Equation of State of Detonation Products Based on Exponential‐6 Potential Model and Analytical Representation of the Excess Helmholtz Free Energy

Abstract

One of the most important tasks associated with theoretical prediction of performance of explosives by thermochemical calculation is accurate description of the equation of state (EOS) of detonation products. Widely used empirical equations of state, such is Becker‐Kistiakowsky‐Wilson (BKW EOS), have limited accuracy when it comes to energetic materials with unusual elemental composition. Replacing empirical EOS with more sophisticated and theoretically based EOS, the accuracy of thermochemical calculations can be increase. We present an equation of state of detonation products based on the Buckingham α‐exponential‐6 equation (Exp‐6) and an analytical representation of the excess thermodynamic functions for classical fluid mixture. The excess Helmholtz free energy, as a function of reduced density, temperature, and stiffness parameter, is calculated applying KLRR perturbation statistical mechanical theory, and so obtained data are approximated by multinomial coefficients. The interpolation domain is defined so to describe accurately the range of pressures, densities, and temperatures relevant for detonation studies. The equation is incorporated in EXPLO5 thermochemical code. Good agreement with Monte‐Carlo calculations is obtained, as well as between calculated and experimental detonation parameters for a series of explosives.

BKW EOS: History of Modifications and Further Improvement of Accuracy with Temperature‐Dependent Covolumes of Polar Molecules

“…In this work, the thermochemical equilibrium code EXPLO5 is used. The code has several equations of state built-in: BKW EOS, modified BKW (MBKW) EOS, and theoretically based EXP-6 EOS (based on exponential-6 potential and analytical representation of the excess Helmholtz free energy) [17]. Like other thermochemical codes, EXPLO5 uses thermodynamics to solve simultaneously the state variables and chemical composition of detonation products, and thus obtain detonation parameters of explosives.…”