Effect of metal additives on the composition and combustion characteristics of primary combustion products of B-based propellants

The application of a metal additive is an effective way to improve the performance of B-based propellants. This study focused on the effect of metal additives on the energy release properties of primary combustion products of B-based propellants (hereafter referred to as primary combustion products) to facilitate an understanding of the stages of the secondary combustion of B-based propellants. Mg–Al alloy (MA), Mg metal, Al metal, and Ti metal were used to prepare the primary combustion product samples. A comparative analysis was also made of samples (with MA) obtained under different gas generator pressures. X-ray diffraction, X-ray photoelectron spectroscopy, and inductively coupled plasma chromatography were used to analyze the sample components. The ignition, combustion, and thermal oxidation properties of the samples were studied with a laser ignition experimental system and a thermobalance, respectively. The primary combustion product samples mainly contained C, B13C2, B4C, B2O3, H3BO3, NH4Cl, BN, B, and their respective metal additives. The degree of primary combustion of the samples increased with the gas generator pressure. The presence of MA effectively increased the combustion intensity of the samples. The average combustion temperature of the samples with added MA reached 1440.36 °C. The ignition delay time of the samples ranged between 61 and 146 ms. The self-sustaining combustion time of the samples ranged between 1174 and 1254 ms. MA and Ti both helped to shorten the ignition delay time and prolong the self-sustaining combustion time. The samples obtained under higher gas generator pressures exhibited inferior combustion characteristics. MA decreased the initial oxidation temperature of C (492.6 °C), and Ti decreased the initial oxidation temperature of B (738.1 °C). Mg could improve the oxidation efficiency of B at high-temperature conditions. Among the four metal additives, MA was the most beneficial to the energy release of the primary combustion products, whereas Al had the weakest effect.