Development and validation of a detailed reaction mechanism for the condensed phase decomposition of ammonium perchlorate

Abstract

The primary objective of the current research is to develop and validate a detailed reaction mechanism for the condensed-phase decomposition of ammonium perchlorate (AP), which is crucial for understanding the combustion behavior of AP-based propellants that are extensively used in solid rocket propulsion systems. Quantum mechanics calculations were performed at the B3LYP/6–311++G(d,p) level of theory to investigate the elementary reactions in the condensed phase, utilizing the Integral Equation Formalism of the Polarizable Continuum Model (IEFPCM) to simulate these reactions. Transition state theory was employed to determine the kinetic parameters, while the CBS-QB3 method was used to calculate the thermodynamic properties of the reactions. Experimental validation was achieved by comparing the computational results with data from laser pyrolysis and Fourier-transform infrared spectroscopy (FTIR) experiments, conducted at four isothermal conditions (410 °C, 430 °C, 450 °C, and 470 °C) in terms of mass loss and gas-phase mole fraction profiles. The computational model, incorporating a detailed reaction mechanism and product evaporation, closely matched experimental observations, with minor deviations attributed to experimental uncertainties. The model assumes that 40 % of AP undergoes sublimation, forming NH₃ and HClO₄ in the gas phase, while the remaining 60 % reacts in the condensed phase, producing species such as H₂O, HCl, NO₂, N₂O, ClO₂, HNO₃, and Cl₂, which evaporate into the gas phase. This validated reaction mechanism represents a significant advancement in modeling AP decomposition, providing valuable insights for safety and performance assessments in industrial applications.