Standard Free Energies of Formation of CaO-Al₂O₃ Intermediate Compounds by Means of EMF Measurement of Galvanic Cells

Abstract

The standard free energies of formation of CaO-Al₂O₃ intermediate compounds formed of CaO and Al₂O₃ have been measured by means of Galvanic cells using 4CaO·P₂O₅ solid electrolyte. The following results were obtained ;
CaO·6Al₂O₃ : ΔG°f =- 16380-37.58 T (± 1 730) (1 3731 873K)
CaO·2Al₂O₃ :ΔG°f =- 15 650- 25.82 T (± 900) (1 3731 873K)
CaO·Al₂O₃ :ΔG°f = - 17 910-17.38 T (± 790) (1 3731 843K)
3CaO·Al₂O₃ : ΔG°f = - 11 790-28.27 T (± 1 190) (1 3731 635K)
The unit is J/mol. The activity of CaO in liquid slag in equibrium with solid CaO·Al₂O₃ was 0.248 at 1 773K and that in equibrium with solid 3CaO·Al₂O₃ was 0.619. The standard state of CaO is pure solid.