The role of MnO2 crystal facets in aluminothermic reaction of MnO2/ nAl composite

The available oxygen repositories of metal oxide play vital role in aluminothermic reactions. The contact surface of an oxidizer to metal fuel (aluminum) in high density energetic materials especially nanothermites control its chemical reactivity and combustion performance. MnO2 exposed facets {310}, {110}, {100} are hydrother-mally synthesized with different precursors, physical mixed with nano-aluminum and MnO2/nAl composite came into existence. So far, the metal oxides around aluminum are theoretically well explained but experimentally lack some information about oxygen activity at interface. The VB-XPS, TEM, DSC in cooperation with density func-tional theory (DFT) calculations were used to investigate the exposed facet activity. Crystal facets have different surface oxygen and bulk arrangements where oxygen and vacancy electrostatic balance at interface engulfed aluminum, start pinching the alumina layer just before the onset temperature and finally breach the alumina in to aluminum. The activity of exposed facets to aluminum directly controls the reaction temperature, heat release and combustion pressure. The coherence between experimental and theoretical calculations shown MnO2-310 facet with lowest surface energy 1.12 J/m2 not only expedite O2 activation at interface but also increase Al2O3/ nAl oxidation activity with more heat release due to more oxygen vacancy formation. The MnO2 facet effect in MnO2/nAl composite is obvious from onset temperature 542 degrees C, 535 degrees C, 529 degrees C to peak temperature 586 degrees C, 578 degrees C, 560 degrees C with heat release 2368 J/g, 2297 J/g, 765.5 J/g for {310}, {110}, {100} facets respectively. This research is presenting significance of MnO2 surface chemistry, comprehension facet activity to nAl and strategy to explore facet engineering in nanothermite.