The structure and morphology of electrodeposited nickel-cobalt alloy powders

Abstract

Nanostructured nickel and cobalt alloy powder deposits from three different electrolyte compositions were obtained by electrodeposition from an ammonium sulfatechloride solution in a galvanostatic regime. The influence of current density and the Ni2+/Co2+ ratio in the bath on the microstructure and phase composition of the Ni-Co deposits were studied by SEM and X-ray diffraction methods. Both, bath composition and current density influence strongly the deposit growth mechanism as well as the deposit composition, microstructure, grain size and surface morphology. When electrodeposition was performed at high overpotentials, far from equilibrium conditions, face-centered cubic (FCC) mixtures of Ni and Co were generated while at low overpotentials, as well as at higher content of cobalt in the electrolyte, hexagonal close packed (HCP) of Co was formed with a lower rate of hydrogen evolution. The increase in the concentration of HCP phase in the nanocrystalline deposits was caused by increasing the overall Co content in the materials prepared as well as by decreasing deposition current density. Differential scanning calorimetry (DSC) and X-ray diffraction analysis were used to examine the effects of structural changes on magnetic properties of the nanocrystalline powders electrochemically obtained in the temperature interval from room temperature to 650°C. Each stage of the structural changes caused corresponding changes in the magnetic permeability for the alloys prepared. © 2010 by Nova Science Publishers, Inc. All rights reserved.