A Study of the Electrochemistry and Morphology of Electrodeposited Nickel-Molybdenum Alloys

Summary

The electrodeposition of Ni-Mo alloys from ammoniacal citrate solutions has been studied under potentiostatic conditions. Polarization data for the individual cathode reactions show that deposition is principally diffusion controlled through a cathode layer whose resistance is substantially independent of overpotential; a limiting current density for alloy deposition of ca 0·08 A/cm² is reached when the local nickel ion activity falls to zero. Satisfactory deposits are hard (650 VPN), bright, cracked and highly stressed and they possess a randomly orientated microcrystalline structure on a scale of ca 400Å. Although the deposits are nodular, with diameters of 1–5 μm depending on deposit thickness, the nodules are smooth and generally less than hemispherical. At overpotentials greater than 1·0V, the nodules tend to be larger and more complex; besides being more completely spherical they agglomerate to form columnar outgrowths. Such deposits are dull, softer (350 VPN) and more ductile.