Suspension properties of hexagonal BN powders: effect of pH and oxygen content

Suspension characteristics for two types (HCV and HCP) of hexagonal boron nitride (h-BN) powder have been examined and correlated to the amount of boric oxide present (B2O3) on the BN surface. The effects of B2O3 on the suspension behavior of HCV-BN and HCP-BN were determined by measuring the zeta (zeta) potential and viscosity as a function of pH. Results indicate the poor suspension quality of HCV-BN powders is linked to the increased presence of B2O3 On the particle surface. Because of its weak ionization characteristics, B2O3 acts to prevent stable suspension formation by decreasing the double layer length, thereby lowering the barrier to agglomeration. Hence, as the amount of B2O3 increases on the HCV-BN powder surfaces, the stability decreases and the particles agglomerate, rapidly settling out of higher viscosity suspensions. In contrast, HCP-BN having less B2O3 on the powder surface, exhibits higher zeta-potentials and increased stability against agglomeration. Therefore, HCP-BN forms suspensions of single, unagglomerated particles which are less viscous, settle at a slower rate and are more suitable for slip casting operations. (C) 1999 Kluwer Academic Publishers.