Ionic Liquids (ILs) have been identified as a promising sustainable alternative to volatile organic compounds as solvents in industry. Although they have been widely applied in research, ILs are still not employed regularly on a large scale. A crucial reason for this is the relatively unexplored chemistry of IL corrosion.

This study investigated the physicochemical properties of three 1-alkyl-3-methylimid azolium chloride ILs (n=0,4,8) in aqueous solution. CuCl2 and ZnCl2 complexation in IL solution and corrosion caused by the IL solutions were also analysed.

It was concluded that there are three regimes of behaviour in solution, at low concentrations IL behaviour is salt like. As concentration increases ion pairs form and further IL addition causes a hydrogen bonding network to develop. Protic IL solutions
demonstrated higher conductivity, higher density, and reduced viscosity compared to aprotic Ils.

When metal chlorides are dissolved, at low water concentrations distorted tetrahedral Cu-hydroxychloro complexes and IL-complexed ZnCl4 2 are the major complexes in 1-butyl-3-methylimidazolium chloride ([C4C1im]Cl) solutions and betaine
hydrochloride ([Bet]HCl) solutions. As IL concentration decreases both metals form octahedral hydrated complexes.

For all solutions with greater than 0.5 mol% IL, Cu and Zn corrosion rates are higher than the acceptable industrial limit. Protic ILs have significantly higher corrosion rates than Aprotic ILs, particularly for Zn. For Cu corrosion behaviours were dominated by Cl concentration, whereas for Zn pH was also a significant factor, demonstrating that IL cation can have a significant impact on corrosion rate.

The work has presented a holistic investigation of IL solution properties and their contribution to corrosion mechanisms. Cl K-Edge XANES experiments have demonstrated a novel technique for investigating the hydrogen bonding in IL solutions. It has provided a framework for future investigation, highlighting the importance of
establishing fundamental chemistry before IL corrosion can be understood and predicted.