Phase Equilibria Studies in the SiO2-K2O-CaO System

Phase equilibria in the SiO2-K2O-CaO system have been experimentally investigated in the SiO2-rich area. High-temperature equilibration, rapid quenching, and electron probe X-ray microanalysis (EPMA) techniques have been used in this study. K2O may vaporize during EPMA measurements causing significant uncertainties. In the present study, optimum EPMA operating conditions have been determined in order to accurately measure K2O concentrations in the quenched samples. The compositions of all phases present in the quenched sample were measured using EPMA with optimum operating parameters. The following primary phase fields were identified in the composition range investigated: SiO2, CaO·SiO2, 2CaO·SiO2, K2O·2CaO·2SiO2, and K2O·6CaO·4SiO2. The isotherms between 1273 K and 1473 K (1000 °C and 1200 °C) in these primary phase fields have been determined. The presence of the compounds K2O·2CaO·2SiO2 and K2O·6CaO·4SiO2 has been confirmed.