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