Thermal reaction mechanisms of nano- and micro-scale aluminum powders in carbon dioxide at low heating rate

Abstract

Thermal reaction mechanisms of nano- and micro-scale aluminum powders with a mean particle diameter of 50 nm and 1–2 µm were investigated by a thermogravimetric analysis coupled with a differential scanning calorimetry. Thermal reaction characteristics of nano-scale aluminum powder are significantly different from that of micro-scale aluminum powder. The key reaction of nano-scale aluminum powder takes place in the low-temperature region, while for micro-scale aluminum powder, the key reaction takes place in the high-temperature region. Scanning electron microscopy and X-ray diffraction were also conducted to analyze the thermal reaction products. There is a striking difference for the thermal reaction products, which are the oxide shell disruption of micro-scale aluminum particles. X-ray diffraction patterns indicate that γ-Al2O3 is detected before aluminum melting point for nano-scale aluminum powder, but for micro-scale aluminum powder, γ-Al2O3 is detected after aluminum melting point. Alumina crystal structures of nano- and micro-scale aluminum powders are different at different mass gain stages. The sequence of the products of nano- and micro-scale aluminum powders is amorphous oxide → γ→α-Al2O3 and amorphous oxide → γ→θ → α-Al2O3, respectively. Furthermore, thermal reaction mechanisms of nano- and micro-scale aluminum powders are discussed at a low heating rate.