Phase Relations in the KOH–TiO2–SiO2–H2O System at 500°C and 0.1 GPa

The compounds crystallizing in the system KOH–TiO2(rutile)–SiO2–H2O at 500°C, 0.1 GPa, and different TiO2, SiO2, and KOH concentrations are K2TiSi6O15 (Ti davainite structure), K2TiSi3O9 (Zr wadeite structure), and K2Ti6O13 (Ti jeppeite structure). The matrix-assembly model is used to examine the formation of the K2TiSi6O15 structure (sp. gr. P\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document} $$\overline 1 $$ \end{document}) from subpolyhedral structural units. A centrosymmetric cyclic 12-polyhedron cluster of composition K2M2T10 is identified, in which the K atoms lie in center positions above and below the plane of the MT ring. The precursor cluster K2M2T10 is identical in structure to the Cs2M2T10 cluster in Cs2TiSi6O15, a titanosilicate which has a topologically different MT framework. The mechanisms of the assembly of the three-dimensional MT frameworks in these titanosilicates differ at the level of primary MT chains: the condensation of the clusters in K2TiSi6O15 involves five common corners, while that in Cs2TiSi6O15 involves only three corners.