Mechanism and Kinetics for Ammonium Perchlorate Sublimation: A First-principles Study

Abstract

We have studied for the first time the kinetics and mechanism for the sublimation/decomposition of NH4ClO4 by first-principles calculations, using a generalized gradient approximation with the plane-wave density functional theory. Supercells containing 4, 8, and 16 NH4ClO4 units were used; the predicted enthalpic change for solid NH4ClO4 to gaseous NH3 and HClO4 is 45.0 ± 1.5 kcal/mol. The calculated desorption activation energies for NH3, HClO4, and H3N···HOClO3 molecular complexes, individually, from the relaxed surface are 45.3, 43.5, and 28.1 kcal/mol, respectively. The rate constant for the dominant sublimation process desorbing H3N···HOClO3 as a pair can be presented by k sub.= 6.53 × 1012 exp (−28.8 kcal/mol/RT) s−1, which is in reasonable agreement with available experimental data. Expectably, the decomposition of H3N···HOClO3 (g) to NH3 (g) and HOClO3 (g) is considerably faster, about 1 × 107 times greater than that for the sublimation process in the same temperature range. The rate constant for the gas-phase dissociation step can be expressed by 1.20 × 1015 exp (−14.6 kcal/mol/RT) sec−1. This study further confirms that the activation energy for the sublimation of an ammonium salt is significantly lower than the enthalpic change and that the molecular complex of acid and base sublimes concurrently as a pair.

An ab initio chemical kinetic study on the reactions of H, OH, and Cl with HOClO3

“…The key results have been reported in a review chapter on propellant chemistry [13]. Recently, we have computationally confirmed that HOClO 3 and NH 3 are the main sublimation/decomposition products of solid AP [14]. The unimolecular decomposition of HOClO 3 gives rise to OH + ClO 3 , which can undergo bimolecular reaction with near gas-kinetic efficiency producing HO 2 and OClO [15].…”

From Ni-YSZ to sulfur-tolerant anode materials for SOFCs: electrochemical behavior, in situ characterization, modeling, and future perspectives

“…A prerequisite for making the most of kinetic simulations for these complex systems is to have a reliable prediction of the rate constant for each elementary step involved. 210,211 Finally, an atomic force field approach may use parameters derived from DFT calculations and may be combined with molecular dynamics (MD) simulations to study the time-dependent evolution and temperature-dependent properties of anode systems. These atomistic simulations may also provide input phenomenological parameters needed for larger-scale continuum modeling for electrochemical measurements such as impedance spectroscopy.…”

Synthesis of Ferrocene‐based Esters as Burning Rate Catalysts and their Anti‐migration Study

“…For the T d of AP, several potential pathways have been devised. [ 21 ] A possible BR catalytic mechanism for T d of AP catalyzed by Es‐Fcs is shown in Figure 10. Once Es‐Fcs are exposed to heat, the length between Cp rings and iron atom increases, and then the Fc components start to decompose, resulting in the oxidation of Cp rings of Fc to produce CO 2 .…”