Electrodeposition of well-crystalline Ni-Co alloy thin films on steel substrates from aqueous solutions containing citrate anions

Abstract

The electrochemical deposition of Ni-Co alloy thin films onto steel coupons was carried out from aqueous solutions containing citrate anion under various operating conditions. The deposition process was investigated from a bath containing MSO4.6H2O, CoSO4.7H2O, Na3C6H5O7.2H2O, and Na2SO4. The impact of bath constituents, applied current, and temperature on current efficacy (CCE) and composition of the alloy was investigated. The plating of the alloy belongs to the regular type, in which the nobler metal (Ni) is preferably deposited. The CCE is very high and rises with a rising [Ni2+] / [Co2+] ratio in the bath and stirring speed of the plating solution. However, it tends to decrease as the current density, temperature, or concentration of citrate ions increases. The quantity of Co metal in the plated alloy is ameliorated with increasing stirring speed, temperature, and Co2+ ions concentration. The appearance and the crystal texture of the coatings were checked by electron microscope and X-ray diffraction tools. The deposits obtained from the given bath are well-crystalline and have an (FCC) structure. The throwing power and throwing index of the tub are estimated and revealed that the alkaline citrate tub has good throwing power.