On the high-temperature oxidation of Cu-rich Cu-Ni alloys

Cu-2 Wt.%Ni and Cu-5wt. %Ni were oxidized at 800 to 1050 degrees C and oxygen pressures from from 5 x 10(-4) to I atm. The oxidation, as measured by thermogravimetry, was approximately parabolic. The oxide scales could be divided in two main regions: An outer region consisting of copper oxides and an inner porous region, which consists of Cu2O with dispersed NiO particles. NiO particles exists as internal-oxide particles. The interface between the two layers reflects the original surface, which shows that the outer part grows by outward Cu diffusion via vacancies. The inner part grows by outward diffusion of copper and inward transport of gaseous oxygen by the dissociative-transport mechanism. The amount of porosity, the relative thickness of the inner layer compared to the total thickness of the scale, and the oxidation rate as function of Ni content was dependent on the reaction conditions.