Shiny Copy & Verdigris: Calling a metallurgist

Discussion in 'Homebrewing' started by pweis909, Feb 8, 2013.

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  1. pweis909

    pweis909 Grand Pooh-Bah (3,250) Aug 13, 2005 Wisconsin
    Pooh-Bah

    Weirdness. I had copper manifold parts soaking in two different vessles with star san. I intended to do this for a few hours to clean them up, but forgot and left them for 10 days. Parts came out of one vessel covered in verdigris. Due to size limitations, the long piece of my manifold went in a different container, and it emerged brilliantly shiny. The verdigris vessel was stainless steel. The other was plastic. What gives?
     
    #1 pweis909, Feb 8, 2013
  2. Hands22

    Hands22 Initiate (0) Oct 14, 2011 Florida

    There's a slight galvanic potential between copper and stainless steel. Not enough to normally be an issue, but when you add in that the electrolyte was an acid (starsan) instead of just water then oxidation will happen. Plastic has no galvanic potential thus why there was no verdigris on the copper in that container.
     
    #2 Hands22, Feb 8, 2013
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  3. inchrisin

    inchrisin Pooh-Bah (2,013) Sep 25, 2008 Indiana
    Pooh-Bah

    SHOWOFF! :sunglasses:
     
    #3 inchrisin, Feb 8, 2013
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  4. pweis909

    pweis909 Grand Pooh-Bah (3,250) Aug 13, 2005 Wisconsin
    Pooh-Bah

    The winner! John Palmer (Namedropper Alert!) confirmed this to me in an email a few minutes ago. But you may have beaten him to the punch. I should have realized it (undergrad chem major) but the evidence didn't sink in. There was also a residue coating the stainless pot, which now that I think about it, seems like some Galvanic cell diagram from a text book.

    I love when homebrewing teaches me new stuff, or in this case, reminds me that 30 years ago my Dad scraped up several thousand dollars so I could get an education. Ironic how beer prevented me from learning \back then and now it is helping me learn. Dad would be so proud. Or pissed. I'm not really sure. I don't think I'll tell him.
     
    #4 pweis909, Feb 8, 2013
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  5. Hands22

    Hands22 Initiate (0) Oct 14, 2011 Florida

    Haha, glad I could help jog your memory.
     
    #5 Hands22, Feb 8, 2013
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  6. good_gracious

    good_gracious Initiate (0) Aug 19, 2012 Maryland

    One more thing to add to this answer. In addition to needing ionic conductivity in your solution and a nonzero difference in reduction potentials, you also need to have a current conduction path between the two. If you have ions flowing but no electrons the cell is incomplete. So in other words if your copper parts were not touching the stainless at all (if they were placed on a plastic spacer for example) then you would have been fine.
     
    #6 good_gracious, Feb 8, 2013
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  7. jmw

    jmw Initiate (0) Feb 4, 2009 North Carolina

    Nicely done gents. Very impressive.
     
    #7 jmw, Feb 8, 2013
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