Interaction forces between alpha-alumina fibres in aqueous electrolyte measured with an atomic force microscope

The surface charging properties of polycrystalline alpha-alumina fibres in aqueous electrolyte solutions have been investigated by direct force and st reaming potential measurements. The presence of both Al and Si on the surfa ce of the fibres resulted in a chemically heterogeneous surface. The hetero geneous distribution of Si resulted in large attractive forces between the fibres at moderate to low pH values and a pzc/iep at a pH value of approxim ately 5.5. The origin of this force was electrostatic in nature as the forc e profiles were well described by the DLVO theory of colloid stability. The agreement between the direct force and streaming potential measurements wa s good both in terms of the magnitude of the potentials and the position of the pzc/iep. By acid washing the fibres the chemical heterogeneity of the surface was reduced and the attractive force profiles at lower pH values we re not observed. Instead repulsive forces were observed which were well des cribed by DLVO theory at all separation distances greater than 8 nm. At sma ller separation distances an additional repulsive force was measured which was attributed to the presence of a Al(OH)(3) like layer on the surface of the alumina. The acid washing treatment also resulted in a shift in the pH at which the pzc/iep occurred to a value of 6.5, presumably due to a lower surface silica concentration. (C) 1999 Elsevier Science B.V. All rights res erved.