1988-6-1 The diffusion rate of oxygen in magnetite (Fe 3 O 4) has been measured under hydrothermal conditions between 800° and 500°C at 1000 bars pressure, and yields the Arrhenius relation: D = 3.5 × 10 −6 exp(−/45,000RT) kcal/g-atom O. The diffusion rate was found to be the same, within the estimated uncertainty of a factor of 2, for measurements at 100, 1000, and 2000 bars (20–200 MPa ...
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magnetite-hematite, Ni-NiO and fayalite-magnetite-quartz oxygen buffers. Oxygen-fugacity ratios between buffers A and B can be obtained by using a relation: f02 (A)/f02 (B) = [CH2 (B)/CH2 (A)]2, where CH2 (A) and CH2 (B) are equilibrium H2 concentrations in the systems A
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2019-1-1 The addition of oxygen in the system does trigger the oxidation of Fe 2+ to Fe 3+ resulting in the overgrowth of hematite on the surface. Our experiments further reveal that magnetite replacement by hematite is a fast process at moderate temperatures (200
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2019-10-18 The stability of magnetite under oxidizing hydrothermal conditions was evaluated at temperatures of 120, 150, 180 and 275 °C. A well-characterized sample of commercially-available magnetite with a particle size of approximately 690 nm was oxidized by dissolved oxygen (DO) under alkaline hydrothermal conditions in t
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The zircon grains have Ce4+/Ce3+ ranging from 10.8 to 50.5. The ore minerals mainly include chalcopyrite, bornite and chalcocite, and the absence of magnetite, hematite and sulfates. The oxygen ...
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2017-8-7 Hematite, Fe 2 O 3, is a potential oxygen carrier material, which can be reduced in the hydrocarbon fuel cycle to magnetite; this material can subsequently be
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2018-11-27 When oxygen gas reaches the particle surface, the interfacial chemical oxidation reaction of magnetite to hematite becomes dominant with a release of exothermic energy. Thereafter, oxygen diffuses into the particle through the grain boundaries or via micro-cracks in the hematite product layer because of the concentration gradient, and proceeds ...
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2019-10-18 The magnetite concentration in each specimen was calculated. based on the Fe(II)/Fe ratio obtained from titration, assuming. ... magnetite to hematite, excess oxygen could oxidize the.
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2017-5-15 It is possible that the concentration of Fe(II) dissolved in the ferruginous oceans was high enough to catalyze the recrystallization of ferrihydrite to a stable phase such as hematite (Pedersen et al., 2005) and therefore hematite bands in Archean BIFs (e.g., Sun et al., 2015), but not high enough to precipitate magnetite as we demonstrated in ...
More2019-10-18 The magnetite concentration in each specimen was calculated. based on the Fe(II)/Fe ratio obtained from titration, assuming. ... magnetite to hematite, excess oxygen could oxidize the.
More2019-10-18 The stability of magnetite under oxidizing hydrothermal conditions was evaluated at temperatures of 120, 150, 180 and 275 °C. A well-characterized sample of commercially-available magnetite with a particle size of approximately 690 nm was oxidized by dissolved oxygen (DO) under alkaline hydrothermal conditions in t
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2012-3-15 Between 10 and 10 4.3 Pa the protective hematite coverage over magnetite kept the parabolic rate constants low regardless of oxygen partial pressure. At 10 5 Pa a sharp increase of the parabolic rate constant was observed due to the simultaneous growth of hematite and magnetite. The oxygen concentration in water for the inhibition of the ...
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Hematite is the oxide with the highest oxygen content, followed by magnetite and wüstite. Wüstite is only stable at temperatures above 570 °C. Below 570 °C, it decomposes to Fe 3 O 4 and Fe. With increasing temperature, the stability area of wüstite expands
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2003-8-5 Magnetite (Fe3O4) and maghemite (ç-Fe2O3) are widespread in the environment, despite the fact that both are thermodynami-cally unstable with respect to hematite (R-Fe2O3) in the presence of oxygen. They are found in bacteria and insects, weathered soils and clays, rocks, natural-atmospheric and polluted aerosols,
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2021-11-16 As with other oxygen scavengers, temperature, pH, initial dissolved oxygen concentration, catalytic effects, and scavenger concentration affect the rate of reaction with dissolved oxygen. When fed to the feedwater in excess of oxygen demand or when fed directly to the condensate, some organic oxygen scavengers carry forward to protect steam and condensate systems.
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2018-11-30 magnetite, which elevated the oxidation potential of sul-fate (Sun et al., 2013). Once ferrous iron concentration is lowered enough by magnetite crystallization, the oxygen fugacity is controlled by the magnetite–hematite buffer (Eq. (4)), which does not change with pH. When both sul-fate-S. 3. and hematite–magnetite buffers are active, the
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2019-8-20 The microstructures of porous magnetite formed on gaseous reduction of dense hematite have been examined using high-resolution scanning electron microscopy. It has been shown that cellular pores are formed on reduction in the temperature range 573 K to 973 K (300 °C to 700 °C). Dendritic shaped gas pores are formed on reduction at temperatures between 1073 K and 1273 K (800 °C and
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2021-11-10 Specifically, we show that all the 3-fold coordinated lattice oxygen atoms on a defect-free single-crystalline “r-cut” (\(1\bar{1}02\)) surface of hematite (α-Fe 2 O 3) are exchanged with ...
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2017-7-5 magnetite, subjected to increased laser power in the course of the Raman experiment conducted in air, was oxidized to the trivalent iron oxide hematite (˛-Fe 2O 3. The presence of the two bands at around 300 and 410 cm 1 in the early stages of the oxidation of magnetite may lead to their incorrect assignment as intrinsic Raman modes of this ...
More2012-3-15 Between 10 and 10 4.3 Pa the protective hematite coverage over magnetite kept the parabolic rate constants low regardless of oxygen partial pressure. At 10 5 Pa a sharp increase of the parabolic rate constant was observed due to the simultaneous growth of hematite and magnetite. The oxygen concentration in water for the inhibition of the ...
More2019-10-18 The stability of magnetite under oxidizing hydrothermal conditions was evaluated at temperatures of 120, 150, 180 and 275 °C. A well-characterized sample of commercially-available magnetite with a particle size of approximately 690 nm was oxidized by dissolved oxygen (DO) under alkaline hydrothermal conditions in t
More2018-11-30 magnetite, which elevated the oxidation potential of sul-fate (Sun et al., 2013). Once ferrous iron concentration is lowered enough by magnetite crystallization, the oxygen fugacity is controlled by the magnetite–hematite buffer (Eq. (4)), which does not change with pH. When both sul-fate-S. 3. and hematite–magnetite buffers are active, the
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The transformation of magnetite to hematite can be expressed in term of a redox reaction, e.g., 2Fe3O4(mt) þ 0.5 O2(g) 43Fe2O3(hm) (I) with: log f O2(g) ¼ 2 logK(P,T) Most previous studies have interpreted the interconversion of magnetite and hematite as a near-equilibrium redox reactions (e.g.,
More2003-8-5 Magnetite (Fe3O4) and maghemite (ç-Fe2O3) are widespread in the environment, despite the fact that both are thermodynami-cally unstable with respect to hematite (R-Fe2O3) in the presence of oxygen. They are found in bacteria and insects, weathered soils and clays, rocks, natural-atmospheric and polluted aerosols,
MoreHematite is the oxide with the highest oxygen content, followed by magnetite and wüstite. Wüstite is only stable at temperatures above 570 °C. Below 570 °C, it decomposes to Fe 3 O 4 and Fe. With increasing temperature, the stability area of wüstite expands
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Hematite is a potential mineral for reconstructing the oxygen isotope composition and paleotemperature of paleowater. A highly accurate analysis of oxygen isotopes is essential. However, relative to other oxygenated minerals, we lack hematite reference materials that allow for internationally comparable analyses between different laboratories.
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Wüstite (FeO), magnetite (Fe 3 O 4), and hematite (α-Fe 2 O 3) are all based on a close-packed O 2– anion lattice and differ primarily in the number, oxidation state, and distribution of the cations among octahedral and tetrahedral interstitial sites, Fe oct and Fe tet .
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2021-3-19 Zeta potential measurements of pyrite, hematite, and magnetite particles suspended in a buffer solution of varying pH (1–13) were conducted as a function of salt type (NaCl, CaCl 2, MgCl 2, NaHCO 3, and Na 2 SO 4) and concentrations found in the reservoir to quantify the effect of salts on the charge modification of the mineral surfaces ...
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2021-11-16 As with other oxygen scavengers, temperature, pH, initial dissolved oxygen concentration, catalytic effects, and scavenger concentration affect the rate of reaction with dissolved oxygen. When fed to the feedwater in excess of oxygen demand or when fed directly to the condensate, some organic oxygen scavengers carry forward to protect steam and condensate systems.
More