Determination of milling parameters useful on the formation of CoSb3 thermoelectric powders by low-energy mechanical alloying

In this paper, CoSb3 polycrystalline powders were prepared from the raw material powders of Co and Sb using a combined process of mechanical alloying and heat treatment. Ball milling parameters: weight ratio of ball to powder (BPR) and milling times (t(M)) in the low energy planetary ball mill of CoSb3 powder were optimized. The milled samples were characterized through X-ray diffraction, scanning electron microscopy, thermogravimetric analysis, dynamic light scattering, Raman spectroscopy and heat capacity. By using a simplified model, the mechanical milling parameters as collision duration, contact radius, compression of the balls, average maximum impact pressure on the contact surfaces and temperature of collision, were calculated. We have attempted to quantify the energy transferred per impact and per unit of mass for the formation of CoSb3. Our results predict that the optimum cumulative kinetic energies required for mechanical activation of the first trace of CoSb3 powder by grinding media was found to 10 kJ/g for BPR 80:1 with t(M) = 5 h. A close relation between this energy and the enthalpy of formation was observed.