Modeling of iron diffusion in the iron oxides magnetite and hematite with variable stoichiometry

Hallström, Samuel; Höglund, Lars; Ågren, John

doi:10.1016/j.actamat.2010.08.032

Cited by 84 publications

(72 citation statements)

References 9 publications

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“…This is accomplished through an oxidation process, which offers new sites for accommodation of the excess Fe 3+ cations. The empty sites in the oxygen sublattice serve as the pathways for cation migration, as shown by Fe selfdiffusion studies (Amami et al 1999;Sabioni et al 2005;Hallström et al 2011). It has been demonstrated that at higher temperatures, the diffusion of Fe along the c-axis of (10)…”

Section: Discussionmentioning

confidence: 99%

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Topotaxial reactions during the genesis of oriented rutile/hematite intergrowths from Mwinilunga (Zambia)

Rečnik

Stanković

Daneu

2015

Contrib Mineral Petrol

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samples. Using a HRTEM and high-angle annular dark-field scanning TEM methods combined with energy-dispersive X-ray spectroscopy, we identified remnants of ilmenite lamellae in the vicinity of rutile exsolutions, which were an important indication of the high-T formation of the primary ferrian-ilmenite crystals. Another type of exsolution process was observed in rutile crystals, where hematite precipitates topotaxially exsolved from Fe-rich parts of rutile through intermediate Guinier-Preston zones, characterized by tripling the {101} rutile reflections. Unlike rutile exsolutions in hematite, hematite exsolutions in rutile form {301} R |{030} H equilibrium interfaces. The overall composition of our samples indicates that the ratio between ilmenite and hematite in parent ferrianilmenite crystals was close to Ilm 67 Hem 33 , typical for Fe-Tirich differentiates of mafic magma. The presence of ilmenite lamellae indicates that the primary solid solution passed the miscibility gap at ~900 °C. Subsequent exsolution processes were triggered by surface oxidation of ferrous iron and remobilization of cations within the common oxygen sublattice. Based on nanostructural analysis of the samples, we identified three successive exsolution processes: (1) exsolution of ilmenite lamellae from the primary ferrian-ilmenite crystals, (2) exsolution of rutile lamellae from ilmenite and (3) exsolution of hematite precipitates from Fe-rich rutile lamellae. All observed topotaxial reactions appear to be a combined function of temperature and oxygen fugacity, fO 2 .Keywords Ilmenite · Hematite · Rutile · Topotaxy · Exsolution · Intergrowth · Geothermometer IntroductionVarious intergrowths of rutile with structurally related minerals are known in nature. They are found in igneous and Abstract Oriented rutile/hematite intergrowths from Mwinilunga in Zambia were investigated by electron microscopy methods in order to resolve the complex sequence of topotaxial reactions. The specimens are composed of up to several-centimeter-large euhedral hematite crystals covered by epitaxially grown reticulated rutile networks. Following a top-down analytical approach, the samples were studied from their macroscopic crystallographic features down to subnanometer-scale analysis of phase compositions and occurring interfaces. Already, a simple morphological analysis indicates that rutile and hematite are met near the �010� R {101} R ||�001� H {110} H orientation relationship. However, a more detailed structural analysis of rutile/hematite interfaces using electron diffraction and high-resolution transmission electron microscopy (HRTEM) has shown that the actual relationship between the rutile and hosting hematite is in fact �010� R {401} R ||�001� H {170} H . The intergrowth is dictated by the formation of {170} H |{401} R equilibrium interfaces leading to 12 possible directions of rutile exsolution within a hematite matrix and 144 different incidences between the intergrown rutile crystals. Analyzing the potential rutile-rutile interfaces, these could be ...

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Section: Discussionmentioning

confidence: 99%

“…Owing to the high Fe-diffusivity rates along the c-axis (Hallström et al 2011), the established diffusion channels serve as convenient sites for exsolution of rutile, forming magnificent rutile pillars. Surface oxidation of ferrous iron controls the rate of rutile exsolution, dictating its topotaxial growth in hematite matrix.…”

Section: Discussionmentioning

confidence: 99%

Topotaxial reactions during the genesis of oriented rutile/hematite intergrowths from Mwinilunga (Zambia)

Rečnik

Stanković

Daneu

2015

Contrib Mineral Petrol

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“…The absence of hematite on the surface in combination with the microstructure of the inward growing scale may explain this. Diffusion through magnetite is known to be faster than through hematite [44,45]. Also, the microstructural investigation showed that the ratio: reaction zone/fully oxidized spinel oxide, was higher in H 2 ?…”

Section: Influence Of the Formation Of Reactions Zones On Oxidation Pmentioning

confidence: 98%

Oxidation After Breakdown of the Chromium-Rich Scale on Stainless Steels at High Temperature: Internal Oxidation

et al. 2016

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“…In contrast to the systematic changes in δ 18 O values with increasing formation temperature for hematite and magnetite, δ 56 Fe values should remain relatively unchanged due to the low solubility of iron in aqueous solutions at hydrothermal temperatures (Chou and Eugster, 1977;Simon et al, 2004), slow diffusion of Fe in hematite and magnetite (Hallstrom et al, 2011), and (Klein, 2005). Siderite typically occurs as minute, single rhomb-shaped crystals or massive layers of microcrystalline aggregates (James, 1951;Trendall and Blockley, 1970;Ayers, 1972).…”

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confidence: 99%

Iron formations: A global record of Neoarchaean to Palaeoproterozoic environmental history

Konhauser

Planavsky

Hardisty

et al. 2017

Earth-Science Reviews

365

257

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Modeling of iron diffusion in the iron oxides magnetite and hematite with variable stoichiometry

Cited by 84 publications

References 9 publications

Topotaxial reactions during the genesis of oriented rutile/hematite intergrowths from Mwinilunga (Zambia)

Topotaxial reactions during the genesis of oriented rutile/hematite intergrowths from Mwinilunga (Zambia)

Oxidation After Breakdown of the Chromium-Rich Scale on Stainless Steels at High Temperature: Internal Oxidation

Iron formations: A global record of Neoarchaean to Palaeoproterozoic environmental history

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