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Corrosion inhibition of mild steel in hydrochloride acid solution was performed by a two pyrazole carboxamides named 5-(4-(dimethylamino)phenyl)-3-phenyl-4,5-dihydro-1H-pyrazole-1-carboxamide DPC-1 and (E)-5-(4-(dimethylamino)phenyl)-3-(4-(dimethylamino)styryl)-4,5-dihydro-1H-pyrazole-1-carboxamide DPC-2 using weight loss measurements, Tafel polarization curves and electrochemical impedance spectroscopies (EIS). The obtained results show that DPC-1 and DPC-2 are effective corrosion inhibitors in 1 mol l−1 HCl solution. The inhibition efficiency η (%) increases with the increase of inhibitors concentration to reach 84.56% at 4 × 10−4 mol l−1 and 80% at 1.6 × 10−4 mol l−1 for DPC-1 and DPC-2 at 303 K, respectively. The adsorption of synthesized pyrazoles on MS surface obeys the Langmuir adsorption isotherm. Tafel polarization curves reveal that DPC-1 and DPC-2 acts as a mixed-type inhibitor and EIS spectra show the increase of the transfer resistance with the inhibitors concentration. The SEM surface analysis shows the formation of protective organic film on steel surface. The relationship between the inhibition performance of pyrazoles and their structural parameters was investigated using DFT calculations.

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