Dr. Elizabeth Glascoe, Lawrence Livermore National Lab

Pressure Dependent Decomposition Kinetics of the Energetic Material HMX

In this study we precompressed an energetic molecular crystal C4H8N8O8, HMX, up to pressures of 4 GPa and monitored the corresponding thermal decomposition kinetics using time resolved Fourier transform infrared, FTIR, spectroscopy. Decomposition rates were determined from the slope of decaying HMX vibrational IR intensities vs. time. Using these rates Arrhenius parameters were then determined using the extended Prout-Tompkins nucleation-growth model. At approximately 1 GPa we find an inflection point in the decomposition rate where the prior positive slope changes sign and applied pressure begins to retard thermally induced reactions. These results indicate that the phase transition in HMX plays a minor role in the thermally induced kinetics. We attribute 0 to 1 GPa rate acceleration to pressure enhanced autocatalysis whereas greater than 1 GPa rate deceleration is attributed to an increasing barrier to bond cleavage, which would result in an increase in volume.

1. A.K. Burnham and R.L. Braun. "Global Kinetic Analysis of Complex Materials" Energy and Fuels, 1999, 13, 1.

This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

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