Quantitative determination of the passive layer on Cu–Ni alloys

Copper–nickel alloys are important materials for application in corrosive environments. As for many other systems, this property is a consequence of thin oxide films that are protective in weakly acidic and alkaline solutions. The passive layer formed potentiostatically in 1 M NaOH on Cu50Ni has been examined with XPS and ISS. Angular‐dependent XPS measurements provide an insight into the layered structure of depth profiles that are confirmed qualitatively and quantitatively by ISS sputter depth profiles. A method is presented to evaluate the XPS results on the basis of a multilayer structure. Thicknesses and the composition of the sublayers of the passive film, as well as the composition of the metal surface underneath, are obtained in dependence on electrochemical parameters such as potential and time of passivation. Thus, on obtains not only the chemical structure but also the changes of the passive layer during its formation. A specimen transfer in a closed system from the electrolyte into the ultrahigh vacuum of the spectrometer prevents possible changes of the passive layer. These measurements are a further example of detailed studies of passivating films on technically important alloys.