CORROSION BEHAVIOUR OF TWO STAINLESS STEELS AND A CHROMIUM CAST IRON IN PHOSPHORIC ACID CONTAMINATED WITH S2- IONS

摘要

Various impurities such as Cl-, F-, SO42- and S2- contained in natural phosphates or introduced by enrichment processes, lead to many corrosion problems in equipment during the production of phosphoric acid by a wet process. Little is known about the action of S2- ions in acidic media. In an attempt to investigate the mechanism of action of S2- ions on stainless steels, the corrosion behaviour of three types of steel 904 L (X1NiCrMoCu25-20-5), 316 L (X2CrNiMo17-12-2) and cast iron containing 32 wt % Cr in industrial phosphoric acid contaminated with S2- ions was studied, using polarization curve analysis. The characterization of the corrosion products formed on the sample surface has enabled the production of a hypothesis on the corrosion and depassivation mechanisms of steels in these media. The effect of copper and molybdenum on the corrosion resistance of the studied materials in phosphoric acid contaminated by S2- ions is noted and discussed in detail. [References: 11]