Exothermic reactions in Al-CuO nanocomposites

Heterogeneous reactions in the Al-CuO system were investigated using differential scanning calorimetry combined with structural and phase analyses of partially reacted samples. The dense nanocomposite 2Al + 3CuO powders used in this study were prepared by arrested reactive milling. Ignition experiments with the powders heated at different rates were also performed and compared to the results of thermal analysis. The results of thermal analysis measurements were processed using isoconversion techniques and a multistep reaction mechanism was proposed to describe the experiments. The reaction between Al and CuO started at similar to 400 K and was well described by four parallel reaction steps. The kinetic descriptions of individual steps depend on the frequency factors specific for the powders used in this study and activation energies that should remain valid for any Al-CuO composite materials. The values of the frequency factors and activation energies were determined as well as the specific reaction mechanisms describing each reaction step. The identified reaction steps were tentatively assigned to specific processes of CuO decomposition followed by diffusion of reacting species through amorphous and then crystalline Al2O3 polymorphs. Ignition of the nanocomposite Al-CuO materials was shown to be driven primarily by the lower-temperature oxidation processes. It was shown that ignition of Al-CuO nanocomposite powders can be described reasonably well using the proposed kinetics of Al-CuO heterogeneous reactions. (C) 2006 Elsevier B.V. All rights reserved.