Experimental Study on the Alumina Shell Protrusions of Aluminum Nanoparticles during the Aerobic Heating Environment

Abstract

The alumina shell plays a crucial role in the energy release of aluminum powder. The experimental results indicate the presence of protrusions on the alumina shells during the process of aerobic heating. To investigate the causes of protrusion formation during the aerobic heating process, in situ transmission electron microscopy was employed to observe the process of protrusion formation. The experiment revealed that within the temperature range of 70–850 °C, the alumina shell undergoes a gradual transition from smooth to rough, accompanied by the emergence of protrusions at 850 °C. This is because, for 35–500 nm aluminum particles (ANPs), larger particle sizes generate greater internal and tensile stresses, thereby increasing the potential for crack formation on the alumina shell. As molten aluminum flows out of the cracks, the potential for protrusion formation increases and the molten aluminum rapidly oxidizes during the fast oxidation process. Moreover, the larger diameter of ANPs results in a higher quantity of active aluminum, leading to greater heights of the protrusions. These results reveal the reasons for the formation of protrusions in the dynamic oxidation process of ANPs and its relationship with the particle size, which complements the current research on the morphology changes in the oxidation process of ANPs, and has important significance for further exploration of the oxidation mechanism of ANPs.