Chemistry of preparation of ceramic powders by sol-gel techniques

Abstract

The sol-gel technique is a unique method for tailoring ceramic powders if the different reaction parameters can be controlled with respect to the powder properties. Reaction control can be achieved by control of hydrolysis and condensation, solvent, temperature, catalyst, additives and complex formers. Especially the use of complex formers have proved to be a successful mean with respect to the control of the gel structure, the generation of monosized particles and even the control of particle size and distribution. Another mean for controlling rates is the homogeneous generation of water for condensation within a reacting system by a chemical reaction; e.g. by ester formation. Thus, differences in reaction rates in multicomponent systems can be equilibrized. New synthesis routes, the characterization and the sintering behavior of Al2O3, ZrO2, mullite, cordierite, and BaTiO3 powders are described, especially with respect to the influencing chemical parameters, and the resultsare discussed. With Al2O3, complex formers lead to super amorphous powders which do not undergo crystallization. No boehmite or bayerite phases have been observed. In the case of mullite or cordierite acetyl acetonate or acetic acid ester complexed alumina leads to a better crystallization behavior of the powders. The results show, that proper use of chemistry allows a wide variation of powder properties.