EFFECT OF PARTICLE MORPHOLOGY ON CRITICAL CONDITIONS FOR SHOCK-INITIATED REACTIONS IN TITANIUM-SILICON POWDER MIXTURES

The effect of titanium particle morphology on the shock sensitivity of titanium-silicon powder mixtures has been investigated experimentally. The powder mixtures were tested in a planar recovery capsule, with the shock loading produced by a high explosive booster charge placed on top of the capsule and a PMMA attenuator. Reactions were not observed for equimolar mixtures of large (95 mu m) spherical Ti particles with fine (15 mu m) Si particles for incident peak shock pressures of up to 23 GPa, estimated with LS-DYNA. In contrast, mixtures with fine (40 mu m) spherical Ti particles or irregularly-shaped fine (31 mu m) Ti particles exhibited a threshold attenuator thickness, and hence shock pressure, for reaction initiation. Microscopy and microprobe backscatter analysis were used to identify the degree of intermixing between the particles for shock loading just below the reaction threshold. For the largest spherical Ti particles, little particle intermixing was evident. For the finer particles, penetration of Si particles into the larger, more ductile Ti particles was observed. Although large deformation of the irregular Ti particles was observed, in contrast with the spherical particles, the threshold shock pressure for reaction initiation was 7 +/- 2 GPa, independent of particle morphology.