No abstract

No abstract

The high-temperature corrosion behavior of three polycrystalline Fe-Si alloys containing approximately 4, 5, and 10 at% Si was studied using transmission Mössbauer spectroscopy (TMS), conversion electron Mössbauer spectroscopy (CEMS), and x-ray photoelectron spectroscopy (XPS). The XPS measurements reveal the strong segregation process of silicon atoms to the surface. Moreover, the obtained XPS results suggest that the presence of adsorbed oxygen on the Fe-Si surface effectively enhances the silicon segregation process. On the other hand, the obtained TMS and CEMS spectra show that even 10% of silicon atoms dissolved in the iron matrix do not prevent high-temperature corrosion of the studied Fe-Si alloys. During exposure to air at 870 K, a systematic growth of an α-Fe2O3 compound was observed. Finally, the Mössbauer results show that, during exposure to air, oxygen atoms diffuse to the studied polycrystalline materials not only through the oxide/metal interface on the surface but also along the grain boundaries. Such effects result in the formation of iron oxides in deeper parts of the alloy.

No abstract

The surface segregation of Fe-Cr-Si alloys was studied using the X-ray photoelectron spectroscopy (XPS). The experiment was performed in two stages, for the as-prepared samples and after oxidation process. Analysis of measured XPS spectra allowed one to characterize the changes in the surface chemical composition during the oxidation and thermal treatment procedures. According to the obtained results, it could be stated that the enhanced anti-corrosion properties of the Fe-Cr-Si alloys which contain more than 10 at. pct of Cr and 5 at. pct of Si in the bulk are mainly connected with the strong surface segregation process of both solutes. In the case of alloys which contain less solutes (Fe 0.94 Cr 0.03 Si 0.03 , Fe 0.90 Cr 0.05 Si 0.05), the behavior of Cr atoms is different during the oxidation process. Chromium does not segregate to the surface, instead it diffuses into deeper parts of the material leaving the surface covered only by silicon and iron oxides. This effect is responsible for much worse corrosion resistance of the Fe 0.94 Cr 0.03 Si 0.03 and Fe 0.90 Cr 0.05 Si 0.05 alloys.