Particle size and gas environment effects on blast and overpressure enhancement in aluminized explosives

Aluminized RDX-based explosives were detonated under controlled conditions while varying particle size and atmosphere in an effort to quantify the contribution of aerobic and anaerobic Al reaction to blast and overpressure. Early time reaction of aluminum acts to enhance the primary explosive blast, and this reaction is approximately half aerobic and half anaerobic (i.e. oxidation by detonation products and/or nitridation), suggesting that very rapid early-time mixing occurs in explosive fireballs. Particle size effects are surprisingly negligible over the range of 3-40 μm, which implies that conventional scaling laws for aluminum combustion provide less insight than previously assumed. Quasi-static pressures obtained in the time period from 5 to 10 microns after detonation suggest that oxidation of aluminum is complete in the presence of 20% oxygen. However, for nitrogen environments, oxidation only proceeds to half its theoretical maximum, except for the smallest (3 μm particles) for which oxidation was nearly complete. These results demonstrate that oxidation of aluminum in aluminized explosives is robust in anaerobic environments, and that simulation efforts cannot neglect anaerobic channels, even though aerobic oxidation provides the greatest energy release.