The effect of water vapor on the initial stages of oxidation of the FeCrAl alloy Kanthal AF at 900 degrees C
Artikel i vetenskaplig tidskrift, 2007

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.

DEPENDENCE

ALUMINA SCALES

DRY O-2

FOILS

HIGH-TEMPERATURE OXIDATION

GROWTH

BEHAVIOR

Författare

Mikael Götlind

Chalmers, Kemi- och bioteknik

Fang Liu

Chalmers, Teknisk fysik, Mikroskopi och mikroanalys

Jan-Erik Svensson

Chalmers, Kemi- och bioteknik, Oorganisk miljökemi

Mats Halvarsson

Chalmers, Teknisk fysik, Mikroskopi och mikroanalys

Lars-Gunnar Johansson

Chalmers, Kemi- och bioteknik, Oorganisk miljökemi

Oxidation of Metals

0030-770X (ISSN) 1573-4889 (eISSN)

251-266

Ämneskategorier

Kemi