Assessment of Solid Solution Parameters for Some Silicates

Abstract

Various solid solution models were discussed by Fei et al. (1986). There are two different groups of solution models. The first group of models has their origin in the Flory-Huggins model (Flory, 1953), in which solutions are considered as athermal with zero excess enthalpy of mixing. The later refined versions, which are the Wilson model (Wilson, 1964), the quasi-chemical (Guggenheim, 1952) and the nonrandom two-liquids (NRTL) model (Renon and Prausnitz, 1968), do involve enthalpy of mixing and have been reviewed by Acree (1984). The second group of models simply expresses functions as power series in mole fraction. The Redlich-Kister and the two-constant Margules model fall in this category. We note that there are many studies of the application of the sub-lattice model for minerals with non-equivalent crystallographic sites (e.g. Davidson and Lindsley, 1989; Sack and Ghiorso, 1989). In this book, we are mostly concerned with single-site formulations. In certain cases, we have first used the two-site sub-lattice formulation and then converted the energies to a single-site ionic form (e.g. Shi et al., 1992).