Mechanism for thermite reactions of aluminum/iron-oxide nanocomposites based on residue analysis

Sol-gel method was employed to combine Al and iron-oxide to form nanocomposites (nano-Al/xero-Fe2O3 and micro-Al/xero-Fe2O3). SEM, EDS and XRD analyses were used to characterize the nanocomposites and the results indicated that nano-Al and micro-Al were compactly wrapped by amorphous iron-oxide nanoparticles (about 20 nm), respectively. The iron-oxide showed the mass ratio of Fe to O as similar as that in Fe2O3. Thermal analyses were performed on two nanocomposites, and four simple mixtures (nano-Al+xero-Fe2O3, nano-Al+micro-Fe2O3, micro-Al+xero-Fe2O3, and micro-Al+micro-Fe2O3) were also analyzed. There were not apparent distinctions in the reactions of thermites fueled by nano-Al. For thermites fueled by micro-Al, the DSC peak temperatures of micro-Al/Xero-Fe2O3 were advanced by 68.1 °C and 76.8 °C compared with micro-Al+xero-Fe2O3 and micro-Al+micro-Fe2O3, respectively. Four thermites, namely, nano-Al/xero-Fe2O3, nano-Al+micro-Fe2O3, micro-Al/xero-Fe2O3, and micro-Al+micro-Fe2O3, were heated from ambient temperature to 1020 °C, during which the products at 660 °C and 1020 °C were collected and analyzed by XRD. Crystals of Fe, FeAl2O4, Fe3O4, α-Fe2O3, Al, γ-Fe2O3, Al2.667O4, FeO and α-Al2O3 were indexed in XRD patterns. For each thermite, according to the specific products, the possible equations were given. Based on the principle of the minimum free energy, the most reasonable equations were inferred from the possible reactions.