Crystallization and Solubility of Zircon and Phenacite in Certain Molten Salts

Abstract

Single crystals of zircon as large as 0.7 cm and phenacite as large as 1.5 cm were grown from molten alkali metal vanadates and molybdates. The best crystals were obtained by slow cooling melts of Na2O·3MoO3 or Li2O·3MoO3 saturated with zircon or phenacite from 1400° to 900°C at a rate of 2° per hour. Crystals grown on a seed by a thermal gradient process contained inclusions although rates up to 1 mm per day were obtained. Zircon crystals could be doped with Nd3+, Eu3+, Pr2+, Fe3+, Cr3+, and Mn2+. The rare earths fluoresced at their characteristic frequencies but no fluorescence was observed from the transition metal ions. Zircon crystals had the characteristic habit, being bounded by m (110) and p (111) faces. Phenacite had a rhombohe‐dral habit when grown above 1000° and crystallized as hexagonal needles below that temperature. The solubility of zircon in Na2O·3MoO3 obeys the Van't Hoff equation with a heat of solution of 5.5 kcal per mole. The heat of solution of zircon and phenacite increased when V2O5 was substituted for MoO3 in the solvent, increased when NazO was substituted for Li2O, and increased further when K2O was substituted. The solubility was higher in solvents containing V2O5 than in those containing Moo3. Solvent‐solute interactions were strongest when the solvents were strong Lewis acids since zircon and phenacite behave as bases.