| 1. |
- Ingemarsson, Linda, 1972, et al.
(författare)
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Oxidation behavior of a Mo (Si, Al)(2)-based composite at 300-1000 degrees C
- 2010
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Ingår i: Intermetallics. - : Elsevier BV. - 0966-9795 .- 1879-0216. ; 18:4, s. 633-640
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Tidskriftsartikel (refereegranskat)abstract
- The oxidation behavior of a Mo (Si,Al)(2)-based composite of Mo(Si,Al)(2), Al2O3 and Mo-5(Si,Al)(3) (Kanthal Super ER) in synthetic air was investigated. The samples were oxidized isothermally for up to 72 h at 300-1000 degrees C using a thermobalance. The microstructure was analyzed by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and Auger Electron Spectroscopy (AES) depth profiling. Broad ion beam milling (BIB) was used to prepare cross-sections. Oxidation behavior depended strongly on the composition of the substrate which consisted of a Mo(Si,Al)(2) matrix and the minority phases Mo-5(Si,Al)(3) and Al2O3. At 300-500 degrees C the mass gains were small with parabolic kinetics, oxidation resulting in a mixture of oxides that reflects the substrate composition. At 600 and 700 degrees C the oxide scale is thin and protective and depleted in molybdenum, a mass loss occurring due to MoO3 vaporization. At 1000 degrees C a protective alpha-alumina scale forms.
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| 2. |
- Canovic, Sead, 1979, et al.
(författare)
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Microstructural Investigation of the Initial Oxidation of the FeCrAlRE Alloy Kanthal AF in Dry and Wet O-2 at 600 and 800 degrees C
- 2010
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Ingår i: Journal of the Electrochemical Society. - : The Electrochemical Society. - 1945-7111 .- 0013-4651. ; 157:6, s. C223-C230
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Tidskriftsartikel (refereegranskat)abstract
- The FeCrAlRE (where RE is reactive element) alloy Kanthal AF was exposed isothermally at 600 and 800 degrees C for 72 h in dry O-2 and in O-2 with 10 vol % H2O. The mass gains were 3-5 times higher at the higher temperature. The presence of water vapor increased the oxidation rate at 800 degrees C, while no significant effect was observed at 600 degrees C. A thin two-layered oxide formed at 600 degrees C: an outer (Fe, Cr)(2)O-3 corundum-type oxide, containing some Al, and an inner, probably amorphous, Al-rich oxide. At 800 degrees C a two-layered oxide formed in both environments. The inner layer consisted of inward grown alpha-Al2O3. In dry O-2 the originally formed outward grown gamma-Al2O3 had transformed to alpha-Al2O3 after 72 h. Water vapor stabilized the outward grown gamma-Al2O3 and hence no transformation occurred after 72 h in humid environment. RE-rich oxide particles with varying composition (Y, Zr, and Ti) were distributed in the base oxide at both temperatures and in both environments. The RE-rich particles were separated from the alloy substrate by a layer of Al-rich oxide. At 800 degrees C the Y-rich RE particles were surrounded by thick oxide patches in both dry and humid O-2.
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| 3. |
- Engkvist, Josefin, 1972, et al.
(författare)
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Alumina scale formation on a powder metallurgical FeCrAl alloy (Kanthal APMT) at 900-1100°C in dry O2 and in O2 + H2O
- 2010
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Ingår i: Oxidation of Metals. - : Springer Science and Business Media LLC. - 1573-4889 .- 0030-770X. ; 73:1, s. 233-253
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Tidskriftsartikel (refereegranskat)abstract
- A Rapidly Solidified Powder (RSP) metallurgical FeCrAl alloy, Kanthal APMT, was exposed in dry and humid O-2 for 72 h at 900-1,100 A degrees C. The formed oxide scales were characterized using gravimetry in combination with advanced analysis techniques (SEM, EDX, TEM, XRD, AES and SIMS). The oxide scales were at all exposures composed of two-layered alpha-Al2O3 scales exhibiting a top layer of equiaxed grains and a bottom layer containing elongated grains. A Cr-rich zone, originating in the native oxide present before exposure, separated these two layers. The top alpha-Al2O3 layer is suggested to have formed by transformation of outwardly grown metastable alumina, while the inward-grown bottom alpha-Al2O3 layer had incorporated small Zr-, Hf- and Ti-rich oxide particles present in the alloy matrix. The scale also contained larger Y-rich oxide particles. Furthermore, in the temperature range studied, the presence of water vapour accelerated alloy oxidation somewhat and affected scale morphology.
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| 4. |
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| 5. |
- Engkvist, Josefin, 1972, et al.
(författare)
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Oxidation of FeCrAl foils at 500-900 degrees C in dry O-2 and O-2 with 40% H2O
- 2009
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Ingår i: Materials at High Temperatures. - 0960-3409 .- 1878-6413. ; 26:2, s. 199-210
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Tidskriftsartikel (refereegranskat)abstract
- High temperature resistant FeCrAl alloys are frequently used in high temperature applications Such as heating elements and metal based catalytic converter bodies. When exposed to high temperatures an adherent, slowly growing, dense aluminium oxide layer forms on the surface, which protects the underlying alloy from severe degradation. The composition, structure and properties of the formed oxide layer are strongly dependent on the alloy composition, temperature and oxidation environment. In this study, the Sandvik 0C404 FeCrAl alloy, in the form of 50 mu m thick foils, was exposed isothermally in the temperature range 500-900 degrees C for 168 hours in dry O-2 and in O-2 with 40 vol.% H2O. The surface morphology, composition and microstructure of the grown oxide scales were characterized by using scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), grazing incidence X-ray diffraction (GI-XRD), Auger electron spectroscopy (AES), and time of flight secondary ion mass spectrometry (TOF-SIMS). The oxidation process was faster at 900 degrees C than at 500 and 700 degrees C. At 500 degrees C a thin (10-20 nm) mixed oxide of Fe, Cr and Al was formed. Exposure at 700 degrees C resulted ill a similar (40-50 nm) duplex oxide, in both dry O-2 and in O-2 With 40 vol.% H2O. These oxide scales consisted of all inner and an outer relatively pure alumina separated by a Cr-rich band. This type of duplex oxide scale also formed at 900 degrees C with a thin inward growing alpha-Al2O3 at the oxide/metal interface and an outward growing layer outside a Cr-rich band. However, at 900 degrees C the Outward growing layer showed two types of oxide morphologies; a thin smooth base oxide and a much thicker nodular oxide grown on top of substrate ridges. In dry O-2 atmosphere, the main part of this outward growing layer had transformed to alpha-Al2O3. Only in the outer part of the thick oxide nodules, metastable alumina was found. When exposed in the presence of water vapour the main pall of the metastable alumina remained untransformed.
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| 6. |
- Engkvist, Josefin, 1972, et al.
(författare)
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The initial effect of KCl deposit on alumina scales characterized by ToF-SIMS and AES
- 2013
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Ingår i: Surface and Interface Analysis. - : Wiley. - 1096-9918 .- 0142-2421. ; 45:1, s. 445-448
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Tidskriftsartikel (refereegranskat)abstract
- A FeCrAl alloy was preoxidized to form a protective alumina scale, and the effect of KCl deposits on the alumina scale was investigated while exposed during 1 and 24 h at 600 degrees C. However, impurity concentrations in the alumina scale change the ion conductivity and hence affect its protective properties. Therefore, Auger electron spectroscopy and time-of-flight secondary ion mass spectrometry were used to characterize the alumina scales and detect traces of K and Cl. The results showed that K and Cl existed as large sharp-edged crystals surrounded by a dendritic network after 1 h. However, after 24 h, those were dissolved, and K together with Cl was detected only in the outer layer of the duplex alumina scale, which was formed during preoxidation.
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| 7. |
- Israelsson, Niklas, 1983, et al.
(författare)
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KCl-Induced Corrosion of an FeCrAl Alloy at 600°C in O2 + H2O Environment: The Effect of Pre-oxidation
- 2015
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Ingår i: Oxidation of Metals. - : Springer Science and Business Media LLC. - 1573-4889 .- 0030-770X. ; 83:1-2, s. 29-53
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Tidskriftsartikel (refereegranskat)abstract
- The present study investigates the influence of H2O and KCl on the high temperature corrosion of an FeCrAl alloy at 600 A degrees C. Polished samples were exposed to O-2 or O-2 + H2O and to O-2 + H2O with KCl applied. The samples were investigated using SEM/EDX, XRD, IC, AES and SIMS. It was found that KCl accelerates corrosion and that a rapidly growing iron-rich oxide forms with time. Chromate formation is shown to initiate the formation of a non-protective oxide scale. Pre-oxidising the alloy before exposure in the presence of KCl had a strongly beneficial effect on the corrosion.
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| 8. |
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| 9. |
- Ulf, Bexell, et al.
(författare)
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Comparing 69Ga+ and C60+ for ToF-SIMS sputter depth profiling in a Cr2O3 formed during oxidation of a Ce coated FeCr steel substrate
- 2012
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Ingår i: 8th European Workshop on Secondary Ion Mass Spectrometry, SIMS Europe 2012, Münster, Germany, 9-11 September 2012.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Ferritic (FeCr) stainless steel is often used as interconnects in solid oxide fuel cells (SOFCs) at temperatures between 650-850°C. The chromia (Cr2O3) scale formed upon high temperature exposure has good electron conductivity, but can be further improved by using suitable coatings. Since the electron conductivity in the Cr2O3 scale is crucial for interconnects, the ability to accurately determine the distribution of elements of low concentration are highly important. Hence this study concerns Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS) depth profiling in a 200 nm thin Cr2O3 scale formed on a Ce-coated ferritic stainless steel after exposure at 850°C during 1h. The aim is to investigate the effects of using different sputtering ions. Depth profiles were made using two different ToFSIMS instruments and the obtained sputter depth profiles were compared to a TEM-EDX map of the scale cross section. In the IONTOF TOF-SIMS V instrument C60 + at 10 keV and 700 pA was used for sputtering and Bi3 + at 25keV and 0.15 pA was used for analysis. In the PHI TRIFT II instrument a pulsed Liquid Metal Ion Gun (LMIG) with 69Ga+ at 15 keV and 600 pA was used. In both instruments depth profiles were obtained by sputtering a surface area of 50x50 μm2 and analyzing an area of 25x25 μm2. Furthermore, the effect of having oxygen present in the chamber to a pressure of 1x10-6 torr during analysis in the PHI TRIFT II instrument was investigated. The results showed that the oxide scale was composed of two equally thick layers, an outer Cr/Mn rich layer (100 nm) and an inner Cr rich layer (100 nm). The Ce from the surface coating was observed between those two layers. Additionally, a thin layer (~10nm) rich in Fe/Mn was observed at the outermost oxide surface and Ti was observed in the inner Cr rich layer. The depth profiles obtained by the two SIMS instruments showed similarities in the way of revealing the outer Cr/Mn rich layer and the inner layer richer in Cr as well as the outermost thin Fe/Mn rich layer. However, the Ce enrichment was more clearly revealed using the IONTOF instrument and the enrichments of Mn and Ti at the oxide/metal interface were more obvious in the PHI TRIFT II depth profile. The presence of oxygen enhanced the yield of Fe and Cr when entering the steel matrix. The sputter craters were investigated using a Zeiss ULTRA 55 Scanning Electron Microscope (SEM). A topographic surface results after sputtering with 69Ga+. The presence of oxygen in the chamber significantly decreased that topography although without enhancing the depth resolution in the profile. In the IONTOF C60+ sputter crater a relatively smooth topography was observed. However, a large amount of carbon was deposited, which is believed to deteriorate the depth resolution when analyzing thick layers. Nevertheless, it can be concluded that C60+/Bi3+ renders better depth resolution in thin layers compared to 69Ga+, while carbon deposition from C60+ sputtering makes 69Ga+ a more suitable alternative for thick layers.
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