Inorganic Coatings Research Articles

Enhancement of oxidation and corrosion resistance of flaky carbonyl‑iron powder via SiO2/KH560/PDMS coating applied with sol-gel

The popular magnetic material of flaky carbonyl iron (FCI) is unfortunately vulnerable to electrochemical corrosion when exposed to a salty and foggy environment. This work reports on a sol-gel method that successfully modifies FCI particles, using lithium silicate (Li2SiO3), poly dimethyl siloxane (PDMS), and γ-(2,3-epoxypropoxy) propytrimethoxysilane (KH560), to synthesize Fe@SiO2@KH560@PDMS hybrid composite, related to its organic–inorganic hybrid coatings. The favorable hydrophobicity of organic–inorganic hybrid coatings with the static contact angle of 120° impeded the contact between corrosive medium and FCI core. The results of electrochemical experiments also confirmed its excellent corrosion resistance, since the corrosion potential Ecorr was positively shifted to 0.01 V, and the corrosion current Icorr was three orders of magnitude lower than that of the unmodified FCI particles. Thermogravimetric (TG) analysis indicates that the presence of hybrid coatings also improved the thermal stability of the produced material towards oxidation. Furthermore, the results of molecular dynamics simulation reveal that the hybrid layer inhibits the diffusion of corrosive medium.

Thermal stability and flammability of cotton fabric with TiO2 coatings based on biomineralization

Cotton fabric has a wide application in the textile and furniture industries. However, because of its chemical composition and physical structure, it is highly flammable, which seriously threatens life and property. Incorporating insulating inorganic coatings onto cotton fabrics to mimic the formation of char layer, is a relatively new and effective strategy to improve their flame retardancy. In this study, as an affordable, environmentally friendly, and energy-efficient approach, biomineralization was applied to produce TiO2 coatings on the surface of cotton fabric to form a flame retardant system. The surface morphology and chemical compositions were well characterized first, and the flammability of treated cotton fabric was comprehensively evaluated using different techniques from micro to macro-scale. TiO2 coated cotton shows better flame resistance at the molecular level. The TiO2 coating produced by biomineralization exhibits a strong effect to reduce the burning intensity of cotton. The peak heat release rate is reduced by 5.5%, 27.1%, and 32.6%, respectively for TiO2 coated cotton with 1 cycle, 3 cycles, and 7 cycles of treatment. It also shows the potential to slow down the fire spread rate and the propensity of fire development. The protective effectiveness depends on the number of cycles of treatment. With only 1 cycle of treatment, it is not enough to attain a uniform TiO2 protective coating and thus it shows limited flame retardant performance. Once a uniform TiO2 coating is formed by biomineralization, it shows strong flame retardancy. With 7-cycle treatment, its limiting oxygen index can even reach 21.0%.

Top-Down Formulation of Goethite Nanosuspensions for the Production of Transparent, Inorganic Glass Coatings

This study presents a simple but effective process route for the production of transparent coatings on glass substrates from inorganic pigment goethite. For this purpose, coating suspensions were prepared by wet milling with a stirred media mill. A water/ethanol mixture was used as the liquid medium to take advantage of the resulting low surface tension for the coating process. In this manner, stable suspensions with particles of down to 50 nm in size were obtained, which already showed a significant increase in transparency. With regard to grinding characteristics, particularly low stress energies proved to be energetically reasonable. The coating step was performed by wet film deposition, achieving coating thicknesses in a range of 0.5–2.5 µm via dip coating. Highly transparent coatings were obtained by applying small particles of 50 nm, which exhibited a significantly lower scattering loss of light (≈3%) in comparison to particles of around 300 nm (70–80%). Additionally, the film color could be adjusted through a variation of the drying temperature due to a conversion of goethite to hematite by dehydration. Since transparency was not affected, this provides an easy-to-implement process adaptation for controlling coating colors.

Mammalian Cell Spheroids on Mixed Organic-Inorganic Superhydrophobic Coating.

Three-dimensional cell culture has become a reliable method for reproducing in vitro cellular growth in more realistic physiological conditions. The surface hydrophobicity strongly influences the promotion of cell aggregate formation. In particular, for spheroid formation, highly water-repellent coatings seem to be required for the significant effects of the process. In this work, surfaces at different wettability have been compared to observe their influence on the growth and promotion of aggregates of representative mammalian cell lines, both tumoral and non-tumoral (3T3, HaCat and MCF-7 cell lines). The effect of increased hydrophobicity from TCPS to agarose hydrogel to mixed organic–inorganic superhydrophobic (SH) coating has been investigated by optical and fluorescence microscopy, and by 3D confocal profilometry, in a time scale of 24 h. The results show the role of less wettable substrates in inducing the formation of spheroid-like cell aggregates at a higher degree of sphericity for the studied cell lines.

Nanostructured Poly(methyl Methacrylate)–Silica Coatings for Corrosion Protection of Reinforcing Steel

In the absence of preventive maintenance, corrosion of structural steel by the deterioration of the passive layer due to exposure to aggressive environments is the main failure factor of reinforced concrete. To overcome economic, safety, and environmental implications, present research efforts focus on eco-friendly organic–inorganic hybrid coatings to achieve effective protection of reinforcing steel. Nanostructured PMMA (poly(methyl methacrylate))–silica coatings developed by combining reactions of the polymerization of methyl methacrylate and 3-[(methacryloxy)propyl]trimethoxysilane with the sol–gel hydrolytic condensation of tetraethyl orthosilicate using isopropanol as a solvent represent a promising approach to accomplish this goal. The nanoscale dispersion of silica nodes covalently conjugated with PMMA chains led to transparent, homogeneous, and pore-free coatings deposited with a thickness of 15 μm on 2D and 3D reinforcing steel. Mechanical, thermal, and surface analyses showed a strong adhesion of the coating to the substrate surface (15.9 MPa), a thermal stability of up to 256 °C, and a contact angle of about 75°. Electrochemical assays in standard 3.5 wt % NaCl solution, simulated carbonated, and alkaline concrete pore solutions confirmed effective corrosion protection, with an impedance modulus of up to 100 GΩ cm2 (at 4 mHz) and a lifetime of more than 670 days. Hence, PMMA–silica hybrid coatings are an eco-friendly and efficient alternative to protect reinforcing steel against corrosion, helping to prevent structural failures and fatal accidents.

The enhanced surface properties of geopolymer inorganic coatings by adding with MgO

The enhanced surface properties of geopolymer inorganic coatings by adding with MgO

Hybrid Sol-Gel Coatings Doped with Non-Toxic Corrosion Inhibitors for Corrosion Protection on AZ61 Magnesium Alloy.

Physiological human fluid is a natural corrosive environment and can lead to serious corrosion and mechanical damages to light Mg–Al alloys used in prosthetics for biomedical applications. In this work, organic–inorganic hybrid coatings doped with various environmentally friendly and non-toxic corrosion inhibitors have been prepared by the sol-gel process for the corrosion protection of AZ61 magnesium alloys. Effectiveness has been evaluated by pH measurements, optical microscopy, and SEM during a standard corrosion test in a Hanks’ Balanced Salt Solution. The results showed that the addition of an inhibitor to the sol-gel coating can improve significantly the corrosion performance, being an excellent barrier for the L-cysteine-doped hybrid sol-gel films. The incorporation of TiO2 nanoparticles, 2-Aminopyridine and quinine organic molecules slowed down the corrosion rate of the Mg–Al alloy. Graphene oxide seemed to have the same response to corrosion as the hybrid sol-gel coating without inhibitors.

Inorganic Coatings and Films for Antibacterial and Antivirus Functionality

Inorganic Coatings and Films for Antibacterial and Antivirus Functionality

Начальные стадии возникновения коронного разряда во влажном пористом оксидном слое при прохождении тока высокого напряжения

The physical and chemical processes occurring in non-metallic inorganic porous coatings during the passage of a high-voltage alternating sinusoidal current through metal conductors on which the coatings under study are applied are investigated by the method of mathematical modeling. Compositions of electrolytes and modes of formation of coatings have been developed, and their characteristics have been determined. The option of a wet coating is considered. It was found that at a high voltage in pores filled with a liquid, fast electrode reaction take place, reducing the number of charge carriers in the liquid and increasing the voltage drop in the oxide layer. The simulation results showed the theoretical possibility of corona discharge suppression by 80%. In practice, when an electric current with a voltage of up to 75 kV passes through wires with a diameter of 5.5 mm, the developed coatings reduce power losses for corona discharge by 20% and increase the voltage of corona discharge on the wires by 3 kV.

Methods for the study and control of microplasma processes in the synthesis of coatings

The physical bases for determining the ignition and quenching potentials of microplasma discharges in solutions have been developed. Chronopotentiometric, chronoamperometric dependences on the conditions for obtaining coatings and the dependence of the time constant of the transient process on the voltage and duration of the process, as well as current-voltage dependences at the rates of rise and fall of the potential voltage from 106 to 108 V/s, are obtained. The developed method is applicable to control the process of deposition of microplasma non-metallic inorganic coatings and is the basis of the technique for in situ control of coating deposition. Key words: pulsed microplasma oxidation, current-voltage dependences, controlled synthesis of oxide coatings. Keywords: pulsed microplasma oxidation, current-voltage dependences, controlled synthesis of oxide coatings.

Electrostatic Interaction-Driven Inorganic Coating Layer Toward Improving Battery Performance for 5 V Class High-Voltage Cathode in Secondary Batteries

Electrostatic Interaction-Driven Inorganic Coating Layer Toward Improving Battery Performance for 5 V Class High-Voltage Cathode in Secondary Batteries

Методы исследования и управления микроплазменными процессами при синтезе покрытий

The physical bases for determining the ignition and quenching potentials of microplasma discharges in solutions have been developed. Chronopotentiometric, chronoamperometric dependences on the conditions for obtaining coatings and the dependence of the time constant of the transient process on the voltage and duration of the process, as well as current-voltage dependences at the rates of rise and fall of the potential voltage from 106 to 108 V/s, are obtained. The developed method is applicable to control the process of deposition of microplasma non-metallic inorganic coatings and is the basis of the technique for in situ control of coating deposition. Key words: pulsed microplasma oxidation, current–voltage dependences, controlled synthesis of oxide coatings.

MODIFICATION OF HEAT-RESISTANT OXIDES AND CHLORIDES OF GRAIN SURFACES OF SYNTHETIC DIAMOND GRINDING POWDERS FOR APPLICATION IN GRINDING TOOLS

Further development of modern technologies of diamond processing is connected with application in the diamond tool of powders with new unique properties, special morphology of grains, with the increased chemical and thermal stability. To increase the heat resistance of diamonds, they are covered with a metal (metallization) or glass-ceramic layer, or introduced into the reaction mixture used in the synthesis of diamonds, alloying additives of certain elements. Recently, other methods of coating to increase the heat resistance of diamonds have been developed, such as: vacuum ion-plasma sputtering, epitaxial synthesis, magnetron sputtering, the method of liquid-phase deposition. The latter method is promising for modifying the grain surface of grinding powders of superhard materials by heat-resistant inorganic non-metallic coatings, as it is the most economically advantageous.
 Determining the features of the technology of modification by the method of liquid-phase application of heat-resistant inorganic coatings (oxides and chlorides of metals and nonmetals) on the surface of grains of grinding powders of synthetic diamond brand AC6, used for grinding tools in mechanical engineering.
 Modification was performed by the isothermal method of liquid-phase application of saturated solutions of both heat-resistant oxides (В2О3, Al2O3), chlorides (СаСl2, NaCl, MgCl2, FeCl3), and their mixtures (В2О3+СаСl2, В2О3+NaCl). Based on the analysis of the results of the research, it can be stated that the application of coatings of inorganic substances (some oxides and chlorides) increases the heat resistance of synthetic diamond grinding powders. Modification allows to reduce expenses of diamonds in wheels at grinding.
 Conditions for modification of heat-resistant oxides and chlorides, as well as their mixtures, grain surface of synthetic diamond grinding powders are determined. Modification of the surface of diamond grains with a combination of B2O3+Al2O3 is guaranteed to double the wear resistance of diamond wheels. It is established that in all cases of modification the roughness of the parameter Ra decreases. It is determined that by changing the surface modifier of diamond grains it is possible to affect the bearing capacity of the rough surface obtained by grinding.
 The development of effective ways to increase the heat resistance of grinding powders made of superhard materials, primarily abrasive grinding powders made of synthetic diamond powders, helps to improve the quality of the grinding tool.

Sustainable Materials for Liquid Repellent Coatings

A modern environmental safety approach requires the implementation of green or sustainable strategies, such as banning or significantly lowering the presence of harmful substances on the market or in the industrial environment. To date, the majority of highly performing solutions are still based on fluorine chemistry, even with a growing effort to lower its impact. Economic costs, but also persistence, long-term degradation, and transformation in the environment can raise issues about medium- and long-term effects on human health and wildlife. Coatings with high water and oil repellence are used worldwide in daily life and in industrial and research fields, such as self-cleansing, anti-icing, and anti-biofouling. The combination of a particular geometry or surface structure and low-energy materials results in unique properties related to a range of materials in natural or synthetic categories aiming to build, when possible, a fluorine-free world. This work revises recent and key literature to propose valid alternatives to fluoro compounds in terms of water and oil repellence, as well as stability and resistance to physico-chemical agents. In this paper, natural compounds like fatty acids and waxes are addressed together with more synthetic systems like silicon-based solutions, and polymeric and inorganic nanostructured coatings. Most of the revised papers deal with topics fulfilling environmental requirements but are mainly restricted to highly repellent water and aqueous systems. Nevertheless, new and sustainable strategies for providing suitable, highly oleophobic surfaces to lower fluorine presence have been reported from a small but growing body of literature.

Evaluation of Freeze-Thaw Durability of Silica Fume Concrete with Spraying Inorganic Coating Using Ultrasonic Testing

To study the antifreezing durability of internal coating silicon fume concrete with different external coatings, fast freeze-thaw (FT) cycle testing was performed for three types of external coatings applied to the internal coatings of silicon fume concrete. Using ultrasonic testing and compressive strength tests, we analysed the relationships between the ultrasonic pulse velocity and the mechanical and physical properties of concrete under freeze-thaw action. The results show that the compressive strength and pulse velocity of the studied concrete changed little before the first 100 FT cycles but varied significantly after being subjected to 100 FT cycles and diminished linearly with increasing FT cycles. The dynamic elastic parameters of the concrete were inferred using pulse velocity calculations, and the dependence on FT cycles was very similar to that of ultrasonic pulse velocity. The concrete strength was strongly and positively correlated with ultrasonic pulse velocity. The linear regression model of between ultrasonic pulse velocity, kinetic coefficient, and compressive strength of concrete was also established. The damage incurred to the external coating material (XT-HPA + XT-SS and XT-HPS) was small, and the good performance of the concrete with the added inorganic coating after freeze-thaw cycles indicates good frost resistance.

New Approaches to Increasing the Superhydrophobicity of Coatings Based on ZnO and TiO2

The work presented is devoted to new approaches to increasing the superhydrophobic properties of coatings based on zinc oxide (ZnO) and titanium dioxide (TiO2). There is an innovation in the use of inorganic coatings with a non-polar structure, high melting point, and good adhesion to ZnO, in contrast to the traditionally used polymer coatings with low performance characteristics. The maximum superhydrophobicity of the ZnO surface (contact angle of 173°) is achieved after coating with a layer of hematite (Fe2O3). The reason for the abnormally high hydrophobicity is a combination of factors: minimization of the area of contact with water (Cassie state) and the specific microstructure of a coating with a layer of non-polar Fe2O3. It was shown that the coating of ZnO structures with bimodal roughness with a gold (Au) layer that is 60-nm thick leads to an increase in the wetting contact angle from 145° to 168°. For clean surfaces of Au and hematite Fe2O3 films, the contact angle wets at no more than 70°. In the case of titanium oxide coatings, what is new lies in the method of controlled synthesis of a coating with a given crystal structure and a level of doping with nitrogen using plasma technologies. It has been shown that the use of nitrogen plasma in an open atmosphere with different compositions (molecular, atomic) makes it possible to obtain both a hydrophilic (contact angle of 73°) and a highly hydrophobic surface (contact angle of 150°).

Enhancements on Flame Resistance by Inorganic Silicate-Based Intumescent Coating Materials.

Flame-retardant coatings have drawn much attention in recent years. In this study, an inorganic sodium silicate-based intumescent flame-resistance coating with an excellent flameproof properties is developed by mainly utilizing sodium silicate as the ceramizable binder, via hydrolysis and self-condensation reaction. Fly ash, metakaoline, and wollastonite behave as supplement cementing materials. Major formulation encompasses the combination of the ammonium polyphosphate and pentaerythritol as the flame-retardant additives, and aluminum hydroxide or expandable graphite as the intumescence-improving filler agents. Expandable graphite was found to play an important role in the eventual performance of flame-resistance testing. The results showed that solid interaction forces can be formed between metakaoline and sodium silicate, resulting in a similar material to geopolymer with excellent physical properties. After high-temperature flame testing, a densely complex protective layer of carbon-char created on top of the robust silicon dioxide networks offers notable flame resistance. An optimal ratio in this inorganic intumescent coating contains sodium silicate—metakaoline (weight ratio = 9:1)—ammonium polyphosphate and pentaerythritol, aluminum hydroxide (3, 3, 10 wt.%)—expandable graphite (1 wt.%), which can create 4.7 times higher expansion ratio compared with neat sodium silicate matrix. The results of flame testing demonstrate only 387.1 °C and 506.3 °C on the back surface of steel substrate after one and three hours flaming (>1000 °C) on the other surface, respectively, which could meet the requirements according to the level of fire rating.

Organic and inorganic nanomaterial coatings for the prevention of microbial growth and infections on biotic and abiotic surfaces

The growing threat of pathogenic microbes has increased the rate of morbidity and mortality among the human population. Centres for Disease Control has announced that the world is entering the post antibiotic era, which will increase the death rate by bacterial infections instead of cancer and other fatal diseases. Nonetheless, the emergence of multidrug resistant strains of bacteria has led to finding novel strategies to prevent bacterial growth on abiotic and biotic surfaces. Therefore, nanomaterials are growing as a potential strategy to replace conventional antimicrobial therapy. In recent times, bacterial pathogens have been known to colonize on medical devices, implants, tooth filings, lenses, fabrics, metallic and non-metallic surfaces. Important significance organic and inorganic nanomaterials include silver (Ag), copper (Cu), zinc oxide (ZnO) and gold (Au), titanium (Ti), selenium (Se), iron (Fe) as well as polymer materials have been highlighted as potential coating materials for preventing the growth and attachment of bacteria. Nanoparticles (NPs) have a large surface area to volume ratio and generate reactive oxygen species (ROS) leading to the damage of the bacterial cell walls. The present review has focused on the important role of nanoparticles as a coating material to create antibacterial surfaces for a prolonged time and efficiency. • Bacterial colonization causing biofilm formation is the major cause of mortality and morbidity. • Biofilm forming bacteria colonizes on medical devices and equipment. • Nanoparticles (NPs) are efficient strategy to prevent and inhibits bacterial attachments. • Metallic NPs directly targets the biofilm forming bacterial pathogens. • Non-metallic NPs are used as carriers for drug delivery to prevent contamination on biomedical devices.

Biomimetic Inorganic Nanoparticle-Loaded Silk Fibroin-Based Coating with Enhanced Antibacterial and Osteogenic Abilities.

Poor osseointegration and infection are the main reasons leading to the failure of hard tissue implants; especially, in recent years, the failure rate has been increasing every year owing to the continuously increasing conditions such as injury, trauma, diseases, or infections. Therefore, the development of a biomimetic surface coating of bone tissues with antibacterial function is an effective means to improve bone healing and inhibit bacterial infection. Mimicking the natural bone, in this study, we have designed a silk fibroin (collagen-like structure)-based coating inlaid with nanohydroxyapatite (nHA) and silver nanoparticles (AgNPs) for promoting antibacterial ability and osteogenesis, especially focusing on the bone mimetic structure for enhancing bone health. Observing the morphology and size of the composite nanoparticles by transmission electron microscope (TEM), nHA provided nucleation sites for the formation of AgNPs, forming an nHA/AgNP complex with a size of about 100–200 nm. Characterization of the nHA/Ag-loaded silk fibroin biomimetic coating showed an increased surface roughness with good density and compact performances. The silk fibroin-based coating loaded with uniformly distributed AgNPs and nHA could effectively inhibit the adhesion of Staphylococcus aureus on the surface and, at the same time, quickly kill planktonic bacteria, indicating their good antibacterial ability. In vitro cell experiments revealed that the biomimetic silk fibroin-based coating was beneficial to the adhesion, spreading, and proliferation of osteoblasts (MC3T3-E1). In addition, by characterizing LDH and ROS, it was found that the nHA/Ag complex could significantly reduce the cytotoxicity of AgNPs, and the osteoblasts on the coating surface maintained the structure intact.

Superior Li Metal Anodes By Molecular Layer Deposition of Lithicones

Superior Li Metal Anodes by Molecular Layer Deposition of Lithicones Xiangbo Meng*1, Kah Chun Lau*2, Xiaoxiao Han1, Hua Zhou3 1 Department of Mechanical Engineering, University of Arkansas, Fayetteville, AR 72701, USA 2 Department of Physics and Astronomy, Californica State University Northridge, CA 91330, USA 3 Advanced Photon Source, Argonne National Laboratory, Lemont, IL 60439, USA* Corresponding author: xbmeng@uark.edu; kahchun.lau@csun.eduInterfaces, located between an electrode (either a cathode or an anode) and an electrolyte, are one of the most important components of rechargeable batteries. They are often determinant to batteries’ performance. In pursuing next-generation lithium-ion batteries (LIBs) and beyond, atomic layer deposition (ALD) has emerged and been identified as an important tool to accurately constitute their interfaces of LIBs and beyond at the atomic scale in the past decade.1-7 ALD features its unparalleled capabilities enabling coatings conformally and uniformly at moderate temperatures. It can be performed on either battery powders or prefabricated electrodes. Complementary to inorganic coatings by ALD, polymeric coatings can be deposited by an analogous technique, molecular layer deposition (MLD),8 and recently have been investigated. Having similar merits of ALD, MLD can constitute battery interfaces with flexible polymeric films at the molecular level. In this work, we developed three new lithium-containing polymers, lithicones, using MLD. Particularly, we revealed that the MLD LiGL (GL = glycerol) is very promising as a protective coating over lithium metal anodes. The LiGL-protected lithium metal anodes could achieve superior cyclability over 6,000 cycles without having any sign of failure at 5 mA/cm2 and 1 mAh/cm2. Our experiments and density function theory calculations disclosed that the LiGL lithicone is exceptional in its properties. This work paves a new avenue for developing safety-reliable high-performance lithium metal anodes.