A “Toolbox” for Forensic Engineers

Materials in Distress 53
solutions. In this state they are able to take part in chemical reactions as
positively charged ions (written Fe 2+ or Fe 3+ for iron, depending on whether
two or three electrons have been given up) and the freed electrons are able
to form an electric circuit. This process is called “corrosion,” and results in
a wasting away of the surface of the metal and the formation of a chemical
“corrosion product.” The consequential loss of cross-sectional area thus
reduces the capacity of the component to support load. The propensity to
corrode depends on the potential of the atoms at the surface to enter
solution is called the “electrode potential” of the particular metal. The rate
of corrosion is determined by the current that flows through whatever
electrical circuit is established. Table 2.1 lists the electrode potentials of the
common metals.
Table 2.1 Standard Electrode Potentials of
Common Metals in Conducting Solutions of
Their Ions in Relation to a Hydrogen Electrode
Metal Electrode Potential (V)
Gold 1.42
Silver 0.80
Mercury 0.79
Copper 0.34
Lead -0.13
Tin -0.14
Nickel -0.25
Cobalt -0.27
Cadmium -0.40
Iron -0.44
Chromium -0.70
Zinc -0.76
Titanium -1.63
Aluminum -1.66
Magnesium -2.37