P. E. Meskin

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).

Synthesis of Ultrafine Oxide Powders by Hydrothermal-Ultrasonic Method

In the present work, a novel method of synthesis has been developed to obtain highly dispersed oxide powders. This method is based on the combination of hydrothermal and ultrasonic treatment and uses the effect of acoustic cavitation. Hydrothermal-ultrasonic treatment was carried out under the following conditions: T= 423 523 K, t = 10 min. - 3 h. and ultrasonic frequency ν = 21.5 kHz. The control experiments (without ultrasound) were performed under the same conditions. The products were characterized by X-ray diffraction (XRD), thermal analysis (TGA), transmission electron microscopy (TEM). The specific surface area was determined by the BET method. It was found that high-temperature hydrolysis of cobalt (II) nitrate in ultrasonic field results in formation of considerably smaller particles of Co3O4 in comparison with conventional hightemperatures hydrolysis (mean particle size decreases from 600-650 nm to 60-70 nm). It must be noted that Co3O4 samples obtained by hydrothermal-ultrasonic treatment possess mesoporous structure. Ultrasonic-hydrothermal processing of amorphous gels of zirconyl and titanyl hydroxides leads to significant raise of the rate of crystallization process and formation of nanopowders of zirconia and titania (mean particle size 7-16 nm). It must be pointed that the use of ultrasonic treatment during hydrothermal processing of amorphous gel of zirconyl hydroxide and 0.3 M aqueous solution of H2TiO(C2O4)2 leads to increase of the content of thermodynamically stable phases in the products of synthesis.