Mechanochemical synthesis of Al2O3/Co nanocomposite by aluminothermic reaction

In this work, Al2O3/Co nanocomposite was successfully prepared by mechanochemical reaction between Co3O4 and Al powders in a planetary high energy ball mill. The mechanism of the reaction was dealt using X-ray diffraction (XRD), differential thermal analysis (DTA), and thermodynamics calculations. It was found that Co3O4 reacts with Al through a self-sustaining combustion reaction after an incubation period of 50 min and the reaction between Co3O4 and Al involves two steps. First, Co3O4 reacts with Al to form CoO and Al2O3 at the temperature around melting point of Al, and at higher temperature, CoO reacts with remaining Al to form Co and Al2O3. Mechanical activation process decreases the reaction temperature from 1041 °C for as-received Co3O4 and Al powder mixture to 869 °C for 45 min milled powders. After annealing of powder milled for 12 h, no phase transformation has been detected. The crystallite sizes of both α-Al2O3 and Co remained in nanometeric scale after annealing at 1000 °C for 1 h.