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Crystallization and Phase Transformation of ZrO2-SiO2 Gels
Published online by Cambridge University Press: 28 February 2011
Abstract
Pure SiO2, ZrO2 and SiO2−ZrO2 gels have been prepared by hydrolysis and gelation of tetraethylorthosilicate (TEOS) and zirconium acetate solution. The crystallization and phase transformation of SiO2 and ZrO2 in these gels have been followed up to 1450°C using differential thermal analysis (DTA), thermal gravimetric analysis (TGA) and X-ray diffraction analysis (XRD). The crystallization and phase transformation behavior of SiO2 or ZrO2 is quite different in different gel systems. It was found that in pure SiO2 gel, the cristobalite phase was precipitated out at about 1000°C. In the pure ZrO2 system, tetragonal (t−) phase zirconia was crystallized at about 430°C, t-ZrO2 crystals grew three dimensionally and the activation energy for growth was calculated as about 365 kJmol−1. But in the SiO2-ZrO2 system, the presence of ZrO2 suppressed the crystallization of SiO2 , and SiO2 increased the initial crystallization temperature and the stability of t-ZrO2.
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