Wanjun Zhao,Hui Ren,Tao Yan,Yapeng Ou,Qingjie Jiao,Haiyang Wang,Dylan J. Kline,Michael R. Zachariah
This work explores the ignition mechanism of silicon (Si) based thermites, and it is supposed that the phase change of silica (SiO 2 ) coating on the Si core producing fractures may play a crucial role in the ignition of Si-based thermites. Several Si-based thermites were evaluated by the combustion test and calorimeter, and potassium perchlorate (KClO 4 ) is turned out to be a promising oxidizer given the high reactivity and considerable heat release. Titanium (Ti) nanoparticles with a lower onset oxidization temperature than Si were incorporated into Si/KClO 4 system via a facile sonicating method. The ignition temperature of Si/KClO 4 has reduced markedly by ~80–130 °C with significant increases of ~5-8x in pressurization rate and decreases by a factor of ~2–3 in burn time when adding 30–70% Ti by mole into the fuel. The combustion efficiency is improved dramatically from ~59% to ~73%. The enhanced combustion performance could be attributed to the lower ignition temperature of Ti/KClO 4 leading to the initiation reaction of the ternary composites, thus promoting energy release and the reactivity of the ternary system. This work not only investigates the ignition mechanism of Si-based thermites but also sets a stage for tuning the ignition and combustion of Si-based thermites via facile incorporation of Ti nanoparticles.
The electrical energy injection and ignition mechanisms of HAN-ECSP (hydroxylamine nitrate-based electrically controlled solid propellant) are critical technology limiting its engineering application. The mechanisms are investigated through the characterization and testing of various samples in this paper. The mixed cross-linking of HAN and PVA (polyvinyl alcohol) is a prerequisite for the injection of electrical energy into the propellant. directly bind to PVA, facilitating its dissolution, whereas connect via hydrogen bonding. Boric acid strengthens the cross-linking effect of PVA, resulting in a decrease in the conductivity of the propellant and an increase of the energy injection voltage, making ignition of the propellant more difficult. When the boric acid content is 0%, the propellant conductivity is 2.9 S/m, and at 120 V, the propellant can generate a 1 A electrolysis current. When the boric acid content is 2%, the propellant conductivity is 2.0 S/m, 400 V can only generate a 0.3 A current. At high voltages, the main reaction at the anode is the electrolysis of , while the main reaction at the cathode is the electrolysis of .Due to the higher electrolysis voltage of , electrical energy is concentrated at the anode interface. The propellant needs to reach a temperature above 400 °C to ignite. High boric acid content leads to the concentration of electrical energy at the cathode interface, causing the propellant to burn out and fail at the cathode. Adding water to the anode surface further intensifies this problem.
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