[Show abstract][Hide abstract] ABSTRACT: Nanocasting at high pressure has been recently proposed as a novel strategy for the synthesis of periodic mesoporous materials with crystalline walls. In this study we present results on the synthesis of mesostructured stishovite from mesostructured FDU-12/carbon composite precursor using the multi-anvil press. Results from quenched experiments performed at a pressure of 14 GPa indicate that a minimum temperature of 500 °C is needed to crystallize stishovite from the amorphous silica precursor with a preserved mesostructure. Transmission electron microscopy combined with small angle X-ray scattering measurements confirmed the mesostructure of synthetic stishovite having carbon-filled pores with a diameter of ∼19 nm similar to the pore size of the FDU-12 precursor. Calcination of the stishovite/carbon composite at 450 °C in air at ambient condition leads to amorphization of the stishovite. Our results show that mesostructure materials can be synthesized at very high pressures without loss or critical modification of the mesostructure.
Microporous and Mesoporous Materials 03/2014; 187:145–149. · 3.37 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The first natural-occurring quasicrystal, icosahedrite, was recently discovered in the Khatyrka meteorite, a new CV3 carbonaceous chondrite. Its finding raised fundamental questions regarding the effects of pressure and temperature on the kinetic and thermodynamic stability of the quasicrystal structure relative to possible isochemical crystalline or amorphous phases. Although several studies showed the stability at ambient temperature of synthetic icosahedral AlCuFe up to ~35 GPa, the simultaneous effect of temperature and pressure relevant for the formation of icosahedrite has been never investigated so far. Here we present in situ synchrotron X-ray diffraction experiments on synthetic icosahedral AlCuFe using multianvil device to explore possible temperature-induced phase transformations at pressures of 5 GPa and temperature up to 1773 K. Results show the structural stability of i-AlCuFe phase with a negligible effect of pressure on the volumetric thermal expansion properties. In addition, the structural analysis of the recovered sample excludes the transformation of AlCuFe quasicrystalline phase to possible approximant phases, which is in contrast with previous predictions at ambient pressure. Results from this study extend our knowledge on the stability of icosahedral AlCuFe at higher temperature and pressure than previously examined, and provide a new constraint on the stability of icosahedrite.
[Show abstract][Hide abstract] ABSTRACT: Diamond nanocrystals were synthesized catalyst-free from nanoporous carbon at high pressure and high temperature (HPHT). The synthesized nanocrystals have tunable diameters between 50 and 200 nm. The nanocrystals are dispersible in organic solvents such as acetone and isotropic in nature as seen from dynamic light scattering technique.
Chemical Communications 01/2014; · 6.38 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: High-pressure melting experiments in the Fe–S–C ternary and Fe–S–Si–C quaternary systems have been conducted in the range of 3.5–20 GPa and 920–1700 °C in the multi-anvil press. The mutual solubility, melting relations, and crystallization sequences were systematically investigated with changes of pressure, temperature and bulk composition. Five starting materials of Fe(84.69 wt%)–C(4.35 wt%)–S(7.85 wt%), Fe(84.87 wt%)–C(2.08 wt%)–S(11.41 wt%), Fe(86.36 wt%)–C(0.96 wt%)–S(10.31 wt%), Fe(85.71 wt%)–C(0.33 wt%)–S(11.86 wt%) and Fe(82.95 wt%)–C(0.66 wt%)–S(13.7 wt%)–Si(2.89 wt%) were employed. For Fe(84.69 wt%)–C(4.35 wt%)–S(7.85 wt%), the first crystallized phase is Fe3C at 5 GPa and Fe7C3 at 10–20 GPa. For Fe(84.87 wt%)–C(2.08 wt%)–S(11.41 wt%), Fe3C is the stable carbide at subsolidus temperature at 5–15 GPa. For Fe(86.36 wt%)–C(0.96 wt%)–S(10.31 wt%) and Fe(85.71 wt%)–C(0.33 wt%)–S(11.86 wt%), the first crystallized phase is metallic Fe instead of iron carbide at 5–10 GPa. The cotectic curves in Fe–S–C ternary system indicate only a small amount of C is needed to form an iron carbide solid inner core with the presence of S. Experiments on Fe(82.95 wt%)–C(0.66 wt%)–S(13.7 wt%)–Si(2.89 wt%) showed that a small amount of C does not significantly change the closure pressure of miscibility gap compared with that in Fe–S–Si system. It is observed that S preferentially partitions into molten iron while a significant amount of Si enters the solid phase with temperature decrease. Meanwhile, the C concentration in the liquid and solid iron metal changes little with temperature variations. If S, C and Si partitioning behavior between molten iron and solid iron metal with temperature remains the same under Earth’s present core pressure conditions, the solid inner core should be iron dominated with dissolved Si. On the other hand, the liquid outer core will be S rich and Si poor. Moderate carbon will be evenly present in both solid and liquid cores. Based on our melting data in a multi-component system, no layered liquid core should exist in the Earth, Mars and Mercury.
Geochimica et Cosmochimica Acta 08/2013; 114:220–233. · 3.88 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We report quantitative 3D coherent x-ray diffraction imaging of a molten Fe-rich alloy and crystalline olivine sample, synthesized at 6 GPa and 1800 °C, with nanoscale resolution. The 3D mass density map is determined and the 3D distribution of the Fe-rich and Fe-S phases in the olivine-Fe-S sample is observed. Our results indicate that the Fe-rich melt exhibits varied 3D shapes and sizes in the olivine matrix. This work has potential for not only improving our understanding of the complex interactions between Fe-rich core-forming melts and mantle silicate phases but also paves the way for quantitative 3D imaging of materials at nanoscale resolution under extreme pressures and temperatures.
[Show abstract][Hide abstract] ABSTRACT: A comprehensive P-V-T dataset for bcc-tungsten was obtained for pressures up to 33.5 GPa and temperatures 300–1673 K using MgO and Au pressure scales. The thermodynamic analysis of these data was performed using high-temperature (HT) and Mie-Grüneisen-Debye (MGD) relations combined with the Vinet equations of state (EOS) for room-temperature isotherm and the newly proposed Kunc-Einstein (KE) EOS. The KE EOS allowed calibration of W thermodynamic parameters to the pressures of at least 300 GPa and temperatures up to 4000 K with minor uncertainties (<1% in calculated volume of W). A detailed analysis of room-temperature compression data with Vinet EOS yields V0 = 31.71 ± 0.02 Å3, KT = 308 ± 1 GPa, and KT′ = 4.20 ± 0.05. Estimated thermoelastic parameters for HT include (∂KT/∂T)P = −0.018 ± 0.001 GPa/K and thermal expansion α = a0 + a1T with a0 = 1.35 (±0.04) × 10−5 K−1 and a1 = 0.21 (±0.05) × 10−8 K−2. Fitting to the MGD relation yielded γ0 = 1.81 ± 0.02 and q = 0.71 ± 0.02 with the Debye temperature (θ0,) fixed at 370–405 K. The parameters for KE EOS include two Einstein temperatures, ΘE1o = 314 K and ΘE2o = 168 K, Grüneisen parameter at ambient condition γ0 = 1.67 and infinite compression γ∞ = 0.66, with β = 1.16 (which is a power-mode parameter in the Grüneisen equation), anharmonicity (m = 3.57) and electronic (g = 0.11) equivalents of the Grüneisen parameter, and additional parameters for intrinsic anharmonicity, a0 = 6.2 × 10−5 K−1, and electronic contribution, e0 = 4.04 × 10−5 K−1 to the free energy. Fixed parameters include k = 2 in KE EOS and mE1 = mE2 = 1.5 in expression for Einstein temperature. Present analysis should represent the best fit of the experimental data for W and can be used for a variety of thermodynamic calculations for W and W-containing systems including phase diagrams, chemical reactions, and electronic structure.
Journal of Applied Physics 04/2013; 113(13). · 2.21 Impact Factor
[Show abstract][Hide abstract] ABSTRACT:  Using a two-stage light gas gun, we obtained new shock wave Hugoniot data for an iron-sulfur alloy (Fe-11.8wt%S) over the pressure range of 94–204 GPa. A least-squares fit to the Hugoniot data yields a linear relationship between shock velocity DS and particle velocity u, DS (km/s) =3.60(0.14) +1.57(0.05) u. The measured Hugoniot data for Fe-11.8wt%S agree well with the calculated results based on the thermodynamic parameters of Fe and FeS using the additive law. By comparing the calculated densities along the adiabatic core temperature with the PREM density profile, an iron core with 10 wt.% sulfur (S) provides the best solution for the composition of the Earth's outer core.
Geophysical Research Letters 02/2013; 40(4):687-691. · 3.98 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A comprehensive P-V-T dataset for bcc-Mo was obtained at pressures up to 31 GPa and temperatures from 300 to 1673 K using MgO and Au pressure calibrants. The thermodynamic analysis of these data was performed using high-temperature Birch-Murnaghan (HTBM) equations of state (EOS), Mie-Grüneisen-Debye (MGD) relation combined with the room-temperature Vinet EOS, and newly proposed Kunc-Einstein (KE) approach. The analysis of room-temperature compression data with the Vinet EOS yields V0 = 31.14 ± 0.02 Å3, KT = 260 ± 1 GPa, and KT′ = 4.21 ± 0.05. The derived thermoelastic parameters for the HTBM include (∂KT/∂T)P = −0.019 ± 0.001 GPa/K and thermal expansion α = a0 + a1T with a0 = 1.55 ( ± 0.05) × 10−5 K−1 and a1 = 0.68 ( ± 0.07) × 10−8 K−2. Fitting to the MGD relation yields γ0 = 2.03 ± 0.02 and q = 0.24 ± 0.02 with the Debye temperature (θ0) fixed at 455-470 K. Two models are proposed for the KE EOS. The model 1 (Mo-1) is the best fit to our P-V-T data, whereas the second model (Mo-2) is derived by including the shock compression and other experimental measurements. Nevertheless, both models provide similar thermoelastic parameters. Parameters used on Mo-1 include two Einstein temperatures ΘE10 = 366 K and ΘE20 = 208 K; Grüneisen parameter at ambient condition γ0 = 1.64 and infinite compression γ∞ = 0.358 with β = 0.323; and additional fitting parameters m = 0.195, e0 = 0.9 × 10−6 K−1, and g = 5.6. Fixed parameters include k = 2 in Kunc EOS, mE1 = mE2 = 1.5 in expression for Einstein temperature, and a0 = 0 (an intrinsic anharmonicity parameter). These parameters are the best representation of the experimental data for Mo and can be used for variety of thermodynamic calculations for Mo and Mo-containing systems including phase diagrams, chemical reactions, and electronic structure.
Journal of Applied Physics 01/2013; 113:093507. · 2.21 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Surfactant-containing periodic mesostructured silica materials, namely SBA-16 and FDU-12, were studied under pressures between 1 and 4 GPa and temperatures between 100 and 400 °C. At 4 GPa crystallization of coesite can be achieved already at 200 °C. The mild transition of amorphous to crystalline silica is believed to be accomplished by the inbuilt hydroxyl groups present in the starting material. At 2 GPa the crystallization of quartz is accomplished at a temperature of 400 °C. Both quartz and coesite are obtained in nanocrystalline form.
[Show abstract][Hide abstract] ABSTRACT: Electrical resistivity measurements of polycrystalline iron have been
performed at 5, 7, and 15 GPa and in the temperature range 293-2200 K by
employing a four-wired method. The kinks in electrical resistivity
associated with solid iron phase transitions and the solid to liquid
transition were clearly observed upon increasing temperature. Geometry
corrections due to volume variations with pressure and temperature were
applied to the entire data set. High pressure and temperature thermal
conductivity were calculated by fitting resistivity data through the
Wiedemann-Franz law. The temperature dependences of electrical
resistivity and thermal conductivity for α, γ, and ɛ
solid iron have been determined at high-pressure conditions. Our study
provides the first experimental constraint on the heat flux conducted at
Mercury's outmost core, estimated to be 0.29-0.36 TW, assuming an
adiabatic core. Extrapolations of our data to Martian outer core
conditions yield a series of heat transport parameters (e.g., electrical
resistivity, thermal conductivity, and heat flux), which are in
reasonable comparison with various geophysical estimates.
Geophysical Research Letters 01/2013; 40(1):33-37. · 3.98 Impact Factor
[Show abstract][Hide abstract] ABSTRACT:  The efficiency of heat transfer by conduction in the Earth's core controls the dynamics of convection and limits the power available for the geodynamo. We have measured the room temperature electrical resistivity of iron and iron-silicon alloy to 60 GPa and present a new model of the resistivity at high pressures and temperatures relevant to the Earth's core. The model is compared with available shock wave data and theoretical studies. For a power law and linear temperature dependence of electrical resistivity, the calculated thermal conductivity at the core-mantle boundary is ~67–145 W/m/K for pure Fe and ~41–60 W/m/K for Fe–9 wt % Si. Impurities in the core have a strong effect on the transport properties of iron that could significantly impact core thermal models. The models describing the data indicate higher thermal conductivity at core pressure than previously suggested, requiring additional energy sources in the past to operate the geodynamo.
[Show abstract][Hide abstract] ABSTRACT: Carbon speciation as function of pressure, temperature, and iron content
determined by measuring the oxygen fugacity for the stability of carbon
and carbonate using the Ir redox sensor technique.