THERMAL DECOMPOSITION MECHANISM OF AQUEOUS HYDROXYLAMMONIUM NITRATE
Open Access
- Author:
- Zhang, Kaiqiang
- Graduate Program:
- Mechanical Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- April 23, 2019
- Committee Members:
- Stefan Thynell, Dissertation Advisor/Co-Advisor
Stefan Thynell, Committee Chair/Co-Chair
Richard A Yetter, Committee Member
Adrianus C Van Duin, Committee Member
Michael Matthew Micci, Outside Member - Keywords:
- Energetic Material
Computational Chemistry
Molecular Dynamics
Hydroxylammonium Nitrate
Thermal Decomposition - Abstract:
- The water solutions of hydroxylammonium nitrate (HAN) are the main ingredient of several liquid propellants developed for a variety of propulsion applications. This research focuses on the thermal decomposition mechanism of HAN-water solutions. The detailed chemical mechanisms for solution-phase reacting systems were developed based on the quantum mechanical (QM) calculations using the density functional theory (DFT) and implicit solvation model. The rate constants of elementary reactions were calculated using the barrier-and-diffusion controlled kinetic model. As an intermediate in HAN decomposition, HNO has a strong tendency to dimerize and decompose to N2O and H2O. This study reveals that the related reaction pathways and kinetics are strongly affected by the acid-base equilibria in solution. The mechanism developed for aqueous HAN decomposition describes multiple kinetic processes: nitration of hydroxylamine, HNO dimerization, HONO-scavenging via nitrosation reactions, and HONO regeneration involving hydrogen-abstraction reactions. Kinetic modeling results on dilute HAN solutions show reasonable agreement with the experimental data from previous flow-reactor tests. The sensitivity analysis results suggest an acid-catalyzed nitration-nitrosation pathway, and thus the autocatalysis of aqueous HAN decomposition should be enhanced by the rise of solution acidity. Classical molecular dynamics (MD) simulations were performed to acquire data for the thermophysical properties of HAN-water mixtures as functions of concentration and temperature. The force fields (FF) for the separate ions were developed based on the DFT calculations. Combined with the SPC/E water model and scaled atomic charges, the FFs reasonably reproduce the densities and viscosities of various concentrations at room temperature. Other studied properties include specific heats, enthalpies of vaporization, ionic and thermal conductivities, and radial distribution functions. The isothermal decomposition of 13-16 M HAN was investigated using the confined rapid thermolysis (CRT) experiments and Fourier transform infrared (FTIR) spectroscopy. The major IR-active thermolysis products are H2O, N2O, HNO3, NO, and NO2. Measured species evolutions are reasonably reproduced by the kinetic modeling using optimized reaction and evaporation rate constants. The activation energy was deduced based on the induction periods. Evaluation of the reported Arrhenius parameters for HAN decomposition reveals an approximately linear relation between ln(A) and Ea, which indicates the existence of a kinetic compensation effect.