Showing papers on "Magnetite published in 1976"

Interacting single-domain properties of magnetite intergrowths

Abstract: Recognition that magnetite intergrowths are a common carrier of stable remanence in igneous rocks has prompted a detailed investigation of their magnetic properties. A Tertiary basalt containing homogeneous titanomagnetite grains was oxidized in air to form magnetite/ilmenite intergrowths, the morphology of which has been studied by electron microscopy. The intergrown grains are shown to contain arrays of interacting single-domained magnetites with uniaxial shape anisotropy. Interactions between single domains cause reduction of coercivity from the very large values associated with isolated single domains to values which are, however, many times larger than those measured in multidomained grains. The intergrown grains have an observed IRS/IS value of 0.30, whereas the value of this ratio obtained experimentally under nondemagnetizing conditions is found to be 0.51. The reduction is shown to be entirely explicable in terms of localized array demagnetizing fields arising from surface poles. A similar effect is seen in magnetite/ulvospinel intergrowths. Qualitative evidence that this reduction proceeds mainly by rotation of the spontaneous magnetization from easy axes is seen in a measured anisotropy of low field axial susceptibility having a value 11% higher in a direction perpendicular to the saturation remanence than that parallel to it. This phenomenon may be used to discriminate between rocks containing interacting single domains and those containing either multidomains or noninteracting single domains. These results also apply to magnetic powder experiments reported in the literature, in which reduction in IRS/IS horn 0.5 will occur if single-domained particles of uniaxial anisotropy are clumped together, a situation which is difficult to avoid. Magnetic intergrowth structures commonly observed in subaerial basalts should be regarded as arrays of interacting single-domain magnetite particles capable of carrying a strong remanent magnetization stable over geological intervals of time.

Structural changes and kinetics in the gaseous reduction of hematite

Abstract: The mechanism of the gaseous reduction of hematite grains to magnetite was studied. Gravimetric measurements were carried out for the reduction of Carol Lake hematite pellets and grains in CO-CO2 atmospheres over the temperature range 500 to 1100°C. The pore size distribution in the reduced magnetite was measured by mercury porosimetry. Partially reduced grains were examined by optical microscopy. At temperatures below 800°C, the reduction of a hematite grain to magnetite occurred at a well-defined shrinking-core interface. The average pore size in magnetite formed at 600°C was found to be 0.03 μm. An estimate of the rate of CO diffusion through pores of this size indicated that the reaction rate at 600°C was controlled by a step near the hematite-magnetite interface. At temperatures above 800°C, the reaction mechanism became altered due to the preferential growth of magnetite along a single direction in each hematite grain. The reduction rate decreased with an increase in temperature, and no microporosity was present in magnetite formed at 1000°C and above. It was postulated that the reaction rate was controlled by the rate of formation of fresh nuclei and by their rate of subsequent growth.

Epitaxial process of forming ferrite, Fe{hd 3{b O{HD 4 {B and {65 Fe{hd 2{b O{HD 3 {B thin films on special materials

Abstract: A first thin film of appropriate texture, lattice constant, and crystal structure, such as body centered cubic vanadium or chromium with (110) texture is deposited upon a rigid or flexible substrate forming a plurality of polycrystals. A ferrite such as magnetite (Fe3O4) is sputtered from a target onto the first thin film forming a mixture of gamma Fe2O3 and Fe3O4 substantially completely without formation of Fe or other oxides of iron, providing good magnetic characteristics and resistance to corrosion. The substrate temperature can be maintained as low as 200 DEG C for both steps when sputtering or evaporation is employed.

Crystallization of chromite from nickel-iron sulphide melts

Abstract: An experiment, in which an iron-nickel-copper sulphide melt was heated with synthetic chromite and then cooled, showed that substantial quantities of chromite had dissolved in the melt and had then recrystallized as euhedral crystals rimmed with magnetite. This experiment suggests that the unusual chromite (low in Mg and Al) which is associated with the sulphide phase in Western Australian nickel ores may have formed in a similar way.

Chrome-spinel in progressive metamorphism—a preliminary analysis

Abstract: Progressive metamorphism of serpentinite and allied rocks causes systematic changes in the composition of the chrome-spinel phase, when the latter is in equilibrium with chlorite and two magnesium silicate minerals. The stable spinel in antigorite-serpentinites is Al-poor magnetite, Cr-magnetite, or ferrit-chromite, depending on the local Cr/Fe 3+ ratio in the rock. With increasing metamorphic grade up to middle amphibolite facies conditions (talc + olivine, or Ca-poor amphibole + olivine stable) more chromiferous spinels (chromites) are encountered, containing modest amounts of Al. Further increase in grade (enstatite + olivine stable) extends the range of possible spinel compositions to green MgAl 2 O 4 -rich spinel. The Al-content is governed by P -, T -, and f H 2 O-sensitive equilibria involving chlorite. Mg/Fe 2+ ratios in the spinel are a function of Cr, Al and Fe 3+ in the spinel, and the ratio Mg/Fe 2+ in coexisting silicates. Solid solution in natural chromites on the magnetite-chromite join is complete at ≈500°C, and close to the join chromite-Al spinel (with variable Fe/Mg) it is complete at ≈700°C. The temperature dependence of K D , the olivine-spinel Fe-Mg partition coefficient, is greater than implied by the JACKSON (1969) geothermometer. A tentative, revised, graphical calibration is offered, based on microprobe-analyzed high-grade metamorphic pairs and pairs from basaltic pumice. This new plot gives results which are broadly consistent with relative temperatures of equilibration inferred from other geothermometers, for alpine peridotites, peridotite nodules and meteorites.

A study of iron in fired clay : mössbauer effect and magnetic measurements

Abstract: A potters clay from the Gorgan plain, in N. E. Iran, has been fired successively at temperatures up to the melting point 1 200 °C in an atmosphere of air or 5 % CO in moist CO2. Mossbauer spectra at 296 K and 4.2 K allow the determination of the relative amounts of iron in well-crystallised haematite or magnetite, of poorly-crystallised and fine-particle ferric oxide or hydroxide, and of iron diluted in the ferrous or ferric form in silicate minerals. In an oxidizing atmosphere there is no ferrous iron in firings above 500 °C and at 1 200 °C, all the ferric iron is diluted in the silicate matrix. A peak in the magnetization which reaches 5 emu/g. Fe near 1 100 °C is associated with a decrease in the size of ferric oxide fine particles before their disappearance at 1 200 °C. In a reducing atmosphere, some ferric iron persists up to about 1 200 °C, 12 % of the iron is in the form of magnetite between 600 and 800 °C, and its progressive disappearance from 850 °C accounts for the drop in magnetization from 16 emu/g. Fe at 800 °C to zero at 1 100 °C.

Magnetism of basalt cores from the Nazca Plate and implications for magnetic anomaly interpretation

Abstract: Measurements of magnetic and thermomagnetic properties of basalt from leg 34 of the Deep-Sea Drilling Project indicate that our 46 samples contained stable single-domain (SD) or pseudo-SD magnetite or titanomagnetite. The mean inclination after af and thermal demagnetization is Ī= −15°, close to the present dipole field, at site 321 but is anomalous (Ī = +53°) at site 319. In 31 samples of massive basalt from both sites the stable remanence at 20°C was masked by a low-coercivity component. High-field hysteresis loops are narrow at 20°C and broad below the −155°C magnetite transition. These samples, which we denote type 1, exhibited wide or constricted Rayleigh loops in 10 Oe. Although the magnetite in type 1 samples tends to be coarse (>100 μm), our findings demonstrate that the effective source of type 1 magnetite properties is not multidomain structures but fine predominantly superparamagnetic interacting particles that become stable SD at low temperatures. The other 15 samples (type 2), containing finer-grained magnetite or titanomagnetite, were stable at 20°C, did not show Rayleigh loops, and produced highly irreversible thermomagnetic curves consistent with SD behavior and oxidation upon heating. Between 20° and 105°C all type 1 k-T curves rose spectacularly towards a Hopkinson-type peak, while the natural remanence and the Koenigsberger ratios (∼1–10 at 20°) decreased sharply. Therefore in areas underlain by such rocks, magnetic anomalies must be interpreted with care.

Deposition of magnetite films by reactive sputtering of iron

Abstract: Iron is sputtered reactively in an argon-oxygen glow discharge to form deposits of magnetite. Cycling the oxygen partial pressure between a low and a high value during sputtering causes deposition of alternating layers of Fe-metal and Fe 2 O 3 -oxide. Depending on the cycle length, a layered structure results or homogeneous films form. For all films pronounced magnetite peaks were found by X-ray analysis. In the case of homogeneous films only magnetite was found. The films were hard-magnetic with coercivities between 250 Oe and 550 Oe and squarenesses between 0.6 and 0.8. Magnetic recording of these films on 14-in disks yielded bit-densities of up to 6.5 kT/cm.

Cobalt-doped acicular hyper-magnetite particles

Abstract: Acicular hyper-magnetite particles, that is, acicular particles of (FeO).sub.x Fe.sub.2 O.sub.3 where x is greater than one and not greater than 1.5, are provided with coatings of a cobalt compound, the cobalt providing 1% to 10% of the total weight of the particles. The particles provide superior magnetic recording media.

Production of black iron oxide pigments

Abstract: In a two-stage process for producing black iron oxide pigments wherein an iron salt solution is alkalized in a first stage to precipitate about 55 to 70% of the iron, the solution is oxidized to convert the precipitate to goethite, the solution is further alkalized in a second stage to precipitate the balance of the iron, the precipitated iron II hydroxide is allowed to react with goethite to form magnetite, the improvement which comprises effecting the second stage in the presence of an inorganic ionic compound of at least one metal selected from the group consisting of copper, nickel, aluminum, chromium, titanium, zirconium and vanadium in about 0.05 to 5% calculated as metal based on the weight of the final pigment. The resulting pigment is of high color intensity, narrow grain distribution range and pronounced magnetite structure.

Effect of Hydrogen on the Corrosion of Steels in High Temperature Water

Abstract: The reduction of magnetite by hydrogen to soluble ferrous ions is an important factor in the corrosion behavior of steels in high temperature water. The morphology of the oxide formed in a...

A Mossbauer study of the conduction electron response in doped magnetite

Abstract: A Mossbauer study of slightly doped magnetite has revealed the occurrence of spin and charge oscillations in the B sublattice of magnetite. The Mossbauer spectra, recorded between 130K and 700K of (Fe) (M0.05Fe1.95)O4 with M=Li+, Ni2+, Al3+, V3+, Cr3+, Ti4+, Sn4+ and Mo4+ are interpreted in terms of a charge oscillation model, which describes the electron response in narrow bands.

Manufacture of cobalt-modified γ-iron(III)oxides

Abstract: The invention relates to the manufacture of acicular cobalt-modified γ-iron(III) oxide by coating an acicular α-iron(III) oxide or its hydrate with an inorganic protective coating, subsequent reduction to magnetite at 350° to 650° C, application of the cobalt compound to this magnetite or to the γ-iron(III) oxide obtained therefrom by oxidation, and subsequent heat treatment at 80° to 300° C, if necessary with simultaneous oxidation of the magnetite to the corresponding γ-iron(III) oxide. This iron oxide has high coercivity and can be used as the magnetic component in magnetic recording media for recording high frequencies without having the disadvantage of thermal and mechanical instability.

Manufacture of γ-iron(III) oxide

Abstract: A process for the manufacture of acicular γ-iron(III) oxide of improved crystallinity and high coercive force by heating goethite or acicular alpha-iron(III) oxide particles at temperatures of from 500° to 800° C, reduction of the resulting product at temperatures of from 280° to 600° C and subsequent oxidation of the magnetite to γ-iron(III) oxide of improved crystallinity and high coercive force.

Method for recovering vanadium from magnetite and forming a magnetite product low in sodium and silica

Abstract: Magnetite concentrate comprising essentially iron oxide as Fe 3 O 4 , titanium dioxide and lesser amounts of vanadium and silicious materials is screened and treated with relatively small amounts of sodium to recover from 70 to 90% of the vanadium and at the same time produce a magnetite end-product suitable as feed material for blast furnaces, said end-product containing as low as about 0.3% sodium as Na 2 O and as low as 1.0% SiO 2 .

Susceptibility of the Oxide Film Formed on Steel in Air at 100 to 400 C to Local Breakdown in Borate Buffer Solutions Containing Cl− Anions

Abstract: The susceptibility of steel to pitting corrosion (determined by the depth of the pits) and the susceptibility of oxides of different composition and thickness to local breakdown (determined by the number of pits) were studied. It was found that oxide films consisting of magnetite and hematite are more susceptible to local breakdown but less susceptible to pitting corrosion than magnetite films.

Changes of electric conductivity in the neighbourhood of the curie temperature of basalts

Abstract: In investigating the electric conductivity of rocks σ as a function of the temperature it was found that rocks containing ferrimagnetic minerals display a change in the slope of the functionlg σ=f(1/T) in the neighbourhood of the Curie temperature Θ. In order to explain these changes the curveslg σ=f(1/T) and the Curie temperatures Θ, obtained from the temperature dependence of the saturated magnetization Js=f(T), were compared. Eight samples of basalts, 2 samples of haematite and magnetite were used to demonstrate the relation between Θ and the changes in the pattern of the electric conductivity, caused by the variations of the exchangeable energy of ferrimagnetic minerals.

Bauxite and Hematite Cappings in the Nilgiris, Tamil Nadu-Study from Geomorphic Angle

Abstract: The Nilgiri plateau is marked by a number of bauxite and hematite cappings, the former over charnockites and the latter over magnetite quartzite, as products of residual chemical weathering. A study of disposition in space of about twenty groups of bauxite and six groups of hematite cappings indicates their Occurrence confined around 8000' and 7000' above M.S.L. and these conform to two surfaces already reported on geomorphic evidences. In the absence of datable sediments overlying the cappings, it has not been possible to find the exact age of the laterites. Based on a general finding from worldwide occurrences of bauxite that gibbsite forms first and later transforms over a period of geological time into boehmite and diaspore, it is inferred that the Nilgiri bauxites could be of Tertiary age.

HGMS: Economics, Applications, and Seed Reuse

Abstract: Magnetite is the most useful seed material for HGMS because of its strong magnetic character and availability. Other oxides like Fe203, Cr203, or MnOa could be used as seeding agents, but these paramagnets are not as easily removed during HGMS as is the case with magnetite. Experiments with both chemically prepared and natural magnetite (Fe304) show an insensitivity to the seed source when using coagulants;1 seed age, hydration, and therefore adsorbability are, however, dependent on origin. Secondary seeding materials may become important in HGMS water treatment. Prior to the coagulation and enmeshment procedure, a specific secondary seed can be injected and subsequently bound to the magnetite. One example described earlier is the use of near-colloidal montmorillonite clay to enhance orthophosphate removal.2 Or a finely powdered activated alumina or activated carbon can be added for a specific adsorption task and enmeshed to the magnetite. It is also possible to short-cut this secondary seeding procedure and make an adsorbent material such as activated carbon

Process for production of magnetite spheres with an arc heater

Abstract: A process for the production of magnetic spheres from grit of magnetite ore by introducing the grit into an arc heated gas jet, thus heating the grit to a temperature of at least 1600° C, and allowing the melted magnetite droplets to spheroidize and cool to a solid state.