Studies on ignition and afterburning processes of KClO4/Mg pyrotechnics heated in air

Abstract

Thermal behavior of KClO4/Mg pyrotechnic mixtures heated in air was investigated by thermal analysis. Effects of oxygen balance and heating rates on the TG–DSC curves of mixtures were examined. Results showed that DSC curves of the mixtures had two exothermic processes when heated from room temperature to 700 °C, and TG curve exhibited a slight mass gain followed by a two-stage mass fall and then a significant mass increase. The exothermic peak at lower temperature and higher temperature corresponded to the ignition process and afterburning process, respectively. Under the heating rate of 10 °C min−1, the peak temperatures for ignition and afterburning process of stoichiometric KClO4/Mg (58.8/41.2) was 543 and 615 °C, respectively. When Mg content increased to 50%, the peak ignition temperature decreased to 530 °C, but the second exothermic peak changed little. Reaction kinetics of the two exothermic processes for the stoichiometric mixture was calculated using Kissinger method. Apparent activation energies for ignition and afterburning process were 153.6 and 289.5 kJ mol−1, respectively. A five-step reaction pathway was proposed for the ignition process in air, and activation energies for each step were also calculated. These results should provide reference for formula design and safety storage of KClO4/Mg-containing pyrotechnics.