SYNTHESES OF SUBMICRON TIO2 POWDERS IN VAPOR, LIQUID AND SUPERCRITICAL PHASES, A COMPARATIVE-STUDY

Submicron TiO2 powders have been prepared from titanium isopropoxide by the sol-gel process and thermal decomposition of the pure vapor phase or dissolved in supercritical ethanol. The microstructure and phase transformations in the obtained solids are compared. Differences have been observed in particle size and agglomeration state as well as on the crystallinity of just-prepared powders and its evolution under thermal treatment. The new supercritical route allows to obtain narrow sized, submicron particles (20-60 nm), partly crystallized and softly associated into spherical agglomerates (0.5-2 mum). Such powders are expected to have as low a sintering temperature as sol-gel samples subsequently treated in an autoclave. The supercritical synthesis then appears as a simpler method, avoiding the various powder recovery steps of wet chemistry processes and easily adaptable to continuous production.