Ceramics-Silikáty 42, (3) 99 - 104 (1998)

A concept of the excess Gibbs energy is adopted for calculation of the Gibbs free energy of oxide compounds. A suitable equation for calculation of the excess Gibbs free energy (as a function of temperature and composition) was suggested. The temperature influence was taken into account through two temperature dependent parameters (A(T) and B(T)) while the composition was represented by total number of constitutive oxides (n_tot). The parameters were defined as adequate temperature functions, for the CaO-Al₂O₃ and CaO-SiO₂ systems. This was accomplished by processing the data of following compounds: CaO×Al₂O₃, CaO×2Al₂O₃, 3CaO×Al₂O₃, CaO×6Al₂O₃, CaO×SiO₂, 2CaO×SiO₂, 3CaO×SiO₂ and 3CaO×2SiO₂. Application of the suggested method to the chosen systems enabled estimation of Gibbs free energy values with relative errors less than 1 % (absolute errors between 0.03 and 30 kJ/mol).