Effect of the microporous structure of ammonium perchlorate on thermal behaviour and combustion characteristics

Ammonium perchlorate (AP) is the component with the highest content in composite propellants, and it plays a crucial role in propellant performance. In view of the effects of low-temperature AP thermal decomposition on thermal safety and combustion characteristics, porous ammonium perchlorate (PAP) samples with different mass losses were first prepared by thermal convection heating, and the structures were characterized and analysed. Second, the effects of decomposition degree on the thermal decomposition characteristics of PAP were studied by DSC-TG. Finally, the combustion characteristics of AP/Al binary mixtures were tested with high-speed photography and in a sealed bomb. The results showed that low-temperature decomposition of AP resulted in formation of porous structures for AP particles. The pores first appeared near the surfaces of the particles and began from multiple points at the same time. The pores increased in size to approximately 5 μm and then expanded, and finally, the AP particles were full of pores. After partial decomposition, the crystal structure of AP remained unchanged, but the low and high decomposition temperatures decreased obviously. The decomposition rate accelerated. Due to the porous structure of PAP, the combustion rate of the AP/Al system increased obviously with increasing decomposition of AP. The relationship between the combustion rate and the mass loss was approximately linear under open conditions, and it was exponential for a high-pressure environment. A computational model of the combustion process for the AP/Al binary system was established to explain the effects of pore structure and pressure on the combustion process.