PRESSURE DEPENDENCE OF FLAME ZONE SIZE OF SINGLE ALUMINIUM PARTICLES

Mathematical modeling of geometric dimensions and thermodynamic parameters of flame around single aluminium under combustion in the 79 % Ar + 21 % O2 atmosphere was implemented. The modeling was carried out on the basis of summarizing of experimental data and results of thermodynamic analysis. The dependencies of temperature and oxidizer (oxygen) concentration on the flame boundary and pressure of surrounding medium on particle size were determined. Also relation of flame radius with particle radius was established. The calculations was realized according to model of diffusion mode combustion with taking into account quasistationarity and thermodynamic equilibrium of processes, from the assumption of spherical symmetry of the flame. The flame boundary, oxidizer concentration and temperature on the boundary are determined on the basis of condition of predetermined completeness of aluminium transformation into ultrafine oxide Al2O3. The relative size of flame zone is established to decrease from 4.5 to 6.8 when surrounding medium pressure changes from 0.1 to 6 MPa. The relative size of flame zone and oxidizer concentration on the flame boundary increase as the particle burn out. As the particle radius decreases the part of radiative heat exchange decreases in total balance of it’s energy. And the part of radiative heat exchange does not exceed 8 % for industrial aluminium powders with particles diameter less than 50 m. The surrounding medium pressure influences on values of parameters calculated essentially with the exception of part of radiation heat flow.

Synthesis of Ultrafine Oxide Powders by Hydrothermal-Ultrasonic Method

ABSTRACTIn 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 high-temperatures 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.