TO 1-1-700 - Robins Air Force Base

TO 1-1-700
basic copper sulfate and perhaps hydrated copper carbonate.
The patina in the thin, firmly adhering state actually offers
increased corrosion protection to the base metal, but the patina
in a rough or frosted state should be removed. When coupled
with most metals used in equipment construction, copper is
the less active metal and greatly accelerates corrosion of the
other metals. This is especially true in copper/aluminum couples.
Examples are usually found in electrical components and
in areas where copper bonding strips or wires are fastened to
an aluminum chassis or structural components.
Figure 3-18. Magnesium Corrosion Products
3.8.5 Copper and Copper Alloys. Copper and copper
alloys are quite corrosion resistant and corrosion is usually
limited to staining and tarnish. Generally, such changes in surface
conditions are not dangerous and should ordinarily have
no effect on the part. Copper corrosion is evidenced by the
accumulation of blue or blue-green corrosion products on the
corroded part. Protective paint coatings are seldom required
because of the inherent resistance of the metal. However, paint
finishes may be applied for decorative purposes or if the normal
tarnish or green patina on the copper is objectionable. The
green patina is merely a thin coating consisting mainly of
3.8.6 Cadmium. Metal parts are plated either to increase the
corrosion resistance of the parts or to develop certain physical
properties on the surface of the parts, such as abrasion (wear)
resistance and high temperature oxidation resistance. Parts
may also be plated to create a compatible dissimilar metal
contact, to provide a sacrificial metal layer, or to provide a
satisfactory surface for soldering. Cadmium is used as a coating
to protect steel parts by acting as a sacrificial layer and to
provide a compatible surface when a part is in contact with
other metals such as aluminum alloys. Attack on cadmium is
evidenced by brown to black mottling of the surface or as
white powdery corrosion products. When cadmium shows
mottling and isolated voids or cracks in the coating, the plating
is still performing its protective function. The cadmium plate
on iron or steel continues to protect until such time as actual
iron rust appears (see Figure 3-21). Even then, any mechanical
removal of corrosion products should be limited to metal surfaces
where cadmium has been depleted.
Figure 3-19. Steel Corrosion Products (Rust)
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