Application of the Peng–Robinson Equation of State to Energetic Materials RDX and TNT: Pure Components, Liquid Mixtures, and Solid Mixtures

Continuum simulations of energetic materials, such as cookoff models, rely on thermodynamic information to close the governing equations. Thermodynamic models of unreacted energetic materials, particularly mixtures, have been relatively limited despite the importance of these substances to national security and to a number of different industries. In this presentation of our recently published work, we show that the well-known Peng-Robinson equation of state can be applied to energetic materials, whether they are pure components, liquid mixtures, or solid mixtures. We are specifically interested in two compounds: hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) and 2,4,6-trinitrotoluene (TNT). We model RDX and TNT in both their liquid and solid phases, as well liquid and solid mixtures of the two compounds. Our work examines temperatures and pressures as high as about 500 Kelvin and 2500 bar, respectively. These are conditions relevant to cookoff before explosion occurs. The Peng-Robinson equation of state provides a good representation of experimental volumetric (e.g., density and bulk modulus), thermal (heat capacity), and phase behavior (melting temperature and solubility) data. It can be applied to other energetic materials — ranging in complexity from pure components to multiphase, multicomponent mixtures — by adapting the procedures described in this presentation.