Investigating the effect of NiO and NiF2 on boron carbide combustion

Boron-based fuels, recognized for their high energy density and potential in energetic applications, encounter challenges such as long ignition delays and incomplete combustion, which result in reduced combustion efficiency and limited performance in aerospace propulsion. In this study, boron carbide (B4C) is investigated as an alternative fuel to pristine boron due to its favorable gas-phase combustion. Both metal oxide (nickel oxide (NiO)) and metal fluoride (nickel fluoride (NiF2)) are selected as oxidizing modifiers to enhance the reactivity of B4C. A method combining laser ignition with optical diagnostics is employed to investigate the enhancing effects of different oxidizers on the ignition and combustion characteristics of B4C. Both NiO and NiF2 can significantly increase the combustion radiation intensity and reduce the time to maximum intensity of B4C. Differential scanning calorimetry, in-situ X-ray diffraction, and Fourier transform infrared spectroscopy were used for simultaneous thermal analysis of the B4C composite powders. Combined thermal analysis showed that the effects of NiO and NiF2 on promoting B4C combustion is mainly achieved via the formation of NimBn and the release of a large number of gas products. It is reasonable to speculate that the phase separation at the B2O3/NimBn interface forms new pathways for oxygen diffusion and reaction with the B core. The difference in the combustion mechanism of B4C with NiO and NiF2 lies in the gas phase products, i.e., CO2 and BF3, respectively, thus leading to significant differences in their reaction processes.