The isoelectric point of BaTiO3

The value of the isoelectric point (IEP) of BaTiO3 is highly significant fo r the development of a fully rational basis for the successful processing o f BaTiO3 powder by aqueous routes. We report here experimental evidence tha t the true IEP value for BaTi03 is in the neutral pH range (6-7). However, Ba2+ ions are also selectively adsorbed at BaTi03 particle surfaces, raisin g the zeta-potential; IEP values greater than pH 7 can occur when the conce ntration of Ba2+ in the aqueous phase is high. Studies of the effects of Ba 2+ and CO32- additions on the zeta-potential of BaTi03 and on the rheology of aqueous suspensions, indicate that the reason for the wide range of zeta -potential and IEP values found for BaTi03 is in large measure the presence of impurity BaCO3 in the BaTi03 powders used. Fully dehydrated BaTi03 powd er has a low IEP value (similar to 4), which slowly rises on ageing in wate r. The IEP appears not to be influenced by Nb2O5 doping at the levels norma lly used. (C) 2000 Elsevier Science Ltd. All rights reserved.