The isoelectric point of BaTiO3

The value of the isoelectric point (IEP) of BaTiO3 is highly significant for the development of a fully rational basis for the successful processing of BaTiO3 powder by aqueous routes. We report here experimental evidence that the true IEP value for BaTiO3 is in the neutral pH range (6–7). However, Ba2+ ions are also selectively adsorbed at BaTiO3 particle surfaces, raising the ζ-potential; IEP values greater than pH 7 can occur when the concentration of Ba2+ in the aqueous phase is high. Studies of the effects of Ba2+ and CO32− additions on the ζ-potential of BaTiO3 and on the rheology of aqueous suspensions, indicate that the reason for the wide range of ζ-potential and IEP values found for BaTiO3 is in large measure the presence of impurity BaCO3 in the BaTiO3 powders used. Fully dehydrated BaTiO3 powder has a low IEP value (∼4), which slowly rises on ageing in water. The IEP appears not to be influenced by Nb2O5 doping at the levels normally used.