Abstract:
The corrosion inhibitions of mild steel in 0.5M H2SO4 solution by synthetized 5-(Phenyl)-4H-
1,2,4-triazole-3-thiol (5-PTT) and 5-(2-hydroxyphenyl)-1,3,4-oxadiazole-2-thiol (5-HOT) inhibitors
have been investigated by different methods (weight loss, electrochemical impedance spectroscopy
(EIS) and potentiodynamic polarization techniques…) at various concentrations and temperatures. The
results obtained revealed that these compounds performed excellently as corrosion inhibitors for mild
steel in 0.5M H2SO4 solution. It was found that the inhibition efficiencies increased with inhibitor's
concentration to reach efficiencies up to 91 % at 0.5 mM. The addition of potassium iodide to PTT in
solution increased the inhibition efficiencies of these latter. A synergistic effect was observed between
KI and inhibitor with optimum of concentration of 0.5 mM / inhibitor + 0.2% potassium iodide.
Potentiodynamic polarization studies have shown these inhibitors act as mixed-type inhibitors retarding
the anodic and cathodic corrosion reactions with predominant effect on the cathodic reaction.
The effect of temperature on the inhibition efficiency was also determinate in the range from
25°C to 50°C; some thermodynamic parameters such as apparent activation energy and adsorption free
energy have been calculated and discussed. Adsorption of inhibitors alone or in combination with
potassium iodide on the metal surface obeyed the Langmuir adsorption isotherm. The values of free
energy of adsorption (∆G°ads) indicated that adsorption of inhibitors derivatives is a spontaneous
process and they are adsorbed chemically as well as physically in the absence and presence of KI and
inhibited the corrosion of mild steel by blocking the active site of the metal.
Scanning electron microscopy (SEM) study confirmed that the inhibition of corrosion of mild
steel by these inhibitors is through adsorption of the extract molecules on surface of metal. Quantum
chemical parameters were also calculated to characterize adsorption mechanisms. Acceptable
correlations were obtained between experimental (inhibition efficiencies, ΔG°ads, Ea) and quantum
calculation parameters (dipole moment, EHOMO, ELUMO). Results obtained with different methods are in
good agreement.
Originality/value – Electrochemical techniques have been used for the first time to study synergistic
effect of studied inhibitors and potassium iodide KI on the inhibition corrosion of mild steel in 0.5M
H2SO4 solution. The results suggest that the mixture (inhibitor + KI) could find practical application in
corrosion control in aqueous acidic environment.
