Environmental Engineering Reference
In-Depth Information
Figure 6.6
Boundaries of the composition range showing catastrophic oxidation for
Fe-Mo-Cr and Fe-Mo-Ni alloys after 2 h in air at 1273 K [19].
on other oxides, such as Fe
2
O
3
and Cr
2
O
3
, and this fluxing may be further acceler-
ated by the enthalpy of formation of Fe
2
O
3
and Cr
2
O
3
, which tends to increase
the temperature at the alloy-scale interface. In such a situation, Fe
2
O
3
and Cr
2
O
3
are transported through the molten MoO
3
layer and precipitated at the MoO
3
(liquid)-solid oxide interface, which is comparatively cooler.
In the above-described mechanism, it has been assumed that a crack in the
solid oxide initiates catastrophic oxidation. However, it may also be hypothesized
that the crack is the result rather than the initiating cause of such attack. During
Figure 6.7
Mechanism of catastrophic oxidation for Fe-Mo-Cr alloys [19].
