CORROSION THEORY DOE-HDBK-1015/1-93 Corrosion CH-02 Rev. 0 Page 4 TABLE 1 Electromotive - Force Series (77?F) Element Electrode Standard Electrode Reaction Potential, v Sodium Na Na   + e -2.712 + Magnesium Mg Mg     + 2e -2.34 ++ Beryllium Be Be    + 2e -1.70 ++ Aluminum Al Al + 3e -1.67 +++ Manganese Mn Mn    + 2e -1.05 ++ Zinc Zn Zn    + 2e -0.762 ++ Chromium Cr Cr + 3e -0.71 +++ Iron Fe Fe + 3e -0.44 +++ Cadmium Cd Cd    + 2e -0.402 ++ Cobalt Co Co    + 2e -0.277 ++ Nickel Ni Ni    + 2e -2.250 ++ Tin Sn Sn    + 2e -0.136 ++ Lead Pb Pb    + 2e -0.126 ++     Hydrogen     H 2H   + 2e              0.000 (reference) + Copper Cu Cu    + 2e +0.345 ++ Copper Cu Cu   + e +0.522 + Silver Ag Ag  + e +0.800 + Platinum Pt Pt    + 2e +1.2 ++ Gold Au Au + 3e +1.42 +++ The surface of any metal is a composite of a very large number of micro-electrodes, as illustrated in Figure 2.  In order for corrosion to occur, the micro-cells must also be connected through some conducting path external to the metal.  Usually the external connection is provided by water or an aqueous solution and the cells produce a current, allowing the chemical reactions responsible for corrosion to proceed.