1999 Fiscal Year Final Research Report Summary
Corrosion Behavior of Titanium in Deaerated Aqueous Solutions
| Project/Area Number |
10650683
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Structural/Functional materials
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| Research Institution | HOKKAIDO UNIVERSITY |
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Principal Investigator |
AZUMI Kazuhisa Hokkaido Univ., Fac. Engi., Ass. Prof., 大学院・工学研究科, 助教授 (60175875)
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| Co-Investigator(Kenkyū-buntansha) |
FUSHIMI Koji Hokkaido Univ., Fac. Engi., Instr., 大学院・工学研究科, 助手 (20271645)
SEO Masahiro Hokkaido Univ., Fac. Engi., Prof., 大学院・工学研究科, 教授 (20002016)
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| Project Period (FY) |
1998 – 1999
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| Keywords | Titanium / Oxide Film / Depassivation / Hydrogen absorption / Bentonite / Impedance / Resistmetry / AFM |
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| Research Abstract |
Titanium is one of the candidates for overpacking material of glass log containing high level radioactive waste produced in power plants. The overpacking material has to protect its contents over 1000 years from environment such as underground water containing chemical composition dissolved from bentonite clay and high temperature up to 100 degree due to heat production of nuclear fission reaction. In this study Ti specimens were immersed in deaerated water in contact with bentonite powder, borate buffer solution, or carbonate solution, and obtained following results. (1) Oxide layer grows on Ti mechanically polished even in deaerated aqueous solution. (2) Electric barrier property degraded during long term immersion. (3) Immersion potential became unstable after long term immersion. (4) Dissolution traces of general corrosion were observed after 20 weeks immersion. (5) Initiation of localized corrosion was observed in aqueous solution in contact with bentonite powder. (6) Corrosion traces and degradation of the film was more obvious at 80 degree than 25 degree. From impedance results, the corrosion rate and degradation of the oxide film were mostly affected by the presence of sulfate ion. From impedance results and AFM observation the anodic oxide film formed on Ti in the solutions containing sulfate ion such as bentonite contact solution has porous structure and electric defects at high density, resulting in more susceptible to the degradation and corrosion. In the present study crevices with a few tenth nm in depth were observed on Ti after 20 weeks immersion. Therefore, it is important to evaluate the possibility that the crevice grows to more serious localized corrosion.
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