XPS depth profiling of oxide scales of stainless steels formed in high‐temperature aqueous conditions
ABSTRACT In this work, we studied the oxide scales of AISI 304 and AISI 316 stainless steels formed under high-temperature aqueous conditions using X-ray photoelectron spectroscopy (XPS) together with sputter depth profiling. Two samples of SS 304 and 316 were prepared by exposing them to water at 300 °C containing 100 ppm boric acid and 7 ppm lithium hydroxide in an autoclave.In the case of sputtering with 3 keV argon ions, the elemental distribution as a function of the sputtering time was obtained. The formation of two oxide layers was observed—one mainly iron-based on top, and a second at a greater depth, consisting mainly of chromium-iron oxides. The depth scale of the profiles was calibrated by measuring the oxygen profile using Rutherford backscattering spectroscopy (RBS). On the basis of the distribution of the three oxidised alloying constituents (Fe, Cr, Ni) with respect to depth and elemental state, a relative increase of Fe2+ at the surface was found, while the chromium was depleted at the surface and Cr3+ tended to increase at the oxide/substrate interface. In order to estimate possible ion-beam-induced effects due to the ion sputtering, the profiles were compared to the computer-simulated ones obtained by a dynamic TRIM computer code. The simulations included only collisional effects during the sputtering process. Copyright © 2006 John Wiley & Sons, Ltd.
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ABSTRACT: The corrosion behavior of an austenitic stainless steel (UNS S30400) has been characterized in a 10,000 h test conducted in hydrogenated, ammoniated water at 260 °C. The corrosion kinetics were observed to be parabolic, the parabolic rate constant being determined by chemical descaling to be 1.16 mg dm−2 h−1/2. X-ray photoelectron spectroscopy, in combination with argon ion milling and target factor analysis, was applied to provide an independent estimate of the rate constant that agreed with the gravimetric result. Based on the distribution of the three oxidized alloying constituents (Fe, Cr, Ni) with respect to depth and elemental state, it was found that: (a) corrosion occurs in a non-selective manner, and (b) the corrosion film consists of two spinel oxide layers––a ferrite-based outer layer (Ni0.2Fe0.8)(Fe0.95Cr0.05)2O4 on top of a chromite-based inner layer (Ni0.2Fe0.8)(Cr0.7Fe0.3)2O4. These compositions agree closely with the solvi phases created by immiscibility in the Fe3O4–FeCr2O4 binary, implying that immiscibility plays an important role in the phase separation process.Corrosion Science 10/2002; · 3.62 Impact Factor
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ABSTRACT: The oxidation and subsequent vacuum annealing of an Fe/Cr alloy has been studied by X-ray photo-electron spectroscopy (XPS). In addition to the conventional ways of extracting compositional depth information with this spectroscopy (i.e. by ion sputtering and angle resolved XPS), a special study has been made of the use of energy loss features within the XPS spectra to provide such information. There are three classes of energy losses that may prove useful: (i) the height of the inelastically scattered electron background immediately adjacent to the peak of interest which is defined by the term electron energy loss tail height (ELTH), (ii) the slope of the background some distance (e.g. 25 eV) from the photo-electron peak, the post-peak slope (P-PS), and (iii) the slope of the base line associated with the spectrum itself. The former categories provide definitive information concerning the hierarchy of discrete layers on the surface of a material, whilst the latter provides a means of identifying subtle concentration gradients that exist within the XPS sampling depth. The use of these methods in addition to the more conventional depth profiling studies have enabled a series of comprehensive models to be proposed for the formation of passivating layers on the Fe/Cr alloy in a variety of oxidation and reduction conditions at modest temperatures (200–300°C). The methods described have the added advantage that they provide the electron spectroscopist with the possibility of carrying out a retrospective depth profile long after the analysis has been completed.Corrosion Science. 01/1990;
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ABSTRACT: The oxide film formed on type 304 stainless steel (SS, UNS S30400) i high-temperature, high-purity water containing oxygen (Oâ), hydrogen (Hâ), and hydrogen peroxide (HâOâ) was analyzed by Auger electron spectroscopy (AES), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Electrochemical corrosion potential (ECP) measurements also were conducted under various water chemistry conditions. A more rapid shift of ECP to the noble direction was observed when HâOâ was present in 288 C water, compared to ECP values measured at the same levels of Oâ. This could have resulted from electrochemical and/or chemical changes on the oxide film. AES data indicated a thicker oxide was formed under 200 ppb Oâ or 200 ppb HâOâ conditions than under 150 ppb Hâ. The oxide film consisted of two layers: the outer oxide layer with different particle sizes and the inner, fine-grained layer. Structures of the outer oxide particles (large or small) formed in 200 ppb Oâ, in 200 ppb HâOâ, and in 150 ppb Hâ were mainly hematite (Î±-FeâOâ), maghemite (Î³-FeâOâ), and magnetite (FeâOâ), respectively. The inner, fine oxide layers with an iron chromate (FeCrâOâ) structure were formed in 200 ppb Oâ and in 150 ppb HÂ², while HâOâ promoted formation of the Cr-deficient/Ni-enriched magnetite structure (nickel ferrite [NiFeâOâ]) in the inner oxide layer with the Î³FeâOâ structure in the outer oxide particles.Corrosion. 01/1999; 55(1):81-88.