Corrosion Inhibition of 2-Mercaptopyrimidine to Cold Rolled Steel in Acetic Acid Solution

The corrosion inhibition of 2-mercaptopyrimidine (MP) on cold rolled steel (CRS) in acetic acid (CH₃COOH) solution was studied by weight loss method, electrochemical techniques, scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). The results show that MP had an effective corrosion inhibition for CRS in acetic acid solution, and the maximum inhibition efficiency values tested by weight loss method were higher than 92% when the MP concentration was 2.0 mmol/L and the temperatures were in the range of 20-40℃. The adsorption of MP on CRS surface obeyed Temkin adsorption isotherm. It was an exothermic adsorption process accompanied by the increase of entropy. This adsorption process also involved both physical and chemical adsorptions. MP was a mixed-type corrosion inhibitor, which worked through "geometric blocking effect". Nyquist plots exhibited an individual depressed capacitive loop with only one time constant, and the charge transfer resistance value increased prominently after adding MP to acetic acid solution, but the double layer capacitance decreased notably. An adsorption layer formed on the surface of CRS, which was mainly composed of MP, Fe(CH₃COO)₂, FeOOH and Fe₂O₃.