Ceramics-Silikáty 38, (2) 69 - 74 (1994)

An original algorithm and a FORTRAN program developed to calculate phase diagrams and/or thermodynamic characteristics in simple eutectic multicomponent systems yet not experimentally measured, was extended to the systems that may contain incongruently melting compounds. Additionally, enthalpy of fusion as a function of temperature was taken into account. Complete statistical analysis of results was also proposed. The method was applied to the binary system CaSiO₃.Ca₂SiO₄ containing the compound rankinite (Ca₃Si₂O₇) which melts incongruently at the temperature 1464 °C. The enthalpy of this decomposition was estimated to be 72 kJ mol⁻¹. Other unknown parameters, i.e., the enthalpy and the heat capacity of fusion of dicalciumsilicate and hypothetical temperature of fusion of rankinite were calculated by the least squares method. The obtained values are 81.6 ± 1.2 kJmol⁻¹, 90 ± 3 Jmol⁻¹K⁻¹ and 1497 ± 11 °C, respectively.