Phase relations in the CaO-SiO2-H2O system to 200°C at saturated steam pressure

Phase relations in the title system were studied using crystalline and amorphous precursors. These were treated in sealed steel alloy autoclaves for periods ranging up to 12 months. Many of the synthetic precursors crystallised to give high purity, single-phase preparations. Although the CaO - SiO2 - H2O system is marked by metastable phase formation, it is demonstrated that a number of reactions important to establish the low-temperature phase relationships can be shown to occur reversibly and therefore define the phase equilibrium. New stability data are presented for hillebrandite, afwillite, xonotlite, tobermorite and jennite. Synthetic jennite is shown to have a Ca/Si atomic ratio similar to 1.45, rather less than the reported 1.5 ratio. A phase diagram revised in light of new knowledge is presented. (C) 2003 Elsevier Ltd. All rights reserved.