Time-Resolved Mass Spectrometry of Nano-Al and Nano-Al/CuO Thermite under Rapid Heating: A Mechanistic Study

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 (105 to 106 K/s), Al-containing vapor species (Al and Al2O) are observed to slowly increase with increasing temperature, followed by a rapid increase in concentration at ∼2030 K. The temporal evolution of Al, Al2O 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 Al2O3, implies that the penetration of Al into the shell probably decreases its melting point. The measurements lead to an effective overall diffusion coefficient of ∼10–10 cm2/s. Time-resolved mass spectra of nano-Al/CuO thermite show for the first time the existence of Al, Al2O, AlO, and Al2O2 intermediate reaction products, with Al2O the main intermediate oxidation product, in agreement with thermochemical calculations.