(612a) Effect of Heating Rate on Combustion of Nano-Composite Thermites Prepared By Arrested Reactive Milling

Stoichiometric nanocomposite thermites were prepared by Arrested Reactive Milling (ARM). These thermites utilized aluminum or zirconium as the fuel and were milled with various oxidizers (CuO, MoO₃, WoO₃, Fe₂O₃, and Bi₂O₃). The powders were ignited by both CO₂ laser beam and electrostatic discharge (ESD). The two ignition methods provided different heating rates with the laserâ??s heating rate (10⁶K/s) being three orders of magnitude lower than that achieved in the ESD (10⁹K/s). The first set of experiments dealt with small particle ignition events in ESD; powders were spread in a monolayer across a carbon film on a brass substrate and ignited by a high voltage spark. The optical emission from these combustion events was recorded using a single photomultiplier tube (PMT) filtered at 568 nm. In different experiments, the same powders were fed in the CO₂ laser beam using an air jet feeder system. The resulting particle combustion emission was recorded using the same, 568-nm filtered PMT. In addition, a couple of PMTs filtered at 700 and 800 nm were used to obtain time-resolved color temperature traces for the burning particles. It was observed that particles ignited by the ESD had shorter burn times than those ignited by the laser. These observations are interpreted assuming that the nano-composite structure of the particles was maintained following their very rapid heating by ESD; however, the scale of mixing between metal and oxidizer was not retained for the particles heated by the CO₂ laser beam. The correlation between the scale of mixing between metal and oxidizer and burn rate was supported by scanning electron microscopy analyses of partially burned and quenched particles of different materials.