Experimental and theoretical investigation of organic compounds as inhibitors for mild steel corrosion in sulfuric acid medium

Three synthesized organic compounds were tested as corrosion inhibitors for mild steel in sulfuric acid medium by potentiostatic polarization, FTIR spectroscopy and SEM techniques. Quantum chemical parameters were also calculated to characterize adsorption mechanism. Acceptable correlations were obtained between inhibition efficiency and the calculated quantum chemical parameters. It was found that the investigated compounds exhibit a good inhibition effect especially at 8-10 ppm range concentration, which makes them commercially important. The adsorption of inhibitors on the surface obeys Langmuir adsorption isotherm. The values of activation energy and the thermodynamic parameters, such as K_ads, , and were calculated.     

Inhibition of mild steel corrosion in acid solution by Pheniramine drug: Experimental and theoretical study

Inhibition of mild steel corrosion in 1 M HCl solution by Pheniramine drug was studied using weight loss, electrochemical impedance spectroscopy, linear polarization resistance, and potentiodynamic polarization measurements. The values of activation energy (E_a) and different thermodynamic parameters such as adsorption equilibrium constant (K_ads), free energy of adsorption , adsorption enthalpy and adsorption entropy were calculated and discussed. The adsorption process of studied drug on mild steel surface obeys the Langmuir adsorption isotherm. Potentiodynamic polarization measurements showed that Pheniramine is mixed-type inhibitor. Further, theoretical calculations were carried out and relations between computed parameters and experimental inhibition efficiency were discussed.     

Inhibitive effect of diethylcarbamazine on the corrosion of mild steel in hydrochloric acid

Potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), weight loss measurements and atomic force microscopy techniques were used to investigate the inhibitory effect of diethylcarbamazine (DECM) on corrosion of mild steel in HCl solution. The inhibitor showed >90% inhibition efficiency at 5.01 × 10⁻⁴ M. Results obtained revealed that inhibition occurs through adsorption of inhibitor molecules on metal surface without modifying the mechanism of corrosion process. Potentiodynamic polarization studies suggested that it is a mixed type inhibitor, predominantly controls cathodic reaction. Activation parameters (E_a, ΔH and ΔS) and thermodynamic parameters (, and ) were calculated to investigate mechanism of inhibition.     

Effect of 4-(N,N-diethylamino)benzaldehyde thiosemicarbazone on the corrosion of aged 18 Ni 250 grade maraging steel in phosphoric acid solution

4-(N,N-diethylamino)benzaldehyde thiosemicarbazone (DEABT) was studied for its corrosion inhibition property on the corrosion of aged 18 Ni 250 grade maraging steel in 0.67 M phosphoric acid at 30–50 °C by potentiodynamic polarization, EIS and weight loss techniques. Inhibition efficiency of DEABT was found to increase with the increase in DEABT concentration and decrease with the increase in temperature. The activation energy E_a and other thermodynamic parameters (Δ, Δ, Δ) have been evaluated and discussed. The adsorption of DEABT on aged maraging steel surface obeys the Langmuir adsorption isotherm model and the inhibitor showed mixed type inhibition behavior.     

Effect of Cefazolin on the corrosion of mild steel in HCl solution

The adsorption and inhibition effect of Cefazolin on mild steel in 1.0 M HCl at 308-338 K was studied by weight loss, EIS, potentiodynamic polarization and atomic force microscopy techniques. The results showed that inhibition efficiency increased with inhibitor concentration. The adsorption of Cefazolin on mild steel surface obeys the Langmuir adsorption isotherm equation. Both thermodynamic (enthalpy of adsorption , entropy of adsorption and free energy of adsorption ) and kinetic parameters (activation energy and pre-exponential factor A) were calculated and discussed. Polarization curves showed that Cefazolin acted as mixed-type inhibitor controls predominantly cathodic reaction.     

Effect of nitrogen on crevice corrosion in austenitic stainless steel

Corrosion properties of high nitrogen austenitic steels in chloride solutions have been investigated. Nitrogen behavior was evaluated at various electrode potentials, and analysis of the surface film was carried out with XPS. The alloy used for the experiments had a composition of 23%Cr-4%Ni-0-1%Mo-0.7-1%N and was obtained through electro-slag remelting (ESR) under high nitrogen pressure. High nitrogen austenitic steel produced in the solution by crevice corrosion under a constant potential of 0.2 V (SCE). In the transpassive region and at 0.7 V (SCE), the products in the solution were , and . The amount of dissolved and increased with the electrode potential. in the solution suppressed decreases of pH, having a re-passivation effect. For crevice corrosion under a higher electrode potential than 0.4 V (SCE), the number of crevice corrosion points and the corrosion loss decreased as the electrode potential increased. This behavior can be attributed to the corrosion suppressing effect of dissolved in the solution as a product of crevice corrosion. The presence of chromium and iron oxides in the passivation film and crevice corrosion surface film were identified from XPS analysis. N 1s spectra indicated the presence of a nitride (CrN) or NH₃.     

Photoelectron spectroscopy study of the inhibition of mild steel corrosion by molybdate and nitrite anions

Passive films formed on mild steel in aqueous 8.6 mM NaCl solutions (pH 8), containing either or , have been studied with X-ray photoelectron spectroscopy. For either anion these films are ∼5 nm deep, and the primary chemical state of iron is Fe³⁺. Following exposure to , the film consists of a sub-layer (∼4.1 nm) composed largely of ferric oxide/hydroxide, overlaid by Fe₂(MoO₄)₃ (∼0.6 nm). As regards , spectra are consistent with the film being closely related to γ-Fe₂O₃. Furthermore, a reduction product of , potentially N₂, is present, displaying a depth profile comparable to that of molybdate.     

Electrochemical behavior of tin in sodium borate solutions and the effect of halide ions and some inorganic inhibitors

The corrosion of tin electrode in sodium borate (Na₂B₄O₇) solutions was investigated using cyclic voltammetry and potentiostatic current transient techniques. In absence of halide ions, the E/j response exhibits active/passive transition. The active region involves one anodic peak corresponding to the formation of Sn(OH)₂ and/or SnO. Addition of Cl⁻, Br⁻ or I⁻ (C ? 0.01 M) ions inhibits the active dissolution of tin, but higher concentrations enhance the active dissolution and tend to breakdown the passive film and induce pitting attack. The effect of , , and as inorganic inhibitors on the pitting corrosion of tin in (0.1 M Na₂B₄O₇ + 0.1 M NaCl) solution has also been studied. The presence of these anions (except ) inhibits pitting corrosion. Chronoamperometry measurements showed that nucleation of pit takes place after an incubation time (t_i). The rate of pit nucleation () increases with increasing halide ions concentration and applied potentials, but decreases with increasing the concentration of the inorganic inhibitors (except ). The inhibition efficiency of these inhibitors decreases in the order:

     

Thermodynamic studies on corrosion inhibition of aqueous solutions of amino/carboxylic acids toward copper by EMF measurement

Electromotive force (E) measurements were made on an electrochemical cell [Cu_xHg|CuCl₂(m) in a solvent S|AgCl-Ag] (where S is a dilute aqueous solution (0.01 m) of amino acid (glycine, alanine, methionine and glutamic acid) or aliphatic carboxylic acid (formic acid, acetic acid, n-butyric acid and glutaric acid)) at 30 °C. These measured E values were used to compute the dissociation constants (K₁ and K₂) and the degree of dissociation (α₁ and α₂) by iterative procedures. The standard cell potential (E°) and the mean activity coefficient (γ_±) of CuCl₂ were also determined. The E° data were next used to evaluate the Gibbs energy of transfer of CuCl₂ from water to dilute aqueous solutions of the amino/carboxylic acids. The negative values suggested that these acids act as potential corrosion inhibitors. The magnitudes of values show that the amino acids act as better corrosion inhibitors towards copper than the aliphatic carboxylic acids.     

Voltammetric current oscillations due to general and pitting corrosion of tantalum: Implications for electrochemical-mechanical planarization

Anodic corrosion of Ta is examined for potential applications in electrochemical-mechanical planarization (ECMP) of diffusion barriers. This strategy involves electro-oxidation of Ta in the presence of (or Br⁻) to form mechanically weak surface-oxide films, followed by mechanical removal of the latter. The voltammetric currents exhibit oscillatory behaviour with frequencies that are signature attributes of localised pitting by Br⁻ or general surface corrosion by . SEM, voltammetry, and impedance spectroscopy are used to probe these corrosion mechanisms. Apart from their relevance for ECMP, the results also address certain fundamental aspects of pitting and general corrosion of valve metals.     

On the fundamentals of electrochemical corrosion of X65 steel in CO2-containing formation water in the presence of acetic acid in petroleum production

Electrochemical corrosion behavior of X65 steel in CO₂-containing oilfield formation water in the presence of acetic acid (HAc) was investigated by various electrochemical measurements and analyses as well as thermodynamic calculations of ionic concentrations, reaction rate constants and equilibrium electrode potentials. A conceptual model was developed to illustrate corrosion processes of steel in oilfield formation water system. The anodic reactions of the steel contain a direct dissolution of Fe, Fe → Fe²⁺ + 2e, and the formation of corrosion scale, FeCO₃, by Fe + → FeCO₃ + H⁺ + 2e. The cathodic processes contain the reduction of H⁺, , H₂O and HAc, where reduction of HAc has the least negative equilibrium potential and thus dominates the cathodic process. With addition of HAc in the solution, both cathodic and anodic reaction rates increase remarkably. It is attributed to the fact that HAc inhibits or degrades the formation of protective scales due to the decrease of solution pH. Upon electrode rotation, the measured impedance decreases with the increase in HAc concentration. The FeCO₃ scale will not form on electrode surface. When HAc concentration is less than 1000 ppm, the adsorbed intermediate product is not significant, resulting in generation of a low-frequency inductive loop in EIS plots. When HAc concentration is more than 3000 ppm, the adsorption of intermediate product is significant, generating overlapped capacitive semicircles in EIS measurements.     

Corrosion inhibition of tin, indium and tin-indium alloys by adenine or adenosine in hydrochloric acid solution

The influence of the concentration of adenine (AD), adenosine (ADS) on the electrochemical corrosion behavior of tin, indium and tin-indium alloys in 0.5 M HCl solution at different temperatures was studied. The investigation involved potentiodynamic cathodic polarization and extrapolation of cathodic and anodic Tafel lines techniques. The inhibition efficiency (IE%) increases with an increase in the concentration of adenine or adenosine of all investigated electrodes. The inhibition process was attributed to the formation of adsorbed film on the surfaces of the electrodes that protects the surface against corrosive agent. The data exhibited that the inhibition efficiency slightly decreases with increasing temperature.Frumkin adsorption isotherm fits well the experimental data. The plots of ln K vs. 1/T in the presence of the two studied inhibitors showed linear behavior. The standard enthalpy, , entropy, and free energy changes of adsorption were evaluated; the calculated values of and were negative while those for were positive. Mainly, all the above results are suggestive of physisorption of the inhibitor molecules on the surfaces of the investigated electrodes.     

Pitting and pitting control of Al in gluconic acid solutions - Polarization, chronoamperometry and morphological studies

The anodic behaviour of Al in gluconic acid (HG) solutions was studied. Al was found to pit in such solutions. Surface and cross-sectional views of the SEM images recorded beyond the breakdown potential (E_b) revealed the occurrence of intense pitting attack with the formation of large hemispherical pits. The effect of adding some environmentally acceptable inorganic inhibitors (tungstates, molybdates or silicates) on the pitting corrosion behaviour of Al in HG solutions was also studied. Measurements were carried out under the influence of various experimental variables based on polarization and chronoamperometric techniques. These measurements were complemented by ex situ scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) examinations of the electrode surface. The presence of these compounds in HG solutions decreased the passive current density (j_pass) and increased E_b. In HG solutions, chronoamperometric measurements showed that the anodic current density first decreased, due to growth of a passive oxide film, then increased with time after a pit incubation time, t_i and finally attained a steady-state value. Value of t_i was shortened and simultaneously the steady-state current was elevated, corresponding to an increase in the rate of pit initiation and growth, with increasing applied anodic potential and HG concentration. The rate of pit nucleation () was found to decrease to an extent depending on the type and concentration of the introduced inhibitor. The inhibitory effect of these compounds decreased in the order:  >  > .     

Corrosion of niobium in sulphuric and hydrochloric acid solutions at 75 and 95 °C

New Pourbaix diagrams were calculated at 25, 75 and 95 °C for the Nb-H₂O system. The species and were considered. Potentiodynamic polarization and mass loss experiments (14 days) were conducted in concentrated H₂SO₄ (20, 40 and 80 wt%) and HCl (20 and 38 wt%) solutions at 75 and 95 °C. Nb forms a metastable pentoxide (Nb₂O₅) in H₂SO₄ and HCl solutions which dissolves as . Corrosion rates decrease between the 40% and the 80% H₂SO₄ solutions. SEM micrographs show generalized pitting in the 20% and 40% H₂SO₄ solutions. Mass loss corrosion rates did not exceed 306 μm/yr. Corrosion rates estimated by Tafel extrapolation were within two orders of magnitude of those measured by mass loss and it is shown that this finding is consistent with the thickening of the oxide.     

Corrosion behaviour of vacuum induction-melted Ni-based alloy in sulphuric acid

A vacuum induction-melted (VIM) Ni-based alloy was immersed in 60% H₂SO₄ solution to investigate its corrosion behaviour and resistance. The results indicate that the microstructure contains a γ-Ni solid solution + Ni₃Si particles, dendrite Ni₃Si, Ni₃B, Cr₇C₃, and CrB. The corrosion started at the zones of the γ-Ni solid solution + Ni₃Si particles and dendrite Ni₃Si. These zones transformed to oxide films and protected the alloy from significant attack. However, the pitting corrosion created paths for acid solution and/or to further attack. Therefore, the corrosion rate decreased and then stabilised at a high value as the immersion time increased.     

Critical pitting temperature dependence of 2205 duplex stainless steel on dichromate ion concentration in chloride medium

In this study, the influence of various concentrations of dichromate and chloride ions on critical pitting temperature (CPT) of duplex stainless steel 2205 (DSS 2205) is investigated by employing potentiodynamic and potentiostatic CPT measurement methods. Potentiostatic results indicate that by adding 0.01 M to 0.1 M NaCl solution the CPT raised by 12 °C. Based on potentiodynamic CPT measurements in the solutions with ratio equal to one for solutions containing 0.1 M NaCl + 0.1 M and 0.01 M NaCl + 0.01 M , no CPT was detected up to 75 °C.     

Influence of anions on the formation of β-FeOOH rusts

The artificial β-FeOOH rusts were synthesized by oxidation of FeCl₂ solutions and hydrolysis of FeCl₃ solutions. Various Na salts such as sulfate, biphosphate, nitrate, and silicate were added to the starting solutions at different anion/Fe molar ratios of 0-0.05. The XRD patterns of the products showed only the diffraction peaks of β-FeOOH. The crystallinity of the products was noticeably reduced by adding and but slightly influenced by adding . The addition of markedly crystallized the products by the hydrolysis of FeCl₃. The N₂ adsorption revealed that the products with were porous particles assembled by β-FeOOH subcrystals. and strongly coordinating to Fe(III) markedly lowered the crystallinity of the products and remained in the formed particles.     

The effect of ultrasonic irradiation during electropolymerization of polypyrrole on corrosion prevention of the coated steel

Ultrasonic irradiation was imposed during electropolymerization of polypyrrole (PPy) in acid phosphate solution containing molybdophosphate () ions and pyrrole monomer. Corrosion of the steel coated by the PPy film prepared under ultrasonic irradiation was tested in 3.5 wt.% NaCl solution and compared with corrosion of the steel coated by the PPy film without ultrasonic irradiation. The PPy film prepared under ultrasonic irradiation kept the steel in the passive state one and a half times as long as that prepared without ultrasonic irradiation. Imposition of ultrasound enhanced the doping of and decreased the doping of . The surface morphology of the PPy film was changed with imposition of ultrasound in electropolymerization process. Under imposition of ultrasound, a dense and compact PPy layer was formed. The structure of the PPy film obtained under ultrasonic irradiation was assumed to result from change in nucleation-growth mechanism.     

Inhibition of iron corrosion in acid solutions by Cefatrexyl: Behaviour near and at the corrosion potential

The corrosion inhibition of iron in HCl, HClO₄, H₂SO₄ and H₃PO₄ solutions (1M for each) by cefatrexyl has been studied by polarization resistance (R_p) and electrochemical impedance spectroscopy (EIS) at the corrosion potential. The results obtained at 30 °C revealed that cefatrexyl acts as a weak inhibitor in HCl solution while it shows excellent inhibition performance in the remaining acids. Adsorption of cefatrexyl in HCl solution obeys Langmuir’s isotherm with a very low value of the free energy of adsorption (physisorption) while its adsorption in the other acids follows Temkin’s isotherm with very high negative values of (chemisorption). Data obtained from EIS measurements were analyzed to model the corrosion inhibition process through appropriate equivalent circuit models. The calculated values of the apparent activation energy (E_a) and the pre-exponential factor (λ) indicate that cefatrexyl blocks nearly the whole active centers of iron surface in H₃PO₄ solution even at elevated temperatures. The inhibition mechanism of cefatrexyl was discussed.     

Perchlorate pitting corrosion of tin in Na2CO3 solutions and effect of some inorganic inhibitors

The anodic behaviour of tin electrode in Na₂CO₃ solutions containing different concentrations of Na₂ClO₄ was studied by potentiodynamic technique and complemented by scanning electron microscope. In perchlorate free carbonate solutions; the polarization curves exhibit two anodic peaks assigned to the electroformation of Sn(II) and Sn(IV) species, respectively, prior to the permanent passivation region. The passivity is due to the presence of SnO and SnO₂ layers on the electrode surface. Addition of to the carbonate solution breaks down the passive layer and initiate pitting corrosion at a certain critical pitting potential. The pitting potential decreases with an increase in concentration but increases with increasing both Na₂CO₃ concentration and scan rate. Addition of increasing concentration of , or causes a shift of the pitting potential in the positive direction indicating the inhibition effect of added anions, while addition of anion accelerates the perchlorate pitting corrosion.