Showing papers on "Magnetite published in 1974"

The Crystallization of Spinel from Basaltic Liquid as a Function of Oxygen Fugacity

Abstract: The effect of changing oxygen fugacity on the equilibrium crystallization of two basaltic melts has been determined at 1 atm total pressure. Liquidus curves for spinel (chromite-titaniferous magnetite), hexagonal oxide, olivine, pyroxene, and plagioclase are represented on temperature versus $$log f_{O_{2}}$$ diagrams covering the $$log f_{O_{2}}$$ range -0.68 (air) to -14.0 atm and a temperature range of l,100°C-1,325°C. Particular emphasis has been placed on the role of oxygen fugacity as applied to the relationship between chromite and titaniferous magnetite and the ferrous-ferric ratio. Complete solid solution between chromite and titaniferous magnetite is demonstrated at basaltic liquidus temperatures, however at oxygen fugacities below about $$10^{-8} atm$$ the crystallization of early chromite is interrupted by the crystallization of clinopyroxene. At lower temperatures, a spinel again crystallizes as titaniferous magnetite together with pyroxene and other silicates. This supports the suggestion of...

Isothermal compression of magnetite to 320 KB

Abstract: The effect of pressure on the lattice parameter of magnetite has been determined at room temperature up to 320 kbar by means of X ray diffraction employing a diamond anvil high-pressure cell. By using the Birch-Murnaghan equation with a (∂KT/∂P)T∣P=0 value of 4 ± 0.4 the isothermal bulk modulus at zero pressure was calculated to be 1.83 ± 0.10 Mbar. The X ray diffraction study also revealed that at pressures greater than 250 kbar, magnetite transforms to a high-pressure phase, which reverts to magnetite at pressures below 50 kbar. It is possible to index this high-pressure phase as being monoclinic. If it is assumed that the unit cell contains two molecules, the density is in agreement with the density predicted for a phase of Fe3O4 having all of the iron atoms in sixfold coordination.

Iron-containing mica flake pigments

Abstract: Novel mica flake pigments optionally coated with TiO2, ZrO2 and/or the hydrates thereof, having a uniform iron-containing layer thereon consisting of an iron(III) oxide hydroxide, magnetite and/or the Fe2O3 modifications obtained therefrom by annealing at a temperature below 1,100* C., are produced by gradually adding an aqueous solution of an iron salt in the presence of an oxidizing agent, to an aqueous suspension of the mica flakes at a constant temperature and a constant pH, thereby forming on the mica flakes a continuous uniform layer consisting solely of a single iron(III) oxide hydroxide modification or of magnetite. The thus-coated flakes are then separated, washed, dried and optionally annealed in a conventional manner at a temperature of up to 1,100* C. to convert the layer to Alpha Fe2O3 or gamma -Fe2O3.

Maghemite in soils and its origin ii. maghemite syntheses at ambient

Abstract: AB S T R ACT: The products of air oxidation of mixed Fe(II)-Fe(III) chloride solutions at pH 6 and 7, at 20 and 60~ and at normal pressure contain green rust, maghemite, lepidocrocite, goethite and a paracrystalline ferric hydroxide (ferrihydrite). Among these maghemite, a cubic ferromagnetic iron oxide (Fe203) found in many soils, is favoured by slow oxidation rate, high total Fe concentration, the presence of small amounts of Fe(IlI) in the original predominantly Fe(lI) solution, higher temperature and at pH 7 rather than pH 6. The green rust is believed to be an essential precursor of maghemite. On slow oxidation it will form maghemite probably via magnetite. Fast oxidation prevents the cubic phase from being formed and lepidocrocite is the end product. At higher Fe(III) proportions ferrihydrite can be formed which under certain influences converts to goethite and/or hematite. The common iron oxides are seen to form from the same system from small variations in environment which is to be expected from their common associations in soils.

Maghemite in soils and its origin. II. Maghemite syntheses at ambient temperature and pH 7

Abstract: The products of air oxidation of mixed Fe(II)-Fe(III) chloride solutions at pH 6 and 7, at 20 and 60°C and at normal pressure contain green rust, maghemite, lepidocrocite, goethite and a paracrystalline ferric hydroxide (ferrihydrite). Among these maghemite, a cubic ferromagnetic iron oxide (Fe2O3) found in many soils, is favoured by slow oxidation rate, high total Fe concentration, the presence of small amounts of Fe(III) in the original predominantly Fe(II) solution, higher temperature and at pH 7 rather than pH 6. The green rust is believed to be an essential precursor of maghemite. On slow oxidation it will form maghemite probably via magnetite. Fast oxidation prevents the cubic phase from being formed and lepidocrocite is the end product. At higher Fe(III) proportions ferrihydrite can be formed which under certain influences converts to goethite and/or hematite. The common iron oxides are seen to form from the same system from small variations in environment which is to be expected from their common associations in soils

Non-Topochemical reduction of iron oxides

Abstract: Non-topochemical behavior was studied during reduction of porous spheres of hematite by stages through the intermediate oxides and also continuously to iron by CO/CO2 mixtures at temperatures of 600 to 900°C (873 to 1173 K). The behavior became more nearly topochemical as temperature increased. Shrinking occurred during the reduction of hematite to magnetite and of magnetite to wustite, whereas swelling was observed during the reduction of wiistite to iron. Shrinking was greater, and swelling less, at higher temperatures. The total surface area of the solid decreased with increasing extent of reduction during each of the three stages. A non-topochemical model was developed which satisfies, better than previously proposed models, the reduction data for the single reactions and the three reactions occurring simultaneously. The model provides for variation in particle size and local changes in porosity and effective diffusivity. An empirical “sintering exponent” was introduced to describe changes in reacting surface area.

Low-temperature oxidation of a single-domain magnetite

Abstract: Excited oxygen gas has been used to oxidize single-domain magnetite particles at temperatures of 50° and 200°C. The magnetite particles were long thin submicron rods with a length to width ratio of 11:1. The samples were given an anhysteretic remanent magnetization and then oxidized with a field perpendicular to the original remanence. The samples were completely oxidized to maghemite and the intensity of initial remanence was reduced by 12%. No chemical remanent magnetization (CRM) was detected in any of the samples, the indication being that either shape anisotropy dominated any CRM growth or there is a positive exchange interaction between magnetite and maghemite.

High‐temperature magnetostriction of magnetite

Abstract: The magnetostriction coefficients λ111 and λ100 of magnetite have been measured by a high-temperature strain gage technique between 20° and 500°C. The measurements were performed on discs cut from two natural single crystals and one synthetic single crystal. The value of λ111 shows a linear decrease from about 80 × 10−6 at 20°C to about 7 × 10−6 at 500°C. Although λ100 values are subject to greater error, they remain negative between 20° (−20 × 10−6) and 500°C (−9 × 10−6). These results permit the estimation of the temperature dependence of coercive force and indicate that magnetostrictive interactions between crystal defects and domain walls can be responsible for thermoremanent magnetization in multidomain grains of magnetite.

Oxygen Fugacity Geothermometry of the Oka Carbonatite

Abstract: In order to learn more about the petrogenesis of the carbonatite at Oka, Quebec, a solid electrolyte oxygen fugacity sensot was used to study coexisting olivine (Fo*), magnetite, and niobian perovskite (latrappite). Plots of fO,-T data obtained for each of these three minerals show a triple intersection at 710' -f l5'C and an fO, of 1F"''=05 atm. The hypothesis is that this temperature and fOn represents the last solid-liquid-vapor equilibration among these three minerals. The temperature is in agreement with OfO'o work (Conway and Taylor, 1959), and the fO, value is consistent with standard solid and gaseous fO, buffer curves. Wyllie and Tuttle (1960) found the presence of a liquid phase at similar low temperatures throughout a wide range of synthetic carbonate systems at various total pressures. The temperature measured by this technique when compared with synthetic phase equilibria work supports a magmatic origin for the Oka carbonatite.

Note on the space group of magnetite

Abstract: From a neutron scattering study it is concluded that the space group F43m(Td2) recently suggested for several spinels does not apply to magnetite, Fe3O4.

Iron hydroxides as magnetic scavengers

Abstract: In the application of magnetic separation procedures, ferrous and ferric hydroxide gels are proposed as magnetic seeding materials to remove many metal ions from waste water. Ferric hydroxide gel, which has been well known as an excellent scavenger, has been found to be strongly magnetic and almost amorphous. Inspection of Mossbauer spectra suggests that, in addition to adsorption, occlusion is responsible for the excellent scavenging effect of ferric hydroxide gel. Ferrous hydroxide has been found to be especially efficient for removing mercury from solution. A redox reaction occurs between mercuric and ferrous ions on the surface of ferrous hydroxide gel, resulting in the formation of metallic mercury and magnetite. Metallic mercury, adsorbed on the surface of the magnetite, is easily removed by magnetic separation.

Magnetic recording medium comprising cobalt or cobalt alloy coated particles of spicular magnetite

Abstract: A magnetic recording medium is disclosed as comprising powdered magnetic particles upon which there is deposited a ferro-magnetic metal or alloy such as cobalt or a cobalt alloy. Each magnetic particle is a spiculate magnetite and the deposite of cobalt or a cobalt alloy is in the range of 0.5 wt.% to 30 wt.%. The particles are heat treated in either a reducing or inert atmosphere to a sufficient temperature to improve the magnetic characteristics of the particles including their coercive force, Br/ρ and Bm/ρ. A layer of the recording medium is disposed on a support layer of polyester to form a magnetic tape.

Oxidation of molten ferrous sulphide

Abstract: Molten ferrous sulfide of sulfur content lower than stoichiometric FeS was oxidized at 1200 and 1230°C in a stream of oxygen and argon gas mixture under conditions where the overall reaction rate was controlled by the diffusion rate of the gaseous components. The weight change of the sample during the oxidation experiment was recorded continuously. Initially, the melt absorbed a certain amount of oxygen and reached a composition very close to the FeS-FeO pseudo-binary system. Following this, the FeS oxidized to produce FeO and the sample weight decreased. As the mole fraction of FeO increased, the activity of magnetite was found to increase rapidly and the formation of appreciable amounts of magnetite occurred.

Method for producing coarse powder, hardened iron oxide material from finely divided raw material substantially consisting of hematite and/or magnetite

Abstract: A method for agglomerating finely divided iron oxide material, substantially consisting of hematite and/or magnetite, preferably enriched iron ore concentrates, and hardening the agglomerates thus formed The fine material is agglomerated by rolling, micropelletizing or other granulating methods to a particle size distribution convenient fluidizing purposes, whereafter the material is transferred to a fluidized bed furnace in which the bed is heated by introducing gaseous or liquid fuel and gas containing free oxygen or by hot gases The major portion of the material is then removed from the bed in an agglomerated and hardened condition

Process for producing iron ore oxidized pellets from magnetite concentrate

Abstract: Iron-ore oxidized pellets are produced from magnetite concentrate by the addition to the magnetite concentrate of at least one calcium compound selected from the group consisting of slaked lime, quicklime and limestone, to a basicity of 1 to 5, granulating the mixture thus prepared, drying the same, preheating the same at a temperature of from 1000° to 1150°C for 3 to 10 minutes, and thereafter firing the same.

Spatial Distribution and Origin of Magnetite in an Intrusive Igneous Mass

Abstract: A quantitative technique was developed to aid the determination of the spatial distribution of magnetite to the constituent minerals in an igneous rock. The results show the magnetite to be preferentially associated with the ferromagnesian silicates; they further lend support that the magnetite was formed by precipitation, oxidation reaction, and alteration. The amount of magnetite formed by each process can be estimated and was found to be in decreasing order, as listed above. The technique allows intergranular relations to be noted and quantified. This permits a more justified speculation as to the crystallization history of an igneous pluton.

Gold-Bismuth-Copper mineralisation in the Tennant Creek district, Northern Territory, Australia

Abstract: Gold, bismuth and copper mineralisation at Tennant Creek occurs in transgressive magnetite- and hematite-rich lodes within the Carraman Formation of the Lower Proterozoic Warramunga Group. Rocks of the Warramunga Group are dominantly felsic greywackes and shales with features indicative of turbidity current deposition. These are interbedded with massive pyroclastic rocks, rhyolitic lavas, preconsolidation slump breccias and minor lenses of banded iron formation. The magnetite-hematite lodes (locally referred to as ironstones) have an ellipsoidal to pipe-like shape commonly flattened in the direction of the regional east-west cleavage. They are typically localised in small anticlinal structures within the greywacke-shale turbidites adjacent to thin lenses of hematite-chlorite-calcite bearing banded iron formations or hematite-rich shales. A smaller number of mineralised ironstones have replaced the preconsolidation slump breccia horizons within the felsic sediment pile. Silicate, oxide and carbonate gangue minerals within the lode structures are grouped into a series of compositionally distinct zones which exhibit sharp contacts against one another and the enclosing country rocks , Massive magnetite (>80%) and Fe-Mg chlorite (<20%) commonly constitute the core of the mineralised lode and are surrounded by vari ous umbrella-shaped zones. These may be: talc-magnet.ite; dolomite; chloritised sediments, as at J·uno Mine, or quartz-hematite; hematitemagnetite; hematite-chlorite; chloritised sediments, as at Gecko Mine. The magnesium content of the chlorites (dominantly ripidolites) increases from the base, to the top, of the lode structures. The chemical and mineralogical characteristics of these zones indicate contemporaneous formation and growth, resulting from the flow of hydrothermal solutions which reacted with the host rocks and suffered continual, and systematic, changes in chemistry. A zone of intense chloritisation extends below each of the orebodies and constitutes what is thought to be a channel of hydrothermal alteration. This investigation deals with the structure, mineralogical constitution, mineral zoning, textures, and origin of the lode rocks in the three largest operating mines in the goldfield, namely the Juno, Gecko and Warrego deposits. At the Juno and Warrego mines, gold, bismuth and copper mineralisation has been shown to occur in three overlapping zones within the magnetite-rich lodes e Gold is concentrated at depth, and is overlain above by an umbrella shaped zone rich in bismuth sulphosalts. Chalcopyrite is concentrated at the top of the lode structures enveloping the bismuth zone. At Gecko (anomaly 2), bismuth and copper show a similar vertical zonation but gold is completely lacking. Within the bismuth zone at Juno, the sulphur/selenium and bismuth/ lead ratios of the bismuth sulphosalts increase from its inner edge (overlapping the gold zone) to its outer edge (overlapping the copper zone). The most common bismuth sulphosalt at Juno is junite, a new mineral, unique to Juno, which has been shown by microprobe analysis to have the formula Bi8PbJCu2 (S,Se) 16 , containing 3.8 to 11.6 wt.% selenium. Junite is easily distinguished from other lead-bismuth sulphosalts by its characteristic x-ray powder pattern. The second most abundant bismuth sulphosalt has a composition close to Bi10Pbg(S,Se) 23 and may be equivalent to the mineral wittite , previously reported from Falun, Sweden by Johansson in 1924 . Other selenium bearing sulphosalts at Juno include heyrovskyite and members of the aikinite-bismuthinite series. Colloform textures occur throughout all the lode structures in the goldfield, strongly indicating that replacement of the sediment host rocks to form the ironstone bodies was achieved by the processes of dispersive metasomatism. Replacement of this type involves the gradual hydrolysis Mg 2+ 1' .n t h e of the host sediments and permits ready exchange of Fe 2+ and hydrothermal solutions with si4+, Al3+, Na+ and K+ in the hydrolysed sediment matrix. Most of the magnetite in the central lode zones replaced needle-shaped a - FeO(OH) and S - Fe203.H20 crystal forms which probably developed from ageing of ferric hydroxide gels. Thermodynamic considerations of gangue mineral stabilities in hydrothermal solutions of the type which may have caused mineralisation at Tennant Creek, suggests that the solutions were initially acidic in nature and capable of 1 each1•. ng the I base catl.' ons I Fe 2+ and Mg 2+ (p 1 us ore metals) from the Carraman sediments at depth. There is evidence of leaching of this type in the lowest parts of the Juno hydrothermal channel. The process of metasomatic lode formation was most probably initiated by interaction of rising, chloride-rich, hydrothermal solutions with the calcite bearing banded_ iron formation or with particularly porous horizons containing abundant pore fluids (e.g., preconsolidation slump breccias) leading to an increase in solution pH and f02 which caused the deposition of amorphous, hydrated, ferric oxides. Under the influence of increasing solution p~the gangue minerals at Juno, were deposited in the order:- iron-rich chlorite at depth, followed by hematite, magnetite, talc and dolomite, to form a well zoned lode structur e . The progressive drop in f02 associated with the deposition of magnetite probably resulted in the increase in sulphur/selenium and sulphur/metal ratios of sulphides passing up the Juno lode structure, and may have also lead to the zonal distribution of gold, bismuth and copper . Sulphur isotope studies at Juno lend support to this proposal. The 16o;18o and 12c;13c ratios in dolomites from the outer envelope zone at The 32 S/34 S ratlio of syngenetic sulphides in the tuffaceous greywackes and vein sulphides in the hydrothermal channel, below the orebody, supports a proposal that the sediments of the Lower Carraman Formation provided the source for the sulphur. These sediments also contain sufficient trace quantities of gold, bismuth and copper to constitute a source for the ore components. Connate wate.rs (pore water and interlayer water) released from the argillaceous sediments in the vicinity of granitic and rhyolitic porphyry intrusions provides the most probable source for the hydrothermal solutions. Such solutions moved upwards continually leaching iron, magnesium and ore elements from the sediments in their path and were eventually channelled into low pressure anticlinal sites and deposited their metal load in favourable structural-lithological traps.

An experimental study of a direct route from iron oxide superconcentrate to strip

Abstract: A direct route from commercially available high-purity magnetite superconcentrate to thin steel strip has been investigated on a laboratory scale. The experimental procedure was first to produce an oxide strip prepared from a thick aqueous slurry of the superconcentrate and an organic binder. After drying, the strip was reduced and sintered in hydrogen or a hydrogen-carbon monoxide mixture to produce a coherent strip of iron sponge. The sponge was then hot and cold rolled to give fully dense strip. In some cases a thin layer of iron powder was bonded to one side of the iron oxide strip in order to increase its coherence during processing. On a microscale the product is characterized by a fine grain size and a large number of uniformly distributed fine inclusions. The inclusions vary from 25 μm down to submicron size and are derived from the residual impurities in the concentrate, most of which were originally in the magnetite lattice. After suitable working and heat treatment, strength and ductili...

Magnetic recording material prodn. - with annealing in static magnetic field to improve sensitivity

Abstract: A magnetic recording material is produced by applying a strip of a magnetic material onto a carrier under pressure and at an elevated temp. and, simultaneously or subsequently, subjecting the material to annealing in a static magnetic field in the direction in which the magnetic recording will be effected. The sensitivity of the magnetic material is improved; the coercive force, the residual magnetisation and the squareness ratio are considerably increased. The magnetic material contains a fine ferromagnetic powder of maghemite, magnetite or berthollideferric oxide with addition of 0.2-35 atom. % of cobalt. The magnetic material is applied onto a substrate (e.g. PVC, polycarbonate, polyacrylonitrile, glass fibre-reinforced polyester, ABS resin, metal plate or glass sheet) under a press of 3-300 kg./cm.2 at 50-300 degrees C. A magnetic field of 100-3000 G. is applied, and the annealing is carried out for 5 mins. to 3 hrs. at a rate of 5.32 degrees C/min. Optionally, the ferromagnetic material may contain 0.1-20 atom. % of Mn, Cr, Ni or Zn.

Comments [on “Superparamagnetic and single‐domain threshold sizes in magnetite” by D. J. Dunlop]

Abstract: Cation deficient (CD) magnetite phases may show peculiar hysteresis properties, as was inferred from recent experiments. Dunlop's estimate of superparamagnetic to single-domain threshold sizes for CD magnetite from hysteresis measurements may thus be misleading. Also critical size estimates may be more reliable if they are deduced from magnetic studies on pure magnetite samples containing a narrow range of particle sizes rather than on those with some cation deficiency and a large size variation, as were used by Dunlop.

Influence of the Chemical Composition on the Curie-Temperatures of Magnetites

Abstract: At the Curie-temperature, ferromagnetic substances like nickel or the mineral magnetite lose their ferromagnetism and become paramagnetic. This change of magnetic properties, which is very characteristic for each ferromagnetic material, can be recognized in a DTA curve as a very slight but still sharp endothermic peak (ΔT: 0.04–0.3° C). By using a nickel block sample holder or nickel crucibles, the Curie-temperature of nickel can be seen in the DTA curve at 360° C. The Curie-temperature of pure magnetite, Fe3O4, occurs at 580 ± 2° C (Schmidt and Vermaas; Blum et al.). It will not be modified during the ensuing heating or cooling. Substitutions of Fe2+ and Fe3+ by Al3+, Cr3+, Ti4+, Mg2+, Ni2+, Ca2+, Mn2+ and others which are partly very common in natural magnetites lower the Curie-temperature Θ after Vincent et al. from 580° for 100 weight-% Fe3O4 to 450° C for a magnetite consisting only of 80 Weight-% Fe3O4, to 300–350° C for 60 weight-% and down to 100–150° C for 40 weight-% Fe3O4 (the remainder being TiO2, Cr2O3, MgO etc.). More suitable than a diagram of Curie-temperature versus Fe3O4− content (in weight-%) as Vincent et al. have drawn it, will be the construction of a diagram of Curie-temperature versus TiO2, Cr2O3 etc. (see below).