mechanochemical reduction of Cobalt oxide by Aluminum and carbon and investigating the effect of milling parameters on the production of Co-Al2O3 composite powder

In this study, cobalt-alumina composite was prepared in-situ by mechanochemical process using cobalt oxide as a raw material in the presence of aluminum and carbon as reducing agents, for this purpose released heat from aluminothermic reaction was used in order to activate the carbothermic reaction. In this respect, milling the powder mixture of Co3O4-Al-C was done by a high energy ball milling device (fast mill) and also, the effect of different parameters such as speed, time, and ball-to-powder ratio on the final production was investigated. The milled powders were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). According to the results of XRD analysis and distribution map of elements after 12 hours of milling, the redox reaction completely occurred and as a result, the peaks corresponding to the cobalt and alumina phases appeared in the diffraction pattern. The increase in milling time from 12 to 36 resulted in a decrease in the crystallites size of the cobalt and alumina phases up to 9 and 20.3 nm, respectively. On the other hand, with an increase in the speed of 350 to 450 rpm, the particle size distribution has been uniformly and size of the agglomerates produced in the powder mixture has decreased. Also, according to SEM images, increasing the ball to powder ratio from 15:1 to 40:1 resulted in a reduction in the average particle size below 1 μm and a more uniform distribution of the alumina reinforce phase in the cobalt background.