Inhibition of low carbon steel (LCS) corrosion in 0.5 M H2SO4 solution by three bipyridinium dihalides (TMbPyBr2, HMbPyBr2 and MPhbPyCl2) was evaluated by potentiodynamic polarization curves, EIS and SEM techniques. The effectiveness of the inhibitors is ranked as follows: MPhbPyCl2 ≅ TMbPyBr2 > HMbPyBr2. The compounds behave as mixed-type inhibitors and their adsorption on the steel surface obeys the Langmuir adsorption isotherm. EIS measurements indicate that charge transfer controls the corrosion of steel in the absence and presence of the inhibitors and the equivalent circuit Re(RctQdl) represents the electrode/solution interface either at the corrosion potential or at −75 and 30 mV versus Ecorr. The compounds show maximum inhibition efficiency at 35 °C. The mechanism of corrosion inhibition was discussed in the light of the molecular structure of the bipyridinium salts.
