Abstract
Corrosion inhibition efficiency of alizarin red (AZR) as corrosion inhibitor on C38 steel in acid solution was investigated by means of weight loss, potentiodynamic polarization curve, electrochemical impedance spectroscopy (EIS) and Quantum chemical method. The inhibition efficiency was found to increase with increase in AZR concentration but decreased temperature. Weight loss measurements gave an inhibition efficiency of about 65.8 % in the presence of 1x10(-5) M alizarin red, which increased to about 96.3 % at AZR concentration of 1x10(-2) M. EIS results revealed that alizarin red took effects excellently as a corrosion inhibitor for C38 steel in 1 M hydrochloric acid media, and its efficiency attains more than 96.5% at 1x10(-2) M at 298 K. Changes in impedance parameters (charge transfer resistance, R-ct, and double layer capacitance, C-dl) were indicative of adsorption of AZR on the C38 steel surface, leading to the formation of protective films. Potentiodynamic polarization measurements showed that the presence of AZR in 1 M hydrochloric acid solutions decreased corrosion currents to a great extent. The above results showed that AZR acted as a mixed-type corrosion inhibitor. The adsorption of used compound on the steel surface obeys Langmuir's isotherm. The apparent activation energie, enthalpie and entropie of the dissolution process and the free energie were determined and discussed. The correlation between the inhibition efficiency and quantum chemical parameters was investigated in order to elucidate the inhibition mechanism of the investigated compound.