Gel technology in ceramics

The use of sol-gel techniques to prepare ceramic materials ranks high among those areas in ceramic science and technology which are changing most rapidly and which offer the greatest promise for outstanding improvements in both understanding and applications. This paper reviews the important theoretical considerations, processing techniques and applications related to sol-gel derived ceramics.The gelation behavior of colloidal and polymeric gels, in general, and the influence of such variables as solvent type and concentration, pH, catalyst concentration, temperature, etc. on several oxide systems including silica are considered. The importance of capillary stresses and the various techniques used to minimize them during drying are discussed as are the relevant theories which describe the sintering and firing behavior of the dried gels. To produce ceramics containing more than one oxide, appropriate chemical techniques must be employed to obtain the desired homogeneity. The addition of salts, partial hydrolysis, and alkoxide complexation are among the more widely employed techniques reviewed. A review of current and potential applications of sol-gel derived ceramics, which includes specific examples from the areas of novel glasses, fibers, abrasives, thin films and coatings, is included as well. The paper closes with recommendations and suggestions for future work especially in areas which would benefit from the expertise of physicists and chemists.