01 March 2005
Clear Water - Colorless water containing no visible
Critical Humidity - The relative humidity, under a
specific set of conditions, at which a metal or an alloy will
begin to corrode. In the presence of hygroscopic
Combustible Liquid - Any liquid capable of igniting
(moisture absorptive) solids of corrosion products, the
and burning at or above 100F, but below 200F.
critical humidity will be lowered. For example, steel will
not corrode if the relative humidity is less than 30% in a
Concentration Cell - An electrolytic cell consisting of
an electrolyte and two electrodes of the same metal or
alloy that develops a difference in potential as a result
Cure - The process by which a coating or sealant is
of a difference in concentration of ions (most often metal
converted from the liquid to the solid state. Enamel
ions) or oxygen at different points in a solution.
paints cure; lacquers do not cure.
Conformal Coating - A closely adhering moisture and
Cure Rate - The length of time required for a coating or
gas barrier applied to circuit boards to prevent corrosion
sealant to obtain the minimum hardness required by the
and breakdown of electrical insulation.
Corona - A faint glow adjacent to the surface of an
electrical conductor at high voltage.
Deionized Water - Water which has had various organic
Corrosion Fatigue - A reduction in the ability of a metal
and inorganic materials removed by means of an ion
to withstand cyclic stress due to its exposure to a
Deposit Attack - When foreign material (dirt, corrosion
Corrosion Rate - The speed of corrosion attack. It is
products) is deposited on the surface of a metal, it may
usually expressed in terms of weight loss per unit of time
shield the metal from the oxygen necessary to regenerate
or depth of penetration per unit of time.
a protective oxide layer. An oxygen concentration cell is
formed, and serious corrosion may result.
Couple - Two or more metals or alloys in electrical
contact with each other. These usually can act as the
Desiccant - A drying agent which acts by absorbing
electrodes of a cell if they are immersed in an electrolyte.
Cracking - (1) Breaking of a metal or alloy in a brittle
Distilled Water - Water which has had various organic
fashion along a narrow path or network. (2) Localized
and inorganic materials removed by means of an
breaking of a paint film to expose the underlying material.
Crazing - The formation of surface cracks, often as a
Dry to Tape - The drying time required to allow a coating
fine network, that changes the properties of the film.
the ability to resist marring by adhesive tape.
Crazing does not usually penetrate into the underlying
Durability - Ability of components to function and
sustain stresses in field service for a specified period of
time with economical maintenance. This is measured in
Crevice Corrosion - Corrosion occurring within a
terms of minimum acceptable failure free lifetime (MFL)
crevice. The crevice may be formed at the mating
and expected maximum lifetime (EML) including repair
surfaces of two or more parts of the same or different
(avionics components), and mean time between failure
metals, or by a metal and nonmetallic material. Stainless
(MTBF) (aircraft components).
steel and aluminum alloys are particularly susceptible
to crevice corrosion. Crevice corrosion is an example of
concentration cell corrosion.
Critical Avionic Components - Miniature or
Elastomer - A synthetic material with the elastic
properties of natural rubber.
microminiature circuits, including the components,
printed circuit boards, tunable coils, tuned circuits, and
devices with gold/silver plated connectors or contacts.