CaO-SiO2 assessment using 3rd generation CALPHAD models

Abstract

This contribution reviews current best practices for thermodynamic model fitting in oxide systems and applies it to the most important binary-oxide system for cement clinker, CaO-SiO2. The thermodynamic properties of all solid phases are regressed simultaneously to maximize accuracy and a new Akaike-Information-Criterion led approach is used to model the liquid phase which results in a simpler model than previously published without sacrificing accuracy. Simplicity is vital as many higher-order systems will be built on this system to cover the full cement system. New heat capacity measurements for C3S2 and the C2S polymorphs as well as DFT calculations are presented and included in the new assessment. The assessment also distinguishes between the polymorphs of alite (C3S) even though data is limited, as this will also be important to capture in higher-order systems. The oxide melt is modelled using an associate model and the full phase diagram is computed which compares favourably with all available experimental data.