Modeling and simulation of pressure waves generated by nano-thermite reactions

This paper reports the modeling of pressure waves from the explosive reaction of nano-thermites consisting of mixtures of nanosized aluminum and oxidizer granules. Such nanostructured thermites have higher energy density (up to 26 kJ/cm3) and can generate a transient pressure pulse four times larger than that from trinitrotoluene (TNT) based on volume equivalence. A plausible explanation for the high pressure generation is that the reaction times are much shorter than the time for a shock wave to propagate away from the reagents region so that all the reaction energy is dumped into the gaseous products almost instantaneously and thereby a strong shock wave is generated. The goal of the modeling is to characterize the gas dynamic behavior for thermite reactions in a cylindrical reaction chamber and to model the experimentally measured pressure histories. To simplify the details of the initial stage of the explosive reaction, it is assumed that the reaction generates a one dimensional shock wave into an air-filled cylinder and propagates down the tube in a self-similar mode. Experimental data for Al/Bi2O3 mixtures were used to validate the model with attention focused on the ratio of specific heats and the drag coefficient. Model predictions are in good agreement with the measured pressure histories.