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CPCs have been used by the aircraft industry for many years as a means of protecting against corrosion. These treatments are often recommended by the manufacturer in the maintenance manuals as a way to help prevent the onset of corrosion in specific locations on the aircraft. However CPCs are not used everywhere and time has shown that the original protective coatings on aircraft components have a finite lifetime and hence corrosion incidences do occur and increase with the age of the aircraft. CPCs could be used more widely in a temporary capacity to provide an extra layer of protection in these areas where the original protective coating has degraded.
There is a large range of CPCs that are commercially available ranging from water displacing to non-water displacing soft film and water displacing to non-water displacing hard film. The exact compositions of CPCs are not known due to their proprietary nature however information contained in the Materials Safety Data Sheets (MSDSs) reveal that they may include (i) an oil, grease or resin based film former, (ii) a volatile, low surface tension carrier solvent, (iii) a non volatile hydrophobic additive and (iv) various corrosion inhibitors or surface active agents. The water displacing CPCs act by spreading across surfaces, into cracks and crevices where they displace any moisture present, leaving behind a residue to act as a further barrier after the carrier solvent has evaporated. The hard film CPCs dry to a waxy or hard resin like finish after application and provide a barrier film to corrosive environments. The following is a list of the CPCs tested, by CPC type: (reference)
However, it is difficult to identify the exact composition of CPCs because of the proprietary nature of that information. The Material Safety Data Sheets provide the following details, CPCs may contain:
Some CPCs act by spreading across surfaces and into crevices, displacing any water which may be present. The carrier solvent evaporates and leaves a residue consisting of the film, hydrophobic additive and the inhibitors. Others dry to a waxy or hard resin like finish after application and provide a barrier film.
