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Diffusion of Corrosion Products of Iron in Compacted Bentonite.

Published online by Cambridge University Press:  01 January 1992

K. Idemitsu ,
H. Furuya  and
Y. Inagaki
K. Idemitsu
Affiliation:
Kyushu Univ., 6-10-1 Hakozaki, Higashi-ku, Fukuoka 812, JAPAN
H. Furuya
Affiliation:
Kyushu Univ., 6-10-1 Hakozaki, Higashi-ku, Fukuoka 812, JAPAN
Y. Inagaki
Affiliation:
Kyushu Univ., 6-10-1 Hakozaki, Higashi-ku, Fukuoka 812, JAPAN
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Abstract

Carbon steel is one of the candidate overpack materials for high-level waste disposal. The corrosion rate of carbon steel is reduced by the presence of buffer materials such as bentonite and seems to be affected by the diffusion of corrosive materials and corrosion products through the buffer material.

The apparent diffusivities of corrosion product of iron were measured in some bentonite specimens in contact with carbon steel. The apparent diffusivities of iron were also measured without carbon steel for comparison. The apparent diffusivities of corrosion product were on the order of 10−12 m2/s and showed a tendency to decrease with increasing density of the bentonite specimen. There was no significant effect of silica sand on the apparent diffusivities. The apparent diffusivities of iron in the system without carbon steel were in the range of 10−14 m2/s and showed a tendency to increase with increasing silica sand content. The difference of the diffusivities between corrosion product and iron without carbon steel seems to be due to the difference of diffusing species. The color of the corrosion product was dark-green during contact with bentonite specimens and became red on exposure to air in a few minutes. Gas bubbles were also observed in the corrosion product. This suggests hydrogen generation during corrosion of the carbon steel. Thus the diffusing species seems to be in a reduced state, probably ferrous ion. On the other hand, the diffusing species of iron without carbon steel was probably a ferric hydroxide complex that was negatively charged. This suggests that ferrous ion could diffuse in the surface water adsorbed on bentonite, while ferric complex was excluded.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 294: Symposium V – Scientific Basis for Nuclear Waste Management XVI , 1992 , 467
Copyright
Copyright © Materials Research Society 1993

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References

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