Experimental and Mathematical Methods for Monitoring Dicyandiamide as an Inhibitor for Carbon Steel Corrosion in an Acidic Solution

The inhibition effect of dicyandiamide (DCDA) on the carbon steel (CS) corrosion in 0.5 M HCl solution was evaluated using chemical and electrochemical methods. The maximum inhibition efficiency (%IE) and the optimal dose were 95.7% and 0.30 mg/L of DCDA inhibitor, respectively. The temperature effect in the %IE is measured using chemicals by gravimetric loss tests. Potentiodynamic polarization (PD-P) tests clarified that DCDA is a mixed-type inhibitor, while EIS tests revealed that the charge transfer resistance (Rct) increased with inhibitor concentration. The mixed (chemical and physical) adsorption mode appears on the CS surface following a Langmuir isotherm. UV-vis spectra revealed the chemical interaction of DCDA with the CS surface. Atomic force microscopy (AFM) examination revealed the creation of a protective film from DCDA molecules on the metal surface. Correlations between experimental data and theoretical energies derived from DFT analysis were computed using the density functional theory (DFT) method. Additionally, explore the favorite active sites of the DCDA molecule and their interactions with the CS surface.