Thermodynamic properties of ternesite (Ca5(SiO4)2SO4) from 0 K up to clinkering temperatures

Ternesite (Ca 5 (SiO 4 ) 2 SO 4 ) is a cementitious phase that can be found in the production of calcium sulfoaluminate (CSA) based cements and other alternative binders. Ternesite has received interest due to its potential hydraulic reactivity (under certain conditions) whilst having a low temperature of formation. Despite this, the ternesite phase is not thermodynamically well understood, reducing the ability to accurately model its formation, stability and phase co-existence in clinker. In this work, pure ternesite was synthesised and the high temperature heat content (874–1174 K) and low temperature heat capacity (2−302 K ) was measured using drop calorimetry and PPMS respectively. These data were then combined with enthalpy of formation results from DFT and previous experiments to model the thermodynamics properties of ternesite using the 3rd generation CALPHAD function. This allows for a single function to describe the thermodynamic properties of ternesite for use in extending existing thermodynamic databases as part of predictive calculations at a temperature range from 0 K to above the clinkering temperature.