Synthesis of Ni-Co alloy nanocrystalline powder by a novel chemical method and their characterization

Abstract

The bimetallic or trimetallic alloy nanoparticles (NPs) are sought after in different applications due to their enhanced activity caused by the synergistic characteristics and increased surface area inherent to nano particles. The Ni-Co nanoparticles (NPs) have wide applications in biomedical field, magnetic storage media, ferrofluids, hydrogen storage, generation of hydrogen and catalytic oxidation reactions due to their good chemical stability and high magnetic anisotropy. Ultrafine particles of Ni-Co alloy were synthesized by a novel chemical method in aqueous medium using aluminum as a reducing agent. The uniqueness of this approach is that there is no need of any extra inert atmosphere to conduct the NPs synthesis. The Ni-Co alloy particles were obtained by co-reducing the nickel and cobalt metal precursors in the desired molar ratios with fixed quantity of aluminum powder. The Ni-Co NPs synthesized were having grain size less than 20 nm. The effect of cobalt content on the structure and magnetic properties of Ni-Co alloys were studied. It was observed that the formation of Ni-Co NPs alloy proceeded upto 70 % of Co. Compositional analysis showed that the precursor ratio was almost preserved in the Ni-Co alloy powders. X-ray diffraction indicated FCC structure for Ni-Co solid solution. The annealing of the synthesized Ni-Co NPs at 400 ˚C in furnace for an hour (in nitrogen atmosphere) indicated forming of well defined FCC crystalline peaks. Saturation magnetization increased as a function of Co content in Ni-Co alloy and the alloy with high Co content saturates only at a high field.