Synthesis Of Thiazole Derivatives With Surface Activity And A Study On Their Inhibition Performance And Mechanism During Carbon Steel Acid Pickling Process

Acid pickling is one of the commonly used methods to effectively remove rust on the surface of metal, but pickling often causes corrosion of the metal itself. Two kinds of thiazole derivatives with surface activity as corrosion inhibitors were synthesized in order to solve the corrosion of carbon steel. Surface activity could increase the adsorption amount of inhibitors on metal surface and improve the efficiency of corrosion inhibition, which could reduce the use of corrosion inhibitors as well as their emissions in the environment at the same time.Two thiazole derivatives with surface activity, called CHMN and COMN, had been synthesized using cyanuric chloride, straight chain aliphatic amines with different number of carbon atoms, 2-mercaptobenzothiazole(MBT) and N, N- dimethyl-1,3-propanediamine as raw materials, and their structures were characterized by FT-IR, ESI-MS and 1H-NMR.MBT could lower the surface tension of HCl aqueous solution to a centain extent with increasing concentrations that as the concentration increased from 0.005 mM to 1mM, the surface tension reduced from 72.45mN/m to 52.99mN/m. CHMN could lower the surface tension of HCl aqueous solution from 67.74 mN/m to 41.19 mN/m as its concentration increased from 0.0005 mM to 1mM. Its critical micelle concentration(cmc) and the corresponding surface tension(γcmc) were 0.5mM, 41.67mN/m, respectively. COMN had higher surface activity that the surface tension reduced from 62.34mN/m to 32.09mN/m as the concentration increased from 0.005 mM to 0.2mM. Its cmc and γcmc were 0.1 mM, 32.17mN/m, respectively.Weight loss experiment, electrochemical impedance spectroscopy, potentiodynamic polarization curves and super depth 3D microscopy study had been used to investigate the inhibition action of MBT as well as CHMN and COMN on carbon steel in 1 M HCl solution. Results indicated that corrosion inhibition efficiency increased with the increase of the inhibitor concentration, while decreased with the increase of the temperature. The corrosion inhibition effect of COMN was better than CHMN, MBT was the worst. The corrosion inhibition efficiency of 0.2mM COMN was up to more than 98% at 20oC, while decreased to 28.83% with the increasing of temperature to 50oC. Electrochemical tests showed that the corrosion inhibition mechanism of CHMN and COMN was different from MBT. MBT was a negative cathodic corrosion inhibitor of carbon steel. CHMN and COMN were excellent mixed type corrosion inhibitor for carbon steel. In super depth 3D microscopy study, the surface state of carbon steel with COMN was the closest to the uncorroded one.Adsorption thermodynamic study showed that the adsorption of MBT on carbon steel electrode obeyed the Freundlich isothermal adsorption, while the adsorption of CHMN and COMN on carbon steel electrode obeyed the Langmiur isothermal adsorption. The adsorption process of CHMN and COMN was spontaneous and temperature was not favorable for the adsorption process. The adsorption of CHMN and COMN on the surface of carbon steel was through the joint action of physical adsorption and chemical adsorption. Compared with CHMN, COMN was more easily to adsorb on the surface of carbon steel.Density functional theory(DFT) method in quantum chemistry calculation was used to study the relationship between corrosion inhibitor structure and inhibition efficiency in theory, the results showed that: as the number of carbon atoms increased from 6 to 8, COMN had higher EHOMO and lower ELUMO, both of wich made it more easily to bond with metal to form an adsorbed film than CHMN. Smaller ΔE and larger dipole moment indicated that COMN was more tended to adsorb on the carbon steel surface in corrosive media, and the adsorption ability was also stronger.