The Effects of Stoichiometry and Sample Density on Combustion Dynamics and Initiation Energy of Al/Fe2O3 Metastable Interstitial Composites

The effect of the stoichiometry (i.e., the Al/Fe ratio) and the compressed density of the sample on the dynamics of energy release from a series of Al/Fe2O3 metastable intersitital composites (MIC) were investigated. The reaction was initiated photothermally with a single 8 ns pulse of the 1064 nm fundamental of a Nd:YAG laser. The reaction dynamics were measured by using time-resolved spectroscopy of the light emitted from the igniting and deflagrating material. Two fundamental parameters are measured by this approach: the time to initiation and the duration of the deflagration. The effect of Al particle size on these parameters shows that they attain a minimum value at 100 nm, Al with 120 and 50 nm both having longer initiation and deflagration times. The amount of active Al metal relative to the amount of oxide explains this trend as the Al particle size decreases. As the Al/Fe ratio was varied from stoichiometric (1:1 Al:Fe) to slightly fuel rich (1:5:1) there is a significant decrease in the initiation and deflagration times. When fuel is present in larger excess (2:1) the values of these two parameters begin to increase again. For the range of Al sizes, samples were prepared with different applied pressure to yield samples of increasing density. It was found that the initiation time and deflagration duration decreased with increasing density and reached a minimum value at 50-60% theoretical maximum density. This trend was analyzed in terms of the close packing of the particles using Monte Carlo simulations. From this analysis it was determined that the minimum value corresponded to the point at which the maximum packing fraction was reached.