Hydrothermal Synthesis of Some Varieties of Zircon

Abstract

Some varieties of zircon which contain yttrium, niobium, and phosphorus in solid solution have been synthesized at temperatures 500–550 °C and under pressures 700–1000 kg/cm2. In zircon containing yttrium, the unit cell constants a and c increase with increase in yttrium content up to 70 mol%. From IR and TGA studies, a valence compensation accompanying the substitution of yttrium is assumed to be effected by a concomitant substitution of OH for O sites, and the variety is represented by a formula (Zr,Y)Si(O,OH)4. On the other hand, the substitution of Nb5+ for Zr4+ is followed by a decrease in the cell constants. Zircon phase did not form from starting materials with more than 20 mol% of niobium content. From the syntheses of zircon containing both yttrium and niobium, the formula (Zr,Y,Nb) Si(O,OH)4 is found to be appropriate for naegite. An attempt was made to synthesize some solid solutions between zircon and xenotime. The unit cell constant c of the products is found to decrease with the substitution of PO4 for SiO4.