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.     

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.     

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.     

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.     

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.     

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.     

Effect of the strain rate on stress corrosion crack velocities in face-centred cubic alloys. A mechanistic interpretation

Constant extension rate tests on smooth samples, with strain rate (SR) values from 10⁻⁶ s⁻¹ up to 20 s⁻¹, were used to study stress corrosion cracking (SCC) systems in face-centred cubic alloys. It was found that by increasing the SR a monotonic increase of the (crack propagation rate) takes place. It was also observed that the slope α in vs. plots had different values for different SCC morphologies. Intergranular SCC is more steeply accelerated by SR, α_IG=0.5-0.7, than transgranular SCC, α_TG=0.2-0.3. The differences found between intergranular SCC and transgranular SCC were analysed under the light of the available SCC mechanisms.     

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.     

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.     

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.     

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.     

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.     

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.