Showing papers on "Magnetite published in 1972"

Magnetic Mineralogy of Unheated and Heated Red Sediments by Coercivity Spectrum Analysis

Abstract: Summary A method of deriving the remanent coercivity spectrum from the isothermal remanence vs. applied field characteristic is described and applied to a series of Triassic sandstones and late Cretaceous–early Tertiary clays and limestones from France. Low- (0-1 kOe), intermediate- (1-3 kOe), and high- (3-18 kOe) coercivity remanence fractions are identified with magnetite, specularite, and haematite pigment respectively. In the limestones, specularite is the only important magnetic phase; the sandstones contain in addition considerable pigment; and the clays contain all three phases. The relative pigment content indicated magnetically agrees with the colour of each rock type. When the sandstones are heated in air, enough magnetite is produced below 675°C to account for 20-25 per cent of the saturation remanence. Secondary magnetite production may therefore be serious when red beds are thermally demagnetized, even though the heating is done in air. The source of this secondary magnetite seems to be a non-magnetic mineral, rather than haematite. Secondary haematite production is insignificant below 675°C, but the pigment coercivity spectrum becomes harder with annealing, as observed previously with synthetic fine-particle haematites. Either annealing-out of defect ferromagnetism or impurities entering the haematite lattice could explain the results. Either coercivity spectra or rotational hysteresis curves can be used to estimate pigment/specularite ratios in red beds and to monitor mineralogical changes resulting from heating, but the coercivity spectrum method is much simpler to use.

Magnetite: Behavior near the Single-Domain Threshold.

Abstract: Maximum values for the single-domain threshold d(0) and superpara-magnetic threshold d(8) in pure magnetite are found to be 570+/-50 and 350+/-50 angstroms, respectively. Particles larger than do but smaller than about 0.25 micron have size-dependent saturation remanences and coercive forces like those of multidomain particles, but intense and stable thermoremanent magnetization like that of single-domain particles. The presence of magnetite grains in this size range could account for the essentially single-domain character of stable natural remanence in many volcanic and intrusive rocks.

Magnetic and mineralogical changes associated with low-temperature oxidation of magnetite

Abstract: An excited oxygen gas has been used to oxidize pure magnetite at temperatures between 50°C and 200°C. The oxidation products are either maghemite or hematite, depending on the water content of the initial material. In all cases the intensity of remanent magnetization, ARM or TRM, is reduced on oxidation with only small changes in the microscopic coercive force spectra. A chemical remanent magnetization, which is relatively weak with respect to the initial remanence, is always acquired during oxidation. These results are useful in the interpretation of intensity changes in some linear magnetic anomalies of ocean floors and in the interpretation of changes in direction and intensity of remanence in land outcrops that have undergone low-temperature oxidation.

Impurity Effects on the Transition Temperature of Magnetite

Abstract: Influence of oxidization and various impurities on the transition temperature of the Verwey order in magnetite was studied experimentally. A small amount of impurities such as Li, Ni, Co, Cr, Al, Ti, Mg, Zn and Ga was doped and the transition temperature was determined by magnetic measurement. The decreases of the transition temperature of the specimens doped with the impurities are not simply related to the amount of the ferrous ions on the B sites but become larger as the ionic configurations deviate from the stoichiometric one. Oxidation of magnetite also decreases the transition temperature and this effect is smaller for the specimens sintered at lower temperature. For the Ga-doped specimens, the concentration dependence of the transition point is found to show a sharp change at a small (0.3%) Ga concentration.

Magnetite and Ilmenite in the Sudbury Nickel Irruptive

Abstract: Magnetite and ilmenite occur throughout the Sudbury Nickel Irruptive. The magnetite almost invariably contains oriented lamellae of ilmenite and the ilmenite often contains lamellae of oxide magnetite and/or hematite. The upper and oxide-rich gabbros and the micropegmatite contain between 1 and 10 percent oxide minerals with magnetite far in excess of ilmenite. The felsic and south range norites contain 0.1 to 2 percent oxide minerals with ilmenite in excess of magnetite. The mafic norite, a unit developed intermittently around the perimeter of the north range of the intrusion, contains 0.5 to 1 percent oxide (largely magnetite) while the quartz-rich norite, developed continuously along the margin of the south range, contains the same amount of oxide, largely ilmenite.Electron microprobe data on magnetite, coupled with estimates of the proportion of ilmenite lamellae developed within grains, indicates that magnetite from the upper levels of the Irruptive was very much richer in titanium at the time of its crystallization than that from lower levels. Chromium shows the reverse trend. Magnetite from the upper part of the mafic norite contains 8 to 13 percent Cr 2 O 3 but this decreases rapidly to less than 2 percent across the 10-50 ft transition zone between the mafic and over-lying felsic norite and then falls more gradually to less than 0.1 percent in the micro-pegmatite. Magnetite from the upper part of the quartz-rich norite and lower south range norite is also rich in Cr 2 O 3 (3-5 wt %) and this decreases upwards to less than 1.5 percent halfway up this unit. These variations in magnetite composition support previous evidence (Naldrett et al., 1970) of cryptic variation in the Irruptive.The final partitioning of iron and titanium between magnetite and ilmenite occurred at high ( nearly equal 900 degrees C) temperatures on the north range and much lower (<600 degrees C) temperatures on the south range, indicating a very different cooling history for the two ranges. This is consistent with the hypothesis that the Irruptive is funnel shaped and that the south range is a section through a deeper, thicker portion of the funnel.

Magnetite thin films

Abstract: A low temperature process for converting hematite (α-Fe 2 O 3 ) thin films into magnetite (Fe 3 O 4 is described. The films produced are unambiguously identified as magnetite by several complementary methods of analysis. These include α-backscattering spectrography, X-ray powder diffractometry, and observations of electrical, magnetic, and optical properties.

Artificial meteor ablation studies: Iron oxides

Abstract: Artificial meteor ablation was performed on natural minerals composed predominantly of magnetite and hematite by using an arc-heated plasma stream of air. Analysis indicates that most of the ablated debris was composed of two or more minerals. Wustite, a metastable mineral, was found to occur as a common product. The 'magnetite' sample, which was 80% magnetite, 14% hematite, 4% apatite, and 2% quartz, yielded ablated products consisting of more than 12 different minerals. Magnetite occurred in 91% of the specimens examined, hematite in 16%, and wustite in 30%. The 'hematite' sample, which was 96% hematite and 3% quartz, yielded ablated products consisting of more than 13 different minerals. Hematite occurred in 47% of the specimens examined, magnetite in 60%, and wustite in 28%. The more volatile elements (Si, P, and Cl) were depleted by about 50%. This study has shown that artificially created ablation products from iron oxides exhibit unique properties that can be used for identification.

Method of making magnetically-anisotropic permanent magnets

Abstract: A method of making a permanent magnet of the hard ferrite type having a formula [SrO.6 Fe2O3] SrO.6Fe 2O3 is disclosed. The process comprises the critical step of adding a compound selected from the group consisting of boric acid and boric oxide to magnetite and a source of SrO during the mixing [a] and milling step prior to calcining of the mixture. Superior magnets are produced over those achieved by the process where the boric acid or boric oxide is introduced after calcining of magnetite and a source of SrO.

Iron-titanium oxide minerals in the Upper Layered Series, Kap Edvard Holm, East Greenland

Abstract: Electron-probe data are presented for coexisting magnetite and ilmenite from seven gabbro cumulates and a gabbro pegmatite, and bulk FeO-Fe2O3-TiO2 analyses for ten magnetite-ilmenite assemblages. The oxides equilibrated at 580 to 720 °C and oxygen fugacities of 10−15·0 to 10−20·5 bar. Late-stage alteration, associated with growth of hydrothermal silicates, resulted in the breakdown of ilmenite to rutile and the dissolution of magnetite. Higher levels in the intrusion equilibrated at lower temperatures than deeper levels. All features described are consistent with the retention of the initial water content of the magma within the walls of the intrusion.

Method of forming magnetite thin film

Abstract: A magnetite film is produced by depositing a thin film of pure iron on a substrate, oxidizing the film, depositing a second film of iron on the iron oxide film, and annealing the composite film at a temperature below about 560*C and preferably from 350*C to 400*C and then stripping excess iron from the film.

Method of producing solid solutions of magnetic oxides

Abstract: A solid solution of oxides of iron and of another divalent metal such as cobalt, more particularly for use in the manufacture of magnetic tapes and like magnetic carriers, is obtained first by preparing a mixed oxalate by co-precipitation of a solution of ammonium oxalate and of a solution containing Fe3 ions together with ions of the divalent metal, second by heating the mixed oxalate in air to decompose same while eliminating most of the carbon therefrom; third by heating the decomposed product in a wet hydrogen atmosphere to produce a substituted magnetic substantially free from residual carbon; and fourth by heating in air this substituted magnetite to oxidize same. The solid solution obtained corresponds to the formal ( gamma - Fe2O3)1 y (CoFe2O4)y in which y is comprised between zero and unity.

Method of improving the magnetic properties of cobalt substituted magnetite

Abstract: A method of improving the magnetic properties of cobalt substituted magnetite by magnetizing the material to the saturation level in the desired direction, and then removing the magnetizing field. The material will retain a level of magnetization normally referred to as the remanent state of magnetization or simply remanence. The magnetized material is then subjected to a heat treatment to anneal the material. The above process significantly improves coercivity, hysteresis loop squareness ratio, and resistance to remanence loss due to external forces.

Method of increasing the coercivity of magnetite films

Abstract: A method of increasing the coercivity of a magnetic device having a magnetite film reduced from alpha ferric oxide. The alpha ferric oxide film is reduced to magnetite by subjecting it to a temperature greater than 400° C in a reducing atmosphere. The temperature of the film is then changed to between about 150° and 300° C, and the reducing atmosphere is replaced by an oxidizing atmosphere. The film is subjected to the oxidizing atmosphere while the temperature is held between 150° and 300° C, thus causing the magnetite film to become partially oxidized to form a solid solution of magnetite and gamma ferric oxide as represented by the formula, (1-x)Fe 3 O 4 .sup.. xFe 2 O 3 , where x is between 0.49 and 0.85.

Magnetite coating composition

Abstract: A MAGNETITE COATING COMPOSITION BY REACTING AN AQUEOUS SOLUTION OF FERRIC AND FERROUS SALTS WITH AMMONIUM HYDRROXIDE, HEAING THE RESULTING PRODUCT TO CONVERT IT T MAGNETITE, ADDING A SICCATIVE OIL TO PRODUCE A DISPERSION OF MAGNETITE I OIL AND ADDING A SOLVENT THINNER TO PRODUCE A COATING COMPOSITION SUITABLE AS A PAINT OR A PRINTING INK.

Magnetic susceptibility and magnetite content [discussion]

Abstract: For reference to original paper by Balsley and Buddington, see Econ. Geol., Vol. 53, p. 777, 1958

Improvements in or relating to electric storage heaters

Abstract: 1,262,465 Storage heaters ELECTRICITY COUNCIL 22 Oct, 1969 [30 Oct, 1968], No 51481/68 Heading F4U The core of an electric storage heater comprises blocks formed of sintered particles of ferric oxide The blocks may be formed by compressing finely divided iron oxide, eg magnetite or haematite, and then sintering in air for oxidization at a temperature above 1000‹ C, or the iron oxide may be ferric oxide