Chemical variations in barium titanate powders and dispersants

Commercial raw materials for multilayer ceramic capacitors-barium titanate (BT) and ammonium polyacrylate (APA) dispersant-were examined for lot-to-lot variations which cause poor reproducibility in BT slips and in capacitor chips. Two lots of BT supplied by a commercial source were different with respect to surface species examined by Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, electrokinetic sonic amplitude and total carbon analysis. It was found that there was more APA dispersant chemisorption on BT when the BT surface was more hydroxylated and less carbonated. For the dispersant, the two lots differed in pH and ammonium ion content. The amount of APA dispersant adsorbed on BT depended more on the ceramic powder surface species than on the chemical differences in APA lots. The electrokinetic sonic amplitude (ESA) and zeta potentials of the two lots of as-received BT were small but positive. The BT lot with more surface hydroxyls exhibited slightly higher zeta potential values. The BT with more carbonate was more stable in terms of aging rate in water. Aging in water increased the positive zeta potential by increasing \hboxBa(2+) dissolution and adsorption. With the APA dispersant, the BT surface became less positive, but more stable and exhibited an isoelectric point of similar to 10.6. It can be concluded that the dispersion of BT in the as-dispersed pH range is mainly by steric stabilization with little contribution from electrostatic charges.