Electrochemical corrosion behaviour of type 316 stainless steel in acid media containing fluoride ions

Abstract The corrosion behaviour of type 316 stainless steel has been investigated in F- containing dilute hydrochloric acid and acetic acid solutions aerated with oxygen gas at 25°C using electrochemical measurement techniques. Both electrochemical impedance spectroscopy spectra and polarisation curves illustrate that 316 stainless steel can passivate in these solutions at the corrosion potential. The passive impedance decreases slightly with increasing F- concentration. The anodic polarisation curves show that low concentrations of F- ion have no significant influence on the passivity of 316 stainless steel, but the passivity is reduced by high concentrations of F- ions. In 0·1 M NaF solutions, an anodic current peak occurs at below the pitting potential. This does not appear in solutions with low concentrations of NaF, and is related to the F- accelerated reactions. During anodic polarisation, the selective dissolution of the Fe component takes place in the above solutions.