On the corrosion inhibition of carbon steel in 1 M HCl with a pyridinium-ionic liquid: chemical, thermodynamic, kinetic and electrochemical studies

Abstract

The efficiency of 1-hexylpyridinium bromide (NR3) ionic liquid for the corrosion inhibition of carbon steel in 1 M hydrochloric acid has been investigated by gravimetric, linear polarization (LPR), electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM) techniques. Increasing NR3 concentration led to increasing inhibition efficiency (IE%) following the increasing surface coverage (θ). Thermodynamic studies revealed a decreasing IE% with increasing temperature proven to be due to the physical nature of the adsorption mechanism of NR3 which was shown to obey a Langmuir isotherm. LPR elucidated the mixed type inhibition effect of NR3 and its effective blocking of both cathodic and anodic corrosion sites on the carbon steel surface leading to decreased current densities of both Tafel branches without altering the corrosion mechanism. EIS results confirmed the adsorptive behavior of the investigated ionic liquid in replacement of the initially adsorbed water molecules and the formation of a protective film leading to increasing charge-transfer resistance as a result of decreasing double layer capacitance with increasing concentrations. The IE% attained ca. 88.6% in the presence of as low as 3 × 10⁻³ M NR3 inferring the high inhibitory effect of the studied compound. SEM micrographs confirmed the formation and growth of a protective layer reaching a dense coverage at the optimum concentration.