Combustion Characteristics of Stoichiometric Al-CuO Nanocomposite Thermites Prepared by Different Methods

Three nanocomposite materials with the same nominal stoichiometric thermite composition of 2Al-3CuO were prepared by three different methods: ultrasonic mixing (USM) of constituent nanopowders, electrospraying (ES), and arrested reactive milling (ARM). Prepared powders were placed in a 6.7-mm diameter, 0.5-mm-deep cavity in a brass substrate and ignited by electro-static discharge. The experiments were performed in air, argon, and helium. The mass of powder removed from the sample holder after ignition was measured in each test. Using a multi-anode photo-multiplier tube coupled with a spectrometer, time-resolved light emission traces produced by the ignited samples were recorded in the range of wavelengths of 373–641 nm. Time-resolved temperatures were then determined by fitting the recorded spectra assuming Planck’s black body emission. Temporal pressure generated by ignition events in the enclosed chamber showed that the powder’s combustion properties were tied to both their preparation technique as well as the environment they were ignited in. We found that agglomeration of nanoparticles hindered combustion of USM powders; while it was not observed for the ES powders. In oxygen-free gas environments, lower temperatures and pressures were observed for USM and ES powders prepared using starting nano-particles. For the ES powders, the effect of gas environment was less significant, which was interpreted considering that ES materials included gasifying nitrocellulose binder, enhancing heat, and mass transfer between individual Al and CuO particles. Higher pressures and temperatures were observed in inert environments for the ARM-prepared powder.