Investigation of the corrosion inhibition effect of 3-methyl-6-oxo-4-(thiophen-2-yl)-4,5,6,7-tetrahydro-2H-pyrazolo[3,4-b]pyridine-5-carbonitrile (TPP) on mild steel in hydrochloric acid

The corrosion inhibition effect of the synthesized compound 3-methyl-6-oxo-4-(thiophen-2-yl)-4,5,6,7-tetrahydro-2H-pyrazolo[3,4-b]pyridine-5-carbonitrile (TPP) on the corrosion of MS in 1 M HCl was investigated using weight loss, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) methods. The results obtained for TPP showed a good inhibition effect on the MS in the 1 M HCl solution. The inhibition efficiency was found to increase with a corresponding increase in the TPP concentration, and the best inhibition of 96.83% occurred at a TPP concentration of 200 ppm. The potentiodynamic polarization studies revealed that TPP behaved as mixed-type of inhibitor that predominantly inhibited the cathodic reaction. The impedance parameters were indicative of the high inhibitory efficiency and the adsorption of TPP on MS. Amongst the Frumkin, Temkin and Langmuir isotherms, the studied compound more closely followed the Langmuir adsorption isotherm. The scanning electron microscopy (SEM) examinations of the electrode surface confirmed the existence of such an adsorbed film.