Breakaway, a sharp increase of corrosion rate of zirconium alloys, was evidenced to be caused by mechanical detachment of protective oxide films, through observation of a remarkable contrast change in SEM secondary electron images of alloy surfaces oxidized in 633 K water. The contrast change was explained by the loss of electrical discharge circuit caused by detachment of oxide films.
The above explanation was supported by examination of Zircaloy samples corroded in 673 K steam, which showed blistering of oxide films and no breakaway in kinetics. Reported changes of oxide microstructure before breakaway also support the film detachment hypothesis.
(Received August 4, 1979)
*This paper was originally published as a part of the reference (8).
**Mitsubishi Atomic Power Industries Inc. 1-297, Kitabukuro-machi, Omiya 330, Japan.
© 2002 The Japan Institute of Metals
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