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Composite ZrO2-SiO2 powders were prepared using a gel route. Morphological and crystallographic features of ZrO 2 particles formed during the heat treatment, and the particle sizes of the composites have been investigated. The following polymorphic changes have been observed during the heat treatment: amorphous -+ metastable-cubic/tetragonal ZrO 2 --~ tetragonal ZrO2 ~ monoclinic ZrO2. SiO2 crystallizes above 1273 K. The martensitic transformation of Zr02 (t -, m) was observed in situ, when exposed to a high-energy electron beam. These results are important in the production of ZrO2-toughened ceramics of controlled microstructure.

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