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Corrosion Of Iron - Differential Aeration Principle

  1. Feb 27, 2007 #1


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    Hi. In chemistry, we are currently studying electrochemical cells. We are doing corrosion at the moment. Corrosion of iron, to be specific.

    If i have a piece of iron exposed to the air, it will form a thin layer of iron oxide, right? However, this oxide will have fine cracks and be quite porous, so corrosion can continue.

    At the areas where fractures/weaknesses in the oxide layer are present, moisture can still come into contact with the iron, and cause the oxidation of the iron into iron (II) ions. Therefore, these sites are the anodic sites of the corrision process.

    The oxygen from the air is reduced to hydroxide ions, using the electrons from the oxidation of iron. Iron (II) hydroxide is then formed, which further reacts to form rust.

    That is what i understand from reading my textbook. If there are any problems with it, please let me know.

    Now, the book then goes on to explain that the areas most exposed to oxygen become cathodic sites, and thus, protected from oxidation. This is what im not really understanding. Is this saying that the areas of the iron oxide layer most exposed become cathodic? And why does this protect them from corrosion? The book refers to this as the differential aeration principle.

    Thanks in advance,
    Last edited: Feb 27, 2007
  2. jcsd
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