Inhibition of corrosion of cast iron by nitrite, hydrogen phosphate, and molybdate ions in corrosive water

摘要

The inhibitive action of nitrite, hydrogen phosphate, and molybdate ions at various concentrations on cast iron under different experimental conditions like period of immersion, temperature, and flow velocities in corrosive water were studied by weight loss and electrochemical methods. Molybdate ions show a maximum inhibition efficiency relative to other inhibitors. The plot of log theta/1 - theta versus log C is a straight line, which shows that the inhibitor obey the Langmuir adsorption's isotherm. Thermodynamic parameters like activation energy, heat of adsorption, free energy of adsorption, and entropy of adsorption were computed along with the kinetic parameters like open circuit potential (OCP), corrosion current (I-corr), Tafel slopes (beta(c), beta(a)), Tafel constant (beta) and corrosion rate.