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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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Many investigations have been conducted proving that most corrosion inhibitors are sensitive to temperature. The objective of this research is to investigate the corrosion inhibition performance of two pyrazole carboxamide derivatives at different temperature conditions. The corrosion inhibition properties of mild steel were investigated in hydrochloride acid solution 1 M HCl and in the presence of DPC-1, DPC-2 inhibitors using potentiodynamic polarization technique and electrochemical impedance spectroscopies. The adsorption film on the steel surface was characterized by Fourier transform infrared spectroscopy (FTIR). The results exhibit excellent inhibition performance of pyrazole in all temperatures studied. Tafel curves indicate that DPC-1 and DPC-2 behave as mixed-type inhibitors. EIS measurements display maximum corrosion inhibition efficiency around 97 % at 40 °C for DPC-1 (400 µM) and 96.91% ; 96.59% at 40 °C and 60 °C for DPC-2 (160 µM), respectively. The calculated thermodynamic parameters reveal the predominance of chemisorption process, in particular at higher temperatures. The FTIR spectra confirm the chemical interactions of pyrazole on the steel surface.