The isoelectric points of sapphire crystals and alpha-alumina powder

Abstract

Streaming potential measurements and atomic force microscropy (AFM) were used to determine the zeta potentials, diffuse layer potentials and isoelectric points (ieps) of alpha alumina sapphire single crystals for four different crystallographic orientations: c-plane, 0001; a-plane, 112̄0; m-plane, 101̄0; and r-plane, 11̄02. Both types of measurements indicated that the iep of the sapphire crystals was between about pH 5.0 and 6.0 for all crystals investigated. Unfortunately the techniques utilized could not conclusively differentiate any subtle differences in iep between the four orientations studied. The iep of alpha alumina powder was found to be pH 9.4. The difference in the ieps of the t..