Galvanization is the process of coating one metal with another to protect it against corrosion or to improve its appearance. It is a surface coating process using electrolysis, where the metal to be coated acts as the cathode and the coating metal acts as the anode (an inert material can also be used as the anode). The electrolytic solution must contain a salt composed of cations of the metal intended for the coating. The thickness of the layer deposited by the electrogalvanization process is controlled through mathematical models.
The coating of metallic surfaces can also occur by immersing the metal to be coated into the molten metal that will cover it. However, the electrolytic process allows for better (more homogeneous) coverage, although both methods are equally utilized. In this immersion process, the coating thickness is controlled by the speed at which the part passes through the metallic bath, the furnace temperature of the coating metal, and the application of a nitrogen jet at the end of the process.
Different metals can be used for coating a part. The process of coating with chromium, for example, is called “chrome plating”; if the coating is nickel, it is called “nickel plating.” We also have zinc, tin, magnesium, gold, copper, silver, etc. Each coating metal can provide different characteristics to the galvanized material according to its properties, such as higher or lower conductivity, or resistance to extreme temperatures.
The coating of thin steel sheets with tin results in a product called “tinplate,” used in the manufacture of cans to store various products such as preserves, oils, etc. Tin is used for this application because it is a metal that exhibits greater resistance to oxidation when in contact with water, which is generally present in these products. The process of coating steel with tin is generally performed by immersion.
In the case of iron, the most common corrosion protection is achieved through the deposition of metallic zinc. Zinc has the characteristic of oxidizing faster than iron. Thus, if a crack or peeling occurs in a galvanized iron* plate, leaving the iron exposed, the zinc will oxidize faster than the iron. Therefore, as long as there is zinc, the iron will not be oxidized.
*Zinc-coated iron is generally referred to as “galvanized iron.”
Sources:
http://www.cdcc.usp.br/exper/medio/quimica/6eletroquimg.pdf
http://educar.sc.usp.br/ciencias/quimica/qm1-3.htm#termica
http://www.cienciamao.usp.br/dados/t2k/_quimica_q23d.arquivo.pdf
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