FORMATION OF POLYCRYSTALLINE ZIRCON (ZRSIO4) FROM AMORPHOUS SILICA AND AMORPHOUS ZIRCONIA

Formation process of zircon (ZrSiO4) from an equimolar mixture of amorphous silica and amorphous zirconia has been studied mainly by means of a high-temperature X-ray diffraction technique. It is shown that zircon is formed at temperatures as low as 1200-degrees-C, predominantly from amorphous silica and tetragonal zirconia. Formation of zircon dominates over the transformation of amorphous silica to cristobalite. It is inferred from the crystallite-size analysis that tetragonal-zirconia crystallites are Converted to ZrSiO4 crystallites upon saturation of Si species in tetragonal-zirconia crystallites. Tetragonal --> monoclinic transformation of unreacted zirconia in the reaction mixture is shown to occur during the quenching process.