Effects of zircon addition on the crystallization of fused silica - a kinetic study -

Abstract

SiO2-ZrSiO4 powder mixture was prepared from powders of fused silica and zircon with a high-speed stirrer at 2400rpm for 5min. Mixtures were, then, heated at the soaking temperature between 1275°C and 1350°C for different time periods. The fraction of cristobalite precipitated was determined by a quantitative X-ray diffraction (QXRD). It was found that zircon affects the rate of transformation of fused silica to cristobalite. In the initial stage of the heating, the presence of zircon assists the crystallization of fused silica. However, it retards the crystallization as the soaking time is increased. The EDS analysis shows that zirconium diffuses into the surface layer of silica particle to form a solid solution, resulting in the lattice distortion which may generate a compressive stress on the surface layer. From the kinetic analysis, the time exponent, n, in Avrami equation decreases with increasing zircon additions suggesting that the transformation kinetic is controlled by long-range diffusion mechanism from two dimensional plate-like growth to one dimensional needlelike growth.