TY  - THES
AU  - Michalik, Marek
AU  - Hänsel, Michael
AU  - Quadakkers, Willem J.
TI  - Effect of water vapour on growth and adherence of chromia scales on pure chromium
VL  - 67
PB  - RWTH Aachen
VL  - Dr. (Univ.)
CY  - Jülich
M1  - PreJuSER-58936
SN  - 978-3-89336-486-2
T2  - Schriften des Forschungszentrums Jülich. Reihe Energietechnik / Energy Technology
PY  - 2007
N1  - Record converted from VDB: 12.11.2012
N1  - RWTH Aachen, Diss., 2007
AB  - The oxidation behaviour of chromium was studied in the temperature range 950 to 1050$^{\circ}$C. A number of atmospheres such as Ar-O$_{2}$, Ar-H$_{2}$-H$_{2}$O, and more complex N$_{2}$-O$_{2}$-H$_{2}$O and N$_{2}$-H$_{2}$-H$_{2}$O were used, to allow the effects of oxygen and water vapour partial pressures to be determined. It was shown that the oxide scale formed in Ar-O$_{2}$ environments was dependent on the oxygen partial pressure. Decreasing the pO$_{2}$ in such gas mixtures lowered the oxidation rate and improved scale adherence. Different behaviour was found in Ar-H$_{2}$-H$_{2}$O. Scale adherence remained good in all low pO$_{2}$ gases and decreasing the pO$_{2}$ in the gas (this was done by using gases of higher H$_{2}$/H$_{2}$O ratio) led to an increase in the oxidation rate. The main finding of the work was that the oxide scale formed on chromium in Ar-H$_{2}$O and Ar-H$_{2}$- H$_{2}$O gases significantly differs from that formed in Ar-O$_{2}$. It appeared that oxide grains were much smaller in low pO$_{2}$ gases containing water vapour than in dry high pO$_{2}$ gases. It is believed that this effect of water vapour on the oxide morphology development is due to the faster adsorption and dissociation of H$_{2}$O at the outer surface compared with O$_{2}$, which enhance the inward transport of oxygen ions to the metal/oxide interface. It is proposed that increased oxygen grain boundary diffusion is the dominant process but molecular transport of H$_{2}$ and H$_{2}$O through the scale could also operate and contribute to the inner scale growth. The tracer study combined with SNMS techniques showed that in low pO$_{2}$ gases a significant amount of the scale was formed at the metal/oxide interface and this supports the observations that smaller oxide grains promote inward oxygen transport. It was also found that the extent of inward growth was higher in Ar-H$_{2}$-H$_{2}$O than in Ar-H$_{2}$O gas. This may indicate that the oxygen partial pressure of the gas or the hydrogen partial pressure were also factors determining the oxidation behaviour in low pO$_{2}$ gases. [...]
LB  - PUB:(DE-HGF)11 ; PUB:(DE-HGF)3
UR  - https://juser.fz-juelich.de/record/58936
ER  -