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Quantitative studies of the initial oxidation stages of FeCrNi alloys using factor analysis and least‐squares fitting methods applied to low‐energy AES spectra
Author(s) -
Steffen H. J.,
Hofmann S.
Publication year - 1992
Publication title -
surface and interface analysis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.52
H-Index - 90
eISSN - 1096-9918
pISSN - 0142-2421
DOI - 10.1002/sia.740190130
Subject(s) - oxide , oxygen , chemisorption , alloy , metal , chemistry , monolayer , analytical chemistry (journal) , oxidation state , nickel , transition metal , spectral line , inorganic chemistry , catalysis , adsorption , biochemistry , physics , organic chemistry , chromatography , astronomy
The oxidation behaviour of the alloys Fe–19 at.% Cr–9 at.% Ni and Ni–40 at.% Fe–20 at.% Cr was studied in situ at room temperature and oxygen pressures below 10 −4 Pa by AES using low‐energy M 23 VV transitions between 20 and 70 eV. Quantitative determination ofthe relevant components by factor analysis and least‐squares fitting methods enabled a much more detailed analysis of the initial oxidation stages as compared to earlier studies. For all alloy elements, factor analysis revealed the presence of an intermediate chemical state before oxidation which is due to binding with chemisorbed oxygen. Least‐squares fitting with standrd spectra of the pure elements in their metallic, oxidic and intermediate states disclosed the sequential oxidation of Cr, Fe and Ni with increasing oxygen exposure. Preferential oxygen chemisorption on Cr and oxidation of Cr is accompanied by oxygen‐induced segregation and is followed by Fe and Ni oxidation on top of the previously formed oxide for the Ni‐rich alloy. Nickel oxidation is drastically reduced in Fe‐rich alloys. After exposure to 900 L of oxygen, oxidation results in a layered structure as confirmed by AES sputter depth profiles which can be resolved into oxide and pure metal components. Together with the small electron escape depth of only 2–4 atomic layers, this procedure gives well‐resolved depth distributions within the total oxide thickness of ∼6–7 monolayers for NiFe40Cr20 and 11–12 monolayers for FeCr19Ni9.