Chemical Equilibrium and Carbon Kinetics in Explosives

摘要

Chemical reactions "freeze-out" and carbon kinetics (usually assumed to include nucleation, phase transformation and coagulation) have long been invoked to explain deviations of the energy delivered by detonating explosives (e.g., measured in cylinder experiments) from ideal behavior. Chemical equilibrium hydrodynamic calculations of cylinder detonation for PETN, a high energy, low carbon content explosive, show that gas phase chemistry "freeze-out" is not a major effect determining energy output, and it probably occurs at relatively low temperatures (1500K), as proposed decades ago. In carbon producing explosives, often modeled using full chemistry "freeze-out" temperatures higher that 2000K, chemical reactions between the condensed carbon and the gas products are most likely to be the limiting steps in energy release. Indeed, comparisons of calculated and recovered carbon amounts indicate that such reactions likely slowdown significantly at temperatures around 2300K. Hydrodynamic simulations using a simple chemical kinetics model for the transfer of carbon to the gas phase reproduce both energy output and carbon production of TNT, a graphite-producing explosive, and COMP-B, a diamond-producing explosive. Calculations that also include the diamond - graphite phase transformation suggest that it is a relatively small contribution to energy output. A new carbon aggregation model is introduced and parameterized using experimental data, but its full application to detonation requires additional experimental and/or simulation guidance.