Conclusions oxidation of copper

Oxidation of pure copper in 0.3 M NaNO2 solution under certain electro-

chemical conditions results in Hasiguti peaks on the temperature dependence of low-frequency internal friction.

Formation of an oxide layer on the surface of copper in the studied passivating environment is accompanied with generation of excessive amounts of metal vacancies at the Cu/Cu2O interface, which then diffuse into the bulk metal.

the metal surface in a passivating environment inducing EAC is accompanied with long-range effects in the bulk metal.

100 150 200 250 300 350 400 450 500 0 10 20 30 40 1-st run 3-rd run 4-th run a In te rn a l F ric ti o n , Q -1 , x10 4 Temperature, K 100 150 200 250 300 350 400 450 500 2,20 2,25 2,30 2,35 2,40 2,45 2,50 2,55 1-st run 3-rd run 4-th run b Fr equ e ncy 2 , H z 2 Temperature, K

Figure 4. Temperature dependence of internal friction Q-1 (a) and oscillation frequency f 2 (b) for copper: A-samples were polarized in 0.3 M NaNO2 solution

for 2 h at -150 mVSCE and for 10 h at +100 mVSCE at 353 K (80°C). During first

run and second run (not shown) heating was performed up to 320 K, and during third and fourth runs up to 450 K.

7. Conclusions

A new Selective Dissolution - Vacancy Creep (SDVC) model for environmentally assisted cracking (EAC) of materials in high temperature water is described. The model is based on the idea of selective dissolution or oxidation, production of vacancies as well as deformation localisation to a shear band at the crack tip. The experimental observations made for intergranular stress corrosion cracking (IGSCC) of Alloy 600, hydrogen charging of Alloy

600, selective dissolution of brass and oxidation of copper support SDVC- mechanism.

8. Acknowledgements

The reported work was part of the Finnish Research Programme on the Structural Integrity of Nuclear Power Plants 1995 - 1998, subproject RAVA3 on Material Degradation due to Corrosive Environment.

Co-operation with Erkki Muttilainen from TVO Ltd. and Ossi Hietanen from IVO Ltd. together with many other colleagues is gratefully acknowledged.

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