Effects of lead on oxidation behavior of Alloy 690TT within a high temperature aqueous environment

- The films on 690TT in high-temperature water with and without lead were studied.
- Lead traces participated in the oxidation and were added into the oxide films.
- Lead contamination could block the dehydration of hydroxides within the films.
- Lead impurities could cause the production of amorphous structures in the films.
- A duplex layer model was proposed for the evolution of the lead-doped films.

The chemical compositions, phases and structures of two oxide films on Alloy 690TT following exposure for 4400 h in pure water with and without lead at 320 °C were studied by surface analysis techniques. The analysis of a lead-doped oxide film prepared by a focused ion beam (FIB) demonstrated that both Cr-rich and Ni-rich oxides were alternatively distributed within the outer layer, whereas the inner layer was porous and poorly protected, causing severe corrosion of the alloy and a thicker film was formed. A duplex film model was proposed for the effects discussion of lead on the oxidation mechanism.

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