Behaviors of New Zinc Alloys as Galvanic Anodes

For the purpose of improving the performance characteristics of high purity zinc anode in corrosion prevention, the anode behaviors of a number of new zinc alloys, prepared by adding a small amount of indium or related elements to special high grade zinc, were determined under following experimental conditions: anode current density: 1mA/cm2; electrolyte: synthetic sea water at 30°C (no agitation); duration: 300-1, 000hr. Throughout the test anodic potential was regularly observed. At the end of each test, the amount of adherent corrosion product and the weight loss of the anode were measured. The results revealed were:1) The anodic potential of new zinc alloys containing 0.01-3% of In, Tl, Hg, Cd or Wood's Metal did not increase throughout the tests, whereas that of special high grade zinc increased more or less markedly.2) The anodic current efficiencies of special high grade zinc was 94-96% and the amount of adherent corrosion products were 10-20% (based on dissolved Zn), while in the case of new zinc alloys they were 97-99% and 2-6% respectively.3) The decreased corrosion products of new zinc alloys were further characterized by their softness and jelly like appearances; they were removed easily by spraying or mild rubbing. The long sustained anodic potential of new zinc alloys could be ascribed to the properties of their corrosion products.4) A statistical correlation between anode efficiency and the amount of adherent corrosion product was evident.An actual shiphull test of the new zinc alloy showed the superior characteristics compared with the usual anode of high purity zinc.