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Kinetics of hematite to magnetite transformation by ...

2019-8-1  Charcoal gasification with both air and CO 2 led to the formation of CO.. Charcoal gasification started at 300 °C with the air and at 600 °C with CO 2.. 5% of CO is enough to convert hematite into magnetite. • A low CO concentration makes the reduction safer and less energy-consuming.

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MH, NNO and FMQ oxygen buffers - J-STAGE

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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Mechanism and kinetics of magnetite oxidation under ...

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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Effect of Oxygen Partial Pressure on Oxidation of Iron at ...

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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Investigation of Magnetite Oxidation Kinetics at the ...

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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(PDF) Mechanism and kinetics of magnetite oxidation

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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Magnetite Fe O Nanocrystals: Spectroscopic Observation

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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Water Handbook - Preboiler Industrial Boiler Corrosion ...

2021-11-14  The first and most important is the 0.0002-0.0007 in. (0.2-0.7 mil) thick magnetite formed by the reaction of iron and water in an oxygen-free environment. This magnetite forms a protective barrier against further corrosion. Magnetite forms on

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Slow oxidation of magnetite nanoparticles elucidates the ...

2021-11-4  Drawings show the oxygen concentration gradient dC/dr in magnetite nanoparticles at 0, 70, and 140 days of aging time, calculated for D = 10 −19 cm 2 /s, a

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Isothermal Oxidation of Magnetite to Hematite in Air and ...

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 reoxidized to hematite. In a previous paper[ 3 ] the microstructural changes that take place during the reduction of hematite

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(PDF) Mechanism and kinetics of magnetite oxidation

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.

More

Mechanism and kinetics of magnetite oxidation under ...

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

More

Effect of Oxygen Partial Pressure on Oxidation of Iron at ...

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 ...

More

Conversion of magnetite to hematite in iron-ore pellets

Moreover, oxygen adsorption at the magnetite surface determines the concentration gradient of iron and oxygen ions and hence their diffusion. Thus, in the reaction zone, diffusion is always ...

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Magnetite Fe O Nanocrystals: Spectroscopic Observation

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,

More

Reduction of Iron Oxides with Hydrogen—A Review ...

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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Raman study of magnetite (Fe3O4): laser-induced

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 ...

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Factors controlling sulfur concentrations in volcanic ...

Factors controlling sulfur concentrations in volcanic apatite ... The SO 3 contents of the experimental apatite increase with increasing oxygen fugacity (f O 2), from ≤0.04 wt% in reduced charges buffered by fayalite-magnetite-quartz (FMQ), to 1.0–2.6 wt% in oxidized charges buffered by manganosite-hausmanite (MNH) or magnetite-hematite ...

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Impact of Iron Minerals in Promoting Wettability ...

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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Conversion of magnetite to hematite in iron-ore pellets

Moreover, oxygen adsorption at the magnetite surface determines the concentration gradient of iron and oxygen ions and hence their diffusion. Thus, in the reaction zone, diffusion is always ...

More

Effect of Oxygen Partial Pressure on Oxidation of Iron at ...

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 ...

More

Mechanism and kinetics of hydrothermal replacement of ...

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.,

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The genetic association between magnetite–hematite

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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Reduction of Iron Oxides with Hydrogen—A Review ...

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

More

Magnetite Fe O Nanocrystals: Spectroscopic Observation

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,

More

Potential Reference Materials for Hematite Oxygen Isotope ...

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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Impact of Iron Minerals in Promoting Wettability ...

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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Subsurface cation vacancy stabilization of the magnetite ...

(A) Minimum-energy structure of the distorted bulk truncation model (10, 12). (B and C) Perspective and plan views of the subsurface cation vacancy structure.A pair of Fe oct cations from the third layer is replaced by an interstitial Fe tet (labeled Fe int) in the second layer.(E) Surface energy as a function of oxygen chemical potential, μ O, for both structures.

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Factors controlling sulfur concentrations in volcanic ...

Apatite crystals from two types of samples were analyzed by electron microprobe for 15 major and trace elements: (1) apatite in H 2 O- and S-saturated experimental charges of the 1982 El Chichón trachyandesite and (2) apatite in volcanic rocks erupted from 20 volcanoes. The SO 3 contents of the experimental apatite increase with increasing oxygen fugacity (f O 2), from ≤0.04 wt% in reduced ...

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