炭酸塩水溶液およびケイ砂混合ベントナイト中における純銅のアノード分極挙動

Anodic polarization behavior of pure copper in carbonate solutions and in bentonite/sand mixture

川崎 学*; 谷口 直樹 ; 川上 進

Kawasaki, Manabu*; Taniguchi, Naoki; Kawakami, Susumu

オーバーパック候補材料の一つである銅の酸化性期間における腐食挙動評価に資することを目的として、炭酸塩を含む水溶液中および緩衝材を模擬したケイ砂混合ベントナイト中で80にてアノード分極測定を実施した。水溶液中での試験の結果、塩化物イオン濃度が高くなると活性溶解型の分極挙動を示し、炭酸水素イオン濃度が高くなると不動態型の分極挙動を示す傾向が認められた。硫酸イオン濃度による分極形態への影響は認められなかった。また、皮膜破壊電位は塩化物イオン濃度、硫酸イオン濃度が高くなると卑化し、炭酸水素イオン濃度が高くなると貴化する傾向が確認された。これらの結果を30で実施された既往のデータと比較すると、温度が高くなると不動態型の分極挙動を示す領域が広がることが示唆された。しかし、皮膜破壊電位に対する温度の違いによる影響は今回の実験条件の範囲では認められなかった。ケイ砂混合ベントナイト中では水溶液中に比べて溶液組成の違いによるアノード分極曲線への影響は小さく、概ね活性溶解型に近い分極挙動を示すことが確認された。

Copper is one of the candidate materials for overpacks. Anodic polarization curves of pure copper were measured at 80C in carbonate solution and in bentonite/sand mixture in order to understand the corrosion behavior of copper overpack at oxidizing period. The experimental results in carbonate solutions indicated that the anodic polarization curves became active dissolution type with increase in chloride ion concentration, while anodic polarization curves became passive type with increase in bicarbonate ion concentration. No effect of sulfate ion concentration was observed on the type of anodic polarization curve. The passive film break down potential became less noble with increase in chloride ion concentration and sulfate ion concentration. In contrast, the passive film break down potential became noble with increase in bicarbonate ion concentration. By the comparison of these experimental results with previous study performed at 30 C, it was indicated that anodic polarization curves become passive type with the rise of temperature. However, no effect of temperature on passive film break down potential was observed within the experimental conditions. As to the results in bentonite/sand mixture, the effect of the composition in test solutions on the anodic polarization curves were small and the anodic polarization curves were almost active dissolution types.