A. A. Burukhin

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 .

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.

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.

Synthesis of Nanostructured Iron Oxide(III) Powders by Rapid Expansion of Supercritical Fluid Solutions

Nanostructured a-Fe 2 O 3 powders were generated by rapid expansion of supercritical fluid solutions (RESS, T=773 K, P=100 MPa) and by rapid thermal decomposition of precursors in solution ( RTDS, T=623 K, P=100 MPa) on lab RESS-setup from 0,040 M and 0,10 M aqueous solutions of Fe(NO 3 ) 3 . The size of subcrystallites is about 22-29 nm. Comparison of reactivity of α-Fe 2 O 3 powders in a model solid state reaction between a-Fe 2 O 3 powders (generated by RESS from 0,040 M solution) and Li 2 CO 3 (mole ratio 1:1) with literature data on a-Fe 2 O 3 powders produced by other methods shows that its reactivity is markedly higher. A basic essence possibility of zinc ferrite ZnFe 2 O 4 formation immediately at the stage of the rapid expansion (T=773K; P=100 MPa) of a supercritical aqueous solution of zinc and iron nitrates (molar ratio Zn:Fe=1:2; C=0. 1 M) was shown.

Characterization of ultrafine zirconia and iron oxide powders prepared under hydrothermal conditions

Abstract Nanocrystalline zirconia (6-20 nm) and iron oxide (20-80 nm) powders were produced by hydrothermal treatment of corresponding hydroxides and nitrate solutions. The synthesis parameters (temperature, duration, concentration) allow fabrication of ultrafine oxide powders with various particle size and morphology. The smallest particles were produced by short-time (4-7 s) treatment of nitrate solutions (PH ≈ 1). Prepared nanocrystalline powders exhibit high activity in model solid state reactions.