Atomistic insight into dehydrogenation and oxidation of aluminum hydride nanoparticles (AHNPs) in reaction with gaseous oxides at high temperature

Abstract

Metal hydride additives, aluminum hydride in particular, have extensively been applied in solid rocket motor propellants. This work employed the reactive force field molecular dynamics to elaborate the underlying mechanism for the oxidation of highly active aluminum hydride nanoparticles (AHNPs) by gaseous oxides (CO, CO2, NO, and NO2). The results showed that AHNPs first went through four stages: dehydrogenation (<84 ps), Al nucleation and growth (>25 ps), micro-explosion (~31 ps), and oxidation (>28 ps). The dehydrogenation of AHNPs surface overlaps with the Al nucleation in the preheating stage and prevents the oxidation of Al by gaseous oxides. Only a small part of Al on the surface is oxidized to form a thin and uneven oxide film (0.18–0.54 nm). In the core, the formed H2 is hindered by the shell and gradually gathers into H2 bubbles. H2 bubbles have great kinetic energy and become a micro-explosion promoter, eventually causing nanoparticles to burst at high temperatures. The micro-explosion accelerates the dissociation of gaseous oxides. This study provides an in-depth understanding of the mechanism of dehydrogenation and oxidation of metal hydride nanoparticles.