Page 18 - Curriculum Visions Dynamic Book

Zinc protects large structures
Objects such as ships, pipelines, oil or natural gas storage tanks and bridges are too large to be protected by galvanising. Instead, they are protected either using paintw or by connecting them to a number of large zinc blocks buried
in damp ground. The moisture in the damp ground provides the electrolyte and allows the object and attached zinc block to behave as a battery. The zinc blocks supply ions to the steel, becoming corroded away in the process. The steel acquires the ions and releases electrons to the air. As a result, the iron is not corroded.
The zinc blocks are called sacrificial anodes because they are the anodes of the cell that forms between the damp environment, steel structure and protective zinc block. The blocks are sacrificed to protect the steel structure, it being a relatively easy process to replace the zinc periodically.
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