THERMODYNAMICS OF MIXING AND ORDERING IN THE DIOPSIDE-JADEITE SYSTEM: II. A POLYNOMIAL FIT TO THE CVM RESULTS

Abstract

In Part I (Vinograd, 2002) the relationship between temperature, composition and free energy of the diopside-jadeite solid solution was described using a CVM model. Here the same relationship is described using a combination of Redlich-Kister (RK) polynomials and Gaussian functions. The use of the Gaussians permits an accurate description of the free energy dip centred at Jd50, which is caused by the long-range ordering, while the effect of the short-range ordering can be easily modelled using the RK polynomial. The simplified RK-Gaussian description is extended to the three-component diopside-jadeite-hedenbergite solid solution. The polynomial description permits an easy incorporation of the derived activity-composition relations into phase-equilibrium computation software.