MORPHOLOGICAL EVOLUTION OF ZRO2-SIO2 COMPOSITE GEL AND STABILITY OF TETRAGONAL ZRO2

Composite ZrO2-SiO2 gels were prepared using fumed silica and ZrOCl2 s olution as starting materials. Morphological evolution of ZrO2 particl es formed during heat treatment, and the particle sizes of the composi tes were investigated by transmission electron microscopy. The morphol ogy of the ZrO2 particles experiences several changes during heat trea tment, i.e. the initially loose sponge-like body changes to dense spon ge-like agglomerates, then to spherical particles which are embedded i n the silica matrix, and finally to larger spherical particles. The st ability of tetragonal zirconia in the gels is discussed in the light o f the particle-size effect. The martensitic transformation of ZrO2 (to the monoclinic phase) was found to occur in situ, when irradiated by a high-energy electron beam.