Showing papers on "Iron oxide published in 1990"

Biomineralization of Ferrimagnetic Greigite (Fe3S4) and Iron Pyrite (FeS2) in a Magnetotactic Bacterium

Abstract: THE ability of magnetotactic bacteria to orientate and navigate along geomagnetic field lines is due to the controlled intracellular deposition of the iron oxide mineral, magnetite (Fe3O4)1,2. The function and crystal chemical specificity of this mineral has been considered to be unique amongst the prokaryotes3. Moreover, the bacterial production of magnetite may represent a significant contribution to the natural remanent magnetism of sediments4,5. Here we report, the intracellular biomineralization of single crystals of the ferrimagnetic iron sulphide, greigite (Fe3S4), in a multicellular magnetotactic bacterium common in brackish, sulphide-rich water and sediment. We show that these crystals are often aligned in chains and associated with single crystals of the non-magnetic mineral, iron pyrite (FeS2). Our results have important implications for understanding biomineralization processes and magnetotaxis in micro-organisms inhabiting sulphidic environments. Furthermore, the biogenic production of magnetic iron sulphides should be considered as a possible source of remanent magnetization in sediments.

Chemical aspects of iron oxide coagulation in water: laboratory studies and implications for natural systems.

Abstract: Initial coagulation rates of colloidal hematite (α-Fe2O3) particles (diameter less than 0.1 µm) were measured experimentally in well-defined laboratory systems at constant temperature. The relative stability ratio,W, was obtained at various ionic strengths in NaCl medium and at pH values in the range from 3 to 12. ExperimentalW values ranged from 1 to 104 in various systems. The results delineate the roles ofspecific andgeneralized coagulation mechanisms for iron oxides. Among the specifically-interacting species (ΔG ads 0 >ΔG coul 0 ) studied were phosphate, monomeric organic acids of various structures, and polymeric organic acids. The critical coagulation-restabilization concentrations of specifically-interacting anions (from 10−7 to 10−4 molar) can be compared with the general effects of non-specific electrolyte coagulants (10−3 to 10−1 molar). The laboratory results are interpreted with the help of a Surface Complex Formation/Diffuse Layer Model (SCF/DLM) which describes variations of interfacial charge and potential resulting from variations of coagulating species in solution. Comparison of these laboratory experiments with observations on iron behavior in estuarine and lake waters aids in understanding iron removal mechanisms and coagulation time scales in natural systems.

Anaerobic microbial remobilization of toxic metals coprecipitated with iron oxide

Abstract: An anaerobic N{sub 2}-fixing Clostridium sp. solubilized Cd, Cr, Ni, Pb, and Zn coprecipitated with goethite ({alpha}-FeOOH) by (i) direct action due to enzymatic reduction of ferric iron and the release of metals associated with iron and (ii) indirect action due to metabolic products. The extent of dissolution depended upon the nature of the association of the metals with goethite. Substantial amounts of Cd and Zn, which were closely associated with iron, were released due to direct action. Nickel was solubilized by direct and indirect actions, while a small amount of Cr was solubilized only by direct action. The nature of association of Pb in the coprecipitate was not affected by the presence of other cations and it was solubilized by indirect action. In the presence of bacteria, the concentration of soluble Pb decreased due to biosorption. These results show that there could be significant remobilization of toxic metals coprecipitated with iron oxides in wastes, contaminated soils, and sediments due to microbial iron reduction.

Hepatic cirrhosis and hepatitis: MR imaging enhanced with superparamagnetic iron oxide.

Abstract: Superparamagnetic iron oxide was applied as a reticuloendothelial contrast agent in the diagnosis of cirrhosis and hepatitis in seven patients. Three patients had compensated cirrhosis, and four had active hepatitis. T1- and T2-weighted spin-echo magnetic resonance images were obtained before and 1 hour after the administration of iron oxide. Eight patients without diffuse liver disease served as a control group. Normal liver tissue showed a 75% +/- 9% reduction in signal intensity after the administration of iron oxide, and the liver appeared homogeneously hypointense. Cirrhotic liver tissue showed a smaller response (P less than .05) to iron oxide, with a 52% +/- 13% reduction in liver signal intensity. Inhomogeneous structures could be observed in enhanced images and are thought to represent fibrous bands or regenerating nodules. Liver tissue with active hepatitis showed a markedly reduced response to iron oxide (11% +/- 2%) (P less than .05), and the parenchyma appeared homogeneous. The authors conclu...

Use of Raman Spectroscopy and Rotating Split Ring Disk Electrode for Identification of Surface Layers on Iron in 1M NaOH

Abstract: In situ Raman spectroscopy and rotating split‐ring disk electrode were used to identify products formed on iron in at 22°C at various peaks of cyclic voltammograms. The peak at the most active potential of the cathodic reverse sweep has been ascribed to the reduction of to Fe2+ species: this peak suggested that started to form at the first peak of anodic sweep and that it built up at nobler potentials. The Raman spectroscopy has revealed the formation of in the wide range of potentials, of and/or at peak III of anodic sweep, and of after prolonged polarization at a potential of 0.27 V (SCE). Rapid cycling or long exposure resulted in the formation of and . It is suggested that the passivating film on iron in is composed of an inner layer and of an outer layer containing other products.

Structural properties of lead-iron phosphate glasses by X-ray diffraction☆

Abstract: The structural properties of lead-iron phosphate glasses have been investigated by X-ray diffraction in an attempt to understand the chemical and mechanical characteristics presented by lead metaphosphate glass as the result of the addition of iron oxide. Information on FeO bond lengths and coordination numbers was obtained by a comparison of radial distribution functions of glass samples containing iron oxide and of the iron-free glass matrix. Stable structural arrangements around Fe(III) atoms were detected, which could be responsible for the stabilizing effect of Fe2O3 on lead metaphosphate glass.

Mechanisms of porous iron growth on wustite and magnetite during gaseous reduction

Abstract: The iron/iron oxide interface morphologies formed during the reduction of dense wustite and magnetite samples have been examined using scanning electron microscopy. Under conditions where porous iron products are obtained, a range of structures, which depend critically on the gas composition, reaction temperature, and bulk oxide composition, may be formed at the inter-face during reduction. Three principal mechanisms of porous iron growth have been identified: (1) a continuous coupled reaction, involving cooperative pore and iron growth, (2) a continuous dendritic growth mechanism, in which pores advance ahead of the iron formation, and (3) a discontinuous mechanism, involving the successive formation and breakdown of dense iron lay-ers on the oxide surface. The reaction mechanisms are explained in terms of the relative mag-nitudes of the various chemical reactions and mass transport processes which occur during the decomposition of the solids.

Iron or iron oxide grains in the interstellar medium

Abstract: La chimie des grains de fer dans le milieu interstellaire diffus est analysee pour determiner leur abondance dans les grains interstellaires et circumstellaires

Analysis of oxide layers on stainless steel (304, and 316) by conversion electron Mössbauer spectrometry

Abstract: Stainless steels of type SUS304 and SUS316 were chemically treated and heated at various temperatures, and the oxide films formed on the surface were analysed by Auger electron spectrometry and conversion electron Mossbauer spectrometry. The outermost oxide layers of stainless steels were enriched with iron and chromium after heat treatment below 600° C and above 700° C, respectively. It was found that at least two magnetic components of iron species were present in the oxide layers of stainless steel heated below 600° C and that the fine particles of iron oxide are produced in the inner oxide layers of the samples prepared by heating at temperatures higher than 700° C. Only paramagnetic iron species were detected in the oxide layers of the stainless steel prepared by chemical treatment. The structures of the oxide layers produced by those heat and chemical treatments are proposed.

Synthesis and magnetic properties of Fe5C2 by reaction of iron oxide and carbon monoxide

Abstract: The formation behaviour and magnetic properties of Fe5C2 were investigated. Iron oxides, as starting material, were carburetted with carbon monoxide gas by heat treatment. Fe5C2 was formed as a single phase in the reaction temperature range 350 to 375° C. The amount of carbon monoxide gas was controlled by mixing with nitrogen gas to prevent free carbon deposition by the disproportionation of carbon monoxide. Synthesized Fe5C2 particles were identified as a single phase by XRD and the weight change measurement of reactants. The saturation magnetization of Fe5C2 was about 100e.m.u.g–1, regardless of the reaction temperature. The coercive force decreased from 800 to 400 Oe with increasing reaction temperature.

Mechanism of potassium loss by desorption from an iron oxide catalyst for the styrene process

Abstract: Several types of experiments have been done with molecular beam and mass spectrometric methods to characterize the desorption processes of potassium from a commercial styrene (potassium promoted iron oxide) catalyst. The loss of potassium as desorption of K is found to be mainly thermal, with an activation energy close to 1.0 eV (97 kJ/mole), which probably is associated with release of K from the initially bound positions in the bulk. The directly measured rate of loss as K appears too small to account for the experimentally observed total rate of loss. A new loss mechanism as electronically excited but not easily field ionizable potassium atoms is detected with an activation barrier of 1.7 eV (164 kJ/mole). Excited states may be important for the total loss both through direct emission of excited K atoms, and since excited states may give rise to cluster formation at the surface and more rapid loss as clusters Kn.

The selective chlorination of iron from llmenite ore by CO-Cl2 mixtures: Part I. intrinsic kinetics

Abstract: The intrinsic kinetics of the selective chlorination of iron from ilmenite ore using carbon monoxide as the reducing agent were studied in a shallow fluidized bed. Experiments on the effects of chlorination temperature, carbon monoxide and chlorine gas partial pressures, and particle size were conducted in the absence of mass- and heat-transfer influences. Results indicate that the kinetics in the temperature range 923 to 1123 K are represented by the following pore-blocking rate law: λ[ exp (XFe/λ) − 1 ] = 33.7 exp (− E/RT)pco0.5220.32t where E is 37.2 kJ/mol and p and t are in atm (=101.3 kPa) and minutes, respectively. The partial pressure of carbon monoxide was found to affect the chlorination rate more strongly than that of chlorine. A reaction mechanism in which iron in ilmenite reacts with chlorine before the liberated oxygen is removed by carbon monoxide is proposed.

Catalyst composition for the oxidation of carbon monoxide

Abstract: A composition of matter comprises (a) a titania-containing support material, (b) platinum metal, (c) iron oxide, and (d) at least one alkali metal compound (preferably potassium compound). The composition of matter is used as catalyst in the reaction of carbon monoxide and free oxygen to carbon dioxide.

Some Properties of Soil and Synthetic Iron Oxides

Abstract: The sizes of Fe-oxide crystals in soils usually range between 10 and 100 nm. Together with the poorly crystalline Al-silicates, such as allophane and the humic substances, the iron oxides are among the smallest particles found in soils. From a comparison of the sizes of common soil minerals it can be seen that iron oxides usually belong to those soil minerals which have very small particle sizes. Consequently, iron oxide particles can contribute significantly to the total surface area of soils even when they compose only a few per cent of the components.

Corrosion of Iron by Li2 CO 3 Melt at 1073 K

Abstract: The corrosion of iron has been studied gravimetrically in the presence of melt in atmosphere at 1073 K in order to examine the effect of the amount of the melt on the metal on the corrosion process. When the surface of Fe was covered with a thin film of melt, the total weight of the specimen increased, the corrosion reaction followed a linear rate law, and the major product was iron oxide. At that time the weight gain was proportional to the metal loss. When the metal was fully immersed in the melt the weight of the cell decreased. The corrosion reaction of Fe was relatively slow in this case and the major product was while a small amount of could also be formed.

Mixed Oxidation of Iron–Chromium Alloys in Gases Containing Oxygen and Chlorine at 900 to 1200°K

Abstract: The mixed oxidation of three binary Fe-Cr alloys containing 1, 5, and 20 wt% Cr in Ar-50%O2−1%Cl2 and in Ar-50%O2−025%Cl2 at temperatures between 900 and 1200 K has been investigated using thermogravimetric analysis and examination of the corrosion products by scanning electron microscopy At 1000 K and above, the alloys experience accelerated corrosion associated with the formation of a porous two-layered oxide scale Iron oxide is concentrated in the outer layer and chromium oxide in the inner layer Iron chloride deposits are detected near the scale-metal interface at 1000 K, but not at higher temperatures Although the 20% Cr alloy is much more resistant to oxidation than the other alloys in uncontaminated O2, the rates of corrosion of all three alloys are very similar in the chlorine-containing environments at 1000 K A mechanism proposed for the accelerated oxidation in these environments is based on the formation, diffusion, and reoxidation of volatile iron chlorides

Interfacial electron transfer in colloidal spinel iron oxide silver ion reduction in aqueous medium

Abstract: the redox behavior of spinel iron oxide colloids has been evidenced by studying silver reduction by magnetic using potentiometry, X-ray diffraction and Mosshauer spectroscopy. At pH ⩾6, silver reduction involves an interfacial electron transfer without iron desorption, and the Fe 3 O 4 → γ−Fe 2 O 3 transformation. In reverse, the γ−Fe 2 O 3 colloid can be refilled with electrons by Fe II adsorption, which results in the growth of a Fe 3 o 4 surface layer. This reduced colloid is much more reactive than the intial Fe 3 O 4 particle.

The reduction of zinc from slags by an iron-carbon melt

Abstract: An experimental investigation was undertaken to study the mechanism of reduction of zinc from slags in the presence of a carbon-saturated iron melt. Batch tests were performed at 1400 °C, and the variation of the zinc and iron concentration in the slag during reduction was determined by sampling the slag at intervals during the test. In graphite crucibles, zinc in slags containing iron was reduced faster than zinc in iron-free slags, both when an iron bath was present and when it was absent. Zinc was reduced faster from slags containing iron when an iron bath was present than when an iron bath was absent. The dominant mechanism of reduction of zinc from slags containing iron appears to be the reaction of Zn2+ ions with Fe2+ ions to form zinc vapor and Fe3+ ions. When an iron bath is present, the Fe3+ ions are reduced back to Fe2+ predominantly by reaction with iron from the bath. Mass transfer of Fe3+ ions in the slag appears to be the rate-controlling step. Reduction of iron from slag by carbon occurred in parallel with the reduction of zinc, and whether there was a net increase or decrease of iron in the slag depended on the relative rates of production and consumption of iron. Lead and copper in the slag were reduced to low levels. The lead volatilized and the copper dissolved in the alloy.

Relation between Sulfur Pressure and Sticking of Fine Iron Ores in Fluidized Bed Reduction

Abstract: Fourteen kinds of iron ore fines (0015-0021 cm diameter) were reduced to iron in a laboratory batch fluidized bed with a 90%CO-10%CO2 mixture (flow rate: 8 times the minimum fluidization velocity Umf) at 700-900°C to investigate the relation between sticking behavior and sulfur activity in gas phase of bed during metallization (aS), which could be evaluated from chemical analysis of sulfur species in exhausted gas, relative to iron/iron sulfide equilibriumValues of aS obtained in all of tests were in the range of 001-1 The tests showing middle sulfur activities around 01, fell into sticking state soon after initial metallization, accompanied with long iron whiskers at higher temperatures The tests showing activities other than the above conditions, induced short iron whiskers and porous or plain irons, indicating fluidized state until higher reduction degrees at lower temperatures These temperature and sulfur activity dependences of product morphologies, which were in nearly agreement with authors' previous researches about abnormal swelling during reduction of iron oxide pellets prepared from reagent, corresponded to a sticking tendency of bed These results give one reasonable idea by which the ore kind dependence of sticking can be interpreted

Reduction of solid wustite in H2/H2O/CO/CO2 gas mixtures

Abstract: The reduction of dense wustite in H2/H2O/CO/CO2 gas mixtures has been carried out at temperatures between 1073 and 1373 K. The critical conditions for the formation of porous iron product morphologies have been identified and the results discussed in relation to the breakdown of dense iron layers on wustite surfaces.

Electrophotographic one component magnetic developer comprising hydrophobic silica and toner containing iron oxide

Abstract: Disclosed is an electrophotographic magnetic toner comprising 40-80% binder resin, a waxy material such as a low molecular weight polypropylene or polyethylene, a charge control agent and 20-60% iron oxide having a number average particle size of 0.2-0.7 microns and wherein trivalent Fe is present in excess and wherein the iron oxide contains 16-25% FeO and about 75-84% Fe2O3.