Corrosion behaviour of sintered austenitic stainless steel filters in sulphuric acid solutions

Abstract

The corrosion behaviour of porous sintered 316L stainless steel in sulphuric acid media has been investigated and compared to that of a wrought material of similar composition. Potentiodynamic polarisation studies and the variation of open circuit electrode potential with time have been used to evaluate the corrosion behaviour. The effect of porosity on the corrosion process has been examined. A significant difference between the electrochemical behaviour of porous and wrought material was observed. Compared to wrought material, the limiting current in the cathodic region is lower for sintered steels and the criticalcurrent in the anodic region is higher. The open circuit electrode potential of the sintered samples decreased continuously from 0 to –280 m V ( SCE) after 40 h of exposure, then remained constant; for the wrought material, it increased from ∼0 to +150mV(SCE), becoming steady after 25 h. SEM observations and XPS studies on the surface film of the samples revealed penetration of sulphuric acid into the specimen during the corrosion process. The overall trend in the corrosion behaviour remained the same with changing electrolyte concentration. It is suggested that the inferior corrosion resistance of sintered samples is due to the formation of hydrogen ion concentration cells following entrapment of electrolyte in the pores.