Faculty Profiles - TERASAKI Hidenori

Papers - TERASAKI Hidenori

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Stability of Fe-Ni hydride after the reaction between Fe-Ni alloy and hydrous phase (delta-AlOOH) up to 1.2 Mbar: Possibility of H contribution to the core density deficit Reviewed

Hidenori Terasaki, Eiji Ohtani, Takeshi Sakai, Seiji Kamada, Hidetoshi Asanuma, Yuki Shibazaki, Naohisa Hirao, Nagayoshi Sata, Yasuo Ohishi, Tatsuya Sakamaki, Akio Suzuki, Ken-ichi Funakoshi

PHYSICS OF THE EARTH AND PLANETARY INTERIORS 194 18 - 24 2012.3

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER

The hydrous mineral, delta-AlOOH, is stable up to at least the core-mantle boundary, and therefore has been proposed as a water carrier to the Earth's deep mantle. If delta-AlOOH is transported down to the core-mantle boundary by a subducting slab or the mantle convection, then the reaction between the iron alloy core and delta-AlOOH is important in the deep water/hydrogen cycle in the Earth. Here we conducted an in situ X-ray diffraction study to determine the behavior of hydrogen between Fe-Ni alloys and delta-AlOOH up to near the core-mantle boundary conditions. The obtained diffraction spectra show that fcc/dhcp Fe-Ni hydride is stable over a wide pressure range of 19-121 GPa at high temperatures. Although the temperature of formation of Fe-Ni hydride tends to increase up to 1950 K with increasing pressure to 121 GPa, this reaction temperature is well below the mantle geotherm. delta-AlOOH was confirmed to coexist stably with perovskite, suggesting that delta-AlOOH can be a major hydrous phase in the lower mantle. Therefore, when delta-AlOOH contacts with the core at the core-mantle boundary, the hydrogen is likely to dissolve into the Earth's core. Based on the present results, the amount of hydrogen to explain the core density deficit is estimated to be 1.0-2.0 wt.%. (C) 2012 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.pepi.2012.01.002

Compression of Fe88.1Ni9.1S2.8 alloy up to the pressure of Earth's inner core Reviewed

Takeshi Sakai, Eiji Ohtani, Seiji Kamada, Hidenori Terasaki, Naohisa Hirao

JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH 117 2012.2

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

Fe88.1Ni9.1S2.8 alloy was compressed up to 335 GPa, corresponding to the pressure at the Earth's inner core, and the hexagonal close-packed structure was found to be stable. The axial (c/a) ratio gradually decreased with increasing pressure. A linear fit as a function of pressure gave c/a = 1.605(2)-6.1(9) x 10(-5)P for P in GPa. The compression curve of Fe88.1Ni9.1S2.8 alloy was expressed by the third-order Birch-Murnaghan equation of state, giving K-0 = 167.0 +/- 15.0 GPa, K-0' = 4.46 +/- 0.14, and V-0 = 22.93 +/- 0.29 angstrom(3). Our results indicate that the hcp Fe-5 wt % Ni-5.7 wt % S alloy can account for the density of the inner core at 328.9 GPa, assuming a linear relationship exists between the density and the nickel and sulfur content.

DOI： 10.1029/2011JB008745

Density measurements of liquid Fe-Si alloys at high pressure using the sink-float method Reviewed

Ryuji Tateyama, Eiji Ohtani, Hidenori Terasaki, Keisuke Nishida, Yuki Shibazaki, Akio Suzuki, Takumi Kikegawa

PHYSICS AND CHEMISTRY OF MINERALS 38 ( 10 ) 801 - 807 2011.12

Language：English Publishing type：Research paper (scientific journal) Publisher：SPRINGER

The compositional dependence on the density of liquid Fe alloys under high pressure is important for estimating the amount of light elements in the Earth's outer core. Here, we report on the density of liquid Fe-Si at 4 GPa and 1,923 K measured using the sink-float method and our investigation on the effect of the Si content on the density of the liquid. Our experiments show that the density of liquid Fe-Si decreases from 7.43 to 2.71 g/cm(3) non-linearly with increasing Si content (0-100 at%). The molar volume of liquid Fe-Si calculated from the measured density gradually decreases in the compositional range 0-50 at% Si, and increases in the range 50-100 at% Si. It should be noted that the estimated molar volume of the alloys shows a negative volume of mixing between Fe and Si. This behaviour is similar to Fe-S liquid (Nishida et al. in Phys Chem Miner 35:417-423, 2008). However, the excess molar volume of mixing for the liquid Fe-Si is smaller than that of liquid Fe-S. The light element contents in the outer core estimated previously may be an underestimation if we take into account the possible negative value of the excess mixing volume of iron-light element alloys in the outer core.

DOI： 10.1007/s00269-011-0452-1

Phase stability and compression study of (Fe-0.89,Ni-0.11)(3)S up to pressure of the Earth's core Reviewed

Takeshi Sakai, Eiji Ohtani, Hidenori Terasaki, Seiji Kamada, Naohisa Hirao, Masaaki Miyahara, Masahiko Nishijima

AMERICAN MINERALOGIST 96 ( 10 ) 1490 - 1494 2011.10

Language：English Publishing type：Research paper (scientific journal) Publisher：MINERALOGICAL SOC AMER

An in situ synchrotron powder X-ray diffraction study on (Fe-0.89,Ni-0.11)(3)S was conducted up to 141 GPa and 1590 K. (Fe-0.89,Ni-0.11)(3)S has a tetragonal structure, which is the same structure as Ni-free Fe3S. Fitting a third-order Birch-Murnaghan equation of state to data at ambient temperature yielded a bulk modulus of K-0 = 138.1(7.2) GPa and its pressure derivative K'(0) = 4.5(3) with a zero pressure volume V-0 = 375.67(4) angstrom(3). The density of (Fe-0.89,Ni-0.11)(3)S under the core-mantle boundary condition is 1.7% greater than that of Fe3S. The axial ratio (c/a) of (Fe-0.89,Ni-0.11)(3)S decreases with increasing pressure. The addition of nickel to Fe3S leads to a softening of the c-axis. Assuming that the nickel content of the outer core is about 5 at%, we estimated 12.3-20.8 at% sulfur in the outer core for the given 6-10% density deficit between the outer core and pure iron at 136 GPa.

DOI： 10.2138/am.2011.3822

Static compression of Fe0.83Ni0.09Si0.08 alloy to 374 GPa and Fe0.93Si0.07 alloy to 252 GPa: Implications for the Earth's inner core Reviewed

Hidetoshi Asanuma, Eiji Ohtani, Takeshi Sakai, Hidenori Terasaki, Seiji Kamada, Naohisa Hirao, Yasuo Ohishi

EARTH AND PLANETARY SCIENCE LETTERS 310 ( 1-2 ) 113 - 118 2011.10

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

The pressure-volume equations of state of iron-nickel-silicon alloy Fe0.83Ni0.09Si0.08 (Fe-9.8 wt.% Ni-4.0 wt.% Si) and iron-silicon alloy Fe0.93Si0.07 (Fe-3.4 wt.% Si) have been investigated up to 374 GPa and 252 GPa, respectively. The present compression data covered pressures of the Earth's core. We confirmed that both Fe0.83Ni0.09Si0.08 and Fe0.93Si0.07 alloys remain in the hexagonal close packed structure at all pressures studied. We obtained the density of these alloys at the pressure of the inner core boundary (ICB), 330 GPa at 300 K by fitting the compression data to the third order Birch-Murnaghan equation of state. Using these density values combined with the previous data for hcp-Fe, hcp-Fe0.8Ni0.2, and hcp-Fe0.84Si0.16 alloys and comparing with the density of the PREM inner core, we estimated the Ni and Si contents of the inner core. The Si content of the inner core estimated here is slightly greater than that estimated previously based on the sound velocity measurement of the hcp-Fe-Ni-Si alloy at high pressure. (C) 2011 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.epsl.2011.06.034

Density measurement of liquid FeS at high pressures using synchrotron X-ray absorption Reviewed

Keisuke Nishida, Eiji Ohtani, Satoru Urakawa, Akio Suzuki, Tatsuya Sakamaki, Hidenori Terasaki, Yoshinori Katayama

AMERICAN MINERALOGIST 96 ( 5-6 ) 864 - 868 2011.5

Language：English Publishing type：Research paper (scientific journal) Publisher：MINERALOGICAL SOC AMER

The density of liquid iron sulfide (FeS) was measured up to 3.8 GPa and 1800 K using an X-ray absorption method. The compression curve of liquid FeS was fitted using the Vinet equation of state. The isothermal bulk modulus and its temperature and pressure derivatives were determined using a nonlinear least-squares fit. The parameter sets determined were: K(0T) = 2.5 +/- 0.3 GPa at T = 1500 K, (dK(0)/dT)(P) = 0.0036 +/- 0.0003 GPa/K, and (dK(0)/dP)(T) = 24 +/- 2. These results suggest that liquid FeS is more compressible than Fe-rich liquid Fe-S.

DOI： 10.2138/am.2011.3616

Density of carbonated peridotite magma at high pressure using an X-ray absorption method Reviewed

Tatsuya Sakamaki, Eiji Ohtani, Satoru Urakawa, Hidenori Terasaki, Yoshinori Katayama

AMERICAN MINERALOGIST 96 ( 4 ) 553 - 557 2011.4

Language：English Publishing type：Research paper (scientific journal) Publisher：MINERALOGICAL SOC AMER

The density of carbonated peridotite magma was measured up to 3.8 GPa and 2100 K using an X-ray absorption method. A fit of the pressure-density-temperature data to the high-temperature Birch-Murnaghan equation of state yielded the isothermal bulk modulus, K(T0) = 22.9 +/- 1.4 GPa, its pressure derivative, K'(0) = 7.4 +/- 1.4, and the temperature derivative of the bulk modulus (partial derivative K(T)/partial derivative T)(P) = -0.006 +/- 0.002 GPa/K at 1800 K. The bulk modulus of carbonated peridotite magma is larger than that of hydrous peridotite magma. The partial molar volume of CO, in magma under high pressure and temperature conditions was calculated and fit using the Vinet equation of state. The isothermal bulk modulus was K(T0) = 8.1 +/- 1.7GPa, and its pressure derivative was K'0 = 7.2 +/- 2.0 at 2000 K. Our results show that the partial molar volume of CO(2) is less compressible than that of H(2)O, suggesting that, on an equal molar basis, CO(2) is more effective than H(2)O in reducing peridotite melt density at high pressure.

DOI： 10.2138/am.2011.3577

Pressure and temperature dependence of the viscosity of a NaAlSi2O6 melt Reviewed

Akio Suzuki, Eiji Ohtani, Hidenori Terasaki, Keisuke Nishida, Hiromi Hayashi, Tatsuya Sakamaki, Yuki Shibazaki, Takumi Kikegawa

PHYSICS AND CHEMISTRY OF MINERALS 38 ( 1 ) 59 - 64 2011.1

Language：English Publishing type：Research paper (scientific journal) Publisher：SPRINGER

The viscosity of a silicate melt of composition NaAlSi2O6 was measured at pressures from 1.6 to 5.5 GPa and at temperatures from 1,350 to 1,880 degrees C. We employed in situ falling sphere viscometry using X-ray radiography. We found that the viscosity of the NaAlSi2O6 melt decreased with increasing pressure up to 2 GPa. The pressure dependence of viscosity is diminished above 2 GPa. By using the relationship between the logarithm of viscosity and the reciprocal temperature, the activation energies for viscous flow were calculated to be 3.7 +/- 0.4 x 10(2) and 3.7 +/- 0.5 x 10(2) kJ/mol at 2.2 and 2.9 GPa, respectively.

DOI： 10.1007/s00269-010-0381-4

Hydrogenation of FeSi under high pressure Reviewed

Hidenori Terasaki, Yuki Shibazaki, Tatsuya Sakamaki, Ryuji Tateyama, Eiji Ohtani, Ken-ichi Funakoshi, Yuji Higo

AMERICAN MINERALOGIST 96 ( 1 ) 93 - 99 2011.1

Language：English Publishing type：Research paper (scientific journal) Publisher：MINERALOGICAL SOC AMER

Hydrogen is the most abundant element in the solar system, suggesting that hydrogen is one of the plausible light elements in the planetary cores. To investigate the solubility of hydrogen into FeSi and phase relations of the FeSi-H system under high pressure, we performed in situ X-ray diffraction experiments on the FeSi-H and FeSi systems at high pressure and high temperature. Hydrogen starts to dissolve in FeSi (hydrogenation) and form FeSiH(x) with cubic B20 structure above 10 GPa. Hydrogen content (x), estimated from the volume difference between the FeSi-H and FeSi systems, increases from 0.07 to 0.22 with increasing pressure for P > 10 GPa. Comparing the present results with hydrogenation pressure of Fe, presence of Si in metal increases the minimal pressure for H incorporation. Hydrogen, therefore, can only incorporate into the Fe-Si core at the deeper part (P > 10 GPa) in the planetary interior.

DOI： 10.2138/am.2011.3628

Effect of hydrogen on the melting temperature of FeS at high pressure: Implications for the core of Ganymede Reviewed

Yuki Shibazaki, Eiji Ohtani, Hidenori Terasaki, Ryuji Tateyama, Tatsuya Sakamaki, Taku Tsuchiya, Ken-ichi Funakoshi

EARTH AND PLANETARY SCIENCE LETTERS 301 ( 1-2 ) 153 - 158 2011.1

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

We have carried out in situ X-ray diffraction experiments on the FeS-H system up to 16.5 GPa and 1723 K using a Kawai-type multianvil high-pressure apparatus employing synchrotron X-ray radiation. Hydrogen was supplied to FeS from the thermal decomposition of LiAIH(4), and FeSH(x), was formed at high pressures and temperatures. The melting temperature and phase relationships of FeSH(x) were determined based on in situ powder X-ray diffraction data. The melting temperature of FeSH(x) was reduced by 150-250 K comparing with that of pure FeS. The hydrogen concentration in FeSH(x) was determined to be x = 0.2-0.4 just before melting occurred between 3.0 and 16.5 GPa. It is considered that sulfur is the major light element in the core of Ganymede, one of the Galilean satellites of Jupiter. Although the interior of Ganymede is differentiated today, the silicate rock and the iron alloy mixed with H(2)O, and the iron alloy could react with H(2)O (as ice or water) or the hydrous silicate before the differentiation occurred in an early period, resulting in a formation of iron hydride. Therefore, Ganymede's core may be composed of an Fe-S-H system. According to our results, hydrogen dissolved in Ganymede's core lowers the melting temperature of the core composition, and so today, the core could have solid FeSH(x) inner core and liquid FeH(x)-FeSH(x) outer core and the present core temperature is considered to be relatively low. (C) 2010 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.epsl.2010.10.033

Hydrogenation of FeSi and FeS alloys at high pressure and high temperature Reviewed

Hidenori Terasaki, Yuki Shibazaki

Review of High Pressure Science and Technology/Koatsuryoku No Kagaku To Gijutsu 21 ( 3 ) 197 - 205 2011

Language：English Publishing type：Research paper (scientific journal)

Hydrogenation of iron-light element alloys, such as Fe-Si and Fe-S, under high pressure is important to understand the composition and the thermal structure of the planetary cores. Here, we report the hydrogenation pressures of FeSi and FeS, hydrogen solubilities into these alloys and the effect of hydrogen on their phase relations based on in situ X-ray diffraction experiment of FeSi-H and FeS-H systems up to 17 GPa and 2123 K. Hydrogenation of FeSi and FeS occurs at the pressures more than 10 GPa and 3 GPa, respectively. The H solubilities (x) are estimated to be x~0.2-0.3, which are well below compared to the H solubility into pure iron (x~1.0). This small amount of H solubility into the alloys causes only small depressions (150-250 K) of their melting temperaure whereas dissolution of H into Fe decreases its melting temperature significantly. © 2011 The Japan Society of High Pressure Science and Technology.

DOI： 10.4131/jshpreview.21.197

Liquidus and solidus temperatures of a Fe-O-S alloy up to the pressures of the outer core: Implication for the thermal structures of the Earth’s core. Reviewed

Terasaki H, Kamada S, Sakai T, Ohtani E, Hirao N, Ohishi Y

Earth and Planetary Science Letters 304 ( 3-4 ) 559 - 564 2011

X-ray imaging of melts and its application to Earth and planetary interior.

Ohtani, E, Suzuki, A, Terasaki, H, Nishida, K, Shiraishi, R, Tateyama, R

Photon Factory Activity Report 2009 (KEK Progress Report 2010-4) 27 188 2010.12

Stress relaxation experiments of olivine under conditions of subducted slab in Earth's deep upper mantle Reviewed

Yu Nishihara, Ken-ichi Funakoshi, Yuji Higo, Noriyoshi Tsujino, Takaaki Kawazoe, Tomoaki Kubo, Akira Shimojuku, Hidenori Terasaki, Norimasa Nishiyama

PHYSICS OF THE EARTH AND PLANETARY INTERIORS 183 ( 1-2 ) 164 - 174 2010.11

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

Stress relaxation experiments of olivine were conducted under high-pressure and high-temperature conditions up to 10 GPa and 1273 K using a Kawai-type multi-anvil apparatus. A pre-sintered San Carlos olivine sample rod was inserted between two dense Al2O3 pistons to yield high stress at high-pressure within an octahedral pressure medium. Stress was determined from the two-dimensional diffraction pattern taken using monochromatic X-rays and an imaging-plate, and sample length was determined from an X-ray radiograph. In these experiments, pressure was first increased at room temperature, and then the temperature was increased and kept at 673, 873, 1073, and 1273 K. Four relaxation cycles, in total, were carried out in two experimental runs. The magnitude of deviatoric stress was calculated from five diffraction peaks with the following hkls: 02 1, 1 01, 1 30, I 3 1, and 11 2. The calculated deviatoric stress was significantly different depending on which diffraction peak was used (up to a factor of similar to 2) due to plastic deformation within the polycrystalline sample. The deviatoric stress decreased with increasing temperature in all of relaxation cycles. At given temperatures, the final-state value of deviatoric stress increased with increasing pressure. The upper bound for the plastic strain rate in the final-state was determined to be 10(-7) s(-1) based on a comparison between the total sample length determined from the radiograph and the d-spacings along the piston direction determined from X-ray diffraction. Present results suggest a positive activation volume for the low-temperature rheology of olivine. (C) 2010 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.pepi.2010.07.006

Stress relaxation experiments of olivine under conditions of subducted slab in Earth's deep upper mantle Reviewed

Yu Nishihara, Ken-ichi Funakoshi, Yuji Higo, Noriyoshi Tsujino, Takaaki Kawazoe, Tomoaki Kubo, Akira Shimojuku, Hidenori Terasaki, Norimasa Nishiyama

PHYSICS OF THE EARTH AND PLANETARY INTERIORS 183 ( 1-2 ) 164 - 174 2010.11

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

Stress relaxation experiments of olivine were conducted under high-pressure and high-temperature conditions up to 10 GPa and 1273 K using a Kawai-type multi-anvil apparatus. A pre-sintered San Carlos olivine sample rod was inserted between two dense Al2O3 pistons to yield high stress at high-pressure within an octahedral pressure medium. Stress was determined from the two-dimensional diffraction pattern taken using monochromatic X-rays and an imaging-plate, and sample length was determined from an X-ray radiograph. In these experiments, pressure was first increased at room temperature, and then the temperature was increased and kept at 673, 873, 1073, and 1273 K. Four relaxation cycles, in total, were carried out in two experimental runs. The magnitude of deviatoric stress was calculated from five diffraction peaks with the following hkls: 02 1, 1 01, 1 30, I 3 1, and 11 2. The calculated deviatoric stress was significantly different depending on which diffraction peak was used (up to a factor of similar to 2) due to plastic deformation within the polycrystalline sample. The deviatoric stress decreased with increasing temperature in all of relaxation cycles. At given temperatures, the final-state value of deviatoric stress increased with increasing pressure. The upper bound for the plastic strain rate in the final-state was determined to be 10(-7) s(-1) based on a comparison between the total sample length determined from the radiograph and the d-spacings along the piston direction determined from X-ray diffraction. Present results suggest a positive activation volume for the low-temperature rheology of olivine. (C) 2010 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.pepi.2010.07.006

Fe-Mg partitioning between post-perovskite and ferropericlase in the lowermost mantle Reviewed

Takeshi Sakai, Eiji Ohtani, Hidenori Terasaki, Masaaki Miyahara, Masahiko Nishijima, Naohisa Hirao, Yasuo Ohishi, Nagayoshi Sata

PHYSICS AND CHEMISTRY OF MINERALS 37 ( 7 ) 487 - 496 2010.7

Language：English Publishing type：Research paper (scientific journal) Publisher：SPRINGER

Fe-Mg partitioning between post-perovskite and ferropericlase has been studied using a laser-heated diamond anvil cell at pressures up to 154 GPa and 2,010 K which corresponds to the conditions in the lowermost mantle. The composition of the phases in the recovered samples was determined using analytical transmission electron microscopy. Our results reveal that the Fe-Mg partition coefficient between post-perovskite and ferropericlase (K (D) (PPv/Fp) ) increases with decreasing bulk iron content. The compositional dependence of K (D) (PPv/Fp) on the bulk iron content explains the inconsistency in previous studies, and the effect of the bulk iron content is the most dominant factor compared to other factors, such as temperature and aluminum content. Iron prefers ferropericlase compared to post-perovskite over a wide compositional range, whereas the iron content of post-perovskite (X (Fe) (PPv) , the mole fraction) does not exceed a value of 0.10. The iron-rich ferropericlase phase may have significant influence on the physical properties, such as the seismic velocity and electrical conductivity at the core-mantle boundary region.

DOI： 10.1007/s00269-009-0349-4

Density measurement of Fe3C liquid using X-ray absorption image up to 10 GPa and effect of light elements on compressibility of liquid iron Reviewed

H. Terasaki, K. Nishida, Y. Shibazaki, T. Sakamaki, A. Suzuki, E. Ohtani, T. Kikegawa

JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH 115 ( B6 ) B06207 2010.6

Language：English Publishing type：Research paper (scientific journal) Publisher：AMER GEOPHYSICAL UNION

Density of liquid iron alloy under high pressure is important to constrain the amount of light elements in the Earth's core. Density measurement of solid and liquid Fe3C was performed using X-ray absorption image technique up to 9.5 GPa and 1973 K. Density of liquid Fe3C increases from 6.94 g/cm(3) to 7.38 g/cm(3) with a pressure of 3.6-9.5 GPa at 1973 K. The bulk modulus of liquid Fe3C is obtained to be 50 +/- 7 GPa at 1973 K. The effect of carbon on the compressibility of liquid iron is similar to that of sulfur, which significantly decreases the bulk modulus of liquid iron. Since carbon dissolution into liquid iron causes reduction of rho and K-0T, carbon could be excluded from the candidates of alloying light elements in the Earth's outer core.

DOI： 10.1029/2009JB006905

Melting of iron-silicon alloy up to the core-mantle boundary pressure: implications to the thermal structure of the Earth's core Reviewed

Hidetoshi Asanuma, Eiji Ohtani, Takeshi Sakai, Hidenori Terasaki, Seiji Kamada, Tadashi Kondo, Takumi Kikegawa

PHYSICS AND CHEMISTRY OF MINERALS 37 ( 6 ) 353 - 359 2010.6

Language：English Publishing type：Research paper (scientific journal) Publisher：SPRINGER

The melting temperature of Fe-18 wt% Si alloy was determined up to 119 GPa based on a change of laser heating efficiency and the texture of the recovered samples in the laser-heated diamond anvil cell experiments. We have also investigated the subsolidus phase relations of Fe-18 wt% Si alloy by the in-situ X-ray diffraction method and confirmed that the bcc phase is stable at least up to 57 GPa and high temperature. The melting curve of the alloy was fitted by the Simon's equation, P(GPa)/a = (T (m)(K)/T (0)) (c) , with parameters, T (0) = 1,473 K, a = 3.5 +/- A 1.1 GPa, and c = 4.5 +/- A 0.4. The melting temperature of bcc Fe-18 wt% Si alloy is comparable with that of pure iron in the pressure range of this work. The melting temperature of Fe-18 wt% Si alloy is estimated to be 3,300-3,500 K at 135 GPa, and 4,000-4,200 K at around 330 GPa, which may provide the lower bound of the temperatures at the core-mantle boundary and the inner core-outer core boundary if the light element in the core is silicon.

DOI： 10.1007/s00269-009-0338-7

Density measurement of Fe<inf>3</inf>C liquid using X-ray absorption image up to 10 GPa and effect of light elements on compressibility of liquid iron Reviewed

H. Terasaki, K. Nishida, Y. Shibazaki, T. Sakamaki, A. Suzuki, E. Ohtani, T. Kikegawa

Journal of Geophysical Research: Solid Earth 115 ( 6 ) 2010.6

Publishing type：Research paper (scientific journal)

Density of liquid iron alloy under high pressure is important to constrain the amount of light elements in the Earth's core. Density measurement of solid and liquid Fe3C was performed using X-ray absorption image technique up to 9.5 GPa and 1973 K. Density of liquid Fe3C increases from 6.94 g/cm3 to 7.38 g/cm3 with a pressure of 3.6-9.5 GPa at 1973 K. The bulk modulus of liquid Fe3C is obtained to be 50 ± 7 GPa at 1973 K. The effect of carbon on the compressibility of liquid iron is similar to that of sulfur, which significantly decreases the bulk modulus of liquid iron. Since carbon dissolution into liquid iron causes reduction of ρ and K0T, carbon could be excluded from the candidates of alloying light elements in the Earth's outer core. Copyright © 2010 by the American Geophysical Union.

DOI： 10.1029/2009JB006905

Phase relationships of the Fe-FeS system in conditions up to the Earth's outer core Reviewed

Seiji Kamada, Hidenori Terasaki, Eiji Ohtani, Takeshi Sakai, Takumi Kikegawa, Yasuo Ohishi, Naohisa Hirao, Nagayoshi Sata, Tadashi Kondo

EARTH AND PLANETARY SCIENCE LETTERS 294 ( 1-2 ) 94 - 100 2010.5

Language：English Publishing type：Research paper (scientific journal) Publisher：ELSEVIER SCIENCE BV

In situ X-ray diffraction experiments in the Fe-FeS system were performed up to 220 GPa and 3300 K using a laser-heated diamond anvil cell. Fe3S and epsilon-Fe coexisted stably up to 220 GPa and 3300 K, and thus, Fe3S is likely to be the stable S-bearing iron alloy under the Earth's core conditions. The solid iron (E-Fe) also contained 7.6(0.8) at.% of sulfur at 86 GPa and 2200 K. The amount of sulfur in the solid iron increased with increasing pressure at the eutectic temperatures. If the sulfur content obtained in this study is extrapolated to the conditions at the inner core, all the sulfur in the solid inner core can be stored in epsilon-Fe.
The eutectic composition becomes nonsensitive to pressure and seems to be constant around 20 at.% of sulfur at pressures above 40 GPa. The pressure gradient of the melting curve of the Fe-FeS system is 13.4 (0.7) K/GPa. Based on our results of melting relationship, the temperature at the core-mantle boundary should be greater than 2850(100) K, assuming that sulfur is the only light element in the Earth's liquid outer core. (C) 2010 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.epsl.2010.03.011

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