Electrochemical and thermodynamic studies to evaluate inhibition effect of 2-[(4-phenoxy-phenylimino)methyl]-phenol in 1 M HCl on mild steel

Inhibition of the corrosion of mild steel in 1.0 M HCl solution by a Schiff base compound named 2-[(4-phenoxy-phenylimino)methyl]-phenol (APS) was investigated at different temperatures (25–55 °C) using electrochemical measurements. The inhibition efficiency increased as APS concentration and temperature increased. It was found that adsorption for APS on mild steel complies with the Langmuir adsorption isotherm in all studied temperature. Thermodynamic parameters (ΔG_ads, ΔH_ads and ΔS_ads) for APS adsorption on mild steel were found out and discussed at each temperature. Time dependency of mild steel in 1.0 M HCl solution in the absence and presence of APS was also studied. The surface morphology of mild steel was examined via SEM analysis.     

The synergistic inhibition effect of rare earth cerium(IV) ion and iso-vanillin on the corrosion of cold rolled steel in 1.0 M H2SO4 solution

The synergistic inhibition effect of rare earth cerium(IV) ion and iso-vanillin (3-hydroxy-4-methoxy-benzaldehyde) on the corrosion of cold rolled steel (CRS) in 1.0 M H₂SO₄ solution was first investigated by weight loss and potentiodynamic polarization methods. The results revealed that iso-vanillin had a moderate inhibitive effect on the corrosion of CRS in 1.0 M H₂SO₄ solution, while cerium(IV) ion had a negligible effect. However, incorporation of Ce⁴⁺ with iso-vanillin significantly improved the inhibition performance. The inhibition efficiency for Ce⁴⁺ in combination with iso-vanillin was higher than the summation of inhibition efficiency for single Ce⁴⁺ and single iso-vanillin, which was synergism in nature.     

Ruthenium–ligand complex,an efficient inhibitor of steel corrosion in H3PO4 media

The effect of a ruthenium–ligand complex (RuLC) on the corrosion of steel in 2 M H₃PO₄ has been investigated at various temperatures using electrochemical techniques (impedance spectroscopy (EIS), polarisation curves) and weight loss measurements. Inhibition efficiency (E%) increases with RuLC concentration to attain 90% at 5 × 10^− 4 M. EIS measurements show that the dissolution process of steel occurs under activation control. Polarisation curves indicate that RuLC acts as a cathodic inhibitor. E% values obtained from various methods used are in good agreement. The temperature effect on the corrosion behaviour of steel in 2 M H₃PO₄ without and with the inhibitor at various concentrations was studied in the temperature range from 298 to 338 K. Thermodynamic parameters such as adsorption heat (ΔH_ads°), adsorption entropy (ΔS_ads°) and adsorption free energy (ΔG_ads°) have been calculated. Kinetic parameters for the corrosion reaction at different concentrations of RuLC were determined. Adsorption of RuLC on the mild steel surface in 2 M H₃PO₄ follows the Langmuir isotherm model.     

The inhibition of mild steel corrosion in 1 M hydrochloric acid solutions by triazole derivative

The title compound 1-(4,5-dihydro-3-phenylpyridine-1-yl)-2-(1H-1,2,4-triazole-1-yl)ethyl ketone (DTE) was synthesized and its inhibiting action on the corrosion of mild steel in 1 M hydrochloric acid solutions was investigated by means of weight loss, potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and scanning electronic microscope (SEM). Results obtained revealed that DTE performed excellently as a corrosion inhibitor for mild steel in 1 M hydrochloric acid media and its efficiency attains more than 90.9% at 1.0 × 10^− 3 M at 298 K. Polarization curves indicated that the inhibitor behave mainly as mixed-type inhibitor. EIS showed that the charge transfer controls the corrosion process in the uninhibited and inhibited solutions. Adsorption of the inhibitor on the mild steel surface followed Langmuir adsorption isotherm. And the values of the free energy of adsorption ΔG_ads indicated that the adsorption of DTE molecule was a spontaneous process and was typical of chemisorption.     

Corrosion inhibition of carbon steel and antibacterial properties of aminotris-(methylenephosphonic) acid

In this work, the corrosion inhibition property and the antibacterial activity of the aminotris-(methylenephosphonic) acid (ATMP) have been studied. ATMP has been evaluated as a corrosion inhibitor for carbon steel in 1 M HCl solution using weight loss, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques. According to the experimental results, the inhibition efficiency increased with increasing inhibitor concentration. Tafel polarization study showed that the ATMP acts as a mixed inhibitor. Data, obtained from EIS measurements, were analyzed to model the corrosion inhibition process through appropriate equivalent circuit models. Adsorption of ATMP on the carbon steel surface obeyed the Langmuir adsorption isotherm. The calculated ΔG_ads value showed that the corrosion inhibition of the carbon steel in 1 M HCl is mainly controlled by a physisorption process. In addition, the effect of immersion time on the corrosion of carbon steel was also studied in this work using ac impedance technique. The corrosion inhibition mechanism of ATMP was discussed. This inhibitor can be also used as biocide in aqueous environments. Our results showed that ATMP have an antibacterial effect against both Gram positive and Gram negative bacteria. The lowest MIC (0.2 mg l^?1) was measured for Pseudomonas fluorescens while the highest MIC was measured for Escherichia coli (3.1 mg l^?1). In addition, the results showed that the MIC of ATMP against Listeria innocua in a buffered medium (pH 6.5) was of ca. 4-fold higher than MIC measured in unbuffered medium. Thus, our findings showed that the antibacterial activity of ATMP is a result of a combined effect of the pH solution and the chemical nature of the used phosphonate molecule.     

Green approach to corrosion inhibition of mild steel in hydrochloric acid and sulphuric acid solutions by the extract of Murraya koenigii leaves

The inhibition of the corrosion of mild steel in hydrochloric acid and sulphuric acid solutions by the extract of Murraya koenigii leaves has been studied using weight loss, electrochemical impedance spectroscopy (EIS), linear polarization and potentiodynamic polarization techniques. Inhibition was found to increase with increasing concentration of the leaves extract. The effect of temperature, immersion time and acid concentration on the corrosion behavior of mild steel in 1 M HCl and 0.5 M H₂SO₄ with addition of extract was also studied. The inhibition was assumed to occur via adsorption of the inhibitor molecules on the metal surface. The adsorption of the extract on the mild steel surface obeys the Langmuir adsorption isotherm. The activation energy as well as other thermodynamic parameters (Q, ΔH^*, and ΔS^*) for the inhibition process was calculated. These thermodynamic parameters show strong interaction between inhibitor and mild steel surface. The results obtained show that the extract of the leaves of M. koenigii could serve as an effective inhibitor of the corrosion of mild steel in hydrochloric and sulphuric acid media.     

The use of Euphorbia falcata extract as eco-friendly corrosion inhibitor of carbon steel in hydrochloric acid solution

Euphorbia falcata L. extract (EFE) was investigated as eco-friendly corrosion inhibitor of carbon steel in 1 M HCl using gravimetric, ac impedance, polarization and scanning electron microscopy (SEM) techniques. The experimental results show that EFE is good corrosion inhibitor and the protection efficiency is increased with the EEF concentration. The results obtained from weight loss and ac impedance studies were in reasonable agreement. Impedance experimental data revealed a frequency distribution of the capacitance, simulated as constant phase element. Polarization curves indicated that EFE is a mixed inhibitor. The corrosion inhibition was assumed to occur via adsorption of EFE molecules on the metal surface. The adsorption of the E. falcata extract was well described by the Langmuir adsorption isotherm. The calculated ΔG_ads^o value showed that the corrosion inhibition of the carbon steel in 1 M HCl is mainly controlled by a physisorption process.     

Experimental and theoretical investigations on the inhibition of mild steel corrosion in the ground water medium using newly synthesised bipodal and tripodal imidazole derivatives

Two new imidazole derivatives, namely 1,4-bis(N-imidazolylmethyl)-2-5-dimethoxybenzene (BIDM) and 1,3,5-tris(N-imidazolylmethyl)-2,4,6-trimethoxybenzene (TITM), were synthesised and their effects on the inhibition of mild steel corrosion in ground water medium are reported. The study was carried out using gravimetric and electrochemical techniques in order to determine the corrosion inhibition efficiencies of the bipodal and tripodal structured imidazoles. Further, the quantum chemical calculations using density functional theory (DFT) gave a profound insight into the inhibitory action mechanism of BIDM and TITM and their calculation parameters, such as E_HOMO, E_LUMO and ΔE were in good agreement with the results of the experimental studies. BIDM and TITM exhibited lowest corrosion current densities of circa 7.5 μA cm⁻² and 4.1 μAcm⁻² at the optimum concentrations of 0.67 and 0.49 mM, respectively. All measurements thus confirmed that both BIDM and TITM behaved as good inhibitors for mild steel corrosion in ground water medium.     

Synthesis of novel hexagon SnO2 nanosheets in ethanol/water solution by hydrothermal process

The novel hexagon SnO₂ nanosheets are successfully synthesized in ethanol/water solution by hydrothermal process. The samples are characterized by X-ray diffraction (XRD), infrared ray (IR) and transmission electron microscopy (TEM). By changing the reaction conditions, the size and the morphology can be controlled. Comparison experiments show that when the temperature increased from 140 °C to 180 °C, the edge length of the hexagon nanoparticles increases from 300-450 nm to 700-900 nm. On the other hand, by adjusting the ratios of water to ethanol from 2 to 0.5, SnO₂ nanoparticles with different morphologies of triangle and sphere are obtained. When the concentration of NaOH is increased from 0.15 M to 0.30 M, a hollow ring structure can be obtained.     

Corrosion inhibition of aluminum in hydrochloric acid solution by alkylimidazolium ionic liquids

The effects of newly synthesized three alkylimidazolium ionic liquids—1-butyl-3-methylimidazolium chlorides (BMIC), 1-hexyl-3-methylimidazolium chlorides (HMIC) and 1-octyl-3-methylimidazolium chlorides (OMIC)—on the corrosion of aluminum in 1.0 M HCl were investigated using potentiodynamic polarization, electrochemical impedance spectroscopy and weight loss methods. All measurements showed that the inhibition efficiency increased with increase in the concentration of inhibitor and the effectiveness of these inhibitors was in the order of OMIC > HMIC > BMIC. Polarization curves revealed that the studied inhibitors were mixed type inhibitors. The adsorption of the inhibitors on the aluminum surface obeyed Langmuir adsorption isotherm and had a physical mechanism. 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 free energy of adsorption (ΔG_ads) were calculated to elaborate the mechanism of corrosion inhibition.     

Intralaminar fatigue crack growth properties of conventional and interlayer toughened CFRP laminate under mode I loading

Intralaminar and interlaminar fatigue crack growth behaviours under mode I loading were investigated with conventional and interlayer toughened unidirectional CFRP laminates. For intralaminar crack growth tests, initial defects were introduced using “intralaminar film insertion method”, in which a release film is inserted inside a single lamina prepreg. A fatigue test under a constant maximum energy release rate, G_max, was carried out using DCB specimens. It was found that the intralaminar fatigue crack growth property of the interlayer toughened CFRP laminates was the same as that of the conventional CFRP laminates. For the interlayer toughened CFRP laminates, the G_max with a given crack growth rate, da/dN, was much lower for intralaminar crack growth than for interlaminar crack growth. The da/dN-G_max curve at zero crack extension, Δa = 0, which was estimated by extrapolating the da/dN-Δa relationship, was not affected by bridging fibres, and most conservative for the interlayer toughened CFRP laminates.     

Effects of Cr contents in Fe-based bulk metallic glasses on the glass forming ability and the corrosion resistance

Fe-based bulk metallic glasses of Fe_69.9?xC_7.1Si_3.3B_5.5P_8.7Cr_xMo_2.5Al_2.0Co_1.0 (x = 0.0, 2.3–12.3) with high glass forming ability and good corrosion resistance were fabricated using industrial raw materials. Glass forming ability of the Fe-based bulk metallic glasses tends to decrease with the Cr content, while the corrosion resistance increases with the Cr content. A homogeneous passive layer on the amorphous sample with 12.3 at% Cr can be formed leading to superior corrosion resistance of the amorphous sample to an austenitic stainless steel (SUS304) in the 0.5 M H₂SO₄ and 1N HCl solutions at 298 K. Fe-based bulk metallic glasses with an optimum combination of glass forming ability and corrosion resistance can be produced in large quantities through a systematic control of the Cr content for extensive practical applications.     

Quantitative correlation between geometric parameters and stress concentration of corrosion pits

Pitting corrosion damage often occurs in aluminum alloy structures and can significantly reduce the service life of structures and cause structural failures. In this research, three-dimensional corrosion pit morphology of 7075-T6 aluminum alloy was observed with the Sensofar PLμ confocal imaging profiler and scanning electron microscope. According to the corrosion pit morphology, we systematically investigated the quantitative correlation between the stress state and geometric features of a corrosion pit idealized as a semi-ellipsoidal pit. It is found that the stress concentration factor (SCF) increases with R_s (the ratio of pit width to length) and R_d (the ratio of pit depth to half-length). The maximum possible SCF is independent of R_d and increases linearly with R_s. The SCF of a rotated pit increases with the orientation angle in a cos²θ relation when R_s < 1.0. The empirical equations are also proposed to correlate the SCF to R_s, R_d and θ.     

Influence of halide ions on inhibitive performance of cetyl trimethyl ammonium bromide in various concentrations of phosphoric acid for cold rolled steel

The influence of chloride ions on inhibitive performance of cetyl trimethyl ammonium bromide (CTAB) in 1.0-4.0 M of phosphoric acid (H₃PO₄) for cold rolled steel has been studied using weight loss and Tafel polarization techniques. The effect of acid concentration on corrosion inhibition and the effectiveness of inhibitors at 1.0-4.0 M of H₃PO₄ have been examined. The results reveal that a synergistic effect has been observed for CTAB with NaCl at each acid concentration. In 1.0 M H₃PO₄, the polarization curves show that the complex is a mixed-type inhibitor.     

Green approach to corrosion inhibition of mild steel in two acidic solutions by the extract of Punica granatum peel and main constituents

The effect of the extract of Punica granatum (PG) and their main constituents involve ellagic acid (EA) and tannic acid (TA), as mild steel corrosion inhibitor in 2 M HCl and 1 M H₂SO₄ solutions was investigated by weight loss measurements. The results obtained from the weight loss measurements show that the inhibition efficiency of TA even in high concentration is very low. Thus, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) investigations were used for different concentrations of PG and EA and best concentration of TA. Potentiodynamic polarization curves indicated that PG and EA behave as mixed-type inhibitors. EIS measurements show an increase of the transfer resistance with increasing inhibitor concentration. The temperature effect on the corrosion behavior of steel without and with the PG extract was studied. The inhibition action of the extract was discussed in view of Langmuir adsorption isotherm.     

Electrochemical and quantum chemical study of 4-[(E)-[(2,4-dihydroxy phenyl) methylidine] amino]-6-methyl-3-sulphanylidine-2,3,4,5-tetra hydro-1,2,4-triazin-5-one [DMSTT]

The inhibition of mild steel in aerated 1 M hydrochloric acid solution was studied using conventional weight loss method, potentiodynamic polarization studies (Tafel), linear polarization studies (LPR), electrochemical impedance spectroscopy (EIS) and quantum chemical calculation in the presence and absence of different concentrations of DMSTT. The inhibition efficiency increased markedly with increase in the additive concentrations, but slightly decreased with increasing temperature. The presence of DMSTT decreases the double layer capacitance and increases the charge-transfer resistance. The value of activation energy (E_a) for mild steel corrosion and thermodynamic parameters such as adsorption equilibrium constant (K_ads), free energy of adsorption (ΔG_ads) values were calculated and discussed. The inhibitor molecule first adsorbed on mild steel surface according to Langmuir adsorption isotherm.     

Corrosion and impedance studies on magnesium alloy in oxalate solution

Corrosion behavior of AZ91E alloy was investigated in oxalate solution using potentiodynamic polarization and electrochemical impedance measurements (EIS). The effect of oxalate concentration was studied, where the corrosion rate increases with increasing oxalate concentration. The effect of added ions (Br⁻, Cl⁻ or SiO₃²⁻) on the electrochemical behavior of magnesium alloy in 0.1 M Na₂C₂O₄ solution at 298 K, was investigated. It was found that the corrosion rate of 0.1 M oxalate solution containing silicate ion is lower than the blank (0.1 M Na₂C₂O₄). This was confirmed by scanning electron microscope (SEM) observations. However, for the other added ions Br⁻ or Cl⁻, the corrosion rate is higher than the blank.     

Hydrogen sensing properties of Pd-doped SnO2 sputtered films with columnar nanostructures

Pd-doped SnO₂ sputtered films with columnar nanostructures were deposited using reactive magnetron sputtering at the substrate temperature of 300 °C and the discharge gas pressures of 1.5, 12, and 24 Pa. Structural characterization by means of X-ray diffraction and scanning electron microscopy shows that the films composed of columnar nanograins have a tetragonal SnO₂ structure. The films become porous as the discharge gas pressure increases. Gas sensing measurements demonstrate that the films show reversible response to H₂ gas. The sensitivity increases as the discharge gas pressure increases, and the operating temperature at which the sensitivity shows a maximum is lowered. The highest sensitivity defined by (R_a − R_g) / R_g, where R_a and R_g are the resistances before and after exposure to H₂, 84.3 is obtained for the Pd-doped film deposited at 24 Pa and 300 °C upon exposure to 1000 ppm H₂ gas at the operating temperature of 200 °C. The improved gas sensing properties were attributed to the porosity of columnar nanostructures and catalytic activities of Pd doping.     

Phosphonium iodine as nickel corrosion inhibitor in 1 M sulfuric acid medium

The inhibiting action of alkyltriphenylphosphonium iodine salt ((C₈H₁₇)Ph₃P⁺,I⁻) towards the corrosion behaviour of nickel in 1 M H₂SO₄ solution has been studied. This compound was found to retard both anodic and cathodic reactions of nickel corrosion. At constant temperature, the corrosion rate decreases with increasing inhibitor concentration. On the other hand, the increase in temperature leads to an increase in the corrosion rate. The activation energy, ΔE _a, were calculated. They were found 19.3 kJ mol⁻¹ and 71.1 kJ mol⁻¹, respectively for the uninhibited solution and in the presence of 10⁻³ M of phosphonium salt. The inhibitor adsorption was identified to occur according to Langmuir isotherm. The equilibrium constant, k, as well as the free energy of adsorption, Δ_ads G°, for inhibitor process were then calculated. Phosphonium iodine exhibited a singular behaviour for T ≥ 318 K where inhibitor desorption increases.     

Influence of the Al(Co,Ni) layer on the corrosion resistance of a cobalt based alloy (Mar‐M‐509®)

In the present work, the results of studies on the structure and corrosion resistance of Al(Co, Ni) layer are shown. The diffusion Al(Co, Ni) layer was created on the cobalt alloy Mar‐M‐509 substrate by chemical vapor deposition (CVD) method with aluminum trichloride (AlCl₃) under the hydrogen atmosphere. The scanning electron microscope (SEM) observations and microtomography measurements of layers were performed. Also an analysis of the chemical (energy‐dispersive X‐ray spectroscopy (EDS)) and phase (X‐ray diffraction (XRD)) composition was carried out. By the X‐ray diffraction method (sin² φ) also the residual stresses were calculated in the matrix of the material. The corrosion resistance was tested with impedance and potentiodynamic methods in 0.1 M Na₂SO₄, 0.1 M H₂SO₄ solutions and acidulous 0.1 M NaCl solution (pH = 4.2) at room temperature. The results indicate that the analyzed layer with a thickness of about 14 μm have a similar corrosion resistance compared to the base material – Mar‐M‐509^® cobalt alloy. Only in the strongly acidic environments, the corrosion resistance of the layer is remarkably decreased.