Experimental and theoretical investigations of benzoic acid derivatives as corrosion inhibitors for AISI 316 stainless steel in hydrochloric acid medium: DFT and Monte Carlo simulations on the Fe (110) surface.

The inhibition efficiency of benzoic acid (C1), para-hydroxybenzoic acid (C2), and 3,4-dihydroxybenzoic acid (C3) towards enhancing the corrosion resistance of austenitic AISI 316 stainless steel (SS) has been evaluated in 0.5 M HCl using weight loss (WL), open circuit potential (OCP), potentiodynamic polarization method, electrochemical impedance spectroscopy (EIS), and scanning electron microscopy (SEM) analysis. The results obtained from the different experimental techniques were consistent and showed that the inhibition efficiency of these inhibitors increased with the increase in concentration in this order C3 > C2 > C1. In addition, the results of the weight loss measurements showed that these inhibitors followed the Villamil isotherm. Quantum chemical calculations and Monte Carlo simulations have also been used for further insight into the adsorption mechanism of the inhibitor molecules on Fe (110). The quantum chemical parameters have been calculated by density functional theory (DFT) at the B3LYP level of theory with 6-31G+(2d,p) and 6-31G++(2d,p) basis sets in gas and aqueous phase. Parameters such as the lowest unoccupied (E LUMO) and highest occupied (E HOMO) molecular orbital energies, energy gap (ΔE), chemical hardness (η), softness (σ), electronegativity (χ), electrophilicity (ω), and nucleophilicity (ε) were calculated and showed the anti-corrosive properties of C1, C2 and C3. Moreover, theoretical vibrational spectra were calculated to exhibit the functional hydroxyl groups (OH) in the studied compounds. In agreement with the experimental data, the theoretical results showed that the order of inhibition efficiency was C3 > C2 > C1.

Transport of kaolinite colloids through quartz sand: influence of humic acid, Ca(2+), and trace metals.

To evaluate the risk of contaminant transport by mobile colloids, it seems essential to understand how colloids and associated pollutants behave during their migration through uncontaminated soil or groundwater. In this study, we investigated at pH 4 the influence of flow velocity, humic acid, solution Ca(2+) concentrations, and trace metals (Pb(2+), Cu(2+)) on the transport and deposition of kaolinite particles through a pure crystalline quartz sand as porous medium. A short-pulse chromatographic technique was used to measure colloid deposition. Adsorption of humic acid to the kaolinite increase its negative surface charge and then decrease colloid deposition. Experiments with different flow rates showed that humic-coated kaolinite colloid deposition followed a first-order kinetic rate law. The deposition rate coefficients of humic-coated kaolinite colloids increase with increasing Ca(2+) concentration in the suspension. The effect of trace metals on the mobility is studied by injecting two suspensions with different concentrations of Pb(2+) and Cu(2+). At very low cation concentration, the fraction of colloids retained is low and roughly independent of the nature of divalent cations. At high concentration, the deposition is higher and depends on the affinity of divalent cations toward humic-coated kaolinite colloids.