Fabrication Of Coatings Research Articles

Design and fabrication of photocatalytic coatings with α/β-Bi2O3 and recycled-fly ash for environmental remediation and solar fuel generation

To promote a circular economy, alkali-activated recycled fly ash (AAFA) can be used as an alternative binder for fabricating mortar coatings. The AAFA binder can also be functionalized with photocatalysts for application in environmental remediation. Here, α/β-Bi2O3 homojunction photocatalysts were incorporated into AAFA mortar coatings to confer photocatalytic properties for two applications, namely, self-cleaning and solar fuel generation from CO2 photoconversion. The α/β-Bi2O3 homojunctions were prepared using three methods. The homojunctions had a higher proportion of the β-Bi2O3 phase compared to α-Bi2O3; additionally, they exhibited with a 2D morphology and a bandgap suitable for visible-light activation. X-ray diffraction and energy dispersive spectroscopy analysis of the mortar coatings showed that the inorganic matrix comprised two frameworks based on calcium silicate hydrate and aluminosilicate hydrate, with high porosity. The photocatalytic mortar coatings exhibited self-cleaning activity, with the highest efficiency of 31%. This result was corroborated by total organic carbon analysis, which showed ~15% mineralization. The specimens also showed high activity for CO2 photoconversion to solar fuels such as formic acid (1932 μmol/g) and methanol (6 μmol/g) under visible light. These results were related to the synergistic effect of the mesoporous framework developed after alkaline activation, more efficient charge transfer in the homojunctions, enhanced CO2 affinity, and the presence of CaO, MgO, Na2O, and SiO2 in the binder. The efficiencies for both applications are comparable to those reported previously. The present approach is potentially applicable not only for minimizing the environmental impact of waste materials by reducing the disposal of fly ash in landfills, but also for producing value-added compounds and reducing the maintenance cost of buildings.

Facile fabrication of antibacterial and antiviral perhydrolase-polydopamine composite coatings

In situ generation of antibacterial and antiviral agents by harnessing the catalytic activity of enzymes on surfaces provides an effective eco-friendly approach for disinfection. The perhydrolase (AcT) from Mycobacterium smegmatis catalyzes the perhydrolysis of acetate esters to generate the potent disinfectant, peracetic acid (PAA). In the presence of AcT and its two substrates, propylene glycol diacetate and H2O2, sufficient and continuous PAA is generated over an extended time to kill a wide range of bacteria with the enzyme dissolved in aqueous buffer. For extended self-disinfection, however, active and stable AcT bound onto or incorporated into a surface coating is necessary. In the current study, an active, stable and reusable AcT-based coating was developed by incorporating AcT into a polydopamine (PDA) matrix in a single step, thereby forming a biocatalytic composite onto a variety of surfaces. The resulting AcT-PDA composite coatings on glass, metal and epoxy surfaces yielded up to 7-log reduction of Gram-positive and Gram-negative bacteria when in contact with the biocatalytic coating. This composite coating also possessed potent antiviral activity, and dramatically reduced the infectivity of a SARS-CoV-2 pseudovirus within minutes. The single-step approach enables rapid and facile fabrication of enzyme-based disinfectant composite coatings with high activity and stability, which enables reuse following surface washing. As a result, this enzyme-polymer composite technique may serve as a general strategy for preparing antibacterial and antiviral surfaces for applications in health care and common infrastructure safety, such as in schools, the workplace, transportation, etc.

One‐step fabrication of wear‐resistant superhydrophobic coating based on aminosilane‐functionalized diatomaceous earth

AbstractFacile fabrication of superhydrophobic coatings with excellent mechanical robustness is highly desired in practical application. Herein, a convenient and effective strategy for one‐step fabrication of robust volumetric superhydrophobic coating was developed containing aminosilane‐functionalized cylindrical diatomaceous earth (DE) particles and a polyurethane (PU) resin. Due to the strong chemical cross‐linking between the amino groups and the isocyanates, the superhydrophobic DE particles were strongly anchored to the PU resin, thus improving the wear resistance of the coating. The coating could withstand 20 m sandpaper abrasion under a constant pressure of 2.6 kPa. The wear resistance of the coating improved nearly 471% compared with the superhydrophobic DE/PU composite coating prepared by physical‐blending. Moreover, the coating also demonstrated great self‐cleaning performance, excellent chemical stability and underwater durability. Additionally, the as‐prepared coating could be easily applied to various substrates and exhibited high rigidity (3H‐4H), good adhesion (4B‐5B), and great flexibility (impact resistance of 1 Kg·m).

Mussel-inspired facile fabrication of dense hexagonal boron nitride nanosheet-based coatings for anticorrosion and antifriction applications

Although great progress has been made recently in the research of hexagonal boron nitride (h-BN) nanosheets, their practical applications are limited due to the difficulties of processability. Existing methods to modify h-BN usually suffer from tedious steps and chemical oxidation reaction conditions, which are being phased out owing to human health and environmental concerns. Herein, inspired by the mussel, dopamine is selected to functionalize h-BN (polydopamine-functionalized hexagonal boron nitride [h-BN@PDA]) nanosheets which can improve interfacial compatibility thus enhancing their processability. As expected, dense h-BN@PDA nanosheet-based coatings can be fabricated through a facile environmentally friendly spraying process in the assistance of polyvinyl alcohol (PVA). The as-obtained coatings present excellent thermal stability because of the hydrogen bonds formed between h-BN@PDA and PVA. Additionally, suitable PVA is beneficial for load transfer, thus improving the mechanical properties of the coatings. More importantly, the composite coatings show good anticorrosion and antifriction performance since the h-BN@PDA nanosheets can act as physical barrier to corrosive medium and oxygen, or be stored in the worn surface as lubricant to reduce the friction and strengthen the friction stability. The facile fabrication process combined with the good thermal stability, anticorrosion and antifriction properties makes the h-BN@PDA nanosheet-based coatings promising candidates for practical applications.

Slot-Die Process of a Sol–Gel Photocatalytic Porous Coating for Large-Area Fabrication of Functional Architectural Glass

The slot-die process is an appealing technology for the fabrication of coatings on large-area substrates. However, its application on the production of photocatalytic coatings based on sol–gel formulations remains virtually unexplored. Thus, assessing the suitable formulation of the sol and operational parameters that allow one to yield high-efficacy photocatalyst coatings is a current challenge. This work aims to analyze the transferability of titania sol formulation optimized for dip-coating processes to slot-die technology. In this sense, firstly, the sol formulation is optimized by analyzing the influence of several types of surfactants on the microstructural features and photoactivity of TiO2 coatings’ growth on glass substrates. All formulations rendered a meaningful porosity and nanoscopic anatase crystallites (11–15 nm) with optical band gap values close to the expectation (3.25–3.31 eV). Accordingly, the performance of the photocatalytic dye degradation was closely related to the porosity and crystallite size led by each titania sol, and no meaningful differences were found between the results provided by the coatings developed by dip-coating and the slot-die method, which demonstrates the capability of the latter for its application on a large-scale fabrication of photocatalytic coatings.

Fabrication and Characterization of Zr Microplasma Sprayed Coatings for Medical Applications

Abstract This paper presents new results of studying the influence of parameters of microplasma spraying (MPS) of Zr wire on the structure of Zr coatings. The coating experiments were accomplished in a two level fractional factorial design. Individual particles of sprayed Zr wire and their splats on the substrate were collected under various spraying parameters (amperage, spraying distance, plasma gas flow rate and wire flow rate) and evaluated by Scanning Electron Microscopy (SEM) to establish the effect of particle size and shape on the coating microstructure. The particles were characterized by measurement of their sizes and the obtained results were evaluated in terms of their degree of melting. This was compared with the experimentally observed coating microstructure type and finally correlated to the investigated coating porosity to select the specific MPS parameters of Zr coatings depositing onto medical implants from Ti alloy. It was found that the main parameters influencing the size of the sprayed Zr particles and the porosity of the Zr coatings are the plasma gas flow rate and amperage. It was demonstrated that it is possible to control the porosity of Zr microplasma coatings in the range from 2.8% to 20.3% by changing the parameters of the MPS. The parameters of microplasma spraying of Zr wire were established to obtain medical implant coatings with porosity up to 20.3% and pore size up to 300 μm.

Fabrication of all-organic superhydrophobic coatings

Fabrication of all-organic superhydrophobic coatings

Fabrication of NO-containing calcium phosphate coatings via direct introduction of argon-nitrogen-mixtures applied in reactive RF-magnetron sputtering

Nitric oxide plays a crucial role in the human body, due to its regulatory effect on vascular tone, cell adhesion, vascular permeability, etc. The introduction of nitric oxide into calcium phosphate coatings can increase the bioactivity significantly. This article proves the possibility of deposition of nitric oxide-containing calcium phosphate coatings on titanium substrates. Therefore, various argon-nitrogen working gas mixtures were used in reactive radiofrequency magnetron sputtering of hydroxyapatite. The amount of nitric oxide increases with the concentration of nitrogen in the working gas mixture. Coatings characterized by a higher deposition rate of nitric oxide are showing also a higher roughness of the surface. Due to the adjustment of these deposition parameters, the morphology of the coating surfaces can be regulated.

Icephobic properties of anti-wetting coatings for aeronautical applications

Ice accretion on surfaces exposed to supercooled drops is a major issue in several fields, especially for aircraft. The severity and hazardousness of this phenomenon largely depends on the environmental conditions met by the surface. Currently, active ice protection systems are applied to limit the risks related to ice accretion on aircraft, but intense efforts are devoted to the development of passive ice protection systems to overcome their limitations. Anti-wetting materials have been explored as potential icephobic surfaces, with the Slippery, Liquid-Infused Porous Surfaces approach (SLIPS) being one of the most innovative and intriguing possible solutions. However, the literature lacks a proper characterization of the behavior of SLIPS in icing wind tunnel tests that simulate the different icing conditions. In our work, we report the fabrication of ceramic-based coatings as per the SLIPS approach, utilizing two different ceramic porous matrixes and several infused liquids; we also assess the ability of these coatings to reduce ice accretion in icing wind tunnel tests in both glaze and rime icing regimes, as well as their properties in terms of reduced ice adhesion. Observing the remarkable icephobic behavior displayed by these materials in both types of tests, SLIPS gain significant consideration as candidate passive ice protection systems for aeronautical applications.

Fabrication of Thermal Plasma Sprayed NiTi Coatings Possessing Functional Properties

Thick NiTi shape memory alloy coatings (300–500 µm) were produced on graphite and AISI 304 substrates by radio frequency inductively-coupled plasma spray technology (RF-ICP) from feedstock NiTi powders. Their microstructure as well as chemical and phase composition were characterized and a methodology for the characterization of functional shape memory properties of the thick coatings was developed. The coatings exhibited cubic to monoclinic martensitic transformation and shape memory effect. The presented results prove that NiTi coatings with functional thermomechanical properties can be easily produced on structural materials by RF-ICP. Further optimization will be needed to prepare NiTi coatings with better microstructural and chemical homogeneity.

Bioactive Functional Nanolayers of Chitosan-Lysine Surfactant with Single- and Mixed-Protein-Repellent and Antibiofilm Properties for Medical Implants.

Medical implant-associated infections resulting from biofilm formation triggered by unspecific protein adsorption are the prevailing cause of implant failure. However, implant surfaces rendered with multifunctional bioactive nanocoatings offer a promising alternative to prevent the initial attachment of bacteria and effectively interrupt biofilm formation. The need to research and develop novel and stable bioactive nanocoatings for medical implants and a comprehensive understanding of their properties in contact with the complex biological environment are crucial. In this study, we developed an aqueous stable and crosslinker-free polyelectrolyte–surfactant complex (PESC) composed of a renewable cationic polysaccharide, chitosan, a lysine-based anionic surfactant (77KS), and an amphoteric antibiotic, amoxicillin, which is widely used to treat a number of infections caused by bacteria. We successfully introduced the PESC as bioactive functional nanolayers on the “model” and “real” polydimethylsiloxane (PDMS) surfaces under dynamic and ambient conditions. Besides their high stability and improved wettability, these uniformly deposited nanolayers (thickness: 44–61 nm) with mixed charges exhibited strong repulsion toward three model blood proteins (serum albumin, fibrinogen, and γ-globulin) and their competitive interactions in the mixture in real-time, as demonstrated using a quartz crystal microbalance with dissipation (QCM-D). The functional nanolayers with a maximum negative zeta potential (ζ: −19 to −30 mV at pH 7.4), water content (1628–1810 ng cm–2), and hydration (low viscosity and elastic shear modulus) correlated with the mass, conformation, and interaction nature of proteins. In vitro antimicrobial activity testing under dynamic conditions showed that the charged nanolayers actively inhibited the growth of both Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) bacteria compared to unmodified PDMS. Given the ease of fabrication of multifunctional and charged biobased coatings with simultaneous protein-repellent and antimicrobial activities, the limitations of individual approaches could be overcome leading to a better and advanced design of various medical devices (e.g., catheters, prosthetics, and stents).

Fabrication and characterization of high-performance Mo-doped TiN coatings

To realize the fabrication of Ti–Mo–N coatings with novel properties predicted towards industrial applications, Mo-doped TiN coatings have been fabricated by multi-arc ion plating with varied substrate bias, and systematically characterized. The as-deposited coatings show a 1.5 at% Mo content deficit due to melting point difference between Mo and Ti elements. X-ray diffraction (XRD) and X-ray photoelectron spectrum (XPS) results show the as-deposited coatings demonstrate a fcc-TiN + bct-Ti2N dual phase structure, with Mo solution into TiN lattice. The hardness of TiMo0.08N coatings is above 31.97 GPa, which first increases then decreases slightly, peaking at 34.26 GPa. The phenomenon is correlated to the decreased (111) while enhanced (220) preferred orientation. All coatings show adhesion properties above 65 N (>100 N when bias voltage is above −50 V) and friction coefficients (COFs) below 0.24, which is attributed to the formation of lubricant MoO3 phase in a surface tribochemical process, as confirmed by XPS and Raman spectra evidences. Electrochemical polarization curves reveal that all samples have higher corrosion potential and corrosion currents two order of magnitudes lower than the WC-Co substrates. Additionally, substrate bias voltage has little impacts on structures and properties of the coatings, which means a wide process window.

Electrodeposition and structural characterization of MCrO3 (M = La, Pr, Nd, Gd, Dy and Y) perovskite oxide coatings on stainless steel substrates

One of the significant challenges of the effective use of functional oxide materials in device applications is to obtain them in the form of thin films or thick coatings. In this work, we show cathodic electrodeposition technique as a cost effective method for fabrication of perovskite chromite coatings. Amorphous precursor hydroxide coatings of M (M = La, Pr, Nd, Gd, Dy, Y) and Cr were co-deposited on stainless steel electrode by cathodic electrodeposition from a nitrate bath. These precursor coatings were further heat treated to obtain MCrO3 perovskite oxide coatings. Heat treatment of La–Cr hydroxide precursor coatings at 600 °C and 800 °C resulted in coatings of La2CrO6 and LaCrO3 phases respectively. The other M−Cr hydroxides on heating at 800 °C for 2 h formed respective single phase MCrO3 perovskite coatings. Interestingly, the SEM images of heat treated perovskite coatings show different morphologies with varying M in MCrO3 (M = La, Pr, Nd, Gd, Dy and Y).

Fabrication and Characterization of Hydrophobic Porous Metallic Membranes for High Temperature Applications

Hydrophobic porous metallic membranes can be integrated in a microreactor for in situ separation of steam at high temperatures. This study investigates the fabrication and characterization of hydrophobic coatings on metallic substrates. Two different coating methods were explored: (1) Plasma Enhanced—Chemical Vapor Deposition (PE-CVD) to form amorphous carbon silicon-doped a-C:H:Si:O thin films and (2) Direct Immersion in fluoroalkyl silane (FAS-13) solution using dip coating to form Self-Assembled Monolayers. The results on wettability as well as SEM images and EDS/WDS analyses indicate that the coated sintered stainless steel membranes are adequate as hydrophobic surfaces, maintaining the porosity of the substrate and withstanding high temperatures. Especially the FAS-13 coating shows very good resistance to temperatures higher than 250 °C. These findings are of special significance for the fabrication of porous metal membranes for separation of steam in high temperature applications.

Large-Scale Spraying Fabrication of Robust Fluorine-Free Superhydrophobic Coatings Based on Dual-Sized Silica Particles for Effective Antipollution and Strong Buoyancy.

With the rapid development of bionic science and manufacturing technology, superhydrophobic surfaces have received extensive attention and research. However, the cumbersome steps, high cost, fluorine pollution, and poor durability greatly restrict its commercial promotion and application. Here, a simple spraying method is used to construct wear-resistant superhydrophobic coatings on various substrates such as glass, filter paper, copper sheets, and polyethylene terephthalate films, using an integrated fluorine-free suspension consisting of silica micropowder, nanofumed silica, epoxy resin, and polydimethylsiloxane. The prepared superhydrophobic coating can withstand 75 sandpaper abrasion cycles and can still maintain good superhydrophobic performance after other physical tests (e.g., hand kneading and tape peeling after knife scraping). In addition, the coating is extremely water-repellent under harsh conditions such as strong UV irradiation and extreme chemical corrosive media. In the buoyancy test, the coated filter paper can bear 39 times its own gravity. This water-repellent interface also has the ability to self-clean in air and oil environments due to its ultralow adhesion to water droplets. Thanks to its simplicity, cheapness, and environmental friendliness, this superhydrophobic coating has promising applications in the fields of construction, chemicals, transportation, and electronics.

Surfactant-free commercial electroless bath with low concentration of SiC nanoparticles to prepare the NiP-SiC nanocomposite coatings

Fabrication of NiP-SiC nanocomposite coatings through the electroless deposition in a commercial electrolyte containing the low concentrations of SiC nanoparticles on carbon steel substrate was studied in this work. The confirmation of co-deposition of Ni matrix and SiC nanoparticles was investigated by evaluating the effect on morphology, crystal structure, and corrosion behavior of the heat-treated coatings which were investigated by scanning electron microscope, x-ray diffraction (XRD), and electrochemical measurements, respectively. The XRD results revealed that the heat-treated NiP and NiP-SiC coatings consisted of Ni and Ni3P phases, which the calculated faction of Ni3P phase for NiP and NiP-SiC samples is 58.2 and 62.2%, respectively. The corrosion resistance of nanocomposite samples is higher than that of pure NiP sample (9 to 76% corrosion inhibition efficiency. The tribological behavior of the coatings was characterized by microhardness measurement and ‘pin on disk’ wear test. By co-deposition of SiC nanoparticles, the hardness of heat-treated NiP is significantly increased (near 25%) and the wear loss is reduced (near 48%), especially at high sliding distance during wear test. The sample prepared through the surfactant-free electroless bath containing the 1 g l−1 SiC nanoparticle showed the best corrosion as well as wear resistance.

Effect of high Fe content on the microstructure, mechanical and corrosion properties of AlCoCrFeNi high-entropy alloy coatings prepared by gas tungsten arc cladding

Abstract Arc cladding high-entropy alloy (HEA) coatings have the advantages of low cost and flexibility. It exhibits economic value to increase the proportion of Fe element in HEA systems. As a result, low-cost AlCoCrFeNi (Fe content of 42.5 at.%, 44.9 at.%, 47.5 at.%, 50.4 at.%) HEA coatings are prepared by gas tungsten arc (GTA) cladding and their microstructure, mechanical properties, and corrosion properties are investigated by XRD, SEM, EBSD, microhardness, nanoindentation, OCP, potentiodynamic polarization, and EIS. The valence electron concentration (VEC) plays an important role in the formation of phase structure. With the increase of Fe content, the phase structure of coating alloys changes from BCC to BCC + FCC, and the morphology changes from equiaxed grains to a dendritic structure. Coating alloy with higher Fe content displays lower microhardness and more active creep deformation due to the higher FCC fraction. The dual-phase (BCC + FCC) structure induces galvanic corrosion and deteriorates the corrosion properties. This work contributes to the fabrication of large-thickness and large-area HEA coatings at a low cost and provides an experimental basis for Fe-rich HEA design.

Large-Area Ti3C2Tx-MXene Coating: Toward Industrial-Scale Fabrication and Molecular Separation.

Large-scale fabrication of MXene films is in high demand for various applications, but it remains difficult to meet industrial requirements. In this study, we develop a slot-die coating method for the preparation of large-area MXene membranes. The technique allows the fabrication of continuous and scalable coatings with a rapid coating speed of 6 mm s-1. The thickness can be readily controlled from the nanometer scale to the micrometer scale, and the alignment of the nanosheet is enhanced by the shear force of the slot-die head. Molecular separation experiments employing a film with a thickness of approximately 100 nm are performed. A nanofiltration performance with water permeance of 190 LMH/bar and molecular weight cutoff of 269 Da is achieved, surpassing previously reported results obtained using MXene-based nanofiltration membranes. The stability of the membrane is highlighted by its nanofiltration performance of 30 days under harsh oxidizing conditions, which is the longest operation ever achieved for a 2D material-based membrane. The extraordinary stability of the film suggests its high potential for industrial and practical applications. The antioxidizing phenomena can be attributed to self-protection of the MXene surface by adsorbed organic molecules, which are particularly stabilized with positively charged molecules via chemisorption.

Functional Antimicrobial Surface Coatings Deposited onto Nanostructured 316L Food-Grade Stainless Steel.

In our study, we demonstrated the performance of antimicrobial coatings on properly functionalized and nanostructured 316L food-grade stainless steel pipelines. For the fabrication of these functional coatings, we employed facile and low-cost electrochemical techniques and surface modification processes. The development of a nanoporous structure on the 316L stainless steel surface was performed by following an electropolishing process in an electrolytic bath, at a constant anodic voltage of 40 V for 10 min, while the temperature was maintained between 0 and 10 °C. Subsequently, we incorporated on this nanostructure additional coatings with antimicrobial and bactericide properties, such as Ag nanoparticles, Ag films, or TiO2 thin layers. These functional coatings were grown on the nanostructured substrate by following electroless process, electrochemical deposition, and atomic layer deposition (ALD) techniques. Then, we analyzed the antimicrobial efficiency of these functionalized materials against different biofilms types (Candida parapsilosis, Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, and Staphylococcus epidermidis). The results of the present study demonstrate that the nanostructuring and surface functionalization processes constitute a promising route to fabricate novel functional materials exhibiting highly efficient antimicrobial features. In fact, we have shown that our use of an appropriated association of TiO2 layer and Ag nanoparticle coatings over the nanostructured 316L stainless steel exhibited an excellent antimicrobial behavior for all biofilms examined.

Laser-induced scanning transfer deposition of silver electrodes on glass surfaces: A green and scalable technology

A pulsed laser ablation backwriting technique with high repetitive rates is implemented for the fabrication of silver coatings on glass surfaces. This method enables geometrical constraint-free deposition of metallic coatings. These exhibit sufficiently low electrical resistance to be used as electrodes in dielectric barrier discharge (DBD) plasma elements.Ambient air deposition of metallic silver electrodes on standard glass slides is explored using a sub-ns UV laser source, combined with hybrid beam scanning methods. The green nature of the overall deposition process includes a preliminary irradiation scan to homogenise the target surface before the subsequent backwriting step. Metal transfer is achieved by combining two phenomena within a simple beam scanning process: LIRT (laser-induced reverse transfer) of silver from the target to the glass, with a partial and secondary LIFT (Laser-Induced Forward Transfer) of silver from the glass to the target.Appropriate selection of pulse energy and pulse repetition rates, beam scanning velocities and target motion enable the growth of sufficiently thick Ag deposits on glass with the required low electrical resistivity and nearly 2D constraint-free geometry. This method avoids the use of vacuum and liquids, resulting in a cheap, facile and green methodology for the deposition of silver electrodes onto transparent substrate surfaces.