Shipboard Evaluation of Zinc Galvanic Anodes Showing the Effect Of Iron, Aluminum and Cadmium on Anode Performance

A commercial zinc anode with desirable long term galvanic performance characteristics has been developed. Aluminum plus cadmium added to zinc has produced this improved anode. The tolerance for iron in zinc anodes has been increased by the aluminum plus cadmium addition. Less adherent corrosion products and uniform anode attrition also have been achieved without adverse effects on anode current efficiency. Improved zinc anode performance obtained with the aluminum plus cadmium addition is independent of anode current density or electrolyte temperature. In the absence of other constituents, controlling the iron content at 0.0014 percent does not give a zinc anode with optimum galvanic properties. Best performance is obtained when the iron content is on the order of 0.0002 percent. Barrier shields serve no useful purpose on the faying surface of zinc anodes installed on steel ship hulls. Long term performance tests on five active ships and quiescent marine exposures, using commercial size zinc anodes, provide the basis for these conclusions. 5.2.2