Hydrothermal preparation of a gehlenite hydrate

Abstract

Hydrothermal treatment of synthetic gehlenite (2CaO ? AI2O3 ? SiO2) or of various mixtures of oxides, hydrates, etc., approximating the composition of gehlenite, at 260 to 6500 ?C, produced a hitherto unreported compound having the composition 2CaO ? AI2O3 ? SiO2 ? H2O. Other phases, usually hydrogarnet, were always present in small amounts. A natural gehlenite containing Fe2O3 and MgO was partly converted to the same hydrate at 450 ?C. The compound 2CaO ? AI2O3 ? SiO2 ? 8H2O was converted to a hydrogarnet at 250 ?C, but formed 2CaO ? AI2O3 ? SiO2 ? H2O at 350 ?C. The new compound has a body-centered cubic structure, with a0 = 8.83 ?. The index of refraction is 1.628. An x-ray diffraction pattern is given, and some similarities between CaO ? Al2O3 ? SiO2 ? H2O and the ternary compound 4CaO ? 3AI2O3- ? 3H2O are pointed out.