Effects of dithionite ion on corrosion of type 304 stainless steel in sulphuric acid solution

Corrosion behaviour of type 304 stainless steel was investigated, with particular attention to additive effects of hydrosulphite (Na₂S₂O₄) on corrosion in 0.1 mol/l H₂SO₄ solution with various amounts of Na₂S₂O₄ up to 60 mmol/l.Corrosion of SUS304 occurred below pH 3.0 at 30 °C in a 0.1 mol/l H₂SO₄ solution in which Na₂S₂O₄ was added to 0.1-20 mmol/l. The maximum corrosion rate at 30 °C was measured as 7.2 g/m² h (7.9 mm/y) in 0.1 mol/l H₂SO₄-10 mmol/l Na₂S₂O₄ at pH 1.2. Microscopic surface observation revealed that active dissolution was accompanied by intergranular corrosion at the metal surface.The SUS304 was easily passivated in 0.1 mol/l H₂SO₄ solution with more than 30 mmol/l Na₂S₂O₄. NiS was detected in the passivated film.