Protection of mild steel corrosion with Schiff bases in 0.5 M H2SO4 solution

Three new Schiff bases, viz., N,N′-ethylen-bis (salicylidenimine) [S₁], N,N′-isopropylien-bis (salicylidenimine) [S₂], and N-acetylacetone imine, N′-(2-hydroxybenzophenone imine) ortho-phenylen [S₃] have been investigated as corrosion inhibitors for mild steel in 0.5 M H₂SO₄ using Tafel polarization and electrochemical impedance spectroscopy (EIS). The three Schiff bases function as good inhibitors reaching inhibition efficiencies of ∼97-98% at 300 ppm concentration. The fraction <theta> of the metal surface covered by the inhibitor is found to increase with inhibitor concentration. Of the three Schiff bases, the S2 shows better efficiency than the other two Schiff bases. The adsorption of the inhibitor follows Langmuir isortherm. Thermodynamic calculations indicate the adsorption to be physical in nature.     

Some Schiff Base Surfactants as Steel-Corrosion Inhibitors

Two series of Schiff base amphiphiles were prepared by condensation of benzaldehyde or anisaldehyde with three different alkyl chain length fatty amines namely: dodecyl, hexadecyl and octadecyl amine. The chemical structures of the prepared Schiff bases were confirmed by using different techniques, (elemental analysis, FTIR and ¹H-NMR spectra). The data of structural analysis for these compounds were confirmed by the purity of the synthesized amphiphiles. The synthesized Schiff bases were evaluated as corrosion inhibitors for low carbon steel (mild steel) in various acidic media (HCl and H₂SO₄) using a weight loss technique. The corrosion inhibition measurements of these inhibitors showed high protection against corrosion process in the tested acidic media at different doses (50, 100, 150 and 200 ppm) as well as their having a good biocidal effect against sulphate reducing bacteria. The discussion correlated the efficient corrosion inhibition of these inhibitors to their chemical structures.     

Schiff bases: An overview of their corrosion inhibition activity in acid media against mild steel

Abstract

This paper deals with a review of the inhibition activity of various reported Schiff bases on the deterioration of mild steel in hydrochloric acid and sulfuric acid media. Mild steels find wide applications in structural, automobile and petrochemical industry, where acid solutions such as hydrochloric acid, sulfuric acid are commonly being used as pickling or descaling agents. The undue deterioration of metal during pickling can be controlled by adding a suitable inhibitor to the pickling solution. Schiff bases are widely being employed in such applications. This paper highlights the influence of structure–inhibition activity relationship of Schiff base compounds on their performance as corrosion inhibitors of mild steel in acid media. The information provided finds a useful practical application for different industrial fields in the selection of best-performing inhibitors and also for the researchers involved in the development of new novel corrosion inhibitors for mild steel in acid media.     

Effect of Schiff Bases Containing Pyridyl Group as Corrosion Inhibitors for Low Carbon Steel in 0.1 M HCl

The inhibiting effect of four newly synthesised Schiff bases containing pyridyl group was investigated on the corrosion of low carbon steel in 0.1 M hydrochloric acid solution under various conditions by potentiodynamic polarisation method and impedance measurements. The Schiff bases used were 2-((1Z)-1-aza-2-(2-pyridyl)vinyl)benzene-1-thiol, (1Z)-1-aza-1,2- di(2-pyridyl)ethene, [((1Z)-1-aza-2-(2-pyridyl)vinyl)amino]benzene-1-thione and 2-((1Z)-1-aza-2-(2-pyridyl)vinyl)benzothiazole. All the Schiff bases inhibit corrosion of low carbon steel and their inhibition efficiencies increase with decrease in temperature and increase in concentration. The difference in protection actions of the inhibitors can be attributed to the presence of substituents in the structures that increase or decrease the electron density on the azomethine (–C=N–) group. Polarisation curves indicate that the Schiff bases act as anodic inhibitors. AC impedance and potentiodynamic polarisation measurements reveal that the compounds are adsorbed on the steel surface and the adsorption obeys the Temkin isotherm. Activation parameters (E_a, ΔH*, ΔS*) for the corrosion of low carbon steel in 0.1 M HCl were calculated and showed that corrosion was much reduced in the presence of inhibitors.     

Corrosion inhibition of mild steel by alkylimidazolium ionic liquids in hydrochloric acid

The acid corrosion inhibition process of mild steel in 1 M HCl by 1-butyl-3-methylimidazolium chlorides (BMIC) and 1-butyl-3-methylimidazolium hydrogen sulfate ([BMIM]HSO₄) has been investigated using electrochemical impedance, potentiodynamic polarization and weight loss measurements. Potentiodynamic polarization studies indicate the studied inhibitors are mixed type inhibitors. For both inhibitors, the inhibition efficiency increased with increase in the concentration of the inhibitor and the effectiveness of the two inhibitors are in the order [BMIM]HSO₄ > BMIC. The adsorption of the inhibitors on mild steel surface obeyed the Langmuir's adsorption isotherm. The effect of temperature on the corrosion behavior in the presence of 5 × 10⁻³ M of inhibitors was studied in the temperature range of 303-333 K. The associated activation energy of corrosion and other thermodynamic parameters such as enthalpy of activation (ΔH), entropy of activation (ΔS), adsorption equilibrium constant (K_ads) and standard free energy of adsorption (ΔG_ads) were calculated to elaborate the mechanism of corrosion inhibition.     

5-CM-Salophen Schiff Base as an Effective Inhibitor for Corrosion of Mild Steel in 0.5 M HCl

5-CM-Salophen Schiff base was examined as an inhibitor for corrosion of mild steel in 0.5 M hydrochloric acid (HCl). The gravimetric data revealed corrosion inhibition effectiveness of the Schiff base even at low concentrations. Polarization measurements showed that the Schiff base is a mixed-type corrosion inhibitor. The polarization resistance (R_p) increased with increasing the Schiff base concentration. Also, the values of the double-layer capacitance decreased after addition of the inhibitor due to adsorption of the Schiff base on the surface. The inhibition mechanism was investigated by plotting the Langmuir adsorption isotherm and calculating the potential of zero charge (E_PZC) for mild steel samples. Scanning electron microscopy (SEM) analysis confirmed the results of the corrosion tests.     

Aldimines — Effective Corrosion Inhibitors for Mild Steel in Hydrochloric Acid Solution

New and effective aldimine types of corrosion inhibitors namely, N-methylidene octylamine (MOA), N-ethylidene octylamine (EOA) and N-propylidene octylamine (POA) have been synthesized. Their inhibition efficiency was investigated for the corrosion of mild steel in 1 M HCl solution by various corrosion monitoring techniques. A preliminary screening of the inhibition efficiency of the inhibitors was carried out by weight loss and gasometric studies. They were found to behave as good inhibitors in 1 M HCl solution. Potentiodynamic polarization measurements show that aldimines are mixed type inhibitors. The extent of the decrease in the hydrogen permeation current through the mild steel surface was studied by the hydrogen permeation technique and it was found that the decrease was in the order POA > EOA > MOA. Double layer capacitance and charge transfer resistance values were derived from Nyquist plots obtained from AC impedance studies. The adsorption of these compounds on mild steel from 1 M HCl solution obeys the Temkin adsorption isotherm.     

Physiochemical interactions of chiral Schiff bases on high carbon steel surface: Corrosion inhibition in acidic media

(S)1-N-(1-hydroxy-1,1-diphenyl-3-methylbut-2-yl)-2-hydroxybenzaldimine (DPV) and (S)1-N-(1-hydroxy-3-methylbut-2-yl)-2-hydroxybenzaldimine (LV) were synthesized and investigated as inhibitors for the corrosion of the high carbon steel (HCS) in 1.0 M HCl by electrochemical measurements. According to the electrochemical methods, inhibitor DPV showed higher efficiency in comparison to that of LV. The Tafel polarization method revealed the mixed-mode inhibition of chiral Schiff bases with predominant control of the anodic reaction. The adsorption of the inhibitor molecules onto the HCS surface was found to follow the Langmuir adsorption isotherm. The values of the Gibbs free energy of adsorption strongly supported spontaneous physicochemical adsorption of inhibitor molecules on the HCS surface. The adsorption mechanism for inhibition was supported by Fourier transforms infrared (FTIR), wide-angle X-ray diffraction (WAXD), scanning electron microscopy–energy-dispersive X-ray (SEM–EDS) spectroscopic methods, and adsorption isotherms.     

Thiazoles as corrosion inhibitors for mild steel in formic and acetic acid solutions

2-(N,N-dimethylamino) benzylidene imino-4-(4-methyl phenyl)-1,3-thiazole (DIMPT), 2-benzylidene imino-4-(4-methyl phenyl)-1,3-thiazole (BIMPT), 2-salicylidene imino-4-(4-methyl phenyl)-1,3-thiazole (SIMPT) and 2-cinnamylidene imino-4-(4-methyl phenyl)-1,3-thiazole (CIMPT) were synthesized in the laboratory and their influence on the inhibition of corrosion of mild steel in 20 formic acid and 20 acetic acid was investigated by weight loss and potentiodynamic polarization techniques. The inhibition efficiency of these compounds was found to vary with their nature and concentration, temperature, immersion time and acid concentration. The values of activation energy and free energy of adsorption of the thiazoles were calculated to investigate the mechanism of corrosion inhibition. The adsorption of all the thiazoles on mild steel surface was found to obey Langmuir adsorption isotherm. The potentiodynamic polarization result revealed that the compounds studied are mixed type inhibitors. Electrochemical impedance spectroscopy was used to investigate the mechanism of corrosion inhibition.     

Inhibiting Effect of Ionic Liquids on the Corrosion of Mild Steel in H2S and HCl Solution

Four imidazolium-based ionic liquids (ILs) were selected to investigate the inhibiting effect of ILs with various alkyl chain lengths on the corrosion of mild steel in H₂S and HCl solution using electrochemical experiments, weight loss and surface analyses, and quantum chemical study. The results demonstrated that these ILs acted as mixed-type inhibitors and efficiently inhibited the corrosion of mild steel in H₂S and HCl solution. Their excellent corrosion inhibition ability was due to their adsorption process on the metal surface, which followed the Langmuir adsorption isotherm. Furthermore, extending the alkyl chain length in the ILs could improve their inhibition performance.     

Adsorption and corrosion inhibition behaviour of N-(phenylcarbamothioyl)benzamide on mild steel in acidic medium

Corrosion inhibition property of N-(phenylcarbamothioyl)benzamide (PCB) on mild steel in 1.0 M HCl solution has been investigated using chemical (weight loss method) and electrochemical techniques (potentiodynamic polarization and AC impedance spectroscopy). The inhibition efficiencies obtained from all the methods are in good agreement. The thiourea derivative is found to inhibit both anodic and cathodic corrosion as evaluated by electrochemical studies. The inhibitor is adsorbed on the mild steel surface according to Langmuir adsorption isotherm. The adsorption mechanism of inhibition was supported by spectroscopic (UV-visible, FT-IR, XPS), and surface analysis (SEM-EDS) and adsorption isotherms. The thermodynamic parameter values of free energy of adsorption (ΔG_ads) reveals that inhibitor was adsorbed on the mild steel surface via both physisorption and chemisorption mechanism.     

Effect of amino acids containing sulfur on the corrosion of mild steel in phosphoric acid solutions polluted with Cl−, F− and Fe3+ ions–behaviour near and at the corrosion potential

Research on non‐toxic inhibitors is of considerable interest in investigations into the replacement of hazardous classical molecules. This paper reports the action of four amino acids containing sulfur on the corrosion of mild steel in phosphoric acid solution with and without Cl^?, F^? and Fe³⁺ ions near and at the corrosion potential (E_corr) using both the polarization resistance method and electrochemical impedance spectroscopy (EIS). Both cysteine and N‐acetylcysteine (ACC) showed higher inhibition efficiency than methionine and cystine. Adsorption of methionine onto a mild steel surface obeys the Frumkin adsorption isotherm and has a free energy of adsorption value (ΔG °_ads) lower than those obtained in the presence of cystine, cysteine and ACC whose adsorption isotherms follow that of Langmuir. Both F^? and Fe³⁺ ions stimulate mild steel corrosion while Cl^? ions inhibit it. The binary mixtures of methionine, cysteine or ACC with Cl^? or F^? ions are effective inhibitors (synergism) while the combinations of the amino acid with Fe³⁺ or the ternary Cl^?/F^?/Fe³⁺ mixture have low inhibitive action (antagonism). EIS measurements revealed that the charge transfer process mainly controls the mechanism of mild steel corrosion in phosphoric acid solution in the absence and presence of the investigated additives. The mechanism of corrosion inhibition or acceleration is discussed. © 2002 Society of Chemical Industry     

Inhibiting and accelerating effects of aminophenols on the corrosion and permeation of hydrogen through mild steel in acidic solutions

The influence of aminophenols on the corrosion and hydrogen permeation of mild steel in 1 M HCl and 0.5 M H₂SO₄ has been studied using weight loss and gasometric measurements and various electrochemical techniques. All the isomers of aminophenol inhibit the corrosion of mild steel in 1 M HC1 and accelerate it in 0.5 M H₂SO₄. They behave predominantly as cathodic inhibitors. Aminophenols, except PAP in I M HCI, enhance the permeation current in both the acids. The adsorption of PAP on the mild steel surface in 1 M HCl obeys the Langmuir adsorption isotherm. Surface analysis and ultraviolet spectral studies are also carried out to establish the mechanism of corrosion inhibition and acceleration of mild steel in acidic solutions.     

2-[(E)-{(1S,2R)-1-Hydroxy-1-phenylpropan-2-ylimino}methyl]phenol for Inhibition of Acid Corrosion of Mild Steel

2-[(E)-{(1S,2R)-1-hydroxy-1-phenylpropan-2-ylimino}methyl]phenol has been synthesized and its influence on corrosion of mild steel in 1?M HCl solution has been studied by means of weight loss and electrochemical measurements under various circumstances. The inhibitor showed a maximum of 91?% of inhibition efficiency at 100?ppm. Interestingly, the inhibition efficiency has decreased on increasing the inhibitor concentration. This abnormal behavior is attributed to the release of phenolic hydrogen from the molecule. The mechanism of corrosion inhibition follows Langmuir adsorption isotherm. The negative ?G _ads indicates the spontaneous adsorption of the inhibitor on mild steel surface. Potentiodynamic polarization studies show that it is a mixed type inhibitor with predominant cathodic inhibition. UV?CVisible spectroscopy of the inhibitor and inhibitor adsorbed on the mild steel confirmed the chemical interaction of the inhibitor with the metal surface.     

Experimental and Quantum Chemical Studies on Corrosion Inhibition Performance of Thiazolidinedione Derivatives for Mild Steel in Hydrochloric Acid Solution

In the present investigation, two thiazolidinedione derivatives, 5-[(2-(3,4,5-trimethoxyphenyl)-6-phenylimidazo[2,1-b][1,3,4]thiadiazol-5-yl)methylidene]-1,3-thiazolidine-2,4-dione (Inh I) and 5-[2-(3,4,5-trimethoxyphenyl)-6-(4-methoxylphenyl)-imidazo[2,1-b][1,3,4]thiadiazol-5-yl)methylidene]-1,3-thiazolidine-2,4-dione (Inh II) were synthesized and investigated as inhibitors for mild steel corrosion in 15% HCl solution using the weight loss, electrochemical polarization, and electrochemical impedance spectroscopy (EIS) techniques. It was found that the inhibition efficiency of these inhibitors increased with increasing concentration. The effect of temperature on the corrosion rate was investigated, and some thermodynamic parameters were calculated. Polarization studies showed that both studied inhibitors were of mixed type in nature. The adsorption of inhibitors on the mild steel surface in acid solution was found to obey the Langmuir adsorption isotherm. Scanning electron microscopy (SEM) was performed on inhibited and uninhibited mild steel samples to characterize the surface. The semi-empirical AM1 method was employed for theoretical calculation of highest (E _HOMO), and lowest unoccupied molecular orbital (E _LUMO) energy levels, energy gap (E _LUMO ? E _HOMO), dipole moment (μ), global hardness (γ), softness (σ), binding energy, molecular surface area, chemical potential (Pi), and the fraction of electrons transferred from the inhibitor molecule to the metal surface (ΔN). The results were found to be consistent with the experimental findings.     

Influence of 2,5-bis(4-dimethylaminophenyl)-1,3,4-thiadiazole on corrosion inhibition of mild steel in acidic media

An example of a new class of corrosion inhibitors, namely, 2,5-bis(4-dimethylaminophenyl)-1,3,4-thiadiazole (DAPT) was synthesized and its inhibiting action on the corrosion of mild steel in 1 M HCl and 0.5 M H₂SO₄ at 30 °C was investigated by various corrosion monitoring techniques. A preliminary screening of the inhibition efficiency was carried out using weight loss measurements. At constant acid concentration, inhibitor efficiency increases with concentration of DAPT and is found to be more efficient in 0.5 M H₂SO₄ than in 1 M HCl. Potentiostatic polarization studies showed that DAPT is a mixed-type inhibitor. The effect of temperature on the corrosion behaviour of mild steel in 1 M HCl with addition of DAPT was studied in the temperature range from 25 to 60 °C. Its was shown that adsorption is consistent with the Langmuir isotherm for 30 °C. The negative free energy of adsorption in the presence of DAPT suggests chemisorption of thiadiazole molecules on the steel surface.     

ac impedance, X-ray photoelectron spectroscopy and density functional theory studies of 3,5-bis(n-pyridyl)-1,2,4-oxadiazoles as efficient corrosion inhibitors for carbon steel surface in hydrochloric acid solution

The corrosion inhibition properties of a new class of oxadiazole derivatives, namely 3,5-bis(n-pyridyl)-1,2,4-oxadiazoles (n-DPOX) for C38 carbon steel corrosion in 1 M HCl medium were analysed by electrochemical impedance spectroscopy (EIS). An adequate structural model of the interface was used and the values of the corresponding parameters were calculated and discussed. The experimental results showed that these compounds are excellent inhibitors for the C38 steel corrosion in acid solution and that the protection efficiency increased with increasing the inhibitors concentration. Electrochemical impedance data demonstrate that the addition of the n-DPOX derivatives in the corrosive solution decreases the charge capacitance and simultaneously increases the function of the charge/discharge of the interface, facilitating the formation of an adsorbed layer over the steel surface. Adsorption of these inhibitors on the steel surface obeys to the Langmuir adsorption isotherm. X-ray photoelectron spectroscopy (XPS) and the thermodynamic data of adsorption showed that inhibition of steel corrosion in normal hydrochloric solution by n-DPOX is due to the formation of a chemisorbed film on the steel surface. Quantum chemical calculations using the Density Functional Theory (DFT) and the Quantitative Structure Activity Relationship (QSAR) approach were performed on n-DPOX derivatives to determine the relationship between molecular structure and their inhibition efficiencies. The results of the quantum chemical calculations and experimental inhibition efficiency were subjected to correlation analysis and indicate that their inhibition effect is closely related to E_HOMO, E_LUMO, and dipole moment (μ).     

Inhibition of mild steel corrosion in the presence of fatty acid triazoles

The influence of some fatty acid triazoles namely, 4-Phenyl-5-undecyl-4H- [1,2,4] triazole-3-thiol (PUTT), 5-Heptadec-8-enyl-4-phenyl-4H- [1,2,4] triazole-3-thiol (HPTT), and 5-Dec-9-enyl-4-phenyl-4H- [1,2,4] triazole-3-thiol (DPTT) on the corrosion of mild steel in 1 M hydrochloric acid (HCl) and 0.5 M sulfuric acid (H₂SO₄) was studied by weight loss and potentiodynamic polarization methods. The values of activation energy and free energy of adsorption of all the triazoles were calculated to investigate the mechanism of corrosion inhibition. The potentiodynamic polarization studies were carried out at room temperature, according to which all the compounds were mixed type inhibitors and inhibit the corrosion of mild steel by blocking the active sites of the metal. The adsorption of all the triazoles on mild steel surface in both the acid solutions was found to obey the Langmuir adsorption isotherm. All the compounds showed good inhibition efficiency in both acids. The inhibition efficiency of the compounds was found to vary with their nature and concentration, solution temperature and immersion time. Electrochemical impedance spectroscopy was also used to investigate the mechanism of the corrosion inhibition.     

Pongamia Pinnata as a Green Corrosion Inhibitor for Mild Steel in 1N Sulfuric Acid Medium

Due to the harmful nature of the traditional inhibitors, in recent years researchers have an interest in using eco-friendly corrosion inhibitors. The plant extracts exhibit efficient corrosion inhibition properties due to the presence of a mixture of organic constituents starting from terpenoids to flavonoids. In the present study the inhibition of corrosion of mild steel in 1N H₂SO₄ solution using the leaf extract of Pongamia pinnata (P. pinnata) was investigated by the weight loss method, potentiodynamic polarization method and electrochemical impedance spectroscopy (EIS) technique. Characterization of the leaf extract of P. pinnata was carried out using Fourier transform infrared spectroscopy (FTIR) and gas chromatography-mass spectrometry (GCMS) analysis. The effect of temperature and immersion time on the corrosion behavior of mild steel in sulfuric acid with different concentrations of P. pinnata was also studied. From the results it was found that the inhibition is mainly attributed to the adsorption of inhibitor molecules on the mild steel electrode surface. It was found that the adsorption of inhibitor molecules takes place according to the Langmuir, Temkin, and Freundlich adsorption isotherms. Kinetic as well as thermodynamic parameters were calculated, also confirming the strong interaction between inhibitor molecules and the electrode surface. The inhibition efficiency (I.E in %) was found to increase with increase in concentration of the inhibitor molecules and the maximum inhibition efficiency was attained at 100 ppm of the leaf extract. From the electrochemical studies it was found that the corrosion process was controlled by a mixed inhibition process and single charge transfer mechanism. Fourier transform infrared spectroscopy (FTIR) provided the confirmatory evidence for the adsorption of the extract molecules on the mild steel surface, which is responsible for the corrosion inhibition. Scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDX) experiments also confirmed the presence of inhibitor molecules on the mild steel surface. From all these experimental results, it can be concluded that the leaf extract of P. pinnata acted as a good corrosion inhibitor for mild steel in 1N sulfuric acid medium even at lower inhibitor concentrations.