MIL-HDBK-1110
1.4
Control of Facilities Deterioration. While coating of
surfaces is the most commonly used method of protecting them, it
can be used most effectively in conjunction with other control
methods. These include but are not limited to proper design of
components, proper selection of materials and components,
cathodic protection, controlling the environment, and use of
corrosion inhibitors.
1.4.1
Corrosion Control by Coatings. Coatings protect metals
from corrosion by interfering with one or more of the conditions
necessary for corrosion to occur. The three protective
mechanisms of coatings are:
a)
Barrier
b)
Inhibitors
c)
Cathodic protection
Regardless of the mechanism(s) of protection imparted
by coatings, a multiple coat system is normally recommended for
maximum protection of metals. The primer is formulated to bond
well to the substrate and provide a good surface for adhesion of
additional coats. Zinc or inhibitive primer pigments can provide
corrosion control, as described above. Intermediate coats
provide additional barrier protection and unite the primer and
finish coats. The finish coat provides additional barrier
protection as well as resistance to weathering, and color,
texture, and gloss.
1.4.1.1
Barrier Protection. Most coatings provide corrosion
protection by forming a barrier that is relatively impermeable to
moisture and electrolytes (usually salts) necessary for
corrosion. No organic coating is completely impermeable, but
some are much more so than others. Obviously, the coating film
must be thick enough and free of discontinuities (holidays) to
achieve maximum barrier protection.
1.4.1.2
Inhibitive Pigments. Some pigments are used in primers
for metals to inhibit the corrosion reaction at the metal/primer
interface. Red lead and zinc chromate pigments, used for this
purpose for many years, are seldom used today because of health
and environmental concerns. Acceptable alternate corrosion
control pigments are available.
1.4.1.3
Cathodic Protection. Some coatings have a high loading
of fine zinc particles to provide cathodic protection to steel
surfaces. They convert anodic areas on the steel to cathodic
areas. The zinc particles must be in electrical contact with
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