Schiff Bases Derived from Triazoles as Corrosion Inhibitors for Maraging Steel in Acid Mixtures: Experimental and Theoretical Studies

Abstract

The ability of two triazole derived Schiff bases, namely,4-[(furan-2-ylmethylidene)amino]-5-methyl-4H-1,2,4-triazole-3-thiol [FAMTT] and 4-[(4-chlorobenzylidene)amino]-5-methyl-4H-1,2,4-triazole-3-thiol [CAMTT], to inhibit corrosion of maraging steel by 2:1 mixture of HCl and H₂SO₄ was evaluated. Temperature range of 30-45 °C and inhibitor concentration range of 5-25 ppm for FAMTT and 5-50 ppm for CAMTT were employed. An increase in inhibitor concentration and temperature resulted in an increase of inhibition efficiencies of both inhibitors. The inhibition efficiencies of FAMTT were significantly larger than CAMTT in weight loss studies, a maximum of 94.4% observed at 25 ppm for FAMTT and a maximum of 82.4% at 50 ppm observed for CAMTT. However, in the electrochemical studies, though FAMTT performed better than CAMTT, the differences in their efficiencies were somewhat less than that observed in weight loss method. In polarization studies, FAMTT showed maximum efficiency of 96.2% at 25 ppm and 45 °C, while, CAMTT showed a maximum of 90.8% at 50 ppm and 45 °C, and, in electrochemical impedance studies (EIS), maximum efficiency was 97.4% at 25 ppm and 45 °C for FAMTT, and 96.5% at 50 ppm and 45 °C for CAMTT. Inhibition properties of both were verified by kinetic and thermodynamic analyses. Both exhibited mixed type inhibitory action by chemisorbing on the metal surface and followed Langmuir adsorption isotherm. The adsorption of the inhibitors on the steel surface was confirmed by Scanning Electron Microscopy-Energy-dispersive X-ray studies (SEM-EDS) analyses. Density Functional Theory (DFT) calculations were made to predict the inhibition property, and to correlate molecular structure with the corrosion inhibition property. There was a good agreement between experimental observation and theoretical prediction- that FAMTT has higher inhibition potential than CAMTT.

Keywords:

• Schiff bases
• Maraging Steel
• Corrosion
• Corrosion inhibition efficiency
• Weight loss method
• Tafel polarization
• EIS
• DFT