バフ研摩した純鉄表面皮膜のクロム酸水溶液中における電気化学的性質
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概要
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The relations between electrode potentials of buffed surface of iron in chromate solutions and pH values of the solutions were studied in relation to the corrosion region (pH<4) in the Pourbaix diagram for the Fe-CrO_3-H_2O system at 25℃. The results obtained were as follows : The buffed surface is covered with thin Fe_3O_4 films. The electrode potentials vary with the pH values and the presence of anions, Cl- and SO^<2->_4. The surface reactions are estimated from the observed pH-potential relations as follows : (1) 0<pH<2 ; 3Fe+6Fe_3O_4+4CrO^<2->_4_<aq>+26H^+=3Fe^<2+>+9γ-Fe_2O_3+4Cr^<3+>_<aq>+13H_2O (2) 2<pH<4 ; 3Fe+6Fe_3O_4+4CrO^<2->_4_<aq>+10H^+=3Fe^<2+>+9γ-Fe_2O_3+4CrO^-_2_<aq>+5H_2O The electrode potentials of the Fe_3O_4 film depend on the presence of anions, Cl^- and SO^<2->_4, and on the structure of chromic ion species, and concerned with the solid state electrolyte reaction, i.e. the dissolution of Fe^<2+> ion from iron crystal surface into the thin Fe_3O_4 film. The Fe_3O_4 film is rapidly dissolved in the solution by the presence of Cl^- or SO^<2->_4 ions, and the surface reactions of pure iron without oxide film are estimated from the observed potentials as follows : (1) 0<pH<2 ; Fe+CrO^<2->_4_<aq>+8H^+_<aq>=Fe^<3+>_<aq>+Cr^<3+>_<aq>+4H_2O (2) 2<pH<4 ; Fe+CrO^<2->_4_<aq>+3H^+_<aq>=FeOH^<2+>_<aq>+CrO^-_2_<aq>+H_2O The dissolution reactions and their electrode potentials of pure iron in chromate solutions depend on the structures of both chromic ion and ferric ion species.
- 社団法人日本鉄鋼協会の論文
- 1972-07-01