Comprehensive revelation of the influence mechanism for the thermal decomposition of ammonium perchlorate by ammonium oxalate

Abstract

Rate inhibitors for combustion are crucial to decrease the burning rate and prolong the working time of solid propellants. Ammonium oxalate (AO), the most frequently utilized and effective rate inhibitor in propellants, faces the challenge of an unclear influence mechanism regarding ammonium perchlorate (AP). Therefore, it is necessary to elucidate the influence mechanism of AO on the thermal decomposition of AP. This study fabricated AP/AO composites with varying AO content via wet milling, the structural, thermal decomposition processes and products of these composites were investigated. Additionally, the adsorption between AP and NH₃ was simulated. The findings indicate that the inclusion of AO inhibits the low-temperature decomposition (LTD) of AP while enhancing its high-temperature decomposition (HTD). Furthermore, it was observed that the heat release of AP/AO composites was lower than that of AP. The Gibbs free energy (ΔG^≠) of the AP/AO composites exceeded that of the AP at the LTD stage and was lower than that of AP at the HTD stage. Further study using molecular dynamics simulations revealed that as the increase of NH₃ concentration, its adsorption on the AP surface intensifies during LTD, inhibiting the forward progress of the AP decomposition reaction. However, NH₃ molecules desorbed from the AP surface and actively participated in gas-phase reactions with increasing temperature, thereby promoting the HTD of AP. This work is helpful to fully understanding the mechanism of AO in the process of the LTD and the HTD of AP but also contributes to the exploration of novel inhibitors and advances the development of low-burning rate solid propellants.