ELECTRODEPOSITION MECHANISM OF NI-MO-P ALLOY IN THE SOLUTION OF AMMONIAC CITRATE

The induced codeposition mechanism of Mo, P and Ni from the solution o f ammoniac citrate was studied by means of steady-state polarization, AC impedance and X-ray Photoelectron Spectroscopy (XPS). The result of electrochemical measurements proved that [NiCit(NH3)(2)](-) is the el ectro-active species of nickel, though nickel ions exist mainly as [Ni Cit(NH3)(3)](-) in ammoniac citrate. XPS experiments proved the existe nce of tetravalent molybdenum corresponding to MoO2 on the surface of some deposits. The intermediate product, MoO2, was probably reduced to Mo in the alloy deposit by atomic hydrogen adsorbed on the induced me tal nickel. The reduction of H2PO2- occurs through two distinctive ste ps with PH3 as an, intermediate, which subsequently reacts with atomic hydrogen to form P in the alloy deposit. The electrodeposition mechan ism was proposed in this paper.