Synthesis of Ultrafine Oxide Powders by Hydrothermal-Ultrasonic Method
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Synthesis of Ultrafine Oxide Powders by Hydrothermal-Ultrasonic Method Pavel E. Meskin 1, Yury V. Kolenko 1, Alexander E. Baranchikov 2, Vladimir K. Ivanov 2, Bulat R. Churagulov 1, Nikolay N. Oleynikov 1,2 1 2
Department of Chemistry, Moscow State University, Moscow, Russia Kurnakov Institute of General and Inorganic Chemistry, Moscow, Russia
Abstract 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. Introduction It is well known that nanomaterials can be obtained by a number of methods, including mechanochemical, cryochemical, hydrothermal, sol–gel, and so on [1]. Each of these methods is useful to obtain nanoparticles with definite morphology and size distribution. However, the characteristics of these powders can sometimes be deliberately changed under the action of additional external factors, such as, e.g., microwave heating [2], ultrasonic treatment [3], etc. Note that high-power ultrasonic treatment is one of the most promising methods that alter processes in the liquid phase. The passage of acoustic vibrations through liquid gives rise to cavitation, which is accompanied by a number of extreme effects (a local increase in temperature to 5000 K and in pressure to 100 MPa, formation of intense liquid microflows, etc. [3, 4]). This considerably changes the physicochemical parameters of the processed medium. Thus, we believe that acoustic cavitation holds much promise for controlled change in the microstructure of powders obtained under hydrothermal conditions. However, no information on studies of acoustic cavitation under hydrot
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