What is a volatile corrosion inhibitor (VCI) and how it works

How does a volatile corrosion inhibitor protect metal in a closed package?

A volatile corrosion inhibitor protects metal in a closed package in three steps: it volatilizes from a carrier, diffuses through the enclosed air, and condenses on and acts chemically with the metal surfaces in that space (Henderson and Lyublinski, 2010). The TIS cargo guide of the German Insurance Association (GDV) describes VCI products as polar organic or inorganic compounds that sublime from their carrier, saturate the enclosed atmosphere and deposit on bare metal as an invisible monomolecular film (GDV TIS, accessed 2026). Carriers include paper, paperboard, film, foam and emitters, and the inhibitor can also be added to powders, sprays, oils and water (GDV TIS, accessed 2026). Because the inhibitor travels as vapor, it reaches recesses and internal cavities that are hard to coat (Ansari et al., 2018). The adsorbed VCI film is in dynamic equilibrium: molecules keep desorbing from the metal and are replaced from the saturated air (Luchkin et al., 2021). The enclosure therefore matters as much as the chemical. NACE TM0208-2024 frames VCI protection the same way: temporary protection is afforded as long as there is a moderately sealed enclosure containing the parts and the VCI source, which may be the package itself (AMPP, 2024). The TIS guide adds two practical conditions for VCI packaging: metal surfaces should be as clean as possible, and the VCI carrier should be no further than 30 cm from the metal (GDV TIS, accessed 2026).

Which chemicals act as volatile corrosion inhibitors?

Volatile corrosion inhibitors are mostly amines and amine salts, nitrite salts and azoles, often blended so that one package can protect more than one metal. The background section of a 2020 patent by the VCI maker EXCOR names amine carbonates, nitrites, nitrates, molybdates and carboxylates, primarily amine benzoates and caprylates, as the most common VCIs for ferrous materials (US 10753000 B2, 2020). A peer-reviewed review cites the protection of US military equipment with dicyclohexylammonium nitrite (DICHAN) in the 1940s as the first work on VCIs (Ansari et al., 2018). The table below shows which VCI chemistry family fits which metal, how its vapor behaves and what to watch for.

The key row for mixed-metal assemblies is the nitrite row: the EXCOR patent reports that known DICHAN recipes have proven unsuitable for parts that combine steel with aluminum, copper or galvanized steel (US 10753000 B2, 2020). A ferrous-only VCI is therefore a poor match for a multimetal assembly, and the product data should state which metals the VCI covers.

How long does VCI vapor take to protect a closed package?

VCI vapor starts protecting a closed package as soon as the first inhibitor molecules reach and adsorb on the metal, and full protection follows when the package air is saturated; the sources reviewed here give no single fixed time for field packages. A VCI maker's guidance says the time depends mainly on package volume and the temperature inside the enclosure, that smaller, tightly sealed packages saturate faster, and that cooler conditions slow diffusion without stopping it (Zerust FAQ on VCI timing, accessed 2026). Laboratory practice gives a scale. In a NACE conference paper on VIA jar tests, the authors call it good practice to allow conditioning, typically up to 24 hours, before heat or accelerants are introduced, so the VCI can first travel to the specimen (Henderson and Lyublinski, 2010). Volatility sets the pace: inhibitors with a saturated vapor pressure below 10⁻⁵ mmHg are almost unsuitable for traditional vapor phase protection, because their molecules do not reach the metal in sufficient amount before corrosion causes noticeable damage (Luchkin et al., 2021). The EXCOR patent calls the delay the development phase and ties it to the VCI depot: the finest possible powder and the permeability of the pouch walls regulate it (US 10753000 B2, 2020). This suggests sealing parts while they are clean and dry, and keeping a freshly sealed VCI package out of condensing conditions during the build-up period.

Why does VCI protection fade after the package is opened?

VCI protection fades after the package is opened because the adsorbed inhibitor layer stays on the metal only through an equilibrium with inhibitor vapor in the enclosed air. Molecules of a volatile inhibitor continuously desorb and evaporate from the metal, and the loss is replaced from the saturated atmosphere; if the airtightness of the space is broken, the inhibitor escapes and the protective adsorption films gradually degrade (Luchkin et al., 2021). How fast the VCI film degrades depends on how strongly the inhibitor adsorbs and on its vapor pressure (Luchkin et al., 2021). One VCI maker reports that in laboratory tests using electron spectroscopy for chemical analysis (ESCA), the layer on steel panels was no longer detectable about 2 to 4 hours after removal from the package (Zerust FAQ on removal, accessed 2026). The same source describes the time after opening as a short handling buffer whose length depends on surface cleanliness, relative humidity, airborne contaminants and condensation (Zerust FAQ on removal, accessed 2026). The same mechanism has an upside: the TIS guide says goods can be used or processed immediately after unpacking, because the molecular VCI film volatilizes automatically (GDV TIS, accessed 2026). If VCI-packed parts will wait after unpacking, the maker's guidance is to repackage them with VCI or apply a suitable rust preventive (Zerust FAQ on removal, accessed 2026). Resealing a VCI package restarts the build-up, which rebuilds protection over time (Zerust FAQ on VCI timing, accessed 2026).

Volatile corrosion inhibitor vs contact inhibitor: what is the difference?

A volatile corrosion inhibitor reaches metal through the air of a closed space, while a contact inhibitor, such as a rust preventive oil or coating, protects only the surfaces it is applied to. NACE TM0208-2024 defines VCI materials by this feature: they protect the surfaces of metal parts that are not in contact with the inhibitor (AMPP, 2024). The TIS cargo guide describes the VCI method as acting through both vapor phase and contact phase inhibitors, and lists VCI oils, applied by painting, dipping or spraying, as the direct-contact form beside VCI paper, foam, film and emitters (GDV TIS, accessed 2026). The practical difference follows from the mechanism. A contact film has to reach every surface that needs protection, and it does not depend on a sealed space. A vapor film needs a sealed space but no removal step: the TIS guide says no steps are necessary to remove the VCI protection from the packaged goods (GDV TIS, accessed 2026). Mixing VCI products carries its own risk, because the TIS guide states that VCI products from different manufacturers are not compatible, since their chemical composition varies, and advises using products from one manufacturer only (GDV TIS, accessed 2026). When parts combine several metals, or a storage plan mixes VCI packaging with oils, a corrosion specialist should check the inhibitor chemistry against each metal; Lubinpla can organize such a case from your own documents, such as the TDS and SDS, and return one cited document for review.

Related terms

• Vapor-inhibiting ability (VIA): the property that NACE TM0208-2024 evaluates for VCI materials on ferrous metal surfaces.

• DICHAN: dicyclohexylammonium nitrite, an early and long-used VCI for ferrous metals.

• Contact inhibitor: an inhibitor applied directly to the metal as a film, such as a rust preventive oil.

• Desiccant method: a separate packaging method that removes moisture instead of adsorbing an inhibitor on the metal.

• Multimetal VCI: a VCI blend formulated to protect ferrous and non-ferrous metals in the same package.