Abstract
The value of the isoelectric point (IEP) of BaTiO 3 is highly significant for the development of a fully rational basis for the successful processing of BaTiO 3 powder by aqueous routes. We report here experimental evidence that the true IEP value for BaTiO 3 is in the neutral pH range (6–7). However, Ba 2+ ions are also selectively adsorbed at BaTiO 3 particle surfaces, raising the ζ-potential; IEP values greater than pH 7 can occur when the concentration of Ba 2+ in the aqueous phase is high. Studies of the effects of Ba 2+ and CO 3 2− additions on the ζ-potential of BaTiO 3 and on the rheology of aqueous suspensions, indicate that the reason for the wide range of ζ-potential and IEP values found for BaTiO 3 is in large measure the presence of impurity BaCO 3 in the BaTiO 3 powders used. Fully dehydrated BaTiO 3 powder has a low IEP value (∼4), which slowly rises on ageing in water. The IEP appears not to be influenced by Nb 2O 5 doping at the levels normally used.
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