Mechanism of reaction in metal + metal oxide systems

Abstract

PYROTECHNICS frequently consist of intimate mixtures of powdered metals and metal oxides. The exothermicity of such reactions is often very high, as, for example, in the thermite process. Considerable self-heating occurs and the reaction often becomes explosive. Little experimental work has been carried out on the mechanism of these reactions, largely because the participation of solid phases and the high evolution of heat make them difficult to study. It is to be expected, however, that such mechanisms would normally involve solid phases, with the possible addition of a liquid phase when a low melting point reactant or intermediate is present. We report here that such reactions often occur through a gas phase process. Furthermore, when one of the constituents is magnesium, which is frequently the case in pyrotechnics, the reaction rate is controlled almost solely by the evolution of magnesium vapour.