Possibility to control the microstructure of ceramic materials via gel

In many cases the production of advanced ceramics is still limited in reliability and reproducibility of material performances by inadequate technologies. Above all this is due to the fact that a real control of all the microstructure parameters (chemical composition, phases distribution and composition, surface compositional gradients, grain size, etc.), on which the properties of the ceramic mainly depend, has not been yet achieved. Till now the approach to the ceramic material has been almost exclusively physical, whereas a real progress can results from microstructure control, above all achieved through the control of the raw material, that is the preparation of a ceramic powder of defined and controlled chemistry and geometry. The sol-gel processes, object of intense study during the last 25 years, seem to give very interesting prospects. In a gel process, if the gel is produced by hydrolysis of salts or alkoxides, it is possible to 'plan' the ceramic powder and consequently to achieve a ceramic of predetermined characteristics. Obviously many parameters control the microstructure of a powder prepared via gel; in this paper some of these parameters (precipitation pH, hydrolysis temperature, gel aging, gel washing, dehydration conditions) have been investigated and their effects on the microstructural characteristics of the powder and the ceramic have been shown.