Effect of Impurities (Carbon and Manganese) on Iron Oxidation at High Temperature: Impurties-Rare Earth Element (Cerium) Interactions

摘要

After oxidation of ceria coated iron specimens, (T = 700deg C, pO_2 = 0.04 Pa), cerium is located inside the wustite matrix as a CeFeO_3 phase. The CeFeO_3 formation is attributed to an oxido-reduction process between the CeO_2 coating and the FeO nuclei at the beginning of the oxidation test. On ceria coated Fe-Mn-C steel samples, carbon and manganese impurities have a strong influence on the oxidation rate and on the rare-earth element location. After the coated steel oxidation, cerium is located at the scale-gas interface as a CeO_2 phase and it is not incorporated inside the iron oxide scale. The role of each impurity is established: manganese prevents the formation of CeFeO_3 because no contact between the reducing FeO germs and the oxidant CeO_2 phase is permitted. This lack of contact is due to the high vapor pressure of manganese oxides which evaporate at the beginning of the reaction and promote the CeO_2 coating spallation. On the other hand, carbon does not hinder the CeFeO_3 formation but it always favours the wustite scale spallation after some hours oxidation, due to the carbon segregation in the metal at the steel-oxide interface.