RATE-CONTROLLED SYNTHESIS AND SINTERING OF NANOCRYSTALLINE BARIUM-TITANATE POWDER

The densification and grain size during sintering as well as particle size,of the barium titanate powder during Pechini decomposition-synthe sis depends on the heating rate and this dependence originates from th e kinetic competition between elementary transformation mechanisms, in herent in the two processes. The given competition is the main reason for development of the optimum mode of the mentioned thermal activated processes. As developed at the NCSU (USA) the Rate-Controlled Sinteri ng (RCS) is known to allow the obtaining of dense and finegrained cera mics with improved properties. As developed at the IPMS (Ukraine) the Rate-Controlled Synthesis is directed to prepare nanocrystalline unagg lomerated ceramic powders suitable for RCS. The extreme behavior of th e BaTiO3 particle size as a function of heating rate is established an d the optimal temperature-time path is calculated and verified to obta in the best powder of 20-25 nm particles. The change in microstructure and phase composition with heating rate is considered in details. The advantages of the RCS to achieve density of 99.9% and grain size arou nd 100-150 nm are presented in comparison with the linear heating rate regime. (C)1998 Acta Metallurgica Inc.