Synergistic Effect of Ammonium Perchlorate on HMX: From Thermal Analysis to Combustion

Abstract

The thermal decomposition and combustion of binary mixture of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) and ammonium perchlorate (AP) are investigated at various concentrations. Thermal stability was investigated by thermal analysis techniques, i.e., DSC/TGA, combined with FTIR spectrometry, and accelerating rate calorimetry (ARC). Twofold HMX/AP interaction result is observed: ammonium perchlorate as synergistic additive effectively (in 60 °C) reduces the onset decomposition temperature of HMX, whereas gaseous products of the HMX thermolysis, in turn, catalyze the AP decomposition. Burning rate of mechanical mixtures exceeds the HMX level at 4 MPa, when HMX content lies in the range close to above synergistic effect at thermolysis, and AP particle size is fine (10 μm). Addition of large AP particles to HMX does not enhance the burning rate. Comparative analysis of the combustion parameters of the mechanical mixtures and large HMX crystals covered with AP layer revealed that the direct contact between components is not a necessary condition for the HMX/AP interaction for compositions without binder, proving the gas-phase character of this effect. However, for compositions with active binder, the direct contact between components is important. Finally, the synergistic effect changes the decomposition pathway for mixtures with HMX content above 40 % and below 90 % and noticeably increases the burning rate of HMX-based compositions with active binder. Formulations with active binder and coated HMX provide higher burning rate than those ones with mechanical mixtures of HMX with fine AP. It means the possibility to use the considerably less amount of ammonium perchlorate to achieve the same level of the burning rate.