Detonation tube studies of aluminum particles dispersed in air

Abstract

A 5.487-m vertical detonation tube of 152-mm inside diameter instrumented to monitor both shock front (piezoelectric transducers) and reaction front (fiber-optic/light-detector probes) was used to study the detonation of both flake and atomized aluminum powders dispersed in air. Effects of concentration, surface-to-mass ratio, aluminum oxide coating, and type of initiation were evaluated. Flake-aluminum powder with a surface-to-mass ratio of 3 to 4 m 2 /g was readily detonated with detonation velocities as high as 1.65 km/sec and detonation pressures of about 5 MPa (compared to the Chapman-Jouguet values of 1.85 km/sec and about 2.5 MPa). The nominal 5-μm, 0.34 m 2 /g atomized-aluminum powder was also detonated, but with greater difficulty and some loss in detonation characteristics; i.e. maximum detonation velocities of 1.35 km/sec and detonation pressures of at most 3 MPa. Furthermore, in the case of the flake aluminum the induction times between shock and reaction fronts were often in the range characteristic of homogeneous detonations, approaching the limits of the instrumentation (about 1 μsec) whereas the atomized aluminum consistently gave substantially higher values: e.g., 14 μsec being the lowest. Increasing the aluminum oxide coating of either powder caused deterioration of detonation characteristics and tended to decouple, the shock and reaction fronts. Detonability and detonation characteristics were very sensitive to surface-to-mass ratio and rather insensitive to overall concentration. Spinning detonation was identified in all instances investigated for this phenomenon. Initiation of detonation in all cases required shock wave energy as obtained from the detonation of small charges of high explosive.