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Showing papers on "Iron oxide published in 1984"


Journal ArticleDOI
01 Nov 1984
TL;DR: In this paper, a conceptual model of the dissolution process is presented and validated through studies of citrate adsorption to lepidocrocite, net iron oxide dissolution under a variety of conditions, and solution phase redox reactions.
Abstract: The light-induced dissolution of the iron oxide, lepidocrocite (γ-FeOOH), has been investigated and found to be greatly enhanced in the presence of citrate. A conceptual model of the dissolution process is presented and validated through studies of citrate adsorption to lepidocrocite, net iron oxide dissolution under a variety of conditions, and solution phase redox reactions. The initial dissolution rate is directly related to the concentration of the surface bound ferric citrate and the first order rate constant for the photodissolution process is very similar to that found for the photodissociation of soluble ferric citrate. Dissolution most likely occurs through direct excitation of charge transfer bands of the surface bound ferric citrate. At low pH (pH 4.0), a constant rate of dissolution is observed while at higher pH (pH 6.5 and 8.2), the dissolution rate decreases on continued photolysis. This decrease is due to (1) an oxygen-dependent deactivation process occurring at the surface and (2) loss of photo-produced iron from solution by “ligand-like” adsorption of soluble iron citrate complexes by the colloidal iron oxide. Superimposed on the dissolution process at these higher pH is a rapid oxidation-reduction cycle involving solution phase iron species with the reduction step induced by photodissociation of ferric citrate complexes and the oxidation step controlled by the formation of ferrous citrate.

159 citations


Journal ArticleDOI
TL;DR: In this paper, the interlayer cations of the montmorillonite are exchanged with the partially hydrolyzed trinuclear acetato complex ions, which are converted into iron oxide pillars which keep the silicate layers apart and form micropores between the layers.

142 citations


Journal ArticleDOI
TL;DR: In this article, the products of surface oxidation of a natural sample of the copper iron sulphide mineral, bornite, have been determined from analysis of linear potential sweep voltammograms and from X-ray photoelectron spectroscopic examination of the oxidized layer.
Abstract: The products of surface oxidation of a natural sample of the copper iron sulphide mineral, bornite, have been determined from analysis of linear potential sweep voltammograms and from X-ray photoelectron spectroscopic examination of the oxidized layer. Anodic oxidation of bornite in alkaline media results initially in the formation of an iron(III) oxide/hydroxide and an iron-free copper sulphide of stoichiometry Cu5S4. The latter species is oxidized further at higher potentials to form a copper sulphide of lower copper content and cupric hydroxide. Air oxidation involves the first of these two steps. In acid solution, anodic oxidation yields iron(II) ions rather than an iron oxide in the first stage and copper(II) ions in the second. Sulphate and elemental sulphur are not formed under the experimental conditions investigated.

97 citations



Journal ArticleDOI
01 May 1984-Geoderma
TL;DR: In this paper, 19 samples from deeper layers of as many terraces forming agesequences in five basins were collected from depths of 1 m or more, with some below 3 m. Redness ratings were calculated from sample colors and related to amounts of extractable iron by regression.

87 citations


Journal ArticleDOI
TL;DR: A characterization of optical and electronic properties for p-type and n-type (Si-doped) iron oxides used in the photoelectrolysis of water is presented in this article.
Abstract: A characterization of optical and electronic properties is presented for p-type (Mg-doped) and n-type (Si-doped) iron oxides used in the photoelectrolysis of water. Photocurrent vs. wavelength spectra for these electrodes indicate that ..cap alpha..-Fe/sub 2/O/sub 3/ is the active optical component for both p-type and n-type materials. Band-edge locations for p-type and n-type iron oxides in sodium hydroxide aqueous solution are determined from differential capacitance measurements. The thermodynamic feasibility of the catalytic photodissociation of water without external potential is demonstrated for a short-circuited p/n diode assembly on an energy level diagram of the electrode/electrolyte interfaces. The open-circuit voltage (V/sub oc/) and short-circuit current (I/sub sc/) generated by the p/n assembly as a function of the intensity of laser irradiation indicate that these doped iron oxides are low mobility, high carrier density semiconductors. Photo-oxidation of water at the n-type anode is verified through oxygen detection. Gas evolution is monitored from an operating diode assembly using mass spectrometry and isotopically labeled water (H/sub 2//sup 18/O). Photocurrent from these p/n assemblies show excellent long-term stability in aqueous solution and Auger analysis of the semiconductor surfaces indicates no evidence of electrode dissolution.

82 citations


Journal ArticleDOI
01 Mar 1984-Nature
TL;DR: In this paper, it was shown that at initial particle concentrations (n 0) characteristic of those in the lake (1010-1011 dm−3), the colloid stability of the iron oxide is governed by the opposing forces of van der Waals' attraction and electrostatic repulsion, as predicted from model experiments on synthetic haematite particles coated with aquatic humic substances.
Abstract: Direct measurements of the aggregation rates of natural particles can help to explain the behaviour of material suspended in natural waters, and are a stringent test of predictions from model studies. The iron oxide which accumulates each summer in Esthwaite Water in Cumbria, UK is a natural colloid consisting of a sufficiently homogeneous population of particles to allow such direct measurements to be made. Here we show that, at initial particle concentrations (n0) characteristic of those in the lake (1010–1011 dm−3), the colloid stability of the iron oxide is governed by the opposing forces of van der Waals' attraction and electrostatic repulsion, as predicted from model experiments on synthetic haematite particles coated with aquatic humic substances. However, at higher particle concentrations and with Ca2+ concentrations greater than 0.01 mol dm−3 it is found that the aggregation rate constant depends on n0, possibly indicating the participation of bridging flocculation in the aggregation process under these conditions.

73 citations


Journal ArticleDOI
TL;DR: Two stages of decay of activity of the water-gas shift catalyst have been found by experiments, with fresh and ex-plant catalyst, in micro-reactor and semi-technical units as discussed by the authors.

69 citations


Journal ArticleDOI
TL;DR: In this paper, the impregnation of Fe3(CO)12 on Cab-O-Sil has been studied by ir spectroscopy, Mossbauer spectrography, and mass spectrometry.

64 citations


Journal ArticleDOI
TL;DR: In this article, the authors investigated the water-gas shift reaction in a microreactor and in a semi technical plant at pressures up to 30 bar over a commercial iron oxide/chromia catalyst.

63 citations


Journal ArticleDOI
TL;DR: Copper and silver were found to interact very differently with the oxidized iron catalyst as discussed by the authors, and the intimate contact between copper oxide and iron oxide and the facile reduction of copper oxide are responsible for the ability of copper to enhance the reduction of iron oxide.

Journal ArticleDOI
TL;DR: In this paper, the nonstoichiometry of the iron oxide clusters is found, the composition rapidly approaching Fe0.9O as cluster size increases, and the relation of these results to the similar nonstochymyometry found in bulk FeO is discussed.
Abstract: Molecular beams of oxidized iron clusters are produced by pulsed laser evaporation of iron followed by reaction of the resulting iron clusters with O2 in a continuous flow reactor. Nonstoichiometry of the iron oxide clusters is found, the composition rapidly approaching Fe0.9O as cluster size increases. The relation of these results to the similar nonstoichiometries found in bulk FeO is discussed.

Journal ArticleDOI
TL;DR: In this article, the system iron-enstatite-water was investigated at pressures around 5 GPa and at temperatures ranging from 1000 to 1200°C, using several different kinds of starting materials.

Journal ArticleDOI
TL;DR: In this article, a qualitative model of the breakdown process involving the nucleation of gas bubbles and the expansion of these bubbles in the iron layer is presented, and possible mechanisms of the initial dense iron layer breakdown are examined and compared with the experimental observations.
Abstract: Examination of wustite single crystals reduced in CO/CO2 and H2/H2O gas mixtures has shown that in all cases a dense iron layer is formed initially on the oxide surface and that the porous growth of iron which is obtained under certain experimental conditions occurs as a direct result of the breakdown of this initial dense iron layer. Possible mechanisms of the iron layer breakdown are examined and compared with the experimental observations. A qualitative model of the breakdown process involving the nucleation of gas bubbles and the expansion of these bubbles in the iron layer is presented.

Journal ArticleDOI
TL;DR: In this paper, the behavior of spinel-like iron oxide colloids in the presence of metal ions, and especially Fe2+, has been studied protometrically and structurally.
Abstract: The behaviour of aqueous spinel-like iron oxide colloids in the presence of metal ions, and especially Fe2+, has been studied protometrically and structurally. Fe2+ adsorption is shown to proceed reversibly with the release of two protons per adsorbed ion; subsequent implication of an Fe3O4 outer shell is demonstrated. All the experimental features support electron transfer involving an octahedral site sub-lattice of the whole colloid.

Journal ArticleDOI
TL;DR: In this article, the product morphologies obtained on the reduction of wustite in CO/CO2 gas mixtures between 1073 and 1373 K were reported, and three types of product morphology were identified.
Abstract: The product morphologies obtained on the reduction of wustite in CO/CO2 gas mixtures between 1073 and 1373 K are reported. Three types of product morphology are identified, namely, type A (porous iron), type B (porous wustite covered with dense iron), and type C (dense wustite covered with dense iron). The reactions which occur during the reduction of wustite in CO/CO2 and H2/H2O systems both before and after iron nucleation are examined. The product morphologies obtained on reduction are explained qualitatively in terms of the relative rates of the chemical reaction with the gas and the mass transport processes both in and on the solid.

Journal ArticleDOI
25 May 1984
TL;DR: In this article, artificial ground water containing 40 mg/l Ca and varying concentrations of Fe(II), Fe(III) and Si were rapidly oxidized with air, and the ferrihydrite forming was similar to those found in natural Finish ground waters.
Abstract: Artificial ground water containing 40 mg/l Ca and varying concentrations of Fe(II), Fe(III) and Si were rapidly oxidized with air. The ferrihydrite forming is similar to those found in natural Finish ground waters.

Journal ArticleDOI
TL;DR: In this article, the activation energy for the water-gas shift reaction over an iron oxide/chromium oxide catalyst was calculated to be 129.4-2.1 kJ mol −1 from microreactor experiments, in good agreement with the value of 121.8 kJmol −1 deduced from semi-technical experiments with the same catalyst.

Journal ArticleDOI
TL;DR: In this article, the electrochemical behavior of Fe2O3 is studied by means of a carbon paste electrode with acidic binder, and the current-potential curves when sweeping from +0.6 to −0.7 V vs. SCE usually exhibit two peaks.

Journal ArticleDOI
TL;DR: In this article, the dissolution of synthetic samples of zinc ferrite in aqueous hydrochloric acid is stoichiometric and the rate appears to be controlled by a chemical reaction on the solid surface.
Abstract: The dissolution of synthetic samples of zinc ferrite in aqueous hydrochloric acid is stoichiometric The rate appears to be controlled by a chemical reaction on the solid surface, and dependence of the dissolution rate on hydrochloric acid activity is of the first order Activation energy of 83 kJ mol-1 was found Zinc ferrite leaching is a slow solubilization process in the hydrochloric acid treatment of dead-roasted Iberian pyrite ashes The most favorable conditions are 05-1 M HC1 at 90 to 100 ‡C, when preferential solubilization of the spinel phases takes place on the hematitic matrix Extensive extraction of zinc (~90 pct of total zinc) in one to two hours and low solubilization of iron (~8 pet of total iron) results under these conditions

Journal ArticleDOI
TL;DR: A review of the literature concerning the dissolution of iron oxide and removal of metal surfaces from metal surfaces is given in this article, where studies of electrochemical phenomena and reaction kinetics are discussed.
Abstract: Recent literature concerning the dissolution of iron oxide and removal of iron oxide from metal surfaces is reviewed. Studies of electrochemical phenomena and reaction kinetics are discuss...

Journal ArticleDOI
TL;DR: In this paper, the effect of pretreating rice hulls (addition of iron) on the amount of volatile matter and residual carbon present after the coking process was studied.

Journal ArticleDOI
TL;DR: In situ Mossbauer experiments on silica-supported bimetallic FeRu and FeRh catalysts in various gaseous environments are reported in this paper, where the reduced catalysts contain iron in two states: zero-valent iron in FeRu or FeRh alloy particles, and trivalent Iron in a highly dispersed iron oxide.

Journal ArticleDOI
TL;DR: In this article, a viscosimeter with high accuracy was constructed and built for viscosity measurements in CaO, FeO-FeO,Fe2O3SiO2 slags at temperatures up to 1700°C.
Abstract: For viscosity measurements in CaO-FeO-Fe2O3SiO2 slags at temperatures up to 1700°C a viscosimeter with high accuracy was constructed and built. Measurements were undertaken mainly at 1600°C under air and carbon dioxide atmospheres at CaO/SiO2-ratios of 0.66, 1.00 and 1.50. Additional measurements were carried out at 1500 and 1700°C under air. The results are:(1) At low iron oxide contents the viscosity strongly depends on the basicity. The highest viscosities are found in acid slags.(2) Increasing iron oxide content decreases the viscosity. The decrease is stronger in acid than in basic slags since at high iron oxide contents the viscosity values approach each other.(3) The degree of oxidation influences the viscosity only a little.(4) At Fe2O3/(FeO+CaO)=0.5 the viscosity changes due to a change in the atomic structure of the slag.The results could be interpreted by the slag structure. The viscosity depends on the size and the concentration of the atomic structural units of viscous flow. These units are the silicate and the ferrite anions. Their size and concentration are influenced by the slag composition.

Journal ArticleDOI
TL;DR: In this paper, the oxidation behavior of a low-carbon Fe-30Mn-10Al-Si alloy was studied at 1100 and 1150 c in a hot-stage environmental scanning electron microscope.
Abstract: The oxidation behavior of a low-carbon Fe-30Mn-10Al-Si alloy was studied at 1100 and 1150†C in a hot-stage environmental scanning electron microscope. The oxidation experiments were performed in pure oxygen at a partial pressure of 10 −4 atm. Under these conditions, nodule nuclei of manganese and iron oxide appeared after a few minutes of oxidation, indicating the local destruction of the protective Al2O3 scale. The nodules grew and coalesced and finally overgrew the entire specimen surface. The composition of the nodules changed during the growth process; the amount of iron decreased, and the manganese content increased to about 95 wt%. All the nodules were located in symmetrically shaped pits which intrude into the metal.

Journal ArticleDOI
TL;DR: In this paper, a model of continuous melting and reduction was proposed to determine the rate of reduction during continuous continuous melting, based on experimental results of the reduction of FeO bearing slag as described.
Abstract: (I) Reduction of molten iron oxide and FeO bearing slag by H2-Ar plasma was studied using water cooled Cu crucible. The sample weights were 25 to 75g, the flow rate of mixture-gas was 20l/mm and DC electric power of plasma was 8.3kW. Results obtained were as follows:(1) The reduction of molten iron oxides proceeds linearly with time and the reaction rate is proportional to the partial pressure of atomic hydrogen. Therefore, it is considered that the rate determining step is the chemical reaction between FeO and the atomic hydrogen formed by thermal dissociation in the plasma.(2) The rate of reduction of FeO bearing slag is lower than that of molten iron oxide and is proportional to the FeO concentration in slag. It is presumed that the reduction rate is controlled by both the chemical reaction rate of FeO with atomic hydrogen at the gas-solid interface and the mass transport rate of FeO across the boundary layer between the interface and the molten slag bulk.(3) The reduction of molten iron oxide and FeO bearing slag by H2-Ar plasma takes place only on the cavity formed at the surface of melt by the momentum of plasma jet gas.(II) Continuous melting of pre-reduced ore powder, obtained by a fluidized bed reduction was examined using MgO crucible and H2-Ar plasma.Following results were obtained:(1) Carry-over loss of the pre-reduced ore powder during the melting in plasma arc furnace was small, when the condition of powder feeding and plasma arc were properly chosen.(2) Reduction of FeO in slag, accompanied in fed material, by H2-Ar plasma, could be described by a simple model of continuous melting and reduction, based on experimental results of the reduction of FeO bearing slag as described (1-2).With this model, the rate of reduction during continuous melting was determined.

Patent
19 Nov 1984
TL;DR: Calcia-alumonosilicate glass and fiber glass compositions formed by adding at least one alkaline earth metal component to naturally occurring zeolite have a low iron oxide content and may be added to cementitious bodies for reinforcement as mentioned in this paper.
Abstract: Calcia-alumonosilicate glass and fiber glass compositions formed by adding at least one alkaline earth metal component to naturally occurring zeolite. The alkaline-resistant fiber glasses formed from such a batch have a low iron oxide content and may be added to cementitious bodies for reinforcement.

Journal ArticleDOI
Kai-Kuo Lee1, Jai-Young Lee1, Donggyu Kim1
TL;DR: The dominant nonmetallic inclusions in AISI 5160 spring steel were found to be Al2O3, SiO2 and iron oxides using scanning electron microscopy and energy-dispersive X-ray analysis as discussed by the authors.

Journal ArticleDOI
TL;DR: In this article, the effect of CaF2 on the distribution ratio of phosphorus between liquid iron and flux was examined and the rate of reaction was analyzed on the assumption that the reaction was controlled by the simultaneous transport of phosphorus, oxygen and sulfur.
Abstract: Dephosphorization of liquid iron by CaF2-base fluxes was studied at 1600°C. Iron oxide was added to metal or flux as the oxidizing agent. Dephosphorizing reaction proceeded rapidly and the rate increased with increasing CaF2 content of flux. The rate of reaction was analyzed on the assumption that the reaction was controlled by the simultaneous transport of phosphorus, oxygen and sulfur.The effect of CaF2 on the distribution ratio of phosphorus between liquid iron and flux was examined.

PatentDOI
TL;DR: In this paper, a magnetic layer is formed on a non-magnetic substrate through a nonferromagnetic layer, which contains spherical, non-fromagnetic fine granular iron oxide.
Abstract: A magnetic layer is formed on a non-magnetic substrate through a non-ferromagnetic layer. This non-ferromagnetic layer contains spherical, non-ferromagnetic fine granular iron oxide. Alternatively, it contains non-structural carbon having a mean grain size of 10 to 60 nm, a specific surface area of up to 150 cm2/g by a BET method and a DBP oil absorption quantity of up to 100 ml/100 g in addition to, or in place of, this iron oxide. In this way, a magnetic recording medium having excellent surface property and electromagnetic conversion characteristics can be accomplished.