Formation Free Energies of Solid Solution between Tri‐Calcium Phosphate and Di‐Calcium Silicate

In order to determine the free energy changes for the reaction$$3\left\langle {{\rm Ca}_3 {\rm SiO}_3 } \right\rangle + {{4{\rm y} - 3} \over {1 - {\rm y}}}\left\langle {{\rm Ca}_2 {\rm SiO}_4 } \right\rangle + \{ {\rm P}_2 {\rm O}_5 \} = {1 \over {1 - {\rm y}}}\left\langle {{\rm Ca}_{(3 - {\rm y})} {\rm Si}_{\rm y} {\rm P}_{(2 - 2{\rm y})} {\rm O}_{(8 - 4{\rm y})} } \right\rangle$$molten copper containing phosphorus was brought into equilibrium with mixtures of tri‐calcium silicate + di‐calcium silicate + solid solution between tri‐calcium phosphate and di‐calcium silicate in a stream of Ar + H 2  + H 2 O gas mixture at temperatures between 1548 and 1598 K, and the results are expressed as$$\Delta G^\circ /{\rm J} \cdot {\rm mol}^{ - 1} = RT\,\ln \,a_{P_{\rm 2} O_{\rm 5} } = - 1,106,000 + 194.7\,(T/{\rm K}) \pm 20,000$$