Zinc Alloys

Chemical composition

The POLCOR zinc anodes for Hull & Ballast tank of the Ships, Piers,Pilling,Pipelines and offshore application follow the US MIL-A-18001K.

In the following ,the chemical composition as well as the electrochemical properties of zinc anodes are presented:

Alloy Composition

• ----- USMIL 18001K-  ASTM B418-95a
• ----- ASTM B418-95a -----

• Al- 0.1-0.5 %- <0.005%
• Cd- 0.025-0.07%- <0.003%

• Fe- <0.005%- <0.004%
• Pb- <0.006%- <0.003%
• Cu- <0.005%- <0.002%
• Other single- <0.02%- <0.02%
• Total Others- <0.10%- <0.10%
• Zn- Balance- Balance

• Capacity- 780 Ahr/Kg- 740 Ar/Kg
• Potential (Ag/AgCl)- -1,05 V- -1.03V
• Consumption rate- 11.2Kg/year- 11.9Kg/year

Cadmium is used as depassivating agent. However it should not exceed a maximum percentage for environmental reasons. Aluminium is added to improve electrochemical characteristics. Lead, copper and Iron are considered to be impurities and should not exceed the presented maximum percentages.

Iron is the impurity with the most profound effect on the anode performance.

Zinc is not recommended in environments where the pH is over 8, or where the temperature of the electrolyte is over 600C. Under these situations, zinc becomes Cathodic, rather than anodic, and should be avoided.

When used strictly as an anode, for Cathodic protection current, zinc is well suited to low resistance environments such as seawater, salt marshes, and brackish water. Zinc normally becomes impractical for protecting large bare areas when the resistance of the electrolyte exceeds 1,500 ohm centimeters.