Ask the Expert Question-and-Answer Archive

by Ron Joseph

November, 2003

Vapor Corrosion Inhibitors

Q. Do volatile corrosion inhibitors (VCIs) contaminate the surface of bare metals? VCIs are anti-corrosive coatings for metal contained within their packaging protection. Once the packaging is removed the VCIs are supposed to volatilize into the workspace. However, I've heard some VCI chemicals, such as benzotriazole, chemically bond with some metals and others saturate the surface.

A. I don't know the total answer to your question, but I do know that VCIs are intended to form a microscopic layer on exposed metal surfaces. In fact, if they do not contact the surface at all, I don't see how they can function as corrosion inhibitors. The fact that they are contained in small packages is irrelevant if they can't contact the exposed metal. When the metal object, machine, instrument, etc., is packaged together with a small package containing the VCI, the chemicals in the small package are intended to evaporate inside the larger package, saturate the air and deposit on the exposed metal surfaces. During shipping if any moisture enters the larger package the VCI that is in contact with the metal surface protects the surface from corrosion. What I don't know is for how long the chemicals remain on the metal surfaces or whether or not they form a chemical reaction. In any case, these corrosion inhibitors are deposited in such microscopically thin layers that I'm wondering why you are concerned? In all probability they only provide very temporary corrosion protection to the surface and might well evaporate soon after the metal surface is removed from its package. Please feel free to write back and let me know what your concern is.