Page 158 - Fundamentals of Air Pollution 3E

9

Effects on Materials

and Structures

I. EFFECTS ON METALS
The principal effects of air pollutants on metals are corrosion of the
surface, with eventual loss of material from the surface, and alteration in
the electrical properties of the metals. Metals are divided into two catego-
ries—ferrous and nonferrous. Ferrous metals contain iron and include
various types of steel. Nonferrous metals, such as zinc, aluminum, copper,
and silver, do not contain iron.
Three factors influence the rate of corrosion of metals—moisture, type
of pollutant, and temperature. A study by Hudson (1) confirms these three
factors. Steel samples were exposed for 1 year at 20 locations throughout
the world. Samples at dry or cold locations had the lowest rate of corrosion,
samples in the tropics and marine environments were intermediate, and
samples in polluted industrial locations had the highest rate of corrosion.
Corrosion values at an industrial site in England were 100 times higher
than those found in an arid African location.
The role of moisture in corrosion of metals and other surfaces is twofold:
surface wetness acts as a solvent for containments and for metals is a
medium for electrolysis. The presence of sulfate and chloride ions acceier-

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