Corrosion Inhibition of Mild Steel in Hydrochloric Acid Environment Using Terephthaldehyde Based on Schiff Base: Gravimetric, Thermodynamic, and Computational Studies

Abstract

Using traditional weight-loss tests, as well as different electrochemical techniques (potentiodynamic polarization and electrochemical impedance spectroscopy), we investigated the corrosion-inhibition performance of 2,2′-(1,4-phenylenebis(methanylylidene)) bis(N-(3-methoxyphenyl) hydrazinecarbothioamide) (PMBMH) as an inhibitor for mild steel in a 1 M hydrochloric acid solution. The maximum protection efficacy of 0.0005 M of PMBMH was 95%. Due to the creation of a protective adsorption layer instead of the adsorbed H2O molecules and acidic chloride ions, the existence of the investigated inhibitor reduced the corrosion rate and increased the inhibitory efficacy. The inhibition efficiency increased as the inhibitor concentration increased, but it decreased as the temperature increased. The PMBMH adsorption mode followed the Langmuir adsorption isotherm, with high adsorption-inhibition activity. Furthermore, the value of the ∆Gadso indicated that PMBMH contributed to the physical and chemical adsorption onto the mild-steel surface. Moreover, density functional theory (DFT) helped in the calculation of the quantum chemical parameters for finding the correlation between the inhibition activity and the molecular structure. The experimental and theoretical findings in this investigation are in good agreement.

Keywords: DFT; EIS; Schiff base; corrosion inhibitor; terephthaldehyde; weight loss.

Figure 1

The chemical structure of PMBMH.

Figure 2

Gravimetric-curve relationship of metal coupons in 1 M HCl between corrosion rate and inhibition efficiency: different exposure periods at 303 K.

Figure 3

Gravimetric-curve relationship of metal coupons in 1 M HCl between corrosion rate and inhibition efficiency against concentration of PMBMH at different temperatures for 5 h exposure period.

Figure 4

The log (C_R) versus 1/T graph for the various concentrations of PMBMH and different temperatures.

Figure 5

A plot of Arrhenius modified equations of $log\left\{\frac{C_R}{T}\right\}$ versus $\frac{i}{T}$ for tested metal with different concentrations of the examined inhibitor.

Figure 6

Langmuir adsorption model of tested inhibitor on the surface of mild steel in 1 M HCl at 303 K from the gravimetric data.

Figure 7

Polarization curves of tested coupons in 1 M HCl solution with different concentrations of PMBMH.

Figure 8

Nyquist plots of mild steel in 1 M HCl without and with the addition of various concentrations of PMBMH.

Figure 9

The model of equivalent circuit that was used to fit the experimental data (A) without and (B) with the addition of the tested inhibitor.

Figure 10

SEM micrographs showing the surface morphology of mild-steel-coupon surface in absence (A) and presence (B) of 0.0005 M PMBMH in 1 M HCl environment for 5 h at 303 K.

Figure 11

The optimized chemical structure (a), highest occupied molecular orbital (b), and lowest unoccupied molecular orbital (c) of the tested inhibitor.

Figure 12

Suggested corrosion-inhibition mechanism of mild steel in 1 M HCl with the addition of the examined inhibitor.