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Showing papers on "Iron oxide published in 1989"


Journal ArticleDOI
TL;DR: In this article, a variety of iron oxides were identified by X-ray diffraction in sediments receiving acid drainage from mine tailing and coal refuse impoundments, and the major iron oxide species was ferrihydrite which gave diffuse diffraction bands at angles corresponding to 2.5, 2.2 and 1.5A.

157 citations


Journal ArticleDOI
TL;DR: In this article, it was shown that ultrafine iron oxide particles with a mean diameter of 6.9 nm and a very narrow size distribution have been studied by electron microscopy, Mossbauer spectroscopy, and X-ray diffraction.
Abstract: Ultrafine iron oxide particles with a mean diameter of 6.9 nm and a very narrow size distribution have been studied by electron microscopy, Mossbauer spectroscopy, and X-ray diffraction. Electron micrographs and electron diffraction patterns show that the particles form ‘super crystals’, that is, three-dimensional ordered close-packed structures, with a nearest neighbour distance of 9.1 nm.

149 citations


Journal ArticleDOI
TL;DR: Amorphous and crystalline aluminum and iron oxide minerals play a major role in stabilizing soil structure as measured by aggregate stability and clay dispersion as discussed by the authors, and the presence of these minerals has a favorable effect on soil physical properties, increasing aggregate stability, permeability, friability, porosity, and hydraulic conductivity.
Abstract: Amorphous and crystalline aluminum and iron oxide minerals play a major role in stabilizing soil structure as measured by aggregate stability and clay dispersion. Aluminum and iron oxide interactions with clays are pH dependent. At low pH, where the oxides carry sufficient positive charge, they precipitate on clay surfaces. These coatings, once formed, are stable at higher pHs. Precipitation of oxides at high pH occurs as phases separate from the clays. Aluminum and iron oxides stabilize clay minerals by decreasing critical coagulation concentration, clay dispersion, water uptake, and clay swelling and by increasing microaggregation. The presence of aluminum and iron oxide minerals in soils has a favorable effect on soil physical properties, increasing aggregate stability, permeability, friability, porosity, and hydraulic conductivity, and reducing swelling, clay dispersion, bulk density, and modulus of rupture.

104 citations


Patent
10 Nov 1989
TL;DR: In this paper, a process of producing alpha alumina ceramic abrasive grain by sintering α alumina monohydrate is improved by seeding with a crystalline oxide of iron having a particle size of less than 150 nm.
Abstract: A process of producing alpha alumina ceramic abrasive grain by sintering alpha alumina monohydrate is improved by seeding with a crystalline oxide of iron having a particle size of less than 150 nm.

95 citations


Journal ArticleDOI
TL;DR: Etude des effets de coordinats organiques solubles (acides humique et tannique) sur ladsorption des sulfates par la kaolinite and des oxydes de fer amorphes as mentioned in this paper.
Abstract: Etude des effets de coordinats organiques solubles (acides humique et tannique) sur l'adsorption des sulfates par la kaolinite et des oxydes de fer amorphes

72 citations


Journal ArticleDOI
TL;DR: The results suggest that several different mechanisms contribute to relaxation effects in the presence of iron oxide particles and they depend strongly on the way the particles are sequestered.
Abstract: The proton relaxation rate enhancements produced by two types of iron oxide particles, M4125 and AM125 (Advanced Magnetics, Cambridge, MA) designed as potential MR contrast agents, have been measured in polyacrylamide gels and in liver and spleen. The organ uptakes, time courses, and biodistributions of these materials have been measured using radiolabeling. The relaxation rate enhancements produced by these particles have been related to the concentration of iron per gram material at different magnetic field strengths. The relaxation rates increase linearly as a function of concentration at field strengths varying from 0.15 to 7 T. The relaxation effects of these particles in tissue are significantly different from the behavior in vitro. These results suggest that several different mechanisms contribute to relaxation effects in the presence of iron oxide particles and they depend strongly on the way the particles are sequestered. Diffusion effects for a specified TE may be enhanced using gradient or single-spin echoes rather than multiple echoes. AMI25 is significantly more effective as a relaxation agent than paramagnetic metal ions only at relatively high fields, while M4125 is less effective per unit concentration. © 1989 Academic Press, Inc.

66 citations


Journal ArticleDOI
TL;DR: Using measurements of the relative effects on different sequences, the contributions of different relaxation mechanisms have been quantified and gradient‐echo sequences were found to be more than twice as sensitive to the effects of the agent as single spin‐echo imaging sequences.
Abstract: The effects of different pulse sequences and timing parameters on the increase in transverse relaxation rate produced by superparamagnetic iron oxide particles have been studied. Gradient-echo, single spin-echo, and multiple-echo images recorded at 2.0 T were used to evaluate the reduction in signal intensity per unit concentration of iron oxide for different echo times and in different media. For the same echo time, gradient-echo sequences were found to be more than twice as sensitive to the effects of the agent as single spin-echo imaging sequences, while multiple-echo sequences were much less affected than either. Using measurements of the relative effects on different sequences, the contributions of different relaxation mechanisms have been quantified. © 1989 Academic Press, Inc.

66 citations


Journal ArticleDOI
TL;DR: In this article, the authors investigated the variation in the concentration of defect centers (S(A)) along seven lateritic weathering profiles from Cameroon using electron paramagnetic resonance (EPR) and showed that the A-center defects are caused by an inherited irradiation of the kaolinites during the first stages of rock weathering and their subsequent crystallization.
Abstract: Stable structural point defects (A-centers) have been studied in kaolinite using electron paramagnetic resonance (EPR). The variation in the concentration of defect centers (S(A)) has been systematically investigated along seven lateritic weathering profiles from Cameroon. Petrological and geochemical data have been obtained on the same samples. A-centers result from an external irradiation of kaolinite. There is no relation between defect center concentration and textural changes, the Fe content of the kaolinite lattice, and the crystalline order of this mineral. On the contrary there does exist a relationship between the integrated intensity of the EPR signal on one hand and the Fe and the U-Th content of the bulk samples on the other.A possible radiation source has to be sought in the radioactive elements disseminated through the weathered materials and mainly accumulated in ferruginous materials. However, the present-day U-Th content is too low to explain the measured concentration of defect centers. By taking into account the efficient chemisorption of radioactive elements on poorly crystallized iron oxides, the A-center defects are attributed to an inherited irradiation of the kaolinites during the first stages of rock weathering and their subsequent crystallization. The major implication of the proposed model is that iron oxide gels precipitate at the weathering front and adsorb the radionuclides released by primary minerals. The evolution of iron oxides toward a more crystalline structure leads to a release of the radioactive elements, and the A-centers are thus the memory of their transit. At the same time, the concentration of defect centers gives an efficient fingerprint of the successive generations of kaolinites during weathering processes.

59 citations


Journal ArticleDOI
TL;DR: In this article, the authors found that the photocatalytic activities for photodecomposition of acetic acid were higher at the iron oxide microcrystallites than those of α-Fe2O3 powder, the activity difference exceeding the surface area difference.
Abstract: Iron oxide microcrystallites incorporated in sodium montmorillonite clay interlayers exhibited ca. 0.28 eV greater band gap than α-Fe2O3 bulk powder, and the Fermi level of the former was 0.23 V more negative than that of the latter. Photocatalytic activities for photodecomposition of acetic acid was higher at the iron oxide microcrystallites than those of α-Fe2O3 powder, the activity difference exceeding the surface area difference between the two.

58 citations


Patent
24 Apr 1989
TL;DR: In this article, an effective process is provided for cleanly and safely combusting coal or other carbonaceous material in a manner which enhances the environment by reducing emission of pollutants, such as nitrogen oxide and sulfur oxide emissions during combustion.
Abstract: An effective process is provided for cleanly and safely combusting coal or other carbonaceous material in a manner which enhances the environment by reducing emission of pollutants. In order to reduce nitrogen oxide and sulfur oxide emissions during combustion, combustion is carried out in the presence of one or more additives comprising an alkali metal salt, such as sodium chloride. To further enhance the reaction and removal of sulfur oxides and nitrogen oxides, the additive can include an iron-containing compound, such as iron oxide, and/or a metal oxide, such as manganese oxide.

52 citations


Journal ArticleDOI
TL;DR: In this paper, fine iron oxide particles have been prepared by an aerosol technique and the particles are spherical with a mean size of 0.1 μm. Heat treatment in air or nitrogen at various temperatures for various times leads to a variety of phase mixtures of α-Fe 2 O 3, γ-Fe O 3 and Fe 3 O 4.

Journal ArticleDOI
TL;DR: In this article, the water adsorptivity of activated carbon fibres (ACF) was investigated using the Dubinin-Serpinsky equation and the number of polar sites on the surface was estimated and compared with the data from an analysis of the evolved gas.
Abstract: The Fe K-edge X-ray absorbtion near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) and the water adsorptivity of iron oxide-dispersed activated carbon fibres (ACF) have been investigated. Also, Fe K-edge XANES and EXAFS of various kinds of powdered iron oxides have been measured in order to characterize the species disperesed on the ACF. The XANES and EXAFS indicated that α-FeOOH-like ultrafine particles transform into α-Fe2O3-like particles on the ACF through heating in vacuo. The adsorption isotherms of water on the α-FeOOH-dispersed ACF were of type V. The water adsorption isotherms were analysed by the Dubinin–Serpinsky equation; the number of polar sites on the surface was estimated and compared with the data from an analysis of the evolved gas. The relationship between the water adsorptivity and the states of the iron oxides on the ACF is discussed. A comparison of nitrogen and water adsorption shows that the layer of water adsorbed on iron oxides dispersed on the ACF has a more sparse structure than normal water, and that the iron oxide-dispersed and preoxidized ACF samples exhibit an excess of water adsorptivity owing to both molecular-sieve effects and surface fractal structure.

Journal ArticleDOI
TL;DR: Chlorofluorocarbons such as CClF3 and CCl2FCClF2 were readily decomposed by the reaction with water vapor at temperatures higher than 450 °C in the presence of iron oxide supported on activated carbon.
Abstract: Chlorofluorocarbons such as CClF3 and CCl2FCClF2 were readily decomposed by the reaction with water vapor at temperatures higher than 450 °C in the presence of iron oxide supported on activated carbon.

Patent
02 Mar 1989
TL;DR: In this paper, the acicular magnetic iron oxide particle powder was used to maintain an excellent erasing characteristic and to enhance coercive force by coating a resin compsn. contg. on a substrate.
Abstract: PURPOSE:To maintain an excellent erasing characteristic and to enhance coercive force by coating a resin compsn. contg. the acicular magnetic iron oxide particle powder the surfaces of which are coated with the double layers consisting of the lower layer which is a Co compd. layer and the upper layer which is a specific ferrite layer onto a substrate. CONSTITUTION:The resin compsn. contg. the acicular magnetic iron oxide particle powder the surfaces of which are coated with the double layers consisting of the lower layer which is the Co compd. layer and the upper layer which is the spinel type ferrite layer contg. Mn and Zn or any among Mn, Ni and Zn is coated on the substrate. Acicular maghemite particles, acicular magnetite particles and the particles contg. 1 or >=2 kinds among Co, Ni, Si, Al, Zn, P, etc., therein are used for the iron oxide particles. The ferrite layer is 1.0-10.0wt.% by the weight of Mn.Zn, Ni.Zn or Mn.Ni.Zn with respect to the weight of the acicular iron oxide particles coated with the Co compd. on the particle surfaces and the ratios of Mn.Ni and Mn.Ni are 0.1-80atm.% of Mn, Ni and Zn.

Patent
17 Jan 1989
TL;DR: A pigment dispersion of enhanced viscosity and heat stability characteristics for use in coating systems is provided in this paper, which comprises a pigment carrier, a pigment of the type having a hydrophilic surface, and a surfactant functional as a dispersant in a relatively non polar matrix and which is present on the surface of the pigment in an effective amount.
Abstract: A pigment dispersion of enhanced viscosity and heat stability characteristics for use in coating systems is provided. The pigment dispersions generally comprise a pigment carrier, a pigment of the type having a hydrophilic surface, and a surfactant functional as a dispersant in a relatively non polar matrix and which is present on the surface of the pigment in an effective amount. Pigment carriers include water-based carriers and organic solvent-based carriers. Finished coatings having improved viscosity and heat stability are also provided. The finished coatings comprise a coating base and the surfactant treated pigments. Such pigments include iron oxide pigments yellow iron oxide pigment, black iron oxide pigment, divalent ferrite pigments, zinc ferrite pigment, and magnesium ferrite pigment. Such surfactants include trimethylol propane, and trimethylol ethane.

Journal ArticleDOI
TL;DR: The catalytic properties of hydroxyl surfaces in the oxidative dehydrogenation of 1-butene have been studied in detail by investigating both pure iron oxyhydroxides and hydrated iron oxides.

Journal ArticleDOI
01 Jun 1989
TL;DR: A modified method for impregnating filter paper strips with iron oxide was developed by exposing the FeCl3-treated paper to ammonia vapor instead of immersing it in NH4OH solution as mentioned in this paper.
Abstract: The Pi soil test, a new approach to measure plant-available P, uses strips of filter paper impregnated with iron oxide as a collector for P in the soil suspension. A modified method for impregnating the paper strips with iron oxide was developed by exposing the FeCl3-treated paper to ammonia vapor instead of immersing it in NH4OH solution. The paper strips prepared by the vapor technique had a more uniform deposit of iron oxide, and the P extracted from four soils ranging in pH from 4.5 to 8.2 and fertilized with two P sources and three rates correlated significantly with dry-matter yield (r = 0.751) of maize. The vapor technique was effective in preparing strips impregnated with both Fe and Al oxides. The ratio of Fe and Al on the strips was about the same as that in the solutions in which the papers were immersed. Strips containing iron oxide alone extracted more P than did strips containing both Fe and Al oxides. The dry-matter yield and P uptake of maize correlated significantly with P extracted by the strips impregnated with Fe, Al, or (Fe + Al) oxides. Phosphorus extracted by the paper impregnated with Fe oxide, and a mixture of Fe and Al oxide in the ratio of 2:1 correlated best with dry-matter yield (r = 0.751 and r = 0.736) and P uptake (r = 0.776 and r = 0.777).

Patent
21 Jul 1989
TL;DR: Improved iron oxide catalysts for the dehydrogenation of ethylbenzene to styrene were made by forming a blend of chromium oxide and yellow iron hydrate and heating the blend to convert the yellow IR hydrate to red IR oxide prior to forming the catalyst as mentioned in this paper.
Abstract: Improved iron oxide catalysts for the dehydrogenation of ethylbenzene to styrene are made by forming a blend of chromium oxide and yellow iron hydrate and heating the blend to convert the yellow iron hydrate to red iron oxide prior to forming the catalyst.

Journal ArticleDOI
TL;DR: In this article, sulfate-promoted iron oxide with pyridine or ammonia was investigated by means of infrared spectroscopy and temperature-programmed desorption/reaction coupled with mass spectrometry.

Patent
16 Mar 1989
TL;DR: In this article, the authors proposed a method for manufacturing a porosity of at least 30% of a ceramic article having a crystalline and continuous silicon nitride phase, iron and a rare earth oxide, having a surface area of 3.5 m 2 /g, and a thermal expansion coefficient smaller than 6×10 -6 m/m/°C.
Abstract: This invention relates to a ceramic article having a crystalline and continuous silicon nitride phase, iron and a rare earth oxide, the article having a surface area of at least 3.5 m 2 /g, a thermal expansion coefficient smaller than 6×10 -6 m/m/°C. measured in the range 20°-800° C. and a porosity of at least 30%. The ceramic article may also contain a discrete porous oxide phase such as alumina, aluminates, silica, spinel, titania, zirconia, zeolites and mixtures thereof. Further, the porous oxide may also contain a metal oxide such as barium oxide, nickel oxide, iron oxide, rare earth oxides and mixtures thereof. The ceramic article may be used as a catalyst support. Methods of manufacturing the ceramic article are also disclosed.


Patent
20 Dec 1989
TL;DR: In this paper, a hot reducing offgas from a smelting vessel into a vertical riser duct without substantial cooling of the offgas and, by way of inlet, particulate iron oxide containing material is entrained in the hot offgas as the gas is conveyed upwardly through the duct.
Abstract: Prereduced iron oxides are supplied to a smelting vessel (1) for the production of iron or steel by directing a hot reducing offgas from the vessel (1) into a vertical riser duct (8) without substantial cooling of the offgas and, by way of inlet (16), particulate iron oxide containing material is entrained in the hot reducing offgas as the gas is conveyed upwardly through the duct (8). The hot gas heats the entrained material to a temperature at which partial reduction of the iron oxide occurs, the hot gas thereby losing sensible heat. Additional materials may be introduced to the duct (8) for entrainment in the gas. Particulate material is separated in a cyclone (9) from the gas and the separated partially reduced material is introduced to the smelting vessel by way of passage (12). The particulate material, or part of it, may be recycled by way of passage (15) through the vertical riser duct before the partially reduced material is introduced to the smelting vessel and only part of the hot reducing offgas emitted by the vessel may be directed into the duct.

Journal ArticleDOI
01 Jun 1989-Catena
TL;DR: In this article, the iron oxide mineralogy of two river terrace sequences of the rivers Jarama and Henares, Central Spain, which are in close proximity, was studied.
Abstract: The iron oxide mineralogy of soils of two river terrace sequences of the rivers Jarama and Henares, Central Spain, which are in close proximity, was studied. The degree of weathering increases with age, as shown by several mineralogical and geochemical indicators, such as the increase in the ratio dithionite extractable (free) Fe / total Fe. Low values for oxalate extractable Fe indicate that the Fe oxides are essentially crystalline. In the Jarama sequence goethite is the dominant pedogenic Fe oxide. In the Henares sequence both goethite and hematite are present in significant amounts. The difference is attributed to pedoenvironmental differences, such as the lower pH and the moister pedoclimate of the Jarama sequence soils. The sensitivity of the goethite-hematite system to pedoenvironmental factors shows the limited value of iron oxides for the estimation of paleoclimatic conditions or relative age in chronosequences, even in relatively small geographical areas.

Journal ArticleDOI
Hans Bosch1, Annemie Bongers1, Gerd Enoch1, Ruud Snel1, Julian R.H. Ross1 
TL;DR: In this paper, the effect of alkali metals on the selective reduction of nitric oxide with ammonia has been studied on bulk iron oxide and bulk vanadium oxide and the results of these experiments gave rise to the idea that some kind of surface compound of the bronze type could be responsible for the increased activity which was measured with vanadia catalysts enriched with Li, Na or K.

Patent
23 Feb 1989
TL;DR: In this paper, a pigment of irregular-shaped particles is described which comprises crystallites of the empirical formula A x B y C z wherein A and B are different; A is cobalt, nickel, copper, zinc, cadmium, iron, manganese or any combination thereof; B is aluminum, chromium, molybdenum, IMO, vanadium, MANGANESE or any combinations thereof; C is oxygen, selenium, tellurium or sulfur; x is 1, 2 or 3; y is 2 or three; and z
Abstract: A pigment of irregular-shaped particles is described which comprises crystallites of the empirical formula A x B y C z wherein A and B are different; A is cobalt, nickel, copper, zinc, cadmium, iron, manganese or any combination thereof; B is aluminum, chromium, molybdenum, iron, vanadium, manganese or any combination thereof; C is oxygen, selenium, tellurium or sulfur; x is 1, 2 or 3; y is 2 or 3; and z is greater than 3; the crystallites have an average size of from about 75 to about 600 Angstroms; and the surface area of the pigment particles is greater than zero up to about 20 m 2 /g. In one embodiment, when the pigment contains a mixture of copper oxide, iron oxide, manganese oxide and no chromium, the pigment contains no more than 10% of manganese, and when the pigment contains copper oxide, chromium oxide, and manganese oxide, the pigment contains up to about 5% of manganese oxide, the mole ratio of chromium to copper is no greater than about 1.3 to 1.

Patent
21 Apr 1989
TL;DR: In this paper, magnetic iron oxide particles have been shown to have a spindle shape and a substantially uniform particle size and shape, and are substantially free of dendrites and have a large axial ratio.
Abstract: Disclosed herein are magnetic iron oxide particles which have a spindle shape and a substantially uniform particle size and shape, and are substantially free of dendrites and have a large axial ratio (major axial diameter/minor axial diameter) and an excellent print-through characteristic, and a method of producing the same.

Patent
18 Aug 1989
TL;DR: Magnetic iron oxide containing silicon element is produced in the form of generally octahedral particles having a sharp particle size distribution through reaction of an aqueous solution of a ferrous salt having a controlled Fe(II)/Fe(III) ratio and containing a silicic compound with a little excess of an alkali, followed by oxidation of the resultant ferrous hydroxide as mentioned in this paper.
Abstract: Magnetic iron oxide containing silicon element is produced in the form of generally octahedral particles having a sharp particle size distribution through a reaction of an aqueous solution of a ferrous salt having a controlled Fe(II)/Fe(III) ratio and containing a silicic compound with a little excess of an alkali, followed by oxidation of the resultant ferrous hydroxide. The magnetic iron oxide particles have an overall content of silicon element of 0.1-1.5 wt. % based on the iron element with the silicon localized at the core of the particles. The magnetic iron oxide particles have uniform surface properties not markedly changed under various conditions and have good dispersibility in a resin.

Journal ArticleDOI
TL;DR: In this paper, the velocity for removal of particles adhering on a wall has been measured for polystyrene latex (PSL) and iron oxide particles at laminar and turbulent flow in a glass cell.
Abstract: The velocity for removal of particles adhering on a wall has been measured for polystyrene latex (PSL) and iron oxide particles at laminar and turbulent flow in a glass cell. The results indicate that larger particles detache at lower flow velocities and the width of the velocity range for removing adhering particles is wider when the particle size is smaller in the laminar flow regime. Both the viscous drag force for removing particles determined experimentally and the adhesive force obtained theoretically are proportional to the particle diameter, and the coefficients of friction were estimated to be 0.01–0.08 and 0.01–0.02 for PSL and iron oxide particles, respectively. The ranges of the viscous force, the adhesive force and the coefficient of friction are not so far from the values given by Kanaoka et al. [2].

Journal ArticleDOI
TL;DR: The reactivity of spinel iron oxide colloids towards adsorption has been investigated by protometry, electron microscopy, X-ray diffraction and Mossbauer spectroscopy as discussed by the authors.
Abstract: The reactivity of spinel iron oxide colloids towards adsorption has been investigated by protometry, electron microscopy, X-ray diffraction and Mossbauer spectroscopy. The conversion Fe3O4-γFe2O3 can occur in various aqueous anaerobic media. It is ruled by electron transfers through the interface draining out the mobile electrons of the core, with correlative iron diffusion. Interfacial electron transfers can proceed in either way, making the reaction somewhat reversible.

Journal ArticleDOI
F. J. C. M. Toolenaar1
TL;DR: In this paper, the formation of zinc ferrite from zinc oxide and iron oxide was evaluated with high temperature X-ray diffraction experiments and the energy and entropy of activation were derived.
Abstract: The formation of zinc ferrite from zinc oxide and iron oxide is evaluated with high temperature X-ray diffraction experiments. Despite the problem of accurately determining the temperature of the part of the sample actually investigated, a kinetic analysis of the isothermal formation is shown to be possible. From these data the energy and entropy of activation are derived. It is further shown that neither corrections for grain growth during formation nor the presence of impurities have any influence on these results. On the other hand, the size of the reactant iron oxide particles is found to have a strong influence on both the energy and entropy of activation.