Cathodic protection of aluminum generally requires small current densities, e.g., roughly 10 times less than the current requirement for steel in sea water. Potentiostatic tests carried out in flowing natural sea water with selected alloys in the 1000, 5000 and 6000 series indicate that this results from the destruction of cathodic sites on the surface after the onset of cathodic protection. This occurs by crevice corrosion of the matrix adjacent to the cathodic intermetallic particles and detachment of particles from the surface without exposing new ones from the bulk matrix. The exposed matrix area is quickly covered by a protective oxide film. The steady-state current requirement is normally of the order of a few mA/m2 and independent of the flow rate. Although calcareous deposits are detected, these are thought to play a minor role in the polarization of the surface.

Subject
Cathodic polarization, Electric current, Steel surfaces, Water, Cathodic protection, Cathodic potential, Metal surfaces, Aluminum, Cathodic current, Cathodic current density, Steel, Aluminum alloys, Alloys
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1989
Association for Materials Protection and Performance (AMPP)
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