Abstract
The inhibition of mild steel corrosion in 1 M HCl solution by some ionic liquids (ILs) namely, 1-hexyl-3-methylimidazolium trifluoromethanesulfonate [HMIM][TfO], 1-hexyl-3-methylimidazolium tetrafluoroborate [HMIM][BF4], 1-hexyl-3-methylimidazolium hexafluorophosphate [HMIM][PF6], and 1-hexyl-3-methylimidazolium iodide [HMIM][I] was investigated using electrochemical measurements, spectroscopic analyses and quantum chemical calculations. All the ILs showed appreciably high inhibition efficiency. At 303 K, the results of electrochemical measurements indicated that the studied ILs are mixed-type inhibitors. The adsorption studies showed that all the four ILs adsorb spontaneously on steel surface with [HMIM][TfO], [HMIM][BF4] and [HMIM][I] obeying Langmuir adsorption isotherm, while [HMIM][PF6] conformed better with Temkin adsorption isotherm. Spectroscopic analyses suggested the formation of Fe/ILs complexes. Some quantum chemical parameters were calculated to corroborate experimental results.
Highlights
Mild steel is extensively used in industries for various applications including construction of tanks, gas cylinders, pipelines, heat exchangers among others due to its excellent mechanical strength and relatively low cost
Since an inhibitor can only be regarded as anodic or cathodic type when the displacement in Ecorr is greater than 85 mV [32,33], the studied ionic liquids (ILs) behave as mixed-type inhibitors
Association into aggregates by ILs as well as micelle formation by surfactants are affected by a number of factors, which include alkyl chain, nature of counterions and interactions with water [35,36,37]
Summary
Mild steel is extensively used in industries for various applications including construction of tanks, gas cylinders, pipelines, heat exchangers among others due to its excellent mechanical strength and relatively low cost. Various organic compounds containing nitrogen, oxygen, phosphorus and/or sulfur heteroatoms, and/or π-electron systems have been reported as inhibitors of metal corrosion in different aggressive media [1,2,3,4,5,6,7,8,9,10,11]. These groups of atoms or bonds facilitate electronic interactions between organic corrosion inhibitors and metal surface thereby aid adsorption of the inhibitors onto metal surface [9]. Researches in the field of corrosion inhibitors in the recent years have been directed towards the design and quest for “green” corrosion inhibitors due to the new generation of environmental regulations requirements for the replacement of toxic chemicals with the so-called “green chemicals” [12,13,14,15,16]
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