NATIONAL BUREAU OF STANDARDS GAITHERSBURG MD INST FOR MATERIALS SCIENCE AND E NGINEERING
A new spectroscopic method was developed which permits kinetic measurements of reactions in energetic materials at high pressures. The method utilizes FTIR in conjunction with a diamond anvil high pressure cell. Measurements were made on HMX and nitromethane. The rate of thermal decomposition for HMX was found to have a negative pressure dependence, which, when coupled with the observed thermodynamic activation quantities, led to a unimolecular decomposition mechanism - ring expansion prior to bond scission. Contrary to the HMX case, the decomposition rate for nitromethane was observed to have a positive pressure dependence leading to a bimolecular reaction mechanism which is the result of increased intermolecular interactions. A dynamic stress-induced catastrophic reaction was observed in protonated nitromethane at room temperature, but not in the deuterated form. Keywords Thermal decomposition, Kinetics, Pressure, Reaction mechanism, Chemical stability, HMX, Nitromethane.