Study on the effect of imidazolium ionic liquid as a modulator of corrosion inhibition of anionic surfactant sodium dodecyl sulfate (SDS) on mild steel in sodium chloride solution

Present paper reports investigation done on two organic compounds to test them as corrosion inhibitors for mild steel exposed to neutral NaCl solution. Organic compounds capable of corrosion inhibition must form a protective film over the metal surface. This is usually possible since many of these organic compounds possess strong interaction properties with metal and get adsorbed over its surface. These organic compounds contain electronegative functional groups and atoms like S, N, P, and O, which form center for establishment of adsorption process. Accordingly, SDS and DMImCl were chosen as organic compounds to test as corrosion inhibitors. Electrochemical polarization tests, performed in this study, reveal decrease in corrosion rate of mild steel in NaCl solution by 14.3 to 6.08 mpy (mils per year) corresponding to increased inhibition efficiency of 57.3% on addition of up to 200 ppm SDS. On mixing 200 ppm of DMImCl in NaCl + SDS solution, the inhibition efficiency enhances to 85.1%. Similar outcome is also noticed from Electrochemical impedance and weight loss test results. Analysis of results obtained through FTIR, SEM/EDAX indicate adsorption of SDS/DMImCl mixture on the mild steel surface. Tensiometry tests, on ionic solution, reveal decrease in surface tension on addition of inhibitors with consequently increased surface activity and hydrophobic interaction between chains of the two inhibitors. Calculation done on the adsorption process indicates it to be ‘Langmuir adsorption isotherm’. This inference suggests that binding sites on steel surface are identical and homogeneously distributed. This layer is covered with a monolayer of adsorbed molecules i.e. DMImCl and SDS which is responsible for corrosion inhibition.