The effect of pre-corrosion on corrosion inhibition performance and mechanism of quinoline quaternary ammonium salts

The influence of pre-corrosion on the corrosion inhibition performance and corrosion inhibition mechanism of quinoline quaternary ammonium salt (QQAS) on Q235 carbon steel in 1 wt% HCl solution at 60 degrees C were investigated by weight loss experiment, molecular dynamics simulation. The results of IR vibrational spectra and NMR hydrogen spectra indicate the successful synthesis of QQAS. The results of weight loss experiments show that the corrosion inhibition performance of the synthesized QQAS increase with the increasing of the concentration under the condition of Q235 carbon steel with and without pre-corrosion. But the pre-corrosion obviously decreases the corrosion inhibition efficiency by 17.28% when the concentration is 50mg.L-1. Analysis of thermodynamic parameters shows that the adsorption of QQAS on the steel surface is a spontaneous and exothermic process, which conforms to the Langmuir isothermal formula and is mainly based on chemical adsorption. The results of molecular dynamics simulation indicate that pre-corrosion changes the equilibrium adsorption conformations of QQAS molecules, and decreases the adsorption energies, and decreases the density of the film for the different oxidization extent of Q235 carbon steel. As a result, the corrosion inhibition performance of QQAS is decreased by the pre-corrosion. The results are in good agreement with the results of weight loss experiments. The corrosion inhibition performance of QQAS is the best when the number of QQAS molecules is 18. The corrosion inhibition mechanism is a single molecular layer adsorption mechanism. The results of this study can provide a reference for studying the corrosion inhibition performance and corrosion inhibition mechanism of corrosion inhibitors under the action of pre-corrosion. [GRAPHICS] .