First-Principles Calculations of the Adsorption of Nitromethane and 1,1-Diamino-2,2-dinitroethylene (FOX-7) Molecules on the Al(111) Surface
AIR FORCE RESEARCH LAB EDWARDS AFB CA PROPULSION DIRECTORATE
Pagination or Media Count:
First-principles calculations based on spin-polarized density functional theory DFT and the generalized gradient approximation GGA have been used to study the adsorption of nitromethane NM and 1,1-diamino-2,2-dinitroethylene FOX-7 molecules on the Al111 surface. The calculations employ 3x3 aluminum slab geometries and 3D periodic boundary conditions. Based on these calculations, we have determined that both dissociative and nondissociative adsorption mechanisms are possible, depending on the molecular orientation and the particular surface sites involved. In the case of dissociative chemisorption, O abstraction by Al surface atoms is seen to be the dominant mechanism. The dissociated oxygen atom forms strong Al-O bonds with the neighboring Al sites around the dissociation sites. Additionally, the radical species obtained as a result of oxygen atom elimination remains bonded to the surface. In some instances, both oxygen atoms of the nitro group dissociate and oxidize the aluminum surface. Finally, for the case of nondissociative adsorption, various N-O-Al bridge-type bonding configurations can be formed. Based on the data provided from these studies, it can be concluded that oxidation of the aluminum surface readily occurs, either by partial or complete dissociation of the oxygen atoms from the NO2 group.
- Physical Chemistry
- Rocket Propellants