Showing papers on "Magnetite published in 1980"
01 Mar 1980
TL;DR: In this article, the formation of iron oxides by aging ferrous hydroxide gels at elevated temperatures was studied as a function of various parameters, including the nature of the anions present in the system.
Abstract: The formation of iron (hydrous) oxides by aging ferrous hydroxide gels at elevated temperatures was studied as a function of various parameters. It was found that the composition and the morphology of the resulting solids depended strongly on the nature of the anions present in the system. Spherical magnetite particles of narrow size distribution, with mean diameters ranging between 0.03 and 1.1 μm, were obtained if FeSO4 was interacted with KOH in the presence of nitrate ion and the resulting gelatinous suspension was kept at 90°C for several hours. The particle size distribution of the magnetite sol was affected by the excess concentration of Fe(II) species in equilibrium with the ferrous hydroxide precipitate. If oxygen was present in addition to nitrate ion, rodlike α-FeOOH particles crystallized along with the magnetite on aging of some ferrous hydroxide gels. A mechanism of the magnetite formation under the conditions of these experiments is offered.
610 citations
TL;DR: In this paper, a well defined hematite and magnetite colloidal particles of different morphologies were prepared by hydrothermal aging of strongly alkaline solutions of ferric salts and triethanolamine (TEA) at 250°C.
173 citations
TL;DR: Very fine particles of magnetite, nickel ferrite, and cobalt ferrite were produced by grinding coarser powders in a ball mill with a carrier fluid and a surfactant.
Abstract: Very fine particles of magnetite, nickel ferrite, and cobalt ferrite were produced by grinding coarser powders in a ball mill with a carrier fluid and a surfactant. The particles were examined by means of chemical analysis, electron microscopy, x-ray diffraction, magnetic measurements, and Mossbauer spectroscopy. Properties were determined before and after removing the surfactant coating. The most significant observation was that in some systems a large fraction of the spins was pinned in extremely high anisotropy fields as a result of bonding to the surfactant molecules. Anomalous magnetic hysteresis behavior was also noted when the surfactant coating was present.
160 citations
TL;DR: In this paper, the role of absorbed moisture in stabilizing Maghemite is investigated, showing that the formation of the latter from Fe3−x O4−x is markedly retarded, and its decomposition to α-Fe2O3 greatly accelerated, under hydrothermal conditions relative to the rates of the corresponding reactions of the dry solids.
Abstract: Maghemite, prepared in the usual way (but with exclusion of silica, eg, from glassware) by precipitation of non-stoichiometric magnetite Fe3−xO4−x in aqueous MOH (M = Na, K) followed by air oxidation, picks up moisture from the air to reach the limiting composition MδH1−δFe5O8, where δ ~ 002–003 for fresh material, but changes under hydrothermal conditions because of ion exchange Despite the role of absorbed moisture in stabilizing maghemite, formation of the latter from Fe3−x O4−x is markedly retarded, and its decomposition to α-Fe2O3 greatly accelerated, under hydrothermal conditions relative to the rates of the corresponding reactions of the dry solids The rate of hydrothermal decomposition of maghemite is strongly retarded by silica Over the range 160–187 °C at least, silica-free maghemite decomposes in water according to the empirical equation −ln (1 − α) = (kt)n, where α is the fractional extent of decomposition, and n ~ 25 for neutral water (with k = 13 × 10−5 s−1 at 160 °C and 31 × 10−5
84 citations
TL;DR: In this paper, the authors investigated the magnetic relaxation spectrum of stoichiometric and vacancy-doped magnetite in the temperature range between 4·2 and 130 K. The observed relaxation processes are classified as short and long-range rearrangements of Fe2+ and Fe3+ ionic states within domain walls.
Abstract: The magnetic relaxation spectrum of stoichiometric and vacancy-doped magnetite has been investigated in the temperature range between 4·2 and 130 K. The observed relaxation processes are classified as short- and long-range rearrangements of Fe2+ and Fe3+ ionic states within domain walls. It is proposed that below 35 K a coherent tunnelling process governs the mobility of electrons, but that above 50 K is replaced by a thermally activated hopping process leading to the Verwey transition at 123 K.
83 citations
TL;DR: The simultaneous diffusion of 52Fe and 59Fe has been measured in Fe3O4 as a function of equilibrium oxygen partial pressure (10−9 ) as mentioned in this paper, where the diffusion is defined as the product of the diffusion of two elements.
81 citations
TL;DR: In this paper, a detailed sampling within layers of massive magnetite indicates that the Cr content frequently shows an extremely rapid but regular depletion with height, with sudden reversals of variable magnitude.
78 citations
73 citations
Journal Article•
64 citations
TL;DR: Mossbauer, ESR and magnetization measurements have been carried out on a basalt glass heat-treated at different temperatures (600, 650, 700, 800 and 900°C for 8 h).
Abstract: Mossbauer, ESR and magnetization measurements have been carried out on a basalt glass heat-treated at different temperatures (600, 650, 700, 800 and 900°C for 8 h). The as-annealed glass and the above five samples showed two-doublet Mossbauer spectra, while the last two samples also showed a six line magnetic hyperfine pattern at 300 K. At 4 K, the last four samples showed magnetic hyperfine patterns, while the as-annealed glass showed that there was already short range magnetic ordering present. High field Mossbauer data at 4 K showed that the surface spins are canted. The minimum quadrupole splitting and the maximum isomer shift around 700°C are related to the improved symmetry of the magnetite lattice. ESR spectra showed paramagnetic resonances at g = 4.3 and g = 2.0 for the first two samples, while the last four samples showed superparamagnetic resonance centred around g = 2.0 at 300 K. At lower temperatures, the 650 and 700°C samples showed ferrimagnetic resonance. Magnetization curves against H/T superpose well both at 300 and 77 K, showing the typical superparamagnetic behaviour of the small magnetite particles. The saturation magnetization (at 270 K) showed a sharp change around 700°C, showing the formation of magnetite. The magnetic structure of the small magnetite particles are discussed in terms of the above results.
TL;DR: In this article, it was shown that significant amounts of oxygen-18 were observed within the inner layer in addition to growth of 18O-rich magnetite at the outer surface.
Abstract: Oxide layers have been grown on Fe-9% Cr, Fe-9% Cr-0.3% Si, and Fe 9% Cr-0.6% Si alloys in carbon dioxide at 853 °K. It is known that such oxides are duplex, the outer layer being magnetite, formed by iron transport. The inner layer is Fe-Cr spinel but little is known about its growth mechanism so this has been investigated using oxygen-18 as a tracer. Oxides were grown first in C16O2 and then in C18O2 and the distribution of oxygen-18 in the scale measured using nuclear techniques. For all the alloys used, significant amounts of oxygen-18 were observed within the inner layer in addition to growth of18O-rich magnetite at the outer surface. The two possibilities of the oxygen-18 being present as a consequence of isotopic exchange or because new oxide had formed within the spinel layer are discussed. Our conclusion is that it is very unlikely that significant isotopic exchange had occurred in any part of the scale, and we deduce that at least a substantial amount of the oxygen-18 in the inner layer was deposited as a result of new oxide formation within that layer. The results also indicate that the location of growth sites within the inner layer differed between the alloys.
TL;DR: In this paper, a series of measurements have been made on dispersions of particles which appear to be pure magnetite with only a non-magnetic gangue-mineral impurity, and the results are not in agreement with either the previously proposed value of the shape factor nor with the properties of mixed particle-sizes.
TL;DR: In this article, the authors propose a mechanism for deep-seated ore formation in which electronic conduction through the magnetite layers in BIF connects a cathodic region near the surface, where oxygen is reduced, to an anode at depth, where iron (II) from magnetite, carbonates and silicates is oxidized and precipitated as iron hydroxyoxides.
Abstract: Very large iron ore deposits have formed in many parts of the world, evidently by the supergene alteration of Precambrian banded-iron formation (BIF). Some of these deposits extend to great depths, ranging to 2,400 m at Krivoyrog1, beyond the likely reach of oxygenated water. We propose here, on the basis of studies in the Hamersley Ranges, Western Australia, a mechanism for deep-seated ore formation in which electronic conduction through the magnetite layers in BIF connects a cathodic region near the surface, where oxygen is reduced, to an anode at depth, where iron (II) from magnetite, carbonates and silicates is oxidized and precipitated as iron (III) hydroxyoxides. The electrical circuit is completed by ionic conduction through groundwaters. The model is based broadly on a mechanism suggested by Sato and Mooney2 to explain self-potentials associted with sulphide ore bodies. It is based more specifically on a model demonstrated by Thornber3 for the weathering of massive nickel–iron sulphide deposits at Kambalda, Western Australia, but with substantial differecnes in the physical situation and the reactions at depth.
TL;DR: The influence of iron oxide additions on coal pyrolysis has been studied by thermogravimetry and the analysis of the evolved gases as mentioned in this paper, showing that the presence of iron oxides reduces the primary devolatilization rate of coal, between 300 and 600 °C.
TL;DR: In this paper, a simple technique was reported for the preparation of Fe 3 O 4 compact electrodes by cold pressing of powdered magnetite admixed with carbon, and the electrochemical behaviour of these compacts was shown to be similar with that of polycrystalline magnetite in respect of their potentiodynamic polarisation response.
TL;DR: In this article, a selection of ashes produced in a Lurgi gasification plant and fly ash from a pulverized coal combustion were analyzed using IRMS and X-ray diffraction methods.
TL;DR: In this article, magnetite crystals were grown hydrothermally for the first time at temperature as low as 250°C, at low pressures of 150-450 atm using formic acid as a good mineraliser and an effective reducing agent.
TL;DR: In this paper, the geology significance of magnetic mineral bearing (generally magnetite bearing) rock units traced out by magnetic surveying is discussed, especially as boundaries of magnetitebearing rock units sometimes do not coincide with boundaries of geologically mapped rock units.
Abstract: Complete magnetic interpretation involves understanding the geological significance of magnetic mineral bearing (generally magnetite bearing) rock units traced out by magnetic surveying ? especially as boundaries of magnetite bearing rock units sometimes do not coincide with boundaries of geologically mapped rock units.
TL;DR: The cathodic reduction of passive film on iron has been investigated by the potentiodynamic and galvanostatic techniques in phosphate-borate buffer solutions of various pH values as mentioned in this paper.
TL;DR: In this paper, the electrochemical response of magnetite to positive potential pulses is investigated in acid solutions and current-controlling factors have been identified as proton diffusion in the crystal matrix and changes in solution pH and the effect on dissolution of the crystal ions.
TL;DR: In this paper, the optical properties of magnetite Fe3O4 were investigated and the authors proposed a method for determining the optical and magnetic properties of the magnetite magnetite.
Abstract: (1980) Optical properties of magnetite Fe3O4 Philosophical Magazine B: Vol 42, No 3, pp 431-432
TL;DR: Paleozoic and Mesozoic-Cenozoic granitoids of the Chilean Andes were studied magnetically in the area between Latitude 22-35•KS.
Abstract: Paleozoic and Mesozoic-Cenozoic granitoids of the Chilean Andes were studied magnetically in the area between Latitude 22-35•KS. The Paleozoic granitoids are found to be composed of the ilmenite-series and weakly magnetic magnetite-series, whereas all the Mesozoic-Cenozoic ones appear to be the magnetite-series. Lack of significant sulfide deposits in the Paleozoic terrains may have been resulted from the reducing nature of the granitic magmatism. Within the magnetite-series terrains of Mesozoic-Cenozoic age, magnetic susceptibility of the granitoids seems to increase continentward. Granitoids related to porphyry copper deposits in the Andean Cordillera have higher magnetic susceptibility than those occurring in the Coast Range which could be genetically associated with manto-type deposits. The different styles of mineralization may possibly be in consequence of the different oxidation status of the granitic magmatism.
TL;DR: In this article, it was concluded that there is not yet a basis in laboratory experiments for inferring that UV photostimulated oxidation of magnetite occurs naturally on the surface of Mars.
Abstract: The kinetics of magnetite oxidation in O2-bearing atmospheres in the presence of electromagnetic radiation was studied. No perceptible oxidation of magnetite by ultraviolet (UV) photostimulation occurred. These results do not corroborate previous conclusions by Huguenin (1973, 1974) as to the occurrence of this process. Therefore, although the possibility that the process actually occurs cannot be ruled out, it is concluded that there is not yet a basis in laboratory experiments for inferring that UV photostimulated oxidation of magnetite occurs naturally on the surface of Mars.
TL;DR: Oxygen isotope fractionation between magnetite and siderite, if produced by an equilibrium reaction, indicates that magnetite formed diagenetically at a temperature not exceeding 65 degrees C as mentioned in this paper.
Abstract: Geology and stable isotope geochemistry of the Devonian ironstones of Wadi Shatti, Libya, suggests that they are shallow water, nonmarine deposits possibly formed in a deltaic environment. The Wadi Shatti occurrence is notable for the presence of magnetite, rarely reported in unmetamorphosed Phanerozoic ironstones, and for the presence of thin coal seams, uncommon in older ironstones.Oxygen isotope fractionation between magnetite and siderite, if produced by an equilibrium reaction, indicates that magnetite formed diagenetically at a temperature not exceeding 65 degrees C. The average delta 18 O of siderite is 18.6 per mil and the maximum delta 18 O is 21.2 per mil vs. SMOW. The minimum delta 18 O of magnetite is --9.7 per mil. These values are best explained in terms of an equilibrium reaction with fresh or brackish water to produce goethite which was later diagenetically altered to produce magnetite and siderite.Variable and extremely low delta 13 C values for Wadi Shatti siderite (-- 12 to -- 30 per mil, vs. PDB) indicate that complex organic reactions were important in the formation of this deposit.
TL;DR: In this article, the orientations of magnetite crystals on an (001) S NaCl substrate by reactive evaporation were examined by electron microscopy and diffraction, and the epitaxial temperature and orientation relationships were compared with those of the metal iron.
TL;DR: The following geochemical rules-of-thumb seem to hold for vanadium: 1) magnetites as a group have higher V contents than either hematites or ilmenites.
Patent•
27 Mar 1980
TL;DR: A biologically pure culture of a bacterium of the genus Aquaspirillum, designated MS-1, has been found to contain chains (so-called magnetosomes) of single domain magnetite particles as discussed by the authors.
Abstract: A biologically pure culture of a bacterium of the genus Aquaspirillum, designated MS-1, has been found to contain chains (so-called magnetosomes) of single domain magnetite particles. The magnetite particles are roughly cubic and are about 500 A on a side and each of the chains contains approximately 290 magnetite particles. These magnetite particles can be recovered from the bacterium and usefully employed in magnetic recording devices and the like.