Abstract
The addition of sodium arsenite to an acid solution was found to affect the polarisation and corrosion behaviour of AISI type 304 austenitic stainless steel with a low phosphorus content in deaerated 0·5M H2 SO4 at 50°C. The presence of arsenite drastically changed the anodic and cathodic polarisation behaviour of the stainless steel. The active anodic dissolution of the steel was accelerated at lower arsenite concentrations (≤1 × 10-4M), but suppressed at higher concentrations. In the former case, an amorphous–crystalline arsenic layer was observed on the surface of the steel under open circuit conditions. All additions of arsenite created a second anodic current peak in the active–passive region at ∼100 mV (SCE). The extent of the peak depended on the amount of AsO- 2 and the immersion time. The peak attained a maximum value of 1845 μA cm-2 in the presence of 5 × 10-5M NaAsO2 and a minimum value of 86·0 μA cm-2 in the presence of 2·5 × 10-3M. A significant relationship was found between the second anodic peak and the arsenite concentration. This confirmed a previous interpretation that the appearance of the second anodic peak is related to the hydrogenation of the material. By measuring the secondary anodic peak, information about the hydrogenation of stainless steel was obtained. Surface analyses using SEM and X-ray diffraction were carried out.
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