Thermodynamic descriptions of the CaO–Al 2 O 3 and CaO–Al 2 O 3 –SiO 2 systems over the whole composition and temperature ranges

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Abstract
The CaO–Al 2 O 3 –SiO 2 system is a fundamental system in aluminosilicate materials, and its thermodynamic description provides key information for ceramic design, cement production, slag tapping, and geological prediction. However, the existing thermodynamic calculations for the CaO–Al 2 O 3 system show inaccurate heats of formation for the compounds and consequently a decomposition of the CA 2 (CaO⋅2Al 2 O 3 ) phase at a low temperature. Besides, the solid solutions in anorthite and cristobalite have never been considered in the previous thermodynamic assessments for the CaO–Al 2 O 3 –SiO 2 system. Therefore, thermodynamic reassessments of the CaO–Al 2 O 3 and CaO–Al 2 O 3 –SiO 2 systems are carried out in the present work using the CALculation of PHAse Diagram method, considering the solid solution in anorthite and cristobalite for the first time. The anorthite and cristobalite phases are modeled based on the individual mechanism of solid solution, with the anorthite described by (Ca +2 , Va ) 1 (Al +3 , Si +4 ) 2 (Si +4 ) 2 (O −2 ) 8 and the cristobalite described by ( Va , Ca +2 ) 1 (Si +4 , Al +3 ) 2 (O −2 ) 4 . The present assessment solves the above issues and provides consistent thermodynamic descriptions for the liquid and solid phases. Based on the established thermodynamic database, a Scheil solidification simulation is carried out for a cement clinker and the variations of mass fractions of the phases as well as the composition of liquid during Scheil cooling are calculated. The present work guides the design of relevant materials and lays an essential foundation for the establishment of the thermodynamic database of multicomponent aluminosilicate materials.
Funding Information
  • National Key Research and Development Program of China (2019YFC1904901)

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