Corrosion Science and Technology

The Corrosion Science Society of Korea (한국부식방식학회)
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Effects of PbO on the Repassivation Kinetics of Alloy 690

  • Published : 2004.08.01
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Abstract

Effects of PbO on the repassivation kinetics and characteristics of passive film of Alloy 690 were examined to elucidate the influences of PbO on the SCC resistance of that alloy. The repassivation kinetics of the alloy was analyzed in terms of the current density flowing from the scratch, i(t), as a function of the charge density that has flowed from the scratch, q(t). Repassivation on the scratched surface of the alloy occurred in two kinetically different processes; passive film initially nucleated and grew according to the place exchange model in which log i(t) is linearly proportional to q(t), and then grew according to the high field ion conduction model in which log i(t) is linearly proportional to 1/q(t) with a slope of cBV. The cBV is found to be a parameter representing repassivation rate and hence SCC susceptibility of the alloy. The lower the value of cBV, the faster the repassivation rate and the higher the SCC resistance of an alloy. Addition of PbO to pH 4 and 10 solutions increased the value of cBV of alloy 690, reflecting slower repassivation rate than without PbO. The change in the value of cBV was grater in pH 10 than in pH 4. The increase in SCC susceptibility of alloy 690 with the addition of PbO to solution was presumably due to the Cr-depletion in the outer parts of passive film of the alloy with an incorporation of Pb compounds in the film, which was revealed by Mott-Schottky, AES and XPS analyses.

Keywords

Acknowledgement

Supported by : Korea Korea Institute of Nuclear Safety (KINS)

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