The Oxidation of Two Fe-Nb Alloys Under Low Oxygen Pressures at 600-800℃

摘要

The oxidation of two Fe-Nb alloys containing 15 and 30 wt.% Nb has been studied at 600-800℃ under low oxygen pressures, similar to those prevailing in environments of the coal-gasification type. The reaction produced only an internal oxidation of niobium to form two niobium oxides (NbO_2 and Nb_2O_5) and in some cases a double Fe-Nb oxide. The kinetics of this reaction were very slow at 600℃ but rather fast at 700 and 800℃. A peculiar feature of the internal oxidation of these alloys is that the distribution of the internal oxides follows closely that of the Nb-rich phase in the original two-phase alloys. This behavior, as well as the lack of formation of external scales of niobium oxides, is mainly a result of the limited solubility of niobium in iron and of the consequent presence of two metal phases in the alloys.