SYNTHESIS OF BATIO3 AND ZNO VARISTOR PRECURSOR POWDERS BY REACTION SPRAY-PYROLYSIS

High-purity, fine, homogeneous ceramic powders with complex composition which are commonly used for electronic materials (ZnO-based non-linear resistors-varistors and piezoelectric BaTiO3) were synthesized by the reaction spray process. The particles obtained were hollow spherical shells and shell fragments with average particle size ranging from 3 to 4 mum, representing the aggregates of small individual crystallites each less than 1 mum. Owing to the extremely high heating rate of a salt/droplet particle, mixing on an atomic or nanometre scale in the feeding solution should persist in the resulting powder. It was shown that the chlorides BaCl2 and TiCl4 are suitable precursors for BaTiO3 ceramics. Varistor ceramics with a non-linearity coefficient alpha = 30 and breakdown voltage K = 700 V mm-1 were produced by sintering the reaction spray-derived multicomponent ZnO-based powder. The compositional homogeneity of the resulting powders and the phase content were determined by the processing and solution parameters which affect the dehydration, precipitation and decomposition processes.