What is the difference between these two coins

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What is the difference between these two coins?

• http//tides.sfasu.edu2006/cdm4/item_viewer.php?C
  ISOROOT/StoneFortCISOPTR206CISOBOX1REC1

http//tides.sfasu.edu2006/cdm4/item_viewer.php?C
ISOROOT/StoneFortCISOPTR207CISOBOX1REC17
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Corrosion

• Is the primary means by which metals deteriorate
  on contact with water (and moisture in the air),
  acids, bases, salts, oils, aggressive metal
  polishes, and other solid and liquid chemicals.
  The best known case is rusting (oxidation).
• Corrosion processes are usually electrochemical
  in nature, having the essential features of a
  battery (gain and lose electrons).

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Oxidation - Reduction

• Oxidation Lose electrons to produce positive
  ions
• Example all metals oxidate
• Fe ? Fe2 Cu ? Cu
• Reduction gain electrons to produce negative
  ions
• Example non-metals reduce
• O ? O2- Cl ? Cl

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How to prevent corrosion?

• By the process of Electroplating
• Electroplating electro deposition of an
  adherent metallic coating upon an electrode for
  the purpose of securing a surface with properties
  or dimensions different from those of the basis
  material.
• Other words the ability to deposit very thin
  multi-layers of a metal like Copper, Nickel,
  Chromium, Zinc.

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Electroplating metals demonstration
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• Fe(s) CuSO4(aq) FeSO4(aq) Cu(s)
• Half reactions
• Oxidation Fe Fe2 2 e-
• Reduction Cu2 2 e- Cu
• The metal to be electroplated to the surface is
  oxidized to cations which enter the plating
  solution.
• The cations in the plating solution migrate to
  the cathode, where they are reduced to metal and
  deposited onto the surface of the metal being
  plated.