The influence of cerium surface addition on low-pressure oxidation of pure iron at high temperatures

Pure iron oxidation is studied in oxygen partial pressures ranging between p(O-2) = 2 x 10(-4) Pa and p(O-2) = 4 x 10(-2) Pa. These pressures were chosen in order to insure wustite formation in the temperature domain 700-1050 degrees C, Texture analysis and pole figure plotting is made on specimens oxidized at 800 and 950 degrees C under the oxygen partial pressure p(O-2) = 2 x 10(-3) Pa. We have demonstrated that cerium coatings modify the microstructure and texture of a wustite scale grown on pure iron. All the results indicate that the main effect of the coating is to prevent epitaxial relations between iron and the wustite scale. Then, all the surface is covered by a fast growing scale, The pole figures show that the (100) planes of the wustite structure are mainly oriented parallel to the specimen surface. The (100) orientation is always associated with the faster growing scale. On blank specimens, the slow kinetic rate is attributed to the fact that the major part of the iron surface is covered by a non-(100)-oriented wustite scale. A good scale adherence was observed since coating was sufficiently thin and regular to permit the cerium orthoferrite (CeFeO3) formation. This perovskite-type oxide appears to be a good possibility for an homogeneous cerium introduction in oxide scales.