抄録
Interaction of thiosulfate with Alloy 800 was systematically investigated to obtain the kinetics in a neutral simulated steam generator crevice solution. Cyclic polarization showed that the pitting potential in a thiosulfate-chloride solution was much lower than in either a chloride solution or a sulphate-chloride solution, and thiosulfate selectively and distinguishably degraded the oxide film on Alloy 800. The donor density of oxide film formed in a thiosulfate-chloride solution was slightly higher than in either a chloride-only solution or a sulphate-chloride solution. Even in the passivity range the material was degraded due to the slow interaction with S2O32− with oxide, especially when the applied potential was close to the pitting potential. The UV-visible absorption spectra showed that thiosulfate formed a stable complex with Cu2+, and their product was soluble in aqueous solution, which is possible evidence to indicate that thiosulfate assists Cu2+ in dissolving from an oxide film into solution. Also, due to the complexity of the reaction, thiosulfate decreased the oxidation potential of Cu0 to Cu2+. Since the Cu, an impurity in Alloy 800, normally accumulates at the grain boundary, especially at the triple points, thiosulfate induced corrosion is in the form of pitting or intergranular attack.
