Zircon is usually used as a main additive to silica-based ceramic core materials in precise investment casting in order to improve their high temperature properties. But there is still a disagreement in its effect on crystallization behavior of fused silica. In this study, cristobalite crystallization of fused silica in three silica-based core materials containing 10, 30 and 50 wt% zircon respectively were investigated through X-ray diffraction (XRD) and scanning electron microscopy equipped with energy dispersive spectrometer (SEM/EDS). Results showed that zircon addition had neglected effect on cristobalite crystallization during sintering at 1180 oC, 1200 oC, and 1220 oC, but could decrease crystallization during simulated casting process at 1500 oC. It was suggested that diffusion of zirconium atoms played a crucial role in this suppressing behavior of zircon on the cristobalite crystallization. During cooling from 1500 oC, cristobalite transformation from β to α caused microcracks in these samples that containing 10% or 30% zircon. But when zircon content increased to 50%, crack was prevented. Less phase transformation of fused silica→cristobalite and enhanced strength by zircon was supposed to be the reason that was responsible for prevented cracks.

Keywords: Silica-based ceramic cores, Zircon, Cristobalite transformation