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A simple and inexpensive indicator which reveals the tell-tale signs of corrosion long before it affects Air Force equipment has been developed by the Air Research and Development Command. It is based on the principle that a thin metal film deposited on a suitable base changes in appearance when it corrodes. During exposure the electrical resistance of such film increases, since metal oxide is normally a poorer electrical conductor than the base metal.
Engineers who deveolped the process at ARDC's Wright Air Development Center, Ohio, deposited metal films of iron and other metals uniformly over glass and plastic bases through vacuum deposition--a process which "evaporates" metals in a high-vacuum chamber.
The metal is heated in a vacuum chamber until it evaporates.
The condensation of the metal vapors deposits a film on the base material. This process is also used for decorative and protective coatings on such items as toys, automobile parts, and jewelery.
Inspection of stored Air Force equipment is usually accomplished at regular intervals. This requires opening the package, examining and represerving the contents, and then repackaging.
Present corrosion indicators used in packaging are either chemical or electrical devices. Their indicating properties are affected by high temperatures and cannot be used with some of the newer methods of Air Force packaging.
The metal film sensing elements can be used either visually or electrically to indicate a dangerous corrosive condition long before stored equipment is damaged. Further research is in process to develop indicators of various sensitivities by changing the type and thickness of the metal films.
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