Aluminum alloys

Chemical composition

The chemical composition of POLCOR aluminium anodes is based on the well established Al-Zn-In alloy and it is suitable for most sea water applications.

The quality of the anode and especially the alloying procedure is of outmost importance for the performance of aluminium anodes which are generally more susceptible to pasivation than zinc. However aluminium alloys have an electrochemical capacity which is more than 3 times greater than the capacity of zinc and it is nowadays the most widely used alloy for the cathodic protection of ships and other marine metallic structures.

PolCor anodes are manufactured from primary metals of high purity, homogenized in large scale melting furnaces and have pre-casting quality control in order to secure that the concentration of all important elements (either impurities or alloying elements) even in very low concentrations is strictly conforming with the specification.
Other special formulations of Al Alloys are also available but mainly used in special offshore application (protection of sub sea pipelines, jetties etc).

The use of aluminium anodes only limited in the case of oil cargo tanks where their installation should be restricted below a certain height in order to avoid sparking from possible detachment of the anode.

The chemical and electrochemical characteristics of POLCOR aluminium anodes are presented in the following:

Alloy Composition

• Element- PL742- PL842
• Zn- 3.0-5.0%- 3.0-5.0%
• In- 0.02- 0.05%- 0.01-0.025%

Impurities

• Fe- <0.16%- <0.12%
• Si- <0.10%- <0.08%
• Cu- <0.01%- <0.01%
• Other single- <0.02%- <0.02%
• Total Others- <0.10%- <0.10%
• Zn- Balance- Balance

• Capacity- 2680 Ahr/Kg- 2700 Ar/Kg
• Potential (Ag/AgCl)- -1,090 V- -1.1V
• Consumption rate- 3.4Kg/year- 3.4Kg/year