The stability of tobermorite in the system CaO-SiO₂-H₂O at elevated temperatures and pressures

Abstract

Summary Hydrothermal studies in the silica-rich region of the CaO-SiO 2 -H 2 O system have given information on the stability field of tobermorite. At saturated steam pressures tobermorite is unstable relative to xonotlite (C 6 S 6 H) above 140 °C but between 10 000 and 40 000 lb/in. 2 (69 and 276 N/mm 2 ), the decomposition temperature is raised to 285±5 °C. Tobermorite is stable at all compositions between C/S = 0·67 and 1·0 up to this temperature and has a formula close to C 5 S 6 H 5 . Variable compositions reported earlier are thought to be mixtures rather than lime-rich or silica-rich tobermorites. Data have also been collected on the equilibrium assemblages below C/S = 0·67 and between C/S = 1·0 and 1·5 involving truscottite, gyrolite, xonotlite, foshagite, and hillebrandite.