A statistical mechanical model for chemical disorder in interacting systems: Application to phase separation in alkali silicates,alkaline earth silicates and alkaline earth aluminosilicates

The present model provides a formalism for studying the effects of chemical disorder in a system of interacting atoms in which the number of neighbors of each kind of atom need not be the same. When they are the same, this model reduces to the quasi-chemical approximation.It is applied to a model for phase separation in alkali silicates and alkaline earth silicates which involves a mixture of fourfold and sixfold coordinated species. The sixfold coordinated species represents a pseudo-atom comprised of two silicon atoms each bonded to non-bridging oxygen atoms which are strongly associated.A miscibility dome similar to that observed in sodium silicates and barium silicates is predicted. The suppression of phase separation by alumina is predicted.