Typical cells differential aeration cell

P + Pi brasses of similar composition (Cu—38 wt.% Zn and Cu—41 wt.% Zn, respectively), it has been concluded that this is not simply due to an increased Zn concentration in the p phase, but is likely to reflect the structural differences of hoth phases [67]. Other factors that stimulate the dezincification of both O - and a p brasses are the presence of chlorides, high concentrations of CuCl2 ions, stagnant environments, differential aeration cells and elevated temperatures. In chloride solutions, such conditions are typically encountered at a later stage of corrosion when mass transport restrictions by a deposit, corrosion product, or crevice have heen established and create a local environment, in which the copper in the brass is nearly in equilibrium with CU2O, CuCl, and accumulated CuCl2 anions [68,69]. Experimentally, the necessity... 

Corrosion cells not only are formed when two different metals are in contact with each other but also can be the result of differences in the corrosive environment. A typical example is differential aeration cells, which are due to differences in accessibility of oxygen to the surface of a metal. Because the value of the corrosion potential depends on the kinetics of the anodic as well as the cathodic partial reactions, a different accessibility of oxygen results in a difference in corrosion potential and hence in the establishment of a corrosion cell. 

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