Theoretical Studies On Surface Interaction Between Nitro Compounds And Metals

Metallized energetic materials are widely used in underwater weapons, aeroweapon ammunition and rocket propellants due to the properties of high-energy, high temperature in detonation, long-lasting of energy releasing and obvious after-burning effects, and so on. In this dissertation, magnesium, aluminum, alumina, nitroamine and2,4,6-trinitrotoluene were selected as the investigated systems. By the quantum mechanics and molecular dynamics methods, systematical studies were performed in the adsorption and decomposition of nitroamine and2,4,6-trinitrotoluene molecules on the aluminum, alumina and magnesium surface. The main studies are as following,1. The adsorption of the NH2NO2molecule on the Al surface results in the decomposition of the NH2NO2. The NH2NO2is decomposed to four kinds of products, which are NH2NO+O, NH2N+2O, NH2+NO2and NH2+NO+O, respectively. The radical species obtained as a result of N-O and N-N bonds dissociation remain adsorbed the surface. The largest adsorption energy is-893.8kJ/mol. The aluminum surface is readily oxidized by the adsorbate of nitroamine to form strong Al-O and Al-N bonds, either by dissociation of the O and N atoms from the nitro group or the N atom from amino group. For the dissociation adsorption configurations, a significant charge transfer occurs. The most of charge transfer is3.04e from the Al surface to the decomposition products of the NH2NO2molecule. With the number of dissociated bonds of NH2NO2, the charges of N and O atoms decrease sharply while the charges of surface Al atoms increase obviously. In the N-O and N-N bonds dissociated configurations, the peak values of N and O atomic partial DOS shift obviously and the energy bands become broad, which shows the chemical bond interacting is strengthened. For all adsorption configurations, the less the number of the DOS peak of N and O atoms is, the more the number of forming Al-0and Al-N bonds is.2. The binding energy, radial distribution functions and diffusion of NH2NO2molecules on the Al(Ⅲ) surface have been investigated by molecular dynamics (MD) simulations. The NH2NO2molecules diffuse on the Al surface and the surface Al atoms deviate a little from their original position at high temperature, although NH2NO2molecules are packing on the Al surface at low temperature. The maximum binding energy (Ebind) of NH2NO2molecules and Al atoms is-1463.9kJ at250K and0.1GPa, but the minimum one is-1082.1kJ at550K and0GPa. As the temperature increases, the value of the first peak for RDF of Al-N and Al-O bond decreases. Diffusion rates increase with temperature increasing, and first decrease and then increase with pressure increasing below450K. The smallest self-diffusion coefficient (Ds) is0.85×10-6cm2?s-1at250K and0.1GPa, and the largest Ds is123.1×10-6cm2?s-1at550K and1.0GPa for NH2NO2molecules. The largest activation energy for the diffusion of NH2NO2molecules is18.1kJ-mol-1at0.1GPa, and the smallest activation energy is13.8kJ-mol-1at10.0GPa. The influence of pressure on diffusion of NH2NO2molecules on the Al (111) surface is very small.3. When the2,4,6-trinitrotoluene (TNT) molecule is on the Al surface, the nitro groups of TNT are decomposed to two kinds of products (NO+O, N+2O), whereas other bonds, for example C-N, C-C and C-H bonds, do not rupture. The radical species obtained as a result of nitro group dissociation remain adsorbed the Al surface. The N-O bond of the o-NO2group is easier to rupture than that of the P-NO2group after the adsorption of the TNT molecule on the Al (111) surface. The largest adsorption energy is-747.3kJ/mol. The aluminum surface is readily oxidized by the radical fragment of TNT, which is initiated by the dissociated O atoms from the nitro group. The N and O atoms of nitro group form strong Al-O and Al-N bonds with neighboring Al atoms. The most of charge transfer is3.42e from the Al surface to the fragment of TNT molecule. With the number of dissociated bonds of TNT, the charges of N and O atoms decrease sharply while the charges of surface Al atoms increase obviously. The more transfer charge is, the larger the adsorption energy is. In the N-O and N-N bonds dissociated configurations, the peak values of N and O atomic partial DOS shift obviously and the energy bands become broad, which shows the chemical bond interacting is strengthened. For all adsorption configurations, the broader the DOS peak value of N and O atoms is, the more the number of forming Al-O and Al-N bonds is.4. For the adsorption of the NH2NO2molecule on the Al2O3(001) surface, the geometrical structure of the NH2NO2molecule change slightly while the Al-O bond lengths of Al2O3change largely. By the longest distance of Al-O and the smallest distance of O-O in Al2O3, it can inferred that Al-O bonds partially decompose. This implies the Al2O3becomes activate due to the adsorption of the NH2NO2molecule on the Al2O3(001) surface. This can also make clear that the aluminized explosive of NH2NO2keeps high reactivity even if the aluminum is oxidized to form a film of the alumina. The smallest and the largest adsorption energies are-350.2kcal-mol-1and-453.8kcal?mol-1, respectively. The energies of DOS for N and O atoms of the NH2NO2molecule match with those of Al atoms, and Al-O or Al-N bond forms easily at the corresponding energies range. The DOS projections on the N, O and Al atoms occur with obvious shift of peaks, which infers energy bands become broad and the interactions of chemical bonds are strengthened.5. The strong attractive forces between oxygen and Mg atoms induce the N-O bond rupture of the NH2NO2. Subsequently, the dissociated oxygen atoms and radical fragment of NH2NO2oxidize the Mg surface. The largest adsorption energy is-860.5kJ/mol. The most of charge transfer is3.76e from the Mg surface to the fragments of NH2NO2molecule. The Mg surface is readily oxidized by the radical fragments of NH2NO2, which is initiated by the dissociated O atoms from the nitro group. The decomposition mechanism of NH2NO2molecule on the Mg(001) surface were also investigated. The barrier energy of N-O bond dissociation at the Mg-top site is as large as321.6kJ/mol when the N-N bond was initially parallel to the Mg surface, while the barrier energies of N-O bond dissociation for the other configurations are much smaller, in range of11.6to36.5kJ/mol. The reaction energies of the N-O bond decomposition are,consistent with the adsorption energies of NH2NO2on the Mg surface. What’s more, the adsorption and decomposition of NH2NO2on the Mg surface are exothermic.