Probing boron thermite energy release at rapid heating rates

Gottfried, Jennifer L.; Wainwright, Elliot R.; Huang, Sidi; Jiang, Yue; Zheng, Xiaolin

doi:10.1016/j.combustflame.2021.111491

Cited by 23 publications

(1 citation statement)

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“…With the highest oxidative energy density on both gravimetric and volumetric basis, boron (B) is extremenly attractive as a fuel component in propulsion systems requiring maximal energy release rates. − In practice, however, achieving high energy release rates from B is often impeded by the unfavorable properties of the oxide shell on B particles. − B particles oxidize in a shrinking-core manner. When external or oxidative heating is applied, the boron oxide (B 2 O 3 ) shell melts into a nonvolatile liquid at a relatively low temperature (∼720 K) compared to that of the B core, which remains solid during combustion. − The liquid shell devoid of any physical voids impedes the diffusivity of oxygen and hence the B oxidation process. − ,,, By contrast, metals with low melting or boiling points such as Al − and Mg − provide higher energetic performance, although having an inferior energy density compared to that of B, as they burn in the vapor phase. ,,− …”

Section: Introductionmentioning

confidence: 99%

Magnesium-Induced Strain and Immobilized Radical Generation on the Boron Oxide Surface Enhances the Oxidation Rate of Boron Particles: A DFTB-MD Study

Biswas,

Pham,

Zachariah

2023

Langmuir

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Despite their high gravimetric and volumetric energy densities, boron (B) particles suffer from poor oxidative energy release rates as the boron oxide (B 2 O 3 ) shell impedes the diffusivity of O 2 to the particle interior. Recent experiemental studies have shown that the addition of metals with a lower free energy of oxidation, such as Mg, can reduce the oxide shell of B and enhance the energetic performance of B by ∼30−60%. However, the exact underlying mechanism behind the reactivity enhancement is unknown. Here, we performed DFTB-MD simulations to study the reaction of Mg vapor with a B 2 O 3 surface. We found that the Mg becomes oxidized on the B 2 O 3 surface, forming a MgB x O y phase, which induces a tensile strain in the B−O bond at the MgB x O y −B 2 O 3 interface, simultaneously reducing the interfacial B and thereby developing dangling bonds. The interfacial bond straining creates an overall surface expansion, indicating the presence of a net tensile strain. The B with dangling bonds can act as active centers for gas-phase O 2 adsorption, thereby increasing the adsorption rate, and the overall tensile strain on the surface will increase the diffusion flux of adsorbed O through the surface to the particle core. As the overall B particle oxidation rate is dependent on both the O adsorption and diffusion rates, the enhancement in both of these rates increases the overall reactivity of B particles.

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