Recent developments in sustainable corrosion inhibition using ionic liquids: a review

Ionic liquids as corrosion inhibitors: literature survey

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1. Ionic liquids as corrosion inhibitors for iron alloys in HCl

Hydrochloric acid based electrolytes are widely used for academic as

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M ðH₂OÞ SO₄=2Cl þ 2e⁻↔M^2þ þ OH⁻ þ H^þ þ SO²⁻=2Cl⁻ ð4Þ

Therefore, in the presence of chloride and sulphate anions anodic oxida-
tion reactions get accelerated. However, presence of ionic liquids (ILs) retards the anodic oxidation reaction by the adsorption of ionic liquids cation (ILs⁺). Rapid oxidation of metallic component cause accumula- tion of electrons at anode, therefore cations of the ILs get preferably ad- sorb on anodic site. The mechanism of ILs⁺ is illustrated below:

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   Anodic reactions with ionic liquids (ILs)
   

well as industrial purposes. Generally, low concentrated HCl electro- lytes (3–8%) are used for acid descaling process while highly concen- trated HCl based electrolytes (14–16%) are used for acid cleaning and pickling processes. HCl based electrolytes are highly aggressive and cor- rosive. HCl solutions of low concentration (1–5 M) are extensively used by academicians. Ionic liquids are also widely employed as metallic cor- rosion inhibitors for iron and its alloys such as mild steel (MS) and car-

M þ nH₂O↔MðH₂OÞ_nðadsÞ

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MðH₂OÞ_{n ads} þ SO²⁻=2Cl⁻↔MhðH₂OÞ_nSO²⁻=2Cl⁻i
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bon steel (CS). Literature survey showed that imidazolium based ionic liquids is most widely tested anticorrosion ionic liquids. In imidazolium based ionic liquids increase hydrophobicity by introducing the hydro- carbon chain accelerates the anticorrosive effect of the ionic liquids. It

_is believe that electron rich polar hydrophilic imidazolium moiety

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MhðH₂OÞ SO²⁻=2Cl⁻i
þ ILs^þ→MðH₂OÞ SO₄=2Cl−ILsC]⁻_ads ð7Þ
(head) adsorbs on metallic surface and non-polar hydrocarbon chain

_(tail) orients towards the solution side. Deyab et al. [71] studied the an-

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