Investigations Of Some Benzimidazole Derivatives As Corrosion Inhibitors On Mild Steel In Acid Solution

Mild steel is widely used in the transportation industry,machinery manufacturing,bridge construction and shipbuilding industry including oil and gas transportation,shipbuilding and motor manufacturing due to its perfect thermodynamics and mechanical properties.But the corrosion of mild steel is a serious global problem,leading to huge cost in the economy and energy.Therefore,studying the corrosion behavior and the influence on corrosion process of corrosion inhibitor in acidic medium have theoretical and practical significance for choosing effective corrosion inhibitors in practical industries.In this article,two benzimidazole derivatives were studied as corrosion inhibitors,which were thiabendazole(TBD)and 2-(3-pyridyl)-benzimidazole(PBD),respectively.As a comparison,the corrosion inhibition performance of the parent organic compounds under the same conditions were also researched.They are benzimidazole(BD),thiazole(TA),and pyridine(PD).In order to study the corrosion resistance and corrosion protection mechanism of the above corrosion inhibitors for mild steel in acidic solution,the corrosion performance of the above system was studied by using various techniques such as polarization curves,electrochemical impedance spectroscopy,surface morphology and quantum chemical calculation.The main results of this article are as follows:(1)In the research of the corrosion inhibition performance of BD,TA and TBD for Q235 steel in 1 M HCl solution,the corrosion inhibition efficiency of three corrosion inhibitors at the optimum concentration was obtained from the polarization curves:6m M BD,47.9%,8 m M TA,57.3%,10 m M TBD,94.1%.The data shows that the corrosion inhibition of TBD is much better than that of BD and TA.It is also concluded that the three compounds are mixed-type corrosion inhibitors.Surface analysis test and quantum chemistry calculations also prove that the excellent corrosion inhibition of TBD,and the inhibition effect of TBD is much better than BD and TA.In addition,the adsorption results show that the adsorption of TBD on Q235 steel surface in 1 M HCl solution follows the Langmuir adsorption isotherm,and the value of the adsorption Gibbs free energy is negative,indicating that the adsorption of TBD on Q235 steel surface is a spontaneous process.And the adsorption is the result of a combination of physical adsorption and chemical adsorption.XPS results show that TBD adsorbed on the steel surface to forms a covalent bond with the steel surface,which enhances the adsorption of corrosion inhibitors and mild steel,thereby increasing the corrosion inhibition efficiency of inhibitors.(2)In the research of the corrosion inhibition performance of BD,PD and PBD for X65 steel in 0.5 M H₂SO₄ solution,the corrosion inhibition efficiency of the three inhibitors at 10 m M which obtained from the potentiodynamic polarization curves:42.16%(BD),30.30%(PD)and 89.02%(PBD).It can be seen that the corrosion inhibition performance of the corrosion inhibitor PBD is much better than that of BD and PD.And it is also found that the three compounds are mixed-type corrosion inhibitors.Surface analysis and quantum chemical calculations both proved the excellent corrosion inhibition ability of PBD,and the inhibition efficiency of PBD is much better than BD and PD.In addition,the adsorption results show that the adsorption of PBD on X65 steel surface in 0.5 M H₂SO₄ solution follows the Langmuir adsorption isotherm,and the value of calculated adsorption Gibbs free energy is negative,indicating that the adsorption of PBD on X65 steel surface is a spontaneous process.And the adsorption is the result of a combination of physical adsorption and chemical adsorption.(3)Combining the results of the two groups,it was concluded that the two benzimidazole derivatives have good corrosion inhibition ability on mild steel in acidic solution.The corrosion inhibition performance of these inhibitors at the optimum concentration or the same concentration were confirmed in the two experiments.And the excellent corrosion inhibition performance of the multi-site adsorption inhibitors was proved.From the results of quantum chemical calculation,the HOMO and LUMO distributions of the two excellent corrosion inhibitors also confirmed the excellent corrosion inhibition performance of the multi-sites adsorption corrosion inhibitors.