Electrochemical evaluation of Zn-22 wt.% Al- x wt.% Ag (x = 2, 4, 6) sacrificial anodes

The object of the present work was to determine the possibility that Zn-Al eutectoid alloys (Zn-22 wt.% Al), with silver contents of 2, 4 and 6 wt.%, could be used as sacrificial anodes for cathodic protection of steel structures in two test aqueous solutions: substitute ocean water and 0.5 M NaCl. Besides the as-cast condition, some samples were homogenized at 350°C during 96 h and air-cooled. A short-term electrochemical test, DNV RP B401, as well as electrochemical impedance spectroscopy were performed to obtain electrochemical behavior and electrochemical capacity of the anodes, and to reveal any tendencies to passivation. The experimental results suggest that the Zn-Al-Ag sacrificial anodes, with both microstructures, showed a passive behavior in substitute ocean water. However, these alloys exhibited adequate potentials and electrochemical capacities to work as sacrificial anodes in 0.5 M NaCl.