*Member, American Ceramic Society.
Charging Behavior at the Alumina–Water Interface and Implications for Ceramic Processing
Article first published online: 9 OCT 2007
Journal of the American Ceramic Society
Volume 90, Issue 11, pages 3373–3388, November 2007
How to Cite
Franks, G. V. and Gan, Y. (2007), Charging Behavior at the Alumina–Water Interface and Implications for Ceramic Processing. Journal of the American Ceramic Society, 90: 3373–3388. doi: 10.1111/j.1551-2916.2007.02013.x
D. Green—contributing editor
Financial support for our research into alumina surfaces has been provided over a number of years from the Australian Research Council, the University of Melbourne and the University Newcastle.
- Issue published online: 9 OCT 2007
- Article first published online: 9 OCT 2007
- Manuscript No. 23068. Received April 10, 2007; approved July 26, 2007.
The interaction of water and the alumina surface is comprehensively reviewed. Water can be incorporated in the alumina crystal structure resulting in the formation of aluminum hydroxides such as gibbsite. Alumina dissolves into water to an extent that depends primarily upon the solution pH and temperature. The soluble Al (III)aq species (hydrolysis products) likewise depend upon the solution pH, temperature, aluminum, and other salt concentrations. The development of charge on the surface of alumina is controlled by amphoteric surface ionization reactions. The charging behavior of both alumina powders and single crystal faces is compared. The differences can be explained by the reactivities of different types of surface hydroxyl groups. The substantial difference in surface charging behavior of single crystal sapphire and alumina powders indicates that experiments and modeling conducted on single crystals is of limited use in predicting suspension behavior. The atomic scale structure of the hydroxylated sapphire (0001) basal plane is nearly identical to the gibbsite (001) basal plane. The observed surface structures are consistent with the charging behavior of the surfaces. The role of surface charge on the adsorption of processing additives is briefly discussed. How surface charge and processing additives at the alumina aqueous solution interface influence surface forces between particles is reviewed. The influence of these forces on suspension properties such as rheological behavior is outlined. The importance of controlling these behaviors to improve colloidal ceramic powder processing is stressed.