Crevice corrosion bulk solution composition

Brossia and Kelly [26] studied the effect of bulk solution composition on crevice corrosion initiation and the occluded solution composition. As shown in Fig. 23,... 

The addition of nitrate to the bulk solution led to more significant delays in initiation of crevice corrosion (Fig. 7) of 304 SS compared to sulfate. For example, to produce an initiation time of 75 min required 1.5 mM S04 , but only 23 pM NOs. At low bulk [Cl ] [NO3-] ratios ([N03 ] = 1.7 mM), no initiation of crevice corrosion was observed within 180 min, whereas in solutions in which crevice corrosion did occur the composition of the crevice solution was essentially independent of the initial concentration of nitrate in the bulk solution. However, the relative concentration of Cl compared to NO3 in the crevice was nearly three times... 

Crevice corrosion is another type of localized corrosion relevant to non-alloyed and stainless steel. Narrow gaps- caused by the constructive design or the formation of deposits are a necessary requirement. Fig. 1 -9 c. Crevice corrosion as a result of the different compositions of the electrolyte inside and outside the crevice, i.e. depletion of oxygen in the crevice. In a crevice there is a large metal area/electrolyte volume ratio with a long diffusion path. Solution in the depth of a crevice is depleted of oxygen and therefore has a composition different from that of the bulk solution. As a result of the lack of oxygen anodic metal dissolution occurs at the depth of a crevice. Because diffusion in the crevice is almost impossible, the chemical composition becomes acidic... 

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