Thermal explosion induction period in titanium and aluminum powder mixtures

The processes occurring during the induction of a thermal explosion in mixtures of titanium and aluminum powders are analyzed. The role of the oxide film on aluminum particles and the heating rate of samples during the interaction of titanium with aluminum is considered, and various mechanisms of destruction of the oxide film at temperatures near the melting point are proposed. It is shown that, depending on the heating rate of the samples, three mechanisms for the formation of direct contact between titanium and aluminum are possible: mechanical destruction of the oxide film on aluminum, the reaction of aluminum oxide with titanium, and the reaction of aluminum oxide with aluminum. Mechanical activation of the powder mixture lowers the ignition temperature by 20–30$^{\circ}$C. Reducing the average particle size of titanium from 90 to 10 microns lowers the ignition temperature by 100$^{\circ}$C. It is shown that in a number of cases a two-stage ignition mechanism is observed. After the isothermal section of aluminum melting, the stage of a slow temperature rise to 700–800$^{\circ}$C begins, after which the temperature rise rate increases by an order of magnitude.