THERMODYNAMICS OF MIXING AND ORDERING IN THE DIOPSIDE-JADEITE SYSTEM: I. A CVM MODEL

Abstract

Solution calorimetry and phase equilibrium data for the diopside-jadeite system are assessed using a combination of the cluster variation method (CVM) and Redlich-Kister (RK) polynomial expansion. The CVM is used to model part of the free energy of mixing which depends on short-range order (SRO) and long-range order (LRO) effects. The SRO/LRO independent part of the free energy is modelled using an RK polynomial. The parameters of the RK and CVM models are obtained through the fit to the experimental data. The best-fit parameters are used to calculate activity-composition relations and a temperature-composition phase diagram of the diopside-jadeite system.