US Military specification for Zinc Anodes
US Military Specification A-18001K
|Others Total||0.1 max|
Potential 1.05 V silver/silver reference cell
Capacity- 780 amp.hr/kg
The current U.S. Military Specification, A-18001K, is the result of work carried out by scientists for more than five decades. Before the mid 1950s, corrosion prevention was not fully understood with dramatically different results from similar vessels treated with apparently the same Zinc Anode protection.
Investigations into why only some of these vessels suffered from extensive corrosion indicated that some Anodes became passivated when a white crust formed on their surface . The crust was tested as Oxides of Iron and was determined to have been caused by excessive impurities in the product, mainly Iron. The formation of the crust made the Anodes inactive allowing corrosion to take place elsewhere in the vessel.
The first US military specification resulted, which limited the number of impurities in the Zinc used, resulting in the requirement to use high grade Zinc and strict manufacturing practices.
The specification has been refined over the years with the result that modern anodes manufactured to the specification should remain active throughout there lives by producing a thin zinc oxide film which will easily slough off.