Some Crystallographic Features of the Mechanism of Phase Transformations and Chemical Reactions in Solids

Abstract

One of the principal questions forming part of the general problem of the mechanism of reaction diffusion in solids is the question of the mechanism of the formation of phase newly occurring in the reaction zone. The mechanism of the formation of the crystal nuclei of a new phase on the basis of the initial solid phase determines not only the orientation of the developing crystals of the new phase in relation to the crystals of the original phase, but also the fine structure (substructure) of the crystalline formations of the new phase. These structural factors, in their turn, affect many properties of the layers of the reaction product. Primarily, this is of importance for properties such as the mechanical properties (including the strength of the bond between the layer and substrate) and the diffusion properties. With regard to the latter, the function of the substructure is particularly important in a number of cases, due to the fact that diffusion along the boundaries of the structure elements or blocks is much easier than diffusion along sections of the more regular crystal lattice.