Volatile corrosion inhibitors for ferrous and non-ferrous metals and alloys: A review

Volatile corrosion inhibitors (VCIs) or vapor phase inhibitors (VPIs) represent a class of compounds that are employed to protect the corrosion or oxidation of ferrous and non-ferrous metals and alloys where other surface treatments are impractical. The VCIs release slowly inside the sealed airspace and actively adsorb and prevent corrosion. Several VCIs have been employed as effective inhibitors for several metals like iron, zinc, aluminum, etc. and their alloys. Literature study revealed that VCIs protect metallic corrosion either by forming a surface protective film on the metal surface or neutralizing the corrosive surrounding reagents H₂O, SO₂, H₂S and CO₂, etc. Because of the high volatility, VCIs easily vaporize and their vapors condense on the metallic surface as well as the volume available in the crevices, pores and cracks thereby gives complete protection where they used. The VCIs can be inserted into coatings, foams, adhesives, powders, sprays and plastics. Several VCIs are known those act as effective inhibitors by themselves and few other VCIs are also known those hydrolyzed products act as corrosion inhibitors. The inhibition ability as well as quantity of the adsorbed VCIs on metallic surfaces can be determined by several commonly employed techniques such as contact angle, radiotracer, polarographic and electrocapilarity methods. Present review article describes the assortment of previous works published on VCIs as corrosion inhibitors for ferrous and non-ferrous metals and alloys. The present report also deals with salient features of VCIs and mechanism of their action.