Colloidal processing of BaTiO₃ using ammonium polyacrylate as dispersant

The variation of the ζ potential of BaTiO₃ particles in aqueous suspension as a consequence of changing the pH and the concentration of ammonium polyacrylate (NH₄PA) has been studied. An isoelectric point at pH approximately 2.5 was found. The ζ potential decreases upon addition of NH₄PA up to 0.1 g of dispersant/g of powder. Using sedimentation tests, it was found that the stabilization of suspensions is attained at pH greater than or equal to 8 and concentrations greater than or equal to 1.5×10^-3 g of dispersant/g of powder. By rheological measurements, a pseudoplastic behavior and little thixotropy was observed in the suspensions. The maximum solid content attained during this work was 48 vol%. Infrared spectroscopy of the sedimented and dried powder was carried out. It was observed the presence of BaCO₃ and the change of ionization of the NH₄PA molecules when the pH changes. High green density values (up to approximately 60% of the theoretical density) in BaTiO₃ cakes were achieved at pH of 11.3, at 2.5×10^-3 g of dispersant/g of powder and with a solid content between 40 and 48 vol%.