Electrochemical and theoretical performance of new synthetized pyrazole derivatives as promising corrosion inhibitors for mild steel in acid environment: Molecular structure effect on efficiency.

• Studied corrosion inhibitors, M2PyAz and B2PyAz act as efficient inhibitors for MS. • Tafel results revealed that M2PyAz and B2PyAz as a mixed-type inhibitor. • Adsorption of both inhibitors obeyed Langmuir isotherm. • Theoretical calculations results were correlated to the inhibition efficiency. New bi-Pyrazol-Carbohydrazides, N,N-bis (3-Carbohydrazide-5-methylpyrazol-1-yl) methylene ( M2PyAz ) and 1,4-bis (3-Carbohydrazide-5-methylpyrazol-1-yl) butane (B2PyAz), were synthesized and their inhibitor effect against mild steel (MS) corrosion in 1 M HCl solution has been evaluated. Comparative study of inhibitory action of M2PyAz and B2PyAz was conducted first using weight loss measurements (WL), potentiodynamic polarization (PDP), electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM) and theoretical computational methods. The inhibition efficiencies of M2PyAz and B2PyAz can reach 98.6% and 87.8% respectively when the optimal concentration is 10–3 M. This result indicates that M2PyAz behave as excellent corrosion inhibitor towards MS because of its molecular size giving a denticity of electron donor atoms. EIS results indicate that the charge transfer resistance increases with augmentation concentration for both inhibitors and the MS corrosion in this system is controlled by a charge transfer process. PDP curves suggest that the M2PyAz and B2PyAz act as mixed type corrosion inhibitors. Free energy of adsorption obtained from the Langmuir isotherm model for both M2PyAz and B2PyAz implies that both molecules inhibit the acid attack mainly by chemisorption. WL-measurements were carried out in temperature range of 308–348 K, illustrating approximately 98.5% and 89% inhibitory efficiency respectively for M2PyAz and B2PyAz after 6 h immersion at 308 K in 1 M HCl solution. SEM images indicates the protective layer growth on the surface of metal in the presence of both inhibitors. SEM images analysis in the presence of both inhibitors confirmed the electrochemical outcomes. Density functional theory (DFT) method and molecular dynamics simulations (MDs) application suggest that M2PyAz and B2PyAz can show excellent corrosion inhibition character. The trend of reactivity of both molecules M2PyAz and B2PyAz is in agreement with experimental study. [ABSTRACT FROM AUTHOR]