Anodes In Practical Use
A sacrificial anode is a piece of metal that is made to act as an anode and therefore be oxidized, in order to protect another piece of metal from being oxidized. For example, to keep iron or steel from oxidizing (rusting) when in contact with air and moisture, such as when it is being used as a fence post, the post can be connected to a piece of zinc that is buried in the ground next to it. The iron and zinc in the moist soil constitute the two electrodes of a galvanic cell. But because zinc oxidizes more easily than iron, the zinc acts as the anode and is preferentially oxidized. It is said to be "sacrificed" because it gradually gets eaten away by oxidation instead of the iron. For this reason, a cable made of zinc was buried alongside the Alaskan pipeline, the huge steel pipe that transports petroleum from the Alaskan oil fields to the lower states.
Galvanized iron is iron that has been coated with zinc so that it can be used outdoors or in the ground without rusting. The zinc oxidizes in preference to the iron. Galvanized iron is widely used in making garbage cans, pails, and chain-link fencing.
Anodizing is a process in which a piece of metal is made the anode in an electrolytic cell in order to oxidize it deliberately. When aluminum is anodized in this way, a coating of aluminum oxide is built up on its surface. This coating, unlike the metal itself, can take dyes. Many kinds of aluminum utensils and novelties in bright blue, green, red, and gold colors are made of anodized aluminum.
Robert L. Wolke
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