フェライト系ステンレス鋼の硫酸中での電気化学的挙動

抄録

The anodic polarization curves of ferritic stainless steels, Type 405, 430, 446, and E-Brite 26-1, under various conditions of H₂SO₄ concentration and temperature were obtained by means of the potential sweep method. The Flade potential, E_F, with potential scan to the noble direction is more noble than the potential with scan to the backward direction. The critical current density, i_F, at E_F is large compared to the current density, i_F' at the Flade potential, E_F', with the backward scan. The Flade potential tends to noble with the solution temperature, and the critical current also increases. In a relatively dilute solution less than 30% H₂SO₄, the critical current density decreases with increase in Cr content of the alloy, whereas the current increases with the Cr content in 50% and/or 70% H₂SO₄. The critical current is also a function of the H₂SO₄ concentration. That is, a maximum current was observed in 30% H₂SO₄. The critical current decreased in concentrated solutions such as 50% H₂SO₄, probably due to oxidation of steel surface by sulfuric acid. The passivation current density, i_P, is a function of the solution temperature and the set potential, but is almost independent of the H₂SO₄ concentration. The Type 405 steel showed the largest current.