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

Suspension characteristics for two types (HCV and HCP) of hexagonal boron n itride (h-BN) powder have been examined and correlated to the amount of bor ic oxide present (B2O3) on the BN surface. The effects of B2O3 on the suspe nsion 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 poo r suspension quality of HCV-BN powders is linked to the increased presence of B2O3 On the particle surface. Because of its weak ionization characteris tics, B2O3 acts to prevent stable suspension formation by decreasing the do uble 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 vis cosity suspensions. In contrast, HCP-BN having less B2O3 on the powder surf ace, exhibits higher zeta-potentials and increased stability against agglom eration. Therefore, HCP-BN forms suspensions of single, unagglomerated part icles which are less viscous, settle at a slower rate and are more suitable for slip casting operations. (C) 1999 Kluwer Academic Publishers.