Calculation of ternary, quaternary, and higher-order phase diagrams from binary diagrams and binary thermodynamic data

Abstract

We evaluated the binary phase diagrams making up the quaternary diagram CaO-SiO2-MgO-A12O3. First we calculated the glass transition temperatures of the four-oxide system. We used our models both for the interaction parameters in the liquid phase and for the Gibbs energy of fusion as a function of temperature. In the CaO-SiO2 binary system, the compound Ca3SiO5 is quite stable. One approach to achieving a thermodynamic description of the system added, in addition to the repulsive term close to SiO2, a repulsive interaction term close to CaO to describe the miscibility gap and an attractive term to describe the very stable Ca2SiO4 compound. Another approach was to split the CaO-SiO2 system into two subsystems, CaO-Ca2SiO4 and Ca2SiO4-SiO2. The activities of CaO and SiO2 in the liquid calculated at 1873 K do not differ significantly from each other, nor from the method when only two interaction parameters, obtained from the miscibility gap were used. In the other five binaries, no special problems were found, except that the large number of phase diagrams generally do not agree with each other.