Deuterium Isotope Effects During HMX Combustion: Chemical Kinetic Burn Rate Control Mechanism Verified

The appearance of a significant deuterium isotope effect during the combustion of the solid HMX compound verifies that the chemical reaction kinetics is a major contributor in determining the experimentally observed or global burn rate. Burn rate comparison of HMX and its deuterium labeled HMX-d(8) analogue reveals a primary kinetic deuterium isotope effect (1 deg. KDIE) at 500 psig (3.55 MPa) and 1000 psig (6.99 MPa) pressure and selectively identifies covalent carbon-hydrogen bond rupture as the mechanistic step which ultimately controls the further HMX burn rate under the static combustion conditions of this experiment. The 1 deg. KDIE value further suggests the rate-limiting C-H bond rupture occurs during the solid state HMX decomposition/deflagration portion of the overall combustion event and is supported by other independently published studies. A possible anomalous KDIE result at 1500 psig (10.4 MPa) is addressed. This condensed phase KDIE approach illustrates a direct link between lower temperature/pressure thermal decomposition and deflagration processes and their potential applicability to the combustion regime. Most importantly, a new general method is demonstrated for mechanistic combustion investigations which selectively permits an in-situ identification of the compound's burn rate- controlling step. Reprints. (aw) Published in Propellants, Explosives, Pyrotechnics, v14 p93-102 1989.