Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

Abstract

Fe–Ni–S–Si alloy is considered to be one of the plausible candidates of Mercury core material. Elastic properties of Fe–Ni–S–Si liquid are important to reveal the density profile of the Mercury core. In this study, we measured the P-wave velocity (V_P) of Fe–Ni–S–Si (Fe₇₃Ni₁₀S₁₀Si₇, Fe₇₂Ni₁₀S₅Si₁₃, and Fe₆₇Ni₁₀S₁₀Si₁₃) liquids up to 17 GPa and 2000 K to study the effects of pressure, temperature, and multiple light elements (S and Si) on the V_P and elastic properties.

The V_P of Fe–Ni–S–Si liquids are less sensitive to temperature. The effect of pressure on the V_P are close to that of liquid Fe and smaller than those of Fe–Ni–S and Fe–Ni–Si liquids. Obtained elastic properties are K_S0 = 99.1(9.4) GPa, K_S’ = 3.8(0.1) and ρ₀ =6.48 g/cm³ for S-rich Fe₇₃Ni₁₀S₁₀Si₇ liquid and K_S0 = 112.1(1.5) GPa, K_S’ = 4.0(0.1) and ρ₀=6.64 g/cm³ for Si-rich Fe₇₂Ni₁₀S₅Si₁₃ liquid. The V_P of Fe–Ni–S–Si liquids locate in between those of Fe–Ni–S and Fe–Ni–Si liquids. This suggests that the effect of multiple light element (S and Si) on the V_P is suppressed and cancel out the effects of single light elements (S and Si) on the V_P. The effect of composition on the EOS in the Fe–Ni–S–Si system is indispensable to estimate the core composition combined with the geodesy data of upcoming Mercury mission.

DOI： 10.1007/s00269-023-01243-8

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Informa UK Limited  

The density of liquid metals at high pressure and high-temperature provides fundamental and important information for understanding their compression behavior and elastic properties. In this study, the densities of liquid gallium (Ga) were measured up to 10 GPa and 533 K using the X-ray absorption method combined with an externally heated diamond anvil cell. The elastic properties (the isothermal bulk modulus (K-T0), and its pressure derivative (K-T0')) of liquid Ga were obtained by fitting the density data with three equations of state (EOSs) (Murnaghan, third order Birch-Murnaghan, and Vinet). The K-T0 values of liquid Ga were determined to be 45.7 +/- 1.0-51.7 +/- 1.0 GPa at 500 K assuming K-T0' values of 4-6. The obtained K-T0 or K-T0 ' showed almost the same values regardless of the EOS used. Compared with previous results, the compression curve of liquid Ga obtained in this study had a slightly stiffer trend at higher pressures.

DOI： 10.1080/08957959.2021.1998478

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：AIP Publishing  

DOI： 10.1063/5.0029448

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Mineralogical Society of America  

<title>Abstract</title>
Density and thermal expansion coefficient of metals are fundamental characteristics to describe the equation of state. Especially for liquid metals, the reported data for density and thermal expansion coefficient vary in the literature, even at ambient pressure. To determine the density of solid and liquid metals precisely at high temperatures and ambient pressure, we have developed a high-temperature furnace. The densities of solid Sn, Ni, and Fe were determined from the sample image with an uncertainty of 0.11–0.7% in the temperature range of 285–1803 K with increments of 1–10 K. The density of solid Sn decreased linearly with increasing temperature up to 493 K, and then the decrease became drastic until the melting temperature (Tm) was reached. By contrast, for solid Ni and Fe, the densities decreased linearly with increasing temperature up to the Tm (1728 and 1813 K) without any drastic density drop near Tm. This suggests that Ni and Fe do not exhibit the “premelting effect.”


The density of liquid Fe was determined with an uncertainty of 0.4–0.7% in the range of 1818–1998 K with temperature increments of 5 K. The obtained thermal expansion coefficient (α) of liquid Fe was well approximated as either a constant value of α = 2.42(1) × 10–4 K–1 or a linear function of temperature (T); α = 1.37(10) × 10–3 – [6.0(6) × 10–7]T [K–1] up to at least 2000 K.

DOI： 10.2138/am-2021-7509

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

DOI： 10.1016/j.pepi.2020.106640

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

DOI： 10.1038/s41467-020-15755-2

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Other Link： http://www.nature.com/articles/s41467-020-15755-2

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

<title>Abstract</title>Here we report on the effects of material strength factors on the generation of surface structure due to nonuniform laser irradiation. The influence of material strength on the generation of perturbation on a diamond surface subjected to nonuniform laser irradiation was experimentally investigated. Our previous investigations suggested that stiffer and denser materials reduce surface perturbation due to spatially nonuniform laser irradiation, which was reproduced well by calculations with multi-dimensional hydrodynamic simulation code. In this work, we found that local fractures due to yield strength failure are generated by high degrees of irradiation non-uniformity. A characteristic crack-like surface structure was observed, which was not reproduced by the 2D simulation code calculations at all. The 2D simulations showed that the pressure at the diamond surface locally exceeds the Hugoniot elastic limit due to nonuniform irradiation, implying the potential for development of surface perturbations. We also measured the areal-density distribution of perturbations for single-crystal diamond and diamond with a thin high atomic number (high-Z) coating on its surface. The experimental results imply that the combination of a stiff material and thin high-Z coating can suppress the solid-strength effects caused by large irradiation non-uniformity. The knowledge given here is applicable to inertial confinement fusion target design, laser material processing, and universal problems involving solids and high-energy-density plasmas.

DOI： 10.1038/s41598-020-66036-3

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Other Link： http://www.nature.com/articles/s41598-020-66036-3

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of High Pressure Science and Technology  

DOI： 10.4131/jshpreview.30.111

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

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Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

Abstract

Hydrogen is likely one of the light elements in the Earth’s core. Despite its importance, no direct observation has been made of hydrogen in an iron lattice at high pressure. We made the first direct determination of site occupancy and volume of interstitial hydrogen in a face-centered cubic (fcc) iron lattice up to 12 GPa and 1200 K using the in situ neutron diffraction method. The transition temperatures from the body-centered cubic and the double-hexagonal close-packed phases to the fcc phase were higher than reported previously. At pressures &lt;5 GPa, the hydrogen content in the fcc iron hydride lattice (x) was small at x &lt; 0.3, but increased to x &gt; 0.8 with increasing pressure. Hydrogen atoms occupy both octahedral (O) and tetrahedral (T) sites; typically 0.870(±0.047) in O-sites and 0.057(±0.035) in T-sites at 12 GPa and 1200 K. The fcc lattice expanded approximately linearly at a rate of 2.22(±0.36) ų per hydrogen atom, which is higher than previously estimated (1.9 ų/H). The lattice expansion by hydrogen dissolution was negligibly dependent on pressure. The large lattice expansion by interstitial hydrogen reduced the estimated hydrogen content in the Earth’s core that accounted for the density deficit of the core. The revised analyses indicate that whole core may contain hydrogen of 80(±31) times of the ocean mass with 79(±30) and 0.8(±0.3) ocean mass for the outer and inner cores, respectively.

DOI： 10.1038/s41598-019-43601-z

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Other Link： https://www.nature.com/articles/s41598-019-43601-z

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER FRANCE-EDITIONS SCIENTIFIQUES MEDICALES ELSEVIER  

A new experimental setup for simultaneous P-wave velocity (V-P) and density (rho) measurements for liquid alloys is developed using ultrasonic and X-ray absorption methods combined with X-ray tomography at high pressures and high temperatures. The new setup allows us to directly determine adiabatic bulk moduli (K-S) and to discuss the correlation between the V-P and rho of the liquid sample. We measured V-P and rho of liquid Ni68S32 up to 5.6 GPa and 1045 K using this technique. The effect of pressure on the V-P and rho values of liquid Ni68S32 is similar to that of liquid Fe57S43. (Both compositions correspond to near-eutectic ones.) The obtained K-S values are well fitted to the finite strain equation with a K-S0 value (K-S at ambient pressure) of 31.1 GPa and a dK(S)/dP value of 8.44. The measured V-P was found to increase linearly with increasing rho, as approximated by the relationship: V-P [m/s] = 1.29 rho [kg/m(3)] - 5726, suggesting that liquid Ni-S follows an empirical linear relationship, Birch's law. The dV(P)/d rho slope is similar between Ni68S32 and Fe57S43 liquids, while the V-P-rho plot of liquid Ni-S is markedly different from that of liquid Fe-S, which indicates that the effect of Ni on Birch's law is important for understanding the V-P-rho relation of planetary and Moon's molten cores. (C) 2018 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.

DOI： 10.1016/j.crte.2018.04.005

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© 2019, © 2019 Informa UK Limited, trading as Taylor & Francis Group. The Rayleigh–Taylor (RT) instability of liquid iron alloys is important for understanding the core formation mechanism in the Earth. Here we first report the measurement of RT instability growth for a liquid iron–silicon (Fe–Si) alloy, which is one of the major candidate for the material of the Earth’s core, using a high power laser. We optimized the measurement setup and analytical technique to observe the growth of perturbation on an Fe–Si sample surface. The growth of perturbation amplitude on the Fe–Si alloy under high pressure and temperature was successfully observed using in situ X-ray radiography. The growth rate of the RT instability for the Fe–Si alloy on about 1000 GPa was estimated to be 0.3 ns −1 .

DOI： 10.1080/08957959.2019.1575966

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Language：English   Publishing type：Part of collection (book)   Publisher：Elsevier  

Density and elastic properties (such as bulk modulus) of liquid materials under pressure are important to understand the behavior and distribution of magma in the Earth’s interior. The magma behavior is also closely related to mantle differentiation in the early Earth. In this chapter, the currently proposed density, sound velocity, and elasticity measurements for noncrystalline materials at high pressure are reviewed and the advantages and potential problems of these methods are discussed.

DOI： 10.1016/B978-0-12-811301-1.00009-5

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DOI： 10.1080/08957959.2018.1499903

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier Masson SAS  

A technique for density measurement under high pressure and high temperature was developed using the X-ray absorption imaging method combined with an externally heated diamond anvil cell. The densities of solid and liquid In were measured in the pressure and temperature ranges of 3.2–18.6 GPa and 294–719 K. The densities obtained through the X-ray absorption imaging method were in good agreement (less than 2.0% difference) with those obtained through X-ray diffraction. Based on the measured density, the isothermal bulk modulus of solid In is determined as 48.0 ± 1.1−40.9 ± 0.8 GPa at 500 K, assuming K′ = 4 to 6. The compression curve of liquid In approaches that of solid In at higher pressures and does not cross over the solid compression curve in the measurement range. The present technique enables us to determine the densities of both solids and liquids precisely in a wide pressure and temperature range.

DOI： 10.1016/j.crte.2018.04.002

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Language：Japanese  

DOI： 10.18957/rr.6.2.208

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Language：Japanese   Publisher：Japan Association of Mineralogical Sciences  

Elastic wave velocities and density of iron-silicon alloys were determined experimentally up to 6 GPa and 1873 K using ultrasonic and X-ray diffraction methods. We suceeded in determining the pressure- and temperature-dependences of the properties, and also found the difference between bcc and fcc structures.

DOI： 10.14824/jakoka.2017.0_103

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Language：English   Publishing type：Research paper (bulletin of university, research institution)  

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

Carbon is one of the possible light elements in the cores of the terrestrial planets. The P wave velocity (V-P) and density (rho) are important factors for estimating the chemical composition and physical properties of the core. We simultaneously measured the V-P and rho of Fe-3.5 wt % C up to 3.4 GPa and 1850 K by using ultrasonic pulse-echo method and X-ray absorption methods. The V-P of liquid Fe-3.5 wt % C decreased linearly with increasing temperature at constant pressure. The addition of carbon decreased the V-P of liquid Fe by about 2% at 3 GPa and 1700 K and decreased the Fe density by about 2% at 2 GPa and 1700 K. The bulk modulus of liquid Fe-C and its pressure (P) and temperature (T) effects were precisely determined from directly measured rho and V-P data to be K-0,K-1700 K = 83.9 GPa, dK(T)/dP = 5.9(2), and dK(T)/dT = -0.063(8) GPa/K. The addition of carbon did not affect the isothermal bulk modulus (K-T) of liquid Fe, but it decreased the dK/dT of liquid Fe. In the rho-V-P relationship, V-P increases linearly with rho and can be approximated as V-P (m/s) = -6786(506) + 1537(71) x rho (g/cm(3)), suggesting that Birch's law is valid for liquid Fe-C at the present P-T conditions. Our results imply that at the conditions of the lunar core, the elastic properties of an Fe-C core are more affected by temperature than those of Fe-S core.

DOI： 10.1002/2016JB012968

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

Recent advances in techniques for high-pressure and high-temperature experiments enable us to measure the velocity of sound in liquid Fe alloys. However, reported velocities in liquid Fe S differ among research groups (e.g., by &gt;10% at 5 GPa), even when similar methods are used (i.e., the ultrasonic pulse echo overlap method combined with a large volume press). To identify the causes of the discrepancies, we reanalyzed previous data and conducted additional sound velocity measurements for liquid Fe S at 2-7 GPa, and evaluated the potential error sources. We found that the discrepancy cannot be explained by errors in the sound velocity measurements themselves, but by inaccuracies in determining the temperature, pressure, and chemical composition in each experiment. Of particular note are the significant errors introduced when determining pressures from the unit-cell volume of MgO, which is a temperature-sensitive pressure standard, using inaccurate temperatures. To solve the problem, we additionally used h-BN as a pressure standard, which is less sensitive to temperature. The pressure dependence of the sound velocity became smaller than that of the original data because of the revised pressure values. Our best estimate for the seismic velocity of the Moon's liquid outer core is 4.0 +/- 0.1 km/s, given a chemical composition Fe83S17. (C) 2016 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.pepi.2016.06.009

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

The cores of the Earth and other differentiated bodies are believed to be comprised of iron and various amounts of light elements. Measuring the densities and sound velocities of iron and its alloys at high pressures and high temperatures is crucial for understanding the structure and composition of these cores. In this study, the sound velocities (v(P) and v(S)) and density measurements of body-centered cubic (bcc)-Fe were determined experimentally up to 6.3 GPa and 800 K using ultrasonic and X-ray diffraction methods. Based on the measured v(P), v(S), and density, we obtained the following parameters regarding the adiabatic bulk K-S and shear G moduli of bcc-Fe: K-50 = 163.2(15) GPa, partial derivative K-S/partial derivative P = 6.75(33), partial derivative K-S/partial derivative T = -0.038(3) GPa/K, G(0) = 81.4(6) GPa, partial derivative G/partial derivative P = 1.66(14), and partial derivative G/partial derivative T = -0.029(1) GPa/K. Moreover, we observed that the sound velocity-density relationship for bcc-Fe depended on temperature in the pressure and temperature ranges analyzed in this study and the effect of temperature on vs was stronger than that on vp at a constant density, e.g., 6.0% and 2.7% depression for v(S) and v(P), respectively, from 300 to 800 K at 8000 kg/m(3). Furthermore, the effects of temperature on both v(P) and vs at a constant density were much greater for bcc-Fe than for epsilon-FeSi (cubic B20 structure), according to previously obtained measurements, which may be attributable to differences in the degree of thermal pressure. These results suggest that the effects of temperature on the sound velocity density relationship for Fe alloys strongly depend on their crystal structures and light element contents in the range of pressure and temperature studied.

DOI： 10.2138/am-2016-5545

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

The sound velocity (V (P)) of liquid Fe-10 wt% Ni and Fe-10 wt% Ni-4 wt% C up to 6.6 GPa was studied using the ultrasonic pulse-echo method combined with synchrotron X-ray techniques. The obtained V (P) of liquid Fe-Ni is insensitive to temperature, whereas that of liquid Fe-Ni-C tends to decrease with increasing temperature. The V (P) values of both liquid Fe-Ni and Fe-Ni-C increase with pressure. Alloying with 10 wt% of Ni slightly reduces the V (P) of liquid Fe, whereas alloying with C is likely to increase the V (P). However, a difference in V (P) between liquid Fe-Ni and Fe-Ni-C becomes to be smaller at higher temperature. By fitting the measured V (P) data with the Murnaghan equation of state, the adiabatic bulk modulus (K (S0)) and its pressure derivative (K (S) (') ) were obtained to be K (S0) = 103 GPa and K (S) (') = 5.7 for liquid Fe-Ni and K (S0) = 110 GPa and K (S) (') = 7.6 for liquid Fe-Ni-C. The calculated density of liquid Fe-Ni-C using the obtained elastic parameters was consistent with the density values measured directly using the X-ray computed tomography technique. In the relation between the density (rho) and sound velocity (V (P)) at 5 GPa (the lunar core condition), it was found that the effect of alloying Fe with Ni was that rho increased mildly and V (P) decreased, whereas the effect of C dissolution was to decrease rho but increase V (P). In contrast, alloying with S significantly reduces both rho and V (P). Therefore, the effects of light elements (C and S) and Ni on the rho and V (P) of liquid Fe are quite different under the lunar core conditions, providing a clue to constrain the light element in the lunar core by comparing with lunar seismic data.

DOI： 10.1007/s00269-015-0789-y

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Language：English   Publishing type：Part of collection (book)   Publisher：wiley  

The physical properties of liquid Fe alloys are important for understanding the characteristics of the molten outer core. The possible core composition can be constrained by matching the observed seismic data with the measured sound velocity and density of liquid Fe alloys. The transport properties of liquid Fe alloys strongly influence the convection behavior of the outer core. This chapter reviews the latest results on the elastic and transport properties of liquid Fe alloys obtained based on experimental and numerical approaches. Three variables of pressure (P), temperature (T), and specific volume (V), which are indispensable for understanding the structure and properties of Earth's interior, are linked by an equation of state (EOS). Convectional motion of the outer core is controlled by core magneto hydrodynamics. The viscosity of liquid Fe, Fe-S, and Fe-C at high pressures has been measured using the falling sphere method combined with in situ X-ray radiography.

DOI： 10.1002/9781118992487.ch11

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

The equation of state of Fe3S was investigated up to 200 GPa at room temperature using a diamond anvil cell. Fe3S adopts a tetragonal structure up to 200 GPa and no phase transition was observed. The fourth-order Birch-Murnaghan equation of state (EOS) was fitted to present compression data at room temperature. The elastic parameters, such as bulk modulus (K-0), its pressure derivative (K-0'), and K-0 ''(dK'/dP) were determined to be 122.4(50) GPa, 5.36(48), and -0.066(30) GPa(-1), respectively by fixing the zero pressure volume, V-0, to be 377 angstrom(3). Based on fourth-order Birch-Murnaghan EOS of Fe3S, the maximum amount of S in the inner core was estimated to be 11.4(14) at.% based on the density deficit of the inner core. (C) 2013 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.pepi.2013.11.001

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

Planetary cores are considered to consist of an iron-nickel (Fe-Ni) alloy and light elements and hydrogen is one of plausible light elements in the core. Here we have performed in situ X-ray diffraction experiments on an Fe0.9Ni0.1-H system up to 15.1 GPa and 1673 K, and investigated the effect of Ni on phase relations of FeHx under high pressure and high temperature. The experimental system in the present work was oversaturated with hydrogen. We found a face-center-cubic (fcc) phase (with hydrogen concentration up to x similar to 1) and a body-center-cubic (bcc) phase (x &lt; 0.1) as stable phases. The partial melting was observed below 6 GPa. We could not observe a double-hexagonal-close-packed (dhcp) phase because of limitations in pressure and temperature conditions. The stability field of each phase of Fe0.9Ni0.1Hx was almost same as that of FeHx. The solidus of Fe0.9Ni0.1Hx was 500-700 K lower than the melting curve of Fe and its liquidus was 400-600 K lower than that of Fe in the pressure range of this study. Both the solidus and liquidus of Fe0.9Ni0.1Hx were depressed at around 3.5 GPa, as was the solidus of FeHx. The hydrogen contents in fcc-Fe(0.9)Ni(0.1)Hx just below solidus were slightly lower than those of fcc-FeHx, which suggests that nickel is likely to prevent dissolution of hydrogen into iron. Due to the lower hydrogen solubilities in Fe0.9Ni0.1 compared to Fe, the solidus of Fe0.9Ni0.1Hx is about 100-150 K higher than that of FeHx. (C) 2013 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.pepi.2013.12.013

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

We measured the sound velocity of Fe3S at room temperature up to 85 GPa employing inelastic X-ray scattering to better constrain the constitution of the inner core. The density of Fe3S was also determined by X-ray diffraction under the same conditions. The relation of the P-wave velocity (v(P)) and density (rho) of Fe3S follows Birch's law, v(P)(m/s) = 1.14(5) x rho(kg/m(3)) - 2580(410). Based on Birch's law determined here for Fe3S and that for epsilon-Fe reported previously, we found that sulfur decreases both density and compressional velocity of hcp-Fe at the core pressure and 300 K.

DOI： 10.2138/am.2014.4463

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IRON STEEL INST JAPAN KEIDANREN KAIKAN  

We have performed in situ X-ray diffraction measurements under high pressure and high temperature to study hydrogen solubility in Fe3C carbide. Hydrogen solubility can be estimated from a volume expansion associated with hydrogen incorporation into metal. The lattice volumes and phase relations of Fe3C H system and Fe3C were measured up to 14 GPa and 1 973 K. The lattice volumes of Fe3C measured in this study are well fitted using the 3rd order Birch Murnaghan equation of state with the reported elastic parameters of Fe3C. Obtained lattice volumes of Fe3C H are quite consistent with those of Fe3C. No difference between the melting temperatures of Fe3C H and Fe3C was observed. These results demonstrate that hydrogen incorporation into Fe3C does not occur and hydrogen is unlikely to coexist with carbon in iron-alloy up to 14 GPa.

DOI： 10.2355/isijinternational.54.2637

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：NATURE PUBLISHING GROUP  

The boundary between Earth's rigid lithosphere and the underlying, ductile asthenosphere is marked by a distinct seismic discontinuity(1). A decrease in seismic-wave velocity and increase in attenuation at this boundary is thought to be caused by partial melt(2). The density and viscosity of basaltic magma, linked to the atomic structure(3,4), control the process of melt separation from the surrounding mantle rocks(5-9). Here we use high-pressure and high-temperature experiments and in situ X-ray analysis to assess the properties of basaltic magmas under pressures of up to 5.5 GPa. We find that the magmas rapidly become denser with increasing pressure and show a viscosity minimum near 4 GPa. Magma mobility-the ratio of the melt-solid density contrast to the magma viscosity-exhibits a peak at pressures corresponding to depths of 120150 km, within the asthenosphere, up to an order of magnitude greater than pressures corresponding to the deeper mantle and shallower lithosphere. Melts are therefore expected to rapidly migrate out of the asthenosphere. The diminishing mobility of magma in Earth's asthenosphere as the melts ascend could lead to excessive melt accumulation at depths of 80-100 km, at the lithosphere-asthenosphere boundary. We conclude that the observed seismic discontinuity at the lithosphere-asthenosphere boundary records this accumulation of melt.

DOI： 10.1038/NGEO1982

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

Carbon is a plausible light element candidate in the Earth's outer core. We measured the density of liquid Fe-3.5 wt% C up to 6.8 GPa and 2200 K using an X-ray absorption method. The compression curve of liquid Fe-C was fitted using the third-order Birch-Murnaghan equation of state. The bulk modulus and its pressure derivative are K-0.1500K = 55.3 +/- 2.5 GPa and (dK(o)/dP)(T) = 5.2 +/- 1.5, and the thermal expansion coefficient is alpha = 0.86 +/- 0.04 x 10(-4) K-1. The Fe-C density abruptly increases at pressures between 4.3 and 5.5 GPa in the range of present temperatures. Compared with the results of previous density measurements of liquid Fe-C, the effect of carbon on the density of liquid Fe shows a nonideal mixing behavior. The abrupt density increase and nonideal mixing behavior are important factors in determining the light element content in the Earth's core. (C) 2013 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.pepi.2013.08.003

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The phase and melting relations of the C-saturated C-Mg-Fe-Si-O system were investigated at high pressure and temperature to understand the role of carbon in the structure of the Earth, terrestrial planets, and carbon-enriched extraterrestrial planets. The phase relations were studied using two types of experiments at 4 GPa: analyses of recovered samples and in situ X-ray diffractions. Our experiments revealed that the composition of metallic iron melts changes from a C-rich composition with up to about 5 wt.% C under oxidizing conditions (ΔIW = -1.7 to -1.2, where ΔIW is the deviation of the oxygen fugacity (fO2) from an iron-wüstite (IW) buffer) to a C-depleted composition with 21 wt.% Si under reducing conditions (ΔIW < -3.3) at 4 GPa and 1,873 K. SiC grains also coexisted with the Fe-Si melt under the most reducing conditions. The solubility of C in liquid Fe increased with increasing fO2, whereas the solubility of Si decreased with increasing fO2. The carbon-bearing phases were graphite, Fe3C, SiC, and Fe alloy melt (Fe-C or Fe-Si-C melts) under the redox conditions applied at 4 GPa, but carbonate was not observed under our experimental conditions. The phase relations observed in this study can be applicable to the Earth and other planets. In hypothetical reducing carbon planets (ΔIW < -6.2), graphite/diamond and/or SiC exist in the mantle, whereas the core would be an Fe-Si alloy containing very small amount of C even in the carbon-enriched planets. The mutually exclusive nature of C and Si may be important also for considering the light elements of the Earth's core. © 2013 Springer-Verlag Berlin Heidelberg.

DOI： 10.1007/s00269-013-0600-x

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

The P-wave velocity (V-p) of liquid Fe57S43 was measured up to 5.4 GPa using an ultrasonic method combined with the synchrotron X-ray technique. The Vp of liquid Fe57S43 showed little change with temperature, but increased almost linearly from 3105 +/- 11 m/s to 3845 +/- 9 m/s with increasing pressure from 2.4 to 5.4 GPa. This can be approximated by Vp [m/s]=2664+205.4 x P, where P is the pressure in GPa. The V-P of liquid Fe57S43 at 2.4-5.4 GPa was significantly lower than that of pure liquid Fe. However, the pressure dependence of Vp of the liquid Fe57S43 was markedly higher than that of pure liquid Fe. The marked difference in the pressure dependences of VP between pure liquid Fe and liquid Fe57S43 may cause Vp crossover at around 7 GPa. As a result, the Vp of liquid Fe57S43 would become higher than that of pure liquid Fe at pressures higher than 7 GPa. Thus, S decreases Vp at low pressures such as those of the lunar outer core, but would increase it at the high pressures of the Earth's outer core. Assuming the lunar core consists of a liquid Fe-FeS outer core and a solid Fe inner core, the expected Vp in the lunar outer core ranges from 3756 to 4230 m/s. (C) 2012 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.epsl.2012.11.042

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In situ X-ray diffraction experiments in the Fe-Fe3S system were performed up to 175 GPa and 3500 K using a laser-heated diamond anvil cell to investigate melting relationships in the system. Partial melting in the Fe-Fe3S system was observed based on the disappearance of X-ray diffraction peaks of solid Fe3S and texture observation of the recovered samples. The melting relationship of the Fe-Fe3S system as a function of pressure is evaluated based on Kraut-Kennedy law. Our results of melting relationships suggest that the temperature at the inner core boundary is between 4700(160) and 4930(330) K if sulfur is the only light element in the Earth's core. Assuming the adiabatic temperature gradient in the outer core, the temperature at the core-mantle boundary is estimated to be in the range of 3600-3770 K. The present temperature profile of the core is consistent with the core-mantle boundary temperature that can explain the core heat flux to maintain the core dynamo and the seismic structure at the base of the lower mantle. (C) 2012 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.epsl.2012.09.038

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Language：Japanese   Publishing type：Research paper (bulletin of university, research institution)  

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The interfacial tension of Fe-Si liquid was measured using in situ X-ray radiography at high pressure and temperatures using the sessile drop method. The interfacial tension of Fe-Si liquid decreases (from 665 to 407 mN/m) with increasing temperature (1673-2173 K) at 1.5 GPa. The interfacial tension also decreases gradually with increasing Si content (0-25 at%), suggesting that Si behaves as a "moderately" surface-active element. Comparing the effects of different light elements on the interfacial tension of liquid iron, the most effective elements for reducing the interfacial tension lie in the order S &gt; Si &gt; P. although P has almost no effect. The droplet size of emulsified Fe-alloys in a magma ocean are estimated to be larger for Fe-Si and Fe-P liquids and smaller for Fe-S (S &gt; 10 at%) liquid compared with that for pure Fe liquid. Therefore, if droplets in a magma ocean are enriched in S, chemical equilibrium between droplets and silicate melt is established faster in the magma ocean compared to Fe, Fe-Si and Fe-P liquids. (c) 2012 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.pepi.2012.05.002

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A hybrid in-situ characterization system, which couples the laser scanning confocal microscopy (LSCM) with the time-resolved X-ray diffraction (TRXRD) measurement with synchrotron radiation, was used to characterize the microstructure evolution during heat-affected zone (HAZ) thermal cycling of high-strength and blast-resistant steel. The combined technique has a time resolution of 0.3 seconds that allows for high-fidelity measurements of transformation kinetics, lattice parameters, and morphological features. The measurements showed a significant reduction in the martensite start transformation temperature with a decrease in the prior austenite grain size. In addition, the LSCM images confirmed the concurrent refinement of martensite packet size with smaller austenite grain sizes. This is consistent with dilatometric observations. The austenite grain size also influenced the rate of transformation (df (m) /dT); however, the measurements from the hybrid (surface) and dilatometric (volume) measurements were inconsistent. Challenges and future directions of adopting this technique for comprehensive tracking of microstructure evolution in steels are discussed.

DOI： 10.1007/s11661-011-0746-4

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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

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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

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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

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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&apos;(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

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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

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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

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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&apos;(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&apos;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

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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

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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 &gt; 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 &gt; 10 GPa) in the planetary interior.

DOI： 10.2138/am.2011.3628

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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&apos;s core may be composed of an Fe-S-H system. According to our results, hydrogen dissolved in Ganymede&apos;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

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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

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DOI： 10.1016/j.epsl.2011.02.041

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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

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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

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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

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Density of liquid iron alloy under high pressure is important to constrain the amount of light elements in the Earth&apos;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&apos;s outer core.

DOI： 10.1029/2009JB006905

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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&apos;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

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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

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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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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

Synthetic conditions such as stoichiometries, temperature and pressure are optimized to achieve a high quality oxygen deficient SmFeAsO0.6 superconductor. Both electric and magnetic measurements show a sharp superconducting transition at about 55 K. Several important physical parameters are deduced. The apparent superconducting gap observed in heat capacity with 2 Delta(o)/k(B)T(c) of 4.57 larger than that of previous fluorine replaced samples indicate that this superconductivity will not strongly conflict with the phonon-mediated BCS mechanism. The mean free length l = 18.8 nm and the coherent length xi = 2.3-3.3 nm show that the superconductivity is in the clean limit. (C) 2009 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.jpcs.2009.12.019

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Intragranular acicular ferrite is regarded as a most desirable microstructure feature, in view of its strength and toughness, both in weld metals and in the heat-affected zone. This paper systematically investigated the effect of Ti addition on the evolution of intragranular acicular ferrite in the heat-affected zone of C-Mn steel. We also systematically studied the effects of austenite grain size, alloy content and the characteristic of inclusions on the formation of intragranular acicular ferrite. The nucleation and growth of intragranular acicular ferrite was directly observed by laser scanning confocal microscopy. Subsequently, microscopy analysis was used to quantitatively determine and distinguish the potent and inactive inclusions with respect to the nucleation of intragranular acicular ferrite. Finally, some possible reasons are given to explain the formation of intragranular acicular ferrite in the C-Mn steel. (C) 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.actamat.2009.10.043

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DOI： 10.4131/jshpreview.20.181

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：TAYLOR & FRANCIS LTD  

Semi-sintered MgO-and ZrO(2)-based ceramics are the conventional materials used as a pressure-transmitting medium (PM) for large-volume high-pressure experiments. Our experimental data for both MgO and ZrO(2) provide similar pressure generation efficiency. The major requirement for a PM material is low compressibility. However, our experimental data suggest that semi-sintered types of these ceramics are more compressible than can be expected. For instance, the apparent compressibility of semi-sintered magnesia is 35% and 60% higher than the lattice compressibility of MgO at 15 and 30 GPa, respectively. The difference in lattice and apparent compressibilities of semi-sintered ceramics is most probably caused by a residual porosity. The use of a low-porous pressure medium should be considered as an improvement of pressure generation efficiency of high-pressure apparatuses.

DOI： 10.1080/08957959.2010.515079

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IOP PUBLISHING LTD  

A new high-pressure apparatus has been developed for studies of synchrotron radiation-based X-ray microtomography at SPring-8 of Japan. The high pressure tomography apparatus at SPring-8 is a compact hydraulic press with a 0.8 MN capacity and is equipped with an opposed anvil device. It has two wide windows for X-ray access with a 160-degree opening in the equatorial plane to the compression axis. Radiographs are acquired over 180 degree rotation for reconstruction of 3D image, in which some shadows occur, because the press frame blocks a 20-degree angular region. 3D tomography image computed from radiographs obtained using the high pressure tomography apparatus has a reasonably good quality enough to measure physical properties of materials.

DOI： 10.1088/1742-6596/215/1/012026

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DOI： 10.1107/S0909049509034955

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-BLACKWELL  

A system for stress measurement under high pressure has been developed at beamline BL04B1, SPring-8, Japan. A Kawai-type multi-anvil apparatus, SPEED-1500, was used to pressurize polycrystalline KCl to 9.9 GPa in a mechanically anisotropic cell assembly with the KCl sample sandwiched between dense Al2O3 pistons. The variation of deviatoric stress was determined from the lattice distortion measured using two-dimensional X-ray diffraction with monochromatic synchrotron X-rays. The low-pressure B1 phase transformed to the high-pressure polymorph B2 during compression. The deviatoric stress increased with increasing pressure in both the B1 and B2 phases except for the two-phase-coexisting region at a pressure of 2-3 GPa. This new system provides one of the technical foundations for conducting precise rheological measurements at conditions of the Earth's lower mantle.

DOI： 10.1107/S0909049509034955

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We determined the exchange partition coefficients of hydrogen between solid iron and ringwoodite between 16.6 and 20.9 GPa at temperatures up to 1273 K using a Kawai-type multianvil high-pressure apparatus with synchrotron X-ray radiation at the BL04B1 beamline at SPring-8, Japan. The hydrogen concentration in iron hydride was estimated from the volume expansion of iron caused by hydrogenation determined by in situ X-ray diffractions at high pressure and high temperature, and the water content of ringwoodite in the recovered samples was estimated using the Fourier transform infrared spectroscopy (FTIR). According to our results, the exchange partition coefficients of hydrogen between the solid iron and ringwoodite were almost constant, 26, with pressure between 16.6 and 20.9 GPa and 1273 K. These results revealed that hydrogen was strongly partitioned to metallic iron and that iron hydride formed, coexisting with dry ringwoodite under the experimental pressures. Ringwoodite, found in the Martian core-mantle boundary region, is an important hydrogen reservoir. The pattern of quasi-parallel bands of uniformly magnetized crust with alternating positive and negative polarity measured by the Mars Global Surveyor spacecraft strongly shows that a magnetic field did exist in ancient Mars suggesting a possible plate tectonic activity on ancient Mars. Thus, water could have been transported to the deep Martian interior by hydrous minerals during the plate subduction process and stored in ringwoodite in the deep Martian slabs, as is suggested on the Earth today. Our experiments suggested that hydrogen stored in ringwoodite was absorbed by the Martian core at the Martian core-mantle boundary. Thus, water from the ancient Martian ocean may be stored now in the Martian core. © 2009 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.epsl.2009.08.034

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Coupled (186)Os/(188)Os and (187)Os/(188)Os enrichments of plume-derived lavas have been suggested to reflect contributions of materials from the outer core (Brandon et al., 1998). This hypothesis is based on the assumption that the Earth&apos;s liquid outer core has high Pt/Os and slightly high Re/Os ratios as a result of the crystallization of the solid inner core, and shows coupled enrichments in the (186)Os/(188)Os and (187)Os/(188)Os ratios, reflecting the decay of (190)Pt and (187)Re to (186)Os and (187)Os, respectively. Partitioning experiments of Pt-Re-Os between solid and liquid metal were performed at 5-20 GPa and 1250-1400 degrees C, to examine the effects of pressure in the Fe-Ni-S system. The ratios (D(Os)/D(Pt), D(Os)/D(Re)) of measured partition coefficients of Pt, Re and Os are almost constant with increasing pressure. D(Os)/D(Pt) increases significantly, whereas D(Os)/D(Re) decreases, with increasing sulphur content in the liquid metal. On the basis of the present experimental results, it is unlikely that the required Pt-Re-Os fractionation is generated during inner core crystallization, assuming that the light element in the Earth&apos;s core is sulphur. (C) 2009 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.gca.2009.05.055

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Fe-Mg partitioning between perovskite and ferropericlase in the MgO-FeO-SiO2 system has been studied up to about 100 GPa at around 2000 K using a laser-heated diamond anvil cell (LHDAC). The compositions of both phases were determined by using analytical transmission electron microscopy (ATEM) on the recovered samples. Present results reveal that the Fe-Mg apparent partition coefficient between perovskite and ferropericlase [K-D(Pv/Fp) = ((XFeXMgFp)-X-Pv)/((XMgXFeFp)-X-Pv)] decreases with increasing pressure for a constant FeO of the system, and it decreases with increasing FeO content of ferropericlase. The gradual decrease of K-D(Pv/FP) with increasing pressure is consistent with the spin transition in ferropericlase Occurring in the broad pressure range from 50 to 100 GPa at around 2000 K.

DOI： 10.2138/am.2009.3123

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We have experimentally determined the solidus of an alkali-bearing carbonated peridotite (with 5 wt-% CO(2)) between 10 and 20 GPa. Based on K-deficit in all low-temperature runs we assumed that some melt could be present in the low temperature runs and the true solidus of an alkali-bearing carbonated peridotite is placed below 1200 degrees C. However, based on the disappearance of magnesite and the appearance of the visible quenched melt coexisting with silicate phases, the &apos;apparent&apos; solidus, which may be applicable for peridotite with low alkali contents, was identified. The &apos;apparent&apos; solidus temperature increases from similar to 1380 degrees C at 10 GPa to similar to 1525 degrees C at 15 GPa and the &apos;apparent&apos; solidus curve becomes almost flat from 15 GPa to 20 GPa, where it is located near 1550 degrees C. At 10 GPa, the &apos;apparent&apos; solidus of carbonated peridotite is similar to 550 degrees C lower than the solidus Of CO(2)-free natural anhydrous peridotite. The solidus of the present study was also similar to 120 degrees C lower than the solidus determined by Dasgupta and Hirschmann [Dasgupta, R., Hirschmann, M.M., 2006. Melting in the Earth&apos;s deep upper mantle caused by carbon dioxide. Nature, 440, 659-662.] for natural carbonated peridotite. The drop in the solidus temperature is mainly due to the effect of alkalis (Na(2)O, K(2)O). The melt near the &apos;apparent&apos; solidus has high CO(2) (&gt;40 wt.%) and contains &lt;6.0 wt.% SiO(2), &lt;030 wt.% Al(2)O(3) and &lt;0.25 wt.% TiO(2). The composition of near-solidus partial melt is close to that observed at 6-10 GPa in the CMS-CO(2) and CMAS-CO(2) systems, and natural carbonated peridotite, with some variations in Ca/Mg-ratio. High alkali contents in measured and calculated partial melts are consistent with the compositions of deep-seated fluids observed as inclusions in diamonds and may be consistent with the compositions of parental melt, reconstructed for natural magnesiocarbonatite. We have demonstrated that magnesiocarbonatite-like melt can be generated by partial melting of carbonated peridotite at pressure up to at least 20 GPa. The generation of calciocarbonatite and ferrocarbonatite is unlikely to be possible during melting of carbonated peridotite in the deep mantle. (C) 2009 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.chemgeo.2008.12.030

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Interfacial tension is one of the most important properties of the liquid iron alloy that controls the core formation process in the early history of the Earth and planets. In this study, we made high-pressure X-ray radiography and micro-tomography measurements to determine the interfacial tension between liquid iron alloys and silicate melt using the sessile drop method. The measured interfacial tension of liquid Fe-S decreased significantly (802-112 mN/m) with increasing sulphur content (0-40 at%) at 1.5 GPa. In contrast, the phosphorus content of Fe had an almost negligible effect on the interfacial tension of liquid iron. These tendencies in the effects of light elements are consistent with those measured at ambient pressure. Our results suggest that the effect of sulphur content on the interfacial tension of liquid Fe-S (690 mN/m reduction with the addition of 40 at% S) is large compared with the effect of temperature (similar to 273 mN/m reduction with an increase of 200 K). The three-dimensional structure of liquid Fe-S was obtained at similar to 2 GPa and 1373-1873 K with a high-pressure tomography technique. The Fe-S droplet was quite homogeneous when evaluated in a slice of the three-dimensional image. (C) 2009 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.pepi.2009.01.004

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The percolation of liquid iron alloy through crystalline silicates potentially played an important role during core formation in planetary bodies of the early solar system. In order to test the feasibility of percolative core formation, the effects of pressure, composition and mineral assemblage on the dihedral angle between Fe-O-S liquid and mantle minerals have been investigated from 1.5 to 23.5 GPa. Texturally-equilibrated dihedral angles increase from 54 to 106° over this pressure range. The dihedral angle increases with pressure and closely related to the oxygen content of Fe-O-S phase, which decreases with increasing pressure, because oxygen reduces the interfacial energy of Fe-S melt. However, the effect of mineral assemblage on the dihedral angle seems to be negligible. Therefore, percolation is likely to have been the dominant core formation mechanism in small relatively-oxidised planetary bodies with a radius less than abogt 1300 km.

DOI： 10.2465/gkk.38.9

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Physical properties of liquid iron-alloy under high pressure control the planetary core formation, evolution and its dynamics. In this review paper, high pressure behaviors of some physical properties (viscosity, wetting property and interfacial tension) are discussed and applied to the planetary core. The viscosities of Fe-S and Fe-C liquids measured using X-ray radiography falling sphere method up to 16 GPa show low viscosity values (∼10 mPa-s) and the activation volume of viscous flow is also very small (∼1.5 cm 3/mol). The influence of light elements on the viscosity and the activation volume has only a minor contribution. Dihedral angle, i.e. wetting property of Fe-S-O liquid among mantle minerals is mainly controlled by an interfacial energy of liquid iron-alloy and not by that of solid phase. The effect of light elements on interfacial tension of Fe-S and Fe-P liquids measured using sessile drop method depends on element species. Sulphur corresponds to a surface-active element. The trend observed at high pressure is quite consistent with those at ambient pressure.

DOI： 10.4131/jshpreview.19.156

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DOI： 10.1016/j.chemgeo.2008.12.030

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The density of liquid Fe-S was measured at 4 GPa and 1,923 K using a sink/float method with a composite density marker. The density marker consisted of a Pt rod core and an Al(2)O(3) tube surrounding. The uncertainty in the density of the composite marker is much smaller than that of the composite sphere, which had been used in previous density measurements. The density of liquid Fe-S decreases nonlinearly with increasing sulfur content at 4 GPa and 1,923 K. This tendency is consistent with the results measured at ambient pressure. The molar volume of FeS calculated from the measured density gradually increases with sulfur content. The excess molar volume from ideal mixing of Fe and S at 4 GPa was negative value. The new method proposed here is applicable to the density measurement of other Fe alloys at high pressure. The tendency of the molar volume and the excess molar volume with sulfur content at ambient pressure is consistent with these at high pressure at least up to 4 GPa. The excess molar volume at high pressure is essential for estimating the amount of light elements in the outer core.

DOI： 10.1007/s00269-008-0236-4

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The percolation of liquid iron alloy through crystalline silicates potentially played an important role during core formation in small bodies of the early solar system, such as asteroids and planetesimals. This is because heat production by radioactive decay of Al-26 and Fe-60. which is believed to be the main heat source in early-formed small planetary bodies, will initially cause Fe-S melts to form, well before the silicates start to melt. In order to test the feasibility of percolation, the effect of pressure on the dihedral angle between Fe-O-S liquid and olivine has been investigated from 1.5 to 5.0 GPa, a pressure range that is relevant for the interiors of large asteroids. Texturally-equilibrated dihedral angles increase from 54 degrees to 98 degrees over this pressure range. The dihedral angle reaches the critical value of 60 degrees at 2-3 GPa depending on the olivine composition (Fe#). This change in dihedral angle is related to the oxygen content of Fe-O-S phase, which decreases with increasing pressure, because oxygen dissolved in the melt reduces the Fe-S melt/olivine interfacial energy. These results show that Fe-O-S liquid can form an interconnected network and percolate through silicate aggregates under conditions of high oxygen fugacity and low pressure, even when the melt fraction is small. Therefore, percolation is likely to have been the dominant core formation mechanism in small relatively-oxidised planetary bodies with a radius less than about 1300 km. (C) 2008 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.epsl.2008.06.019

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X-ray diffraction experiments were conducted to 257 GPa and high temperature in situ on an iron-silicon alloy containing 3.4 wt% silicon, a candidate for the Earth's inner core forming material. The results revealed that fcc and hcp phases coexist up to 104 GPa. A single hcp phase is stable at higher pressures at least up to 3600 K at 242 GPa and to 2400 K at 257 GPa. Dissolution of silicon in the liquid outer core following reaction with the silicate mantle during core formation strongly suggests the existence of silicon in the solid inner core. Our results revealed that the iron-3.4 wt% silicon alloy in the inner core is likely to possess an hcp structure, which can explain the inner core anisotropy observed in seismology.

DOI： 10.1029/2008GL033863

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High-pressure, high-temperature X-ray tomography experiments have been carried out using a large volume toroidal cell, which is optimized for interfacial tension measurements. A wide anvil gap, which corresponds to a field of view in the radiography imaging, was successively maintained to high pressures and temperatures using a composite plastic gasket. Obtained interfacial tensions of Ni-S liquid against Na, K-disilicate melt, were 414 and 336 mN/m at 1253 and 1293 K, respectively. Three-dimensional tomo-graphy images revealed that the sample had an irregular shape at the early stage of melting, suggesting either non-equilibrium in sample texture and force balance or partial melting of surrounding silicate. This information cannot always be obtained from two-dimensional radiographic imaging techniques. Therefore, a three-dimensional tomography measurement is appropriate for the precise interfacial measurements.

DOI： 10.1080/08957950802208902

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We have performed in situ experiments on liquid immiscibility in Fe-O-S melts at 3 GPa and up to 2203 K using a synchrotron X-ray radiographic technique. The difference between immiscible melts and a miscible melt can be clearly observed in radiographs. The immiscibility gap of the Fe-O-S melt shrinks with increasing temperature at 3 GPa. Two separated phases appeared from a miscible melt during quenching. Without in situ observations, the two phases observed in quench textures would be interpreted as either quench products from primary immiscible melts at high temperature, or those exsolved from a homogeneous melt to immiscible melts passing through the stability field of immiscible melts during quenching. In situ measurements are required in order to determine the immiscibility gap of the liquid Fe with light element(s). Our results have important implications for the formation and chemical composition of the cores of Earth and Mars.

DOI： 10.1029/2007GL030750

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The densities and viscosities of silicate melts depend strongly on pressure, in part because of potentially measurable structural rearrangements. In an attempt to further understand these changes and how they affect macroscopic properties, we have used Al-27 MAS NMR to determine the coordination of the Al cations in a series of alummosilicate glasses quenched from melts at pressures of 2 to 8 GPa, have measured the glass densities, and have applied an in-situ falling sphere method to measure melt viscosities at high pressure. Spectra from these four- and five-component glasses show increasing Al coordination with increasing pressure and with increasing average field strength of the modifier cation, as was previously reported for simpler compositions. These data also indicate that when multiple modifier cations are present (e.g., Ca and K), the Al coordination is lower than what would be expected from linear combinations of the appropriate alummosilicate end-members.
The viscosity of Ca3Al2Si6O18 melts, measured using a falling sphere method that combines multianvil techniques with synchrotron X-ray radiography, may reach a minimum at a pressure below 6 GPa. A quasi-thermodynamic approach using equilibrium constants for the reactions that generate high-coordinated Al suggests that this pressure may be related to a maximum in the concentration of five-coordinated Al. These results further support the concept that pressure-induced network structural transitions have direct implications for the macroscopic properties of high-pressure melts.

DOI： 10.2138/am.2007.2530

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An important aspect of planetary core formation concerns whether interconnectivity of liquid metal can occur in crystalline silicates, which at low melt fractions requires that the dihedral angle between the two phases is &lt; 60 degrees. [Shannon, M.C., Agee, C.B., 1998. Percolation of core melts at lower mantle conditions. Science 280, 1059-1061] previously reported that dihedral angles in mantle assemblages decrease from 108 degrees at upper mantle conditions to 71 degrees at lower mantle conditions as a result of mineral phase transformations. Furthermore [Terasaki, H., Frost, D.J., Rubie, D.C., Langenhorst, F., 2005. The effect of oxygen and sulphur on dihedral angle between Fe-O-S melt and solid silicates under high pressure: implications for Martian core formation. Earth Planet. Sci. Lett. 232, 379-392] observed that dihedral angles between Fe-O-S liquid and solid silicates (olivine and ringwoodite) decrease to 66 degrees at high oxygen and sulphur fugacities. Therefore, it may be possible for liquid metal to form an interconnected network at lower mantle conditions at high 0 and S fugacities. We have investigated the effects of the FeO content of perovskite, with Mg/(Mg + Fe) (Mg#) = 0.84-1.00, on the dihedral angle up to 23.5 GPa and 2223 K. Observed dihedral angles decrease significantly from 102 degrees to 79 degrees with increasing FeO content of the perovskite phase. This tendency is in good agreement with our previous dihedral angle results for olivine and ringwoodite. The dihedral angle is, however, still higher than the critical value of 60 degrees at pressures of the top of the lower mantle, i.e. at this depth efficient core-mantle differentiation is not possible by a percolation mechanism. (c) 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.pepi.2007.01.011

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We have determined phase relations in the Fe-O and Fe-O-S systems in the range of 15-21 GPa and 1825-2300 degrees C. Below the liquidus temperatures, solid FeO and metallic liquids are observed in both the Fe-O and the Fe-O-S systems. An immiscible two-liquid region exists in the Fe-O binary system in the pressure range investigated, and the immiscibility gap between Fe-rich metallic liquid and FeO-rich ionic liquid does not greatly change with either pressure or temperature. On the other hand, an immiscible two-liquid region in the Fe-O-S ternary system narrows significantly with increasing pressure at constant temperature and vice versa, and it almost disappears at 21 GPa, and 2300 degrees C. Immiscible two-liquid regions are thus not expected to exist in the Fe-O-S system in the Earth's core, suggesting that both oxygen and sulfur can be incorporated into the core. Our results are consistent with a geochemical model for the core containing 5.8 wt.% oxygen and 1.9 wt.% sulfur as proposed by McDonough and Sun [McDonough, W.F., Sun, S.-S., 1995. The composition of the Earth. Chem. Geol. 120, 223-253]. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.pepi.2006.09.004

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The viscosity of liquid Fe78S22 was measured up to 16 GPa and 1723 K using a high-speed CCD camera system ( 125 frames/s maximum). In order to prevent a chemical reaction between the sample and a Re viscosity marker sphere, the Re spheres were coated with alumina to a thickness of 1 - 2 mu m. The measured viscosity coefficients were 3.2 - 8.5 mPa-s and the activation volume was estimated to be 1.46 cm(3)/mol. The viscosity of liquid Fe86C14 was also measured up to 4.5 GPa and 1843 K. The viscosity coefficients were 3.8 - 6.3 mPa-s. There was no large difference in viscosity coefficient and activation volume between the Fe-S and Fe-C eutectic liquids in the range of measurement. Viscosities of Fe-S and Fe-C eutectic liquids are likely to remain low in the planetary interior.

DOI： 10.1029/2006GL027147

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Interaction between the lower mantle and core is essential for understanding the nature of D '' layer at the core-mantle boundary (CMB). Here, we report the reaction between post-perovskite (PPv) and metallic iron under the condition of the CMB, for example, 139 GPa and 3000 Kelvin. Analytical transmission electron microscope ( ATEM) analysis revealed that significant amount of oxygen up to 6.3 weight percent (wt.%) and silicon up to 4.0 wt.% can be dissolved into molten iron. The dihedral angle between PPv and molten iron is 67 degrees. Thus, a small amount of core metal of about 2 volume percent (vol.%) can be trapped without separation in the PPv region at the CMB. The amount of core metal trapped by this mechanism can produce the isotopic signature of the outer core in the plume source at the base of the lower mantle.

DOI： 10.1029/2006GL026868

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In-situ failing-sphere viscometry using shadow radiography in a multianvil apparatus was conducted on a series of samples along the NaAlSi3O8-H2O join up to 2.8 wt.% H2O at the Spring-8 synchrotron radiation facility (Hyogo, Japan). This allowed us to determine viscosities normally too low to be measured at ambient pressure for hydrous silicate melts at high temperatures due to rapid devolatilization. Pressure was fixed at 2.5 GPa for all experiments allowing us to gauge the effect of chemical composition on viscosity. In particular, the series of samples allowed us to vary the melt's degree of polymerization while maintaining a constant At to Si ratio. Our results show that, for all samples, viscosity decreases as a function of pressure between 1 atm and 2.5 GPa at 1550 degrees C, indicating that the pressure anomaly can still be observed as depolymerization of the melt increases from nominally 0 (dry albite liquid) to NBO/T=0.8 (assuming water speciation entirely as hydroxyl groups at experimental conditions). We also find that the magnitude of the decrease in viscosity over this pressure interval does not appear to be dependent on the amount of water in the melt (i.e., NBO/T). An explanation for this behavior might be that the molar volume, at least over this limited compositional range, is nearly constant and the effects of compression of these melts, though different in degree of polymerization, are similar. (c) 2006 Published by Elsevier B.V.

DOI： 10.1016/j.chemgeo.2006.01.010

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The viscosity of synthetic peridotite liquid has been investigated at high pressures using in-situ falling sphere viscometry by combining a multi-anvil technique with synchrotron radiation. We used a newly designed capsule containing a small recessed reservoir outside of the hot spot of the heater, in which a viscosity marker sphere is embedded in a forsterite+enstatite mixture having a higher solidus temperature than the peridotitc. This experimental setup prevents spheres from falling before a stable temperature above the liquidus is established and thus avoids difficulties in evaluating viscosities from velocities of spheres falling through a partially molten sample.
Experiments have been performed between 2.8 and 13 GPa at temperatures ranging from 2043 to 2523 K. Measured viscosities range from 0.019 (+/- 0.004) to 0.13 (+/- 0.02) Pa s. At constant temperature, viscosity increases with increasing pressure up to similar to 8.5 GPa but then decreases between similar to 8.5 and 13 GPa. The change in the pressure dependence of viscosity is likely associated with structural changes of the liquid that occur upon compression. By combining our results with recently published 0.1 MPa peridotite liquid viscosities [D.B. Dingwell, C. Courtial, D. Giordano, A. Nichols, Viscosity of peridotite liquid, Earth Planet. Sci. Lett. 226 (2004) 127-138.], the experimental data can be described by a non-Arrhenian, empirical Vogel-Fulcher-Tamman equation, which has been modified by adding a term to account for the observed pressure dependence of viscosity. This equation reproduces measured viscosities to within 0.08 log(10)-units on average. We use this model to calculate viscosities of a peridotitic magma ocean along a liquid adiabat to a depth of similar to 400 km and discuss possible effects on viscosity at greater pressures and temperatures than experimentally investigated. (C) 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.epsl.2005.10.004

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In situ X-ray viscometry of the silicate melts was carried out at high pressure and at high temperature. The viscosity of the silicate melts in the diopside(Di)-jadeite(Jd) system was determined in the pressure range from 1.88 GPa to 7.9 GPa and in the temperature range from 2,003 K to 2,173 K. The viscosity of the Di 25%-Jd 75% melt decreases continuously to 5.0 GPa, whereas the viscosity of the Di 50%-Jd 50% melt increases over 3.5 GPa. The viscosity of the Di50%-Jd 50% melt reaches a minimum around 3.5 GPa. Since the amounts of silicon in the two melts are the same, the difference in the pressure dependence of the viscosity may be controlled by another network-forming element, i.e., aluminum. The difference in the pressure dependence of the viscosities in the melts with two intermediate compositions in the Di-Jd system is estimated to be due to the difference in the melt structures at high pressures and high temperatures.

DOI： 10.1007/s00269-005-0452-0

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A crucial factor in the investigation of terrestrial planet core formation is whether or not a liquid iron-alloy can segregate from a solid silicate matrix. The interconnectivity of a core-forming liquid depends on the dihedral angle between liquid iron alloy and crystalline silicates at low melt fractions. Recent experimental studies at ambient pressure have implied that liquid iron-alloy can wet an olivine matrix under conditions of high oxygen and sulphur fugacities. We have examined the effects of varying sulphur and oxygen contents on the dihedral angle between liquid iron-alloy and crystalline silicates up to 20 GPa. The compositions studied are applicable to core formation on both the Earth and Mars and the pressure range investigated is applicable to over 80% of the depth of the entire Martian mantle. Dihedral angles in texturally equilibrated samples decrease with increasing sulphur content and also decrease significantly with increasing FeO content of silicates. Increasing the FeO content of silicates results in an increase in both the oxygen fugacity and oxygen solubility in the Fe-S, melt. Oxygen is found to have a larger effect in reducing the dihedral angle than sulphur. The dihedral angle between metallic melt and silicate crystals in the Martian mantle would have been closer to the wetting boundary of 60 degrees than in the Earth's interior, but it would be still too large (0 &gt; 60 degrees) to allow percolation to occur to completion. These results show that melting of the silicate mantle is required to obtain complete metal-silicate separation, which therefore supports a magma ocean scenario for core formation on both Mars and Earth. (c) 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.epsl.2005.01.030

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DOI： 10.14824/jampeg.2005.0.92.0

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Carbon dioxide and water are the most important volatile constituents in the Earth and they produce drastic changes in the melting phase relations and partial melt composition of the mantle peridotites. Study of the peridotite-CO₂ system is closely related to petrogenesis of kimberlite and diamond. There are a few high pressure mineral inclusions (i.e. majorite garnet and Ca & Mg perovskite) in diamond which suggest that kimberlites may be originated from the transition zone and lower mantle. Several experimental petrologists have studied the kimberlite and basalt-CO₂ systems, however the phase relations and melt compositions in the CO₂-bearing peridotite at high pressures are poorly constrained. Simplified peridotite-CO₂ system (like CMS or CMAS) has been studied at pressures up to 12 GPa (Canil and Scarfe, 1990), whereas complex peridotite-CO₂ systems have investigated only at lower pressures (up to 4 GPa, e.g. Wendlandt and Mysen, 1980). In this work we report the results on the phase relations and melt compositions of a model peridotite-CO₂ system determined at 10-20 GPa and temperature range from 1200 to 2100^oC.Our results show that solidus of carbonated peridotite is consistent with low-pressure data for CMAS-CO₂ system. Liquidus phase at 10-20 GPa is majorite garnet. At 10-15 GPa, crystallization sequence with decreasing temperature is garnet, olivine and clinoenstatite. Magnesite is the most important CO₂-rich phase stable in peridotite and clinoenstatite is an important phase in carbonated peridotite at 10-15 GPa.The partial melts formed by 10-25% melting at 10-20 GPa has high MgO (26-34 wt.%) and FeO (7.0-10.4 wt.%) and low SiO₂ (18-36 wt.%) and Al₂O₃ (0.5-1.3 wt.%) contents. It contains also 6-12 wt.% CaO, 0.6-2.0 wt.% Na₂O and 0.1-0.3 wt.% K₂O. The CO₂ contents in the melts are 14-32 wt.%. SiO₂-poor composition of partial melts is different to the results for melting of anhydrous or water-bearing peridotite. Partial melting of hydrous peridotite produce SiO₂-rich melts, which can be related to komatiite magmas (e.g. Litasov and Ohtani, 2002). The composition of low degree partial melts (10%) in present experiments is close to magnesiocarbonatites, whereas higher degree melting (20-25%) produce melts, which is close to kimberlite magmas.

DOI： 10.14824/kobutsu.2005.0.13.0

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Karlsruhe Forschungszentrum Karlsruhe gmbH  

Summary: Melting relation in the Fe-FeO-FeS system, especially the immiscible two-liquid region has been investigated by using Kawai-Type multi-Anvil apparatus at 15 GPa, 1800-2200°C. The products recovered from 15 GPa and 2200°C show textures that are totally molten. The immiscible two liquids are observed in the starting compositions with 0-2.6 wt.% sulfur, whereas the miscible liquid is obtained in the composition of 7.5 wt.% sulfur. Sulfur is likely to narrow the immiscible two-liquid region in the Fe-FeO-FeS system at high prebure.

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

In situ X-ray diffraction experiments on Fes up to 22 GPa and 1600 K were carried out using large volume multianvil apparatus, combined with synchrotron radiation at SPring-8. We investigated phase stability relationships of Fes and determined the straight phase boundaries between Fes III (monoclinic phase) and Fes IV (hexagonal phase) to be T (K) = 20P (GPa) + 170 and between Fes IV and Fes V (NiAs-type phase) to be T (K) = 39.6 P (GPa) + 450. We also found anomalous behavior in the c/a ratio, thermal expansion, and isothermal compression of FeS V as well as FeS IV, in the pressure range 4-12 GPa. These anomalies in Fes can be attributed to the spin-pairing transition of Fe, and divides FeS IV and FeS V into the high-spin low-pressure phase (LPP) and the possibly low-spin high-pressure phase (HPP). In order to investigate the internal structure of Mars, we evaluated the equations of state for Fes IV (HPP) and Fes V (HPP). A least square fit to the experimental data yielded K(0T) = 62.5 +/- 0.9 GPa at T = 600 K and (dK(0)/dT) p = -0.0208 +/- 0.0028 GPa/K for Fes IV (HPP), and K(0T) = 54.3 +/- 1.0 GPa at T = 1000 K and (dK(0)/dT) = -0.0117 +/- 0.0015 GPa/K for Fes V (HPP) with fixed K&apos; = 4. Thermal expansion coefficients were alpha = 7.16 x 10(-5) + 6.08 x 10(-8) T for FeS IV (HPP) and alpha = 10.42 x 10(-5) for Fes V (HIPP), respectively. Using these equations of state, we examined the internal structure of Mars that has a model mantle composition [Meteoritics 20 (1985) 367] and Fe-FeS core. Our models show that an Mg-silicate perovskite-rich lower mantle is stable only with the Fe-rich core having less than 20 wt.% sulfur. The polar moment of inertia factor C derived from Mars Pathfinder data [Science 278 (1997) 1749] is consistent with any compositions between Fe and Fes for the Martian core, but it excludes the presence of a crust thicker than 100 km. (C) 2004 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.pepi.2003.12.015

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

The viscosity of liquid sulfur up to 9.7 GPa and 1067 K was measured using the in situ x-ray radiography falling sphere method. The viscosity coefficients were found to range from 0.11 to 0.69 Pa s, and decreased continuously with increasing pressure under approximately constant homologous temperature conditions. The observed viscosity variation suggests that a gradual structural change occurs in liquid sulfur with pressure up to 10 GPa. The L-L' transition in liquid sulfur proposed by Brazhkin et al (1991 Phys. Lett. A 154 413) from thermobaric measurements has not been confirmed by the present viscometry.

DOI： 10.1088/0953-8984/16/10/003

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The viscosity of CaMgSi2O6 (diopside) liquid has been determined up to 13 GPa and 2200degreesC using in situ falling sphere viscometry with X-ray radiography. The experiments were carried out in a 1500 1 multianvil apparatus at the SPring-8 synchrotron (Japan). A new, high-pressure sample assembly was developed with LaCrO3 replacing the traditionally used graphite furnace material, allowing experiments within the diamond stability field to be carried out. The viscosity of CaMgSi2O6 liquid increases slightly from 3.5 to 10 GPa and then decreases slightly at higher pressures. However, over the entire ranges of temperature (2030-2473 K) and pressure (3.5-13 GPa) investigated, variation in viscosity does not exceed +/-0.5 log units. The viscosity results from this study are consistent with those calculated from the pressure dependence of oxygen self-diffusion in CaMgSi2O6 liquid using the Eyring equation with a translation distance (lambda) of 0.45 nm providing the best correlation. Both sets of results indicate a change in pressure dependence at approximately 10 GPa, where viscosity results show a maximum with pressure and silicon and oxygen self-diffusivity results show a minimum. (C) 2003 Elsevier B.V. All rights reserved.

DOI： 10.1016/S0031-9201(03)00143-2

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The viscosities of albite (NaAlSi3O8) melt under high pressures have been measured using an x-ray radiography falling sphere method with synchrotron radiation. This method has enabled us to determine the precise sinking velocity directly. Recent experiments of albite melt showed the presence of a viscosity minimum around 5 GPa (Poe et al 1997 Science 276 1245, Mori et al 2000 Earth Planet. Sci. Lett. 175 87). We present the results for albite melt up to 5.2 GPa at 1600 and 1700degreesC. The viscosity minimum is clearly observed to be around 4.5 GPa, and it might be explained not by the change of the compression mechanism in albite melt but by change of the phase itself.

DOI： 10.1088/0953-8984/14/44/479

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

The viscosity of albite (NaAlSi(3)O(8)) melt was measured at high pressure by the in situ falling-sphere method using a high-resolution X-ray CCD camera and a large-volume multianvil apparatus installed at SPring-8. This system enabled Lis to conduct in situ viscosity measurements more accurately than that using the conventional technique at pressures of up to several gigapascals and viscosity in the order of 10(0) Pa s. The viscosity of albite melt is 5.8 Pa s at 2.6 GPa and 2.2 Pa s at 5.3 GPa and 1973 K. Experiments at 1873 and 1973 K show that the decrease in viscosity continues to 5.3 GPa. The activation energy for viscosity is estimated to be 316(8) kJ mol(-1) at 3.3 GPa. Molecular dynamics simulations suggest that a gradual decrease in viscosity of albite melt at high pressure may be explained by structural changes such as an increase in the coordination number of aluminum in the melt.

DOI： 10.1007/s00269-001-0216-4

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[1] The in situ viscosity measurements of the pure molten Fe under high pressures were made by falling sphere X-ray radiography method. Viscosity coefficients at about 2000 K were 15-24 mPa s at 2.7-5.0 GPa, and 4-9 mPa s at 5.0-7.0 GPa. Drastic decrease was found at around 5 GPa, at which stable solid phase below the melting temperatures change from delta (bcc) to gamma (fcc) phases. The observation indicates the possibility that the structural change in the molten Fe occurs in a narrow pressure interval (1 GPa) at the similar condition with the phase transformation in the solid.

DOI： 10.1029/2001GL014321

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The Fe-FeS melt is thought to be the major candidate of the outer core material. Its viscosity is one of the most important physical properties to study the dynamics of the convection in the outer core. We performed the in situ viscosity measurement of the Fe-FeS melt under high pressure using X-ray radiography falling sphere method with a novel sample assembly. Viscosity was measured in the temperature, pressure, and compositional conditions of 1233-1923 K, 1.5-6.9 GPa, and Fe-Fe72S28 (wt%), respectively. The viscosity coefficients obtained by 17 measurements change systematically in the range of 0.008-0.036 Pa s. An activation energy of the viscous flow, Q = 30.0 +/- 8.6 kJ/mol, and the activation volume, DeltaV = 1.5 +/- 0.7 x 10(-6) m(3)/mol, are determined as the temperature and pressure dependence, and the viscosity of the Fe72S28 melt is found to be smaller than that of the Fe melt by 15 +/- 10%. These tendencies can be well correlated with the structural variation of the Fe-FeS melt. (C) 2001 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0012-821X(01)00374-0

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

Stokes' viscometry combined with in situ X-ray radiographic observation, using the 6-8 type multi-anvil press and synchrotron radiation, has been applied to the viscosity measurement of the Fe-FeS melt up to pressures of 7 GPa. The viscosity is found to be about 2 x 10(-2) Pa-s at 5 to 7 GPa and temperatures about 1350 K, in marked contrast to previous viscosity measurements, which showed high viscosity, 0.5 to 14 Pa-s, at 2 to 5 GPa (LeBlanc and Secco 1996). Our viscosity data, however, is consistent with all other evidence, which include 1 atm viscosity data, X-ray structure analysis, and ab initio simulations. Recent viscosity measurements (Dobson et al. 2000) also showed the viscosity of Fe-FeS melt to be about 10(-2) Pa-s at 2.5 GPa. Thus, we are confident that the viscosity of the Fe-FeS melt is close to a typical value (10(-2) Pa-s) of viscosity for liquid metal even at high pressures.

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DOI： 10.2465/gkk.30.100

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The phase boundary between wadsleyite and ringwoodite in Mg2SiO4 composition was determined by in situ observation using synchrotron X-ray and multi anvil apparatus:in KEK, Tsukuba, Japan. An energy dispersive method:was employed using the Ge solid state detector and the white X-ray beam from the synchrotron radiation source. The pressure was determined by the equation of state of NaCl. The stability field was identified by the change in intensities of diffraction lines of each phases. As a result, the phase boundary is expressed as a linear equation P=10.32(28)+0.00691(9)xT, where P is pressure in gigapascals and T is temperature in degrees Celsius.

DOI： 10.1029/1999GL008425

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Publisher：Tokyo Geographical Society  

DOI： 10.5026/jgeography.109.6_Plate5

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Deep Earth: Physics and Chemistry of the Lower Mantle and Core highlights recent advances and the latest views of the deep Earth from theoretical, experimental, and observational approaches and offers insight into future research directions on the deep Earth. In recent years, we have just reached a stage where we can perform measurements at the conditions of the center part of the Earth using state-of-the-art techniques, and many reports on the physical and chemical properties of the deep Earth have come out very recently. Novel theoretical models have been complementary to this breakthrough. These new inputs enable us to compare directly with results of precise geophysical and geochemical observations. This volume highlights the recent significant advancements in our understanding of the deep Earth that have occurred as a result, including contributions from mineral/rock physics, geophysics, and geochemistry that relate to the topics of: I. Thermal structure of the lower mantle and core II. Structure, anisotropy, and plasticity of deep Earth materials III. Physical properties of the deep interior IV. Chemistry and phase relations in the lower mantle and core V. Volatiles in the deep Earth The volume will be a valuable resource for researchers and students who study the Earth's interior. The topics of this volume are multidisciplinary, and therefore will be useful to students from a wide variety of fields in the Earth Sciences.

DOI： 10.1002/9781118992487

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Language：Japanese   Publisher：The Japanese Society for Planetary Sciences  

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DOI： 10.14824/jakoka.2011.0.227.0

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Language：English   Publishing type：Book review, literature introduction, etc.  

The Earth's core has been considered to contain light elements, and sulfur, in particular, is one of the most plausible light elements. Knowledge of the melting relationships of the iron-sulfide system is thus essential in understanding of the physical and chemical properties of the core. In situ X-ray diffraction experiments in the Fe-Fe3S system were performed up to 220 GPa and 3300 K using a laser-heated diamond anvil cell. Hcp Fe and Fe3S coexisted stably up to 220 GPa and 3300 K. Both phases are therefore candidates of the constitution of the inner core. The solid iron (hcp Fe) contained 7.5 at% of sulfur at 126 GPa and 2370 K. This suggests that the inner core might be able to contain significant amount of sulfur. Our results revealed that the eutectic composition becomes nonsensitive to pressure. This is likely that the eutectic composition becomes to be constant around 20 at% of sulfur at pressures above 40 GPa.

DOI： 10.4131/jshpreview.21.77

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DOI： 10.14824/jakoka.2009.0.179.0

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DOI： 10.14824/jakoka.2008.0.181.0

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DOI： 10.14824/jakoka.2007.0.110.0

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DOI： 10.14824/jampeg.2005.0.71.0

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DOI： 10.14824/jampeg.2005.0.93.0

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Language：English   Publishing type：Research paper, summary (international conference)   Publisher：ELSEVIER SCIENCE BV  

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DOI： 10.14824/jampeg.2004.0.88.0

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Language：Japanese   Publisher：The Japan Society of High Pressure Science and Technology  

In order to understand the formation, evolution and dynamic processes of the molten core of the terrestrial planets, knowledge of the physical properties, such as viscosity and density, of the molten iron alloy is required. Recent progress in the high-pressure technology combined with synchrotron radiation allows us to measure such properties at high-temperature and high-pressure. In this article, recent advances in the high-pressure research of molten iron alloys are reviewed.

DOI： 10.4131/jshpreview.12.138

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DOI： 10.2465/gkk.30.102

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Understanding the evolutionary history of the Earth requires studies on the transport properties of constituent materials at high pressures and high temperatures prevailing deep in the Earth's interior. Utilization of intense synchrotron radiation X-rays combined with large-volumes high-pressure apparatus started in the mid 1980's and has brought about new insights on the science of the Earth's interior. Falling sphere viscometry using X-ray radiography enabled us to determine the pressure and temperature dependence of the viscosity of the Fe-FeS melt, which is a candidate for the outer core of the Earth. Studies on phase transition kinetics using in-situ X-ray diffraction revealed the important role of metastable assemblages in the subduction of slabs and consequent material exchanges between upper and lower mantles. Further development of the experimental and analytical technique is expected in the research fields of deformation mechanics and element diffusion for Earth's materials.

DOI： 10.5026/jgeography.109.6_868

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