Chemical and Electrochemical Studies of para-Hydroazopyrazolone Derivatives as Corrosion Inhibitors for Mild Steel in Hydrochloric Acid Solutions

A comprehensive study on the inhibitory effect of some para-Hydroazopyrazolone (antipyrine) derivatives verse mild steel corrosion in 1 M HCl solution has been performed by chemical method(WL), electrochemical techniques (Tafel polarization, electrochemical frequency modulation (EFM) and electrochemical impedance spectroscopy (EIS)) at 25 degrees C. The efficiency of inhibition rose with addition of inhibitor and decreased with raising temperature. Data of Tafel polarization reveals that these investigated compounds reduced both the anodic and cathodic reactions and thus behaved as mixed-type inhibitors. The ability of these molecules to adsorb on the surface of mild steel best fit with Langmuir's adsorption isotherm. The thermodynamic activation parameters of mild steel corrosion in 1 M HCl were determined and discussed. Scanning electron microscopy and energy dispersive X-ray (SEM & EDX) techniques were employed for surface examination of uninhibited and inhibited mild steel. A good correlation was found between the experimental results and the theoretical data. The % inhibition efficiency (%IE) results from different experiments were in a reasonable agreement.