Vapor phase corrosion inhibitor
Description
A volatile substance used to minimize corrosion or tarnishing of metals. Vapor phase corrosion inhibitors (VPI) can volatilize at room temperature to form a thin deposition layer on nearby surfaces. Their ability to minimize corrosion was first discovered in the early 1900s, but not commercially applied until the 1950s when it was used by Shell to protect military equipment. Some VPI compounds are nonreactive and simply provide a barrier layer that minimizes oxidation and tarnishing of metals. Other VPI compounds are basic, such as the amines, and react with acids in the environment. The strongly basic compounds (sodium hexametaphosphate, Diethylaminoethanol, Morpholine, etc.) are used in HVAC and fire suppression systems to minimize pipe corrosion. Some of the less reactive VPI compounds (Dicyclohexyl amine nitrite (VPI 260), Camphor, Benzotriazole, etc.) have been incorporated in antitarnish papers or enclosed in storage/display cases.
Synonyms and Related Terms
VPI; vapour phase inhibitor; camphor; DICHAN [Cortec] (dicyclohexylammonium nitrite); VPI 260 [Shell] (dicyclohexyl amine nitrite); volatile corrosion inhibitors; guanidine
Risks
- May produce an oily film on materials.
- Many are highly alkaline and hygroscopic (Hatchfield 2002).
- Some VPI materials are suspected carcinogens
Physical and Chemical Properties
- Dicyclohexyl amine nitrite: Vapor pressure = 0.00013 @ 21C; pH of condensate = 10.0
- Benzotriazole: Vapor pressure = 0.04 @ 20C
- Cyclohexylamine carbonate: Vapor pressure = 0.397 @ 25C
- Morpholine: Vapor pressure = 8.0 @ 20C
Resources and Citations
- B.A.Miksic, R.H.Miller, 'The Fundamental Principles of Corrosion Protection with Vapor Phase Inhibitors', 5th European Symposium on Corrosion Inhibitors, Italy, 1980 at Link (contains tables for vapor pressure and pH of selected compounds)
- VCI technical information at http://www.vci2000.com/Technical_Info/technical_info.html
- G.S.Brady, Materials Handbook, McGraw-Hill Book Co., New York, 1971 Comment: p. 67
- Marjorie Shelley, The Care and Handling of Art Objects, The Metropolitan Museum, New York, 1987
- Pam Hatchfield, Pollutants in the Museum Environment, Archetype Press, London, 2002
- L. Selwyn, 'Historical Silver: Storage, Display and Tarnish Removal', J.IIC-GC, 15, 1990
- Naiemy Tarei Parastoo, Submitted information, May 2005
- History of Vapor Phase Corrosion Inhibitors at http://www.cases2go.com/html/vcihistory.html (primarily nitrites)