Corrosion prevention of mild steel in acidic medium by 2-Pyrrolidin-1-yl-1,3-thiazole-5-carboxylic acid: Theoretical and experimental approach

The inhibition efficiency of 2-Pyrrolidin-1-yl-1,3-thiazole-5-carboxylic acid (PTCA) against mild steel (MS) corrosion was investigated in acidic solution by using quantum chemical calculations based on Density Functional Theory (DFT) method and electrochemical measurements. The electrochemical impedance spectroscopy (EIS), potentiodynamic, potential zero charge (pzc) analysis and electrochemical noise (EN) measurements at various concentrations (from 0.1 to 10 mM) and immersion times were utilized in experimental part. The surface analysis was achieved scanning electron microscope (SEM) and contact angle measurements in the absence and presence of 10 mM PTCA. According to DFT results, PTCA exhibited 3.737 eV band gap and 8.130 Debye dipole moment which were a signal of potentially convenient corrosion inhibitor properties. PTCA has a remarkable corrosion inhibition capability to mild steel, which inhibited both anodic and cathodic corrosion rates, relying on it's physically adsorption on the metal solution interface and protection ability was increased with increasing PTCA concentration. The obtained adsorption equilibrium constant was 11.11 × 10³ M^-1 and calculated standard free energy of adsorption was ?33.03 kJ mol^?1. The determined activation energy values were 55.58 kJ mol^?1 and 96.86 kJ mol^?1 in 0.5 M HCl in the absence and presence of 10 mM PTCA, respectively. PTCA demonstrated a strong inhibition efficiency of 98.3%, after 168 h immersion, according to the EIS results. As a consequently, we recommend that PTCA is a convenient inhibitor in 0.1 M HCl for mild steel protection against corrosion.     

Synthesis,characterization and corrosion inhibition efficiency of 2-(6-methylpyridin-2-yl)-1H-imidazo[4,5-f][1,10] phenanthroline on mild steel in sulphuric acid

Phenanthroline derivative, 2-(6-methylpyridin-2-yl)-1H-imidazo[4,5-f][1,10] phenanthroline (MIP) was synthesized and characterized by elemental analysis, FT-IR, ¹H NMR, ¹³C NMR, and single crystal X-ray diffraction study. MIP was evaluated as corrosion inhibitor for mild steel in 0.5 M H₂SO₄ solution using gravimetric and UV–Visible spectrophotometric methods at 303–333 K. Results obtained show that MIP acts as inhibitor for mild steel in H₂SO₄ solution. The inhibition efficiency was found to increase with increase in MIP concentration but decreased with temperature. Activation parameters and Gibbs free energy for the adsorption process using statistical physics were calculated and discussed. The UV–Visible absorption spectra of the solution containing the inhibitor after the immersion of mild steel specimen indicate the formation of a MIP-Fe complex.     

Experimental and theoretical investigation of adsorption and inhibition properties of 2-Amino-1,3,5-triazine-4,6-dithiol against corrosion in hydrochloric acid solution on mild steel

In this work, 2-Amino-1,3,5-triazine-4,6-dithiol (2-ATD) as novel and high efficiency corrosion inhibitor has been investigated for mild steel (MS) corrosion in 0.5 M HCl solution using electrochemical methods, scanning electron microscopy (SEM), energy disperse X-ray spectroscopy (EDX), atomic force microscopy (AFM) and quantum chemical calculation methods. Potentiodynamic polarization (PDP) curves indicate that 2-ATD is mixed type inhibitor, corrosion inhibition efficiency increased with increasing inhibitor concentration and reached its value of 96.5%. Evolution of exposure time versus corrosion behavior of 2-ATD is examined in corrosive medium. While corrosion potential (E_corr) shifted more negative values, polarization resistances (R_p) decreased after 120 h exposure time due to the corrosion process. H₂ volume is measured in uninhibited and inhibited solutions (10 mM 2-ATD) after 120 h exposure time. Very low volume (3.6 mL cm⁻²) of H₂ is obtained on MS electrode in inhibited solution after 120 h of exposure, indicating that 2-ATD covers the entire surface against aggressive attack and retards the both anodic dissolution of MS and cathodic hydrogen evolution reactions. The adsorption process proposal is the Langmuir isotherm which is most suitable. Adsorption and thermodynamic parameters show that 2-ATD has a strong adsorption effect onto MS surface and includes mixed adsorption style (physical and chemical). Corrosion current density increases with increasing temperature and high activation energy (Ea) proves the strong adsorption of 2-ATD on the MS surface. Anti-corrosion mechanism of 2-ATD is described more detail with the potential of zero charge method. SEM, EDX and AFM analysis support the obtained results of electrochemical methods and confirm the existence of protective layer and strong adsorption of 2-ATD on the MS surface. Chronoamperometry test shows that current densities are almost constant whole experiment in the presence of organic film. Finally, quantum chemical calculation method of 2-ATD in blank solution is performed to investigate the active sites for possible attachment with MS surface.     

Experimental and theoretical investigations of adsorption of fexofenadine at mild steel/hydrochloric acid interface as corrosion inhibitor

The present study examines the effect of fexofenadine, an antihistamine drug, on corrosion inhibition of mild steel in molar hydrochloric acid solution using different techniques under the influence of various experimental conditions. Results revealed that fexofenadine is an effective inhibitor and percent inhibition efficiency increased with its concentration; reaching a maximum value of 97% at a concentration of 3.0 × 10⁻⁴ M. Fourier-transform infrared spectroscopy (FTIR) observations of steel surface confirmed the protective role of the studied drug. Polarization studies showed that fexofenadine is a mixed-type inhibitor. The adsorption of the inhibitor on mild steel surface obeyed the Langmuir adsorption isotherm with free energy of adsorption (∆G°_ads) of −40 kJ mol⁻¹. Energy gaps for the interactions between mild steel surface and fexofenadine molecule were found to be close to each other showing that fexofenadine has the capacity to behave as both electron donor and electron acceptor. The results obtained from the different corrosion evaluation techniques are in good agreement.     

Adsorption and inhibitive properties of aminobiphenyl and its Schiff base on mild steel corrosion in 0.5 M HCl medium

Electrochemical measurements were performed to investigate the effectiveness and adsorption behaviour of aminobiphenyl (Aph) and 2-(3-hydroxybenzylideneamino)biphenyl (Aph-S), as corrosion inhibitors for mild steel (MS) in 0.5 M HCl solution. Potentiodynamic polarization, linear polarization resistance (LP) and electrochemical impedance spectroscopy (EIS) techniques were applied to study the metal corrosion behaviour in the absence and presence of different concentrations of Aph and Aph-S. In order to gain more information about adsorption mechanism the AC impedance technique was used to evaluate the potential of zero charge (PZC) from polarization resistance (R_p) versus voltage (E) plot. Potentiodynamic polarization measurements showed that Aph act as cathodic type inhibitor where as Aph-S act mixed type. The inhibition efficiency (IE%) increases with increasing concentration of compounds and reached 92.6% for Aph and 97.2% for Aph-S at 5 × 10⁻³ M. Double layer capacitance (C_dl) and polarization resistance (R_p) values are derived from Nyquist plots obtained from AC impedance studies. The experimental data fit Langmuir isotherm for both Aph and Aph-S, and from the adsorption isotherm some thermodynamic data for the adsorption processes are calculated and discussed. The effect of exposure time on the corrosion behaviour of mild steel in the absence and presence of inhibitor over 168 h was also studied.     

Corrosion inhibitive evaluation and DFT studies of 2-(Furan-2-yl)-4,5-diphenyl-1H-imidazole on mild steel at 1.0M HCl

A novel heterocyclic compound 2-(Furan-2-yl)-4,5-Diphenyl-1H-Imidazole (FDPI) was synthesized by a simple and cost effective one pot synthetic protocol and the structure of FDPI was confirmed by FT-IR, ¹H NMR and ¹³C NMR spectra. The corrosion inhibition activity of FDPI was investigated using gravimetric and electrochemical methods. It resulted a maximum inhibition efficiency of 95.84% at 10 mmolL⁻¹ concentrations of FDPI. The excellent inhibition efficiency is reasoned as the adsorption of FDPI on the mild steel surface as a protective layer immersed in the 1 ​M HCl. The adsorbed layer obeys Langmuir adsorption isotherm and the ΔG^o_ads values of FDPI suggested that process involves physisorption. The polarization curves showed that the FDPI behaves as a mixed type inhibitor. Surface morphology studied by SEM confirmed the formation of a protective film of FDPI on the mild steel surface. The computational studies using DFT have been analyzed for the FDPI to determine the HOMO-LUMO energy gap.     

Study on the Inhibition of Mild Steel Corrosion by Cationic Gemini Surfactant in 1 M HCl

The cationic gemini surfactant 1,2-bis(N-tetradecyl-N,N-dimethylammonium)ethane dibromide (14-2-14) was synthesized using a previously described method. The surfactant was characterized using ¹H NMR. The corrosion inhibition effect of 14-2-14 on mild steel in 1 M HCl at temperatures 30–60°C was studied using weight loss measurements, potentiodynamic polarization measurements and electrochemical impedance spectroscopy. Morphology of the corroded mild steel specimens was examined using scanning electron microscopy (SEM). The results of the studies show that gemini surfactant is an efficient inhibitor for mild steel corrosion in 1 M HCl; the maximum inhibition efficiency (IE) of 98.06% is observed at surfactant concentration of 100 ppm at 60°C. The %IE increases with the increasing inhibitor concentration and temperature. The adsorption of inhibitor on the mild steel surface obeys Langmuir adsorption isotherm. SEM studies confirmed smoother surface for inhibited mild steel specimen.     

Experimental, quantum chemical calculations, and molecular dynamic simulations insight into the corrosion inhibition properties of 2-(6-methylpyridin-2-yl)oxazolo[5,4-f][1,10]phenanthroline on mild steel

2-(6-Methylpyridin-2-yl)oxazolo[5,4-f][1,10]phenanthroline (MOP) was synthesized and characterized by elemental analysis and Fourier-transform infrared (FT-IR), ¹H nuclear magnetic resonance (NMR), and ¹³C NMR spectra. MOP was evaluated as a corrosion inhibitor for carbon steel in 0.5 M H₂SO₄ solution using the standard gravimetric technique at 303–333 K. Quantum chemical calculations and molecular dynamic (MD) simulations were applied to analyze the experimental data and elucidate the adsorption behavior and inhibition mechanism of MOP. Results obtained show that MOP is an efficient inhibitor for mild steel in H₂SO₄ solution. The inhibition efficiency was found to increase with increase in MOP concentration but decreased with temperature. Activation parameters and Gibbs free energy for the adsorption process using statistical physics were calculated and discussed. The adsorption of MOP was found to involve both physical and chemical adsorption mechanisms. Density functional theory (DFT) calculations suggest that nitrogen and oxygen atoms present in the MOP structure were the active reaction sites for the inhibitor adsorption on mild steel surface via donor–acceptor interactions between the lone pairs on nitrogen and oxygen atoms together with the π-electrons of the heterocyclic and the vacant d-orbital of iron atoms. The adsorption of MOP on Fe (1 1 0) surface was parallel to the surface so as to maximize contact, as shown in the MD simulations. The experiments together with DFT and MD simulations provide further insight into the mechanism of interaction between MOP and mild steel.     

Hydroclathrus clathratus marine alga as a green inhibitor of acid corrosion of mild steel

The corrosion inhibitive and adsorption behaviors of Hydroclathrus clathratus on mild steel in 1 M HCl and 1 M H₂SO₄ solutions at 303, 313 and 323 K were investigated by weight loss, electrochemical, and surface analysis techniques. The results show that H. clathratus acts as an inhibitor of corrosion of mild steel in acid media. The inhibition efficiency was found to increase with increase in inhibitor concentration but to decrease with rise in temperature, suggestive of physical adsorption. The adsorption of the inhibitor onto the mild steel surface was found to follow the Temkin adsorption isotherm. The inhibition mechanism was further corroborated by the results obtained from electrochemical methods. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) analyses supported the inhibitive action of the alga against acid corrosion of mild steel.     

Inhibition of mild steel corrosion in 5 % HCl solution by 5-(2-hydroxyphenyl)-1,2,4-triazole-3-thione

A new corrosion inhibitor, namely 5-(2-hydroxyphenyl)-1,2,4-triazole-3-thione (5-HTT), has been synthesized and its influence on corrosion inhibition of mild steel in 5 % HCl solution has been studied using weight loss method and electrochemical measurements. Potentiodynamic polarization measurements clearly reveal that the investigated inhibitor is of mixed type, and it inhibits the corrosion of the steel by blocking the active site of the metal. Changes in impedance parameters were indicative of adsorption of 5-HTT on the metal surface, leading to the formation of protective films. The degree of the surface coverage of the adsorbed inhibitors was determined by weight loss measurements, and it was found that the adsorption of these inhibitors on the mild steel surface obeys the Langmuir adsorption isotherm. The effect of the temperature on the corrosion behavior with addition of 5 × 10^?4 M of the inhibitor was studied in the temperature range 30–60 °C. The reactivity of this compound was analyzed through theoretical calculations based on density functional theory to explain the different efficiency of these compounds as a corrosion inhibitor.     

Xanthione: A new and effective corrosion inhibitor for mild steel in sulphuric acid solution

The adsorption and inhibition effect of xanthione (XION) on mild steel in 0.5 M H₂SO₄ at 303–333 K were studied using gravimetric and UV–visible spectrophotometric methods. The results obtained show that XION acts as an effective corrosion inhibitor for mild steel in sulphuric acid and inhibition efficiency reaches 98.0% at a very low inhibitor concentration of 10 μM. Inhibition efficiency was found to increase with increase in XION concentration but decreased with temperature suggesting physical adsorption mechanism. Arrhenius law and its transition equation lead to estimate the activation parameters of the corrosion process. XION inhibits the corrosion of mild steel effectively at moderate temperature and adsorbs according to the Langmuir isotherm. Thermodynamic parameters governing the adsorption process have been calculated and discussed. The UV–visible absorption spectra of the solution containing the inhibitor after the immersion of mild steel specimen indicate the formation of a XEN–Fe complex. Attempt to correlate the molecular structure to quantum chemical indices was made using density functional theory (DFT).     

Inhibition effect of environmentally benign Karanj (Pongamia pinnata) seed extract on corrosion of mild steel in hydrochloric acid solution

The inhibition of the corrosion of mild steel in hydrochloric acid solution by the seed extract of Karanj (Pongamia pinnata) has been studied using weight loss, electrochemical impedance spectroscopy, potentiodynamic polarization, and linear polarization techniques. Inhibition was found to increase with increasing concentration of the extract. The effect of temperature, immersion time, and acid concentration on the corrosion behavior of mild steel in 1 M HCl with addition of extract was also studied. The adsorption of the extract on the mild steel surface obeyed the Langmuir adsorption isotherm. Values of inhibition efficiency calculated from weight loss, potentiodynamic polarization, and electrochemical impedance spectroscopy are in good agreement. Polarization curves showed that Karanj (P. pinnata) seed extract behaves as a mixed-type inhibitor in hydrochloric acid. The activation energy as well as other thermodynamic parameters for the inhibition process was calculated. The adsorbed film on mild steel surface containing Karanj (P. pinnata) seed extract inhibitor was also measured by Fourier transform infrared spectroscopy. The results obtained showed that the seed extract of Karanj (P. pinnata) could serve as an effective inhibitor of the corrosion of mild steel in hydrochloric acid media.     

The effect of 2-aminoquinoline-6-carboxylic acid on the corrosion behavior of mild steel in hydrochloric acid

The inhibitive effect of 2-aminoquinoline-6-carboxylic acid (AQC) against mild steel corrosion in 1?M HCl solutions was investigated using conventional weight loss, potentiodynamic polarization, linear polarization and electrochemical impedance spectroscopy methods. The weight loss results showed that AQC is an excellent corrosion inhibitor since its efficiency increased with the concentration to attain 91.8?% at 500?mg?l^?1. Electrochemical polarization measurements revealed that AQC acted as a mixed-type inhibitor and the results of electrochemical impedance spectroscopy have shown that the change in the impedance parameters, charge transfer resistance and double layer capacitance, with the change in concentration of the inhibitor is due to the adsorption of the molecule leading to the formation of a protective layer on the surface of mild steel. The adsorption was assumed to occur on the steel surface through the active centers of the molecule. The inhibition action of AQC was discussed in view of Langmuir adsorption isotherm. Density functional theory calculations of quantum parameters were used to explain efficiency in relation with molecular structure.     

Inhibiting effects of 2-mercapto-1-methylimidazole on copper corrosion in 0.5 M sulfuric acid

The inhibiting efficiency of 2-mercapto-1-methylimidazole (MMI) on copper corrosion in sulfuric acid was investigated at 30 °C. Its effectiveness was assessed through electrochemical impedance spectroscopy, potentiodynamic polarization and gravimetric measurements. The results of study reveal that the inhibition efficiency of MMI depends on its concentration and attains approximately 81% at 10^?4 M. The inhibitor was adsorbed on the copper surface according the Langmuir adsorption isotherm model. The value of standard free energy of adsorption was calculated from this isotherm.     

Experimental and theoretical studies on protecting steel against 0.5 M H2SO4 corrosion by new schiff base

In this study, a novel green corrosion inhibitor called 2,2'-((1Z,1′Z)-((piperazine-1,4-diylbis(2,1-phenylene))bis(methanylylidene))bis(azanylylidene)) (PMA) has been tested against corrosion of carbon steel in 0.5 M H₂SO₄. Quantum and electrochemical methods were used to evaluate PMA's ability to inhibit the deterioration of carbon steel in an acidic environment. The results revealed that PMA acted as a mixed inhibitor, primarily anodic, whose inhibition action was enhanced by increasing its concentration. At 298.15 K, the maximum efficiency was around 91% with 1 × 10^?3 M PMA in 0.5 M H₂SO₄. The results showed that the inhibition occurred due to adsorption of the PMA molecules on the surface. The adsorbed layer of PMA satisfied the Langmuir adsorption isotherm. The morphology of the surface was examined using scanning electron microscopy.     

Poly (vinyl alcohol – aniline) water soluble composite as corrosion inhibitor for mild steel in 1 M HCl

Poly (vinyl alcohol – aniline) PVAA composite was tested for its performance in protecting mild steel MS against corrosion in 1 M HCl. The inhibitive parameters were evaluated by means of weight loss, electrochemical polarization and impedance methods. Results indicated that the addition of PVAA to the acid reduces the corrosion of the metal. Inhibition efficiency increases with increase in inhibitor concentration. The results further revealed that PVAA at a concentration of 2000 ppm furnishes a maximum of 92% inhibition efficiency. Thermodynamic parameters such as free energy of adsorption, heat of adsorption, etc., had been evaluated from temperature studies. The adsorption of PVAA followed Langmuir and Temkin adsorption isotherms. Polarization curves revealed that PVAA is a mixed inhibitor.     

Experimental,Monte Carlo and molecular dynamics simulations to investigate corrosion inhibition of mild steel in hydrochloric acid solutions

The efficiency of three furan derivatives, namely 2-(p-toluidinylmethyl)-5-methyl furan (Inh. A), 2-(p-toluidinylmethyl)-5-nitro furan (Inh. B) and 2-(p-toluidinylmethyl)-5-bromo furan (Inh. C), as possible corrosion inhibitors for mild steel in 1.0 M HCl, has been determined by weight loss and electrochemical measurements. These compounds inhibit corrosion even at very low concentrations, and 2-(p-toluidinylmethyl)-5-methyl furan (Inh. A) is the best inhibitor. Polarization curves indicate that all compounds are mixed-type inhibitors, affecting both cathodic and anodic corrosion currents. Adsorption of furan derivatives on the mild steel surface follows the Langmuir adsorption isotherm, and the calculated Gibbs free energy values confirm the chemical nature of the adsorption. Monte Carlo simulations technique incorporating molecular mechanics and molecular dynamics can be used to simulate the adsorption of furan derivatives on mild steel surface in 1.0 M HCl.     

Inhibitive effect of chloroquine towards corrosion of mild steel in hydrochloric acid solution

Corrosion inhibition of mild steel (MS) by chloroquine (CQ) in 1 M HCl was investigated using weight loss, polarization, electrochemical impedance spectroscopy (EIS) and quantum chemical techniques. The inhibitor showed 99 % inhibition efficiency at concentration of 3.1 × 10^?4 M. Polarization studies showed that CQ is a mixed-type inhibitor. Adsorption of inhibitor molecules on the MS surface showed Langmuir adsorption isotherm. Thermodynamic parameters led to the conclusion that adsorption is predominantly chemisorption. Quantum chemical calculations were carried out to investigate the corrosion-inhibiting property of CQ. Various parameters such as energy of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO), softness of molecule, Mullikan charges on various atoms and number of electrons transferred from inhibitor molecule to metal were calculated and correlated with the inhibiting property of CQ.     

Inhibition of aluminium and mild steel corrosion in acidic medium using Gum Arabic

The corrosion behaviour of mild steel and aluminium exposed to H₂SO₄ solution and their inhibition in H₂SO₄ containing 0.1–0.5 g/L Gum Arabic (GA) used as inhibitor was studied at temperature range of 30–60 °C using weight loss and thermometric techniques. Corrosion rate increased both in the absence and presence of inhibitor with increase in temperature. Corrosion rate was also found to decrease in the presence of inhibitor compared to the free acid solution. Inhibition efficiency increases with increase in concentration of the inhibitor reaching a maximum of 37.88% at 60 °C for mild steel and 79.69% at 30 °C for aluminium at 0.5 g/L concentration of GA. The inhibitor, GA was found to obey Temkin and El-Awady et al. thermodynamic kinetic adsorption isotherm for mild steel and aluminium respectively from the fit of the experimental data at all concentrations and temperatures studied. The phenomenon of chemical adsorption is proposed for mild steel corrosion, while physical adsorption mechanism is proposed for aluminium corrosion. Results obtained for the kinetic/thermodynamic studies indicate that the adsorption of GA onto the metals surface was spontaneous. GA is a better corrosion inhibitor for aluminium than for mild steel.     

Corrosion inhibition of mild steel by highly stable polydentate schiff base derived from 1,3- propanediamine in aqueous acidic solution

Recently, the hydrolysis of Schiff bases under experimental conditions gives suspicion for their corrosion inhibition performance. The current study employs a stable Schiff base namely, 2,2′-{propane-1,3-diylbis[azanylylidene (E) methanylylidene]}bis(6-methoxyphenol) (LPD) as corrosion inhibitor for mild steel (MS) in 1 M HCl solution. The presence of the characteristic peak of the imine group in UV-visible spectra was taken as an indicator for LPD stability in acidic media. The inhibition action was examined using electrochemical techniques including potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) besides gravimetric measurement. The inhibition efficiency reached 95.93 % for 0.75 mM LPD after 24 h of immersion at 25 °C. This high efficiency is owing to the presence of the characteristic imine group and other heteroatoms and π- electrons of the aromatic benzene rings. The mechanism of inhibition depends on adsorption phenomena on mild steel surface which obeys Langmuir isotherm model. The calculated values of adsorption equilibrium constant (K_ads), adsorption free energy ΔG_ads, adsorption enthalpy ΔH_ads and adsorption entropy ΔS_ads indicated spontaneous exothermic adsorption process of both physical and chemical nature. By rising temperature, the inhibition efficiency of LPD was decreased. The calculated activation energy was increased as the concentration of LPD increased. LPD was considered as a mixed-type inhibitor as indicated from PDP measurements. The obtained surface morphology and composition analysis using SEM/EDS, AFM and FTIR techniques ensures the high efficiency of LPD as corrosion inhibitor.