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 mea sured by thermogravimetry, was approximately parabolic. The oxide scal es 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 parti cles. The interface between the two layers reflects the original surfa ce, which shows that the outer part grows by outward Cu diffusion via vacancies. The inner part grows by outward diffusion of copper and inw ard transport of gaseous oxygen by the dissociative-transport mechanis m. The amount of porosity, the relative thickness of the inner layer c ompared to the total thickness of the scale, and the oxidation rate as function of Ni content was dependent on the reaction conditions.