The Inhibited effect of Phenolphthalein towards the corrosion of C38 Steel in Hydrochloric Acid

The inhibition of the corrosion of carbon steel in 1 M HCl by Phenolphthalein (Ph) has been investigated in relation to the concentration of the inhibitor as well as the temperature using weight loss and electrochemical measurements. The effect of the temperature on the corrosion behaviour with addition of optimal concentration of Ph was studied in the temperature range 298-323K. Polarisation curves reveal that Ph is a mixed type inhibitor. The value of inhibition efficiency decreases slightly with the increase in the temperature. Changes in impedance parameters (charge transfer resistance, R-t, and double layer capacitance, C-dl) were indicative of adsorption of Ph on the metal surface, leading to the formation of a protective film. Adsorption of Ph on the C38 steel surface is found to obey the Langmuir adsorption isotherm. Some thermodynamic functions of dissolution and adsorption processes were also determined.