ANTI CORROSION ACTIVITY OF ETHYLENE TETRA PHOSPHONIC ACID–Cu2+ SYSTEM ON CARBON STEEL IN H2SO4 SOLUTION

The anti-corrosion activity of a newly synthesized ethylene tetra phosphonic acid (ETPA), namely {Ethylenebis [(2-hydroxy-5,1,3-phenylene) bismethylene]} tetraphosphonic acid, against the corrosion of carbon steel in 0.5-M H2SO4 medium and its synergistic effect with Cu2+ ions were studied using potentiodynamic polarizations and electrochemical impedance spectroscopy (EIS). Potentiodynamic polarization studies indicate that ETPA acts as a mixed-type inhibitor and inhibition efficiency increases with increasing ETPA concentration. The adsorption of ETPA at the surface of carbon steel follows Langmuir adsorption isotherm. EIS results demonstrated the adsorption of ETPA onto the carbon steel surface, leading to the formation of ETPA overlaying film. Addition of 5⋅10−5 M Cu2+, at low ETPA concentration (5⋅10−5 M), results in significant increase in inhibition efficiency (88%), superior to that obtained at high ETPA concentration (81% at 5⋅10−4 M). SEM and EDAX analyses confirmed the existence of a uniform protective film on the electrode surface attributed to ETPA–Cu2+ complex formation.