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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19 pages, 7133 KiB  
Article
Effect of the Injection Structure on Gas Velocity Distribution in a 3D Vertical Oven
by Qiucheng Zhou, Zhanyu Yang, Changsong Zheng, Liping Wei, Dong Li and Xiaoyong Fan
Coatings 2023, 13(10), 1707; https://doi.org/10.3390/coatings13101707 - 28 Sep 2023
Viewed by 1495
Abstract
Gas injection structures were designed for a vertical oven to improve the gas–solid flow countercurrent structure. This work measured the wall temperature distribution of the vertical oven to reflect gas velocity distribution, and simulated the basic gas–solid flow field. The effects of the [...] Read more.
Gas injection structures were designed for a vertical oven to improve the gas–solid flow countercurrent structure. This work measured the wall temperature distribution of the vertical oven to reflect gas velocity distribution, and simulated the basic gas–solid flow field. The effects of the number of gas orifice layers and the injection angle on the gas velocity distribution were examined. The results showed that number of gas injection layers had a significant effect on the gas velocity distribution in the lower zone. Compared with the distributions with one or three injection layers, two injection layers produce more uniform gas flow. A small particle size of 6–15 mm increased the bed resistance and solid fraction standard deviation. A nozzle angle of 45° was conducive to increase the gas velocity in the upper zone and forming a more uniform gas distribution. Full article
(This article belongs to the Special Issue Liquid–Fluid Interfaces and Dynamics)
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15 pages, 36535 KiB  
Article
Bioactivity and Mechanical Properties of Hydroxyapatite on Ti6Al4V and Si(100) Surfaces by Pulsed Laser Deposition
by Salizhan Kylychbekov, Yaran Allamyradov, Zikrulloh Khuzhakulov, Inomjon Majidov, Simran Banga, Justice ben Yosef, Liviu Duta and Ali Oguz Er
Coatings 2023, 13(10), 1681; https://doi.org/10.3390/coatings13101681 - 25 Sep 2023
Cited by 4 | Viewed by 1910
Abstract
In this study, the effects of substrate temperature and ablation wavelength/mechanism on the structural, mechanical, and bioactivity properties of hydroxyapatite (HA) coatings were investigated. HA coatings were deposited on both Si(100) and Ti6Al4V surfaces. Substrate temperature varied from room temperature to 800 °C. [...] Read more.
In this study, the effects of substrate temperature and ablation wavelength/mechanism on the structural, mechanical, and bioactivity properties of hydroxyapatite (HA) coatings were investigated. HA coatings were deposited on both Si(100) and Ti6Al4V surfaces. Substrate temperature varied from room temperature to 800 °C. Depositions were performed in Ar/H2O and vacuum environments. X-ray diffraction, scanning electron microscopy, and atomic force microscopy techniques were used to analyze structural and morphological variations. The adherence of coatings to the substrates was assessed by the pull-out method. The obtained data indicated that with the temperature increase, the coatings steadily crystallized. However, temperatures above 700 °C adversely affected protein adsorption and adhesion properties. Similar trends were confirmed via pull-out testing, protein adsorption, and cell proliferation tests. The ablation mechanism was also proven to play an important role in the deposition process. Overall, this study provides further evidence that crystallinity is a vital factor in the functionality of the coatings and depends on the deposition conditions. However, all measurements directly indicated that beyond 700 °C, the morpho-structural, mechanical, and bioactivity properties degrade. Full article
(This article belongs to the Special Issue Synthetic and Biological-Derived Hydroxyapatite Implant Coatings)
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21 pages, 7189 KiB  
Article
Sustainable Integration of Zinc Oxide Nanoparticles: Enhancing Properties of Poly(ε-Caprolactone) Electrospun Nanofibers and Cast Films
by Johar Amin Ahmed Abdullah, José J. Benítez, Antonio Guerrero and Alberto Romero
Coatings 2023, 13(10), 1665; https://doi.org/10.3390/coatings13101665 - 22 Sep 2023
Cited by 2 | Viewed by 2018
Abstract
This study investigated the impact of adding zinc oxide nanoparticles (ZnO-NPs) to electrospun membranes and cast films made of poly(ε-caprolactone) (PCL). The physicochemical, mechanical, and morphological properties of the samples were analyzed. Physicochemical parameters included water contact angle (WCA), water vapor transmission rate [...] Read more.
This study investigated the impact of adding zinc oxide nanoparticles (ZnO-NPs) to electrospun membranes and cast films made of poly(ε-caprolactone) (PCL). The physicochemical, mechanical, and morphological properties of the samples were analyzed. Physicochemical parameters included water contact angle (WCA), water vapor transmission rate (WVTR), permeance, water vapor permeability (WVP), light transmission (T600), and transparency (T). Mechanical properties, such as maximum stress (Ϭmax), elongation (εmax), and Young’s modulus (MPa), were also evaluated. Morphological properties were analyzed in terms of thickness, dispersion, and surface roughness (measured by the arithmetic (Ra) and quadratic (Rq) averages). The crystallinity and melting point, as well as the functional DPPH scavenging percentage (SP%), were also studied. The results showed that adding 1 wt% ZnO-NPs improved the water barrier properties of PCL membranes and films, increasing WCA by 1%–6% and decreasing WVTR by 11%–19%, permeance by 34%–20%, and WVP by 4%–11%, respectively. The T600 values of PCL/ZnO-NPs membranes and films were 2–3 times lower than those of neat PCL samples, indicating improved optical properties. The mechanical properties of the composite membranes and films also improved, with Ϭmax increasing by 56%–32% and Young’s modulus increasing by 91%–95%, while εmax decreased by 79%–57%. The incorporation of ZnO-NPs also increased the thickness and surface roughness of the samples. The SP% of PCL/ZnO-NPs increased by almost 69%, demonstrating the beneficial effects of ZnO-NPs on the system. These findings suggest that incorporating ZnO-NPs into PCL membranes and films can enhance their properties, making them well suited for various applications, such as those within the realm of materials science and nanotechnology. Full article
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12 pages, 2178 KiB  
Article
Bioactive Paper Packaging for Extended Food Shelf Life
by Anamaria Irimia and Carmen-Mihaela Popescu
Coatings 2023, 13(9), 1658; https://doi.org/10.3390/coatings13091658 - 21 Sep 2023
Cited by 2 | Viewed by 2025
Abstract
Food safety and quality are major problems for food producers and industry, governments, and consumers. Conventional plastic-based food packaging is difficult to dispose of and recycle due to its provenience from fossil resources and resistance to biodegradation. Therefore, currently, the trend is to [...] Read more.
Food safety and quality are major problems for food producers and industry, governments, and consumers. Conventional plastic-based food packaging is difficult to dispose of and recycle due to its provenience from fossil resources and resistance to biodegradation. Therefore, currently, the trend is to develop new eco-friendly food packaging that can replace these materials. The limitations of conventional packaging can be solved by developing new active materials with antimicrobial and antioxidant properties, based on cellulose, a natural biodegradable organic compound derived from renewable resources. In this study, new materials with antioxidant and antibacterial activity were obtained by combining a “green” functionalization approach (enzymatic activation) and surface modification using bioactive agents (essential clove oil and cold-pressed grape seed oil). Kraft paper was firstly activated with cellulase, followed by impregnation with the above-mentioned oil solutions, and then its properties were evaluated. The increased values of the O/C ratio for modified Kraft paper indicate an increased polarity due to the presence of phenolic groups. This resulted in an improved hydrophobicity, with the water contact angle increasing from 97° to over 110°. Following different interactions with the functional groups of vegetable oils, the modified Kraft paper exhibited distinct antioxidant and antibacterial properties. However, modified paper with clove essential oil showed higher antioxidant activity (due to the higher content of phenolic compounds), while modified paper with cold-pressed grape seed oil had better antimicrobial activity against Escherichia coli (−), Salmonella enteritidis (−), and Listeria monocytogenes (+) bacterial strains, and was more effective at reducing bacterial growth on fresh beef and fresh curd. The newly obtained bioactive paper provides an effective packaging material that can help control foodborne pathogens in food, thus extending its shelf life and safety. Full article
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15 pages, 6110 KiB  
Article
Influence of Bilayer Thickness on Mechanical and Tribological Properties of (Ti-Al)N/MoN Nanostructured Hard Coatings Deposited by Cathodic Arc Ion Plating
by Muhammad I. Yousaf, Tushagu Abudouwufu, Bing Yang, Alexander Tolstoguzov and Dejun Fu
Coatings 2023, 13(9), 1654; https://doi.org/10.3390/coatings13091654 - 21 Sep 2023
Cited by 2 | Viewed by 1272
Abstract
Deposition of (Ti-Al)N/MoN multilayered coatings was carried out through a cathodic ion-plating system in an argon and then nitrogen atmosphere. Bilayer thickness (Λ) of all the samples were achieved, from 22 to 104 nm, by organizing substrate holder rotational speed (SRS). To obtain [...] Read more.
Deposition of (Ti-Al)N/MoN multilayered coatings was carried out through a cathodic ion-plating system in an argon and then nitrogen atmosphere. Bilayer thickness (Λ) of all the samples were achieved, from 22 to 104 nm, by organizing substrate holder rotational speed (SRS). To obtain the optimum properties of the (Ti-Al)N/MoN coatings, the Ti and Al ratio was maintained at a level of 1:1. X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy were utilized to analyze the crystal structure and morphology of the coatings. Mechanical and tribological properties were examined by nanohardness and atomic force microscopy (AFM). The preferred orientation of the (Ti-Al)N/MoN nanoscale multilayer films was TiAlN (200) and MoN (200), which had face centered cubic (fcc) and hexagonal structures, respectively. The hardness increased with the decrease in Λ (104 nm to 26 nm), and then it increased. The highest hardness of 37 GPa was revealed at Λ = 26 nm, whereas the least wear rate of 8.09 × 10−7 mm3/N.m was attained at Λ = 22 nm. Wear rate, roughness, and coefficient of friction were decreased with decreasing bilayer period. EDS results showed that Al and Ti contents were almost the same in all samples, as per design of the experiment. Full article
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18 pages, 13323 KiB  
Article
High-Temperature Oxidation Properties of Ti-Hf-Mo-Ta-Nb-B Composite Coating Deposited on Ti60 Alloy with Laser Cladding
by Kaijin Huang and Xianchao Han
Coatings 2023, 13(9), 1646; https://doi.org/10.3390/coatings13091646 - 20 Sep 2023
Cited by 4 | Viewed by 1989
Abstract
In order to improve the high-temperature oxidation resistance of Ti60 alloy, a Ti-Hf-Mo-Ta-Nb-B composite coating was prepared on Ti60 alloy with Ti, Hf, Mo, Ta and Nb powder and B powder as raw materials using laser cladding. The microstructure and oxidation behavior of [...] Read more.
In order to improve the high-temperature oxidation resistance of Ti60 alloy, a Ti-Hf-Mo-Ta-Nb-B composite coating was prepared on Ti60 alloy with Ti, Hf, Mo, Ta and Nb powder and B powder as raw materials using laser cladding. The microstructure and oxidation behavior of the coating before and after oxidation at 1100 °C × 120 h in static air were studied with XRD, SEM, EDS and isothermal oxidation techniques. The results show that the coating was mainly composed of six phases, (Ti0.2Hf0.2Mo0.2Ta0.2 Nb0.2)B2, TiB, HfB2, Mo4.00 B3.40, TiHf and Hf1.86Mo0.14. The high-temperature oxidation of the coating and Ti60 alloy followed parabolic law, and the oxidation weight gain rate of the coating after 110 °C × 120 h was only 1/4.8 of that of the Ti60 alloy. The improvement of the high-temperature oxidation resistance of the coating may benefit from high-temperature oxidation resistance (Ti0.2Hf0.2 Mo0.2Ta0.2Nb0.2)B2, HfB2 and TiB boride ceramic phases. Full article
(This article belongs to the Special Issue Laser-Assisted Coating Techniques and Surface Modifications)
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19 pages, 5381 KiB  
Article
Initial Multidisciplinary Study of Oxidized Chromium-Coated Zirconium Alloy for Fuel Cladding of SCW-SMR Concept: Weight-Gain and Thermal Conductivity Measurements and Coating Cost Evaluation
by Kittima Khumsa-Ang, Alberto Mendoza, Armando Nava-Dominguez, Chukwudi Azih and Hussam Zahlan
Coatings 2023, 13(9), 1648; https://doi.org/10.3390/coatings13091648 - 20 Sep 2023
Cited by 1 | Viewed by 2040
Abstract
One of the challenges of small modular reactors (SMRs) in comparison with large reactors is the greater difficulty in achieving high burnups in smaller cores. With greater neutron leakage through the periphery, a key factor is the neutron economy of the fuel cladding. [...] Read more.
One of the challenges of small modular reactors (SMRs) in comparison with large reactors is the greater difficulty in achieving high burnups in smaller cores. With greater neutron leakage through the periphery, a key factor is the neutron economy of the fuel cladding. However, all large supercritical water-cooled reactor (SCWR) concepts have employed neutron-absorbing stainless steels and nickel-based alloys in order to meet all the requirements in terms of corrosion and thermalhydraulics. In order to achieve higher burnups and extend the time between refueling in a SCW-SMR, the use of chromium-coated zirconium alloy as a potential fuel cladding candidate has been explored. Chromium coatings up to a few micrometers thick have shown improved oxidation resistance of zirconium-based claddings under operating conditions relevant to SCWR concepts. In this study, Zr-2.5Nb alloy (UNS R60904) from pressure tube samples was coated using a physical vapor-deposition (PVD) method. Oxidation tests were performed on coated samples at 500 °C and approximately 25 MPa in a refreshed autoclave. The effects of the oxide on heat transfer and hydraulic resistance are also discussed in this study. Last, but not least, this study evaluates the coating cost of the fuel cladding with chromium in a vacuum plasma spray process. Full article
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11 pages, 1484 KiB  
Article
Eco-Friendly Capsaicin-Containing Water-Based Antifouling Coatings for Marine Aquaculture
by Zeynep Beyazkilic, Mirko Faccini, Ana Maria Escobar and Lorenzo Bautista
Coatings 2023, 13(9), 1616; https://doi.org/10.3390/coatings13091616 - 15 Sep 2023
Cited by 2 | Viewed by 2006
Abstract
Natural antifoulants have received significant interest in the search for non- or less-toxic antifouling coating systems for marine structures. Capsaicin, a natural compound that can be found in chili peppers, is known as an environmentally friendly antifouling agent with an excellent performance and [...] Read more.
Natural antifoulants have received significant interest in the search for non- or less-toxic antifouling coating systems for marine structures. Capsaicin, a natural compound that can be found in chili peppers, is known as an environmentally friendly antifouling agent with an excellent performance and a low environmental impact. However, controlling its release from the coating matrix is still an issue to be solved. With the aim of developing an eco-friendly antifouling system with prolonged long-term activity, in this study, we incorporated capsaicin in combination with dichlofluanid into water-based acrylic coating formulations. The antifouling activity of the resulting coatings was studied by examining the survival behavior of a Gram-negative marine bacterium Aeromonas Salmonoid ATCC 33658, and the release rate of capsaicin from the paint matrix was also assessed. The combination of 0.75 wt.% capsaicin and 0.75 wt.% dichlofluanid into the same matrix showed an antibacterial performance of up to 99.9% cfu reduction with an antibacterial value R 2.5–3 times higher than those obtained with the single biocides at 1.5 wt.%. The association between the two organic biocides created a synergistic effect on the antifouling performance, further resulting in a prolonged activity. Full article
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22 pages, 4933 KiB  
Article
Preparation and Characterization of Ag2O Thin Films on Construction Textiles for Optoelectronics Applications: Effect of Aging on Its Optical and Structural Properties
by Valentina Krylova, Vaida Dobilaitė and Milda Jucienė
Coatings 2023, 13(9), 1613; https://doi.org/10.3390/coatings13091613 - 15 Sep 2023
Viewed by 1489
Abstract
The aim of the research was to modify the surface of construction textiles by means of the use of thin silver oxide films, investigate the structure and optical and mechanical properties, and determine the structure, optical and mechanical properties of the aged composites. [...] Read more.
The aim of the research was to modify the surface of construction textiles by means of the use of thin silver oxide films, investigate the structure and optical and mechanical properties, and determine the structure, optical and mechanical properties of the aged composites. Thin films of silver oxide (Ag2O) were synthesized on a flexible PET/PVC construction textile (CT); the structural, optical, and physical properties, as well as the effect of artificial aging on these properties, were investigated. The SILAR method (successive ionic layer adsorption and reaction) was used to synthesize thin Ag2O films on the CT surface. Before the thin films were deposited, the CT surface was mechanically roughened and pretreated with acidic and alkaline solutions at an elevated temperature. XRD analysis showed that the deposited films were a polycrystalline mixed phase material consisting of Ag2O, AgO, and metallic Ag. Diffuse reflectance spectra in the ultraviolet and visible ranges (UV-Vis) were used to study the optical properties of the deposited thin films. The synthesized Ag2O/CT composites were direct-gap semiconductors (the optical band gap (Eg) was 0.89 ± 0.02 eV). Eg and refractive indices (n) increased as the aging tests were carried out. Higher Eg and n meant that the composites were a good material for optoelectronic applications. The results showed that, after modification, the structural properties and tear strength of the PET/PVC fabric remained the same while the tensile strength decreased. The same tendencies remained after artificial aging. Full article
(This article belongs to the Special Issue Compositionally Complex Coatings)
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16 pages, 4835 KiB  
Article
The Behavior of TiAlN and TiAlCrSiN Films in Abrasive and Adhesive Tribological Contacts
by Wadim Schulz, Vitalij Joukov, Florian Köhn, Wolfgang Engelhart, Veit Schier, Tim Schubert and Joachim Albrecht
Coatings 2023, 13(9), 1603; https://doi.org/10.3390/coatings13091603 - 14 Sep 2023
Cited by 5 | Viewed by 2377
Abstract
Chromium and silicon are often introduced to increase the performance of TiAlN hard coatings in dry tribological contacts. The addition of Cr and Si during a high-power impulse magnetron sputtering (HiPIMS) deposition process leads to high-quality TiAlCrSiN films. In this paper, the analysis [...] Read more.
Chromium and silicon are often introduced to increase the performance of TiAlN hard coatings in dry tribological contacts. The addition of Cr and Si during a high-power impulse magnetron sputtering (HiPIMS) deposition process leads to high-quality TiAlCrSiN films. In this paper, the analysis of friction and wear of these films is conducted by oscillation tribometry under dry conditions with a subsequent mapping of the surface topography. Both abrasion- and adhesion-dominated conditions are realized using different steel counter bodies. Oscillation-frequency-dependent experiments show a significant impact of the compositional variation on friction and wear. It is shown that the TiAlCrSiN coating investigated has a higher coefficient of friction and a lower wear resistance compared to counterparts made of 100Cr6. The friction coefficient could be reduced by using a V2A counterpart. The results can be understood in terms of a reduced adhesion of both oxidic and metallic wear debris at the TiAlCrSiN surface. The study provides valuable progress towards the development of advanced cutting tools, e.g., for stainless steel. Full article
(This article belongs to the Special Issue Mechanical Properties and Tribological Behavior of Alloy/Coatings)
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12 pages, 34895 KiB  
Article
Ultra-High-Sensitivity and -Stability Thin-Film Heat Flux Sensor Based on Transverse Thermoelectric Effect
by Hao Chen, Yong Wang, Zao Yi, Bo Dai, Bin Tang, Xibin Xu and Yougen Yi
Coatings 2023, 13(9), 1610; https://doi.org/10.3390/coatings13091610 - 14 Sep 2023
Cited by 9 | Viewed by 1638
Abstract
In this study, we investigate the sensitivity properties of YBa2Cu3O7-δ thin films with a 15° tilting angle in relation to heat flux density. The films were prepared using the laser pulsed deposition (PLD) technique, and their characteristics were [...] Read more.
In this study, we investigate the sensitivity properties of YBa2Cu3O7-δ thin films with a 15° tilting angle in relation to heat flux density. The films were prepared using the laser pulsed deposition (PLD) technique, and their characteristics were evaluated using various techniques, including X-ray diffraction (XRD), transmission electron microscopy (TEM), atomic force microscopy (AFM), and infrared steady-state and laser transient calibration systems. The YBa2Cu3O7-δ films prepared in this study were found to be of good quality, exhibiting a single-phase structure with strict (001) orientation. Both the substrate and film diffraction peaks were sharp and consistent with the step-flow growth mode, indicating high crystalline quality. Ultra-high sensitivity in the range of 0 to 100 kW/m2, the maximum sensitivity is 230 μV/(kW/m2), and an uncertainty is only 3%. According to the infrared steady-state heat flux calibration system test, when the single output power of the quartz lamp array is 0.2 kW, 0.3 kW, 0.4 kW and 0.5 kW, the maximum output voltage is 0.19 mV, 0.41 mV, 0.63 mV and 0.94 mV, respectively, indicating that the output voltage of the sensor increases with the increase in heat flux, showing a good linear characteristic, and the fitting linearity is 0.99. Through the test of the laser transient thermal current calibration system, the sensors are found to have excellent response–recovery characteristics at 500 kHz and 1000 kHz fiber laser frequencies, and the maximum voltage output is 8.83 mV and 9.09 mV, respectively. Moreover, the component has excellent repeatability, and the maximum measurement error is only 1.94%. Our findings demonstrate the potential of YBa2Cu3O7-δ thin films for use in heat flux sensing applications. Full article
(This article belongs to the Special Issue Micro-Nano Optics and Its Applications)
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16 pages, 3309 KiB  
Article
Using an Interlayer to Toughen Flexible Colorless Polyimide-Based Cover Windows
by Yusuke Matsuda, Yinjie Cen, Luke Bu, Jieqian Zhang, Kostantinos Kourtakis, Tao Huang, Yixuan Song, Mobin Yahyazadehfar, Derek Caputo, John Podhiny, Leopoldo Carbajal and Aref Samadi-Dooki
Coatings 2023, 13(9), 1597; https://doi.org/10.3390/coatings13091597 - 13 Sep 2023
Viewed by 1164
Abstract
Colorless polyimide (PI)-based flexible cover windows are a critical component of flexible electronics to protect devices from unwanted chemical and mechanical damage. The integration of flexible colorless PI-based windows into electronics applications is limited by the embrittlement of some colorless PI films when [...] Read more.
Colorless polyimide (PI)-based flexible cover windows are a critical component of flexible electronics to protect devices from unwanted chemical and mechanical damage. The integration of flexible colorless PI-based windows into electronics applications is limited by the embrittlement of some colorless PI films when they are coated with hard coats. Here, we investigate the embrittlement mechanism of hard-coated colorless PI films and the role of interlayers in toughening the colorless PI-based cover windows for flexible electronics applications. A fracture mechanics approach combined with finite element analysis (FEA) models is employed to compute fracture strain, εc, for different crack cases in the bilayer (hard coated colorless PI) and trilayer (with an additional interlayer) cover windows. For the model inputs and validation, the material properties of the cover windows are characterized. We show that the embrittlement is attributed to the fracture behavior of the cover windows, and placing a ductile interlayer increases the εc of colorless PI films. Using the fracture analysis as a design guide, we fabricate a trilayer cover window with an acrylic thermoset interlayer and demonstrate an improvement of the εc of the colorless PI cover window by ~42%. We believe our analysis provides insights into design guides for mechanically robust cover windows using colorless PI films and flexible HCs for emerging flexible electronics. Full article
(This article belongs to the Special Issue Polymer Films/Membranes: Structure, Properties, and Applications)
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19 pages, 4252 KiB  
Review
Functionalization of Fabrics with Graphene-Based Coatings: Mechanisms, Approaches, and Functions
by Yang Liu, Bin Fei and John H. Xin
Coatings 2023, 13(9), 1580; https://doi.org/10.3390/coatings13091580 - 11 Sep 2023
Cited by 1 | Viewed by 2252
Abstract
Due to their unique surface-active functionalities, graphene and its derivatives, i.e., graphene oxide (GO) and reduced graphene oxide (rGO), have received enormous research attention in recent decades. One of the most intriguing research hot spots is the integration of GO and rGO coatings [...] Read more.
Due to their unique surface-active functionalities, graphene and its derivatives, i.e., graphene oxide (GO) and reduced graphene oxide (rGO), have received enormous research attention in recent decades. One of the most intriguing research hot spots is the integration of GO and rGO coatings on textiles through dyeing methods, e.g., dip-pad-dry. In general, the GO sheets can quickly diffuse into the fabric matrix and deposit onto the surface of the fibers through hydrogen bonding. The GO sheets can be conformally coated on the fiber surface, forming strong adhesion as a result of the high flakiness ratio, mechanical strength, and deformability. Moreover, multiple functions with application significance, e.g., anti-bacteria, UV protection, conductivity, and wetting control, can be achieved on the GO and rGO-coated fabrics as a result of the intrinsic chemical, physical, electronic, and amphiphilic properties of GO and rGO. On the other hand, extrinsic functions, including self-cleaning, self-healing, directional water transport, and oil/water separation, can be achieved for the GO and rGO coatings by the integration of other functional materials. Therefore, multi-scale, multifunctional, smart fabrics with programmable functions and functional synergy can be achieved by the design and preparation of the hybrid GO and rGO coatings, while advanced applications, e.g., healthcare clothing, E-textiles, anti-fouling ultrafiltration membranes, can be realized. In this review, we aim to provide an in-depth overview of the existing methods for functionalizing fabrics with graphene-based coatings while the corresponding functional performance, underlying mechanisms and applications are highlighted and discussed, which may provide useful insights for the design and fabrication of functional textiles and fabrics for different applications. Full article
(This article belongs to the Special Issue Advanced Nanocomposite Coatings for Biomedical Engineering)
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12 pages, 2576 KiB  
Article
Influence of Deposition Conditions and Thermal Treatments on Morphological and Chemical Characteristics of Li6.75La3Zr1.75Ta0.25O12 Thin Films Deposited by Nanosecond PLD
by Mariangela Curcio, Sergio Brutti, Arcangelo Celeste, Agostino Galasso, Angela De Bonis and Roberto Teghil
Coatings 2023, 13(9), 1496; https://doi.org/10.3390/coatings13091496 - 24 Aug 2023
Cited by 1 | Viewed by 1836
Abstract
The production of thin films has been extensively studied due to their unique properties that make them highly useful in a wide range of scientific and technological applications. Obtaining thin films with well-defined stoichiometry and crystallinity is a challenging task, especially when dealing [...] Read more.
The production of thin films has been extensively studied due to their unique properties that make them highly useful in a wide range of scientific and technological applications. Obtaining thin films with well-defined stoichiometry and crystallinity is a challenging task, especially when dealing with materials of complex stoichiometry. Among diverse methodologies for the manufacture of thin films, pulsed laser deposition (PLD) stands out as a versatile technique for producing crystalline films with complex chemical compositions. In this study, nanosecond PLD was employed to manufacture thin films of Ta-doped Li7La3Zr2O12 (LLZTO), a garnet-like oxide that has been proposed as solid electrolyte for Li-ion solid state batteries. Two distinct deposition atmospheres were investigated: vacuum conditions at 10−3 Pa and an oxygen-enriched environment with 10 Pa of O2 gas buffer. To mitigate lithium losses during deposition, a minor addition of lithium oxide was incorporated into the target. The effects of deposition atmosphere and the impact of post-deposition annealing on the structural, compositional, and morphological properties of LLZTO thin films were analysed through a multi-technique approach. The results suggest deposition under oxygen pressure led to the growth of compact, crystalline films characterized by homogenous elemental distribution across the surface and throughout the film’s depth. These films closely resemble the composition of the target LLZTO material, offering valuable insights for the fabrication of high-quality complex oxide thin films. Full article
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24 pages, 7460 KiB  
Article
Evaluation of Antimicrobial and Antioxidant Activities of Alginate Edible Coatings Incorporated with Plant Extracts
by Ana I. Lopes, Adma Melo, Cristina Caleja, Eliana Pereira, Tiane C. Finimundy, Tiago B. Afonso, Sara Silva, Marija Ivanov, Marina Soković, Freni K. Tavaria, Lillian Barros and Manuela Pintado
Coatings 2023, 13(9), 1487; https://doi.org/10.3390/coatings13091487 - 23 Aug 2023
Cited by 9 | Viewed by 3596
Abstract
Plant extracts (PEs) are natural substances that perform interesting bioactivities. However, they have some limitations. In this work, PEs from licorice, eucalyptus, sage, and thyme were produced and characterized. These extracts showed good bioactive properties. Alginate-based edible coatings and films incorporated with the [...] Read more.
Plant extracts (PEs) are natural substances that perform interesting bioactivities. However, they have some limitations. In this work, PEs from licorice, eucalyptus, sage, and thyme were produced and characterized. These extracts showed good bioactive properties. Alginate-based edible coatings and films incorporated with the extracts were produced and their antimicrobial and antioxidant properties were determined. The results showed that the coatings completely inhibited or reduced the growth of all bacteria (E. coli, P. aeruginosa, B. cereus, L. monocytogenes, and S. aureus), except the coating with sage extract. However, only the films incorporated with licorice and eucalyptus could inhibit the growth of Gram-positive bacteria and none of the films were able to inhibit Gram-negative bacteria. The film incorporated with sage extract was the one with the best antifungal property. All films possess a good antioxidant property (ABTS: 942.52–5654.62; DPPH: 1040.67–5162.93 Trolox equivalents (µM)/mg film). Based on the results, it is possible to conclude that alginate coatings and films with PEs present good bioactive properties and can potentially be used as new, biodegradable packages. However, further experiments need to be performed to assess their safety profile, and to prove that they can be a real alternative to traditional food packaging. Full article
(This article belongs to the Section Coatings for Food Technology and System)
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18 pages, 2633 KiB  
Article
Temperature Dependent Anti-Icing Performance of the Microstructure Surface: Wettability Change and Ice Nucleation
by Yi Lu
Coatings 2023, 13(9), 1485; https://doi.org/10.3390/coatings13091485 - 22 Aug 2023
Cited by 2 | Viewed by 1765
Abstract
Icing has caused much inconvenience to daily production and life. A microstructure surface possessing a hydrophobic property is an effective countermeasure to impede or delay ice formation for anti-icing purposes. However, surface wettability is sensitive to environmental conditions such as temperature and humidity. [...] Read more.
Icing has caused much inconvenience to daily production and life. A microstructure surface possessing a hydrophobic property is an effective countermeasure to impede or delay ice formation for anti-icing purposes. However, surface wettability is sensitive to environmental conditions such as temperature and humidity. In the worst-case scenario, a Wenzel state drop forms and causes degradation of surface anti-icing performance. In this study, a copper alloy was used as the testing sample, and the surface was fabricated using mechanical polishing, micro-milling machining and ultrafast laser etching to form the desired topology and microstructures. The hydrophobicity and icephobicity of four types of surfaces including smooth flat, rough flat, rough microstructure and smooth microstructure were tested by depositing droplets from room temperature to an ultralow subzero temperature condition (below −30 °C). At −10 °C, the icephobicity of the surface was consistent with the surface wettability at room temperature. However, the hydrophobicity of the surface slightly decreased, and a Wenzel state drop formed on the microstructure surface. At −30 °C, the apparent contact angle and the ice–substrate contact area were mainly affected by ice nucleation rather than surface wettability. The bottom layer of the droplet froze after immediate contact with the substrate due to a higher degree of supercooling. The formation of a Cassie state drop reduced the ice–substrate contact area and created more air cushions, which facilitated the extension of the icing process of the drop. The enhancement in the anti-icing performance of the microstructure surface was analyzed from a theoretical basis. Full article
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20 pages, 7439 KiB  
Article
Effect of Post-Fabrication Heat Treatments on the Microstructure of WC-12Co Direct Energy Depositions
by Cindy Morales, Annalisa Fortini, Chiara Soffritti and Mattia Merlin
Coatings 2023, 13(8), 1459; https://doi.org/10.3390/coatings13081459 - 19 Aug 2023
Cited by 2 | Viewed by 2939
Abstract
Laser-Directed Energy Deposition (L-DED) is an additive manufacturing technique that has lately been employed to deposit coatings of cemented carbides, such as WC-Co. During deposition, complex microstructural phenomena usually occur, strongly affecting the microstructural and mechanical behavior of the coatings. Post-fabrication heat treatments [...] Read more.
Laser-Directed Energy Deposition (L-DED) is an additive manufacturing technique that has lately been employed to deposit coatings of cemented carbides, such as WC-Co. During deposition, complex microstructural phenomena usually occur, strongly affecting the microstructural and mechanical behavior of the coatings. Post-fabrication heat treatments (PFHTs) may be applied to homogenize and strengthen the microstructure; nevertheless, to the best of the authors’ knowledge, just a few papers deepened the effect of these treatments on cemented carbides fabricated by additive manufacturing. This work evaluates the influence of four PFHTs on the microstructural evolution and hardness of L-DED WC-12Co. For each treatment, different combinations of solubilization time and temperature (between 30 and 180 min and from 400 °C to 700 °C, respectively) were adopted. The microstructure was investigated by optical and scanning electron microscopy equipped with energy-dispersive spectroscopy, whereas the mechanical properties were determined by Vickers hardness measurements. Based on the results, high microstructural heterogeneity in terms of WC particles, η-phase structures, and Co distribution was observed in the sample in the as-built condition. Some cracking defects were also observed in the samples, irrespective of the heat treatment conditions. Finally, a finer microstructure and a lower amount of brittle ternary η-phase, together with an increase in hardness (1030 ± 95 HV10), were found for the highest dwelling times (180 min) and for solubilization temperatures in the range of 500–600 °C. Full article
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30 pages, 15807 KiB  
Article
Characterization and Corrosion Behavior of Zinc Coatings for Two Anti-Corrosive Protections: A Detailed Study
by Alina Bianca Pop, Gheorghe Iepure, Aurel Mihail Titu and Sandor Ravai-Nagy
Coatings 2023, 13(8), 1460; https://doi.org/10.3390/coatings13081460 - 19 Aug 2023
Cited by 1 | Viewed by 3801
Abstract
The purpose of this research is to characterize and evaluate the corrosion behavior of zinc coatings used for corrosion protection, with a special focus on the S235 steel material. The introduction highlights the need for corrosion protection in industrial settings, as well as [...] Read more.
The purpose of this research is to characterize and evaluate the corrosion behavior of zinc coatings used for corrosion protection, with a special focus on the S235 steel material. The introduction highlights the need for corrosion protection in industrial settings, as well as the importance of understanding corrosion processes and the development of corrosion products to develop more effective solutions. The study’s goals are to undertake an extensive analysis of corrosion products formed on the zinc coating’s surface, to evaluate the performance of these coatings under atmospheric circumstances, and to investigate the effect of deposition parameters on coating quality. The essential message provided to readers is the critical significance of knowing corrosion product formation mechanisms and zinc coating corrosion behavior in developing long-lasting and effective protection measures. The study methodology includes cycle testing, morphological and chemical examination of corrosion products, as well as optical and electron microscopy and energy-dispersive spectroscopy. Corrosion resistance is assessed using accurate measurements. The results show that zinc coatings have exceptional corrosion resistance under air settings, with the produced corrosion products offering further protection to the underlying material. Furthermore, the study demonstrates that the surface roughness of S235 steel has a substantial impact on the quality and corrosion behavior of hot-dip galvanized coatings. The findings emphasize the necessity of detailed characterization of corrosion products, the effect of depositional factors on zinc coating performance, and the need for novel corrosion protection methods. These discoveries have significant implications for the corrosion protection sector, providing the potential to improve the longevity and efficiency of protective systems used in industrial applications. Full article
(This article belongs to the Special Issue Surface Modification of Magnesium, Aluminum Alloys, and Steel)
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14 pages, 3280 KiB  
Article
Green Synthesis and Antibacterial Activity of Silver Nanoparticles Obtained from Moringa oleifera Seed Cake
by Nuno Coelho, João P. Jacinto, Rodrigo Silva, Jéssica C. Soares, Alice S. Pereira and Pedro Tavares
Coatings 2023, 13(8), 1439; https://doi.org/10.3390/coatings13081439 - 16 Aug 2023
Cited by 3 | Viewed by 1907
Abstract
In the present work, we report a simple, cost-efficient, and eco-friendly green method to synthesize silver nanoparticles with antimicrobial activity. An ethanolic extract from Moringa oleifera seed residue was used as a reducing and stabilizing agent in an aqueous solution of silver nitrate. [...] Read more.
In the present work, we report a simple, cost-efficient, and eco-friendly green method to synthesize silver nanoparticles with antimicrobial activity. An ethanolic extract from Moringa oleifera seed residue was used as a reducing and stabilizing agent in an aqueous solution of silver nitrate. The synthesized silver nanoparticles’ hydrodynamic radius, polydispersity index, and zeta-potential were evaluated by Dynamic Light Scattering. Scanning Electron Microscopy was employed to confirm the size and morphology of the nanoparticles. Synthesis of spherical particles with 127 ± 24 nm was confirmed. After sintering, the product of the synthesis was analyzed by X-ray diffraction. The X-ray diffraction pattern attributed to reflections of the (111), (200), (220), and (311) planes, which are characteristic of silver nanoparticles, confirms the successful synthesis of crystalline face-centered cubic nanoparticles. The antimicrobial activity of the bionanoparticles was tested against Escherichia coli BL21(DE3) cells and compared with the effect of a Moringa oleifera seed cake extract. Herein, we show that the growth of Escherichia coli is significantly affected by the addition of the synthesized bionanoparticles. Addition of the bionanoparticles inhibited the growth and lengthened the lag phase of the bacterial culture. Full article
(This article belongs to the Section Bioactive Coatings and Biointerfaces)
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20 pages, 19407 KiB  
Article
Fe/TaC Coatings Produced on 145Cr6 Steel by Laser Alloying—Manufacturing Parameters and Material Characterization
by Dariusz Bartkowski and Aneta Bartkowska
Coatings 2023, 13(8), 1432; https://doi.org/10.3390/coatings13081432 - 15 Aug 2023
Viewed by 2197
Abstract
This paper focuses on Fe/TaC composite coatings produced on 145Cr6 steel by laser alloying a TaC precoat in paste form. Fe/TaC coatings were produced in two consecutive steps. The first stage was the application of a precoat in paste form made from tantalum [...] Read more.
This paper focuses on Fe/TaC composite coatings produced on 145Cr6 steel by laser alloying a TaC precoat in paste form. Fe/TaC coatings were produced in two consecutive steps. The first stage was the application of a precoat in paste form made from tantalum carbide and water glass on a steel substrate. Three TaC precoat thicknesses were produced: 30 µm, 60 µm and 90 µm. In the second step, the TaC precoat was remelted on a steel substrate using a 3 kW rated diode laser beam. A constant laser beam scanning speed of 3 m/min and three laser beam powers were used: 500 W, 800 W and 1100 W. In the study, microstructure, microhardness, chemical and phase composition and wear resistance were tested. The aim of the research was to check the possibility of producing composite coatings in which the reinforcing phase will be TaC, and the role of the matrix will be played by the material from the substrate. It was found that it is possible to produce the continuous composite coatings by remelting the TaC precoat with steel substrate. As microhardness increased, so did wear resistance. The coating microhardness obtained ranged from about 750 to 850 HV0.05 depending on the parameters used. Full article
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10 pages, 2672 KiB  
Article
Coating of Carbonized Leather Waste with the Conducting Polymer Polyaniline: Bicontinuous Composites for Dye Adsorption
by Jaroslav Stejskal, Fahanwi Asabuwa Ngwabebhoh, Tomáš Sáha and Jan Prokeš
Coatings 2023, 13(8), 1419; https://doi.org/10.3390/coatings13081419 - 13 Aug 2023
Cited by 2 | Viewed by 2344
Abstract
Leather waste carbonized at 800 °C in an inert atmosphere was coated in situ with the conducting polymer polyaniline. The composition of composites varied from neat carbonaceous to polyaniline. Due to the fibrous collagen structure of the original leather after carbonization, the composites [...] Read more.
Leather waste carbonized at 800 °C in an inert atmosphere was coated in situ with the conducting polymer polyaniline. The composition of composites varied from neat carbonaceous to polyaniline. Due to the fibrous collagen structure of the original leather after carbonization, the composites had a bicontinuous conducting morphology. The resistivity of composites determined as a function of applied pressure from 0.1 to 10 MPa fell mainly into the range of units to tens of Ω cm. In contrast to neat polyaniline, the composites maintained a good level of conductivity even under alkaline conditions. The application of a composite as an adsorbent of organic-dye pollutants in water treatment was illustrated using methylene blue and methyl orange with an eye to future functional adsorbents controllable by applied electrical potential. Full article
(This article belongs to the Special Issue Functional Polymer Films and Their Applications)
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15 pages, 3824 KiB  
Article
Assessing the Bioreceptivity of Biobased Cladding Materials
by Karen Butina Ogorelec, Ana Gubenšek, Faksawat Poohphajai and Anna Sandak
Coatings 2023, 13(8), 1413; https://doi.org/10.3390/coatings13081413 - 11 Aug 2023
Cited by 2 | Viewed by 1849
Abstract
Materials exposed to the outdoors are prone to various deterioration processes. Architectural coatings are designed to protect surfaces against environmental and biotic degradation and to provide a decorative layer. The objective of this work was to examine the early colonisers on a diverse [...] Read more.
Materials exposed to the outdoors are prone to various deterioration processes. Architectural coatings are designed to protect surfaces against environmental and biotic degradation and to provide a decorative layer. The objective of this work was to examine the early colonisers on a diverse set of coated and non-coated biobased façade materials. A set of 33 wood-based cladding materials were exposed to four cardinal directions and monitored in outdoor conditions. The surfaces were sampled using a wet swab and plated on DG-18 agar, which prevents the growth of bacteria and limits the growth of fast-growing fungi. Pure cultures were then isolated and identified through PCR amplification and Sanger sequencing of specific DNA regions/genes. The response of cladding materials to weathering and fungal infestation was assessed. The proposed techniques enabled the identification of features that promote/inhibit fungal colonisation and revealed the preference of certain fungi for specific materials. Both the material type and the climate condition at the exposure site influence fungal colonisation. This study is a starting point for more exhaustive assays that aim to develop a novel coating system based on controlled and optimized fungal biofilm formation, and is proposed as a nature-inspired alternative for the protection of architectonic surfaces. Full article
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38 pages, 17603 KiB  
Review
Materials, Structures, and Applications of iTENGs
by Yuan Xi, Yubo Fan, Zhou Li and Zhuo Liu
Coatings 2023, 13(8), 1407; https://doi.org/10.3390/coatings13081407 - 10 Aug 2023
Cited by 2 | Viewed by 1589
Abstract
Implantable triboelectric nanogenerators (iTENG) have emerged as a promising technology for self-powered biomedical devices. This review explores the key aspects of materials, structures, and representative applications of iTENGs. The materials section discusses the core triboelectric layer, electrode layer, and encapsulation layer, emphasizing the [...] Read more.
Implantable triboelectric nanogenerators (iTENG) have emerged as a promising technology for self-powered biomedical devices. This review explores the key aspects of materials, structures, and representative applications of iTENGs. The materials section discusses the core triboelectric layer, electrode layer, and encapsulation layer, emphasizing the importance of biocompatibility and mechanical flexibility. The structural design section delves into three common modes: contact–separation mode, single-electrode mode, and free-standing mode, highlighting their working principles and advantages. The application section covers diverse areas such as cardiac devices, sterilization processes, and anticancer therapies, showcasing the potential of iTENGs to revolutionize healthcare. Moreover, it discusses the challenges and future directions for material development, structural design optimization, conformal matching, and practical implementation of iTENGs. This comprehensive review provides valuable insights into the materials, structures, and applications of iTENGs, serving as a resource for researchers and engineers in the field. Full article
(This article belongs to the Special Issue Advanced Polymer and Thin Film for Sustainable Energy Harvesting)
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17 pages, 2753 KiB  
Article
Effect of Mucilage-Based Edible Coating Enriched with Oregano Essential Oil on Postharvest Quality and Sensorial Attributes of Fresh-Cut Loquat
by Giorgia Liguori, Giuseppe Greco, Francesco Gargano, Raimondo Gaglio, Luca Settanni and Paolo Inglese
Coatings 2023, 13(8), 1387; https://doi.org/10.3390/coatings13081387 - 7 Aug 2023
Cited by 5 | Viewed by 2234
Abstract
Due to pulp browning, weight loss, firmness loss, and decay, loquat fruits, and even more minimally processed fruits have a very short post-harvest life. The aim of our study was to evaluate the effect of Opuntia ficus-indica mucilage-based edible coating enriched with oregano [...] Read more.
Due to pulp browning, weight loss, firmness loss, and decay, loquat fruits, and even more minimally processed fruits have a very short post-harvest life. The aim of our study was to evaluate the effect of Opuntia ficus-indica mucilage-based edible coating enriched with oregano oil on postharvest quality, microbial growth, and sensorial attributes of fresh-cut cv Martorana loquat fruit during cold storage. Fresh-cut loquat fruits were dipped in the mucilage-based solution enriched with oregano essential oil (MO-EC) and in distilled water used as control (CTR). According to our results, the mucilage-based edible coating enriched with oregano oil significantly improved the postharvest life of minimally processed loquat fruits by preserving quality, nutraceutical value, and sensory aspects. MO-EC had a barrier effect on fresh-cut loquat fruit, reducing weight and firmness losses, inhibiting TSS, TA, ascorbic acid content decrease, and enhancing the antioxidant activity until the end of the cold storage period (11 days at 5 °C). Microbiological analysis revealed that coated loquat fruits were characterized by a cell density of spoilage microorganisms 1 Log cycle lower than control fruits. The mucilage-based coating enriched with OEO positively affects the visual appearance of fresh-cut loquat fruits, at the end of the cold storage period, MO-EC samples did indeed report visual ratings that were five times greater than CTR samples. Our research suggests that applying mucilage-based coating enriched with OEO improves peeled loquat fruit shelf-life and allows the producers to sell products that are usually considered unmarketable (fruit with epicarp with large spot areas) to the market. Full article
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17 pages, 8388 KiB  
Article
Production and Characterization of Graphene Oxide Surfaces against Uropathogens
by Samuel Belo, Francisca Sousa-Cardoso, Rita Teixeira-Santos, Luciana C. Gomes, Rita Vieira, Jelmer Sjollema, Olívia S. G. P. Soares and Filipe J. Mergulhão
Coatings 2023, 13(8), 1324; https://doi.org/10.3390/coatings13081324 - 28 Jul 2023
Cited by 3 | Viewed by 2207
Abstract
Graphene and its functionalized derivatives have been increasingly applied in the biomedical field, particularly in the production of antimicrobial and anti-adhesive surfaces. This study aimed to evaluate the performance of graphene oxide (GO)/polydimethylsiloxane (PDMS) composites against Staphylococcus aureus and Pseudomonas aeruginosa biofilms. GO/PDMS [...] Read more.
Graphene and its functionalized derivatives have been increasingly applied in the biomedical field, particularly in the production of antimicrobial and anti-adhesive surfaces. This study aimed to evaluate the performance of graphene oxide (GO)/polydimethylsiloxane (PDMS) composites against Staphylococcus aureus and Pseudomonas aeruginosa biofilms. GO/PDMS composites containing different GO loadings (1, 3, and 5 wt.%) were synthesized and characterized regarding their morphology, roughness, and hydrophobicity, and tested for their ability to inhibit biofilm formation under conditions that mimic urinary tract environments. Biofilm formation was assessed by determining the number of total and culturable cells. Additionally, the antibacterial mechanisms of action of GO were investigated for the tested uropathogens. Results indicated that the surfaces containing GO had greater roughness and increased hydrophobicity than PDMS. Biofilm analysis showed that the 1 wt.% GO/PDMS composite was the most effective in reducing S. aureus biofilm formation. In opposition, P. aeruginosa biofilms were not inhibited by any of the synthesized composites. Furthermore, 1% (w/v) GO increased the membrane permeability, metabolic activity, and endogenous reactive oxygen species (ROS) synthesis in S. aureus. Altogether, these results suggest that GO/PDMS composites are promising materials for application in urinary catheters, although further investigation is required. Full article
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16 pages, 11179 KiB  
Article
Development of a Transparent Thermal Reflective Thin Film Coating for Accurate Separation of Food-Grade Plastics in Recycling Process via AI-Based Thermal Image Processing
by Ali Salimian and Uchechukwu Onwukwe
Coatings 2023, 13(8), 1332; https://doi.org/10.3390/coatings13081332 - 28 Jul 2023
Viewed by 3120
Abstract
This paper presents the development of a specific thin film coating designed to address the challenge of accurately separating food-grade plastics in the recycling process. The coating, created using a plasma sputtering process, is transparent to the visible spectrum of light while effectively [...] Read more.
This paper presents the development of a specific thin film coating designed to address the challenge of accurately separating food-grade plastics in the recycling process. The coating, created using a plasma sputtering process, is transparent to the visible spectrum of light while effectively reflecting infrared emissions above 1500 nm. Composed of a safe metal oxide formulation with a proprietary composition, the coating is applied to packaging labels. By employing thermal imaging and a computer vision AI model, the coated labels enable precise differentiation of plastics associated with food packaging in the initial stage of plastic recycling. The proposed system achieved a remarkable 100% accuracy in separating food-grade plastics from other types of plastics. This innovative approach holds great potential for enhancing the efficiency and effectiveness of plastic recycling processes, ensuring the recovery of food-grade plastics for future use. Full article
(This article belongs to the Special Issue Advanced Coatings and Films for Food Packing and Storage)
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15 pages, 4909 KiB  
Article
Improving the Technical Characteristics of Untreated and Heat-Treated Ayous Wood against Accelerating Ageing by Testing Two Application Modalities of an Innovative Polyurethane Coating for Outdoor Uses
by Gianluca Rubino, Angela Lo Monaco, Luca Lanteri and Claudia Pelosi
Coatings 2023, 13(8), 1312; https://doi.org/10.3390/coatings13081312 - 26 Jul 2023
Cited by 1 | Viewed by 1437
Abstract
This paper presents the results of tests of a new mono-component polyurethane coating for wood with the aim of evaluating its effect on Ayous (Triplochiton scleroxylon K. Schum), which is a wood species used in Europe for various applications, especially outdoors, after [...] Read more.
This paper presents the results of tests of a new mono-component polyurethane coating for wood with the aim of evaluating its effect on Ayous (Triplochiton scleroxylon K. Schum), which is a wood species used in Europe for various applications, especially outdoors, after being heat treated. The coating was tested on both untreated and thermally treated samples, as the latter procedure is commonly used in the wood industry to modify the material’s characteristics. Moreover, two kinds of coating application were tested: coatings applied via brushing and coatings applied via spraying; in this test, we also verified the most suitable and effective modality. Samples were investigated using the following techniques: colour measurement, roughness mapping, contact angle measurement, surface micro-hardness and the wearing test; these techniques were applied before and after a period of artificial ageing under simulated solar irradiation. Upon synthesizing the main results, we identified the following results: (i) the polyurethane coating reduced the colour variation as a result of artificial aging of the untreated Ayous wood; in contrast, heat-treated wood underwent large colour changes; (ii) the coating acted effectively as a hydrophobic agent on the surface of the wood in each case examined, though even a short aging time altered the initial wettability characteristics; and (iii) the application of the coating caused a decrease in the roughness of both untreated and heat-treated surfaces, though this trend was much more evident in the case of the spray modality of application; however, aging always induced an increase in roughness, which was mainly observed in uncoated wood samples. Full article
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11 pages, 3606 KiB  
Article
Influence of Surface Roughness on Nanocrystalline Diamond Films Deposited by Distributed Antenna Array Microwave System on TA6V Substrates
by Azadeh Valinattaj Omran, Chaimaa Mahi, Romain Vayron, Céline Falentin-Daudré and Fabien Bénédic
Coatings 2023, 13(7), 1300; https://doi.org/10.3390/coatings13071300 - 24 Jul 2023
Cited by 1 | Viewed by 2626
Abstract
In this study, the characteristics of nanocrystalline diamond films synthesized at low surface temperature on Ti-6Al-4V (TA6V) substrates using a distributed antenna array microwave reactor aiming at biomedical applications were investigated. The surface roughness of the TA6V substrates is varied by scratching with [...] Read more.
In this study, the characteristics of nanocrystalline diamond films synthesized at low surface temperature on Ti-6Al-4V (TA6V) substrates using a distributed antenna array microwave reactor aiming at biomedical applications were investigated. The surface roughness of the TA6V substrates is varied by scratching with emery paper of 1200, 2400, 4000 polishing grit. Nanocrystalline diamond (NCD) coatings with morphology, purity, and microstructure comparable to those obtained on silicon substrates usually employed in the same reactor and growth conditions are successfully achieved whatever the polishing protocol. However, the latter has a significant effect on the roughness parameters and hardness of the NCD films. The use of the finest polishing grit thus permits us to enhance the hardness value, which can be related to the work-hardening phenomenon arising from the polishing process. Full article
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21 pages, 1088 KiB  
Review
Present and Future of ZrO2 Nanostructure as Reservoir for Drug Loading and Release
by Ramona-Daniela Radu (Dușman) and Doina Drăgănescu
Coatings 2023, 13(7), 1273; https://doi.org/10.3390/coatings13071273 - 20 Jul 2023
Cited by 5 | Viewed by 2179
Abstract
Extensive research has been conducted on ZrO2 nanostructures due to their favorable biocompatibility, low toxicity, and promising prospects in various biomedical applications. They can be used as drug carriers, facilitating the administration of therapeutic substances into the body while enhancing their effectiveness [...] Read more.
Extensive research has been conducted on ZrO2 nanostructures due to their favorable biocompatibility, low toxicity, and promising prospects in various biomedical applications. They can be used as drug carriers, facilitating the administration of therapeutic substances into the body while enhancing their effectiveness and safety. This is achieved by regulating the timing, location, and rate at which drugs are released within the body. Several factors can influence the effectiveness of drug loading onto ZrO2 nanostructures, such as the physicochemical characteristics of the drugs, the surface properties of the ZrO2 nanostructures, and the specific methods used for drug loading. A wide range of drugs may be loaded onto ZrO2 nanostructures including anti-cancer drugs, antibiotics, anti-inflammatory drugs, antifungal drugs, anti-osteoporotic drugs, etc. The release kinetics of drugs can be influenced by different factors, such as the size and shape of ZrO2 nanostructures, the pH and temperature of the release medium, and the characteristics and molecular weight of the specific drug being released. While ZrO2 nanostructures have demonstrated significant potential as drug delivery systems, further research on these structures is essential to optimize drug loading and release strategies. Full article
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21 pages, 10324 KiB  
Article
Effect of Zn on Phase Evolution and Shear Resistance of Stainless Steel and Aluminum Alloy Interface by Laser Cladding
by Keyan Wang, Xianqing Yin, Chengxin Li and Kaiping Du
Coatings 2023, 13(7), 1267; https://doi.org/10.3390/coatings13071267 - 19 Jul 2023
Cited by 1 | Viewed by 1229
Abstract
The connection between aluminum and iron alloys is of immense significance in the pursuit of lightweight industrial products. However, the Fe-Al interface’s inherent weakness restricts its widespread application. This study investigates the impact of Zn at the interface of Al-Fe laser cladding on [...] Read more.
The connection between aluminum and iron alloys is of immense significance in the pursuit of lightweight industrial products. However, the Fe-Al interface’s inherent weakness restricts its widespread application. This study investigates the impact of Zn at the interface of Al-Fe laser cladding on the phase and mechanical properties of the interface. Specifically, we examine the influence of the applied Zn powder layer and alloying Zn layer on the morphology of the Fe-based cladding layer. The inclusion of Zn enhances the spreadability of the Fe-based cladding layer. Additionally, we elucidate the effect of Zn on the composition and phase of the Fe-Al laser cladding interface. Notably, the affinity between Zn and the η phase surpasses that of the θ phase, and an increased Zn content significantly thickens the η phase. Shear tests reveal that the failure mode of shear fracture encompasses both brittle and ductile fractures. Density functional theory (DFT) calculations indicate that Zn has a limited effect on the strength of the η phase but reduces the enthalpy of formation of the η phase. Our findings demonstrate that the alloyed Zn layer initially facilitates the formation of a continuous and uniform η layer, while an increased Zn content enhances and stabilizes the shear strength of the interface. Full article
(This article belongs to the Special Issue Laser Cladding Coatings: Microstructure, Properties, and Applications)
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11 pages, 12980 KiB  
Article
Quasi Non-Destructive Quality Assessment of Thermally Sprayed AISI 316L Coatings Using Polarization Measurements in 3.5% NaCl Gel Electrolyte
by Maximilian Grimm, Pia Kutschmann, Christian Pluta, Olga Schwabe, Thomas Lindner and Thomas Lampke
Coatings 2023, 13(7), 1256; https://doi.org/10.3390/coatings13071256 - 16 Jul 2023
Viewed by 1216
Abstract
There is currently a lack of suitable methods of non-destructive quality assessment of thermally sprayed coatings. Therefore, this study investigates the suitability of polarization measurements that are adapted to the special needs of thermally sprayed coatings for non-destructive quality testing. For this purpose, [...] Read more.
There is currently a lack of suitable methods of non-destructive quality assessment of thermally sprayed coatings. Therefore, this study investigates the suitability of polarization measurements that are adapted to the special needs of thermally sprayed coatings for non-destructive quality testing. For this purpose, a gel electrolyte containing 3.5% NaCl and a measuring cell based on the three-electrode arrangement were developed to prevent the corrosion medium from infiltrating the typical microstructure of thermally sprayed coatings (pores and microcracks). The newly developed method was evaluated on AISI 316L coatings deposited by high velocity air fuel (HVAF) and atmospheric plasma spraying (APS). The polarization curves showed significant differences as a result of spraying process-related changes in the coating microstructure. Even slight differences in oxide content within the AISI 316L coating produced by APS can be detected by the new method. In order to verify the new findings, the coatings were analyzed regarding their microstructure by optical microscope, scanning electron microscope and energy dispersive X-ray spectroscopy. The measuring cell and gel electrolyte developed offer a promising opportunity to evaluate the quality of thermally sprayed coatings in a largely non-destructive manner using polarization curves. Full article
(This article belongs to the Special Issue Advances in Novel Coatings)
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9 pages, 5005 KiB  
Article
Optoelectronic Properties of Ferroelectric Composites of Bi3.25La0.75Ti3O12 (BLT) and Co-Doped BLT Thin Films Modified by FeCo-Doped BLT
by Rui Tang, Rui He, Sangmo Kim and Chung Wung Bark
Coatings 2023, 13(7), 1223; https://doi.org/10.3390/coatings13071223 - 8 Jul 2023
Viewed by 1130
Abstract
Driven by the growing demand for renewable and clean energy, the photovoltaic effect of various solar cells and materials was investigated for the conversion of light energy into electricity. We modified the Bi3.25La0.75Ti3O12 (BLT) and Co-doped [...] Read more.
Driven by the growing demand for renewable and clean energy, the photovoltaic effect of various solar cells and materials was investigated for the conversion of light energy into electricity. We modified the Bi3.25La0.75Ti3O12 (BLT) and Co-doped BLT (Co–BLT) composites with Fe and Co-doped BLT (FeCo–BLT) films to narrow the bandgap and increase visible light absorption, thereby improving the efficiency of the photovoltaic reaction. In this study, BLT and Co–BLT thin films were fabricated by off-axis sputtering and then modified with FeCo–BLT thin films to produce dual-ferroelectric, thin-film composite materials that improved the photovoltaic power generation performance. Photoelectric test results showed that the modified double-ferroelectric, thin-film composites had superior optoelectronic properties. The current density was significantly enhanced by modifying the BLT films with doped Fe and Co. Therefore, this modification improved the efficiency of ferroelectric thin-film photovoltaic reactions. Full article
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14 pages, 5148 KiB  
Article
High-Entropy Composite Coating Based on AlCrFeCoNi as an Anode Material for Li-Ion Batteries
by Dávid Csík, Gabriela Baranová, Róbert Džunda, Dóra Zalka, Ben Breitung, Mária Hagarová and Karel Saksl
Coatings 2023, 13(7), 1219; https://doi.org/10.3390/coatings13071219 - 7 Jul 2023
Cited by 4 | Viewed by 3651
Abstract
In this study, a high entropy composite coating was synthesized by oxidizing a high entropy alloy, AlCrFeCoNi, at elevated temperatures in a pure oxygen atmosphere. X-Ray diffraction (XRD) analysis revealed that the prepared material was a dual-phase composite material consisting of a spinel-structured [...] Read more.
In this study, a high entropy composite coating was synthesized by oxidizing a high entropy alloy, AlCrFeCoNi, at elevated temperatures in a pure oxygen atmosphere. X-Ray diffraction (XRD) analysis revealed that the prepared material was a dual-phase composite material consisting of a spinel-structured high entropy oxide and a metallic phase with a face-centered cubic structure. The metallic phase can improve the electrical conductivity of the oxide phase, resulting in improved electrochemical performance. Scanning electron microscopy with energy dispersive spectroscopy (SEM/EDS) analysis unveiled the compositional homogeneity of the composite material. The prepared material was utilized as an anode active material in lithium-ion batteries. Cyclic voltammetry (CV) revealed the oxidation and reduction regions, while the electrochemical impedance spectroscopy (EIS) measurements showed a decrease in the charge transfer resistance during the cycling process. A long-term rate capability test was conducted at various current densities: 100, 200, 500, 1000, and 2000 mA g−1. During this test, a notable phenomenon was observed in the regeneration process, where the capacity approached the initial discharge capacity. Remarkably, a high regeneration efficiency of 98% was achieved compared with the initial discharge capacity. This phenomenon is typically observed in composite nanomaterials. At a medium current density of 500 mA g−1, an incredible discharge capacity of 543 mAh g−1 was obtained after 1000 cycles. Based on the results, the prepared material shows great potential for use as an anode active material in lithium-ion batteries. Full article
(This article belongs to the Section Ceramic Coatings and Engineering Technology)
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16 pages, 20266 KiB  
Article
Thin 1,2,4-Triazole Films for the Inhibition of Carbon Steel Corrosion in Sulfuric Acid Solution
by Yaroslav G. Avdeev, Tatyana A. Nenasheva, Andrey Yu. Luchkin, Andrey I. Marshakov and Yurii I. Kuznetsov
Coatings 2023, 13(7), 1221; https://doi.org/10.3390/coatings13071221 - 7 Jul 2023
Cited by 5 | Viewed by 1197
Abstract
Etching of steel items in sulfuric acid solution is used in various human activities (oil and gas industry, metal production, utilities, transport, etc.). This operation is associated with significant material costs due to corrosion losses of the metal. It has been found that [...] Read more.
Etching of steel items in sulfuric acid solution is used in various human activities (oil and gas industry, metal production, utilities, transport, etc.). This operation is associated with significant material costs due to corrosion losses of the metal. It has been found that an efficient way to prevent corrosion of steel in sulfuric acid solution involves the formation of thin protective films consisting of corrosion inhibitor molecules of triazole class on its surface. It has been shown that the protection of steels with a 3-substituted 1,2,4-triazole (3ST) in H2SO4 solution is accompanied by the formation of a polymolecular layer up to 4 nm thick. The 3ST layer immediately adjacent to the steel surface is chemisorbed on it. The efficiency of this compound as an inhibitor of corrosion and hydrogen absorption by steel is determined by its ability to form a protective organic layer, as experimentally confirmed by XPS and AFM data. The kinetic constants of the main stages of hydrogen evolution and permeation into steel in the H2SO4 solution were determined. A significant decrease in both the reaction rate of cathodic hydrogen evolution and the rate of hydrogen permeation into steel by the triazole in question was noted. It has been shown that the preservation of the metal plasticity in the acid medium containing the triazole under study is due to a decrease in the hydrogen concentration in the metal bulk. Full article
(This article belongs to the Section Corrosion, Wear and Erosion)
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12 pages, 5771 KiB  
Article
Stoichiometric and Nonstoichiometric Surface Structures of Pyrochlore Y2Zr2O7 and Their Relative Stabilities: A First-Principles Investigation
by Huajian Wu, Jianning Zhang, Yiren Wang, Jiacheng Shang and Yong Jiang
Coatings 2023, 13(7), 1203; https://doi.org/10.3390/coatings13071203 - 5 Jul 2023
Viewed by 1010
Abstract
First-principle total energy calculations were performed to investigate the atomic structures and relative stabilities of two low miller-index surfaces of pyrochlore Y2Zr2O7. The stoichiometric Y2Zr2O7 (110) and (100) surfaces were predicted, with [...] Read more.
First-principle total energy calculations were performed to investigate the atomic structures and relative stabilities of two low miller-index surfaces of pyrochlore Y2Zr2O7. The stoichiometric Y2Zr2O7 (110) and (100) surfaces were predicted, with lowest formation energies of 1.20 and 1.47 J/m2, respectively. Based on a thermodynamic defect model, non-stoichiometric Y2Zr2O7 surface energies were further evaluated as a function of environmental oxygen partial pressure (pO2) and temperature (T). With all of the results, we were able to construct the surface phase diagrams for T = 300 and 1400 K. The strong correlation between the structural stabilities and the surface stoichiometry was revealed as varying T and pO2. At a given T, the most stable termination of the (110) surfaces would change from a (Y,Zr)−rich (ns−2Y2Zr6O) to O−rich ones (ns−4O_2 and ns−4O_1) as increasing pO2, while that of the (100) surfaces would change from the stoichiometric (stoi−1Y1Zr_1) to the O−rich one (ns−5O). The critical pO2 value for termination transition moves to its higher end as increasing T. Full article
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15 pages, 3658 KiB  
Article
Epoxy Coating Modification with Metal Nanoparticles to Improve the Anticorrosion, Migration, and Antibacterial Properties
by Marina Samardžija, Ivan Stojanović, Marija Vuković Domanovac and Vesna Alar
Coatings 2023, 13(7), 1201; https://doi.org/10.3390/coatings13071201 - 4 Jul 2023
Cited by 2 | Viewed by 4135
Abstract
Nanoparticles are capable of making more durable and stronger materials with better chemical resistance. They are used for a wide range of applications. Likewise, the potential of metal nanoparticles as antimicrobial agents has been widely studied. In this work, we investigate various nanoparticles [...] Read more.
Nanoparticles are capable of making more durable and stronger materials with better chemical resistance. They are used for a wide range of applications. Likewise, the potential of metal nanoparticles as antimicrobial agents has been widely studied. In this work, we investigate various nanoparticles (Al, Ni, Ag) incorporated into epoxy coating. The anticorrosion and antibacterial properties of the unmodified and modified coatings were evaluated. According to the SEM and EDS analyses, the coating did not contain agglomerates, which confirms the quality of the dispersion of inorganic nanoparticles in the coating. After 24 h and 10days immersions in a 3.5 wt.% NaCl solution, the corrosion behaviour for all nanocomposite was studied by means of EIS investigations. The study included the evaluation of the inhibition zone of the nanoparticles and the antimicrobial properties of the nanocomposite. It was found that the nanoparticles of Al and Ag provide excellent antibacterial properties. The epoxy nanocomposite with Al NP showed the migration of ions in the range from 0.75 to 1 mg/L in a wastewater solution for 30 days, indicating a potential for antimicrobe activity. The 1% Al NP epoxy nanocomposite showed good anticorrosion and antibacterial properties and demonstrated great potential for applications in pipelines. Full article
(This article belongs to the Special Issue Investigation on Corrosion Behaviour of Metallic Materials)
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23 pages, 5911 KiB  
Article
Hybrid Materials Based on ZnO Nanoparticles and Organo-Modified Silica Coatings as Eco-Friendly Anticorrosive Protection for Metallic Historic Artifacts
by Mihaela Ioan, Dan Florin Anghel, Mihai Anastasescu, Ioana Catalina Gifu, Elvira Alexandrescu, Roxana Ioana Matei, Cristian Petcu, Ioana Stanculescu, Georgiana Alexandra Sanda, Daniela Bala and Ludmila Otilia Cinteza
Coatings 2023, 13(7), 1193; https://doi.org/10.3390/coatings13071193 - 3 Jul 2023
Cited by 2 | Viewed by 2928
Abstract
Cultural heritage metallic artifacts are often subjected to environmental factors that promote degradation through corrosion processes. Anticorrosion protection is needed both for the long-term preservation of outdoor monuments and the short-term conservation of archaeological artifacts. In this work, functional nanocoatings based on ZnO [...] Read more.
Cultural heritage metallic artifacts are often subjected to environmental factors that promote degradation through corrosion processes. Anticorrosion protection is needed both for the long-term preservation of outdoor monuments and the short-term conservation of archaeological artifacts. In this work, functional nanocoatings based on ZnO nanoparticles (NPs) in a silica matrix are prepared as a replacement for a commercial Incralac lacquer. Facile sol–gel synthesis is employed for obtaining silica filmogenic materials, using tetraethoxysilane (TEOS) and 3-glycidyloxypropyl trimethoxysilane (GPTMS). Silica-based nanocomposite coatings, with and without ZnO NPs and benzotriazole (BTA) as anticorrosion agents, applied on copper coupons by brushing are characterized by using VIS and FTIR spectroscopy, SEM and AFM and compared to Incralac lacquer as reference materials. The optical and morphological properties of the proposed silica coatings are similar to the Incralac specimens. The protective effect against corrosion is investigated on the copper coupons as model metallic objects subjected to a corrosion test by using potentiodynamic polarization in a 3.5% NaCl solution at ambient temperature. The influence of the presence of BTA and ZnO NPs in both silica and Incralac coatings is studied, and the variations in the anticorrosive, morphological and optical properties with the concentration of ZnO NPs are evidenced. The presence of moderate concentrations of ZnO in both nanomaterials leads to changes in the color parameters slightly above the limit accepted in the field of cultural heritage (ΔE* 5.09 and 6.13), while a high ZnO concentration of 3% leads to higher values (ΔE* > 10). Regarding the anticorrosive effect, the silica-based coatings with ZnO and BTA present similar efficiencies to that of the Incralac reference material (corrosion rates in the range of 0.044–0.067 mm/year for silica coatings compared to 0.055 mm/year for Incralac). Full article
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29 pages, 15287 KiB  
Review
Research Progress on the Wear and Corrosion Resistant Plasma Electrolytic Oxidation Composite Coatings on Magnesium and Its Alloys
by Chen Zhao, Xingwei Wang, Bo Yu, Meirong Cai, Qiangliang Yu and Feng Zhou
Coatings 2023, 13(7), 1189; https://doi.org/10.3390/coatings13071189 - 1 Jul 2023
Cited by 11 | Viewed by 3069
Abstract
Plasma electrolytic oxidation (PEO), as a cost effective and environmentally friendly technology, has been applied on magnesium and its alloys to improve wear and corrosion resistance. Additionally, combining with particles addition in the electrolyte and/or various post-treatments could diminish the intrinsic structural defects [...] Read more.
Plasma electrolytic oxidation (PEO), as a cost effective and environmentally friendly technology, has been applied on magnesium and its alloys to improve wear and corrosion resistance. Additionally, combining with particles addition in the electrolyte and/or various post-treatments could diminish the intrinsic structural defects of the PEO coatings and provide multifunctionalities, including wear resistance, corrosion resistance, self-lubrication, and self-healing. This paper reviews recent progress on PEO composite coatings prepared by in situ incorporation of functional particles and/or post-treatments on magnesium and its alloys. The focus is given to the microstructural and functional changes of the PEO coatings, particularly on the wear and corrosion behaviors. Full article
(This article belongs to the Section Plasma Coatings, Surfaces & Interfaces)
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12 pages, 3861 KiB  
Article
Lignin and Starch Derivatives with Selenium Nanoparticles for the Efficient Reduction of Dyes and as Polymer Fillers
by Anna Modrzejewska-Sikorska, Mariola Robakowska, Emilia Konował, Hubert Gojzewski, Łukasz Gierz, Bartosz Wieczorek, Łukasz Warguła and Wiktor Łykowski
Coatings 2023, 13(7), 1185; https://doi.org/10.3390/coatings13071185 - 30 Jun 2023
Cited by 1 | Viewed by 2645
Abstract
Selenium nanoparticles (SeNPs) were synthesized and stabilized by biopolymers, namely, sodium lignosulfonate (LS) and starch sodium octenyl succinate (OSA). The obtained selenium nanoparticles were studied for their catalytic activity in the reduction of a dye (C.I. Basic Blue 9, methylene blue) by sodium [...] Read more.
Selenium nanoparticles (SeNPs) were synthesized and stabilized by biopolymers, namely, sodium lignosulfonate (LS) and starch sodium octenyl succinate (OSA). The obtained selenium nanoparticles were studied for their catalytic activity in the reduction of a dye (C.I. Basic Blue 9, methylene blue) by sodium borohydride. The SeNPs-OSA and SeNPs-LS nanoparticles were also dispersed in a photosensitive matrix and studied as polymer composites. The research confirmed the catalytic abilities of the prepared SeNPs in the reduction of the organic dye. Mechanical tests on the polymers and their composites showed an improvement in the composites’ strength in all tested cases. An increase in hardness and Young’s modulus values of the filled materials compared to the pure matrix was found as well. Full article
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13 pages, 12441 KiB  
Communication
The Microstructure, Hardness, Phase Transformation and Mechanical Properties of a NiTi Coating Applied to Graphite Substrate via a Plasma Spraying Process
by Sneha Samal, Jakub Zeman, Jaromír Kopeček and Petr Šittner
Coatings 2023, 13(7), 1174; https://doi.org/10.3390/coatings13071174 - 29 Jun 2023
Cited by 3 | Viewed by 1624
Abstract
In this study, Ni50Ti50 powder was coated on the surface of graphite substrate (C) via a plasma spraying process using a radio frequency inductively coupled plasma reactor. The coating was carried out using 12- and 9-kW power under Ar atmosphere. [...] Read more.
In this study, Ni50Ti50 powder was coated on the surface of graphite substrate (C) via a plasma spraying process using a radio frequency inductively coupled plasma reactor. The coating was carried out using 12- and 9-kW power under Ar atmosphere. The cross-section of coating layers and the surface were examined with Scanning Electron Microscope (SEM), Energy Dispersive X-ray Spectrum (EDX), and X-ray Diffractometer (XRD) analyses and microhardness test. The thickness and quality of the coating increased with the input power. Many pores were detected in the cross-sectional surface areas. Higher input power caused a better coating layer of NiTi alloy. The hardness of the coating layer decreases with higher input power. Full article
(This article belongs to the Section Plasma Coatings, Surfaces & Interfaces)
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19 pages, 630 KiB  
Review
Biodegradable Packaging Materials for Foods Preservation: Sources, Advantages, Limitations, and Future Perspectives
by Andreas Panou and Ioannis Konstantinos Karabagias
Coatings 2023, 13(7), 1176; https://doi.org/10.3390/coatings13071176 - 29 Jun 2023
Cited by 21 | Viewed by 10718
Abstract
Biodegradable packaging materials generally comprise a solution to the environmental problem caused by the consecutive use of conventional packaging materials (petroleum-based materials) even though these have a high cost. The monomers resulting from the slow degradation of petroleum-based materials contribute to the pollution [...] Read more.
Biodegradable packaging materials generally comprise a solution to the environmental problem caused by the consecutive use of conventional packaging materials (petroleum-based materials) even though these have a high cost. The monomers resulting from the slow degradation of petroleum-based materials contribute to the pollution of the environment. Biodegradable packaging materials distinguished by high biodegradability and biocompatibility can successfully replace the aforementioned packaging materials and thus solve the environmental problems caused by their use or deposition. Although several of the biodegradable packaging materials present defective properties, mainly mechanical and barrier properties, these are reduced or even eliminated by the addition of various improving additives and by blending them with other biopolymers. Various natural preservatives such as essential oils or other phytochemical extracts can also be incorporated into the biopolymer network to increase its efficacy. This treatment is particularly beneficial since it contributes to the increasing of the shelf life and storability of packaged foods such as fruits, vegetables, dairy products, meat and its products, poultry, and fish. For all the above reasons, the preferences of consumers and the critical thinking/decisions of the food product manufacturing industries in favor of the potential use of biodegradable packaging materials in foods are increasing more and more. In this context, the present review article addresses the most recently used biodegradable packaging materials for foods preservation by presenting their sources, advantages, limitations, and future perspectives. Full article
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11 pages, 7764 KiB  
Article
Optimization of Crystalline Diamond Coating Structure Architecture for Improving Adhesion and Cutting Performance in Milling with Cemented Carbide Inserts
by Georgios Skordaris, Konstantinos-Dionysios Bouzakis, Antonios Bouzakis, Dimitrios Tsakalidis, Apostolos Boumpakis, Spyridon Kompogiannis, Emmanouil Bouzakis, Oliver Lemmer, Werner Kölker and Michael Woda
Coatings 2023, 13(7), 1170; https://doi.org/10.3390/coatings13071170 - 28 Jun 2023
Cited by 1 | Viewed by 2706
Abstract
The adhesion, structure architecture, and residual stresses of crystalline diamond coatings (CDCs) on cemented carbide inserts are the factors that significantly affect tool life. The influence of these factors on cutting performance cannot be investigated separately since interactions among them exist. The paper [...] Read more.
The adhesion, structure architecture, and residual stresses of crystalline diamond coatings (CDCs) on cemented carbide inserts are the factors that significantly affect tool life. The influence of these factors on cutting performance cannot be investigated separately since interactions among them exist. The paper elucidates such dependencies to optimize the CDC architecture and improve cutting performance. In this context, diamond coatings possessing different architectures were deposited on cemented carbide tools. The fatigue endurance and the milling performance of the coated tools were investigated using impact and milling tests, respectively. The residual stresses in the film structures were determined through impact tests and appropriate (Finite Element Analysis) FEA evaluation of the corresponding results. According to the obtained results, the application of a bottom micro-structured CDC prior to the deposition of an upper nanolayered one with inferior thickness improves the coated tools’ cutting performance. An optimum coating architecture is associated with a thickness ratio between the micro-structured bonding to the upper nanolayered CDCs of 2/1. Hereupon, the augmentation of coated tool life via the application of an optimum diamond coating architecture compensates for the high tool cost and improves milling productivity. The latter is further enhanced as the number of tool replacements decreases. Full article
(This article belongs to the Special Issue New Cutting Techniques for Improved Machining)
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59 pages, 9745 KiB  
Article
Principles of Machine Learning and Its Application to Thermal Barrier Coatings
by Yuan Liu, Kuiying Chen, Amarnath Kumar and Prakash Patnaik
Coatings 2023, 13(7), 1140; https://doi.org/10.3390/coatings13071140 - 23 Jun 2023
Cited by 6 | Viewed by 3134
Abstract
Artificial intelligence (AI), machine learning (ML) and deep learning (DL) along with big data (BD) management are currently viable approaches that can significantly help gas turbine components’ design and development. Optimizing microstructures of hot section components such as thermal barrier coatings (TBCs) to [...] Read more.
Artificial intelligence (AI), machine learning (ML) and deep learning (DL) along with big data (BD) management are currently viable approaches that can significantly help gas turbine components’ design and development. Optimizing microstructures of hot section components such as thermal barrier coatings (TBCs) to improve their durability has long been a challenging task in the gas turbine industry. In this paper, a literature review on ML principles and its various associated algorithms was presented first and then followed by its application to investigate thermal conductivity of TBCs. This combined approach can help better understand the physics behind thermal conductivity, and on the other hand, can also boost the design of low thermal conductivity of the TBCs system in terms of microstructure–property relationships. Several ML models and algorithms such as support vector regression (SVR), Gaussian process regression (GPR) and convolution neural network and regression algorithms were used via Python. A large volume of thermal conductivity data was compiled and extracted from the literature for TBCs using PlotDigitizer software and then used to test and validate ML models. It was found that the test data were strongly associated with five key factors as identifiers. The prediction of thermal conductivity was performed using three approaches: polynomial regression, neural network (NN) and gradient boosting regression (GBR). The results suggest that NN using the BR model and GBR have better prediction capability. Full article
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10 pages, 13583 KiB  
Article
Seeking the Oxidation Mechanism of Debris in the Fretting Wear of Titanium Functionalized by Surface Laser Treatments
by María del Carmen Marco de Lucas, Franck Torrent, Gianni-Paolo Pillon, Pascal Berger and Luc Lavisse
Coatings 2023, 13(6), 1110; https://doi.org/10.3390/coatings13061110 - 16 Jun 2023
Viewed by 1752
Abstract
Surface laser treatment (SLT) using nanosecond IR lasers has been shown to improve the tribological behaviour of titanium. Here, we studied the fretting wear of SLT-functionalized pure titanium in a mixture of reactive gases O2 (20 vol.%) + N2 (80 vol.%). [...] Read more.
Surface laser treatment (SLT) using nanosecond IR lasers has been shown to improve the tribological behaviour of titanium. Here, we studied the fretting wear of SLT-functionalized pure titanium in a mixture of reactive gases O2 (20 vol.%) + N2 (80 vol.%). The contact geometry was a ball on a plane and the ball was made of bearing steel. The very small amplitude of relative displacement between reciprocating parts in fretting wear makes the evacuation of wear particles difficult. Moreover, the oxidation mechanism of the debris depends on the accessibility of the surrounding atmosphere to the tribological contact. This work focused in the analysis of debris generation and oxidation mechanisms, and sought to differentiate the role of oxygen forming part of the ambient O2 + N2 gas mixture from oxygen present in the surface layer of the SL-treated titanium. Before the fretting test, the surface of the commercially pure titanium plates was treated with a laser under a mixture of O2 + N2 gases with oxygen enriched in the 18O isotope. Then, the fretting tests were performed in regular air containing natural oxygen. Micro-Raman spectroscopy and ion beam analysis (IBA) techniques were used to analyse the TiO2 surface layers and fretting scars. Iron oxide particles were identified by Raman spectroscopy and IBA as the third body in the tribological contact. The spatial distribution of 18O, Ti, 16O and Fe in the fretting scars was studied by IBA. The analysis showed that the areas containing high concentrations of Fe displayed also high concentrations of 16O, but smaller concentrations of 18O and Ti. Therefore, it was concluded that tribological contact allows the oxidation of iron debris by its reaction with ambient air. Full article
(This article belongs to the Section Laser Coatings)
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19 pages, 3299 KiB  
Article
Bimetallic 3D Nickel-Manganese/Titanium Bifunctional Electrocatalysts for Efficient Hydrogen and Oxygen Evolution Reaction in Alkaline and Acidic Media
by Sukomol Barua, Aldona Balčiūnaitė, Jūrate Vaičiūnienė, Loreta Tamašauskaitė-Tamašiūnaitė and Eugenijus Norkus
Coatings 2023, 13(6), 1102; https://doi.org/10.3390/coatings13061102 - 15 Jun 2023
Cited by 4 | Viewed by 2006
Abstract
In this work, 3D nickel-manganese (NiMn) bimetallic coatings have been studied as electrocatalysts for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline (1.0 M KOH) media and the HER in acidic (0.5 M H2SO4) media. [...] Read more.
In this work, 3D nickel-manganese (NiMn) bimetallic coatings have been studied as electrocatalysts for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline (1.0 M KOH) media and the HER in acidic (0.5 M H2SO4) media. The catalysts have been deposited on a titanium substrate (1 × 1 cm2) using low-cost and facile electrochemical deposition method through a dynamic hydrogen bubble template technique. The electrocatalytic performance of these fabricated catalysts was investigated by using Linear Sweep Voltammetry (LSV) for HER and OER at different temperatures ranging from 25 up to 75 °C and also was characterized by scanning electron microscopy (SEM) and inductively coupled plasma optical emission spectroscopy (ICP-OES). It was found that fabricated NiMn/Ti-5 electrocatalyst with Ni2+/Mn2+ molar ratio of 1:5 exhibits excellent HER activity in alkaline media with overpotential of 127.1 mV to reach current density of 10 mA cm−2. On the contrary, NiMn/Ti-1 electrocatalyst that fabricated with Ni2+/Mn2+ molar proportion of 1:1 and lowest Mn-loading of 13.43 µgcm−2 demonstrates exceptional OER activity with minimum overpotential of 356.3 mV to reach current density of 10 mA cm−2. The current densities increase ca. 1.8–2.2 times with an increase in temperature from 25 °C to 75 °C for both HER and OER investigation. Both catalysts also have exhibited excellent long-term stability for 10 h at constant potentials as well as constant current density of 10 mA cm−2 that assure their robustness and higher durability regarding alkaline water splitting. Full article
(This article belongs to the Special Issue New Advance in Nanoparticles, Fiber, and Coatings)
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14 pages, 4667 KiB  
Article
Characterization of Two Types of Polylactic Acid Coating Loaded with Gentamicin Sulphate Deposed on AZ31 Alloy
by Manuela Elena Voicu, Daniela Ionita, George-Octavian Buica, Doina Draganescu, Valentina Anuta, Florentina Monica Raduly and Ioana Demetrescu
Coatings 2023, 13(6), 1105; https://doi.org/10.3390/coatings13061105 - 15 Jun 2023
Cited by 1 | Viewed by 1406
Abstract
This paper compares two types of polylactic acid (PLA) coating on AZ31 alloy obtained by dip coating and electrospinning. Both types of coating were loaded with gentamicin sulphate (GS) and the drug-loading efficiency and release were assessed. A higher encapsulation and release efficiency [...] Read more.
This paper compares two types of polylactic acid (PLA) coating on AZ31 alloy obtained by dip coating and electrospinning. Both types of coating were loaded with gentamicin sulphate (GS) and the drug-loading efficiency and release were assessed. A higher encapsulation and release efficiency of GS was seen for dip coating (73% and 49.53%, respectively) compared to nanofiber coating (65% and 12.37%, respectively). Furthermore, the antibacterial effect of the samples with and without GS was assessed using Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) bacteria, showing that the samples with the drug encapsulated are more resistant to bacteria than the other samples. The electrochemical data reveal a higher stability in the SBF of the surface obtained by dipping than that obtained by electrospinning. The PLA coating shows a porosity of 46% for the sample obtained through dip coating and 32% for nanofibers, which is in accordance with the BET analysis results. Moreover, a higher adhesion strength was obtained for AZ31-PLA-dip (4.99 MPa) than for the AZ31-PLA-nanofibers (1.66 MPa). All samples were structurally, morphologically, and topographically characterized. Full article
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27 pages, 6140 KiB  
Review
Bioactive Calcium Phosphate Coatings for Bone Implant Applications: A Review
by Richard Drevet, Joël Fauré and Hicham Benhayoune
Coatings 2023, 13(6), 1091; https://doi.org/10.3390/coatings13061091 - 13 Jun 2023
Cited by 17 | Viewed by 6302
Abstract
This review deals with the design of bioactive calcium phosphate coatings deposited on metallic substrates to produce bone implants. The bioceramic coating properties are used to create a strong bonding between the bone implants and the surrounding bone tissue. They provide a fast [...] Read more.
This review deals with the design of bioactive calcium phosphate coatings deposited on metallic substrates to produce bone implants. The bioceramic coating properties are used to create a strong bonding between the bone implants and the surrounding bone tissue. They provide a fast response after implantation and increase the lifespan of the implant in the body environment. The first part of the article describes the different compounds belonging to the calcium phosphate family and their main properties for applications in biomaterials science. The calcium-to-phosphorus atomic ratio (Ca/P)at. and the solubility (Ks) of these compounds define their behavior in a physiological environment. Hydroxyapatite is the gold standard among calcium phosphate materials, but other chemical compositions/stoichiometries have also been studied for their interesting properties. The second part reviews the most common deposition processes to produce bioactive calcium phosphate coatings for bone implant applications. The last part describes key physicochemical properties of calcium phosphate coatings and their impact on the bioactivity and performance of bone implants in a physiological environment. Full article
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17 pages, 3867 KiB  
Article
Copper Nitride: A Versatile Semiconductor with Great Potential for Next-Generation Photovoltaics
by M. I. Rodríguez-Tapiador, J. M. Asensi, M. Roldán, J. Merino, J. Bertomeu and S. Fernández
Coatings 2023, 13(6), 1094; https://doi.org/10.3390/coatings13061094 - 13 Jun 2023
Cited by 7 | Viewed by 4559
Abstract
Copper nitride (Cu3N) has gained significant attention recently due to its potential in several scientific and technological applications. This study focuses on using Cu3N as a solar absorber in photovoltaic technology. Cu3N thin films were deposited on [...] Read more.
Copper nitride (Cu3N) has gained significant attention recently due to its potential in several scientific and technological applications. This study focuses on using Cu3N as a solar absorber in photovoltaic technology. Cu3N thin films were deposited on glass substrates and silicon wafers via radio-frequency magnetron sputtering at different nitrogen flow ratios with total pressures ranging from 1.0 to 5.0 Pa. The thin films’ structural, morphology, and chemical properties were determined using XRD, Raman, AFM, and SEM/EDS techniques. The results revealed that the Cu3N films exhibited a polycrystalline structure, with the preferred orientation varying from 100 to 111 depending on the working pressure employed. Raman spectroscopy confirmed the presence of Cu-N bonds in characteristic peaks observed in the 618–627 cm−1 range, while SEM and AFM images confirmed the presence of uniform and smooth surface morphologies. The optical properties of the films were investigated using UV-VIS-NIR spectroscopy and photothermal deflection spectroscopy (PDS). The obtained band gap, refractive index, and Urbach energy values demonstrated promising optical properties for Cu3N films, indicating their potential as solar absorbers in photovoltaic technology. This study highlights the favourable properties of Cu3N films deposited using the RF sputtering method, paving the way for their implementation in thin-film photovoltaic technologies. These findings contribute to the progress and optimisation of Cu3N-based materials for efficient solar energy conversion. Full article
(This article belongs to the Special Issue Advanced Materials for Energy Storage and Conversion)
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13 pages, 5802 KiB  
Article
Electrophoretic Deposition of Rochelle Salt Nanocrystals on Aluminum Plate
by Rostislav Rusev, Boriana Tzaneva and George Angelov
Coatings 2023, 13(6), 1074; https://doi.org/10.3390/coatings13061074 - 10 Jun 2023
Cited by 1 | Viewed by 3118
Abstract
A straightforward and inexpensive electrophoretic method for obtaining environment-friendly nanocrystalline piezo layers from Rochelle salt (RS) is presented here. The electrophoretic deposition process includes the formation of nanocrystals by precipitation of Rochelle salt/water solutions in ethanol (anti-solvent method) under the influence of a [...] Read more.
A straightforward and inexpensive electrophoretic method for obtaining environment-friendly nanocrystalline piezo layers from Rochelle salt (RS) is presented here. The electrophoretic deposition process includes the formation of nanocrystals by precipitation of Rochelle salt/water solutions in ethanol (anti-solvent method) under the influence of a high electric field. A nanoporous anodic aluminum oxide membrane is used to separate the electrochemical cell into two chambers. The composition of the RS:H2O:EtOH mixture and the spatial separation of the process of precipitation from electrophoretic deposition allow control of the nanocrystal size and the uniformity of the layer. The reaction kinetics, the morphology, and the piezo response to the resulting layers are all investigated. The best samples were obtained at RS:H2O:EtOH ratio 1:22.5:37.5. Under these conditions, the nanocrystals are preferentially oriented on the aluminum substrate and form a dense and homogeneous layer. Although the obtained structure is polycrystalline, the resulting piezo effect is 1120 pC/N, which is comparable to inorganic monocrystals and piezoceramics. This allows the use of electrophoretically deposited polycrystalline piezo layers in applications such as energy harvesting. Full article
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33 pages, 8498 KiB  
Review
Recent Advances in the Plasma-Assisted Synthesis of Silicon-Based Thin Films and Nanostructures
by Pietro Mandracci and Paola Rivolo
Coatings 2023, 13(6), 1075; https://doi.org/10.3390/coatings13061075 - 10 Jun 2023
Cited by 4 | Viewed by 3210
Abstract
Silicon-based thin films and nanostructures are of paramount importance in a wide range of applications, including microelectronics, photovoltaics, large area sensors, and biomedicine. The wide accessibility of silicon and its relatively low cost have driven a continuous improvement of technology based on this [...] Read more.
Silicon-based thin films and nanostructures are of paramount importance in a wide range of applications, including microelectronics, photovoltaics, large area sensors, and biomedicine. The wide accessibility of silicon and its relatively low cost have driven a continuous improvement of technology based on this element. Plasma technology has been widely used for the synthesis of coatings and nanostructures based on silicon. Moreover, it has made a fundamental contribution to continuous improvement of the physicochemical properties of silicon-based materials and allows the synthesis of nanometric structures with well-defined shapes and morphologies. In this work, we have reviewed the most interesting developments in plasma-assisted processes for the synthesis of Si-based materials, both inorganic and organic, in the last five years. Special attention has been paid to new techniques, or modifications of already-existing ones, that open up new possibilities for the synthesis of materials with new properties, as well as nanostructures with novel characteristics. Full article
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