Chemical Reaction Sequences for High Explosive Thermal Explosion Models

摘要

When a high explosive charge is subjected to an intentional or unintentional thermal insult, it is essential to ba able to predict if, when, and where in the charge a thermal runaway reaction will occur. An evaluation of the violence of the runaway reaction needs to be quickly made to advise personnel and first responders in their possible actions. Main charge explosives ar eusually organic materials with 20 to 30 atoms per molecule, which decompose into 7 to 10 moles of gases such as water, carbon dioxide, carbon monoxide, nitrogen, etc. and some solid carbon particles, releasing over 1kcal/g of chemical energy in less than one second after an induction time varies widely from minutes to days with the heating rate caused by the insult. Since a molecule with 20 to 30 atoms cannot transfrom into 7 to 10 smaller molecules in one chemical reaction, the sequence of endothermic bond breaking and exothermic bond formation reactions plus their individual chemical kinetic and thermal properties need to be known as well as possible. Experimental measuremnets of all the possible chemical reaction rates are very difficult and have not been forthcoming as rapidly for solid and liquid explosives as they have for gaseous explosives. So reduced sets of global reaction rate model have been developed based on the available chemical kinetic and thermal property data on the important stages of the decomposition process. This presentation reviews some of the three to seven reaction rate models developed at LLNL, the experimental techniques used to measure basic kinetic and thermal data, the thermal explosion experiments used to obtain times to explosion, locations of the initial runaway reaction, and indications of the violence of the resulting explosions. Several laboratories have contributed to solving this difficult problem: LLNL's ODTX and STEX tests plus modeling; Sandia National Laboratory's SITI test and modeling; LANL's cylindrical heat transfer and explosion test, proton radiography experiments, and modeling; and many other laboratories. Indivduals and groups, such as Ray Rogers (LANL), Tom Brill (University of Delaware), Rich Behrens (Sandia Livermore) developed apparatuses that yielded kinetic rates and species formation sequences that greatly increased the ability to model chemical energy release rates. These and many other efforts have given us a greatly improved undertsanding of the global thermal transfer properties and chemical decomposition kinetics of solid explosives compared to forty years ago. New explosives molecules are always being synthesized, and new uses for explosives are developing. More basic chemical kinetic research is definitely required to build more predictive models.