Isatin thiosemicarbazone derivatives as inhibitors against corrosion of AA6060 aluminium alloy in acidic chloride medium: substituent effects
Qingyun Yuan, Run Cheng, Song Zou, Cheng Ding, Hongxia Liu, Yujie Wang, Di Yang, Xin Xiao, Qiong Jiang, Ruiren Tang, Jingwen Chen
Abstract
Five isatin thiosemicarbazone derivatives bearing different substituents (R) at 5-position of the isatin moiety, ISA-R, being R = -H, -CH3, -F, -Cl and -NO2, were synthesized and fully characterized. The corrosion inhibition action of ISA-R on AA6060 aluminium alloy in acidic chloride medium was studied in relation to the substituent effects using field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), electrochemical potentiodynamic polarization (PDP) and weight loss measurements. The results showed that the inhibition behaviors of ISA-R were strongly correlated with the substituent modifications. ISA-NO2 was found to possess the highest capability to increase the corrosion resistance of the alloy and ISA-Cl exhibited some inhibition efficacy, whereas the others have little action. ISA-H, ISA-F, ISA-Cl and ISA-NO2 acted as cathodic-type inhibitors, and ISA-CH3 as a mixed-type inhibitor primarily retarding the cathodic processes of the alloy in the corrosion solution. ISA-R can be adsorbed on the alloy surface as evidenced by the results of EDS and XPS. The π-electron density on the isatin ring of ISA-NO2 is more deficient over the other ISA-R, which facilitates the adsorption of ISA-NO2 and formation of a barrier film on the alloy surface, and accordingly enhances its anti-corrosive performance for the alloy.