Some characteristics of Ni-Co alloy powders electrodeposited from dilute sulphate baths

Abstract

Electrodeposition of Ni-Co alloy powder was carried out utilizing dilute sulphate electrolytes containing concentrations of Ni 2+ and Co 2+ ions within the range found in some industrial effluents. The electrolytes examined had the composition 0.0125 – 0.0750 mol l -1 NiSO 4·6H 2O, 0.0125 – 0.0500 mol l -1 CoSO 4·7H 2O, 0.23 – 1.00 mol l -1 (NH 4) 2SO 4, 0.2 – 0.4 mol l -1 H 3BO 3 and 0.07 mol l -1 Na 2SO 4·10H 2O. The effects of the bath constituents, pH and current density on some characteristics of the alloy were investigated. Increased concentration of NH + 4 ion in the bath was found to increase both the cathode potential and current efficiency and decrease the nickel content of the alloy. The cathode potential decreased with increasing concentration of either of the metal ions in the bath; a corresponding increase in the current efficiency and the metal content in the alloy were also observed. An increase in pH increased the cathode potential and current efficiency without appreciably affecting the alloy composition. The catalytic activity of the alloy powder towards the decomposition of 0.4% H 2O 2 solution increased with increase in the concentrations of NH + 4 and/or CO 2+ ions in the bath and with raising the pH. The surface morphology of the alloy powder was greatly influenced by the above-mentioned variables. The structure of the alloy, as revealed by X-ray diffraction studies, was dependent on its composition.