Galvanic Corrosion vs. Electrode Potential
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:
Element | Electrode 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.
Related Topics
• Corrosion
Corrosion in piping systems caused by thermodynamic and electrochemical processes - corrosion problems and methods of protection and prevention.
• Electrical
Electrical engineering with units, amps and electrical wiring. Wire gauges, electrical formulas, motors and more.
• Miscellaneous
Engineering related topics like Beaufort Wind Scale, CE-marking, drawing standards and more.
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