Oxide scales which had formed upon samples of pure or La-doped Co-40%Cr alloy were studied. The self-diffusivity of Cr in the scales was measured (figure 1), at temperatures of between 1473 and 1573K, by using a diffusion-evaporation method. It was found that the rate of Cr self-diffusion in the scale on La-doped alloys (2 x 1016/cm3) was more than an order of magnitude lower than that in the scale on undoped alloy. Also, the activation energy for diffusion in the undoped alloy was equal to 364kJ/mol, while that for diffusion in the doped alloy was equal to 422kJ/mol. It was concluded that reactive elements did not completely block the outward diffusion of cations.

A.Gil, S.Mrowec, J.Jedlinski, G.Borchardt: Solid State Ionics, 1992, 58[1-2], 13-21

Figure 1

Diffusivity of Cr in Cr2O3