Toughened glass-ceramics in the ZrO2-Al2O3-SiO2 system prepared by the sol-gel process
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Monolithic glass-ceramics containing Al2O3 or TiO2 were prepared in the ZrO2-SiO2 system by the sol-gel process from metal alkoxides. Tetragonal ZrO2 was precipitated by heat treatment at 900–1200 °C and its crystal growth was increased by adding TiO2 or Al2O3. Further heating at higher temperature resulted in the precipitation of zircon and monoclinic ZrO2 which was transformed from tetragonal ZrO2. The addition of Al2O3 had less effect on both the tetragonal-to-monoclinic ZrO2 transformation and the precipitation of zircon. The fracture toughness increased as the size of tetragonal ZrO2 particles increased and then decreased with the appearance of monoclinic ZrO2 or zircon. The fracture toughness of the glass-ceramics was measured in the glass-forming regions of the ZrO2-Al2O3-SiO2 system. The fracture toughness was sensitively dependent on both Al2O3 and ZrO2 content, of which the highest value achieved was ∼ 9 MPa m1/2 for the 50ZrO2·10Al2O3·40SiO2 composition.
KeywordsPolymer Precipitation TiO2 Zircon Heat Treatment
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