Heterophase Systems

Abstract

Solids that consist of a mixture of crystals of different composition and structure are, of course, more numerous than solid single-phase systems. Such a mixed body can also form in a single-component system if the substance can exist in several polymorphic modifications. But then, such two-phase systems (e.g., a mixture of yellow and red sulphur crystals, or of grey and white tin crystals) can exist in a stable state only at phase equilibrium points of a phase diagram. At a given pressure, equilibrium is attained only at a certain temperature. A two-phase region in the phase diagram can be reached only through eutectic crystallization, or when a solid solution decomposes (disproportionates). These two processes will be examined briefly in this chapter.