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Why does saltwater increase rate of corrosion, really?

  1. Jan 16, 2017 #1
    Why does salt water increase rate of corrosion, really? Most common answer I read was that salt makes water a better electrolyte. No further explanation.

    However, I'm not really getting the mechanism of this. I understand the mechanism of pitting corrosion in presence of chloride ions and I understand how chlorides break down the passive layer. Also, I'm ok with metal chlorides being more soluble so they do not form non-soluble layer of protection for protection from further corrosion.

    However, how does being a better electrolyte make up for higher corrosion rate? In regular NaCl solution, for regular DC current, conductivity is achieved by chloride ions and hydrogen ions attraction towards charged electrodes and redox reactions (and transferring electrons through the loop), not by moving charges themselves. So how does conductivity make up for faster rusting, is there a reaction, a mechanism, an electron transfer? Where?
     
  2. jcsd
  3. Mar 15, 2017 #2
  4. Mar 15, 2017 #3
    Where did you read that the conductivity of water (solution) enhances the corrosion ?

    I think the mechanisms that you read about Cl ions are probably more important than water conductivity.
     
  5. Mar 16, 2017 #4

    anorlunda

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    There are multiple mechanisms of corrosion. Caustic corrosion. Galvanic corrosion. I sounds as if you are thinking of the galvanic kind.

    https://en.wikipedia.org/wiki/Galvanic_corrosion
     
  6. Mar 20, 2017 #5
    Rust formation is basically an electrochemical reaction between iron and oxygen. Iron loses electrons, and oxygen gains them. The electrolytic compound decreases resistance to this reaction.
     
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