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In this article, metoclopramide tablet was thoroughly evaluated as an effective inhibitor for mild steel in 0.5 M sulfuric acid and 1 M hydrochloric acid solutions by different techniques (potentiodynamic polarization and electrochemical impedance spectroscopy [EIS]) and scanning electronic microscopy (SEM). The results revealed that the compound has a proper inhibiting effect at concentrations of 600 ppm for sulfuric acid and 300 ppm for hydrochloric acid solutions. The effect of temperature on the corrosion rate of alloy in the absence and presence of this drug was also studied. The EIS measurements revealed that by the addition of the inhibitor up to a certain concentration, the charge transfer resistance increases and the double layer capacitance decreases. The probe showed that the adsorption of the inhibitor on the alloy surface in both solutions follows Langmuir adsorption isotherm. This process is spontaneous and exothermic. The information obtained from SEM confirmed the formation of the protective layer on the surface of the sample after immersion in solutions containing the compound. K E Y W O R D Scorrosion inhibitor, electrochemical impedance spectroscopy, metoclopramide, mild steel

The inhibition effect of 1‐(4‐(dimethylamino)benzylidene)thiosemicarbazide (DBT) on the corrosion behavior of 304 stainless steel and mild steel in 0.5 M sulfuric acid solution was investigated using weight loss and potentiostatic polarization methods. The experimental results suggest that DBT inhibits the corrosion of the steels in acid solution. The inhibition efficiencies increased as the concentration of the compound was increased. The calculated inhibition efficiencies from the two investigated methods were in good agreement. Potentiostatic polarization measurements indicate that DBT acts as a mixed type inhibitor for both alloys. The adsorption of inhibitor on the steel surfaces obeys Langmuir adsorption isotherm. The structure of DBT was optimized using PM3 semi‐empirical method. Highest occupied molecular orbital (HOMO), lowest unoccupied molecular orbital (LUMO), energy levels, ELUMO − EHOMO (energy gap), dipole moment (µ), and Mulliken charge densities for this molecule were computed and the adsorption mechanism was discussed. Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) were used to characterize the surfaces of the alloys.

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