Thermodynamics of interstital solid solutions

Abstract

On the assumption that within the bounds of one sublattice the interstitial atoms and vacancies are arranged in a disordered manner, while the larger atoms are in complete order, we have compiled an equation for the entropy of formation of an interstitial solid solution with two interstitial sublattices. Equations have been compiled for the free energy of formation and activities of the components and they contain a small number of constants. As a first approximation the activity of a component possessing a large atomic radius is only a function of the crystal structure and composition. The homogeneity of boundaries of isostructural interstitial solid solutions formed with the participation of the same components with a large atomic radius are close to one another, provided the phases in equilibrium with them are also isostructural. A method of using the phase diagram to find the constants in the free energy and activity equations is demonstrated. Briefly considered are the energy and formation entropy of two types of ternary solid solutions (depending on whether two similar components have a large or small atomic radius).