Combustive mechanochemical reactions in off-stoichiometric powder mixtures

Ball milling induces combustion during the synthesis of tin and zinc sulfides from the elements. The mechanochemical reduction of magnetite by magnesium also becomes combustive. These processes have been investigated as a function of the composition of the initial powder mixture. Contrary to expectations, the shortest activation times before ignition are found at compositions far from the stoichiometry of the product phases. The ignition time depends on solid state reactions at the interfaces, reaction heat, and heat transfer, rather than the bulk composition of the powder mixture.