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Why Corrosion is an Electrochemical Process |
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Why Corrosion is an Electrochemical Process Electrochemical Cells Corrosion is electrochemical in nature because the corrosive chemical reactions involve transfer of charge. Iron goes into solution as Fe++ ions. As these ions go into solution, the metal becomes negatively charged (by the electrons left behind) with respect to the electrolyte. A potential difference (voltage) is produced between the electrolyte and the metal. The process in which electrons are given up and positive metal ions are formed is called oxidation. ThThe sites at which the oxidation takes place on the surface of the metal become electrochemical cells made up of micro-electrodes of the two different substances; the metal and the electrolyte. These micro-electrodes set up many micro-cells connected through the bulk of the metal. If a different metal is used, it will go into solution to a greater (or lesser) extent producing a larger (or smaller) potential difference between the metal and electrolyte than was the case for iron, this form of corrosion is called galvanic corrosion or bimetallic corrosion. For example, magnesium and zinc go into solution to a greater extent than iron, and these metals will be more negative with respect to the electrolyte than iron. Nickel, lead, and copper go into solution less readily and produce a smaller potential difference. an lang="it"> Galvanic Corrosion Chart lists the potential differences for various metals in water. The order of the series can change for different electrolytes (for example, different pH, ions in solution). |
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| this article is taken from: DOE FUNDAMENTALS HANDBOOK CHEMISTRY Volume 1 of 2 - DOE-HDBK-1015/1-93 JANUARY 1993 | ||