Reaction Modeling of High Explosive Materials

Richard P. Muller1, Joe Shepherd2, and William A. Goddard, III1

1 Materials and Process Simulation Center, Beckman Institute, Caltech
2 Graduate Aeronautical Laboratory, Caltech

The slides for the full talk are available here.

Abstract:

High explosive materials produce a large amount of energy when they detonate. As such they are important in the construction and mining industries where they are used to remove large amounts of earth and stone, in the rocket propulsion industry as solid fuel propellants, and in the weapons industry, in both conventional and nuclear weapons. Due to their complex reaction mechanisms they also present a particularly difficult challenge to computational chemistry.

We present results for modeling the kinetic reaction networks involved in these detonations, for the high explosive materials HMX and RDX. We do this by extending published mechanisms to include decomposition steps for HMX and RDX. We use density functional theory (B3LYP/6-31G**) to obtain themochemical data for the new species required by these additional reactions. We obtain a mechanism that contains 68 species and 423 reactions. Unlike reduced mechanisms, which include only a few species, we allow a description of essentially all the important species during a decomposition mechanism:

(each line shown above is a separate species). Since the above species plot is too complex for detailed analysis, we can focus on a few important species, as shown below:

With this mechanism, we compute induction times (that is, the time to detonation) for constant volume calculations of HMX and RDX at a variety of pressures; these induction times agree with the sparse data that exists for these species. For further validation, we compute induction times for nitromethane, a smaller molecule that is also used as a racing fuel, and compare our results to Guirguis' shock tube data, with which we agree qualitatively:

 
 

We also discuss future directions of this work, which include computing a more realistic equation of state for the material, adding reaction paths for TATB and PETN, and adding components such as F and Cl from the polymer binders used with the high explosive materials.

This work is supported by DOE-ASCI.

The slides for the full talk are available here.