Electrochemical characteristics of iron in acidic solutions containing some organic sulphur compounds

Corrosion inhibition of bis-n-butyl-sulphinylmethane, bis-n-butyl-sulphonylmethane and ethylene oxide condensates of 2,2′-dihydroxy-n-hexylsulphide on iron in sulphuric and hydrochloric acids was measured by using electrochemical methods. These compounds were excellent inhibitors for acidic corrosion of iron and inhibited the cathodic and the anodic corrosion reactions.     

Morphological and kinetic study of copper corrosion when covered with digenite sulphide layer,in sulphur,under covellite formation conditions

The sulphurization of copper covered with a digenite protective layer, under covelliteformation conditions occurs in two stages: metal valence value change in the sulphide and then metal transformation. The first stage involves an external growth and covellite precipitation in the copper vacancies supersaturated in digenite, the second an external growth similar to that of metals alone.     

The scaling of iron in oxygen and sulfur-containing gases

The following possible conditions for the simultaneous formation of oxide and sulfide on iron in oxygen and sulfur-containing gases are considered: (7) simultaneous thermodynamic stability of oxide and sulfide; (2) temporal changes in gas composition; (3) intermediary cracking of the oxide film; (4) solubility and diffusion of sulfur in the oxide (lattice diffusion); (5) kinetic conditions for simultaneous oxide and sulfide formation at the scale-gas interface.     

Nucleation of graphite in cast iron melts depending on manganese,sulphur and oxygen

Abstract

The form and distribution of graphite in grey iron influences the mechanical properties and depends on numerous factors, such as nucleation and cooling speed conditions. The main focus of the present work is the influence of manganese, sulphur and oxygen on the nucleation of graphite in lamellar cast iron melts. Previous studies showed that the nucleation in GJL melts is initiated by a MnS particle. For investigations in the field of nucleation in grey iron the authors examined several EN-GJL-200 specimens. The specimens were cast with and without inoculant. The studies of the specimens were realised using light microscopy, SEM-EDS (energy dispersive X-ray analysis), WDS (wavelength dispersive X-ray analysis). The experimental results were compared with the software Thermo-Calc calculations. From the experimental results and the Thermo-Calc calculations it can be concluded, that Mn and S contents and the Mn/S ratio respectively plays a very important role for the nucleation. A direct influence of oxygen on the nucleation of graphite could not be observed.     

Kinetic peculiarities of anodic dissolution of silver and Ag–Au alloys under the conditions of oxide formation

The kinetics of anodic dissolution of silver and Ag–Au alloys (X_Au = 0.1–30 at.% Au) in aqueous alkaline solution under the conditions of the formation of silver oxides has been examined. The techniques of cyclic voltammetry, chronoammetry, and photopotential measurements have been used. It was established that the anodic formation and cathodic reduction of Ag₂O on silver and alloys are controlled by migration in the oxide layer. Ag₂O oxide is an n-type semiconductor with an excess of silver atoms. Oxide layers formed on monocrystalline Ag(1 1 1) and Ag(1 1 0) are more stoichiometric than the layer formed on polycrystalline Ag.     

Solvent effects on the formation of iron oxide chloride intercalates with metallocene derivatives

The lamellar compound FeOCl has been shown to form, under suitable reaction conditions, intercalation compounds with ring-substituted ferrocenes as well as with (C₅H₅)₂Ni and (C₅H₅)₂Ru, for which previous synthetic attempts had been unsuccessful. Successful intercalation depends on the appropriate choice of solvents. Co-intercalation of solvent molecules occurs in some cases.     

Use of acoustic emission technique to study the spalling behaviour of oxide scales on Ni-10Cr-8AI containing sulphur and/or yttrium impurity

It is now well established that the presence of small amounts of sulphur impurity in a NiCrAl-based alloy causes a deleterious effect on their high temperature oxidation behaviour. It is, however, not clear whether the adverse effect is due to a decrease in the spalling resistance of the oxide scale or due to an enhanced scale growth. In order to confirm which of the factors is dominating, two independent experimental techniques were used in the investigation of the oxidation behaviour of Ni-10Cr-8AI containing sulphur- and/or yttrium additions: conventional thermogravimetry, to study the scale growth rates and acoustic emission analysis to study the scale adherence. The results indicated that the dominant factor responsible for the deleterious effect of sulphur impurity on the oxidation of a Ni-10Cr-8AI alloy, was a significant change in the growth rate and the composition of the scale. Addition of yttrium improved the oxidation behaviour, not only by increasing the scale adherence, but also by reducing the scale growth due to gettering of sulphur.     

Effect of the milling conditions for nanocrystalline iron powders on their corrosion behavior in neutral electrolytes

The corrosion behavior of nanocrystalline iron powders obtained by milling in oxygen-containing organic media (isopropyl alcohol, acetic acid, oleic acid, and its solutions in heptane) was studied. The high corrosion resistances of iron powders obtained by mechanoactivation in oleic acid were associated with a protective surface layer formed by iron oxide and chemisorbed oleic acid or products of its partial degradation. Nanocrystalline iron-based systems that contain oxide phases without forming protective layers were less resistant to corrosion. Original Russian Text ? S.F. Lomayeva, A.V. Syugaev, S.M. Reshetnikov, A.S. Shuravin, O.M. Nemtsova, V.V. Aksenova, 2007, published in Zashchita Metallov, 2007, Vol. 43, No. 2, pp. 207–215.     

Difference in the inhibitive effect of some Schiff base compounds containing oxygen, nitrogen and sulfur donors

2-(2-Hydroxybenzylideneamino)-2-methylpropane-1,3-diol (BAMP), 2-((2-hydroxynaphthalen-1-yl)methyleneamino)-2-methylpropane-1,3-diol (NAMP), 2-((pyridin-2-ylimino)methyl)phenol (PMP) and N-(thiophen-2-ylmethylene)pyridin-2-amine (TMP) were investigated as corrosion inhibitors of mild steel in 2 M HCl solution using weight loss, polarization and electrochemical impedance spectroscopy techniques. All measurements show that all compounds under study exhibit inhibitor properties for mild steel. Although the effect of molecular size on inhibition efficiency is observed from the results obtained between BAMP and NAMP, the introduction of heteroatoms into the structure is seen to be more pronounced eventhough the molecular size is diminished. TMP is seen to show the highest inhibitor efficiency of 97%.     

The kinetics of growth and the critical conditions for the formation of the most-stable oxide in the oxidation of binary alloys

During the growth of the most-stable oxide BO _v in the oxidation of binary alloys containing nonnoble components A and B, the oxygen pressure prevailing at the alloy-scale interface is higher than the corresponding value for equilibrium between BO _v and pure B. The effects of this change on the rate constant for the growth of BO _v and on the critical concentration of B in the bulk alloy required for the stability of BO _v on its surface are examined and discussed. The general treatment is then applied to the growth of NiO on Cu–Ni alloys and of Cr₂O₃ on Fe–Cr, Co–Cr, and Ni–Cr alloys by using appropriate defect models for these oxides, considering also the possibility of oxide doping.     

The mechanism of formation of iron oxide and oxyhydroxides in aqueous solutions at room temperature

For a better understanding of the atmospheric rusting of iron and steels, the present work is aimed to explore the mechanism of formation of green rusts, Fe₃O₄, α-FeOOH, β-FeOOH, γ-FeOOH, δ-FeOOH and amorphous ferric oxyhydroxide in aqueous solution at room temperature. The formation processes on which end products are determined are strongly affected by the oxidation rate, pH and the structure and composition of initial and intermediate species of iron. The systematic diagram of formation processes of iron oxide and oxyhydroxides has been presented, in which both dissolved and solid species of iron are included.     

Kinetics and morphological development of the oxide scale on iron at high temperatures in oxygen at low pressure

The oxidation properties of iron have been investigated at temperatures in the range 800–1000° C in oxygen over the pressure range 0.3–760 Torr. A duplex scale consisting of wustite and magnetite was formed during the earliest intervals examined. Hematite grew on the magnetite surface after an induction period which decreased with increasing oxygen pressure; this oxide developed as whiskers and platelets at temperatures less than 860° C and as small grains at higher temperatures. Iron transport occurs through the scale and involves short-circuit diffusion in the hematite layer. The oxidation kinetics obeyed a parabolic law independent of oxygen pressure since multilayer scale growth was directly dependent on the lattice diffusivity of iron and the iron gradient established in the wustite layer.This work was sponsored by the National Research Council of Canada.     

Effect of arsenic on spatial pattern of radial oxygen loss and iron plaque formation in rice

The effects of different arsenic (As) treatments on spatial pattern of radial oxygen loss (ROL), iron (Fe) plaque formation and As accumulation in rice were investigated using three rice genotypes, planted under greenhouse conditions. Arsenic was applied to soil at 50 and 100 mg/kg, with untreated soil used as a control having an average As concentration of 8.5 mg/kg. It was demonstrated that the ratio of ROL in root tips to that at the root base slightly decreased with increasing As concentration, suggesting that the spatial ROL patterns in these groups may be shifted from the “tight” barrier towards the “partial” barrier form. Furthermore, increasing As concentration led to a increase in Fe plaque formation on root surfaces. In addition, root As concentrations of genotypes in 50 and 100 mg/kg As treatments were significantly higher than that of control treatment (P<0.05). Grain As concentration of genotype Nanyangzhan (with lower ROL) was significantly higher (P<0.05) than that of genotype CNT87059-3 with higher ROL.     

Mechanism of the action of weak acids and their salts on the passivation of iron by oxygen

Oxygen containing solutions of salts of weak acids passivate iron only when the pH of the solution exceeds a critical value. The dependence of the critical pH on the nature (pK_a) and concentration of the salt (c_s) as well as dissolved oxygen (c₀₂) can often be represented by an equation of the following form: ${pH}_c=log{c}_B?log{c}_{0_2}+{pK}_a?const.$A quantitative explanation for this relationship is derived in terms of the pH shift nearest the iron surface in course of the diffusion controlled corrosion process.     

Mechanism of the action of weak acids and their salts on the passivation of iron by oxygen

Oxygen containing solutions of salts of weak acids passivate iron only when the pH of the solution exceeds a critical value. The dependence of the critical pH on the nature (pK_a) and concentration of the salt (c₈) as well as dissolved oxygen (c₀₂) can often be represented by an equation of the following form: pH_c=log c_s-log c_o2+pK_a-const. A quantitative explanation for this relationship is derived in terms of the pH shift nearest the iron surface in course of the diffusion controlled corrosion process.     

Influence of pitting and iron oxide formation during corrosion of carbon steel in unbuffered NaCl solutions

The corrosion evolution over time of a carbon steel rotating disk immersed in aerated NaCl solutions was analyzed using a superposition model. Using this approach, partial polarization curves for iron oxidation and oxygen reduction were synthesized from experimental current-potential data at different corrosion time in order to determine the kinetics parameters, corrosion potential and current density of the underlying anodic and cathodic subprocesses. The distinctive features of the polarization curves are well described in terms of the simplifying assumptions of the model. In particular, the time evolution of the corrosion current density was linked to the morphology of the corroding surface under different NaCl concentrations.     

Mechanism of the simultaneous formation of oxide and sulfide at the scale surface during the oxidation of a pure metal in mixed atmospheres

During the reaction of a pure metal with complex atmospheres containing both oxygen and sulfur, the formation of sulfide mixed with oxide is often observed at high temperature, contradicting thermodynamic predictions. The mechanism proposed so far to explain the formation of a duplex scale at the scale surface assumes a change in composition of the gas phase in a boundary layer next to the scale-gas interface and a reaction of the metal with the molecules of the two elements. This model is shown to be unable to explain the observed amounts of the less stable phase and the reaction rates when sulfur dioxide is the prevailing reacting species and is substituted by the assumption of a direct reaction with the SO₂ molecules. The thermodynamic equivalence of the two approaches is also pointed out.     

On the mechanism of the oxidation of NiCrAl-base alloys in air and air containing sulphur dioxide

Oxidation studies have been carried out on NiCrAl-base alloys in air and air containing 1% sulphur dioxide at 1000°C. The alloys used were in the cast, forged and single-crystalline form. There was considerable difference in the oxidation behavior of the as-cast alloy and that of forged alloy, when the environment contained sulphur dioxide. In the absence of the latter, the behavior of the two alloys was not very different. The oxidation behavior of the single crystals was also very similar to that of the cast and forged alloys, when the atmosphere was oxidizing. A few single-crystalline alloys, however, underwent catastrophic oxidation when about 1% sulphur dioxide gas was present, in a manner similar to that of the cast alloy. Oxidation tests at 1000°C as well as detailed scale analysis indicated that the different microstructure, especially large difference in grain size was probably the main reason for the large difference in their oxidation behavior.