Coulomb Effect of Intermediate Products of Core-Shell SiO₂@Al Nanothermite

Nanothermites as high-energy-density and high-reaction-rate materials have important applications in civil and military fields. Nevertheless, it is difficult to detect all intermediates and products using conventional experimental methods. In this work, the reaction process of core-shell SiO₂@Al nanoparticles under adiabatic conditions was investigated through molecular dynamics simulations using a reactive force field (ReaxFF). In the microcanonical ensemble, the redox reaction of SiO₂@Al nanothermite becomes explosive due to the huge energy release during Al-O bond formation. The gaseous products are mainly the intermediate products Al₅O and Al₄O as well as the final products Al₂O, AlO, Si and Al. Analyses of the steric charge distributions and evolution show that the Coulomb effect causes the number of intermediates Al₅O (0.32|e|) to increase to the maximum, then slowly decrease and remain stable. But the tetrahedral Al₄O cluster is almost charge-neutral, at -0.05|e|, and the number remained almost constant. This work is expected to provide deeper insights into the complex reaction mechanism of nanothermite.