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In this paper, six quaternary ammonium salts are synthesized using1H-benzo[d]/[1,2,3]triazole as a template and characterized by FT-IR,1HNMR and MS, which named1-((1/Abenzo[d][1,2,3]triazole-1-yl)methyl)pyridine-l-ium iodide(BP),1-((1H-benzo [d][1,2,3] triazol-1-yl)methyl) quinolin-1-ium iodide(BQ),4-((1H-tenzo[d][1,2,3]triazol-l-yl) methyl)-4-methylmorpholin-4-ium iodide(BM),1-((1//-benzo[d][1,2,3] triazol-1-yl) methyl)-3-carbamoyl pyridin-1-ium iodide(BCP), N-((1H-benzo[d][1,2,3]triazol-1-yl)methyl)-N,N-dimethyl-1-phenyl methanaminium bromide (BMPMA) and N-((1H-benzo[d][1,2,3] triazol-l-yl)methyl)-1-(1H-benzo[d][1,2,3]triazol-1-yl)-N,N-dimethyl methanaminium iodide (BBMMA),respectively. And their accurate molecular structures are confirmed by X-ray single crystal diffraction. The synthesis conditions are optimized by single factor experiments. Their thermal stabilities are studied by TG-DTA and the results show that they are stable under the temperatures of187.6℃,179.2℃,193.0℃,178.3℃,183.3℃and136.7℃, respectively. Four representative ones of them, that is BP, BQ, BMPMA and BBMMA, are selected to study their influences on corrosion behavior of mild steel in1.0M HCl solutions by weight loss measurement, electrochemical measurement and scanning electron microscopy (SEM). The data of weight loss tests show that the inhibition efficiencies of them increase with increase in the concentration of inhibitor and decrease with increasing temperature. The inhibitors adsorbe chemically and physically on steel surface in1.0M HC1solution and follow Langmuir’s isotherm. At298K and concentration of5×10-3mol/L, the inhibition efficiencies of BP, BQ, BMPMA and BBMMA reach to96.0%,98.1%,97.0%and97.0%, respectively. And it is higher than that of BTAH (92.6%) at the same conditions. Potentiodynamic polarization tests reveal that these quaternary ammonium salts act as interface-mixed type inhibitors predominantly anodic. Electrochemical impedance spectroscopy studies show that a charge transfer process mainly controls the corrosion process and the addition of inhibitors do not change the corrosion mechanism. The corrosion of mild steel is inhibited via the gradual replacement of water molecules by inhibitor molecules from the surface which decreases the number of active sites necessary for corrosion reaction. The results of SEM analysis show that in presence of inhibitors the surfaces of mile steel samples are remarkably improved with respect to its smoothness indicating considerable reduction of corrosion rate.
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