Time-Resolved Mass Spectrometry
of Nano-Al and Nano-Al/CuO
Thermite under Rapid Heating: A Mechanistic Study
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Abstract
Aluminum nanoparticles (Al-NPs) and nano-Al/CuO thermite
were investigated
in a rapid heating environment by temperature jump time-of-flight
mass spectrometry. Upon rapid heating (10<sup>5</sup> to 10<sup>6</sup> K/s), Al-containing vapor species (Al and Al<sub>2</sub>O) are observed
to slowly increase with increasing temperature, followed by a rapid
increase in concentration at ∼2030 K. The temporal evolution
of Al, Al<sub>2</sub>O species observed in time-resolved mass spectra
of rapid heated Al-NPs supports the hypothesis that Al containing
species diffuse outward through the oxide shell under high heating
rate conditions. The rapid rise in Al-containing species above 2030
K, which is below the bulk melting point of Al<sub>2</sub>O<sub>3</sub>, implies that the penetration of Al into the shell probably decreases
its melting point. The measurements lead to an effective overall diffusion
coefficient of ∼10<sup>–10</sup> cm<sup>2</sup>/s. Time-resolved
mass spectra of nano-Al/CuO thermite show for the first time the existence
of Al, Al<sub>2</sub>O, AlO, and Al<sub>2</sub>O<sub>2</sub> intermediate
reaction products, with Al<sub>2</sub>O the main intermediate oxidation
product, in agreement with thermochemical calculations