A new phase diagram for the CaOAl2O3SiO2H2O hydroceramic system at 200°C

Abstract A new phase diagram is reported for the CaO Al 2 O 3 SiO 2 H 2 O (CASH) system at 200 °C. This system is rare in nature but has applications in cementing geothermal and deep oil wells. The phase diagram was constructed by synthesising a range of hydroceramics with CASH assemblages from oilwell cement, silica flour (quartz) and alumina (corundum). A hydroceramic is defined as any ceramic material incorporating water as H 2 O or OH. At 200 °C, gyrolite, hillebrandite, jaffeite, portlandite, quartz, 11 A tobermorite, xonotlite, hibschite and katoite were observed as product phases. The mineral assemblages produced the following three-phase triangles in the CaO Al 2 O 3 SiO 2 diagram: Gyr + Qtz + Xon; Crn + Tob + Xon; Crn + Hib + Xon; Crn + Hib + Jaf; Crn + Jaf + Kat; Hib + Jaf + Por; Hib + Jaf + Xon; and two reactions are found to be in progress at 200 °C. When alumina is present in the reaction mixture, the thermal stability of tobermorite is extended to higher temperature, and the crystallinity of tobermorite and xonotlite enhanced.