Mechanism and kinetics for ammonium dinitramide (ADN) sublimation: a first-principles study

Area of Science:

• Computational Chemistry
• Materials Science
• Chemical Physics

Background:

• Understanding the sublimation and decomposition mechanisms of energetic materials like ammonium dinitramide (ADN) is crucial for safety and performance.
• Previous studies have provided experimental data, but a detailed quantum-mechanical investigation of the ADN sublimation process was lacking.

Purpose of the Study:

• To elucidate the quantum-mechanical mechanism of ammonium dinitramide (ADN) sublimation.
• To calculate the energy profiles for each step of the sublimation/decomposition process.
• To determine the sublimation and dissociation energies and rate constants.

Main Methods:

• Generalized gradient approximation plane-wave density functional theory (DFT) calculations were employed.
• A slab model with periodic boundary conditions was used to represent the solid ADN surface.
• Lattice constants for bulk ADN were calculated and compared with experimental values.

Main Results:

• A three-step mechanism for ADN sublimation was identified: surface relaxation, molecular complex sublimation, and complex dissociation.
• Sublimation energy for the molecular complex was calculated as 29.4 kcal/mol, and dissociation energy of the complex was 13.9 kcal/mol.
• The calculated total sublimation enthalpy (44.9 kcal/mol) agrees well with experimental and other theoretical predictions. Water molecules were found to increase ADN sublimation enthalpy.

Conclusions:

• The study provides a detailed quantum-mechanical understanding of the ADN sublimation mechanism.
• Calculated sublimation and dissociation energies, along with rate constants, align with experimental observations.
• The findings offer valuable data for predicting the behavior and stability of ADN under various conditions.