Reactivity of boron carbide and metal oxide mixtures

Abstract

Boron-based materials have high energy density making them suitable as additives in propulsion systems. However, the lack of prompt ignition, for example, creates a challenge in harnessing the energy. In this work, mixtures of boron carbide and four common metal oxides (CuO, MnO${}_2$, Bi${}_2$O${}_3$, Fe${}_2$O${}_3$) are studied as a way to increase the reactivity of boron-based materials. Both burning rate and thermal analysis are used to determine the response of mixtures to fast and slow heating rates, respectively. Mixtures with CuO or Bi${}_2$O${}_3$ burned the fastest whereas Fe${}_2$O${}_3$ mixtures would not ignite and MnO${}_2$ samples had a burning rate approximately 15% that of the fastest mixtures. The thermal analysis determined that the gas produced from carbon oxidation was most influential on the combustion rate and not the thermal conductivity or oxygen release temperature of the oxide. Experimental observation indicates that the boron component is oxidized in the condensed phase despite the importance of gas generation. Spectroscopic evidence presented suggests gas generation aids in removing the molten boron oxide layer during combustion which can be utilized to improve the reactivity of boron-based additives in propulsion applications.