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Galvanization and more reactive block

  1. Feb 25, 2012 #1
    When I galvanize iron or attract a more reactive block of metal to iron, that metal will oxidise instead of the iron. I understand that anions need to be present for the reaction to occur as the more reactive metal will have transferred its electrons to iron. So the eg magnesium will oxidise to Mg2+ and react with any anions present. However, when I galvanize an iron bin in the air, and it receives a crack so the iron is exposed too, the iron will not rust. So the zinc layer will transfer electrons to the iron bin, but how can the zinc exist as Zn2+? Since there are no anions in the air? I read a little on galvanising corrosion and it said that if moisture is present then the more reactive metal will corrode, but I thought that this is only true if the moisture has some anions already like in the soil. But in air even if there is moisture there is no anions so how can it rest with the Zn2+ ions? Thanks so much for the help.
     
  2. jcsd
  3. Feb 25, 2012 #2

    Borek

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    Staff: Mentor

    When Zn gets oxidized, oxygen gets reduced to O2- - here is your anion.
     
  4. Feb 25, 2012 #3
    Do u mean that when the iron just starts to oxidise, the electrons from zinc will enter iron so Fe2O3 gets reduced. Then since water in the air able to transfer the oxide ions, they move to the zinc forming zinc oxide?

    Is this the same as the magnesium block underground too, just that there are already some anions like NO3- for it to react with too? So in essence it has a closed circuit?

    Thanks for the help!
     
  5. Feb 26, 2012 #4

    Borek

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    Iron will not start to oxidize as long as it is connected to Zn, so there is no need for reduction of Fe2)3 and further transport of O2-.

    Water in the air is not able to transfer oxide ions, this is completely off for two reasons. First, ions are transported in water solution, not in the vapor. Second, ionic O2- immediately reacts with water producing OH-. It doesn't happen so easily with oxides like Fe2O3 because they are not entirely ionic.
     
  6. Feb 26, 2012 #5
    Oh, so when zinc is in contact even if there is a crack on it the iron will not rust. but i thought it does not rust as the electrons will flow into iron like in the sacrificial metal case. What happens when zinc is attached to iron but iron is exposed too? Will electrons flow into the iron working zinc ions? Then when sacrificial metal is used what happens?
    Thanks for the help!
     
    Last edited: Feb 26, 2012
  7. Feb 26, 2012 #6
    galvanization and more reactive block 2

    Hi I'm writing this because the other thread died before I got an answer. What happens when I use galvanization and sacrificial protection? I leaned thst electrons flow into the less reactive metal so as to reduce any rust.however, I according to Borek, electronics do not flow into iron. So what happens when using through sacrificial metal and galvanization? Thanks for the help.:)
     
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