| 1. |
- Ahmed, Istaq, 1972, et al.
(författare)
-
Structural study and proton conductivity in Yb-doped BaZrO3
- 2007
-
Ingår i: Solid State Ionics. - 0167-2738. ; 178:(7-10), s. 515-520
-
Tidskriftsartikel (refereegranskat)abstract
- Traditional solid state sintering has been used to prepare the perovskite BaZr0.9Yb0.1O3-delta. Analysis of X-ray powder diffraction data shows that an increase of the unit cell parameter, a, was observed compared to undoped BaZrO3. Rietveld analysis of room temperature neutron powder diffraction data confirmed cubic symmetry (space group Pm-3m). Dynamic thermogravimetric analysis (TGA) indicates that the hydration process occurs below 200 degrees C. The strong O-H stretch band, 2500-3500 cm(-1), in the infrared absorbance spectrum clearly manifests the presence of protons in the hydrated material. Proton conductivity was investigated on hydrated and as-prepared samples under dry and wet atmospheres, respectively. Keywords: X-ray diffraction; neutron diffraction; Rietveld refinement; proton conductor; perovskite
|
|
| 2. |
- Canovic, Sead, 1979, et al.
(författare)
-
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
-
Ingår i: Journal of the Electrochemical Society. - : The Electrochemical Society. - 1945-7111 .- 0013-4651. ; 157:6, s. C223-C230
-
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.
|
|
| 3. |
- Engkvist, Josefin, 1972, et al.
(författare)
-
Oxidation of FeCrAl foils at 500-900 degrees C in dry O-2 and O-2 with 40% H2O
- 2009
-
Ingår i: Materials at High Temperatures. - 0960-3409 .- 1878-6413. ; 26:2, s. 199-210
-
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.
|
|
| 4. |
|
|
| 5. |
|
|
| 6. |
- Götlind, Helena, 1978, et al.
(författare)
-
The effect of water vapor on the initial stages of oxidation of the FeCrAl alloy Kanthal AF at 900 degrees C
- 2007
-
Ingår i: Oxidation of Metals. - 1573-4889 .- 0030-770X. ; , s. 251-266
-
Tidskriftsartikel (refereegranskat)abstract
- The effect of water vapor on the initial stages of oxidation of the FeCrAl alloy Kanthal AF is reported. Polished samples were exposed isothermally at 900 degrees C for 1, 24, 72 and 168 h in a well-controlled environment consisting of dry O-2 or O-2 + 40% H2O. The samples were investigated using a combination of gravimetry and several surface-analytical techniques, including XRD, SEM, EDX, FIB, AES and TEM. The presence of water vapor significantly accelerates oxidation during the first 72 h. A two-layered oxide forms in both the dry and wet environments. The bottom layer consists of inward-growing alpha-Al2O3 while the outer layer initially consists of outward-growing gamma-Al2O3. A straight and narrow Cr-enriched band is present at the top of the lower (alpha-Al2O3) oxide, corresponding to the original sample surface. In dry O-2, the top (gamma-Al2O3) layer is converted into a mixture of gamma-Al2-x (Mg,Fe) (x) O-3-(x/2),O- MgAl2O4 and alpha-Al2O3. This transformation does not occur in O-2 + H2O. The initial acceleration of oxidation by H2O is attributed to the stabilization of the outward-growing gamma-alumina layer by the hydroxylation of the gamma-Al2O3 surface. A schematic mechanism of the early stages of oxidation of FeCrAl alloys is presented, emphasizing the influence of water vapor.
|
|
| 7. |
- Liu, Fang, 1975, et al.
(författare)
-
Cyclic oxidation of two FeCrAlRE foils at 1100 oC - The influence of the concentration of minor alloying elements on scale microstructure
- 2008
-
Ingår i: Materials Science Forum. - 1662-9752 .- 0255-5476. ; 595-598, s. 707-716
-
Konferensbidrag (refereegranskat)abstract
- Two FeCrAlRE alloys, a commercial, 0C404, and a model alloy in the form of thin foils,with different Mn, Nb, Mo and Ti concentrations were subjected to cyclic oxidation in lab air at1100°C. The oxidized samples were studied by gravimetry, Grazing-Incidence X-ray Diffraction(GI-XRD), Scanning Transmission Electron Microscopy (STEM), and Energy Dispersive X-ray(EDX) analysis. The two FeCrAl alloys exhibit different oxidation kinetics; however, both alloyshave the same weight gain after 500 hours exposure. During the early stages the scale consistsmainly of α-Al2O3 together with some oxide particles containing Mn, Al, Fe and Cr formed on thealloys. After 500 hours the 0C404 scale locally also consists of larger polycrystalline regions ofMn-Cr-Al spinel. In addition, Si-rich oxide, chromia and Al-Cr oxide could be observed at themetal/oxide interface.
|
|
| 8. |
- Liu, Fang, 1975, et al.
(författare)
-
Early stages of the oxidation of a FeCrAlRE alloy (Kanthal AF) at 900 °C: A detailed microstructural investigation
- 2008
-
Ingår i: Corrosion Science. - : Elsevier BV. - 0010-938X. ; 50:8, s. 2272-2281
-
Tidskriftsartikel (refereegranskat)abstract
- Early stages of the evolution of Al2O3 scales formed on a FeCrAlRE alloy (Kanthal AF) have been investigatedby analytical TEM. The samples were oxidized isothermally at 900 °C in dry O2 or O2 + 40% H2O for1 h or 24 h. All oxide scales exhibited a two-layered structure, with a continuous inward growing a-Al2O3inner layer and an outward growing outer layer. After 1 h, the outer oxide layer consisted of c-Al2O3 inboth environments. After 24 h exposure in dry O2, the c-Al2O3 in the outer oxide layer was partly transformedto a-Al2O3 and spinel oxide (Mg1-xFexAl2O4). In contrast, the c-Al2O3 in the outer layer was nottransformed after 24 h in O2 + 40% H2O, showing that water vapour stabilizes c-Al2O3. All oxide scalescontained a Cr-rich band, a product of the initial oxidation. The inner a-Al2O3 layer is suggested to nucleateon Cr2O3 or Cr2-xFexO3 in the initial oxide.
|
|
| 9. |
- Liu, Fang, 1975, et al.
(författare)
-
TEM Investigation of the Microstructure of the Scale Formed on a FeCrAlRE Alloy at 900 A degrees C: The Effect of Y-rich RE Particles
- 2010
-
Ingår i: Oxidation of Metals. - : Springer Science and Business Media LLC. - 1573-4889 .- 0030-770X. ; 74:1-2, s. 11-32
-
Tidskriftsartikel (refereegranskat)abstract
- Three oxide features: the thin and smooth protective oxide, reactive element (Ti-, Zr- or Y-rich) particles, and patches of thick oxide surrounding the Y-rich reactive element particles, were observed on a commercial FeCrAlRE alloy, Kanthal AF, exposed at 900 A degrees C. The microstructural development of the patches of thick oxide was investigated on samples exposed for 24 or 168 h in either dry O-2 or O-2 + 40% H2O. Analytical transmission electron microscopy in combination with site-precision TEM sample preparation by FIB/SEM was used. In all patches a thin but continuous inward growing alpha-Al2O3 layer was formed under a thick outward growing alumina layer, which initially consisted only of gamma-Al2O3. In dry O-2, transformation of gamma-Al2O3 (in the outer layer) to alpha-Al2O3 had started during 24 h and a considerable amount of gamma-Al2O3 had transformed after 168 h. The transformation originated immediately above the inward growing alpha-Al2O3. No such transformation occurred in O-2 + H2O. The possible effects of the Y-rich RE particles, as well as the effects of water vapour, on the oxidation were discussed.
|
|
