Temperature measurements of Al containing nano-thermite reactions using multi-wavelength pyrometry

Thermite reactions with nano-scale particles have attracted much study due to their high flame temperatures and combustion velocities. The mechanism by which the reaction propagates is not well understood. The reaction temperature, the heating rate, and the reaction zone thickness are critical parameters to understanding the mechanism. Measurements of the reaction temperature for the Al/CuO, Al/MoO₃, and Al/Fe₂O₃ nano-thermite systems were made using multi-wavelength pyrometry for two experimental configurations. In one experiment, the radiative emission from the reaction of a small, unconfined pile (∼10 mg) of reacting nano-thermite is collected over a 50 ms integration time and the temperature is measured. In a second experiment, the radiative emission was collected from a single spot, with a diameter of 1.5 mm, on a transparent tube filled with the nano-thermite as the combustion wave passes and the spectrum is temporally resolved using a streak tube and detected using an intensified CCD camera. Temperature traces from these experiments show a temperature ramping period followed by a plateau in temperature. For Al/CuO, the average temperature from the unconfined pile experiment was 2390 ± 150 K, and the average plateau temperature for the temporally resolved measurements was approximately 2250 ± 100 K. For Al/MoO₃, the unconfined pile experiment yielded an average temperature of 2150 ± 100 K, and the average plateau temperature was the same. The temperature measured from the Al/Fe₂O₃ unconfined pile experiment was 1735 ± 50 K. The measured temperatures suggest that the gases generated during the reactions are primarily from the decomposition or vaporization of the various metal oxides. Furthermore, for Al/CuO and Al/MoO₃, which can be classified as 'fast' nano-thermites, it was shown that the length scale associated with the temperature rise is much longer than classical conduction driven reactions.