B. R. Churagulov

Synthesis of nanocrystalline TiO2 powders from aqueous TiOSO4 solutions under hydrothermal conditions

Abstract Nanocrystalline anatase powders with particle sizes from 8 to 38 nm have been synthesized by hydrothermal treatment of aqueous TiOSO4 solutions and TiO2·nH2O amorphous gel. The products have been characterized by X-ray diffraction (XRD), thermogravimetric analysis (TGA), transmission electron microscopy (TEM), and BET method.

Hydrothermal synthesis of LiCoO2 for lithium rechargeable batteries

Ultrafine powders of LiCoO2 were prepared under mild hydrothermal conditions. Reactant mixtures of aqueous solutions of cobalt (II) nitrate, lithium hydroxide and hydrogen peroxide with different Co/Li and Co/H2O2 ratios were hydrothermally treated at 150–250 °C for 0.5–24 h in a Teflon-lined autoclave. Only HT-LiCoO2 phase was observed by X-ray diffraction (XRD) analysis. Scanning (SEM) and transmission (TEM) electron microscopies revealed the formation of well-crystallized hexagonal platelike particles with average size 70–200 nm. The increase in LiOH concentration results in better crystallinity. Annealing of hydrothermally prepared LiCoO2 at 230 °C leads to decreasing initial capacity from 130 down to 120 mA h/g, but improves cyclability (fade rate drops from 3.1 to 1.6 mA h/g per cycle). Submicrometric particle size and high surface area results in good electrochemical properties for high discharge rate.

On the Possibility of Preparing Fine-Particle Barium Zirconate by Hydrothermal Synthesis

The possibility of preparing fine-particle BaZrO3 by hydrothermal synthesis was examined. The samples prepared using three different starting mixtures were characterized by x-ray diffraction, thermogravimetry, and scanning and transmission electron microscopy techniques. By dissolving solid Ba(NO3)2 in a 0.25 M ZrO(NO3)2 solution (pH 1.5), nanocrystalline powder of the stable polymorph M-ZrO2 was obtained (particle size d = 8–10 nm), independent of the Ba(NO3)2 : ZrO(NO3)2 ratio. Hydrothermal treatment of a ZrO(OH)2 gel in neutral (pH 7.0) and ammonia (pH 11.0) media in the presence of Ba(NO3)2 yielded only the metastable phase T-ZrO2 (d = 10–12 nm), whereas treatment under similar conditions with no Ba(NO3)2 in solution resulted in a mixture of M- and T-ZrO2 . The formation of microcrystalline BaZrO3 (d = 2–5 μm) from a ZrO(OH)2 gel was observed only in a high-pH Ba(OH)2 solution (pH 13.0). Attempts to obtain BaZrO3 by boiling an amorphous ZrO(OH)2 gel at 378 K at atmospheric pressure in a high-pH Ba(OH)2 solution (pH 13.0) for 45 min with the use of microwave heating were unsuccessful: the solid phase consisted of x-ray amorphous ZrO(OH)2 .

IUPAC-NIST Solubility Data Series. 95. Alkaline Earth Carbonates in Aqueous Systems. Part 1. Introduction, Be and Mg

The alkaline earth carbonates are an important class of minerals. This volume compiles and critically evaluates solubility data of the alkaline earth carbonates in water and in simple aqueous electrolyte solutions. Part 1, the present paper, outlines the procedure adopted in this volume in detail, and presents the beryllium and magnesium carbonates. For the minerals magnesite (MgCO 3), nesquehonite (MgCO 3.3H 2O), and lansfordite (MgCO 3.5H 2O), a critical evaluation is presented based on curve fits to empirical and=or thermodynamic models. Useful side products of the compilation and evaluation of the data outlined in the introduction are new relationships for the Henry constant of CO 2 with Sechenov parameters, and for various equilibria in the aqueous phase including the dissociation constants of CO 2(aq) and the stability constant of the ion pair MCO 3 0(M=alkaline earth metal). Thermodynamic data of the alkaline earth carbonates consistent with two thermodynamic model variants are proposed. The model variant that describes the Mg 2+-HCO 3 - ion interaction with Pitzer parameters was more consistent with the solubility data an d with other thermodynamic data than the model variant that described the interaction with a stability constant.

Hydrothermal Synthesis of Nanocrystalline SnO2 for Gas Sensors

Nanocrystalline SnO2 is prepared by hydrothermal synthesis (130–250°C, 2–5 h) using three different precursors and is characterized by x-ray diffraction, transmission electron microscopy, and nitrogen BET measurements. The crystallite size of SnO2 powders (d = 4–5 nm) prepared from amorphous stannic acid gels is found to vary very little with process temperature and duration. Air anneals at 500°C for 1–20 h demonstrate that the highest stability toward crystallite growth is offered by the samples prepared by oxidizing SnSO4 with H2O2 (the crystallite size increases only slightly, from 4–5 to 5–7 nm), whereas the crystallite size of the samples prepared by high-temperature hydrolysis of SnCl4 increases markedly, from 4–5 to 16–17 nm. Nanocrystalline NiO-doped SnO2 is prepared by hydrothermal treatment, and its physicochemical properties are investigated. Both SnO2 and SnO2〈NiO〉 exhibit gas sensitivity, as demonstrated by consecutively exposing the samples to different gaseous atmospheres: O2 → N2 → O2 and O2 → N2 + C2H5OH → O2.

Effect of supercritical drying parameters on the phase composition and morphology of aerogels based on vanadium oxide

Aerogels based on vanadium oxide were obtained by supercritical drying in carbon dioxide (scCO2) and organic solvents (acetone, n-hexane, n-heptane, and n-octane). The performed study allowed us to reveal the effect of experimental parameters (precursor type, type of primary and secondary solvents) on the phase composition and morphology of obtained aerogels. The obtained samples were studied by X-ray diffractometry, scanning electron microscopy, and capillary nitrogen adsorption-desorption (BET) method.

Influence of thermal treatment on the ion transport properties of hydrated zirconia

Properties of hydrated and nanocrystalline zirconia and products of their thermal and chemical modification have been investigated by means of impedance spectroscopy, ion-exchange potentiometric titration, electron probe X-ray spectral analysis and electron microscopy. Regardless of the degree of hydration, all samples exhibit surface charge transfer. It was shown that ion conductivity of the hydrated zirconia could be increased by thermal treatment by one order of magnitude or more.

Microwave-assisted hydrothermal synthesis of fine BaZrO3 and BaHfO3 powders

Fine BaZrO3 and BaHfO3 powders have been prepared by a microwave-assisted hydrothermal (MWHT) process. The powders have been characterized by x-ray diffraction and scanning electron microscopy, and their particle size distribution has been assessed from dynamic light scattering data. The results indicate that microwave processing during hydrothermal synthesis notably reduces the average particle size of the resulting powder and ensures a narrower particle size distribution. BaHfO3 particles prepared under the optimal MWHT synthesis conditions are predominantly spherical in shape and uniform in size, with an average size (1.2 μm) a factor of 2.5 smaller in comparison with particles prepared by a conventional hydrothermal process (2.9 μm).

Study of electrochemical lithium incorporation to whisker structure based on barium-vanadium bronze BaV8O21-δ

Both nanobands and macroscopic (up to 3mm-long) filamentous conducting BaV8O21-δ crystals are prepared for the first time by hydrothermal processing of polymerized gels. They show stable electrochemical characteristics acceptable for their usage in newly elaborated secondary cells (batteries).

Synthesis and photocatalytic activity of anatase-based aerogels

VxTi1–xO2 (x = 5 and 10 mol %) solid solutions have been synthesized through supercritical drying in isopropanol at t = 250°C and p = 10 MPa. Their physicochemical properties and photocatalytic performance have been compared to those of an earlier synthesized ZnxTi1–xO2 aerogel containing 10 mol % Zn [1]. It has been shown that increasing the vanadium content of VxTi1–xO2 from 5 to 10 mol % leads to a decrease in hydrogen evolution rate in methanol/water splitting reaction under UV irradiation from 190 to 32 µL/(min gcatal), whereas in the case of the anatase-based aerogel solid solution containing 10 mol % Zn an opposite picture is observed: the hydrogen evolution rate in methanol/water splitting reaction under UV irradiation increases sharply to 700 µL/(min gcatal).