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The behavior of the ceramic material Ta4HfC5-30 vol % SiC has been studied under the effect of supersonic flow of dissociated nitrogen, which is necessary to assess the potential application of these materials in oxygen-free gas environments at temperatures >1800°C. It has been found that as a result of heating the surface to ~2020°C in a few minutes there is a decrease to ~1915°C followed by a slow decrease to 188°C. This is probably due to the chemical processes occurring on the surface and the formation of an extremely rough microstructure. The ablation rate has been determined; it has been shown that neither at introduction of the sample into a high enthalpy nitrogen flow nor at sharp cooling (temperature drop to ~880°C in 9–10 s) cracking of the sample or detachment of the near-surface region has been observed. X-ray powder diffraction and Raman spectroscopy data allow us to conclude the complete removal of silicon carbide from the surface layer and the transformation of complex tantalum-hafnium carbide into the nitride. [ABSTRACT FROM AUTHOR]

The formation of nanocrystalline Co3O4 by chemical precipitation has been studied. The validation of the obtained semiproduct has been carried out using simultaneous thermal analysis, infrared spectroscopy, and X-ray powder diffraction analysis. The process of thermal decomposition of the semiproduct with the formation of the target oxide, which is a highly dispersed powder (the average CSR size was about 17 ± 2 nm), free of impurities has been investigated. An approach to microplotter printing of miniature planar Co3O4 nanostructures of different geometries on the surface of silicon substrates with the use of functional inks made on the basis of the obtained nanopowder has been proposed. The features of the morphology of the formed thin-film structures have been investigated. It is shown that there is practically no "coffee ring" effect. As part of the local electrophysical characteristics study of the obtained samples, the distribution maps of surface potential and capacitance contrast have been built, and the value of the electronic work function has been calculated. As a result of the study, the possibility of using the developed technology for the manufacturing of electrode structures Co3O4 for supercapacitors of planar type has been shown. [ABSTRACT FROM AUTHOR]

As part of the study, we have developed a method for obtaining a single-layer Ti2CTx MXene by the interaction of Ti2AlC with a mixture of hydrochloric acid and sodium fluoride followed by delamination using a tetramethylammonium hydroxide solution and ultrasonic exposure. The obtained stable aqueous dispersion of Ti2CTx has been applied by microplotter printing onto a specialized sensor chip, which has been dried at a temperature of 150°C under reduced pressure. The coating has been studied using modern physicochemical methods of analysis. According to the data of X-ray spectral elemental microanalysis, the ratio n(Ti) : n(F + Cl) = 2 : (0.82–0.85), n(F) : n(Cl) ≈ 6 : 4; aluminum impurity does not exceed 1.5–2.0%. Data have been obtained on the local electrophysical properties of the Ti2CTx coating: on the value of the electron work function from the surface of the material, the distribution of charge carriers, and the capacitance gradient of the "probe tip–sample microregion" capacitor. For the first time, at an operating temperature of 30°C, extremely high chemoresistive responses of the Ti2CTx receptor layer to the content of 1 and 5% oxygen in nitrogen have been determined, which amounted to 8.6 and >276, respectively. [ABSTRACT FROM AUTHOR]

The process of forming planar electrodes of the composition NiCo2O4 using high-performance high-resolution microplotter printing technology with functional inks based on nanopowders (average size of the coherent scattering region 14 nm) of a similar composition obtained by the method of programmable chemical coprecipitation of metal hydroxides has been studied. The thermal and spectral characteristics of the intermediate and the target oxide, as well as the features of their crystal structure and microstructure, have been studied using a set of methods of physicochemical analysis. According to X-ray phase analysis and Raman spectroscopy, the resulting coatings are single-phase and are characterized by a cubic spinel-type crystal structure. The results of scanning electron microscopy show that the resulting hierarchically organized coatings are homogeneous and contain no defects in the form of gaps or delaminations. The prospects of the developed technology for the manufacture of modern electrode materials of the composition NiCo2O4 are shown. [ABSTRACT FROM AUTHOR]

The synthesis of nano-sized oxide WO3–25 at % VO2 by a combination of sol–gel process and hydrothermal treatment using metal alkoxoacetylacetonates as precursors was studied. The synthesis gave the oxide powder isomorphous to hexagonal tungsten(VI) oxide. The thermal behavior of the powder in an air flow was studied by simultaneous thermal analysis in the temperature range of 25–600°C. The resulting particles were shaped as nanorods. Using Kelvin probe force microscopy, the electron work function of the material surface was determined. [ABSTRACT FROM AUTHOR]

The features of the process of glycol-citrate synthesis of highly dispersed oxide La0.6Sr0.4Co0.2Fe0.8O3 – δ with varying concentrations of the oxidizing agent (nitro group) and reducing agent (ethylene glycol) in the reaction system have been studied. The effect of the parameters indicated on the thermal behavior, spectral characteristics, phase composition, and microstructure of the obtained nanopowders has been determined. It is shown that the proposed synthesis conditions make it possible to reduce the formation temperature of single-phase highly dispersed oxides of a given composition, which are promising as cathode materials for medium-temperature solid oxide fuel cells. [ABSTRACT FROM AUTHOR]

Experiments on heat transfer to HfB2-SiC-based ceramics specimens in underexpanded supersonic flows of high-enthalpy nitrogen are performed on the VGU-4 induction high-frequency (HF) plasmatron of the Institute for Problems in Mechanics of the Russian Academy of Sciences. The nitrogen plasma flows in the discharge channel of the plasmatron and the underexpanded dissociated-nitrogen flow past a cylindrical model with the ceramics specimen was simulated numerically within the framework of the Navier–Stokes and simplified Maxwell equations. Basing on the comparison of the experimental and calculated data the possible range of the effective coefficient of the heterogeneous nitrogen atom recombination on the ceramics surface is determined as a function of its total emissivity at a temperature of 2000°C. The microstructure and the element and phase compositions of the surfaces of the HfB2-SiC-based ceramics specimens and the HfB2-SiC-G-based ceramics specimen modified by two volume percents of graphene are studied after they have been subjected to the action of supersonic flow of partially dissociated nitrogen. [ABSTRACT FROM AUTHOR]

Hydrothermal synthesis of V2O5 using ammonium vanadate and oxalic acid as the starting reactants was studied. The hydrothermal treatment of a solution at 200°C (6 h) gave a dark blue precipitate of vanadium dioxide consisting mainly of the monoclinic (B) phase. Further heat treatment at 350°C for 2 h resulted in vanadium dioxide oxidation to V2O5. The V2O5 particles thus obtained were 1–1.2 µm-long nanorods of 10–20 nm in diameter. The obtained powder was used to form a coating on an aluminum substrate. The distribution of local electrophysical properties over the surface of V2O5 particles was studied using scanning Kelvin probe microscopy and scanning capacitance microscopy. [ABSTRACT FROM AUTHOR]

A relatively low-temperature molten salt assisted synthesis is developed to prepare MAX phase solid solutions in the Ti2AlC–V2AlC system, to be used as precursors for the preparation of heterometallic MXenes Ti2 –xVxC. When the synthesis temperature is 1000°С, Ti1V1AlC, Ti0.5V1.5AlC, and Ti0.2V1.8AlC samples (despite the formation of a MAX phase and a systematic shift of reflection (002) in response to progressing vanadium-for-titanium substitution) typically feature appreciable amounts of impurity phases, namely Al2O3 and vanadium (their reflections are partially overlapping). An increase in synthetic temperature to 1100°С appreciably reduces the amount of impurities and, in a Ti1V1AlC sample, decreases the unit cell parameter a, which yet far exceeds the calculated and published values (while the parameter c corresponds with those values). Thermal analysis of Ti2AlC, Ti1V1AlC, and V2AlC samples in the range 20–1000°С shows that the oxidation resistance decreases in the progress of vanadium-for-titanium substitution in a MAX phase. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) are used to study the microstructure of the prepared Ti2AlC and V2AlC phases. [ABSTRACT FROM AUTHOR]

The production of a NiCo2O4 nanopowder using hydrolytically active heteroligand complexes [M(C5H7O2)x(C4H9O)y] (where M = Ni and Co) as precursors was investigated. A simultaneous thermal analysis was used to study the synthesis of a xerogel by the hydrolysis of the complexes, their polycondensation, and drying of the synthesized gel and the transformation of the produced xerogel to an oxide powder of the desired composition. Advantages were demonstrated for the proposed method of pen plotter printing using the obtained solution of the heteroligand complexes as a functional ink in the production of NiCo2O4 thin films on the surface of substrates of various types. The results of X-ray powder diffraction analysis and scanning and transmission electron microscopy confirmed that the proposed synthesis conditions and printing parameters ensure the efficient synthesis of the oxide of the desired composition as both a nanopowder (with an average size of coherent scattering regions of about 20 nm), and thin films (with an average particle size of 12–15 nm). [ABSTRACT FROM AUTHOR]

Features of the application of the method of spark plasma sintering, as one of the most effective and promising for the manufacture of super-refractory oxygen-free ceramics, have been studied for the reactive consolidation of highly dispersed powder Ta2O5–HfO2–C with a carbon deficiency in comparison with that necessary for the synthesis of metal monocarbides. The initial powder has been obtained by the sol-gel method with a calculated ratio n(Ta) : n(Hf) = 9 : 1, confirmed experimentally using the EDX method. Spark plasma sintering experiments of the resulting system have been carried out in a dynamic vacuum at a pressure of 25 MPa and temperatures of 1600 and 1700°C (higher temperatures led to the outflow of molten oxides from the molds before the beginning of carbothermal synthesis of TaC–HfC). The presence of tantalum subcarbide Ta2C in the obtained ceramic is more advantageous than the oxide impurities and the formation of which under the selected conditions has been predicted by thermodynamic calculations. Its absence can be explained by the fact that equilibrium is not achieved when heating, holding, and cooling the sample. [ABSTRACT FROM AUTHOR]

The synthesis of nanoscale WO3 by chemical precipitation with oxalic acid was studied. The obtained powder was characterized by IR-spectroscopy and powder X-ray diffraction, while its thermal behavior was investigated by simultaneous TGA/DSC analysis. It was found that before heat treatment, the precipitate is a mixture of WO3⋅2H2O and tungsten oxalate. The heat treatment at 400°C results in oxalate decomposition, while treatment at 500°C gives single-phase WO3 with monoclinic crystal structure (mean CSR of 36 ± 4 nm, particle length of 50 ± 5 nm, and particle width of 40 ± 4 nm). The electron work function of the surface of prepared WO3 particles in air was measured using Kelvin-probe force microscopy. It was shown that chemical precipitation of tungsten(VI) oxide using oxalic acid is a promising method for producing the corresponding nanopowder. [ABSTRACT FROM AUTHOR]

Abstract—The synthesis of NiMoO4 hierarchical nanostructures using the hydrothermal method has been studied. The decomposition of NiMoO4·xH2O crystalline hydrate formed during the synthesis has been studied using synchronous thermal analysis upon heating in a stream of air and argon. According to X-ray diffraction as well as scanning and transmission electron microscopies, the proposed conditions allow one to synthesize single-phase nanosized (average CSR size of about 25 ± 2 nm) nickel(II) molybdate, which has a spinel-type monoclinic structure (space group C2/m) without impurity inclusions. [ABSTRACT FROM AUTHOR]

The formation of CoMoO4 anisotropic nanostructures has been studied with a combination of programmed co-precipitation of metal hydroxides and the hydrothermal method. The thermal behavior, phase composition, and microstructure features of the obtained nanopowder have been investigated. Using a set of physicochemical methods of analysis, it has been shown that the proposed synthesis conditions make it possible to form a single-phase nanodispersed (average CSR size of about 30 ± 3 nm) oxide with a monoclinic spinel-type structure (space group C2/m) that does not contain impurity inclusions. [ABSTRACT FROM AUTHOR]

Nb2O5–TiO2 nanomaterials containing 0.5 and 10 mol % TiO2 have been synthesized by the programmed deposition method. The products have been characterized by modern physicochemical methods The Nb2O5–TiO2 nanomaterials have a crystal structure of orthorhombic Nb2O5 (T-phase). Individual niobium oxide is composed of nanoparticles with an average size of 15 ± 3 nm; increasing the TiO2 content entails microstructural changes. For the Nb2O5–TiO2 coatings, a set of chemoresistive gas-sensing properties has been studied. Of all the analyzed gases, the highest sensitivity was recorded for oxygen and hydrogen sulfide. It has been shown that the sample with 5% TiO2 is most sensitive to О2 and H2S, which is explained by the formation of additional oxygen vacancies. [ABSTRACT FROM AUTHOR]

MnOx thin films on various types of substrates (glass, quartz, alumina, and Pt/Al2O3/Pt) were prepared by a combination of the sol–gel method and pen plotter printing, using the hydrolytically active heteroligand complex [Mn(C5H7O2)2 –x(C4H9O)x] as the precursor. The effect of synthesis parameters and printing modes on the microstructure, optical and electrophysical properties of the manufactured planar nanomaterials was studied. The electron work function of the MnOx film surface was assessed by Kelvin probe force microscopy (KPFM). Impedance spectroscopy was used to determine the temperature-dependent electrical conductivity of the prepared films in the temperature range 325–500°С. The proposed synthetic method and printing technology show promise for the formation of thin-film manganese oxide nanostructures for supercapacitor electrodes and optical devices. [ABSTRACT FROM AUTHOR]

Oxidation under exposure to a supersonic dissociated air jet (with heat fluxes in the range 363–779 W/cm2, total exposure time: 2000 s) was studied for HfB2–30 vol % SiC ultra-high-temperature ceramics (UHTC) doped with a lowered amount (1 vol %) of reduced graphene oxide (GO). Doping the ceramics with a relatively low amount of reduced GO (1 vol %) did not prevent a dramatic increase in the average surface temperature to 2300–2400°С. However, the existence time of surface temperatures below 1800–1850°С increased considerably, probably due to an increase in the thermal conductivity of the ceramics. The ablation rate of the material was determined as 6.5 × 10–4 g/(cm2 min), which is intermediate between the respective values for HfB2–SiC ceramics and the ceramics doped by 2 vol % graphene. The microstructure features and elemental composition of the oxidized surface and chips of the material were studied. The structure and thickness of the oxidized near-surface region were determined. [ABSTRACT FROM AUTHOR]