Development of Novel Acidizing Inhibitors for Carbon Steel Corrosion in 15% Boiling Hydrochloric Acid

The inhibitive action of 1-cinnamylidine-3-thiocarbohydrazide (CTCH) and 1,1ʹ-dicinnamylidine-3-thiocarbohydrazide (DCTCH) against the corrosion of carbon steel in 15% hydrochloric acid (HCl) was investigated using nonelectrochemical and electrochemical techniques. Potentiodynamic polarization studies revealed that the compounds were mixed-type inhibitors and exhibited more than 97% inhibition efficiency at 1,500 ppm of inhibitor concentration. The effect of temperature on the corrosion behavior of carbon steel in 15% HCl with 1,500 ppm of inhibitors was studied in the temperature range from 30°C to 110°C. The surface coverage (θ) increased linearly with the logarithm of the inhibitor concentration fitting a Temkin adsorption isotherm. Thermodynamic parameters including the free energy of adsorption, activation energy, enthalpy, entropy, and heat of adsorption were also calculated. The inhibitors reduced the hydrogen permeation current effectively through the steel surface. The protective film formed on the metal surface by the adsorption of organic compounds was confirmed using Fourier transform infrared (FTIR), ultraviolet (UV)-visible reflectance, and scanning electron microscopy (SEM) studies.