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    STUDIA CHEMIA - Issue no. Special Issue 1 / 2009  

  Abstract:  The inhibition effect of several plant extracts on the corrosion of carbon steel in 0.5 M H2SO4 has been investigated by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). One has attempted to determine the corrosion characteristics in the absence and in the presence of natural plant extracts obtained from Allium Sativum and Juglans Regia using VoltaLab 40 potentiostat. Potentiodynamic polarization curves were plotted at a scan rate of 20 mV/min. The EIS investigations have measured the response of the electrochemical system using a 10 mV a.c. potential excitation within a frequency zone ranging from 100 kHz to 50 mHz. Equivalent circuit model was proposed based on fitting the impedance data and hence the main parameters of the corrosion system were obtained. The potentiodynamic polarization curves were employed to represent the Tafel lines and to evaluate the corrosion potential Ecorr and the kinetic parameters namely the corrosion current density icorr and the anodic, ba and cathodic bc Tafel slopes. The corrosion current densities have lower values in the presence of plant extracts. The inhibition efficiency calculated from the potentiodynamic polarization parameters and from EIS measurements were in agreement, the best results were obtained for the mixtures containing 400 ppm AS for all AS/JR concentration ratios.

Keywords: Inhibitors, Electrochemical impedance spectroscopy, Corrosion, Sulphuric acid, Steel
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