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

Abstract

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 (ζ) 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 ζ-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.