Rotating cylinder Hull cell study of anomalous codeposition of binary iron-group alloys

The anomalous codeposition of the iron group metals was investigated using the rotating cylinder Hull (RCH) cell. Single metals and binary alloys of iron, nickel and cobalt were deposited in the RCH cell and the partial current densities were determined as a function of length by position sensitive X-ray fluorescence analysis. The measured overall polarization behaviour was used as a boundary condition for the numerical calculation of the potential distribution along the cylinder using the Laplace equation. By combining the results the partial current density potential curves were established. Experiments performed at different rotation rates confirmed the inhibiting effect of the less noble metal on the deposition of the more noble metal. The inhibiting effect of iron on nickel disappeared when iron reached the limiting current. Strong evidence was found that in binary alloy deposition of iron, cobalt and nickel the reaction rate of the less noble metal is promoted by the presence of the more noble component.