The variation of solution composition during the initiation of crevice corrosion on stainless steel

A novel crevice cell was designed that allowed the dimensions of the crevice gap to be set reproducibly at a value of 3.8 ± 0.1 μm. With this cell the initiation of crevice corrosion of 304 stainless steel in aerated 0.1 N NaCl was investigated. The transient build-up of dissolved Fe, Cr, and Ni species was carried out by inductively coupled plasma spectroscopy. It was found that during the initiation period prior to passivity breakdown the Cr concentration in the crevice solution was far less than its atomic fraction in the alloy, and that the crevice solution pH did not decrease appreciably. After breakdown, the relative concentration of dissolved Fe, Cr, and Ni became virtually the same as their relative atomic fractions in the alloy. The fact that Cr does not present itself during the first few hours of initiation suggests that mechanisms of activation based on pH decrease, supposedly caused by Cr dissolution and hydrolysis, may not be applicable.