Behavior Of Iron Oxide Research Articles

Characterization of the high temperature oxidation behavior of iron based alloys used as exhaust manifolds

Nowadays engine capacities of vehicles spread in a wide range due to different vehicle power demands. Power density of engines affects exhaust gas and therefore exhaust gas temperature varies from 650 °C to 1000 °C in exhaust manifolds. Depending on the exhaust gas temperature, different types of iron based alloys are used as manifold materials such as ferritic ductile cast irons (GGG40, SiMo), austenitic ductile cast irons (Ni-resist D5S), ferritic cast stainless steels (ACIHK30, AISI 409) and austenitic cast stainless steels (CF8C). In this study high temperature oxidation behavior of different cast alloys used as exhaust manifold materials like, (i) GGG40 ferritic ductile cast iron, (ii) SiMo ferritic ductile cast iron (iii) AISI 409 ferritic cast stainless steel and (iv) CF8C austenitic cast stainless steel, were investigated.

Calcium phosphate-forming ability of magnetite and related materials in a solution mimicking in vivo conditions

Iron-based compounds, especially magnetite (Fe3O4), can be a candidate of thermoseeds for hyperthermia therapy. When iron-based compounds are applied for bone tumor treatment, they should have a heat-generating property and a bone-bonding property. However, the bone-bonding property of iron-based compounds is still unclear. The bone-bonding property of materials is estimated by their bone-like apatite formation property in simulated body fluid (SBF). The method to estimate apatite forming ability of materials by utilizing SBF was introduced by Kokubo et al. We thus report fundamental research into the behavior of iron oxides and an iron oxyhydroxide namely: FeO, Fe3O4, α-Fe2O3, γ-Fe2O3, and α-FeOOH, in SBF. Calcium phosphate precipitation was found in Fe3O4 and α-Fe2O3 within 7 and 28 days after soaking in SBF, respectively, while FeO, γ-Fe2O3, and α-FeOOH did not. Our results indicate that Fe3O4 and α-Fe2O3 have a better potential bone-bonding property than FeO, γ-Fe2O3, and α-FeOOH. The induction of apatite precipitation in SBF can be attributed to the specific structure of Fe–OH groups on the surface of Fe3O4 and α-Fe2O3.

Effect of pH, temperature, and H2O2 on the electrochemical oxidation behavior of iron in perchlorate solutions

The effects of pH, temperature, and H2O2 on the electrochemical oxidation behavior of iron were determined in perchlorate solutions. Iron exhibited four distinct oxidation behaviors in perchlorate solutions that had a pH of 3.0. First, the active dissolution potential with two current waves was observed in the range of −0.7 to 0 V. Second, the range of stable passivation was observed between 0 and 0.3 V. Third, unstable passivation was observed in the range of 0.3 to 1.2 V. Finally, pitting corrosion was observed at a potential above 1.2 V. The increase in pH stabilized the passivation of iron, whereas the increase in temperature had a negative influence on both the passivation and pitting behaviors of iron. The presence of H2O2 at concentrations less than 1.45 mM had an adverse effect on the formation of the passive oxide layer. However, H2O2 at concentrations greater than 1.45 mM exerted a beneficial influence on the formation of stable iron oxide in the active dissolution region. In addition, H2O2 mitigated the pitting corrosion of iron regardless of the H2O2 concentration.

Behaviour of iron oxide (Fe3O4) Janus particles in overlapping external AC electric and static magnetic fields

The assembly behaviour of Fe3O4-capped Janus particles with magnetically and electrically anisotropic properties is investigated in overlapping external AC electric and static magnetic fields. Generally, Fe3O4 Janus particles have been shown to form double and staggered chains in external static magnetic and AC electric fields, respectively. Here, the reaction of Fe3O4 Janus particles to sequentially applied AC electric and static magnetic fields in parallel and perpendicular field geometry is studied in order to elucidate to what extend the asymmetric nature of the Janus particle can be addressed independently by each field during assembly. A parallel field geometry leads to contraction of the Janus particle chains, whereas a perpendicular field geometry leads first to the rotation of the Janus particle chains towards the more dominant field followed by rhombohedral stacking of the chains into two-dimensional, two-particle thick sheets as a result of the weaker field. The Janus particle assembly behaviour in each field geometry tested is parameterized by the characteristic angle, θ, and the inter-particle distance, d. The observed response of the Fe3O4 Janus particles is shown to be driven by the interaction of electric and magnetic dipoles generated in the caps by the external AC electric and static magnetic fields, respectively, as well as the polarization of the polystyrene particle. Reversibility of the assembly behaviour correlates strongly with the fact that the electric dipoles disappear immediately after the AC electric field is turned off, whereas the magnetic dipoles remain permanently in the Fe3O4 caps even after the static magnetic field is removed. As a result, the Fe3O4 Janus particle assembly behaviour is responsive to both the electric and the magnetic fields and their behaviour can be manipulated by the sequence and relative orientation of the external fields.

Effects of 0.1 wt.% Manganese, Aluminum, and Silicon on Oxidation and Copper-rich Liquid Phase Formation in an Iron–0.3 wt.% Copper–0.15 Wt.% Nickel Alloy

This study investigated the effect of easily oxidizable impurities on the oxidation behavior of iron containing small amounts of copper and nickel. The motivation for this work stems from a cracking phenomenon in low carbon steels known as hot shortness. This type of cracking is caused by formation of a copper-rich liquid layer and is reduced in the presence of easily oxidizable impurities. This work studied iron alloys with 0.3 wt.% copper, 0.15 wt.% nickel, and 0.1 wt.% (manganese, aluminum, or silicon) oxidized in air at 1,150 °C. Parabolic oxidation rates were not affected by manganese or aluminum but were decreased with silicon additions. Manganese and aluminum additions led to internal MnO and hercynite formation. These slightly increased the amount of material entrapped into the oxide. Silicon additions led to a nearly continuous fayalite layer near the oxide/metal interface that decreased the oxidation rate and therefore the amount of copper-rich liquid.

Effects of Small Additions of Copper and Copper + Nickel on the Oxidation Behavior of Iron

This study was undertaken to investigate the effect of small amounts of copper and copper + nickel additions on the oxidation rate and oxide/metal interface microstructure of iron. Three iron-based alloys were compared: 0.3 wt pct copper, 0.3 wt pct copper-0.1 wt pct nickel, and 0.3 wt pct copper-0.05 wt pct nickel. Alloy samples were oxidized in air at 1150 °C for 60, 300, and 600 seconds. Pure iron oxidized for 300 seconds was used as a reference material. The parabolic oxidation rate for the iron-copper alloy did not differ from that of pure iron, but the parabolic rate for the nickel-containing alloys decreased by a factor of 2. The microstructure of the iron-copper alloy consisted of a thin, copper-rich layer at the oxide/metal interface. Both nickel-containing alloys had perturbed oxide/metal interfaces consisting of alternating solid/liquid regions. The application of ternary alloy interface stability theories show that the perturbed interfaces arise from unequal diffusivities in the solid γ-iron phase. It is suggested that this perturbed interface microstructure causes the observed decrease in oxidation rate, by limiting the iron supply to the oxide.

Comparing pretreatment by iron of electro-flocculation and chemical flocculation

A comparison was made between two technologies: electro flocculation (EF) and chemical flocculation (CF), which may be used as pretreatment in wastewater treatment. Natural water reservoir or wastewater intended for reuse, that contains high concentrations of iron particulates, often requires particle destabilization and removal. These particles can be removed by flocculation process applying ferric chloride (CF) or by Fe 3+ ion (EF) that change to Fe 2+ in a short time. EF, a fairly new environmentally-friendly process has been developed with the aim of reducing, or even avoiding altogether, the amount of chemicals required during pretreatment. The behavior of iron oxide and hydroxide colloid in EF aims at solving the problem of contaminated water or industrial wastewater. In this paper EF with iron electrodes and chemical dosing with ferric chlorides were investigated for several types and different concentrations of iron suspension. The results show a gradual rise in absolute ζ-potential and an increase in particle size with flocculation time. The results of both processes were compared through the efficiency of solid/liquid separations performed by sludge sedimentation and filtration. Preliminary testing identified the process conditions, pH of the water treated, dosage of the coagulant, mixing conditions, conductivity, and current density. The target was to find the method which provides optimum coagulation and avoids excessively high energy consumption in EF.

Thermal transition behaviour of iron oxide–polypyrrole nanocomposites

Abstract Distinct thermal transitions have been observed in nanocomposites based on iron oxide–polypyrrole prepared by simultaneous gelation and polymerization process. The transition behaviour for various iron oxide–polypyrrole compositions was investigated with the help of differential scanning calorimetery. It has been observed that the samples show a magnetic to nonmagnetic transition at 410 °C. The presence of exothermic peak at 410 °C is a strong indication of magnetic transition corresponding to γ-Fe2O3 phase of iron oxide to a nonmagnetic α-Fe2O3 phase in these nanocomposites. However such a transition was not observed in nanocomposites containing lesser concentration of conducting polymer.

Chemical effects at metal/oxide interfaces studied by x-ray-absorption spectroscopy

A chemical and magnetic characterization of ferromagnet/antiferromagnet interfaces is essential to understand the microscopic origins of exchange anisotropy and other magnetic phenomena. We have used high-resolution L-edge x-ray absorption spectroscopy (XAS), which is element specific and sensitive to chemical environment and spin orientation, to investigate the interface of antiferromagnetic oxides with ferromagnetic metals. Clear quantitative evidence of oxidation/reduction reactions at the as-grown metal/oxide interface is presented. In situ-- and ex situ--grown samples of the form oxide $(5--30 \AA{})/\mathrm{metal}$ $(1--10 \AA{}),$ where oxide is either NiO or CoO and metal is either Fe, Co, or Ni, were studied by high-resolution XAS. For all samples, a metal(oxide) layer adjacent to an oxide(metal) layer was partially oxidized(reduced). Quantitative analysis of the spectra showed that one to two atomic layers on either side of the interface were oxidized/reduced. An elemental series of samples showed that the amount of oxidation/reduction was in accord with the difference in oxidation potentials of the adjacent cations, e.g., oxide layers were more strongly reduced by an iron metal layer than by cobalt or nickel metal layers. Annealing to temperatures, typically used to bias devices, was shown to significantly increase the amount of oxidation/reduction. The oxidation behavior of iron was shown to depend on the amount of oxygen available. Our results are believed to provide important information for the improved understanding of exchange anisotropy.

Superparamagnetic behavior of iron oxides supported on porous silica gels

Spinel iron oxide (Fe3O4-γ-Fe2O3) particles were supported on microbeads of silica gel by the calcination of the silica gel base adsorbing citric acid and Fe3+ ions. The X-ray diffraction patterns and the57Fe Mossbauer spectra measured for the spinel iron oxide indicated that the particle size of the oxide was regulated by the mean pore diameter (4–82 nm) of the silica gel support employed. In the case of α-Fe2O3 particles prepared by using the same silica gel beads, it was revealed by the Mossbauer spectra and the electron micrographs that there were relatively large particles of the oxide on the surface of the beads, in addition to the particles in the silica gel micropores.

Oxidation Behavior of Iron and Nickel in Zr2(Fe, Ni) Precipitates in Zircaloy-2

Oxidation Behavior of Iron and Nickel in Zr₂(Fe, Ni) Precipitates in Zircaloy-2

Oxidation Behavior of Iron and Nickel in Zr2(Fe, Ni) Precipitates in Zircaloy-2.

The oxidation behavior of Zr2 (Fe, Ni) precipitate in Zircaloy-2 was examined by microprobe Auger electron analysis focussing attention on the oxidation behavior of iron and nickel. In the pre-transition period, the iron oxide was formed only on the top surface of zirconium oxide layer of the precipitate and the thickness of iron oxide layer increased with the oxidation time, and nickel was oxidized via dissolution in the matrix zirconium oxide near the top surface. In the post-transition period, the oxidation of iron and nickel proceeded also inside the oxide layer. Such variety of oxidation behavior of iron and nickel between the pre- and post-transition period was attributed to the situation whether the oxygen potential gradient existed or not in the matrix zirconium oxide layer.

An electrochemical study of reduced ilmenite carbon paste electrodes

The anodic dissolution of reduced ilmenite has been studied using the carbon paste electrode technique. To understand the polarization behaviour of reduced ilmenite, the polarization behaviour of iron oxide and iron powder carbon paste electrodes has also been investigated. It was shown that synthetic rutile and reduced ilmenite promoted the anodic dissolution of iron.

Electrochemical studies on the oxidation behaviour of iron in NaNO 3-NaNO 2 melt

The oxidation behaviour of iron in NaNO 3-NaNO 2 melt has been studied by potentiodynamic polarisation and electrochemical noise measurements in the temperature range of 250–550°C. The open circuit potential and the repassivation potential shifted in a noble direction with temperature up to 450°C due to the formation of stable oxide film. An opposite effect was found at 550°C due to breakdown of the oxide film. An increase of noise power values with the increase of temperature was observed which indicated an increased diffusion of iron ions in the formation of oxide film. X-ray diffraction investigation of the surface film formed on iron showed the presence of a sodium ferrite layer on the iron surface. The oxidation rate obtained by the Tafel extrapolation method was in agreement with the harmonic current measurements. The activation energy of the process was 57.43 kJ mol −1.

An alternative gibbs-duhem method for the calculation of activities from the redox data for iron oxide in ternary oxide systems

An alternative approach is presented in this article for the calculation of the activity of FeO, Fe2O3, and the other component in ternary oxide slags when the redox behavior of iron oxides is known. The approach avoids the use of the “tangent intercepts” to the iso-oxygen activity curves as required in Schuhmann's method. Favorable comparisons were obtained for the systems of FeO-Fe2O3-CaO and FeO-Fe2O3-SiO2 between the isoactivity curves derived using this method and those established in previous work using Schuhmann's method. Direct calculation of the free energy of mixing from the redox data is also possible. An example is given for the FeO-Fe2O2-CaO system.

Altering the Oxidation Resistance of Iron Via ion Beam Alloying

AbstractFe-Cr, Fe-Y and Fe-Cr-Y surface alloys were produced by direct ion implantation, ion beam mixing, and combinations of implantation and vapor deposition. The influence of these treatments on the oxidation behavior of iron was investigated in 1 atm. of oxygen at 520°C. The oxidation rates were less in all the ion beam alloyed iron samples than in untreated iron. The oxidation follows parabolic kinetics in most cases, with the rate constants, Kp, in the range (3-8)×10−6 mg2cm−4 sec−l versus 2.2×10−5 mg2 cm−4 sec−1 for untreated iron. Yttrium fluences between 5×1014 and 5×lO15 cm−2 did not alter the microstructures of iron significantly. However, fluences of 1×1016, 3×1016, 5x1016 and 1x1017 cm−2 caused the crystalline structure of iron to be replaced by an amorphous phase. The presence of this phase was demonstrated with selected area channeling patterns and transmission electron microscopy.

A mössbauer study of the behavior of iron cations in iron oxide-containing melts at 1400 °C

A Mossbauer spectroscopy technique has been developed to study the distribution of iron cations in slag melts as a function of distance from a reaction surface. A wide range of slag compositions of interest to the nonferrous smelting industry was reduced and oxidized using mixtures of CO, CO2, and Ar. Mossbauer spectra were collected on quenched slag samples for varying conditions between iron saturation and magnetite saturation, l(10-13) to 4(10-6) atm PO2 at 1400 °C. Slag sections were analyzed with a spatial resolution of approximately 500 /am, and details of the ferric and ferrous distribution at the surface and in subsurface regions were studied. In FexO-SiO2-Al2O3 melts exposed to a reducing gas mixture, there is a gradient in ferric iron concen-tration decreasing toward the surface. In the FexO-Al2O3 melt, the reduction of ferric anions at the surface appears to release O2- ions, which increases the coordination of Fe2+. However, in the presence of silica, which is surface active and acidic, reduction of ferric iron does not lead to an excess of O2- at the surface. Lime has a dramatically different effect. It reverses the ferric gradient so that, even during reduction, the ferric concentration at the surface is enhanced. Ferric oxide is surface active in these melts, and under certain conditions, liquid-phase mass transfer is rapid enough to replenish the surface. The presence of a polymer-forming ion, Fe3+, at the surface results in a scarcity of O2- ions and a reduced coordination of Fe2+. In the presence of both SiO2 and CaO, the behavior of ferric iron during reduction depends, to an extent, on the CaO/SiO2 ratio. The behavior of iron oxide melts during reduction is very complex, and the surface-active nature of SiO2 and ferric oxide has a significant influence on the reaction. A quantitative analysis of the overall reaction would have to take these factors into account.

Studies on Non-Isothermal Oxidation Behaviour of Iron and Iron-Chromium Alloys

Studies on Non-Isothermal Oxidation Behaviour of Iron and Iron-Chromium Alloys

The behavior of iron oxides in reducing atmospheres

Comparison of unpromoted α-Fe 2O 3, K, and Tl promoted α-Fe 2O 3 in atmospheres of H 2, CO, 1:1 H 2 CO , and CO following an H 2 prereduction showed that K or Tl promoters do not significantly modify the reduction behavior of α-Fe 2O 3, but can either increase (K) or decrease (Tl) the rate of growth of surface carbon in CO-containing atmospheres.

Effect of aluminium impurities on the oxidation behaviour of iron at room temperature

The influence of aluminium, as an impurity, on the oxidation behaviour of iron films containing about 0.3 wt% of carbon at room temperature is described. In general, the presence of aluminium in the sample helps to form a protective oxide layer after a definite period, mainly decided by the percentage of aluminium in the sample. Further more, the number of breaks observed in the resistance-time oxidation curve of iron, probably due to the compressional stress introduced by the flow of oxygen ions into the sample, is reduced, with increasing aluminium content. Iron films, containing different percentages of aluminium, were etched after different oxidation times. It is found that the presence of aluminium in iron, although it gives corrosion resistance to iron in oxidizing environments, stimulates corrosion in reducing environments.