Review of the phase transformation and synthesis of inorganic solids obtained by mechanical treatment (mechanochemical reactions)

The theoretical background, based on thermodynamical concepts, of experimentally observed polymorphic transformations occurring during comminution processes (e.g. dry grinding of minerals) is discussed. It is shown that both the specific surface energy and volumetric elastic strain energy terms in the overall Gibbs free energy equation for the system in question play a major role in these transformations. Phenomenological kinetic equations are also discussed. Solid state reactions induced by the reactivity of newly exposed surfaces and by stress relaxation are described with the main emphasis on the synthesis of new compounds during the grinding or milling of powdered mixtures (e.g. production of ferrite from a mixture of oxides, mechanical alloying of metals etc.). The similarity between a shock-induced mechanochemical reaction (including its fundamental background) and a comminution process is pointed out. The paper concludes with a review of the applications of mechanochemistry and a list of fields of technology where it can be used to advantage.