SOLUBILITY LIMITS OF SILICATE MELTS

A statistical mechanical model of silica melt is presented in which me tal oxides are incorporated into the bonding network. In this approach a Flory-type lattice model for binary silicate melts is coupled with a set of chemical reactions that determine the extent of metal oxide i ncorporation into the silica network and regulate the distribution of nonbridging oxygens around a central silicon. The theory produces two- and three-phase coexistence curves over a range of parameter space. T he three-phase equilibrium regions coalesce to critical end points, wh ere two of the three phases have become critical, and to a nonsymmetri c tricritical point, where all three phases have simultaneously become critical. The theory captures the qualitative behavior and essential features of simple binary silicate melts. (C) 1997 American Institute of Physics.