Interactions between polysulphides and stainless steel materials

Ability of polysulphide to enhance the potential of digester materials (S30400, S31603, S32205, S32304) was studied in the impregnation stage of the pulping process. Polysulphides were generated by adding elemental sulphur to alkaline sulphide solutions. Polysulphide levels 0.3-0.48, 1.25-2, 5-8 and 12.5-20 g/1 enhanced the potentials of the steels by 70, 90, 170 and 190 mV, respectively. The polysulphide concentrations were calculated values, because concentrations of polysulphides are very difficult to measure in kraft liquors. No weight changes were observed, but slight accumulation of sulphur onto surfaces, particularly onto S31603 was seen in X-ray fluorescence analysis. Otherwise, differences in behaviour among the steel materials were minimal.