Differences in the corrosion inhibition of water extracts of Cassia fistula L. pods and o-phenanthroline on steel in acidic solutions in the presence and absence of chloride ions

The corrosion inhibition of water extract of Cassia fistula L. pods and o-phenanthroline on mild steel in acid solution in the absence and presence of 0.1 M NaCl have been investigated using weight loss measurements in addition to the potentiodynamic polarization technique. FTIR and GC-mass were used to identify the chemical composition of C. fistula L. pods. The inhibition efficiencies of C. fistula L. pods were 95.19% in 2 M H2SO4 and 86.13% in 0.5 M nitric acid solutions in the presence of chloride ions, while o-phenanthroline recorded 86.09 and 72.76% for the above acid solutions, respectively. All the ΔGads were negative which indicates spontaneous adsorption on the steel surface. Consequently the relationship between log (c/) and log c indicates that the adsorption of inhibitor onto steel surface follows the Langmuir adsorption isotherm.