Mechanisms involved by reactive elements upon high temperature chromia scale growth

The influence Of Y2O3, Pr2O3, Nd2O3, Sm2O3 and Yb2O3 coatings on Fe-30Cr alloy oxidation behaviour was investigated at 1000 degreesC in air under atmospheric pressure. Isothermal exposures indicated that the Y2O3 coating was the most protective after 100 hours. Pr2O3. Nd2O3 and Sm2O3 coatings were less effective, but the less beneficial effect was observed when Yb2O3 coating was applied onto the Fe-Cr alloy surface. Two-stage oxidation experiments in O-16(2) and then O-18(2) were performed to get information about the chromia growth phenomena with and without reactive elements. The O-18-tracer distribution was determined by secondary ion mass spectrometry (SIMS) and sputtered neutral mass spectrometry (SNMS). The experiments performed on uncoated samples clearly demonstrated that chromia growth mechanism was controlled by chromium cationic diffusion, whereas on reactive element coated samples the external diffusion of chromium ions was not predominant.