DISSOLUTION AND REACTION OF SULFIDE INCLUSIONS IN STAINLESS-STEEL IMAGED USING SCANNING LASER PHOTOELECTROCHEMICAL MICROSCOPY

The in situ scanning laser photoelectrochemical microscopy technique has been used to image heterogeneity of the surface chemistry around sulfide inclusions in stainless steel under anodic polarization. The deposition around inclusions of a ring of material deduced to be sulfur is demonstrated. Evidence is presented that this ring of material has its origin in the decomposition of thiosulfate produced by the anodic dissolution of the inclusions. The evidence supports models of the initiation of pitting corrosion which attribute the effect of sulfide inclusions to the acceleration of anodic dissolution kinetics caused by adsorbed sulfur.