Fe 0.88 Cr 0.12 and Fe 0.85 Cr 0.15 alloys exposed to air at 870 K studied by TMS, CEMS and XPS

Investigation of Surface Segregation in Fe-Cr-Si Alloys by XPS

“…As it was shown previously, [10][11][12][13][14][15][16] the addition of Cr and/or Si atoms to a-Fe drastically reduces the oxidation process of iron atoms during exposure to air at high temperature. In particular, the results obtained by the 57 Fe transmission Mo¨ssbauer spectroscopy (TMS) as well as by the conversion electron Mo¨ssbauer spectroscopy (CEMS) for the Fe 0.85 Cr 0.10 Si 0.05 alloy indicate that the high-temperature atmospheric corrosion of this material is almost stopped at 870 K and 1070 K. [16] The most plausible explanation of this behavior could be linked to the strong segregation process of Si and/or Cr atoms to the alloy surface.…”

“…This effect is rather surprising since the surface segregation of Cr atoms occurs in the as-obtained Fe-Cr-Si samples (Table I) as well in many binary Fe-Cr alloys which were studied previously. [4,[8][9][10]14] That result could be compared with the Mo¨ssbauer spectroscopy data obtained for similar systems. [16] One of the conclusions which could be drawn from the high-temperature corrosion study of Fe-Cr-Si alloys is that the addition of a relatively small amount of Cr (£ 5 pct) to the dilute iron-based Fe-Si alloy does not improve the anti-corrosion properties of the alloy.…”

“…9 The first, placed at the lowest BE of 574.7 eV, is related to the Cr 0 , the next two at BE of 576.6 and 577.8 eV correspond to Cr 3+ , and the last one, which is the maximum placed at 579.3 eV, represents Cr 6+ . [14,26] In the case of the Si 2p spectrum (Figure 6(h)), two components at BE of 99.9 and 104.8 eV, related to Si 0 and Si 4+ (SiO 2 ), are distinguished. Here, it is worth noting that the signal from SiO 2 appears for the first time in this work.…”

“…This experimental technique collects data from a surface layer of a few nanometers and provides detailed information about atomic concentration of selected elements as well as types of atomic bonds which are present on the surface of studied material. [17] Moreover, the XPS experiments which were performed for Fe-Cr [4,14] and Fe-Si [7,15] systems gave clear evidence that the enhanced anti-corrosion behavior of these binary alloys is connected with the surface segregation of Cr and Si atoms. Taking the above into account, this work is mainly focused on determination of the influence of the surface segregation process on the corrosion resistance properties of ternary Fe-Cr-Si alloys.…”

“…[11,23] The chromium signal (Figure 2(g)) is at the background level; however, the 2p doublet maxima can be distinguished at the positions around 577.2 eV (2p 3/2 ) and 588.3 eV (2p 1/2 ), which represent Cr 3+ species. [14,26] The Si 2p spectrum is composed of two peaks (Figure 2(h)). The main is at the BE of 102.5 eV and corresponds to Fe 2 SiO 4 (fayalite).…”