SURFACE CHARGE OF SOL-GEL DERIVED ALUMINAS AS A FUNCTION OF CALCINATION TEMPERATURE

The sol-gel route for preparing alumina is thought to yield a unique molecular structure. Thus the powder characteristics of sol-gel derived aluminas are expected to be different from alumina powders derived by traditional processing methods. In this study wet alumina gels, after the sol-gel reaction was completed, were dried and calcined at 25^°C, 300^°C, 500^°C, 800^°C, 1100^°C, and 1400^°C following the methods of Yoldas and Clark and Lannutti. The initial points of zeta potential reversal (PZR) of the calcined powders determined from electrophoretic mobilities are 9.4, 10.2, 8.6, 10.6, 4.2 and 8.3, respectively for the above calcination series. The PZR of the alumina powders increased with calcination temperature up to 800^°C, with the exception of the alumina calcined at 500^°C. The PZR's of powders calcined between 800-1400^°C decreased. The anomalous PZR of the alumina calcined at 500^°C is due to catalytically formed carboxylates from the residual sec-butano1. The general trend of PZR change for other phases of gel derived alumina was compared with previously reported electrolcinetic behavior of traditional alumina powders and no significant differences were found.