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Galvanic corrosion: trying to understand

  1. Oct 5, 2012 #1
    Hi, in the course of designing a heat exchanger for my company, I've ran into the problem of galvanic corrosion. I've managed to somehow figure out what to do to prevent it from happening, but I don't fully understand WHY. In other words, I don't have an exact feeling for what happens at the basic level. Let me try to explain the way I understand it, and hopefully I will get some feedback with where I am wrong:

    In this example, we have aluminum and stainless steel, electrically connected and bathed in an electrolyte:

    Since there is a voltage potential difference between the Al and SS, the electrons flow from the Al along the electrical connection to the SS.

    Due to this electrical flow, the Al is now missing some electrons, which means that the Al atoms turn into positively charged ions. These positively charged ions are then attracted to the negatively charged SS. They therefore break away from the Al and float their way through the electrolyte towards the SS. The breaking away from the Al is corrosion.

    Is there anything wrong with the above description of the process?

    If so, please let me know. If not, please let me know also...because I still have many things about the above process which I don't understand.
     
  2. jcsd
  3. Oct 5, 2012 #2

    Astronuc

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    Staff Emeritus
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    On has to understand the anodic and cathodic reactions, or reduction-oxidation reactions, and it helps to know the ranking of metals in the galvanic series. One should have learned this in an introductory chemistry course - redox equations are rather fundamental.

    Two metals in contact form a circuit in conjuction with the electrolyte, which could be water with various ionic species, e.g., saltwater, or other conductive medium.

    One metal will preferentially reduce, while the other will oxidize.

    These guys have a really good site from which one can learn about corrosion.

    http://corrosion-doctors.org/Modules/Modules.htm

    http://corrosion-doctors.org/Definitions/galvanic-series.htm
     
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