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The adsorption and corrosion inhibition behavior of ( E )-2-methyl-N-(thiophen-2-ylmethylidene)aniline ( T ) at steel/1.0 M HCl interface was investigated using gravimetric and electrochemical methods at 308 K. Inhibition efficiency increased with increase in the concentration of new synthesized Tiophene Schiff base. The potentiodynamic polarization studies revealed that this compound as mixed-type inhibitor. Data, obtained from EIS measurements, were analyzed to model the corrosion inhibition process through appropriate equivalent circuit model; a constant phase element (CPE) has been used. The inhibition was assumed to occur via adsorption of the components of the Thiophene derivative on the mild steel surface which can be approximated by Langmuir adsorption isotherm model. Quantum chemical parameters are calculated using the density functional theory (DFT) method. Correlation between theoretical and experimental results is discussed. [ABSTRACT FROM AUTHOR]

The inhibition of mild steel corrosion in 1.0 M HCl by some hydrazine derivatives namely: (1 E ,2 E )-1,2-bis(thiophen-2-ylmethylene)hydrazine ( PP2 ) and (1 E ,2 E )-1,2-bis(1 H -pyrrol-2-ylmethylene)hydrazine ( PP3 ) has been investigated using weight loss, electrochemical studies, SEM and quantum chemical calculations. The results showed that PP3 is the best corrosion inhibitor among the three compounds studied and the inhibition efficiency increases with increase in concentration for all the inhibitors. The adsorption of inhibitor molecules on mild steel surface was found to be spontaneous and obeyed the Langmuir adsorption isotherm. Potentiodynamic polarization investigations indicated that the studied inhibitors were mixed type inhibitors. Electrochemical Impedance Spectroscopic measurements show that the inhibitors form an adsorptive layer on the metallic surface. Some of the inhibitors' quantum chemical parameters are calculated with the DFT method at the B3LYP/6-31G(d,p) level of theory. Among the calculated parameters, the LUMO energy, energy gap between the HOMO and LUMO, dipole moments (μ), global chemical hardness (η), softness (σ), and the fraction of electrons transferred from the inhibitor to the iron surface (ΔN) could well describe the experimental observations. [ABSTRACT FROM AUTHOR]

• Bi-pyrazole derivatives are tested for corrosion protection of mild steel in HCl. • The adsorption of tested compounds follows Langmuir isotherm model. • DFT calculations show a widespread distribution of reactive sites in both molecules. • MD simulations suggest a nearly parallel adsorption of molecules over iron surface. Two new synthesized bi-pyrazole-carbohydrazides, namely 1,1′-(propane-1,3-diyl)bis (5-methyl-1H-pyrazole-3-carbohydrazide) (P2PZ) and 1,1′-(oxy bis (ethane -2,1-diyl)) bis (5-methyl-1H-pyrazole-3- Carbohydrazide) (O2PZ) were evaluated as corrosion inhibitors for mild steel (MS) in 1.0 M HCl media. Comparative study of inhibitory action of P2PZ and O2PZ was conducted first using mass loss and electrochemical measurements (potentiodynamic polarization curves, PPC, and electrochemical impedance spectroscopy, EIS) and it had shown that P2PZ outperforms O2PZ. The electrochemical studies showed a corrosion inhibition efficiency of 95% and 84% at 308 K and 10−3 mol/L of P2PZ and O2PZ, respectively. Their efficiency augmented with augmentation of concentration and decreased with augmentation of temperature. Electrochemical impedance spectroscopy showed that the corrosion inhibition followed a charge transfer process. Polarization curves suggested that the P2PZ and O2PZ acted as mixed-type inhibitors and followed the Langmuir adsorption isotherm. The free energy of adsorption (ΔG ads) values, which lie within the range of -39.94 to -37.36 KJ mol−1, confirmed a physicochemical adsorption process. Scanning electron microscope (SEM) images indicated the formation of a protective layer on the surface of the metal in the presence of both inhibitors. Density Functional Theory (DFT) and molecular dynamics (MD) simulation have been introduced to carry out a theoretical investigation of the inhibitors' reactivity and interaction with the iron surface, respectively. The comparative study based on experimental and theoretical results showed that the trend of inhibition potentials of tested inhibitors depends on their electron-donating/accepting abilities. The trend of reactivity of molecules P2PZ and O2PZ matched well with experimental results. [Display omitted] [ABSTRACT FROM AUTHOR]