報告書番号

284062

タイトル（和文）

コバルト，ニッケル溶解挙動におよぼすステンレス鋼表面皮膜性状の影響

タイトル（英文）

THE EFFECT OF SURFACE FILM OF TYPE 304 STAINLESS STEEL ON THE DISSOLUTION OF COBALT AND NICKEL

概要 （図表や脚注は「報告書全文」に掲載しております）

本報告は，種々の環境条件で形成されるステンレス鋼表面皮膜の性状を詳細に調べることにより，また，高温水におけるコバルト，クロム等の溶解度の計算および分極特性の測定を行い，コバルトとニッケルの溶出挙動に及ぼすステンレス鋼表面皮膜性状の影響について検討したものである。主な結果は以下の通りである。１）温度２０度Ｃでは，コバルト，ニッケルの溶解度は大きいが，ステンレス鋼からの同元素の溶出速度は溶存酸素濃度にかかわらず極めて小さい。このことは，溶解度の極めて小さいクロムの安定な不働態皮膜がステンレス鋼表面を覆って，コバルト，ニッケルの拡散移行を抑制するためと考えられる。２）温度が高くなるとコバルト，ニッケルの溶解度は減少するが，ステンレス鋼からの同元素の溶出速度は増加する。このことは，ステンレス鋼の耐

概要 （英文）

THE EFFECT OF SURFACE FILM ON THE DISSOLUTION OF COBALT AND NICKEL FROM TYPE 304 STAINLESS STEEL WAS STUDIED BY THEANALYSES OF THE SURFACE FILM, AND THE CALCULATIONS OF SOLUBILITIES FORCOBALT, NICKEL AND CHROMIUM, AND BY THE MEASUREMENTS OF POLARIZATION CURVES FOR THESE METALS. THE MAIN RESULTS OBTAINED WERE AS FOLLOWS. THE SOLUBILITIES OF COBALT,NICKEL AND THEIR OXIDE WERE HIGH AT 25DEGREE C. HOWEVER, THE DISSOLUTION RATES OF COBALT AND NICKEL FROM TYPE 304 STAINLESS STEEL WERE VERY LOW IN SPITE OF DISSOLVED OXYGEN CONTENT LEVELS. THE RESULTS OF SURFACE FILM ANALYSES REVEALED THAT TYPE 304 STAINLESS STEEL WAS COVERED WITH CR-ENRICHED PASSIVE FILM AT 25DEGREE C. THE SOLUBILITY OF CHROMIC OXIDE FILM, THE MAIN COMPOSITION OF THIS CR-ENRICHED PASSIVE FILM, WAS EXTREMELY LOW. THEREFORE, THE DISSOLUTIONS OF COBALT AND NICKEL WERE SUPPRESSED BY THE FORMATION OF THIS CR-ENRICHED FILM. ON THE OTHER HAND, THE SOLUBILITIES OF COBALT, NICKEL AND THEIR OXIDES DECREASED WITH INCREASING TEMPERATURE. HOWEVER, THE DISSOLUTION RATES OF COBALT AND NICKEL FROM TYPE 304 STAINLESS STEEL INCREASED AS TEMPERATUREINCREASED. CHROMIUM, THE MAIN COMPOSION WHICH PLAYS AN IMPORTANT ROLE OF CORROSION RESISTANCE FOR TYPE 304 STAINLESS STEEL, BECOME UNSTABLE WITH AN INCREASE IN TEMPERATURE. MOREOVER, THE REACTIONS THAT CHROMIC OXIDE DISSOLVES AS DICHROMATE IONS OR CHROMIC IONS WERE ACCELERATED AT HIGH DISSOLVED OXYGEN LEVELS. FOR THE REASONS MENTIONED ABOVE, THE DISSOLUTION OF COBALT AND NICKEL CAN BE PROMOTED AS TEMPERATURE INCREASES ANDTHE CONCENTRATION OF DISSOLVED OXYGEN BECOMES HIGHER.

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