Magnesium-Enhanced Reactivity of Boron Particles: Role of Mg/B2O3 Exothermic Surface Reactions

Boron offers great promise as a candidate fuel in high-energy composites as a result of its high gravimetric and volumetric energy content; however, its oxidation rate is limited by sluggish diffusion of reactive species across its low-melting oxide shell. On the other hand, Mg nanoparticles (NPs) have been shown recently to undergo fast oxidation following rapid vaporization (similar to 100 its at high heating rates of similar to 105 degrees C/s). This release of vapor-phase Mg can potentially be exploited to react exothermically (Delta Hr = -420 kJ/mol) with the B2O3 layer of boron, inducing surface disrputions and promoting its combustion. In this paper, we explore this effect by evaluating Mg NPs as additive fuel to B/CuO nanoenergetic composites. We observe that incorporating Mg as an additive fuel in B/CuO composites results in a similar to 6-fold enhancement in reactivity with a similar to 60% reduction in burn time. Through thermal and reaction product analysis along with high-speed time-of-flight mass spectrometry (T-jump/TOFMS) and ignition characterization, we investigate the reaction mechanism of Mg/B2O3 particles as a simulant system for the interaction of Mg with the B2O3 shell of boron. These characterizations reveal that exothermic heterogeneous reactions occur between vapor-phase Mg and the molten B2O3 shell of boron at similar to 500-650 degrees C. The role of these exothermic surface reactions in inducing surface modifications and reactivity enhancement of boron particles is discussed.

Automated summary

In this paper, we investigated the effect of incorporating Mg nanoparticles as additive fuel in B/CuO nanoenergetic composites. The results showed that the reactivity of B/CuO nanoenergetic composites was enhanced by approximately 6 times, with a reduction in burn time of about 60%. The exothermic heterogeneous reactions between vapor-phase Mg and the molten B2O3 shell of boron at 500-650°C were found to induce surface modifications and enhance the reactivity of boron particles.