Thermodynamics of Adsorption

The objective of this paper is to investigate the effect of temperature (15-65oC) on the efficiency of succinic acid (SA), as an inhibitor, for the corrosion of a low cabon steel (LCS) electrode in aerated non-stirred 1.0 M HCl solutions (pH 4). Weight loss, potentiodynamic polarization and EIS (electrochemical impedance spectroscopy) techniques were applied to study the metal corrosion behaviour in the absence and presence of different concentrations of SA in this temperature range. Results obtained showed that the inhibition efficiency decreases with increase in temperature, indicating that SA physisorbs on the electrode surface. Activation energies have been calculated in the absence and presence of various concentrations of SA by measuring the temperature dependence of the corrosion rate obtained from the three methods. The adsorptive behaviour of SA on the LCS surface follows Temkin-type isotherm. The standard free energies of adsorption are lower than 40 kJ mol-1, confirming the physisorption of SA on the electrode surface. Surface analysis using EDX (energy dispersive X-ray) confirmed the results obtained from chemical and electrochemical measurements. All the results obtained from the methods employed are in reasonable agreement