Environmental Engineering Reference
In-Depth Information
Figure 6.11
Oxidation behavior of Cu-Zn-Al alloys [23]. (a) Oxygen uptake of Cu-
30%Zn alloy with 0-2 wt% Al after 3 h of oxidation at 1123 K. (b) ZnO surface film
formation to prevent internal oxidation of Al during transient stage. (c) Al
2
O
3
protective
layer formation during the steady-state oxidation.
of oxygen solubility due to the presence of Zn has the same effect as the lowering
of the oxygen solubility in the investigation by Rapp [15] on Ag-In alloys by
reducing the outer oxygen partial pressure from 1 atm to 10
7
atm. Similar exam-
ples are the development of Al
2
O
3
scale on Fe-Cr-Al, Ni-Cr-Al, and Co-Cr-Al
alloy systems whose oxidation behavior is discussed in Sec. 6.5. As much as 20-
30 wt% Al is needed to form a protective layer exclusively of Al
2
O
3
on the
corresponding binary Fe-Al, Ni-Al, and Co-Al alloy systems, but the alloys tend
to become brittle exhibiting extremely poor deformability due to such high con-
tent of Al. However, on addition of 15 wt % Cr to these alloys, the amount of
