VERY HIGH-PRESSURE COMBUSTION - REACTION PROPAGATION RATES OF NITROMETHANE WITHIN A DIAMOND ANVIL CELL

The combustion-front propagation rate of nitromethane has been examined to pressures of 40 GPa. A new and general technique involving pulsed laser ignition of an energic material within a diamond anvil cell and a method for monitoring the rapid decomposition of nitromethane and other explosives to more stable chemical products is described in detail. Nitromethane is shown to exhibit a flame propagation rate that increases smoothly to 100 m/s at 30 GPa as a function of pressure. Above 30 GPa, the final solid-state combustion products change dramatically and the flame propagation rate begins to decrease. The combustion-front propagation rate is analyzed in terms of an existing condensed-phase model that predicts a relationship between the front propagation rate, U, and the pressure derivative of the chemical kinetic activation energy, dE(a)/dP, such that a plot of logU2 vs. P should be linear. The activation energy is analyzed to yield an effective volume of activation, DELTA-V-dagger, of -3.4 ml/mol. The chemical kinetic parameters determined from the combustion-front propagation rate analysis of solid high-pressure nitromethane is compared with results from other thermal decomposition studies of this prototypic molecular explosive.