Corrosion is a phenomenon that cannot be avoided. Corrosion is a chemical or electrochemical reaction that occurs when a material, usually a metal, reacts with its surroundings that causes the materials and their properties to deteriorate. Metal corrosion resistance is a significant industrial and scientific issue. Several methods have been developed and implemented to protect metals from corrosion. The most common of these strategies is the use of corrosion inhibitors [1,2]. Corrosion inhibitors are chemicals that prevent corrosion when they are adsorbed onto the metal-solution interface via physisorption or chemical adsorption. Several heterocyclic molecules in the aromatic or long chain carbon system combining nitrogen, oxygen, and Sulphur have been proved as effective inhibitors [3-5].
The aim of this research was to investigate whether the newly synthesized Furan-2-ylmethylsulfanyl-acetic acid (N-thiobenzoyl)-Hydrazide (C14H15N3S2O2)  could prevent carbon steel from corroding in 0.1 M hydrochloric acid solution, as shown in Figure 1. The effectiveness of inhibition was assessed using potentiodynamic polarization.
Preparation of carbon steel samples
The metallic elements in carbon steel sheet (A106) are presented in Table 1 as a percentage of the total content. Mechanical press cutting of carbon steel into square specimens with a diameter of 2 cm and a thickness of 2 mm was used. The specimens were polished with emery sheets ranging from 80 to 2000 grit, washed in distilled water, degreased in acetone, and dried at room temperature.
The corrosive test environment consisted of 10 mL of dilute concentrations of 0.1 HCl acid medium made with analytical grade HCl acid (37 percent) and distilled water.
Three concentrations of inhibitor (FATH) (400 ppm, 500 ppm, and 600 ppm) were made by dissolving 0.004, 0.005, and 0.006 gm in 10 mL absolute ethanol, respectively, and then transferring each to a 500 mL volumetric flask containing 2.18 mL of 0.1 M HCl previously dissolved in distilled water.
Electrochemical studies were performed using a 500 mL Pyrex corrosion cell with three electrodes, as illustrated in Figure 2. For the electrochemical measurements, a three-electrode compartment cell was used. The reference electrodes were a saturated calomel electrode (SCE) and a platinum electrode, while the counter electrode was carbon steel specimens. The voltage across the open circuit was measured. The potential was recorded, and the polarization curve was started from the open circuit at a scan rate of 2.0 mV s-1 over a potential range of (+200 to -200 mV). The Icorr and Ecorr were both calculated. The output was plotted for the blank solution, as well as with the addition of varied inhibitor doses. Figure 3 illustrates the complete system for polarization measurements.
Result and discussion
Polarization measurements were used to learn more about the kinetics of anodic and cathodic reactions. The polarization is represented by Figure 4 for CS electrode curves in 0.1 M HCl solution with and without varied quantities of additives inhibitor. Icorr (corrosion current density), Ecorr (corrosion potential), CR (corrosion rates), ba (anodic Tafel slope), and bc (cathodic Tafel slope), are electrochemical kinetic characteristics. They are derived using the extrapolation approach, and are shown in Table 2 with temperatures ranging from 298 to 328 K. The protection efficiency (%PE) was calculated using polarization data and the formula below (Equation 1) .
The corrosion current densities for carbon steel electrodes in the absence and presence of inhibitor are i(corr) and i(corr)inh, respectively. By increasing inhibitor concentrations, the corrosion current densities drop and inhibition efficiency PE% increases, as shown in Table 2.
The diminishing inhibition performance as the temperature of the solution rises could be attributed to an increase in the mobility of the inhibitor molecules, which leads to a decrease in the contact between the inhibitor molecules and the carbon steel surface [8-10]. The inhibitory efficacy of FATH was lowered at a higher temperature solution, implying that FATH molecules on metallic surfaces are adsorbing by physical adsorption [11,12], also inhibitor molecule adsorption on the steel surface is facilitated by the presence of heteroatoms (S, O, N) and multiple € bonds in their molecule [13,14].
As shown below, the activation energy (Ea) was computed using the Arrhenius equation (Equation 2) [15,16].
Where A is the pre-exponential factor of Arrhenius, T is the absolute temperature, and R is the gas constant. Table 3 shows the activation energies in the absence and presence of inhibitor FATH based on the slope values of Arrhenius plots (Figure 5).
As in Figure 5, a straight line (R2>0.95) for the Arrhenius plots was confirmed by the validity approach. Because the FATH molecule forms a protective coating at metal-electrolyte interfaces, the activation energies in the presence of the inhibitor are higher than in the absence of the inhibitor, indicating that a higher energy barrier has been reached and the corrosion process has become more difficult .
Understanding the adsorption mechanism of organic molecules on a metallic surface requires a thorough understanding of the adsorption isotherm. The adsorption isotherm study gives structural and thermodynamic information on the electric mono layer. In order to get the isotherm displayed below, the degree of surface covering for the various inhibitor concentrations was estimated (Equation 3).
For FATH compound, various adsorption isotherms such as Freundlich and Langmuir adsorption isotherms were examined, and Langmuir adsorption isotherm fitted the experimental data the best. The relationship of Langmuir isotherm is defined in Equation 4 :
Where ⎝ is the degree of surface covering, C is the mg/L concentration in the bulk of the solution, and Kads is the adsorption equilibrium constant. The plots of C/⎝ vs C (Figure 6) show straight lines with a slope equal to 1/Kads in this case. The adsorption power or binding strength of the FATH compound on the carbon steel surface is represented by the Kads value. The Kads values are displayed in Table 4.
The enthalpy and entropy of adsorption, which are determined using the van't Hoff equation, are two other essential thermodynamic factors. The van't Hoff equation is (Equation 5) :
The enthalpy and entropy of adsorption were calculated by plotting lnK against 1/T (Figure 7). ⊗Hads and ⊗Sads are calculated and reported in Table 5 using the slope (-⊗Hads/R) and intercept (⊗Sads/R + ln 1/55.5). The following relationship (Equation 6) is used to calculate the Gibbs free energy for adsorption ⊗Gads .
The exothermic nature of the dissolution of carbon steel in hydrochloric acid solution is reflected by the negative sign of the change in enthalpy (ΔHads). The entropy change (ΔSads) of FATH inhibitor adsorption on metal surface is negative. This means that when the adsorption process progresses from reactants to a metal adsorbed species reaction complex, the randomness of the process decreases [20,21]. The ΔGads of the studied inhibitors is more negative, indicating that adsorption of FATH on carbon steel surface is more spontaneous .
According to the results of this study, as the concentration of the inhibitor FATH increases, it displays a high efficiency against carbon steel corrosion. Also, the temperature effect suggests that as the temperature rises, the inhibition efficiency diminishes. Another major result that the activation energy (Ea) of inhibited carbon steel is larger than that of uninhibited carbon steel, indicating that inhibition efficiency is temperature dependent. Finally, the exothermic process is shown by the negative value of ΔHads and ΔSads.
I would like to thank all the staff of department of Chemistry, University of Baghdad.
Nbras Hussein Ali: https://orcid.org/0000-0001-9447-6568
How to cite this article: Nbras Hussein Ali, Israa M.H. Almousawi, Intisar Yahiya Mohammed. Experimental study of a new furan-2-ylmethylene-hydrazide as a corrosion inhibitor in acidic media. Eurasian Chemical Communications, 2021, 3(12), 921-928. Link: http://www.echemcom.com/article_139987.html
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