Corrosion Inhibition of Carbon Steel by Some Schiff Base Compounds in HCl and H2SO4 Solutions

The inhibition power of two Schiff bases on carbon steel corrosion in 1 M HCl and 0.5 M H2SO4 solutions has been investigated using weight loss, Tafel polarization, and electrochemical impedance spectroscopy techniques. The results revealed that increasing the concentration of inhibitors in acidic solutions led to a higher inhibition efficiency. The polarization curves indicated that the Schiff bases acted as mixed inhibitors, affecting both the cathodic and anodic reactions. The adsorption of the inhibitors on the carbon steel surface followed the Langmuir adsorption isotherm, and various adsorption isotherm parameters such as Kads, Delta Gads, Delta Hads, and Delta Sads were determined at room temperature. Furthermore, the effect of temperature on the inhibitors ' performance was examined within the range of 25-45 degrees C. The corrosion-related activation energy, pre-exponential factor (k), activation enthalpy, and entropy were calculated to assess the inhibitors ' behavior. Scanning electron microscopy (SEM) was employed to examine some carbon steel samples, revealing differences in inhibition efficiency attributed to the inhibitors ' chemical structure. The results highlighted the highest inhibition efficiency in H2SO4 medium at 93.4 %, with a corresponding free energy of 39.51 KJ/mol indicating physical-chemical adsorption of inhibitor molecules. Furthermore, an enthalpy value of -40.6 KJ/mol suggested an exothermic inhibitor absorption process. The findings are presented and discussed in detail.