Induction Period of a Thermal Explosion in Titanium and Aluminum Powder Mixtures

The processes occurring during the induction of a thermal explosion in titanium and aluminum powder mixtures are analyzed. The role of the oxide film on aluminum particles and the heating rate of samples during interaction between titanium and aluminum is considered, and various mechanisms of the oxide film destruction at temperatures near the melting point are proposed. It is shown that, depending on the heating rate of the samples, there are three possible mechanisms of formation of direct contact between titanium and aluminum: 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°C. As the average titanium particle size reduces from 90 to 10 m, the ignition temperature is lowered by 100°C. It is shown that a two-stage ignition mechanism is observed in a number of cases. The isothermal section of aluminum melting is followed by the stage of a slow temperature rise up to 700–800°C, after which the temperature rise rate increases tenfold.