The surface films that form on AISI 304-type stainless steel have been examined by the Contact Electric Resistance (CER) method in solutions containing varying amounts of thiosulphate, sulphate and chloride anions. The CER technique is a new in-situ method, which is based on an accurate measurement of the electric resistance of the surface films. The surface films were also examined by Secondary Ion Spectrometry (SIMS) to compare the results with CER measurements. Thiosulphate, if present in excess of 10 mg/l, reduces the surface film electric resistance by more than an order of magnitude. Sulphate, when the concentration is 300 mg/l or more, is able to create some kind of passivation layer in the presence of thiosulphate. When a surface film has formed in pure chloride solution, thiosulphate ions added later are not able to displace the chloride ions. If the surface film has formed in a solution containing only thiosulphate, and chloride ions are added afterwards, chloride ions are not able to penetrate through the sulphur-containing film.

Subject
Sulfur, Films, Steel surfaces, Ions, Sulfates, Chloride solutions, Thiosulfate, Film formation, Oxygen, Stainless steel, Chlorides, Electrochemical potential, Samples
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1994
Association for Materials Protection and Performance (AMPP)
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