Showing papers on "Magnetite published in 1977"

The Magnetite-series and Ilmenite-series Granitic Rocks

Abstract: Opaque minerals of common granitic rocks were studied microscopically. The granitoids were divided into (i) a magnetite-bearing magnetite-series and (ii) a magnetite-free ilmenite-series. Each series has the following characteristic assemblages of accessary minerals: Magnetite-series: Magnetite (0.1-2 vol.%), ilmenite, hematite, pyrite, sphene, epidote, high ferric/ferrous (and high Mg/Fe) biotite; Ilmenite-series: Ilmenite (less than 0.1 vol.%), pyrrhotite, graphite, muscovite, low ferric/ferrous (and low Mg/Fe) biotite. The mineral assemblages imply a higher oxygen fugacity in the magnetite-series granitoids than in the ilmeniteseries granitoids during solidification of the granitic magmas. The boundary separating the two series is probably near the Ni-NiO buffer. The magnetite-series granitoids are considered to have been generated in a deep level (upper mantle and lowest crust) and not to have interacted with C-bearing materials; whereas the ilmenite-series granitoids were generated in the middle to lower continental crust and mixed with C-bearing metamorphic and sedimentary rocks at various stages in their igneous history. The former carries porphyry copper-molybdenum deposits and the latter accompanies greisen-type tin-wolframite deposits. Lack of porphyry copper deposits in the Mesozoic orogeny belts in East Asia is related to a general paucity of the magnetite-series granitoids in this terrane.

Magnetic susceptibility of the soil and its significance in soil science – a review

Abstract: Summary The magnetic susceptibility of soil minerals is discussed, and in particular that of the ferrimagnetic minerals, maghemite, magnetite, and the titanomagnetites since one or more of these usually dominates soil magnetic properties. The magnetic susceptibility of soil depends on the shape, size, and concentration of these minerals as well as on the method of measurement. Measurements performed in a weak alternating magnetic field are the most reliable. The identification, formation, and occurrence of soil maghemite is considered in detail since it is usually of pedogenic origin and occurs in (magnetically) detectable amounts in most soils. Moderate concentrations (>1 per cent) of magnetite or titanomagnetite in soils may be accurately measured if some of the material is first magnetically separated and its susceptibility determined. An example is given of the use of susceptibility measurements. Pedogenic maghemite may be determined in soils developed from parent materials of low susceptibility. A very rough value of 8.8 × 10−4 m3 kg−1 is suggested for the mass susceptibility of such maghemite (excluding magnetic concretions). Although susceptibility has been suggested as an indicator of soil forming processes, this is only possible within an area containing fairly uniform parent material.

Geothermometry and Oxygen Barometry Using Coexisting Iron-Titanium Oxides: A Reappraisal

Abstract: Equilibrium thermodynamic methods are used to develop an independent iron-titanium oxide geothermometer and oxygen barometer from the experimental data of Buddington and Lindsley (1964). The geothermometer and oxygen barometer are presented graphically for coexisting ilmenite solid solution and magnetite solid solution in the system FeO-Fe2O3-TiO2. Equations are also given for calculating temperature and oxygen activity for natural coexisting iron-titanium oxides containing other components. Large departures in composition from the system FeO-Fe2O3-TiO3 result in large uncertainties in the calculated temperature and activity of oxygen.

The Viking Magnetic Properties Experiment: Primary mission results

Abstract: Three permanent magnet arrays were mounted on each Viking lander: a strong array fixed on a photometric reference test chart on top of the landers; and two arrays, one strong and one weak, incorporated into the backhoe of the surface sampler. Some or all of the magnetic particles detected could be highly magnetic unoxidized mineral grains (metallic Fe, magnetite, pyrrhotite) forming the core beneath a reddish coating of limonite or hematite; or grains composed of gamma-Fe2O3, with and without other iron oxides; or igneous rock (or mineral particles) which consist of an admixture of unweathered silicate material or minerals with a significant fraction of highly magnetic phase, again with a reddish coating; they could be also igneous rock or mineral particles, intrinsically nonmagnetic, but having a reddish coating containing gamma-Fe2O3; or clay mineral particles which contain and/or are coated with Fe2O3, of which a substantial fraction is in the gamma-Fe2O3 form.

Thickness of the oxide layers formed during the oxidation of iron

Abstract: The theory of the growth of two oxide layers by Yurek et al. has been applied to the oxidation of iron at 1100° C. The theoretical parabolic rate constants for the simultaneous growth of the two oxide layers were calculated from radioactive tracer diffusion coefficients for wustite and magnetite. Good agreement was found between the theoretical and experimental values of the ratio of scale thicknesses.

High voltage microscopy of the reduction of hematite to magnetite

Abstract: The microstructural changes associated with the formation of magnetite in hematite have been studied in specimens which have been partially reduced outside the microscope, thinned until electron transparent, and then examined in the normal way. Three types of structure have been observed in varying proportions which depend on the reduction temperature. At low temperatures, magnetite grows by the propagation of a cellular interface, the gas phase being transported to the cell boundary by a network of tunnels. At intermediate temperatures, magnetite plates are formed, whereas at high temperatures, both plate magnetite and blocky magnetite appear. It is proposed that the factor controlling the morphology which develops is the ratio of the cell boundary diffusivity to volume diffusivity of ferrous ions. It is noted that the decomposition morphologies of hematite and austenite have many similarities. The basic reason for this similarity is that both transformations involve substantial redistribution of elements in the solid state and the microstructures which develop are those that perform this redistribution the most efficiently at the temperatures involved.

Magnetite to maghemite transformation in ultrafine particles

Abstract: The conversion of magnetite to maghemite has been studied kinetically in the ultrafine particle range (77-220A) by chemical analysis. X-ray diffraction, and Mossbauer measurements. The reaction is third order. The activation temperatures are relatively low (8 250-1 1 200 K). Electron hopping in ultrafine magnetite powders is discussed on the basis of the results.

Simulation of long-term changes in the magnetic signal of the oceanic crust

Abstract: We report magnetic properties of submarine basalts 3.5 to 16 Ma in age recovered from depths as great as 530 m in layer 2 near the Mid-Atlantic Ridge at 37° N during Leg 37 of the Deep Sea Drilling Project. The rocks are classified as type-I if they have reversible in-vacuum thermomagnetic curves and as type-Il if they are thermomagnetically irreversible and develop a high-Curie-point phase (believed to be magnetite) when heated. Initial Curie points are low: 140–200 °C in type-I rocks, 250–300 °C in type-II rocks. The phases responsible are thought to be stoichiometric and cation-deficient (oxidized) titanomagnetite, Fe2.4Ti0.6O4, respectively. Only the 3.5 Ma basalts contain any type-I material; the older basalts are completely oxidized.Viscous magnetization is uniformly strong in type-I rocks, weaker and variable in type-II rocks. Hysteresis properties explain this difference. It is not due primarily to the chemical difference between stoichiometric and oxidized titanomagnetites, but to a difference in...

Compositions and Thermodynamics of Metamorphic Solutions

Abstract: The composition of the supercritical fluid phase which is in equilibrium with metamorphic or igneous mineral assemblages can be assessed either through fluid inclusion studies (Touret, 1971; Roedder, 1972; Poty et al 1974), or by considering the nature and composition of the minerals themselves. In this review we restrict ourselves to the latter approach. It is based on a combination of buffer and exchange reactions and fugacity indicators in conjunction with laboratory calibrations. A simple buffer reaction is a reaction between a group of solids and a single gas species. When all participants in the reaction are present, the chemical potential of the gas species remains constant at a given P and T, regardless of any changes in bulk composition, provided the compositions of the solids remain constant. Hematite + magnetite, quartz + calcite + wollastonite, gypsum + anhydrite, pyrite + pyrrhotite, are commonly occurring buffers for oxygen, CO2, H2O and S2 respectively.

A Method of Tracing the Temperature and Oxygen-Fugacity Histories of Complex Magnetite-Ilmenite Grains

Abstract: The formation of ilmenite from titanomagnetite frequently shows separate generations of production. The ilmenite products can be combined with the magnetite host to represent the intermediate stages in this development. Use of the Buddington and Lindsley (1964) geothermometer in conjunction with this method provides a number of points in the temperature and oxygen-fugacity history of a single, complex magnetiteilmenite grain. Application of the method is illustrated by an example from the Freetown layered gabbro. A titanomagnetite exsolved granular ilmenite whilst cooling and this process ceased at 930° and an oxygen fugacity of log ƒ O2 = −11·5. Further cooling and exsolution continued until the grain reached 662 °C and log ƒ O2 = −19·0, producing distinct ilmenite lamellae.

Silica-bearing magnetites

Abstract: Some varieties of magnetite with relatively high content of SiO2 (about 5,4%) were found by the authors Silica-bearing magnetite of the Korshunovskoye scarn deposit is enriched in Ca (up to 199% CaO), Al, Mg, Ti In serpentinites of the Atlantic and Indian oceans Si-magnetite forms pseudomorphs on Cr-spinel and includes impurities of Mn (to 35% MnO), Cr, Mg and Al Distinct quantitative correlations of silica and other trace elements are observed The authors suggest possible models of cation distribution in Si-magnetites and suppose that emplacement of silica into the magnetite crystal structure is due to the presence of chlorine in mineral-forming solutions

Optical Measurements on Magnetite

Abstract: The optical transmission of powdered single crystals of magnetite was measured in the spectral range from 200 to 4000 ${\mathrm{cm}}^{\ensuremath{-}1}$ at temperatures between 77 and 300 K. The measurements are compared with those on Ti-substituted magnetite. The spectrum of pure magnetite shows drastic changes at the Verwey transition. In the low-temperature phase, a small splitting up of the two high-temperature phonon bands is observed.

Effect of magnetic field on reduction of iron oxides: magnetite and wüstite

Abstract: A STRONG magnetic field (500–1,400 Oe) was reported by Skorski1 to cause an increase in the reduction rate of haematite (Fe2O3) to metallic iron when H2 was used as the reducing agent. This effect was attributed to the magnetic properties of the H2, because neither CH4 nor CO produced a similar increase when under the influence of a strong magnetic field. Although Svare2 disputed this explanation, Peters3 offered an alternative one, based on thermodynamics, which indicated that an increase in reaction rate is expected under the influence of a strong magnetic field when the reactants were relatively non-magnetic and the products were strongly magnetic—as with reduction of haematite to iron. We report here our results of studying magnetite and wustite reduction to iron, which show an increased reduction rate for magnetite, under the influence of a strong magnetic field, but an inexplicably decreased rate for the wustite reduction.

Reduction of Hematite to Magnetite under Natural and Laboratory Conditions

Abstract: Thermomagnetic analysis of natural and synthetic samples containing hematite have confirmed Schwarz’S (1969) observations that 1) extensive reduction of hematite occurs when the experiment is perfomed in vacuum but not when it is performed in air 2) the reduction is arrested when the sample is heated in air before the vacuum run. In addition, we have found that the reduction is controlled by backstreaming vacuum pump oils, which buffer the atmosphere in the furnace region, but is not dependent upon reducing agents within the samples. Heating of the sample creates a surface layer which is not permeable to the reducing atmosphere and which thus prevents reduction during subsequent heatings. X-ray diffraction data from reduced synthetic hematite shows that the reduced phase is magnetite. Reducing agents within samples can contribute to reduction, and in some cases are so important that reduction may occur in air. Reduction produces undesirable effects during thermal demagnetization procedures and paleointensity determinations on samples containing hematite, but these effects can be eliminated or controlled if certain precautions are followed.

Green function theory of electron correlations above and below the Verwey transition in magnetite doped with impurities

Abstract: The electron correlation effects in magnetite doped with impurities (MexFe3-xO4 with Me = Zn, Ni, Co, Ti, Sn, Li, Cr, Mg, Al, B-site vacancy) are studied on the basis of a Hamiltonian which describes the electron-electron and the electron-impurity interactions and is an extension of the Cullen-Callen model of magnetite. Treating this model in the case of low impurity concentrations x by means of a cluster approximation for Green functions the temperature dependence of the charge density oscillations around an isolated impurity and the Verwey transition temperature Tv(x) are calculated. The theoretical results for Tv(x) agree well with experiments except for titanium-substituted magnetite. For this ferrite the theory predicts an increase of Tv(x) with increasing x which represents a combined electron correlation and lattice structure effect.

Glass-ceramics with magnetic surface films

Abstract: The instant invention relates to the production of glass-ceramic articles, wherein the predominant crystal phase is beta-quartz solid solution and/or beta-spodumene solid solution, but which have a thin, integral, tightly-bonded surface film containing crystals exhibiting the structure of magnetite. The preferred method of production for such articles requires three general steps. First, a glass article having a particular composition within the Li 2 O--FeO--Al 2 O 3 --SiO 2 field nucleated with TiO 2 is heat treated in air or other oxidizing atmosphere to yield a glass-ceramic article through the crystallization in situ of beta-quartz solid solution and/or beta-spodumene solid solution crystals. Simultaneously during this heat treatment, a surface layer containing hematite is developed. Second, the glass-ceramic article is subjected to a hot acid bath. Third, the acid-washed article is heat treated in a H 2 O-containing reducing atmosphere to convert the hematite crystals to magnetite. The resulting films demonstrate high coercive forces and saturation magnetization comparable to that of magnetite and other ceramic ferrite materials.

Single Domain Oxide Particles as a Source of Thermoremanent Magnetization

Abstract: Single domain (SD) particles have long been suggested as a potentially strong and stable source for the paleomagnetic signal, but their actual occurrence in rocks has been much questioned. Two possible modes of occurrence of SD Fe-Ti oxides can be distinguished. These are as magnetite rods bounded by ilmenite lamellae in intergrown grains (analogous to Alnico permanent magnet alloys), and as isolated ultrafine particles, perhaps representing part of a much broader grain-size distribution (analogous to the oxide coatings used in tape recording). The evidence for the presence in rocks of these two types of magnetic particle is reviewed. Where intergrown grains are present the SD ‘Alnico model’ seems to be valid, and where isolated titanomagnetite grains are involved the SD ‘tape-recorder model’ is satisfactory. Where pure Fe3O4 particles are involved the situation is less clear, and current thinking stresses the role of the so-called pseudo-single domain (PSD) moments.

Thermomagnetic analysis of natural and synthetic hematite

Abstract: Thermomagnetic analysis of natural and synthetic samples containing hematite have confirmed Schwarz's (1969) observations that 1.) extensive reduction of hematite to magnetite occurs when the experiment is performed in vacuum but not when it is performed in air 2.) the reduction is arrested when the sample is heated in air before the vacuum run. In addition, we have found that the reduction is controlled by back-streaming vacuum pump oils, which buffer the atmosphere in the furnace region, but is not dependent upon reducing agents within the samples. Heating of the sample creates a surface layer which is not permeable to the reducing atmosphere and which thus prevents reduction during subsequent heatings. Unusually high Curie temperatures (610°C) of the reduced phase from synthetic hematite samples may be caused by internal stress in the magnetite which coats the hematite grains.

Process for treating acicular magnetite containing co to stabilize the magnetic properties thereof

Abstract: A process for treating acicular magnetite containing Co to stabilize the magnetic properties thereof comprises the steps of heating acicular magnetite containing 0.1 to 2.5% by atom of Co with respect to Fe as starting material at a temperature in the range of 300 - 1000° C in an inert gas atmosphere in which the partial pressure of oxygen is controlled at a value in the range of 0.001 - 1% by weight and for the time sufficient to homogenize the crystal structure of the acicular magnetite by thermal-diffusion of oxygen thereinto, and thereafter saturating the resultant acicular magnetite with oxygen by heating it at a temperature in the range of 40 - 100° C in an oxygen rich atmosphere such as air.

The Verwey Transition in Magnetite

Abstract: We will first review the characteristics of the Verwey transition in magnetite at 123 K. An ordering takes place among Fe2+ and Fe3+ ions on the octahedral sites of the inverse spinel structure, accompanied by a sudden change of electrical resistivity. We shall discuss in some detail recent neutron scattering measurements at Brookhaven in collaboration with Chikazumi’s group at the University of Tokyo.

Mössbauer Study of the Low Temperature Phase of Magnetite (Fe 3 O 4 )

Abstract: Mossbauer spectra of the low temperature phase of single crystal magnetite(Fe 3 O 4 ) have been measured with changing the direction of the applied magnetic field with respect to the crystal axes. Data were analyzed taking into account the relative orientation of the hyperfine magnetic field to the principal axes of the electric field gradient tensor. Consequently details of the electric field gradient of one B site ion were clarified.

Influence of Hydrogen Carbonate and Chloride Ions on the Stability of Oxide Films on Mild Steel in Near-Neutral Solutions

Abstract: In near-neutral solutions, mild steel can be protected by two different passivating films, a ferric oxide film stable at more positive potentials and a magnetite film stable at more negative potentials. In air-saturated solutions of hydrogen carbonate ions at 25°c, as the concentration is increased in the range up to 1O−2 M, the ferric oxide film on steel becomes less stable at its Flade potential; in the range 10−2 to 10−l M, the ferric oxide film increases in stability at its Flade potential until eventually its breakdown is suppressed and at 10−1 M and above, corrosion inhibition occurs. However, inhibition may be unstable, since the stability of the magnetite film at its Flade potential decreases with increasing hydrogen carbonate concentration. In the presence of chloride ions, critical breakdown potentials are observed for both the ferric oxide and the magnetite passivaiing films, but the magnetite film is much more stable than the ferric oxide film. The inhibition of corrosion of steel in a...

Magnetic toner particle coating process

Abstract: A method of coating magnetic toner particles such as magnetite with a fatty acid or a derivative of a fatty acid is disclosed. The magnetite particles coated by this process are found to be particularly suitable for use in formation of field dependent toners that are not humidity sensitive.

Composite magnetic adsorbent for uranium

Abstract: PURPOSE: An adsorbent comprising magnetic fine particles as nuclei and uranium adsorbent deposited over the surface of the fine particles, which is capable of easily separating and grasping uranium (U) from the sea water or an U-containing solution and also is easily recoverable after separating U adsorbed. CONSTITUTION: Average grain size of approx. 0.01 to 5 micron of fine magnetic particles, e.g., magnetite, gamma-Fe 2 O 3 , and other ferromagnetic ferrites are dispersed by an ultrasonic wave irradiation in distilled water, ad then the fine magnetic particles suspension is mixed with stirring by the addition of an aqueous solution of one or several species of meral salts as adsorbents, e.g., titanium sulfate, TiCl 4 , MgCO 3 , MnSO 4 , etc. In this case, the metal salt is added in a mixing ratio of approx. 0.5 to 5 in terms of metal on the basis of the fine magnetic particles. Subsequently, hydrolysis after pH regulation and other usual precipitation operation, etc. are made to deposit them on the surfaces of the fine magnetic particles. These particles are separated by an appropriate magnetic separator, washed, and then dried. COPYRIGHT: (C)1979,JPO&Japio