ANISOTROPY OF CRYSTALLITE GROWTH DURING SINTERING OF SNO2 XEROGELS

The crytallite and pore-size evolution during isothermal sintering (40 0 less than or equal to T less than or equal to 700 degrees C) of SnO2 xerogels was studied by X-ray line broadening and nitrogen adsorption -desorption isotherms. The experimental results show a strong anisotro py of crystallite growth between [110] and [101] directions. The prefe rential growth at [101] is followed by an increase in the mean pore si ze, reduction of the specific surface area and invariance of total por e volume. This behaviour is typical of grain coalescence sintering. Th e kinetic analysis of experimental results suggests that the crystalli te coalescence at [101] is governed by lattice diffusion. The strong a nisotropy of the growth causes pore-size distribution broadening, hind ering the macroscopic shrinkage of the compact during sintering.