The topochemistry of the reaction interface in decomposition processes in solids

Abstract

A number of recent mechanistic studies of thermal decompositions of solids are discussed here with emphasis on the chemistry of the reactions involved. It is argued that greater insight into the sequence of steps participating can be achieved when kinetic observations are complemented with microscopic examinations and chemical analyses of the partially reacted salt as well as the final products. Comparisons with comparable reactions can also be valuable in providing insight into the mechanisms of solid state reactions.

A classification of the roles of nuclei is discussed with reference to a number of selected rate processes. Three types of nuclei are distinguished, these are: functional nuclei, the solid product is a catalyst for the changes proceeding at the reaction interface, fusion nuclei, chemical reaction proceeds preferentially in a molten zone which may be localized and temporary, and fluid-flux nuclei, reaction proceeds in a zone of fluid, condensed product temporarily retained within the nucleus.

It is argued that complementary measurements considered together, (kinetics, microscopy and analyses) provide greater insight into the chemistry of reactions of solids than is usually possible from studies using a less comprehensive experimental approach.