Corrosion control of carbon steel in phosphoric acid by purpald – Weight loss, electrochemical and XPS studies

Highlights: ► AHMT is good corrosion inhibitor for carbon steel in 2 M H3PO4. ► Tafel polarization study indicates that AHMT is mixed-type of inhibitor. ► Weight loss, polarization and EIS methods are in reasonable agreement. ► AHMT adsorption is well described by Langmuir isotherm. ► XPS analysis was used to establish the nature of AHMT adsorption on the carbon steel surface. - Abstract: The corrosion inhibition properties of purpald (4-amino-3-hydrazino-5-mercapto-1,2,4-triazole (AHMT)) on carbon steel in phosphoric acid (2 M H3PO4) solution has been examined and characterized by weight loss, Tafel polarization, electrochemical impedance spectroscopy (EIS) and X-ray photoelectron spectroscopy (XPS) methods. The experimental results reveal that the compound has a good inhibiting effect on the carbon steel in 2 M H3PO4 solution. The protection efficiency increases with increasing inhibitor concentration, but the temperature has hardly effect on the inhibition efficiency of AHMT. The adsorption of AHMT is found to obey the Langmuir adsorption isotherm. Thermodynamic data and XPS analysis clearly show that the adsorption mechanism of AHMT on carbon steel surface in 2 M H3PO4 solution is mainly electrostatic-adsorption. Potentiodynamic polarization studies have shown that AHMT acts as a mixed-type of inhibitor. Data obtained from EIS studies were analyzed to model inhibition process through appropriate equivalent circuit model.