Environmental Engineering Reference
In-Depth Information
Figure 4.7
Effect of concentration of organic inhibitors on corrosion rate.
One gram of this inhibitor saturates about 550 M 3 of air and the protection to steel
is provided over years. Cyclohexylamine carbonate has higher vapor pressure and
is used in packages that must be opened and closed repeatedly.
The mechanism of inhibition is not the same for all vapor phase inhibitors.
Nitrite ions and benzoate ions in association with the oxygen present passivate
the steel surface. Carbonate provides alkalinity to the environment and the or-
ganic amine portion of the inhibitor effectively provides protection through ad-
sorption.
While the vapor phase inhibitors, in general, are effective in prevention of
corrosion in steel, they accelerate the corrosion of some nonferrous metals. The
vapor phase inhibitors based on nitrobenzoate organic compounds have been re-
ported to protect ferrous, copper, and other alloy systems.
4.3 PROTECTIVE COATINGS
The application of a coating, metallic or nonmetallic, on steel and other metals is
an age old and widely used practice for protection against corrosion. The primary
objective of a coating is to provide a physical barrier between the metal and the
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