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Pitting and Crevice corrosion

  1. Dec 30, 2018 #1
    Hi all,
    I am trying to understand how the process of either crevice or pitting corrosion works (I believe they are quite the same)
    I understood the part of how they start and what enhances them or how they can be prevented, but I can't understand an actual scenario.
    Say for example we have stainless steel in a water solution;
    1. From which elements and to which elements do the electrons travel?
    2. With which elements does the water react? -> and does it always change to hydrogen and hydroxide?
    3. How does hydrogen increase the acidity?
    4. Why does the steel where the corrosion take place always become the anode?
    I would really appreciate it if someone could explain this to me!

    Thanks a lot!
     
    Last edited: Dec 30, 2018
  2. jcsd
  3. Dec 30, 2018 #2

    anorlunda

    Staff: Mentor

  4. Dec 30, 2018 #3
    I am actually in my final year of the degree (mechanical engineering) however materials was never my strong point :sorry:
    I did read that information before and I also watched a number of videos on pitting/crevice corrosion, however I couldn't find a suitable example explanation.

    A summary of what I know (will focus on Crevice):
    • the fact that the crevice needs to be big enough for the corrodent to enter but small enough to remain stagnant,
    • the fact that crevices trap pollutants, moisture, and excludes oxygen (not entirely sure about the oxygen however to be honest, since it is required for corrosion to take place)
    • the oxide layer formed between the metal and oxygen to stop electron flow
    • this layer can be broken by mechanical means like scratching
    • and in order for crevice corrosion to take place 2 factors are important:
      1. drop in potential into the crevice
      2. and the chemical composition of electrolyte
    As you can see what I know (assuming it is correct) is only the theoretical aspect, I don't know how it would actually happen.
     
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