Effect of Flow on the Corrosion Mechanism of Zn and Al Galvanic Anodes in Artificial Seawater Media

The effect of hydrodynamics on the corrosion of a commercial Zn and an Al - 14 wt% Zn - 8 wt% Mg alloy galvanic anodes in artificial seawater media at room temperature was studied in a RCE system under turbulent flow conditions. Different rotation rates were studied: 100, 1000, 3000, 5000 and 7000 rpm. The corrosion rates were measured by Linear Polarization Resistance and Electrochemical Impedance Spectroscopy techniques. For the system studied, the steady-state corrosion potential increased with increasing RCE rotation rate. The effect of increasing the rotation rate is to increase the availability of oxygen at the surface, which in turn will polarize the corrosion reaction in the more noble direction. The corrosion rate increases with increasing velocity over the range of rotational rates studied. This reflects the fact that the rate of corrosion is controlled, at least in part, by the rate of mass transfer. In this case, the effect of increasing  rotation rate on the corrosion rate is to increase the interfacial concentration of the reactant (oxygen).