Milling Characteristics of Cu and Ni

Abstract

Nanoparticles have a wide range of applications like biological sensors, optoelectronic devices, catalysis and nanofluids. Bulk synthesis of nanoparticles by a feasible and economically viable technique is therefore a major research area. Here, in the present research work two metals having FCC crystal structure, copper (Cu) and nickel (Ni), have been milled in a high-energy planetary ball mill and their milling characteristics have been investigated. Mechanical milling (MM) of pure elemental Cu and Ni powders was carried out in hardened chrome steel medium. Milling was carried out for a period of 20 h using toluene as a process control agent (PCA). As-milled powder samples were taken out at an interval of 5 h of milling. The as-milled powders were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) high resolution transmission electron microscopy (HRTEM), differential scanning calorimetry and thermogravimetric analysis (DCS/TGA) and particle size analyzer. The variation in crystallite size, lattice strain and lattice parameter of Cu and Ni with milling time was determined from the XRD spectra of the various as-milled powder samples of Cu and Ni. It has been found that both elemental Cu and Ni could be reduced to nanometric dimension within 5 h of milling. From both the XRD and HRTEM analysis of the 20 h milled Cu and Ni powders it could be confirmed that the crystallite size of Cu ( 27 nm) was higher than that of the Ni ( 20 nm). This can be attributed to the higher ductile nature of Cu as compared to Ni which does not allow Cu to be reduced to very fine size. Copper oxide (CuO) peaks could be seen in the XRD plot of the 20 h milled powder of Cu whereas no oxide peaks of Ni could be seen in the XRD plot of 20 h milled Ni. The 20 h milled Cu powder was also heat-treated at 200, 400 and 600oC and the thermal stability of the nanostructured Cu powder was analyzed using various analytical techniques.