Halogenated pyrimidines as promising inhibitors for cold rolled steel in HCl and H2SO4 media: Experiments and theoretical calculations

The study of adsorption mechanism of inhibitors has been the focus in the field of corrosion science, and the in-depth investigation of the adsorption mechanism of inhibitor can help to promote the development of new-type green and efficient inhibitors. In this study, the adsorption mechanism of halogenated pyrimidines on steel surface in acidic media was investigated by a comprehensive method combining experiment and theoretical calculations. Inhibitors are prone to protonation reaction in acidic media, and the effect of protonation reaction on adsorption mechanism was investigated in this study through theoretical calculations. Negative synergistic effect between the protonation products and the original molecule indicates the existence of antagonism between the two. The negative synergistic coefficients of 2-chloropyrimidine (CP) (-4.7 % and −2.2 %) are larger than those of 2-bromopyrimidine (BP) (-1.7 % and −0.3 %), and thus the performance of BP is superior to that of CP. Weight loss method, electrochemical test and scanning vibrating electrode technique (SVET) showed that BP has better inhibition performance than CP in acidic media, which is in agreement with the theoretical calculations. First Principle DFT calculations confirmed the formation of parallel adsorption of BP, CP and their protonation products by electron exchange with Fe(110) plane. Surface characterization also confirmed that halogenated pyrimidine molecules could form adsorption films on steel surfaces. BP had the maximum inhibition efficiency of 92.9 % on steel in HCl media. The outcomes of this study may offer significant insights into adsorption mechanism of halogenated pyrimidine derivatives on CRS surfaces.