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Kei Hirose - One of the best experts on this subject based on the ideXlab platform.
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resistivity saturation of hcp fe si alloys in an internally heated diamond anvil cell a key to assessing the earth s core conductivity
Earth and Planetary Science Letters, 2020Co-Authors: Hayato Inoue, Kei Hirose, Sho Suehiro, Kenji Ohta, Yasuo OhishiAbstract:Abstract Electrical resistivity and thermal conductivity of iron (Fe)-Light Element alloys at high pressure and temperature are key parameters to constrain the dynamics and thermal evolution of the Earth's core. We determined the electrical resistivity of hcp Fe-2, 4 and 6.5 wt.% silicon (Si) alloys up to 117 GPa and 3120 K using a four-terminal method in an internally heated diamond-anvil cell. The temperature dependence of electrical resistivity of hcp Fe-Si alloys was suppressed as both Si concentration and temperature increased, which indicates the resistivity saturation phenomenon: the electrical resistivity of metal asymptotically approaches the “saturation resistivity”. Our results are fully reproduced by a highly resistive saturation model, and the obtained saturation resistivities for hcp Fe-Si alloys are comparable to those for hcp pure Fe at around 100 GPa. If Si is a major Light Element in the Earth's core, the pure Fe like saturation resistivity would keep the core conductivity high enough to induce active dynamics there and rapid growth of the inner core.
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high pressure melting experiments on fe si alloys and implications for silicon as a Light Element in the core
Earth and Planetary Science Letters, 2016Co-Authors: Kei Hirose, Haruka Ozawa, Kyoko Yonemitsu, Yasuo OhishiAbstract:Abstract We carried out melting experiments on Fe–Si alloys to 127 GPa in a laser-heated diamond-anvil cell (DAC). On the basis of textural and chemical characterizations of samples recovered from a DAC, a change in eutectic liquid composition in the Fe–FeSi binary system was examined with increasing pressure. The chemical compositions of coexisting liquid and solid phases were quantitatively determined with field-emission-type electron microprobes. The results demonstrate that silicon content in the eutectic liquid decreases with increasing pressure to less than 1.5 ± 0.1 wt.% Si at 127 GPa. If silicon is a single Light Element in the core, 4.5 to 12 wt.% Si is required in the outer core in order to account for its density deficit from pure iron. However, such a liquid core, whose composition is on the Si-rich side of the eutectic point, crystallizes less dense solid, CsCl (B2)-type phase at the inner core boundary (ICB). Our data also show that the difference in silicon concentration between coexisting solid and liquid is too small to account for the observed density contrast across the ICB. These indicate that silicon cannot be the sole Light Element in the core. Previous geochemical and cosmochemical arguments, however, strongly require ∼6 wt.% Si in the core. It is possible that the Earth's core originally included ∼6 wt.% Si but then became depleted in silicon by crystallizing SiO2 or MgSiO3.
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liquid iron sulfur alloys at outer core conditions by first principles calculations
Geophysical Research Letters, 2014Co-Authors: Koichiro Umemoto, Kei Hirose, Yoichi Nakajima, Saori Imada, Tetsuya Komabayashi, Satoshi Tsutsui, Alfred Q R BaronAbstract:We examined the density, bulk sound (compressional) velocity, and Gruneisen parameter of liquid pure Fe, Fe100H28 (0.50 wt % H), Fe88H40 (0.81 wt % H), and Fe76H52 (1.22 wt % H) at Earth's outer core pressure and temperature (P-T) conditions (~100 to 350 GPa, 4000 to 7000 K) based on first-principles molecular dynamics calculations. The results demonstrate that the thermodynamic Gruneisen parameter of liquid iron alloy decreases with increasing pressure, temperature, and hydrogen concentration, indicating a relatively small temperature gradient in the outer core when hydrogen is present. Along such temperature profile, both the density and compressional velocity of liquid iron containing ~1 wt % hydrogen match seismological observations. It suggests that hydrogen could be a primary Light Element in the core, although the shear velocity of the inner core is not reconciled with solid Fe-H alloy and thus requires another impurity Element.
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compression of fesi fe3c fe0 95o and fes under the core pressures and implication for Light Element in the earth s core
Journal of Geophysical Research, 2010Co-Authors: Nagayoshi Sata, Kei Hirose, Guoyin Shen, Yoichi Nakajima, Yasuo Ohishi, Naohisa HiraoAbstract:[1] The Light alloying Element in the Earth's core has not been identified yet. Here we determined the pressure-volume equations of state of FeSi, Fe3C, and Fe0.95O in the core pressure range by a combination of diamond-anvil cell and synchrotron X-ray diffraction techniques. Both B2-type FeSi and Fe3C cementite were preserved to 180 and 187 GPa, respectively. The rhombohedrally-distorted B1 phase of Fe0.95O was measured up to 186 GPa, and the distorted B8-type Fe0.95O was observed between 170 and 226 GPa. Combined with our previous data on FeS VI and B2-type VII phases to 270 GPa, we discuss the Light Element in the outer core by comparing the densities and compressibilities of these iron compounds with seismologically-estimated density profile in the core. Substitution of Light Element, particularly carbon and oxygen, in iron not only reduces the density but also enhances the compressibility remarkably. The core profile is therefore not reconciled with Fe-C and Fe-O compounds, while the densities and compressibilities of Fe-Si and Fe-S alloys match the observations. Carbon and oxygen may not be a predominant Light Element in the Earth's outer core, leaving silicon and sulfur as strong candidates.
Zizheng Gong - One of the best experts on this subject based on the ideXlab platform.
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evidence for an oxygen depleted liquid outer core of the earth
Nature, 2011Co-Authors: Haijun Huang, Yingwei Fei, Lingcang Cai, Fuqian Jing, Hongsen Xie, Lianmeng Zhang, Zizheng GongAbstract:Earth's liquid outer core consists mainly of liquid iron alloyed with about 10% (by weight) of Light Elements. Oxygen has been proposed as a major Light Element in the core, based on cosmochemical arguments and chemical reactions during accretion, but here Huang et al. report data that virtually rule out oxygen as a major Light Element in the liquid outer core. They compare density and sound-velocity measurements in shock-wave experiments in the Fe–S–O system of Earth's core with geophysical observations. Their findings are consistent with an oxygen-depleted core, and a reduced environment during early Earth accretion, with important implications for early Earth accretion models. On the basis of geophysical observations, cosmochemical constraints, and high-pressure experimental data, the Earth’s liquid outer core consists of mainly liquid iron alloyed with about ten per cent (by weight) of Light Elements1,2. Although the concentrations of the Light Elements are small, they nevertheless affect the Earth’s core: its rate of cooling, the growth of the inner core, the dynamics of core convection, and the evolution of the geodynamo3,4. Several Light Elements—including sulphur, oxygen, silicon, carbon and hydrogen—have been suggested2, but the precise identity of the Light Elements in the Earth’s core is still unclear. Oxygen has been proposed as a major Light Element in the core on the basis of cosmochemical arguments and chemical reactions during accretion5,6. Its presence in the core has direct implications for Earth accretion conditions of oxidation state, pressure and temperature. Here we report new shockwave data in the Fe–S–O system that are directly applicable to the outer core. The data include both density and sound velocity measurements, which we compare with the observed density and velocity profiles of the liquid outer core. The results show that we can rule out oxygen as a major Light Element in the liquid outer core because adding oxygen into liquid iron would not reproduce simultaneously the observed density and sound velocity profiles of the outer core. An oxygen-depleted core would imply a more reduced environment during early Earth accretion.
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evidence for an oxygen depleted liquid outer core of the earth
Nature, 2011Co-Authors: Haijun Huang, Yingwei Fei, Lingcang Cai, Fuqian Jing, Hongsen Xie, Lianmeng Zhang, Zizheng GongAbstract:On the basis of geophysical observations, cosmochemical constraints, and high-pressure experimental data, the Earth's liquid outer core consists of mainly liquid iron alloyed with about ten per cent (by weight) of Light Elements. Although the concentrations of the Light Elements are small, they nevertheless affect the Earth's core: its rate of cooling, the growth of the inner core, the dynamics of core convection, and the evolution of the geodynamo. Several Light Elements-including sulphur, oxygen, silicon, carbon and hydrogen-have been suggested, but the precise identity of the Light Elements in the Earth's core is still unclear. Oxygen has been proposed as a major Light Element in the core on the basis of cosmochemical arguments and chemical reactions during accretion. Its presence in the core has direct implications for Earth accretion conditions of oxidation state, pressure and temperature. Here we report new shockwave data in the Fe-S-O system that are directly applicable to the outer core. The data include both density and sound velocity measurements, which we compare with the observed density and velocity profiles of the liquid outer core. The results show that we can rule out oxygen as a major Light Element in the liquid outer core because adding oxygen into liquid iron would not reproduce simultaneously the observed density and sound velocity profiles of the outer core. An oxygen-depleted core would imply a more reduced environment during early Earth accretion.
Yingwei Fei - One of the best experts on this subject based on the ideXlab platform.
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evidence for an oxygen depleted liquid outer core of the earth
Nature, 2011Co-Authors: Haijun Huang, Yingwei Fei, Lingcang Cai, Fuqian Jing, Hongsen Xie, Lianmeng Zhang, Zizheng GongAbstract:Earth's liquid outer core consists mainly of liquid iron alloyed with about 10% (by weight) of Light Elements. Oxygen has been proposed as a major Light Element in the core, based on cosmochemical arguments and chemical reactions during accretion, but here Huang et al. report data that virtually rule out oxygen as a major Light Element in the liquid outer core. They compare density and sound-velocity measurements in shock-wave experiments in the Fe–S–O system of Earth's core with geophysical observations. Their findings are consistent with an oxygen-depleted core, and a reduced environment during early Earth accretion, with important implications for early Earth accretion models. On the basis of geophysical observations, cosmochemical constraints, and high-pressure experimental data, the Earth’s liquid outer core consists of mainly liquid iron alloyed with about ten per cent (by weight) of Light Elements1,2. Although the concentrations of the Light Elements are small, they nevertheless affect the Earth’s core: its rate of cooling, the growth of the inner core, the dynamics of core convection, and the evolution of the geodynamo3,4. Several Light Elements—including sulphur, oxygen, silicon, carbon and hydrogen—have been suggested2, but the precise identity of the Light Elements in the Earth’s core is still unclear. Oxygen has been proposed as a major Light Element in the core on the basis of cosmochemical arguments and chemical reactions during accretion5,6. Its presence in the core has direct implications for Earth accretion conditions of oxidation state, pressure and temperature. Here we report new shockwave data in the Fe–S–O system that are directly applicable to the outer core. The data include both density and sound velocity measurements, which we compare with the observed density and velocity profiles of the liquid outer core. The results show that we can rule out oxygen as a major Light Element in the liquid outer core because adding oxygen into liquid iron would not reproduce simultaneously the observed density and sound velocity profiles of the outer core. An oxygen-depleted core would imply a more reduced environment during early Earth accretion.
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evidence for an oxygen depleted liquid outer core of the earth
Nature, 2011Co-Authors: Haijun Huang, Yingwei Fei, Lingcang Cai, Fuqian Jing, Hongsen Xie, Lianmeng Zhang, Zizheng GongAbstract:On the basis of geophysical observations, cosmochemical constraints, and high-pressure experimental data, the Earth's liquid outer core consists of mainly liquid iron alloyed with about ten per cent (by weight) of Light Elements. Although the concentrations of the Light Elements are small, they nevertheless affect the Earth's core: its rate of cooling, the growth of the inner core, the dynamics of core convection, and the evolution of the geodynamo. Several Light Elements-including sulphur, oxygen, silicon, carbon and hydrogen-have been suggested, but the precise identity of the Light Elements in the Earth's core is still unclear. Oxygen has been proposed as a major Light Element in the core on the basis of cosmochemical arguments and chemical reactions during accretion. Its presence in the core has direct implications for Earth accretion conditions of oxidation state, pressure and temperature. Here we report new shockwave data in the Fe-S-O system that are directly applicable to the outer core. The data include both density and sound velocity measurements, which we compare with the observed density and velocity profiles of the liquid outer core. The results show that we can rule out oxygen as a major Light Element in the liquid outer core because adding oxygen into liquid iron would not reproduce simultaneously the observed density and sound velocity profiles of the outer core. An oxygen-depleted core would imply a more reduced environment during early Earth accretion.
Fuqian Jing - One of the best experts on this subject based on the ideXlab platform.
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evidence for an oxygen depleted liquid outer core of the earth
Nature, 2011Co-Authors: Haijun Huang, Yingwei Fei, Lingcang Cai, Fuqian Jing, Hongsen Xie, Lianmeng Zhang, Zizheng GongAbstract:Earth's liquid outer core consists mainly of liquid iron alloyed with about 10% (by weight) of Light Elements. Oxygen has been proposed as a major Light Element in the core, based on cosmochemical arguments and chemical reactions during accretion, but here Huang et al. report data that virtually rule out oxygen as a major Light Element in the liquid outer core. They compare density and sound-velocity measurements in shock-wave experiments in the Fe–S–O system of Earth's core with geophysical observations. Their findings are consistent with an oxygen-depleted core, and a reduced environment during early Earth accretion, with important implications for early Earth accretion models. On the basis of geophysical observations, cosmochemical constraints, and high-pressure experimental data, the Earth’s liquid outer core consists of mainly liquid iron alloyed with about ten per cent (by weight) of Light Elements1,2. Although the concentrations of the Light Elements are small, they nevertheless affect the Earth’s core: its rate of cooling, the growth of the inner core, the dynamics of core convection, and the evolution of the geodynamo3,4. Several Light Elements—including sulphur, oxygen, silicon, carbon and hydrogen—have been suggested2, but the precise identity of the Light Elements in the Earth’s core is still unclear. Oxygen has been proposed as a major Light Element in the core on the basis of cosmochemical arguments and chemical reactions during accretion5,6. Its presence in the core has direct implications for Earth accretion conditions of oxidation state, pressure and temperature. Here we report new shockwave data in the Fe–S–O system that are directly applicable to the outer core. The data include both density and sound velocity measurements, which we compare with the observed density and velocity profiles of the liquid outer core. The results show that we can rule out oxygen as a major Light Element in the liquid outer core because adding oxygen into liquid iron would not reproduce simultaneously the observed density and sound velocity profiles of the outer core. An oxygen-depleted core would imply a more reduced environment during early Earth accretion.
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evidence for an oxygen depleted liquid outer core of the earth
Nature, 2011Co-Authors: Haijun Huang, Yingwei Fei, Lingcang Cai, Fuqian Jing, Hongsen Xie, Lianmeng Zhang, Zizheng GongAbstract:On the basis of geophysical observations, cosmochemical constraints, and high-pressure experimental data, the Earth's liquid outer core consists of mainly liquid iron alloyed with about ten per cent (by weight) of Light Elements. Although the concentrations of the Light Elements are small, they nevertheless affect the Earth's core: its rate of cooling, the growth of the inner core, the dynamics of core convection, and the evolution of the geodynamo. Several Light Elements-including sulphur, oxygen, silicon, carbon and hydrogen-have been suggested, but the precise identity of the Light Elements in the Earth's core is still unclear. Oxygen has been proposed as a major Light Element in the core on the basis of cosmochemical arguments and chemical reactions during accretion. Its presence in the core has direct implications for Earth accretion conditions of oxidation state, pressure and temperature. Here we report new shockwave data in the Fe-S-O system that are directly applicable to the outer core. The data include both density and sound velocity measurements, which we compare with the observed density and velocity profiles of the liquid outer core. The results show that we can rule out oxygen as a major Light Element in the liquid outer core because adding oxygen into liquid iron would not reproduce simultaneously the observed density and sound velocity profiles of the outer core. An oxygen-depleted core would imply a more reduced environment during early Earth accretion.
Yasuo Ohishi - One of the best experts on this subject based on the ideXlab platform.
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resistivity saturation of hcp fe si alloys in an internally heated diamond anvil cell a key to assessing the earth s core conductivity
Earth and Planetary Science Letters, 2020Co-Authors: Hayato Inoue, Kei Hirose, Sho Suehiro, Kenji Ohta, Yasuo OhishiAbstract:Abstract Electrical resistivity and thermal conductivity of iron (Fe)-Light Element alloys at high pressure and temperature are key parameters to constrain the dynamics and thermal evolution of the Earth's core. We determined the electrical resistivity of hcp Fe-2, 4 and 6.5 wt.% silicon (Si) alloys up to 117 GPa and 3120 K using a four-terminal method in an internally heated diamond-anvil cell. The temperature dependence of electrical resistivity of hcp Fe-Si alloys was suppressed as both Si concentration and temperature increased, which indicates the resistivity saturation phenomenon: the electrical resistivity of metal asymptotically approaches the “saturation resistivity”. Our results are fully reproduced by a highly resistive saturation model, and the obtained saturation resistivities for hcp Fe-Si alloys are comparable to those for hcp pure Fe at around 100 GPa. If Si is a major Light Element in the Earth's core, the pure Fe like saturation resistivity would keep the core conductivity high enough to induce active dynamics there and rapid growth of the inner core.
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high pressure melting experiments on fe si alloys and implications for silicon as a Light Element in the core
Earth and Planetary Science Letters, 2016Co-Authors: Kei Hirose, Haruka Ozawa, Kyoko Yonemitsu, Yasuo OhishiAbstract:Abstract We carried out melting experiments on Fe–Si alloys to 127 GPa in a laser-heated diamond-anvil cell (DAC). On the basis of textural and chemical characterizations of samples recovered from a DAC, a change in eutectic liquid composition in the Fe–FeSi binary system was examined with increasing pressure. The chemical compositions of coexisting liquid and solid phases were quantitatively determined with field-emission-type electron microprobes. The results demonstrate that silicon content in the eutectic liquid decreases with increasing pressure to less than 1.5 ± 0.1 wt.% Si at 127 GPa. If silicon is a single Light Element in the core, 4.5 to 12 wt.% Si is required in the outer core in order to account for its density deficit from pure iron. However, such a liquid core, whose composition is on the Si-rich side of the eutectic point, crystallizes less dense solid, CsCl (B2)-type phase at the inner core boundary (ICB). Our data also show that the difference in silicon concentration between coexisting solid and liquid is too small to account for the observed density contrast across the ICB. These indicate that silicon cannot be the sole Light Element in the core. Previous geochemical and cosmochemical arguments, however, strongly require ∼6 wt.% Si in the core. It is possible that the Earth's core originally included ∼6 wt.% Si but then became depleted in silicon by crystallizing SiO2 or MgSiO3.
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compression of fesi fe3c fe0 95o and fes under the core pressures and implication for Light Element in the earth s core
Journal of Geophysical Research, 2010Co-Authors: Nagayoshi Sata, Kei Hirose, Guoyin Shen, Yoichi Nakajima, Yasuo Ohishi, Naohisa HiraoAbstract:[1] The Light alloying Element in the Earth's core has not been identified yet. Here we determined the pressure-volume equations of state of FeSi, Fe3C, and Fe0.95O in the core pressure range by a combination of diamond-anvil cell and synchrotron X-ray diffraction techniques. Both B2-type FeSi and Fe3C cementite were preserved to 180 and 187 GPa, respectively. The rhombohedrally-distorted B1 phase of Fe0.95O was measured up to 186 GPa, and the distorted B8-type Fe0.95O was observed between 170 and 226 GPa. Combined with our previous data on FeS VI and B2-type VII phases to 270 GPa, we discuss the Light Element in the outer core by comparing the densities and compressibilities of these iron compounds with seismologically-estimated density profile in the core. Substitution of Light Element, particularly carbon and oxygen, in iron not only reduces the density but also enhances the compressibility remarkably. The core profile is therefore not reconciled with Fe-C and Fe-O compounds, while the densities and compressibilities of Fe-Si and Fe-S alloys match the observations. Carbon and oxygen may not be a predominant Light Element in the Earth's outer core, leaving silicon and sulfur as strong candidates.