Critical thermodynamic evaluation and optimization of the CaO-MnO-SiO2 and CaO-MnO-Al2O3 systems

Abstract

A complete review, critical evaluation, and thermodynamic optimization of phase equilibrium and thermodynamic properties of the CaO-MnO-SiO2 and CaO-MnO-Al2O3 systems at 1 bar pressure are presented. The molten oxide phase was described by the Modified Quasichemical Model, the Gibbs energy of the olivine solid solution was modeled with the Compound Energy Formalism, and the wollastonite s.s., rhodonite s.s., and alpha- and alpha'-Ca2SiO4 solutions were modeled by polynomial expansions of the excess Gibbs energy. Sets of optimized model parameters for all phases were obtained which reproduce all available reliable thermodynamic and phase equilibrium data within experimental error limits from 25degreesC to above the liquidus temperatures over the entire ranges of composition. The liquidus surface of the CaO-MnO-Al2O3 system, which has not been measured, has been predicted. Complex phase relationships in these systems have been elucidated, and discrepancies among the data have been resolved. Phase equilibria between liquid slag and manganese alloys have been calculated. The database of model parameters can be used along with software for Gibbs energy minimization in order to calculate any phase diagram section or thermodynamic property.