EFFECT OF HYDROLYSIS TIME AND TYPE OF CATALYST ON THE STABILITY OF TETRAGONAL ZIRCONIA SILICA COMPOSITES SYNTHESIZED FROM ALKOXIDES

ZrO2-transformation-toughened glass-ceramics have been prepared by the sol-gel process from either colloidal gels (CG) or polymeric gels fro m alkoxides (PG), using, in the latest method, a different catalyst (a cid, basic and without catalyst), and different compositions in the Zr O2.SiO2 system (free ZrO2 included). The different methods of synthesi s of tetragonal zirconia in SiO2 matrix were compared in order to obta in thermal stability, and a high amount of stabilized tetragonal zirco nia. The effect of catalyst, hydrolysis time, chemical composition, cr itical particle size in ZrO2(t)-->ZrO2(m) transformation, the doping w ith vanadium on the ZrO2(t) stability in SiO2 matrix and Vickers micro hardness of samples have also been studied.