*11.5.4.5 Volatile inhibitors or vapor phase inhibitors*

Volatile corrosion inhibitors (VCIs) are compounds which transferred in a closed environment to the site of corrosion by volatilization from a source **(Figure 15).** If the corrosion product is volatile, it volatilizes as soon as it is formed, thereby leaving the underlying metal surface exposed for further attack. This causes rapid and continuous corrosion leading to excessive corrosion. Example, Molybdenum oxide (MoO3), the oxidation corrosion product of molybdenum is volatile. In closed vapor process (shipping containers), volatile solids such as salts of dicyclohexylamine, cyclohexylamine and hexamethylene amine are used as volatile corrosion inhibitors [52].
