Showing papers on "Magnetite published in 1969"
TL;DR: In this paper, it was shown that the fast electron hopping process in magnetite is essentially a pair-localized phenomenon, with the non-paired octahedral Fe 3+ ions not participating in the hopping process.
175 citations
TL;DR: In this paper, the Curie point and saturation moment of the feldspar indicate the presence of about 0.3 percent Fe ion in solid solution and 0.004 percent pure magnetite as a discrete phase.
Abstract: Measurement of natural, thermal, and saturation remanent magnetism and their stability with respect to alternating field and thermal demagnetization of concentrates of plagioclase, pyroxene, and oxide (80 percent ilmenite, 20 percent magnetite) separated from a sample of diabase from the Triassic Lambertville (N. J.) sill, reveal that the stable remanence of the whole rock is associated with the silicates and especially with the plagioclase. Measurement of Curie point and saturation moment of the feldspar indicates the presence of about 0.3 percent Fe ion in solid solution and 0.004 percent pure magnetite as a discrete phase. This magnetite cannot be identified microscopically, nor with an electron probe, and it is inferred to be present as submicroscopic, single domain particles.
90 citations
84 citations
TL;DR: In this paper, it was shown that magnetite inclusions contribute significantly to the TRM and may, in fact, account for virtually all of the remanence in igneous rocks.
Abstract: Experiments designed to elucidate the nature and source of high-stability remanence in igneous rocks have been carried out. Many of the pyroxene grains of the samples used (from the Modipe gabbro of southern Africa) contain small (from a few microns down to the optical limit) magnetite inclusions, some of which are very probably single-domained by virtue of their size and shape. It is shown that these inclusions contribute significantly to the TRM, and may, in fact, account for virtually all of the remanence. Measured coercivities as high as 1800 œ are attributed to the observed shape anisotropy of some of the magnetite inclusions. A discussion of the various theories of coercive force indicates that this is the only mechanism which enables magnetite to possess coercivities in excess of 1000 oersteds.The conclusions reached can be strictly applied only to this particular rock; however, it is felt that the natural occurrence of single-domained magnetite is more common than previously supposed. The reason for the comparative rarity of similar observations may well be the minute size and very small total quantity of magnetite necessary to account for typical TRM's in igneous rocks.
81 citations
69 citations
65 citations
52 citations
TL;DR: In this paper, a Zener double exchange model is formulated for magnetite and is used to describe the electron-hopping process, and the main consequence of this model is that the electrons participating in the hopping process in any imperfect or nonstoichiometric (i.e. real) sample of magnetite can be regarded as being essentially localized to hopping within particular (Fe2+−Fe3+) octahedral cation pairs, and not as being in either some form of 3D conduction band or as participating in a nonlocalized electron-transfer process.
Abstract: A Zener double-exchange model is formulated for magnetite and is used to describe the electron-hopping process. The main consequence of this model is that the electrons participating in the hopping process in any imperfect or nonstoichiometric (i.e. real) sample of magnetite can be regarded as being essentially localized to hopping within particular (Fe2+–Fe3+) octahedral cation pairs, and not as being in either some form of 3d conduction band or as participating in a nonlocalized electron-transfer process. Well-known results on the electrical conductivity, and new results with the Mossbauer effect in magnetite are then explained in terms of this pair-localized electron-hopping model.
36 citations
Patent•
04 Feb 1969TL;DR: In this article, the authors discuss the MANUFACTURE of GLASSCERAMIC ARTICLES, where MAGNETITE CRYSTALS ALONE or in COMBINATION with CLINOPYROXENE CRYstals CONSTITUTE SUBSTANTIALLY all of the CRY STALS PRESENT, by meling NATURALLYOCCURRING BASALTS under OXIDIZING CONDITIONS, COOLING the MOLTEN BASALT TO A GLASS, and then heating TREATING the
Abstract: THIS INVENTION RELATES TO THE MANUFACTURE OF GLASSCERAMIC ARTICLES, WHEREIN MAGNETITE CRYSTALS ALONE OR IN COMBINATION WITH CLINOPYROXENE CRYSTALS CONSTITUTE SUBSTANTIALLY ALL OF THE CRYSTALS PRESENT, BY MELTING NATURALLYOCCURRING BASALTS UNDER OXIDIZING CONDITIONS, COOLING THE MOLTEN BASALT TO A GLASS, AND THEN HEAT TREATING THE GLASS UNDER NON-REDUCING CONDITIONS TO C RYSTALLIZE IN SITU UNIFORMLY FINE-GRAINED CRYSTALS OF MAGNETITE WITH OR WITHOUT CLINOPYROXENE HOMOGENEOUSLY DISPERSED IN A GLASSY MATRIX.
31 citations
TL;DR: In this article, a series of experiments were described in which single crystals of magnetite were annealed under controlled conditions, and structural changes in the magnetite are identified by comparing their activation energies as estimated from the annealing curves with those of known physical processes.
Abstract: A series of experiments is described in which single crystals of magnetite were annealed under controlled conditions. Structural changes in the magnetite were followed by changes in the magnitudes of coercive force and saturation isothermal remanent magnetization. The structural changes were identified by comparing their activation energies as estimated from the annealing curves with those of known physical processes. It seems likely that relaxation of an induced anisotropy by vacancy-assisted cation migration (with activation energy 1–1.5 ev) took place at temperatures well below the Curie temperature. This unstable feature poses a serious problem for certain methods of estimating the paleointensity of the geomagnetic field. A further structural change, which appeared to be thermally activated self-diffusion of dislocations (with activation energy around 6 ev) was apparent at higher temperatures, well above the Curie temperature. Associated with this structural change were pronounced changes in the alternating-field demagnetization curves of both isothermal and thermoremanent magnetizations in the magnetite. Changes in the Curie temperature were observed to accompany both high- and low-temperature effects.
28 citations
TL;DR: The outer rim of the Bucks batholith in northern California consists of a hornblende-biotite quartz diorite that contains both a reversely magnetized ilmenohematite (5 to 10 mol % ilmenite in solid solution with hematite) and a normally magnetized magnetite as mentioned in this paper.
Abstract: The outer rim of the Bucks batholith in northern California consists of a hornblende-biotite quartz diorite that contains both a reversely magnetized ilmenohematite (5 to 10 mol % ilmenite in solid solution with hematite) and a normally magnetized magnetite It is argued that the ilmenohematite has self-reversed in some manner that is not reproducible in the laboratory The mechanism for this self-reversal probably involves a negative exchange interaction between a Ti ordered phase and a Ti disordered phase
TL;DR: In this article, the authors extracted black magnetic spherules, 30-150 μ in dia, extracted from crushed indochinites and other tektites, as well as magnetic fractions of various impact glasses were polished and studied under the reflecting microscope and by the electron microprobe.
TL;DR: In this paper, the same elements were probably removed from granitic gneisses, forming alaskites, and Hornblende granite formed where these fluids were added, where these elements were added.
Abstract: Adjacent to magnetite concentrations, recrystallization of amphibolites to hornblende skarns involved enrichment of ferromagnesian silicates in Mg, release of Fe to form magnetite, and conversion of calcic plagioclase to sodic. Recrystallization controlled by pressure gradients toward shear zones is believed to have caused release of fluids that transported Ca, Al, Fe, Mn, Ti, Ba, Sr, V, Cr, and Zn out of the system. The same elements were probably removed from granitic gneisses, forming alaskites. Hornblende granite formed where these fluids were added.
TL;DR: A review of the iron-oxide reduction research at the University of Toronto can be found in this paper, where the authors focus on the kinetics of hydrogen reduction of sintered briquettes made from reagent grade iron oxide with and without small additions of impurities.
TL;DR: In this article, an octahedron-shaped single crystals of magnetite have been grown from a flux of borax using argon at a pressure of two atmosphere containing one ppm oxygen partial pressure.
TL;DR: In this paper, the degree of wustite breakdown can be easily estimated, based on the ratio 95 : 4 : 1 : 1 for the three oxides FeO, FeO4 and Fe2O4.
Abstract: Davies et al. have shown that, when iron is oxidised at temperatures above 700°, the oxide film present on flat specimens contains mainly wustite (FeO), in fact the three oxides FeO, Fe2O4 and Fe2O4 are all present, approximately in the ratio 95 : 4 : 1. Below 570°, FeO is not stable, as shown by the iron–oxygen equilibrium diagram2 and Collongues & Chaudron3 have shown that in vacuo wustite decomposes to give iron and magnetite at temperatures below 570°. Wustite formed as an oxide layer on iron oxidised at temperatures above 570° should also become unstable on cooling to room temperature. The following results show how the degree of wustite breakdown can be easily estimated.
TL;DR: Magnetite coexisting with sulphides from an iron ore formation in northern Sweden has been investigated with micro-probe and X-ray methods as mentioned in this paper, and the Mg/Mg + Fe ratio in magnetite can be correlated with the presence or absence of coexisting pyrite, indicating varying sulphur pressure in the rocks.
Abstract: Magnetite coexisting with sulphides from an iron ore formation in northern Sweden has been investigated with micro-probe and X-ray methods. The Mg/Mg + Fe ratio in magnetite can be correlated with the presence or absence of coexisting pyrite, indicating varying sulphur pressure in the rocks. Sulphurization of magnetite is assumed to be responsible for the introduction of Mg into the magnetite structure.
TL;DR: In this article, a gas-reaction chamber has been constructed, which allows the in situ transmission electronmicroscopic study of gas-solid reactions at temperatures up to 900°°-1000°C.
Abstract: A gas-reaction chamber has been constructed, which allows the in situ transmission electronmicroscopic study of gas-solid reactions at temperatures up to 900 °–1000 °C. The morphological and crystallographic properties of iron, of iron and wustite, and of magnetite depositing epitaxially on (111) gold substrates, either by the thermal decomposition of Fe(CO)5 or by decomposition and chemical reaction from Fe(CO)5–H2 or from Fe(CO)5–H2–H2O mixtures, are described. In other examples, the oxidation of the initially depositing iron is illustrated. In some of the experiments, polycrystalline iron foils were substituted for the (111) gold substrates, and a profound effect of iron deposition on the rate of grain growth in the iron foil was found. Coalescence of iron crystallites and high mobility of the deposit were observed. Incidental observations on the decomposition of Ni(CO)4 are described. These permit comparison of the epitaxial relationships in the Ni–Au and NiO–Au systems with those of the corresponding...
Patent•
Esso1
TL;DR: In this article, an improved process for the production of metallic iron by direct reduction of iron ores at relatively high temperatures is presented. But the process has special utility with regard to the reduction of specular hematite ores, particularly with carbon monoxide and carbon carbonoxide-containing gases.
Abstract: An improved process for the production of metallic iron by direct reduction of iron ores at relatively high temperatures. The ore is staged in a series of beds, fluidized by contact with ascending gas, and reduced. In ferric reduction zones, ferric oxide (hematite) is reduced to magnetic oxide of iron (magnetite), and the latter is thence reduced to substantially ferrous oxide (wustite). In the ferrous reduction zone, or zones, the ferrous oxide is reduced to metallic iron. By addition or incorporation with the partially reduced ore of a ferrous reduction zone, or zones, of critical amounts of salts formed from Groups I-A, II-A and III-A metals, and metalloids, particularly halide salts and nonoxide-forming hydroxides and carbonates of such metals, the overall rate of reduction of the ore is promoted and metallization increased without significant adverse effects due to bogging. The process has special utility with regard to the reduction of specular hematite ores, particularly with carbon monoxide and carbon monoxide-containing gases.
TL;DR: If pyroxene skarns were formed from iron carbonates less siliceous than but otherwise similar to those of Lake Superior, an outside source for iron and other elements of the skarn and associated magnetite deposits is unnecessary as discussed by the authors.
Abstract: If pyroxene skarns were formed from iron carbonates less siliceous than but otherwise similar to those of Lake Superior, an outside source for iron and other elements of the skarns and associated magnetite deposits is unnecessary. 9Volume losses created by the formation of dense minerals and by subtraction of some elements in released fluids provide openings in which magnetite can be concentrated.9 Biotite and hornblende in gneiss are a potential source of fluids for catalysis and migration of elements. 9Fluids squeezed out of tight areas and into more open, crushed, and sheared rocks may cause melting and formation of hornblende granite and alaskite.9
TL;DR: In this paper, a method using HCl to test for self-reversal in rocks containing two or more magnetic minerals is illustrated by application to specimens from the Bucks batholith in Northern California.
Abstract: A method using etching by HCl to test for self-reversal in rocks containing two or more magnetic minerals is illustrated by application to specimens from the Bucks batholith in Northern California. The etching results support the hypothesis that this batholith contains a self-reversed titanohematite and a normally magnetized magnetite.
Patent•
12 Nov 1969
TL;DR: In this paper, the reduced iron is then ground without prior passivation to all pass 100 mesh and with 60 - 80% passing 325 mesh, and the iron may then be sintered in the range 1600' - 2200'F and reground to size.
Abstract: 1,170,690. Reducing iron ore; HYDROCARBON RESEARCH Inc. Sept.19, 1967, No.42703/67. Heading C7D. Iron for powder metallurgical use is obtained by grinding an iron oxide e.g. hematite, magnetite or millscale to all pass a 20 mesh (Tyler) screen with not more than 25% passing 325 mesh, and reducing the ground ore in a fluidized bed at a temperature in the range 600‹ -1100‹ F and a pressure in the range 200-650 p. s. i. with a hydrogen-rich gas; the reduced iron is then ground without prior passivation to all pass 100 mesh and with 60 - 80% passing 325 mesh. The iron may then be sintered in the range 1600‹ - 2200‹F. and reground to size.
TL;DR: The formation of a sinuous wustite/magnetite interface and outer magnetite surface occurred when thin strip, iron-aluminium alloys (0.005 to 0.2wt.% aluminium) were oxidized at 850 °C in atmospheres of low and high oxygen potential as discussed by the authors.
TL;DR: In this article, the Titanium magnetite and magnetite of iron ore deposits of different genesis are compared and compared using the International Geology Review: Vol. 11, No. 12, pp. 1408-1418.
Abstract: (1969). Titanium magnetite and magnetite of iron ore deposits of different genesis. International Geology Review: Vol. 11, No. 12, pp. 1408-1418.