Effect of saccharin and thiourea on electrodeposition of cobalt and characteristics of deposits

Cobalt electrodeposits have been produced from two types of baths. In the bath containing cobalt sulphate, cobalt chloride and boric acid, saccharin is found effective as a brightener additive. In the bath containing cobalt sulphate, potassium chloride and potassium citrate, thiourea is found to be effective as a brightener additive. Results of solution characteristics such as conductivity of the electrolytes, cathode current efficiency and rate of deposition are compared. The effect of additives on brightness, roughness, orientation of the crystal, grain size and surface morphology of the cobalt deposits are reported. The X-ray diffraction pattern obtained for electrodeposited cobalt showed a polycrystalline nature with hexagonal close packed structure. A smooth uniform and pore free surface was observed under scanning electron microscopy and atomic force microscopy analysis. Potentiodynamic polarisation and electrochemical impedance measurements in sodium chloride solution showed that a higher corrosion resistance was observed for the deposit from the second type of bath containing an additive.