Effect of Mo species on metastable pitting of Fe18Cr alloys—A current transient analysis

The analysis of current transients occurring on Mo containing ferritic Fe-18Cr steels in chloride containing electrolyte in absence or presence of molybdate anions as external inhibitor reveals insight into the role of Mo-species in metastable pitting events, consisting of pit initiation, pit propagation including some metal dissolution, and pit repassivation. A mathematical method on the basis of statistical distribution functions was developed in order to meet the requirements of a systematic data analysis which allows to compare different systems of alloys and electrolytes. The results clearly indicate the beneficial effect of alloyed Mo as well as in the electrolyte in inhibiting (metastable) pitting corrosion. However, the mechanism of inhibition is unlike for alloyed Mo and added into the electrolyte.     

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.     

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.     

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:

     

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.     

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.     

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.     

Adsorption of 3-(4-amino-2-methyl-5-pyrimidyl methyl)-4-methyl thiazolium chloride on mild steel

The adsorption of 3-(4-amino-2-methyl-5-pyrimidyl methyl)-4-methyl thiazolium chloride (AMMPTC) or vitamin B₁ at the mild steel surface from hydrochloric acid (HCl) solution is studied using chemical techniques. The surface coverage with the adsorbed AMMPTC is used to calculate the free energy of adsorption, , of AMMPTC using Bockris-Swinkels isotherm. The dependence of free energy of adsorption, , with surface coverage, θ, is ascribed to surface heterogeneity of the adsorbent. The effect of AMMPTC is discussed from the viewpoint of adsorption model. The adsorption of AMMPTC molecules on the surface occurs without modifying the kinetic of corrosion process which is of first order with respect to mild steel.     

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.     

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.     

Stability, validity, and sensitivity to input parameters of the slip-dissolution model for stress-corrosion cracking

The slip-dissolution model of stress-corrosion crack growth is reviewed and developed from several points of view: the differences between ‘discontinuous’ (Vermilyea) and ‘continuous’ (Ford, Andresen, Shoji) versions of the model; stability and possible multiplicity of predicted crack velocities for given mechanical parameters, and the sensitivity of the predicted crack velocity to small variations in the electrochemical and mechanical parameters. We find that for relatively steep anodic current decays on the bare metal surface at the crack tip (for example, i ∼ t^−m with m = 0.8), the output of the continuous type of model is extremely sensitive to the strain hardening exponent and to the location or cutoff distance in the logarithmic plastic strain distribution at which the crack-tip strain rate is calculated. Difficulties also appear because this distance is likely to be a function of other parameters such as yield stress. The handling of loading rate () effects in Shoji’s treatment appears unrealistic, leading to a much too weak dependence of the crack-tip strain rate on . However, irrespective of how is introduced, dual crack velocity solutions are found for negative ; the stability of these is discussed.     

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 lactate ions on the formation of rust

The formation of rust can be simulated by oxidation of aqueous suspensions of Fe(OH)₂ obtained by mixing solutions of NaOH and a Fe(II) salt. The aim of this study was to investigate the influence of organic species associated with microbially influenced corrosion. The lactate anion, often used as a carbon and electrons source for the development of microorganisms, was chosen as an example. Then, in the first part of the study, Fe(OH)₂ was precipitated using iron(II) lactate and NaOH. Its oxidation process involved two stages, as usually observed. The first stage led to a Fe(II-III) intermediate compound, the lactate green rust, . This compound has never been reported yet. Its existence demonstrates that the GR structure is able to incorporate a very wide range of anions, whatever the size and geometry. The second stage corresponded to the oxidation of . It led to ferrihydrite, the most poorly ordered form of iron(III) oxides and oxyhydroxides. In the second part of the study, the formation of rust in seawater was simulated by oxidation of Fe(OH)₂ in an aqueous media containing both Cl⁻ and anions. The first stage led to the sulphate green rust, , the second stage to lepidocrocite γ-FeOOH. Small amounts of iron(II) lactate were added to the reactants. Lactate ions did not modify the first stage but drastically perturbed the second stage, as ferrihydrite was obtained instead of γ-FeOOH.     

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.     

Reaction model for kinetic of cobalt dissolution in carbonate/bicarbonate media

Cobalt dissolution in a carbonate/bicarbonate media was studied in order to elucidate the kinetic of the metal corrosion processes. Steady-state polarization and electrochemical impedance measurements were carried out during the active metal dissolution at different electrode rotation speeds. A reaction mechanism is presented in order to explain the metal dissolution: cobalt electrodissolution starts with the formation of intermediate (CoHCO₃)_ads on the electrode surface, followed by the simultaneous formation of a complex and the formation of a CoO film. Mass transport is characterised by diffusion of the complex away from the electrode. The reaction model was validated by an accurate simulation of the experimental steady-state polarisation and impedance measurements.