Densities and molar volumes of silicate melts

Abstract

Abstract Expressions are derived for densities and molar volumes of binary and ternary silicate melts based on the interpretation that the constitution of the melts can be described in tern-IS of conventional polymer theory. For simplicity, the treatment is limited to the case in which only linear chains are considered to be present. The assumptions in this approach are that (a) the value of kln for the equilibrium constant of the polymerization process, as expressed in terms of the activities of the constituents, is independent of the chain length n of the reacting species, and (b) the enthalpy change for the mixing of the pure constituents is identical with the change in internal energy. It is readily shown that these are equivalent to the assumptions that there is a constant increment in standard free energy of formation and molar volume on passing from one member to the next along the homologous series of pure liquid silicates and that, for the molar volumes, this increment is equal to that on passing...