The kinetics and mechanism for the sublimation/decomposition of ammonium perchlorate (AP) with and without water present on the decomposing surface have been investigated by first-principles calculations, using a generalized gradient approximation with the plane-wave density functional theory. Calculated results show that H2O can enhance the sublimation of AP; the sublimation energies with (H2O)n (n = 0, 1, 2, 3) from the surface were predicted to be 28.1, 21.4, 18.6, and 14.2 kcal/mol, respectively. Notably, H2O was found not to affect the proton transfer between the NH4 +/ClO4 - ion pair, but was found to significantly enhance the sublimation of AP by co-desorbing with the ion pair. The rate constants for the dominant sublimation processes, the desorption of the molecular complex, H3N· · ·HOClO3, and the codesorption of H2O with AP, (H2O)n· · ·NH4ClO4 (n = 1, 2), predicted by canonical variational transition state theory can be presented by kdes = 6.53 × 1012 exp (-28.8 kcal/mol/RT) (n = 0) s-1, 1.69 × 1010 exp (-20.3 kcal/mol/RT) (n = 1) s-1, and 1.08 × 1011 exp (-17.7 kcal/mol/RT) (n = 2) s-1, respectively, with a significant enhancement by the H2O molecules. Interestingly, the structures of AP in the water complexes are more ionic than those without H2O in the gas phase. In addition, the energy changes for proton transfer on the surface have been compared with those in solution. The calculated proton transfer energies on the crystalline AP surface with (H2O)n (n = 0, 1, 2), 31.1, 29.7, and 32.5 kcal/mol, were found to be close to the corresponding values of 30.8, 30.5, and 30.4 kcal/mol calculated by the (H2O)n-NH4ClO4 complexes in solution using the polarizable continuum model. These calculated proton transfer energies on the surface and in solution are close to the experimental values inside AP solid, 26-31 kcal/mol.
|頁（從 - 到）||493-504|
|期刊||International Journal of Energetic Materials and Chemical Propulsion|
|出版狀態||Published - 1 1月 2010|