Journal of Energetic Materials

Aluminum powder is a common ingredient in energetic materials. Reactivity of this metal can be improved by reducing the particle size, due to their larger surface/volume ratio. In this research, the effects of using nano-structured aluminum powder investigated on physical, thermal, mechanical and explosive characteristics of an HMX-based PBX. The results indicated that the experimental density increased up to 2.5 percent by replacement of the nano-structured aluminum powder instead of micronized aluminum. It has also shown that this replacement caused to the hardness and tensile stress enhanced to 18 Shore D and 0.67 MPa, respectively. On the other hand, the elongation at maximum stress decreased from 10.5 to 9.8 percent. Furthermore, a catalytic effect has been shown in phase transition and self-decomposition temperatures of HMX in DSC analysis. This catalytic effect increased the impact sensitivity of composition up to 7.7 percent. Based on comparative dent test, it is established that the nano-structured aluminum powder has no considerable effect on detonation characteristics of PBX charge.

In this research, the effects of the particle size and shape of aluminum powder on the kinetics and thermodynamic properties of HMX thermal decomposition in a PBX formulation were investigated. Nano-structured aluminum powder has flaked shape and thickness of about 20-30 nm. Kinetics and thermodynamic parameters were calculated by both Kissinger and Flynn-Wall-Ozawa (FWO) methods based on differential scanning calorimetry under non-isothermal condition with heating rate of 5, 10, 15 and 20 °C/min. Results compared with the same composition formulated by micronized aluminum powder. Calculations showed that the activation energy of thermal decomposition of HMX decreased 35 kJ/mol by replacement of nano-structured Al powder instead of micronized particle. Furthermore pre-exponential factor, Critical Temperatures for the Thermal Explosion, and 500-day cookoff temperature decreased significantly.