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Electrode Potential and Galvanic Corrosion

Introduction to electro chemical series and corrosion of metals

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The potential difference between an anode and a cathode can be measured by a voltage measuring device but since the absolute potential of an anode or cathode cannot be measured directly - all potential measurements are made against a standard electrode. The standard electrode potential is set to zero and the measured potential difference can be considered as absolute.

Standard Hydrogen Electrode

  • The half-cell in which the hydrogen reaction takes place is called the Standard Hydrogen Electrode - SHE

Standard Electrode Potential

  • The potential difference measured between a metal M and the Standard Hydrogen Electrode - SHE

The electro-chemical series (electro-motive series) is a list of metals arranged in order of their standard potentials to the hydrogen electrode:

ElementElectrode Potential
(volts)
Lithium -3.04
Rubidium -2.92
Potassium -2.92
Calcium -2.87
Barium -2.80
Sodium -2.71
Magnesium -2.37
Beryllium -1.85
Aluminum -1.67
Manganese -1.19
Zinc -0.76
Chromium -0.74
Tungsten -0.58
Iron -0.44
Cadmium -0.40
Cobalt -0.28
Nickel -0.24
Tin -0.14
Lead -0.13
Hydrogen +0.00
Antimony +0.10
Copper +0.34
Iodine +0.54
Silver +0.80
Mercury +0.85
Bromine +1.07
Platinum +1.20
Chlorine +1.36
Gold +1.50
Fluorine +2.87

Note! - metals higher up in the electro-chemical series displaces metals lower in the series - which means that when connecting two metals with different potentials the metal with the lowest potential corrodes.

Corrosion Problem when Connecting Copper and Iron/Steel

A very common connection in piping systems are copper and iron/steel. with this connection iron/steel corrodes many times faster than iron/steel alone.

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