Ceramics-Silikáty 22, (3) 193 - 297 (1978)

The paper is concerned with the calculation of mixing entropy, Gibbs energy, activities and activity coefficients of components in the melt region of the system akermanite (Ca₂MgSi₂O₇) – diopside (CaMgSi₂O₆). The calculations are based on the determination of partial molar mixing entropy of the components ΔS_mix,l using experimentally determined relative enthalpies H_rel in the temperature range of 1700 K to 1873 K [1] and the phase diagram [2] of the system in question. The calculated concentration dependences of mixing entropy ΔS_mix and those of additional entropy ΔS^E_mix are asymmetrical, thus exhibiting positive values with solutions containing for the most part C₂MS₂ and negative values with solutions comprising mostly CMS₂. The additional Gibbs energy ΔG^E_mix is positive at all x, showing a maximum at x = 0,6. The activity coefficients y are larger than unity with the exception of those of the pure components. The system therefore exhibits a positive deviation from the properties of ideal solutions.