Critical Evaluation of Alumino-silicate Systems

Thermodynamic knowledge of alumino-silicate systems §is useful in steel and ceramic industries and for §understanding geochemical processes. In this work §the CALPHAD approach is applied to the thermodynamic §modelling and assessments of the CaO-Al2O3-SiO2, MgO-§Al2O3-SiO2 and Y2O3-Al2O3-SiO2 systems and their §subsystems. The compound energy formalism is used §for all the solution phases including mullite, YAM, §spinel and halite. In particular, the ionic two sub-§lattice model is applied to the liquid phase. Based §on recent experimental investigations and §theoretical studies a new species AlO2-1 is §introduced to model liquid Al2O3. Thus, the liquid §model corresponding for a ternary Al2O3-SiO2-M2Om §system has the formula (Al+3,M+m)P (AlO2-1,O-2, SiO4-§4,SiO20)Q, where M+m stands for Ca+2, Mg+2 or Y+3. §This model overcomes the long-existing difficulty of §suppressing the liquid miscibility gap in the §ternary systems originating from the Al2O3-free side §during the assessments. All the available phase §diagram and thermochemical data are critically §evaluated and finally a self-consistent §thermodynamic dataset is achieved.