Classical and Quantum Mechanical Studies of Crystalline Ammonium Nitrate

Abstract

Plane-wave ab initio calculations based on density function theory and the pseudopotential method have been used to investigate the structural and electronic properties of phases V, IV, III and II of ammonium nitrate (AN) crystal. The optimizations of the crystal structures have been done with full relaxation of the atomic positions and lattice parameters under the experimentally determined crystal symmetries. The periodic nature of the crystals has been considered in calculations by employing periodic boundary conditions in all three directions. For phases V, IV and II the predicted crystal structures were found in good agreement with those determined experimentally by neutron diffraction data, but for phase III the differences between the experimental and calculated values are more significant. Band structure calculations indicate that AN is an insulator with a band gap in the range 3.18-3.57 eV corresponding to its different phases. The isotropic compression of phase IV has been studied using ab initio total energy calculations in the pressure range 0-600 GPa. It has been found that over this pressure range the crystal volume is compressed by 71% of the equilibrium volume. The increase in pressure determines significant changes of the band structure, large broadening of the electronic bands together with a decrease of the band gap by about 40%.We have developed a set of intra-and intermolecular classical potentials to describe phase V of AN. These potentials are composed by pairwise Lennard-Jones, hydrogen-bonding terms and Coulombic interactions. Crystal-packing calculations performed with these potentials accurately reproduce the main crystallographic features of this phase. These potentials were further tested in isothermal-isobaric molecular dynamics simulations at atmospheric pressure. It is found that increasing the temperature does not change the translational and rotational order of the molecules inside the crystal. The thermal expansion coefficients calculated for the model indicate anisotropic behavior with large expansions along the a and b axes and a very small one along the c axis.

Phase Stability of Ammonium Nitrate with Organic Potassium Salts

“…[44,45]. These results imply that the crystal structure of AN is changed by the addition of the additives we studied.…”

“…Pradeep et al [19] performed research into the mechanisms and found that hydrogen bonding is weaker in phase III of AN than in phases II and IV. Sorescu and Thompson [20] also found that weaker hydrogen bonding interactions in phase III permit large thermal vibration motions of the ammonium ions leading to the disordered character of this phase. According to these results, the selection of chemicals which could form new hydrogen bonding between additives and AN would allow us to change the AN crystallization so as to inhibit AN phase transitions.…”

A 3D Smoothed Particle Hydrodynamics Method with Reactive Flow Model for the Simulation of ANFO

“…Kim and Yoh[ 13] investigated size effect and copper-confined ANFO using an Eulerian method. Besides these continuum models for the mixtures, the purea mmonium nitrate is also an interest in atomistic-level studies,i ncluding mechanicalp roperties [14] and equations of state [15,16].…”

“…Kim and Yoh[ 13] investigated size effect and copper-confined ANFO using an Eulerian method. Besides these continuum models for the mixtures, the purea mmonium nitrate is also an interest in atomistic-level studies,i ncluding mechanicalp roperties [14] and equations of state [15,16].The SPH method was first proposed by Gingold, Monaghan, and Lucy [17, 18] to study astrophysics. Afterwards, due to the advantages of SPH method in tracking moving interfaces and dealingw ith large deformation,i th as been applied to solve fluid dynamic problems and beyond, explosion, andh ypervelocity impact problems.…”

Reactive atomistic simulations of shock-induced initiation processes in mixtures of ammonium nitrate and fuel oil

“…These experimental principal Hugoniot states for unreacted AN are summarized in table 1. In addition to these experimental efforts, several modeling and simulation studies have been published [1,14,15]. For ANFO, Davis and Hill reported the Jones-Wilkins-Lee equation of state, particularly the expansion isentrope on the P-V plane, of prilled ANFO at a density of 0.93 g/cc using cylinder experiments [16], while Souers et al investigated the effects of containment on detonation velocity of emulsified ANFO at 1.07-1.16 g/cc densities using a simple reactive flow hydrodynamics model [17].…”