Noble metals continued passivity

In the natural atmosphere noble metal coatings, such as chromium, nickel, and their alloys, form passive films on carbon steel surfaces. A defect-free continuous layer of chromium provides excellent protection for a carbon steel substrate. However, deposited layers of chromium and nickel commonly have some defects, such as cracks. The corrosion rate of the carbon... 

It follows from Fig. 5.5 that a transfer from the passive state (2) to the active state (3) implies a potential decrease. The greater the difference between the real corrosion resistance of the material based upon passivation (indicated by the rest potential in the passive state) and its thermodynamic nobleness (expressed by the EMF series in Table 3.1), the larger the potential decrease following the transfer from passive to active state. That is, this potential decrease indicates to what extent the real corrosion resistance of the material depends on passivity. Table 5.1 shows examples of such a potential decrease for several metal-environment combinations. The activation is in these cases caused by continuous grinding of the metal surfaces, i.e. the materials are kept active in spite of an otherwise spontaneous passivation tendency for many of the material-environment combinations represented in flie table. 

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