Corrosion inhibition of mild steel by natural product compound

Corrosion inhibition of mild steel in H3PO4 containing chloride or sulphate ions have been studied using different electrochemical techniques. The corrosion and hydrogen evolution of mild steel alloy in 2 M H3PO4 acid containing 0.5 M NaCl can be effectively inhibited by addition of natural product compound, Thymol (IPMP), of different concentrations. However, in 2 M H3PO4 containing 0.5 M Na2SO4 corrosion cannot be effectively inhibited. The results of electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization measurements confirm the synergistic effects which describe the increase in the effectiveness of a corrosion inhibitor in the presence of Cl− ions in the corrosive medium. At any temperature, an increase in it leads to an increase of the corrosion rate and hydrogen evolution on mild steel. Polarization and EIS results are in good agreement with each other. The obtained results were confirmed by surface examination using scanning electron microscope.

► Electrochemical analysis of mild steel in H3PO4 containing Cl− or SO42− have been studied.
► The values of icorr increase with increasing the concentration of SO42− or Cl− in H3PO4.
► Thymol (IPMP) is a good inhibitor for corrosion of mild steel in H3PO4 containing Cl−.
► The order of IE is: H3PO4 + IPMP + Cl− > H3PO4 + IPMP > H3PO4 + IPMP + SO42−.