coupling conditions, the optimal power range for the longest thermal cycling lifetime for both coatings is 39–40 kW. Overall, compared to the YSZ material, the YbYSZ material exhibits superior properties. Full article
(This article belongs to the Section Corrosion, Wear and Erosion)
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22 pages, 6636 KB  
Article
Chemical and UV Durability of Hydrophobic and Icephobic Surface Layers on Femtosecond Laser Structured Stainless Steel
by Roland Fürbacher, Gabriel Grünsteidl, Andreas Otto and Gerhard Liedl
Coatings 2024, 14(8), 924; https://doi.org/10.3390/coatings14080924 - 23 Jul 2024
Cited by 1 | Viewed by 1722
Abstract
Femtosecond laser processing significantly alters the surface structure and chemical composition, impacting its wetting properties. Post-treatments such as immersion in a hydrocarbon liquid (petrol) or storage in a vacuum can significantly reduce ice adhesion, making the surfaces interesting for anti-ice applications. This study [...] Read more.
Femtosecond laser processing significantly alters the surface structure and chemical composition, impacting its wetting properties. Post-treatments such as immersion in a hydrocarbon liquid (petrol) or storage in a vacuum can significantly reduce ice adhesion, making the surfaces interesting for anti-ice applications. This study investigates their durability against acetone, ethylene glycol, and UV radiation. The laser-structured surfaces were immersed in the respective liquids for up to 48 h. The results indicate limited durability of the superhydrophobic and icephobic layers when submerged in acetone and ethylene glycol, with more favorable results for petrol treatment than vacuum treatment. Similar results were obtained after 100 h of UV exposure, showing a decrease in superhydrophobic properties and an increase in ice adhesion. However, repeated vacuum treatments conducted after the chemical durability tests revealed the potential for partial recovery of the hydrophobic and icephobic properties. XPS analysis was performed throughout the experiments to evaluate changes in surface chemistry resulting from the post-laser treatments and the durability tests. Full article
(This article belongs to the Special Issue Recent Advances in Hydrophobic Surface and Materials)
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12 pages, 3243 KB  
Article
Effects of Precursors Ratio and Curing Treatment on the Icephobicity of Polydimethylsiloxane
by Marcella Balordi, Alessandro Casali, Paolo Gadia, Paolo Pelagatti, Francesco Pini and Giorgio Santucci de Magistris
Coatings 2024, 14(7), 901; https://doi.org/10.3390/coatings14070901 - 18 Jul 2024
Viewed by 1604
Abstract
Elastomers are intriguing materials for many applications, one of these being icephobic coatings. Elastic modulus and work of adhesion are the key parameters coming into play in ice detachment mechanisms, and can be related to hardness and wettability. Polydimethylsiloxane (PDMS) is widely used [...] Read more.
Elastomers are intriguing materials for many applications, one of these being icephobic coatings. Elastic modulus and work of adhesion are the key parameters coming into play in ice detachment mechanisms, and can be related to hardness and wettability. Polydimethylsiloxane (PDMS) is widely used for anti-ice applications; however, not many works deal with the correlation between cross-linking grade, curing treatments, and icephobicity. This study focuses on PDMS (Sylgard184®) coatings, encompassing four different pre-polymer to cross-linking agent (A:B) ratios ranging from 5:1 to 30:1, and nine curing treatments. The results indicate that increasing the A:B ratio enhances hydrophobicity, softness, and icephobicity, assessed through shear stress measurements. Curing treatments primarily affect hardness and icephobicity, with longer heat treatments resulting in higher hardness and ice adhesion. All samples exhibit promising performances in lowering shear stress values, up to seven times in respect to the uncoated reference for 30:1 ratio. Additionally, a durability assessment is conducted on samples exposed to stress tests in the climatic chamber. A slight deterioration in hydrophobicity across all samples is observed and, notably, a significant hardness increase, around 13%, is experienced for the 5:1 ratio only. The samples also demonstrate an overall robust icephobicity after stress tests, and, for the 30:1 ratio, an average shear stress value four times lower than the reference is maintained. In this work, we highlight the importance of the fine-tuning of the precursors ratio and thermal treatments on the PDMS properties and durability. Full article
(This article belongs to the Section Surface Characterization, Deposition and Modification)
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15 pages, 7208 KB  
Article
Chemical Bonding of Nanorod Hydroxyapatite to the Surface of Calciumfluoroaluminosilicate Particles for Improving the Histocompatibility of Glass Ionomer Cement
by Sohee Kang, So Jung Park, Sukyoung Kim and Inn-Kyu Kang
Coatings 2024, 14(7), 893; https://doi.org/10.3390/coatings14070893 - 17 Jul 2024
Cited by 3 | Viewed by 1340
Abstract
Glass ionomer cement (GIC) is composed of anionic polyacrylic acid and a silica-based inorganic powder. GIC is used as a filling material in the decayed cavity of the tooth; therefore, compatibility with the tooth tissue is essential. In the present study, we aimed [...] Read more.
Glass ionomer cement (GIC) is composed of anionic polyacrylic acid and a silica-based inorganic powder. GIC is used as a filling material in the decayed cavity of the tooth; therefore, compatibility with the tooth tissue is essential. In the present study, we aimed to improve the histocompatibility of GIC by introducing nano-hydroxyapatite (nHA), a component of teeth, into a silica-based inorganic powder. CFAS-nHA was prepared by chemically bonding nanorod hydroxyapatite (nHA) to the surface of calciumfluoroaluminosilicate (CFAS). The synthesis of CFAS-nHA was confirmed using Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The prepared CFAS-nHA was mixed with polyacrylic acid and cured to prepare GIC containing nHA (GIC-nHA). Cytocompatibility tests of GIC-nHA and GIC were performed using osteoblasts. Osteoblast activity and bone formation ability were superior after GIC-nHA treatment than after control GIC treatment. This enhanced histocompatibility is believed to be due to the improvement of the biological activity of osteoblasts induced by the HA introduced into the GIC. Therefore, to enhance its compatibility with dental tissues, GIC could be manufactured by chemically bonding nHA to the surface of GI inorganic powder. Full article
(This article belongs to the Special Issue Advanced Biomaterials and Coatings)
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22 pages, 4157 KB  
Article
Characterization of Indium Tin Oxide (ITO) Thin Films towards Terahertz (THz) Functional Device Applications
by Anup Kumar Sahoo, Wei-Chen Au and Ci-Ling Pan
Coatings 2024, 14(7), 895; https://doi.org/10.3390/coatings14070895 - 17 Jul 2024
Cited by 5 | Viewed by 4179
Abstract
In this study, we explored the manipulation of optical properties in the terahertz (THz) frequency band of radio-frequency (RF) sputtered indium tin oxide (ITO) thin films on highly resistive silicon substrate by rapid thermal annealing (RTA). The optical constants of as-deposited and RTA-processed [...] Read more.
In this study, we explored the manipulation of optical properties in the terahertz (THz) frequency band of radio-frequency (RF) sputtered indium tin oxide (ITO) thin films on highly resistive silicon substrate by rapid thermal annealing (RTA). The optical constants of as-deposited and RTA-processed ITO films annealed at 400 °C, 600 °C and 800 °C are determined in the frequency range of 0.2 to 1.0 THz. The transmittance can be changed from ~27% for as-deposited to ~10% and ~39% for ITO films heat-treated at different annealing temperatures (Ta’s). Such variations of optical properties in the far infrared for the samples under study are correlated with their mobility and carrier concentration, which are extracted from Drude–Smith modeling of THz conductivity with plasma frequency, scattering time and the c-parameters as fitting parameters. Resistivities of the films are in the range of 10−3 to 10−4 Ω-cm, confirming that annealed ITO films can potentially be used as transparent conducting electrodes for photonic devices operating at THz frequencies. The highest mobility, μ = 47 cm2/V∙s, with carrier concentration, Nc = 1.31 × 1021 cm−3, was observed for ITO films annealed at Ta = 600 °C. The scattering times of the samples were in the range of 8–21 fs, with c-values of −0.63 to −0.87, indicating strong backscattering of the carriers, mainly by grain boundaries in the polycrystalline film. To better understand the nature of these films, we have also characterized the surface morphology, microscopic structural properties and chemical composition of as-deposited and RTA-processed ITO thin films. For comparison, we have summarized the optical properties of ITO films sputtered onto fused silica substrates, as-deposited and RTA-annealed, in the visible transparency window of 400–800 nm. The optical bandgaps of the ITO thin films were evaluated with a Tauc plot from the absorption spectra. Full article
(This article belongs to the Special Issue Thermoelectric Thin Films for Thermal Energy Harvesting)
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21 pages, 6113 KB  
Article
Exploring Heterointerface Characteristics and Charge-Storage Dynamics in ALD-Developed Ultra-Thin TiO2-In2O3/Au Heterojunctions
by Mohammad Karbalaei Akbari, Nasrin Siraj Lopa and Serge Zhuiykov
Coatings 2024, 14(7), 880; https://doi.org/10.3390/coatings14070880 - 14 Jul 2024
Viewed by 1320
Abstract
Directional ionic migration in ultra-thin metal-oxide semiconductors under applied electric fields is a key mechanism for developing various electronic nanodevices. However, understanding charge transfer dynamics is challenging due to rapid ionic migration and uncontrolled charge transfer, which can reduce the functionality of microelectronic [...] Read more.
Directional ionic migration in ultra-thin metal-oxide semiconductors under applied electric fields is a key mechanism for developing various electronic nanodevices. However, understanding charge transfer dynamics is challenging due to rapid ionic migration and uncontrolled charge transfer, which can reduce the functionality of microelectronic devices. This research investigates the supercapacitive-coupled memristive characteristics of ultra-thin heterostructured metal-oxide semiconductor films at TiO2-In2O3/Au Schottky junctions. Using atomic layer deposition (ALD), we nano-engineered In2O3/Au-based metal/semiconductor heterointerfaces. TEM studies followed by XPS elemental analysis revealed the chemical and structural characteristics of the heterointerfaces. Subsequent AFM studies of the hybrid heterointerfaces demonstrated supercapacitor-like behavior in nanometer-thick TiO2-In2O3/Au junctions, resembling ultra-thin supercapacitors, pseudocapacitors, and nanobatteries. The highest specific capacitance of 2.6 × 104 F.g−1 was measured in the TiO2-In2O3/Au junctions with an amorphous In2O3 electron gate. Additionally, we examined the impact of crystallization, finding that thermal annealing led to the formation of crystalline In2O3 films with higher oxygen vacancy content at TiO2-In2O3 heterointerfaces. This crystallization process resulted in the evolution of non-zero I-V hysteresis loops into zero I-V hysteresis loops with supercapacitive-coupled memristive characteristics. This research provides a platform for understanding and designing adjustable ultra-thin Schottky junctions with versatile electronic properties. Full article
(This article belongs to the Special Issue Advanced Films and Coatings Based on Atomic Layer Deposition)
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13 pages, 4598 KB  
Article
Magnetron Sputtered Low-Platinum Loading Electrode as HER Catalyst for PEM Electrolysis
by Antía Villamayor, Alonso Alba, Laura V. Barrio, Sergio Rojas and Eva Gutierrez-Berasategui
Coatings 2024, 14(7), 868; https://doi.org/10.3390/coatings14070868 - 11 Jul 2024
Cited by 2 | Viewed by 2650
Abstract
The development of cost-effective components for Proton Exchange Membrane (PEM) electrolyzers plays a crucial role in the transformation of renewable energy into hydrogen. To achieve this goal, two main issues should be addressed: reducing the Platinum Group Metal (PGM) content present on the [...] Read more.
The development of cost-effective components for Proton Exchange Membrane (PEM) electrolyzers plays a crucial role in the transformation of renewable energy into hydrogen. To achieve this goal, two main issues should be addressed: reducing the Platinum Group Metal (PGM) content present on the electrodes and finding a large-scale electrode manufacturing method. Magnetron sputtering could solve these hurdles since it allows the production of highly pure thin films in a single-step process and is a well-established industrial and automated technique for thin film deposition. In this work, we have developed an ultra-low 0.1 mg cm−2 Pt loading electrode using magnetron sputtering gas aggregation method (MSGA), directly depositing the Pt nanoparticles on top of the carbon substrate, followed by a complete evaluation of the electrochemical properties of the sputtered electrode. These ultra-low Pt content electrodes have been thoroughly characterized and tested in a real electrolyzer cell. They demonstrate similar efficiency to commercial electrodes with a Pt content of 0.3 mg/cm2, achieving a 67% reduction in Pt loading. Additionally, durability tests indicate that these electrodes offer greater stability compared to their commercial counterparts. Thus, magnetron sputtering has been proven as a promising technology for manufacturing optimum high-performance electrodes at an industrial scale. Full article
(This article belongs to the Special Issue Synthesis, Characterization and Performance Enhancement of Electrode Coatings for Energy Sustainability)
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9 pages, 4872 KB  
Article
Enhancing Wear Resistance of A390 Aluminum Alloy: A Comprehensive Evaluation of Thermal Sprayed WC, CrC, and Al2O3 Coatings
by Jaehui Bang and Eunkyung Lee
Coatings 2024, 14(7), 853; https://doi.org/10.3390/coatings14070853 - 8 Jul 2024
Cited by 5 | Viewed by 1837
Abstract
This study comparatively analyzed the wear characteristics and adhesion properties of 86WC–10Co–4Cr (WC) coatings deposited using the high velocity oxygen fuel process and 75Cr3C2–25NiCr (CrC) and Al2O3–3TiO2 (Al2O3) coatings deposited [...] Read more.
This study comparatively analyzed the wear characteristics and adhesion properties of 86WC–10Co–4Cr (WC) coatings deposited using the high velocity oxygen fuel process and 75Cr3C2–25NiCr (CrC) and Al2O3–3TiO2 (Al2O3) coatings deposited using the atmospheric plasma spray process on an A390 aluminum alloy substrate. The adhesion strength and wear test results demonstrated that the WC coating exhibited superior wear resistance. In contrast, the CrC and Al2O3 coatings showed lower adhesion properties and unstable frictional variations due to a higher number of defects compared to the WC coating. The WC coating layer, protected by WC particles, exhibited minimal damage and a low wear rate, followed by CrC and Al2O3. Ultimately, WC coating is highlighted as the optimal choice to enhance the wear resistance of A390 aluminum alloy. Full article
(This article belongs to the Special Issue Additive Manufacturing of Metallic Components for Hard Coatings)
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16 pages, 13325 KB  
Article
Effect of NOX and SOX Contaminants on Corrosion Behaviors of 304L and 316L Stainless Steels in Monoethanolamine Aqueous Amine Solutions
by Eleni Lamprou, Fani Stergioudi, Georgios Skordaris, Nikolaos Michailidis, Evie Nessi, Athanasios I. Papadopoulos and Panagiotis Seferlis
Coatings 2024, 14(7), 842; https://doi.org/10.3390/coatings14070842 - 5 Jul 2024
Cited by 2 | Viewed by 2357
Abstract
This work is devoted to evaluating the corrosion behaviors of SS 304L and SS 316L in monoethanolamine solutions (MEA) containing SOX and NOX pollutants, examining both lean and CO2-loaded conditions at 25 °C and 40 °C. Electrochemical techniques (potentiodynamic [...] Read more.
This work is devoted to evaluating the corrosion behaviors of SS 304L and SS 316L in monoethanolamine solutions (MEA) containing SOX and NOX pollutants, examining both lean and CO2-loaded conditions at 25 °C and 40 °C. Electrochemical techniques (potentiodynamic and cyclic polarization) were used along with Scanning Electron Microscopy, Confocal Microscopy and weight loss measurements. The results reveal that the introduction of SOX and NOX pollutants increased the corrosion rate, whereas CO2 loading primarily reduced the corrosion resistance in the lean MEA solution, while its impact on solutions with SOX and NOX was less pronounced. This suggests that SOX and NOX play primary roles in the metal’s dissolution. Also, SS 316L demonstrated superior corrosion resistance compared to 304L in nearly all of the cases examined. Elevated temperatures were also found to intensify the corrosion rate, indicating a correlation between the corrosion rate and temperature. A microscopic observation and EDX analysis revealed that corrosion products are characterized by high concentrations of iron (Fe) and oxygen (O) as well as carbon (C). There is also an indication of the possible formation of amine complexes, suggesting a potential for amine degradation. No pitting corrosion was observed in SS 304L and SS 316L across any tested solution. Finally, the immersion results expose a tendency for passivity in all amine solutions and at both temperatures after several days of exposure. Moreover, they confirm the very low corrosion rate calculated from potentiodynamic curves due to minimal weight loss after 24 days of immersion. Full article
(This article belongs to the Collection Feature Paper Collection in Surface Characterization, Deposition and Modification)
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11 pages, 5061 KB  
Article
Interface Engineering Induced N, P-Doped Carbon-Shell-Encapsulated FeP/NiP2/Ni5P4/NiP Nanoparticles for Highly Efficient Hydrogen Evolution Reaction
by Ting Zhang, Jianguo Zhong, Wei Gao and Yuxin Wang
Coatings 2024, 14(7), 817; https://doi.org/10.3390/coatings14070817 - 1 Jul 2024
Cited by 3 | Viewed by 1812
Abstract
Modifying the electronic structure of a catalyst through interface engineering is an effective strategy to enhance its activity in the hydrogen evolution reaction (HER). Interface engineering is a viable strategy to enhance the catalytic activity of transition metal phosphides (TMPs) in the HER [...] Read more.
Modifying the electronic structure of a catalyst through interface engineering is an effective strategy to enhance its activity in the hydrogen evolution reaction (HER). Interface engineering is a viable strategy to enhance the catalytic activity of transition metal phosphides (TMPs) in the HER process. The interface-engineered FeP/NiP2/Ni5P4/NiP multi-metallic phosphide nanoparticles confined in a N, P-doped carbon matrix was developed by a simple one-step low-temperature phosphorization treatment, which only requires 72 and 155 mV to receive the current density of 10 mA/cm2 in acid and alkaline electrolyte, respectively. This enhanced performance can be primarily attributed to the heterointerface of FeP/NiP2/Ni5P4/NiP multi-metallic phosphides, which promotes electron redistribution and optimizes the adsorption/desorption strength of H* on the active sites. Furthermore, the N, P-doped carbon framework that encapsulates the nanoparticles inhibits their aggregation, leading to an increased availability of active sites throughout the reaction. The results of this study open up a straightforward and innovative approach to developing high-performance catalysts for hydrogen production. Full article
(This article belongs to the Section Surface Engineering for Energy Harvesting, Conversion, and Storage)
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12 pages, 3290 KB  
Article
Anti-Corrosion SiOx-Doped DLC Coating for Raster Steel Linear Scales
by Algirdas Lazauskas, Viktoras Grigaliūnas, Dalius Jucius, Šarūnas Meškinis, Mindaugas Andrulevičius, Asta Guobienė, Andrius Vasiliauskas and Albinas Kasparaitis
Coatings 2024, 14(7), 818; https://doi.org/10.3390/coatings14070818 - 1 Jul 2024
Cited by 2 | Viewed by 1714
Abstract
In this study, we investigated the efficacy of SiOx-doped diamond-like carbon (DLC) films for enhancing the corrosion resistance of raster steel linear scales. The research work highlights the significant role of DLC film materials in enhancing corrosion resistance, making them a [...] Read more.
In this study, we investigated the efficacy of SiOx-doped diamond-like carbon (DLC) films for enhancing the corrosion resistance of raster steel linear scales. The research work highlights the significant role of DLC film materials in enhancing corrosion resistance, making them a promising solution for various industrial applications. The Raman spectroscopy analysis of SiOx-doped DLC films, synthesized via a direct ion beam technique with HMDSO vapor, revealed prominent D and G bands characteristic of amorphous carbon materials, with a high degree of disorder indicated by an ID/IG ratio of 1.85. X-ray diffraction patterns confirmed the amorphous nature of the SiOx-doped DLC films and the minimal impact of the DLC deposition process on the underlying crystalline structure of steel. UV–Vis-NIR reflectance spectra of SiOx-doped DLC on stainless steel demonstrated improvements in the blue wavelength region compared to stainless steel with ripples alone, which is beneficial for applications utilizing blue light. Corrosion tests, including immersion in a 5% salt solution and salt spray testing, showed that SiOx-doped DLC-coated stainless steel exhibited superior corrosion resistance compared to uncoated steel, with no significant signs of corrosion observed after extended exposure. These findings underscore the potential of SiOx-doped DLC coatings to provide long-term corrosion protection and maintain the structural integrity and surface quality of steel components in harsh environments. Full article
(This article belongs to the Special Issue Recent Developments on Functional Coatings for Industrial Applications, Volume II)
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12 pages, 4831 KB  
Article
Lifetime Extension of Atmospheric and Suspension Plasma-Sprayed Thermal Barrier Coatings in Burner Rig Tests by Pre-Oxidizing the CoNiCrAlY Bond Coats
by Jens Igel, Walter Sebastian Scheld, Daniel Emil Mack, Olivier Guillon and Robert Vaßen
Coatings 2024, 14(7), 793; https://doi.org/10.3390/coatings14070793 - 26 Jun 2024
Cited by 1 | Viewed by 2076
Abstract
Oxidation of the bond coat during turbine operation leads to additional stresses in the thermal barrier coating (TBC) system that promotes spalling of the thermal insulation. Therefore, the oxidation behavior of a TBC system plays an important role in the thermal cycling of [...] Read more.
Oxidation of the bond coat during turbine operation leads to additional stresses in the thermal barrier coating (TBC) system that promotes spalling of the thermal insulation. Therefore, the oxidation behavior of a TBC system plays an important role in the thermal cycling of a TBC system. To delay the loss of thermal insulation, research has typically focused for a long time on the composition and microstructure of the ceramic topcoats and metallic bond coats. More recently, heat treatment for the diffusion annealing of the bond coat has also become a focus of research. Several studies have shown that pre-oxidation of the bond coat prior to the application of the ceramic topcoat slows down the subsequent oxidation of the bond coat in service. The improved thermal cyclability has been demonstrated in studies for systems with atmospheric plasma-sprayed (APS), suspension plasma-sprayed (SPS) or electron beam physical vapor deposition (EB-PVD) top coatings. However, no study has directly compared the effects of pre-oxidation on different topcoats. Therefore, this study compared the effect of pre-oxidation on APS and SPS coatings with the same bond coat. For both topcoats, pre-oxidation slowed the subsequent TGO growth and thus increased the lifetime of the coatings. The improvement in lifetime was particularly pronounced for the systems with an SPS topcoat. Overall, the lifetime of the coatings with an APS topcoat was higher as the critical energy release rate within the coating was not exceeded in these coatings. Full article
(This article belongs to the Section Plasma Coatings, Surfaces & Interfaces)
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17 pages, 8596 KB  
Article
Corrosion Efficiency of Zn-Ni/ZrO2 and Zn-Co/ZrO2 Bi-Layer Systems: Impact of Zn-Alloy Sublayer Thickness
by Nelly Boshkova, Daniela Stoyanova, Irina Stambolova, Ognian Dimitrov, Sylviya Simeonova, Georgi Avdeev, Miglena Peshova, Vasil Bachvarov, Sonya Smrichkova and Nikolai Boshkov
Coatings 2024, 14(7), 792; https://doi.org/10.3390/coatings14070792 - 25 Jun 2024
Cited by 2 | Viewed by 1807
Abstract
The presented manuscript demonstrates the effect of the thickness of a zinc alloy sublayer on the corrosion resistance and stability of three types of bi-layer systems composed of Co- or Ni-modified zinc coatings (both as sublayers) and a top sol–gel ZrO2 film [...] Read more.
The presented manuscript demonstrates the effect of the thickness of a zinc alloy sublayer on the corrosion resistance and stability of three types of bi-layer systems composed of Co- or Ni-modified zinc coatings (both as sublayers) and a top sol–gel ZrO2 film in a 5% NaCl solution. In order to obtain more detailed information, the alloy sublayers were electrodeposited with three different thicknesses (1, 5 and 10 µm, respectively) on a low-carbon steel substrate. Three consecutive dip-coated ZrO2 sol–gel layers were deposited thereafter on the individual zinc alloy sublayers. For comparison, an ordinary electrodeposited zinc coating was obtained and investigated. The aim of this study was to evaluate the effect of the thickness of the zinc-based sublayer on the protective characteristics of the bi-layer systems. The surface morphology features and the phase composition of the latter systems were examined using scanning electron microscopy (SEM), atomic force microscopy (AFM), water contact angle (WCA) measurements and X-ray diffraction (XRD) analyses. The corrosion stability was evaluated by means of potentiodynamic polarization (PDP) curves and polarization resistance (Rp) measurements. The zirconia finish layers possessed an amorphous, dense and hydrophobic nature, while the sublayers were multicrystalline. The results confirmed the increased corrosion resistance of the protective system, which contains electrodeposited sublayer of Zn-Co alloy with a 10 µm thickness in a corrosive test medium. 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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18 pages, 7606 KB  
Article
Symbiosis of Sulfate-Reducing Bacteria and Total General Bacteria Affects Microbiologically Influenced Corrosion of Carbon Steel
by Juxing Jin, Yingchao Li, Huaiwei Huang, Yong Xiang and Wei Yan
Coatings 2024, 14(7), 788; https://doi.org/10.3390/coatings14070788 - 24 Jun 2024
Cited by 3 | Viewed by 1800
Abstract
The effects of the symbiosis of sulfate-reducing bacteria (SRB) and total general bacteria (TGB) on the microbiologically influenced corrosion (MIC) of carbon steel were investigated in this research. The SRB was the main corrosive bacterium, and TGB induced slightly general MIC. The symbiosis [...] Read more.
The effects of the symbiosis of sulfate-reducing bacteria (SRB) and total general bacteria (TGB) on the microbiologically influenced corrosion (MIC) of carbon steel were investigated in this research. The SRB was the main corrosive bacterium, and TGB induced slightly general MIC. The symbiosis of SRB and TGB induced more severe MIC and pitting corrosion than SRB. The main corrosion products were FeS, Fe2O3, and FeOOH. The presence of TGB facilitates MIC and pitting corrosion by providing a locally anaerobic shelter for SRB. An MIC mechanism of the symbiosis of SRB and TGB was proposed. Full article
(This article belongs to the Special Issue Investigation on Structure and Corrosion Resistance of Steels/Alloys)
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19 pages, 11634 KB  
Article
Tribological Properties and Surface Wettability of Coatings Produced on the Mg-AZ31B Alloy by Plasma Electrolytic Oxidation
by Mateusz Niedźwiedź, Marek Bara, Joanna Korzekwa, Sławomir Kaptacz, Maciej Sowa, Aleksander Olesiński and Wojciech Simka
Coatings 2024, 14(7), 780; https://doi.org/10.3390/coatings14070780 - 21 Jun 2024
Cited by 5 | Viewed by 2043
Abstract
This paper presents the influence of plasma electrolytic oxidation parameters (peak current density, process time, pulse frequency) on the tribological properties and surface wettability of the produced coatings. The process parameters were selected in accordance with Hartley’s research plan for three input variables [...] Read more.
This paper presents the influence of plasma electrolytic oxidation parameters (peak current density, process time, pulse frequency) on the tribological properties and surface wettability of the produced coatings. The process parameters were selected in accordance with Hartley’s research plan for three input variables with three variable values. Oxide coatings were made on the AZ31B magnesium alloy using a trapezoidal voltage waveform and a two-component alkaline electrolyte. The tribological properties of the coatings were determined as a result of tribological tests carried out on the T-17 tester in reciprocating motion. The tribological partner for the coatings was a PEEK/HPV pin. As a result of tribological tests, the friction coefficient µ, the mass wear of the pin and the average change in sample mass were determined. The tests showed changes in both the friction coefficient and pin wear. Before and after tribological tests, profilographometric measurements of the coatings were performed. The tests allowed for the determination of roughness parameters and the load–bearing curve of the sample surfaces. Surface wettability tests were carried out by determining the contact angles. Full article
(This article belongs to the Special Issue Surface Engineering, Coatings and Tribology)
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13 pages, 8128 KB  
Article
Enhancing Tribological Performance of Micro-Arc Oxidation Coatings on 6061 Aluminum Alloy with h-BN Incorporation
by Xia Zhao, Jingfu Song, Jingyi Lin, Guoqing Wang and Gai Zhao
Coatings 2024, 14(6), 771; https://doi.org/10.3390/coatings14060771 - 19 Jun 2024
Cited by 5 | Viewed by 1677
Abstract
Micro-arc oxidation (MAO) coatings of aluminum alloy have great potential applications due to their high hardness and wear resistance. However, the micro-pores and defects formed in the discharge channels during the MAO process limit its application in the corrosion field. This study delves [...] Read more.
Micro-arc oxidation (MAO) coatings of aluminum alloy have great potential applications due to their high hardness and wear resistance. However, the micro-pores and defects formed in the discharge channels during the MAO process limit its application in the corrosion field. This study delves into the impact of h-BN nanoparticles into MAO coatings on their structure, corrosion resistance, phase composition, and tribological properties. The results show that the incorporation of h-BN particles reduces the porosity and surface roughness of the coating while enhancing its hardness and wear resistance. The best corrosion resistance is obtained at a concentration of 2 g/L h-BN. An analysis of worn surface morphology, corrosion resistance, and friction coefficient change was conducted to evaluate the performance of this coating. This method provides a new approach to enhance the surface hardness and wear resistance of aluminum alloys, which is significant for expanding the application of aluminum alloys in corrosion environments. Full article
(This article belongs to the Special Issue Tribological Behavior and Mechanical Performance of Coatings and Materials)
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21 pages, 21058 KB  
Article
Tribocatalytic Reaction Enabled by TiO2 Nanoparticle for MoDTC-Derived Tribofilm Formation at ta-C/Steel Contact
by Daiki Matsukawa, Jae-Hyeok Park, Woo-Young Lee, Takayuki Tokoroyama, Jae-Il Kim, Ryoichi Ichino and Noritsugu Umehara
Coatings 2024, 14(6), 773; https://doi.org/10.3390/coatings14060773 - 19 Jun 2024
Cited by 2 | Viewed by 2268
Abstract
Tribochemically produced triboproducts are becoming increasingly important in tribosystems and serve to improve system performance by preventing friction or wear. Diamond-like carbon (DLC) is chemically stable, which features a trade-off with tribological pros and cons. Chemically stable DLC is thermally stable and suppresses [...] Read more.
Tribochemically produced triboproducts are becoming increasingly important in tribosystems and serve to improve system performance by preventing friction or wear. Diamond-like carbon (DLC) is chemically stable, which features a trade-off with tribological pros and cons. Chemically stable DLC is thermally stable and suppresses surface damage in a high-temperature operating environment; however, it causes a detrimental effect that hinders the formation of a competent tribofilm. In this study, we dispersed highly reactive TiO2 nanoparticles (TDONPs) in molybdenum dithiocarbamate (MoDTC)-containing lubricant for adhering triboproducts on the DLC surface. In addition, TDONPs contributed to the decomposition of triboproducts by promoting the decomposition of MoDTC through its catalytic role. Rutile TDONPs were more helpful in reducing friction than anatase TDONPs and improved the friction performance by up to ~100%. Full article
(This article belongs to the Special Issue Advanced Tribological Coatings: Fabrication and Application)
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16 pages, 19888 KB  
Article
A Deep Learning Image Corrosion Classification Method for Marine Vessels Using an Eigen Tree Hierarchy Module
by Georgios Chliveros, Iason Tzanetatos and Stylianos V. Kontomaris
Coatings 2024, 14(6), 768; https://doi.org/10.3390/coatings14060768 - 18 Jun 2024
Cited by 3 | Viewed by 2588
Abstract
This paper involves the automation of a visual characterisation technique for corrosion in marine vessels, as it appears in the hull preventive coatings of marine vessels and their surfaces. We propose a module that maximizes the utilisation of features learned by a deep [...] Read more.
This paper involves the automation of a visual characterisation technique for corrosion in marine vessels, as it appears in the hull preventive coatings of marine vessels and their surfaces. We propose a module that maximizes the utilisation of features learned by a deep convolutional neural network to identify areas of corrosion and segment pixels in regions of inspection interest for corrosion detection. Our segmentation module is based on Eigen tree decomposition and information-based decision criteria in order to produce specific corroded spots—regions of interest. To assess performance and compare it with our method, we utilize several state-of-the-art deep learning architectures.The results indicate that our method achieves higher accuracy and precision while maintaining the significance score across the entire dataset. To the best of our knowledge, this is the first Eigen tree-based module in the literature in the context of trained neural network predictors for classifying corrosion in marine vessel images. 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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19 pages, 21066 KB  
Article
The Influence of Bias Voltage and Gas Pressure on Edge Covering during the Arc-PVD Deposition of Hard Coatings
by Otmar Zimmer, Tim Krülle and Thomas Litterst
Coatings 2024, 14(6), 732; https://doi.org/10.3390/coatings14060732 - 7 Jun 2024
Cited by 1 | Viewed by 1854
Abstract
The edge area is especially essential for cutting tools, since this is the contact zone between the work piece and the tool. Hard coatings (PVD or CVD coatings) can protect the edge against wear and they are commonly used. The geometries of the [...] Read more.
The edge area is especially essential for cutting tools, since this is the contact zone between the work piece and the tool. Hard coatings (PVD or CVD coatings) can protect the edge against wear and they are commonly used. The geometries of the cutting edges change during the coating process, with the edge radius increasing. Therefore, the film thickness is limited and the initial radius of the uncoated tool must be smaller than the target radius of the coated edge. A new coating process based on vacuum arc PVD was developed to overcome this limitation. The film growth at the edges can be properly controlled by means of selected coating materials and process conditions. Thus, it is possible to grow edges sharper than the initial edge geometry. Different substrates were coated with different coating systems. Parameters such as the bias voltage, coating pressure, and initial radius were varied within this work. It was found that the application of a bias voltage is crucial for the generation of sharp edges. It was also found that the edge sharpening caused by coatings works best on samples with an initial radius of around 15 µm. Full article
(This article belongs to the Special Issue Advanced Coating Technology by Physical Vapor Deposition and Applications)
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18 pages, 6375 KB  
Article
Automated Crack Detection in 2D Hexagonal Boron Nitride Coatings Using Machine Learning
by Md Hasan-Ur Rahman, Bichar Dip Shrestha Gurung, Bharat K. Jasthi, Etienne Z. Gnimpieba and Venkataramana Gadhamshetty
Coatings 2024, 14(6), 726; https://doi.org/10.3390/coatings14060726 - 6 Jun 2024
Cited by 3 | Viewed by 2981
Abstract
Characterizing defects in 2D materials, such as cracks in chemical vapor deposited (CVD)-grown hexagonal boron nitride (hBN), is essential for evaluating material quality and reliability. Traditional characterization methods are often time-consuming and subjective and can be hindered by the limited optical contrast of [...] Read more.
Characterizing defects in 2D materials, such as cracks in chemical vapor deposited (CVD)-grown hexagonal boron nitride (hBN), is essential for evaluating material quality and reliability. Traditional characterization methods are often time-consuming and subjective and can be hindered by the limited optical contrast of hBN. To address this, we utilized a YOLOv8n deep learning model for automated crack detection in transferred CVD-grown hBN films, using MATLAB’s Image Labeler and Supervisely for meticulous annotation and training. The model demonstrates promising crack-detection capabilities, accurately identifying cracks of varying sizes and complexities, with loss curve analysis revealing progressive learning. However, a trade-off between precision and recall highlights the need for further refinement, particularly in distinguishing fine cracks from multilayer hBN regions. This study demonstrates the potential of ML-based approaches to streamline 2D material characterization and accelerate their integration into advanced devices. Full article
(This article belongs to the Special Issue Advances in Nanostructured Thin Films and Coatings, 2nd Edition)
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20 pages, 13497 KB  
Article
Effects of Dynamic Flow Rates on the In Vitro Bio-Corrosion Behavior of Zn-Cu Alloy
by Xin Zhang, Lu Zhang, Linyuan Han, Jing Bai, Zhihai Huang, Chao Guo, Feng Xue, Paul K. Chu and Chenglin Chu
Coatings 2024, 14(6), 711; https://doi.org/10.3390/coatings14060711 - 5 Jun 2024
Cited by 4 | Viewed by 1319
Abstract
In the complicated real physiological environment in vivo, body fluids and blood are constantly replenished and move dynamically, and therefore, the dynamic impacts of bodily fluids and blood need to be considered in the evaluation of biodegradable materials. However, little research has [...] Read more.
In the complicated real physiological environment in vivo, body fluids and blood are constantly replenished and move dynamically, and therefore, the dynamic impacts of bodily fluids and blood need to be considered in the evaluation of biodegradable materials. However, little research has been conducted on the impact of dynamic flowing circumstances on the corrosion characteristics of zinc-based alloys, particularly at high flow rates. The effects of various flow rates on the bio-corrosion behavior of the Zn-Cu alloy are thoroughly explored in this study. A model is developed using finite element analysis to investigate the impacts of flow rates and fluid-induced shear stress. The results reveal that the corrosion process of the Zn-Cu alloy is significantly accelerated by a higher flow rate, and a large fluid-induced shear stress caused by the boundary effect is found to promote corrosion. Furthermore, the empirical power function between the average flare rates in Hank’s solution and the corrosion rates of the Zn-Cu alloy is established by numerical simulation. The results provide insightful theoretical and experimental guidance to improve and evaluate the efficacy and lifespan of biomedical zinc-based alloy implants. Full article
(This article belongs to the Section Corrosion, Wear and Erosion)
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17 pages, 10024 KB  
Article
Exploring the Impact of Spray Process Parameters on Graphite Coatings: Morphology, Thickness, and Tribological Properties
by Adedoyin Abe, Josue A. Goss and Min Zou
Coatings 2024, 14(6), 714; https://doi.org/10.3390/coatings14060714 - 5 Jun 2024
Cited by 5 | Viewed by 2586
Abstract
This study explores, through a full factorial experimental design, the effects of graphite concentration and spray flow rate on the morphology, thickness, and tribological performance of graphite coatings for potential tribological applications. Coatings were applied to rough substrates using varying concentrations and flow [...] Read more.
This study explores, through a full factorial experimental design, the effects of graphite concentration and spray flow rate on the morphology, thickness, and tribological performance of graphite coatings for potential tribological applications. Coatings were applied to rough substrates using varying concentrations and flow rates, followed by analysis of their morphological characteristics, roughness, thickness, coefficient of friction (COF), and wear behavior. The results revealed distinct differences in the coating morphology based on flow rate, with low-flow-rate coatings exhibiting a porous structure and higher roughness, while high-flow-rate coatings displayed denser structures with lower roughness. A COF as low as 0.09 was achieved, which represented an 86% reduction compared to uncoated steel. COF and wear track measurements showed that thickness was influential in determining friction and the extent of wear. Flow rate dictated the coating structure, quantity of transfer film on the ball, and the extent of graphite compaction in the wear track to provide a protective layer. SEM and elemental analysis further revealed that graphite coatings provided effective protection against wear, with graphite remaining embedded in the innermost crevices of the wear track. Low flow rates may be preferable for applications requiring higher roughness and porosity, while high flow rates offer advantages in achieving denser coatings and better wear resistance. Overall, this study highlights the importance of optimizing graphite concentration and spray flow rate to tailor coating morphology, thickness, and tribological performance for practical applications. Full article
(This article belongs to the Special Issue Friction, Wear, Lubrication and Mechanics of Surfaces and Interfaces)
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13 pages, 3006 KB  
Article
Optimum Design of Coaxial Hydraulic Sealing Systems Made from Polytetrafluoroethylene and Its Compounds
by Andrea Deaconescu and Tudor Deaconescu
Coatings 2024, 14(6), 723; https://doi.org/10.3390/coatings14060723 - 5 Jun 2024
Viewed by 1437
Abstract
Fluidic actuation systems are optimizable as to energy consumption by reducing the friction in the hydraulic cylinders. Polymeric materials with special antifriction properties and good resistance to hydraulic fluids can be deployed to enhance the performance of hydraulic cylinders. Small friction forces can [...] Read more.
Fluidic actuation systems are optimizable as to energy consumption by reducing the friction in the hydraulic cylinders. Polymeric materials with special antifriction properties and good resistance to hydraulic fluids can be deployed to enhance the performance of hydraulic cylinders. Small friction forces can also be ensured by facilitating the hydrodynamic separation of the elements of the friction tribosystem, namely the seal and sealed-off surface, respectively. The study presented in this paper analyzed the hydrodynamic separation phenomenon in hydraulic cylinders with coaxial sealing systems of the pistons. The process underlying the forming of the fluid film between the seal and its contact surface was considered and the formula for calculating film thickness was deduced. This paper presents graphs that describe the variation of the fluid film thickness versus the dimensional and material characteristics of the sealing systems. The study yielded recommendations as to the most adequate polymeric material to be used and the optimum dimensional characteristics of the seal. Full article
(This article belongs to the Special Issue Friction, Wear, Lubrication and Mechanics of Surfaces and Interfaces)
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18 pages, 7265 KB  
Article
Use of Organic Acids as Additives for Plasma Electrolytic Oxidation (PEO) of Titanium
by Federica Ceriani, Luca Casanova and Marco Ormellese
Coatings 2024, 14(6), 703; https://doi.org/10.3390/coatings14060703 - 3 Jun 2024
Cited by 5 | Viewed by 1040
Abstract
The present study investigates the influence of organic acids, added to the electrolytic solution, on the structure, morphology, and corrosion behaviour of plasma electrolytic oxidation (PEO) coatings produced on titanium grade 2. Particular attention is paid to the role of functional groups in [...] Read more.
The present study investigates the influence of organic acids, added to the electrolytic solution, on the structure, morphology, and corrosion behaviour of plasma electrolytic oxidation (PEO) coatings produced on titanium grade 2. Particular attention is paid to the role of functional groups in the modification of the oxide’s properties. For this reason, all three selected acids, namely glutaric, glutamic, and tartaric acid, display two carboxylic groups, thus they interact with the substrate material mainly through –COO− adsorption. However, glutamic acid also has an amine group, while tartaric acid has two hydroxyl groups. The presence of such additional functional groups is found to impact the formation of the PEO coatings. According to scanning electron microscopy (SEM) analyses, the number of defects and their dimension increase with an increasing number of active groups present in the organic molecules. Then, when glutaric acid with only two carboxyl groups, is employed as an additive, smaller pores are produced. The dimension of defects increases when glutamic and tartaric acid are used. X-ray diffraction (XRD) testing demonstrates that rutile and anatase are present in all the coatings and that when using tartaric acid, a relatively high level of amorphism is reached. The electrochemical and corrosion behaviours are evaluated by potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) performed in a heated sulphuric acid solution. It is found that all types of coatings provide protection against corrosion, with oxides produced using glutamic acid showing the lowest corrosion current density (0.58 mA·m−2) and low corrosion rate (1.02 μm·y−1). Full article
(This article belongs to the Section Corrosion, Wear and Erosion)
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12 pages, 6042 KB  
Article
Influence of Flow Rates and Flow Times of Plasma-Enhanced Atomic Layer Deposition Purge Gas on TiN Thin Film Properties
by Ju Eun Kang, Surin An and Sang Jeen Hong
Coatings 2024, 14(6), 673; https://doi.org/10.3390/coatings14060673 - 27 May 2024
Viewed by 2643
Abstract
This study investigated the effect of purge gas flow rate and purge gas flow time on the properties of TiN thin films via chemical reaction simulation and the plasma-enhanced atomic layer deposition (PEALD) process along purge gas flow rates and time settings. Chemical [...] Read more.
This study investigated the effect of purge gas flow rate and purge gas flow time on the properties of TiN thin films via chemical reaction simulation and the plasma-enhanced atomic layer deposition (PEALD) process along purge gas flow rates and time settings. Chemical reaction simulation unveiled an incremental increase in generating volatile products along purge gas flow rates. In contrast, increased purge gas flow times enhanced the desorption of physically adsorbed species flow time in the film surface. Subsequent thin film analysis showed that the increased Ar purge gas flow rate caused a shift of 44% in wafer non-uniformity, 46% in carbon composition, and 11% in oxygen composition in the deposited film. Modulations in the Ar purge gas flow time yielded variations of 50% in wafer non-uniformity, 46% in carbon composition, and 15% in oxygen content. Notably, 38% of the resistivity and 35% of the film thickness occurred due to experimental variations in the Ar purge step condition. Increased purge gas flow rates had a negligible impact on the film composition, thickness, and resistivity, but the film’s non-uniformity on a 6-inch wafer was notable. Extended purge gas flow times with inadequate flow rates resulted in undesired impurities in the thin film. This study employed a method that utilized reaction simulation to investigate the impact of purge gas flow and verified these results through film properties analysis. These findings can help in determining optimal purge conditions to achieve the desired film properties of PEALD-deposited TiN thin films. Full article
(This article belongs to the Special Issue Application of Advanced Plasma Technology in Coatings, Films and Etching)
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16 pages, 6415 KB  
Article
Comparative Study of Multilayer Hard Coatings Deposited on WC-Co Hardmetals
by Mateja Šnajdar, Danko Ćorić and Matija Sakoman
Coatings 2024, 14(6), 674; https://doi.org/10.3390/coatings14060674 - 27 May 2024
Cited by 2 | Viewed by 2091
Abstract
This paper examines the impact of a multilayered gradient coating, applied via plasma-activated chemical vapor deposition (PACVD), on the structural and mechanical attributes of nanostructured WC-Co cemented carbides. WC-Co samples containing 5 and 15 wt.% Co were synthesized through a hot isostatic pressing [...] Read more.
This paper examines the impact of a multilayered gradient coating, applied via plasma-activated chemical vapor deposition (PACVD), on the structural and mechanical attributes of nanostructured WC-Co cemented carbides. WC-Co samples containing 5 and 15 wt.% Co were synthesized through a hot isostatic pressing (HIP) process using nanoparticle powders and coated with two distinct multilayer coatings: titanium nitride (TiN) and titanium carbonitride (TiCN). Nanosized grain formation without microstructural defects of the substrates, prior to coating, was confirmed by magnetic saturation and coercivity testing, microstructural analysis, and field emission scanning electron microscope (FESEM). Nanoindentation, fracture toughness and hardness testing were conducted for uncoated samples. After coatings deposition, characterizations including microscopy, surface roughness determination, adhesion testing, coating thickness measurement, and microhardness examination were conducted. The impact of deposited coatings on wear resistance of produced hardmetals was analyzed via scratch test and dry sliding wear test. Samples with higher Co content exhibited improved adhesion, facilitating surface cleaning and activation before coating. TiN and TiCN coatings demonstrated similar roughness on substrates of identical composition, suggesting Co content’s minimal influence on layer growth. Results of the mechanical tests showed higher microhardness, higher elastic modulus, better adhesion, and overall superior tribological properties of the TiCN coating. Full article
(This article belongs to the Special Issue Advances in Deposition and Characterization of Hard Coatings)
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17 pages, 3740 KB  
Article
Magnetron-Sputtered Long-Term Superhydrophilic Thin Films for Use in Solid-State Cooling Devices
by Maria Barrera, Olaf Zywitzki, Thomas Modes and Fred Fietzke
Coatings 2024, 14(5), 622; https://doi.org/10.3390/coatings14050622 - 14 May 2024
Cited by 2 | Viewed by 1797
Abstract
Pulse-magnetron-sputtered long-term superhydrophilic coatings have been synthesized to functionalize the surfaces of solid-state cooling devices, e.g., electrocaloric heat pumps, where not only a complete wetting of the surface by a fluid is intended, but also fast wetting and dewetting processes are required. The [...] Read more.
Pulse-magnetron-sputtered long-term superhydrophilic coatings have been synthesized to functionalize the surfaces of solid-state cooling devices, e.g., electrocaloric heat pumps, where not only a complete wetting of the surface by a fluid is intended, but also fast wetting and dewetting processes are required. The coatings consist of a (Ti,Si)O2 outer layer that provides lasting hydrophilicity thanks to the mesoporous structure, followed by an intermediate WO3 film that enables the reactivation of the wettability through visible light irradiation, and a W underlayer which can work as a top electrode of the electrocaloric components thanks to its suitable electrical and thermal conductivity properties. Process parameter optimization for each layer of the stack as well as the influence of the microstructure and composition on the wetting properties are presented. Finally, water contact angle measurements, surface energy evaluations, and a contact line dynamics assessment of evaporating drops on the coatings demonstrate that their enhanced wetting performance is attributed not only to their intrinsic hydrophilic nature but also to their porous microstructure, which promotes wicking and spreading at the nanometric scale. Full article
(This article belongs to the Section Thin Films)
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16 pages, 5011 KB  
Article
Effect of Electrolytic Plasma Polishing on Surface Properties of Titanium Alloy
by Dongliang Yang, Huanwu Sun, Gangqiang Ji, Yuxia Xiang and Juan Wang
Coatings 2024, 14(5), 615; https://doi.org/10.3390/coatings14050615 - 13 May 2024
Cited by 6 | Viewed by 2713
Abstract
Electrolytic plasma polishing (EPPo) is an advanced metal surface finishing technology with high quality and environmental protection that has broad application prospects in the biomedical field. However, the effect of EPPo on surface properties such as corrosion resistance and the wettability of biomedical [...] Read more.
Electrolytic plasma polishing (EPPo) is an advanced metal surface finishing technology with high quality and environmental protection that has broad application prospects in the biomedical field. However, the effect of EPPo on surface properties such as corrosion resistance and the wettability of biomedical titanium alloys remains to be investigated. This paper investigated the changes in surface roughness, surface morphology, microstructure, and chemical composition of Ti6Al4V alloy by EPPo and their effects on surface corrosion resistance, wettability, and residual stress. The results showed that Ra decreased from 0.3899 to 0.0577 μm after EPPo. The surface crystallinity was improved, and the average grain size increased from 251 nm to more than 800 nm. The oxidation behavior of EPPo leads to an increase in surface oxygen content and the formation of TiO2 and Al2O3 oxide layers. EPPo can significantly improve the corrosion resistance and wettability of titanium alloy in simulated body fluid and eliminate the residual stress on the sample surface. The surface properties are enhanced not only by the reduction in surface roughness but also by the formation of a denser oxide film on the surface, changes in the microstructure, an increase in surface free energy, and the annealing effect developed during EPPo. This study can provide guidance and references for applying EPPo to biomedical titanium alloy parts. Full article
(This article belongs to the Section Plasma Coatings, Surfaces & Interfaces)
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21 pages, 3508 KB  
Article
Exploring TMA and H2O Flow Rate Effects on Al2O3 Thin Film Deposition by Thermal ALD: Insights from Zero-Dimensional Modeling
by Júlia Karnopp, Nilton Azevedo Neto, Thaís Vieira, Mariana Fraga, Argemiro da Silva Sobrinho, Julio Sagás and Rodrigo Pessoa
Coatings 2024, 14(5), 578; https://doi.org/10.3390/coatings14050578 - 7 May 2024
Cited by 5 | Viewed by 5908
Abstract
This study investigates the impact of vapour-phase precursor flow rates—specifically those of trimethylaluminum (TMA) and deionized water (H2O)—on the deposition of aluminum oxide (Al2O3) thin films through atomic layer deposition (ALD). It explores how these flow rates [...] Read more.
This study investigates the impact of vapour-phase precursor flow rates—specifically those of trimethylaluminum (TMA) and deionized water (H2O)—on the deposition of aluminum oxide (Al2O3) thin films through atomic layer deposition (ALD). It explores how these flow rates influence film growth kinetics and surface reactions, which are critical components of the ALD process. The research combines experimental techniques with a zero-dimensional theoretical model, designed specifically to simulate the deposition dynamics. This model integrates factors such as surface reactions and gas partial pressures within the ALD chamber. Experimentally, Al2O3 films were deposited at varied TMA and H2O flow rates, with system conductance guiding these rates across different temperature settings. Film properties were rigorously assessed using optical reflectance methods and attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy. The experimental findings revealed a pronounced correlation between precursor flow rates and film growth. Specifically, at 150 °C, film thickness reached saturation at a TMA flow rate of 60 sccm, while at 200 °C, thickness peaked and then declined with increasing TMA flow above this rate. Notably, higher temperatures generally resulted in thinner films due to increased desorption rates, whereas higher water flow rates consistently produced thicker films, emphasizing the critical role of water vapour in facilitating surface reactions. This integrative approach not only deepens the understanding of deposition mechanics, particularly highlighting how variations in precursor flow rates distinctly affect the process, but also significantly advances operational parameters for ALD. These insights are invaluable for enhancing the application of ALD technologies across diverse sectors, including microelectronics, photovoltaics, and biomedical coatings, effectively bridging the gap between theoretical predictions and empirical results. Full article
(This article belongs to the Special Issue Functional Films/Coatings Processing Technologies: Deposition and Process)
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20 pages, 13537 KB  
Article
Influence of Selected Parameters of Zinc Electroplating on Surface Quality and Layer Thickness
by Jozef Mascenik, Tomas Coranic, Jiri Kuchar and Zdenek Hazdra
Coatings 2024, 14(5), 579; https://doi.org/10.3390/coatings14050579 - 7 May 2024
Cited by 2 | Viewed by 5420
Abstract
Surface treatment technologies are pivotal across diverse industrial sectors such as mechanical engineering, electrical engineering, and the automotive industry. Continuous advancements in manufacturing processes are geared towards bolstering efficiency and attaining superior product quality. This study aimed to empirically compare practical outcomes with [...] Read more.
Surface treatment technologies are pivotal across diverse industrial sectors such as mechanical engineering, electrical engineering, and the automotive industry. Continuous advancements in manufacturing processes are geared towards bolstering efficiency and attaining superior product quality. This study aimed to empirically compare practical outcomes with theoretical insights. Employing galvanic zinc plating under constant voltage with varying plating durations unveiled a correlation between coating thickness and electrolyte composition alongside plating duration. The graphical representation delineated the optimal electrolyte composition conducive to maximal coating thickness. Notably, an evident decrease in leveling ability was noted with prolonged plating durations. The experiment corroborated the notion that theoretical formulas for coating thickness estimation possess limited accuracy, often resulting in measured values surpassing theoretical predictions. These findings underscore the imperative for refined theoretical models to comprehensively grasp galvanic surface treatment processes. Full article
(This article belongs to the Special Issue Advances in Electrodeposited Composite Coatings: Diversity, Applications and Challenges)
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16 pages, 49708 KB  
Article
Effect of Quenching Cooling Rate on Hydrogen Embrittlement of Precipitation-Hardened Martensitic Stainless Steels
by Sicong Shen, Xingyu Ma, Xiaolong Song, Wenwen Zhao and Yong Shen
Coatings 2024, 14(5), 572; https://doi.org/10.3390/coatings14050572 - 6 May 2024
Cited by 1 | Viewed by 2798
Abstract
Heat treatment plays a decisive role in the microstructure of metallic materials. The effect of cooling rate changes caused by the quenching medium on the microstructure of steel materials should be clarified. In this study, the effect of the quenching cooling rate on [...] Read more.
Heat treatment plays a decisive role in the microstructure of metallic materials. The effect of cooling rate changes caused by the quenching medium on the microstructure of steel materials should be clarified. In this study, the effect of the quenching cooling rate on the microstructure of two precipitation-hardened martensitic stainless steels was investigated. The mechanical properties and hydrogen embrittlement susceptibility effected by the changes in the microstructure were also analyzed. A slow tensile test and hydrogen pre-charging were carried out to obtain the hydrogen embrittlement susceptibility parameters of the specimens. The results show that the quenching cooling rate only affects specific microstructures, including the twin structure and misorientation angle. Before hydrogen charging, the mechanical properties of the precipitation-hardened martensitic stainless steels were not affected by changing the quenching cooling rate. After hydrogen charging, the hydrogen embrittlement susceptibility decreased as the quenching cooling rate increased. Full article
(This article belongs to the Special Issue Deposition, Characterization and Application of Anti-corrosion and Lubricating Coatings)
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15 pages, 2681 KB  
Article
Utilizing Metal Oxide Thin Films for Device Engineering of Solution-Processed Organic Multi-Junction Solar Cells
by Afshin Hadipour
Coatings 2024, 14(5), 525; https://doi.org/10.3390/coatings14050525 - 24 Apr 2024
Cited by 2 | Viewed by 2068
Abstract
Electron and hole transporting layers play a major role in high-performance and stable organic-based optoelectronic devices. This paper demonstrates detailed device engineering of multi-junction organic photovoltaics built on two different metal oxide-based electron and hole transport (buffer) layers prepared by thermal or solution-processed [...] Read more.
Electron and hole transporting layers play a major role in high-performance and stable organic-based optoelectronic devices. This paper demonstrates detailed device engineering of multi-junction organic photovoltaics built on two different metal oxide-based electron and hole transport (buffer) layers prepared by thermal or solution-processed methods. The main focus is on the device processing parameters as well as practical details of preparation of buffer layers to give the research community a clear, step-by-step recipe to successfully replicate and build series and parallel connected multi-junction solution-based organic solar cells for their needs. Here, the recipes and deposition conditions of two metal oxide buffer layers are presented in detail, based on basic commercially available materials and tools, to achieve well-engineered tandem (multi-junction) solution-processed organic solar cells. The buffer layers have appropriate energy levels for electrical selectivity of anode and cathode electrodes, and they are highly stable and chemically compatible with processing of solution-based polymer solar cells. To demonstrate the engineering steps of multi-junction devices, the PCE10:PC70BM blend is used as the active layer for all subcells. Then, to improve the power conversion efficiency of the single-junction photovoltaic device, PCE10:PC70BM blend is used in combination with DPPx:PC70BM with different absorption spectra for bottom and top subcell active layers. An optimized series tandem device with 10.6% power conversion efficiency is demonstrated. Generally, the device structures reported here can also be used for other types of optoelectronic devices, such as light emitting diodes and photodetectors. Full article
(This article belongs to the Special Issue Advanced Metal Oxide Films: Materials and Applications)
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12 pages, 3792 KB  
Article
Controlling the Superconducting Critical Temperature and Resistance of NbN Films through Thin Film Deposition and Annealing
by Yang Pei, Qian Fan, Xianfeng Ni and Xing Gu
Coatings 2024, 14(4), 496; https://doi.org/10.3390/coatings14040496 - 17 Apr 2024
Cited by 5 | Viewed by 3342
Abstract
This study investigated the relationship between the superconducting properties, electrical properties, sputtering process parameters, and post-growth annealing of NbN films. Four series of NbN films were deposited by DC magnetron sputtering using different process parameters. With the assistance of a four-probe method, the [...] Read more.
This study investigated the relationship between the superconducting properties, electrical properties, sputtering process parameters, and post-growth annealing of NbN films. Four series of NbN films were deposited by DC magnetron sputtering using different process parameters. With the assistance of a four-probe method, the superconducting performance presented first an increase and then a decreasing trend as the resistance of the prepared films increased, which could be attributed to the variation of the N/Nb ratio in the films. This correlation implied that it is very challenging to fabricate films with both high Tc and high resistance or high Tc and low resistance by adjusting the sputtering process parameters. In order to overcome these bottlenecks, a series of films were deposited on Si, GaN/Si, SiN/Si, AlN/Si, and AlN/sapphire substrates, and the film deposited on Si was annealed at 900 °C. Annealing reduced the stress of the films on the buffer layer and increased the grain size and crystallinity of the films, except for the films on the GaN/Si substrates. This resulted in a significant decrease in the resistivity of the film and a significant increase in the superconducting transition temperature. Full article
(This article belongs to the Section Thin Films)
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11 pages, 3973 KB  
Article
The Effect of Intumescent Coating Containing Expandable Graphite onto Spruce Wood
by Elena Kmeťová, Danica Kačíková and František Kačík
Coatings 2024, 14(4), 490; https://doi.org/10.3390/coatings14040490 - 16 Apr 2024
Cited by 6 | Viewed by 3036
Abstract
Wood, one of the materials predominantly employed in construction, possesses various advantageous properties alongside certain drawbacks, such as susceptibility to thermal degradation. To enhance wood fire resistance, one approach involves the application of flame retardants. This study compared the fire-retardant effectiveness of expandable [...] Read more.
Wood, one of the materials predominantly employed in construction, possesses various advantageous properties alongside certain drawbacks, such as susceptibility to thermal degradation. To enhance wood fire resistance, one approach involves the application of flame retardants. This study compared the fire-retardant effectiveness of expandable graphite, bonded with water glass, as a coating for spruce wood against commercially available fire-retardant treatments. Spruce wood samples (Picea abies (L.) H. Karst) underwent treatment with three distinct retardants: expandable graphite in combination with water glass, Bochemit Antiflash, and Bochemit Pyro. The fire-technical characteristics of the samples were examined by a non-standard test method—a test with a radiant heat source. The experiment evaluated the fire-retardant properties by recording changes in sample mass, burning rate, and temperature difference. The best results among all flame retardants were achieved by expandable graphite in combination with water glass, in all evaluation criteria. Among all the flame retardants used, expandable graphite in combination with water glass achieved the best results in all evaluation criteria. Full article
(This article belongs to the Special Issue Advances in Surface Modification and Coatings of Wood and Wood Composites)
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22 pages, 3104 KB  
Article
Influence of a UVA-Activated TiO2 Coating on Bacterial Surface Colonization in Water-Bearing Systems
by Linda Steinhäußer, Ulla König, Fred Fietzke and Gaby Gotzmann
Coatings 2024, 14(4), 454; https://doi.org/10.3390/coatings14040454 - 10 Apr 2024
Cited by 2 | Viewed by 3487
Abstract
This study focuses on the use of superhydrophilic titanium dioxide (TiO2) coatings applied to the surfaces of water-bearing systems to prevent surface colonization and biofilm formation. Biofilms in water-bearing systems are a problem in many industrial areas and are associated with [...] Read more.
This study focuses on the use of superhydrophilic titanium dioxide (TiO2) coatings applied to the surfaces of water-bearing systems to prevent surface colonization and biofilm formation. Biofilms in water-bearing systems are a problem in many industrial areas and are associated with risks to hygiene and health, material damage, and high costs for cleaning and maintenance. We investigated the suitability of TiO2 coatings activated by UVA irradiation to achieve a superhydrophilic surface. The well-adherent coatings were deposited on flat and curved substrates (stainless steel, Al2O3) by pulsed magnetron sputtering. Surface characteristics, wettability, and the influence on microbial surface colonization were evaluated by WCA measurements, SEM, and XRD. For microbiological evaluation, Escherichia coli and Staphylococcus warneri were used. An adapted and specialized regime for sample conditioning and testing was developed that allows comparability with upcoming studies in this field. The superhydrophilicity was stable for up to 4 days, and an additional UVA reactivation step revealed comparable results. The microbiological studies proved a successful prevention of bacterial colonization on the activated coatings, which is attributed to their superhydrophilicity. The results demonstrate the potential of UV-activated TiO2 as a long-term coating of water-bearing systems, like pipes, on which it assists in avoiding biofilm formation. Full article
(This article belongs to the Section Plasma Coatings, Surfaces & Interfaces)
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13 pages, 2626 KB  
Article
Electrolyte Influence on Properties of Ultra-Thin Anodic Memristors on Titanium
by Dominik Knapic, Elena Atanasova, Ivana Zrinski, Achim Walter Hassel and Andrei Ionut Mardare
Coatings 2024, 14(4), 446; https://doi.org/10.3390/coatings14040446 - 9 Apr 2024
Cited by 2 | Viewed by 1632
Abstract
Titanium anodic memristors were prepared in phosphate buffer (PB) and citrate buffer (CB) electrolytes. Studying their I-U sweeps, the memristors presented self-rectifying and volatile behaviors. Transmission electron microscopic analysis revealed crystalline protrusions inside a semi-crystalline Ti oxide. Grounded in this, a hybrid interfacial [...] Read more.
Titanium anodic memristors were prepared in phosphate buffer (PB) and citrate buffer (CB) electrolytes. Studying their I-U sweeps, the memristors presented self-rectifying and volatile behaviors. Transmission electron microscopic analysis revealed crystalline protrusions inside a semi-crystalline Ti oxide. Grounded in this, a hybrid interfacial memristive switching mechanism relaying on partial filaments was proposed. Moreover, both analyzed memristor types demonstrated multilevel switching capabilities. The memristors anodized in the PB and CB showed high-to-low resistance ratios of 4 × 104 and 1.6 × 102, respectively. The observed (more than two order of magnitude) ratio improvement of the PB memristors suggests their better performance, in spite of their modestly high resistive state instabilities, attributed to the thermal stress caused by consecutive switching. The endurance and retention of both the PB and CB memristors was measured over up to 106 cycles, indicating very good lifetimes. Phosphate incorporation into the anodic oxide was confirmed by photoelectron spectroscopy analysis and was related to the improved memristive behavior of the PB sample. The presence of phosphate inside the memristively active layer modifies the availability of free O species (vacancies and ions) in the oxide. Taking all this into consideration, Ti anodic memristors anodized in PB are emphasized as candidates for neuromorphic computing. Full article
(This article belongs to the Special Issue Thin Films and Nanostructures for Electronics)
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14 pages, 29865 KB  
Article
The Use of PVD Coatings for Anti-Wear Protection of the Press-In Connection Elements
by Sławomir Kowalski
Coatings 2024, 14(4), 432; https://doi.org/10.3390/coatings14040432 - 4 Apr 2024
Cited by 5 | Viewed by 1596
Abstract
Press-in connections are the commonly used methods for connecting machinery components. In relation to that wide use, those connections are liable to various types of damage and wear. Therefore, this article proposes one of the methods which may improve the life of the [...] Read more.
Press-in connections are the commonly used methods for connecting machinery components. In relation to that wide use, those connections are liable to various types of damage and wear. Therefore, this article proposes one of the methods which may improve the life of the press-in connection. CrN+OX, TiN, and ZrN coatings made in the PVD technology were used. The coatings were applied on shafts mating with sleeves and subjected to a rotational bending moment. Tests and observations were conducted that enabled the assessment of the influence of those coatings on the development of wear, in particular fretting, in the tribological kinematic pair. The tests showed the development of wear on all the observed shaft surfaces, with a lower intensity of damage recorded on coated shafts compared to uncoated ones. The traces of fretting wear were noted each time at the edges of the connection, which is due to the mechanism of wear development under rotational bending conditions. In the case of uncoated shafts, wear occurs at the entire circumference of the axle seat in the form of a 3–4 mm wide ring; however, that width is different on either side. In the case of coated shafts, wear occurs on the circumference of the axle seat in the form of a thin ring 1–3 mm wide, depending on the coating. In the case of a ZrN coating, fretting wear appears locally. The largest surface area occupied by wear is 0.75 cm2. Fretting wear comprises mainly material build-ups, pits, and surface scratches. In addition to fretting wear, damage resulting from the process of forcing the sleeve onto the shaft was observed on the tested surfaces. Full article
(This article belongs to the Section Corrosion, Wear and Erosion)
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12 pages, 2651 KB  
Article
Bioinspired Living Coating System for Wood Protection: Exploring Fungal Species on Wood Surfaces Coated with Biofinish during Its Service Life
by Faksawat Poohphajai, Ana Gubenšek, Anja Černoša, Karen Butina Ogorelec, Lauri Rautkari, Jakub Sandak and Anna Sandak
Coatings 2024, 14(4), 430; https://doi.org/10.3390/coatings14040430 - 3 Apr 2024
Cited by 2 | Viewed by 2223
Abstract
Biofinish is an innovative wood protection system inspired by biological processes. It enhances the hydrophobicity of wood through oil treatment, resulting in improved dimensional stability. Living cells of the fungus Aureobasidium pullulans effectively protect wood from deterioration caused by other decaying fungi. The [...] Read more.
Biofinish is an innovative wood protection system inspired by biological processes. It enhances the hydrophobicity of wood through oil treatment, resulting in improved dimensional stability. Living cells of the fungus Aureobasidium pullulans effectively protect wood from deterioration caused by other decaying fungi. The melanin pigment produced by the fungus provides an appealing dark surface and additionally protects the wood substrate against UV radiation. The significant advantage of Biofinish is its remarkable self-healing ability, which distinguishes it from conventional wood protection methods. This research aimed to explore fungal species colonising surfaces exposed to natural weathering and assess the survival of A. pullulans on wood surfaces coated with Biofinish during its in-service period. This study was performed on a facade composed of European larch wood (Larix decidua) treated with linseed oil and coated with Biofinish at the InnoRenew CoE building in Izola, Slovenia, following a 9-month exposure period. The majority of the detected species belonged to the genera Aureobasidium. The results indicated the survival and effective antagonistic action of A. pullulans, the living and active ingredient of the coating, against other wood-decaying fungi. Full article
(This article belongs to the Special Issue New Challenges in Wood Adhesives and Coatings, 2nd Edition)
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15 pages, 4800 KB  
Article
Dual Strategy Based on Quantum Dot Doping and Phenylethylamine Iodide Surface Modification for High-Performance and Stable Perovskite Solar Cells
by Shulan Zhang, Renjie Chen, Mujing Qu, Biyu Long, Nannan He, Sumei Huang, Xiaohong Chen, Huili Li and Tongtong Xuan
Coatings 2024, 14(4), 409; https://doi.org/10.3390/coatings14040409 - 29 Mar 2024
Cited by 2 | Viewed by 1672
Abstract
High-quality perovskite films (PFs) are crucial for achieving high-performance perovskite solar cells (PSCs). Herein, we report a dual-modification strategy via incorporating CsPbBr3 QDs into MAPbI3 perovskite bulk and capping the interface of the perovskite/hole transport layer (HTL) with phenylethylamine iodide (PEAI) [...] Read more.
High-quality perovskite films (PFs) are crucial for achieving high-performance perovskite solar cells (PSCs). Herein, we report a dual-modification strategy via incorporating CsPbBr3 QDs into MAPbI3 perovskite bulk and capping the interface of the perovskite/hole transport layer (HTL) with phenylethylamine iodide (PEAI) to improve perovskite crystallinity and interface contact properties to acquire high-quality PFs with fewer defects. CsPbBr3 QDs promoted perovskite grain growth and reduced bulk defects, while PEAI surface modification passivated interfaces, improved hydrophobic properties, and prevented carrier recombination at the perovskite/HTL interface. Benefiting from growth control and the effective suppression of both bulk and interface carrier recombination, the resulting devices show a greatly improved photoelectric conversion efficiency (PCE) from 17.21% of the reference cells to 21.04% with a champion Voc of 1.15 V, Jsc of 23.30 mA/cm2, and fill factor (FF) of 78.6%. Furthermore, the dual-modification strategy endows PFs with promoted moisture tolerance, and the nonencapsulated PSCs retain 75% of their initial efficiency after aging for 30 days at 40% relative humidity and room temperature, which is significantly higher than the 59% value of the original PSCs. Good operational stability and the maintained efficiency of the target device over time suggest the potential for future commercialization. Full article
(This article belongs to the Special Issue Perovskite Photovoltaics: From Materials to Device Applications)
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