Polymeric stabilisation of aqueous suspensions of barium titanate. Part II: Effect of polyelectrolyte concentration

This article is the continuation of a study on the optimum conditions for deflocculation of aqueous suspensions of barium titanate powders with anionic and cationic polyelectrolytes. The effect of polyelectrolyte concentration on the stability of the suspension is described here, and stability maps are constructed at different pH values and polymer concentration. Defloculation is possible with 0.1 wt% of the anionic ammonium polyacrylate used (Dispex A40), at alkalyne pH. Maximum flocculation is obtained with this 0.5 wt% of this polymer at pH 4. At pH 6, stabilisation is possible with 0.4 wt% of this polymer. The use of the cationic quaternary alkylammonium polymers DP6 (Mw 150 000) and DPX-1 (Mw 7660) is not advantageous for the stabilisation of the suspension at any pH. At alkalyne pH, a concentration of 1 wt% of these polymers is able to decrease the yield stress and viscosity values, possibly through an electric effect of the adsorbed polymers. At pH 4, any concentration of these cationic polymers results in real yield stress values slightly higher than those corresponding to the suspension without polyelectrolytes, and green density values by slip casting are still low. On the other hand, green densities of 56.5% were obtained with the anionic polyelectrolyte at pH>9.