Deformation of Diopside Single Crystals at Mantle P and T |
| Elodie Amiguet LSPES / CNRS, Université de Lille, France Elodie.Amiguet@ed.univ-lille1.fr P. RATERRON (1), P. CORDIER (1), H. COUVY (2), AND J. CHEN (2) (1) : LSPES / CNRS, Université de Lille, France (2) : Mineral physics Institute and Department of Geosciences, Stony Brook University, NY, USA |
| Facility: NSLS-X17B2 (MAC) Format: Poster |
| Upper-mantle seismic-velocity anisotropy allows characterizing convective flow directions in this region. Seismic anisotropy results from lattice preferred orientations (LPOs) in elastically anisotropic crystals deformed by dislocation creep, which in peridotite are essentially olivine and pyroxenes crystals. Although clino-pyroxenes (cpx) are minor constituents of the upper mantle (~10 vol.%), they present the highest elastic anisotropy and may significantly contribute to upper-mantle seismic anisotropy. CaMgSi2O6 diopside is a good representative of the cpx family and its low-P deformation is fairly well constrained. At high-temperature (T>1000°C), 1-atm experimental data indicate that the easiest dislocation slip systems in diopside are {110}1/2<110>. They are followed in terms of activity by {110}[001], then by (100)[001], and finally by the hardest (100)[010] and (010)[100] systems (see [1] and [2]).
We present here the first high-temperature (1100° |
High P/T investigation of fayalite |
| Matt M Armentrout UCLA armentrout@ucla.edu Abby KAvner |
| Facility: ALS Format: Poster |
| Fayalite is the iron end-member of the olivine group. Although the bulk mantle composition is much richer in magnesium than iron, a possible reaction between core and mantle would likely increase the Fe/Mg ratio. The goal of this work is to measure the phase diagram of the composition Fe2SiO4 at pressures and temperatures throughout the Earth?s mantle. We take a dual approach to this study. First we report in situ laser heating and X-ray diffraction measurements on fayalite, which were performed at beamline 12.2.2 at the Advanced Light Source in Berkeley, CA. We show the phase transformation of fayalite to the spinel structured phase, and demonstrate the breakdown of the spinel structured phase to stishovite and wustite. Additional sets of laser heating experiments were performed in the Mineral Physics Laboratory at UCLA, with measurements of laser hotspot temperatures and temperature gradients coupled with a post-mortem analysis of the reaction products using an electron microprobe. |
An experimental determination of the 60 Kbar liquidus for the Iron rich side of the Fe-FeS system |
| Antonio S Buono Columbia University, LDEO abuono@ldeo.columbia.edu Dave Walker |
| Facility: None Format: Poster |
| An interesting pathology appears in the iron rich side of the 1 bar Fe-FeS liquidus presented by Hansen and Anderko (1958). Strong negative curvature suggests the presence of a metastable solvus near the liquidus resulting in strongly non-ideal liquid solution behavior. Brett and Bell (1969) showed that by 30 Kbar this pathology seemed to be relaxing and the liquid solution was becoming more ideal. We have followed that progression experimentally to 60 Kbar and modeled the liquid solution using an asymmetric Margules form. The Margules form result in large negative excess volume for the liquid. All experiments were conducted in a Walker type multi-anvil using LaCrO3 heaters and MgO capsules. The newly determined liquidus at 60 Kbar in conjunction with the previously determined 1bar and 30 Kbar liquidi for the Fe-FeS system shows that the liquidi become more ideal with increasing pressure. We also see that the 30 and 60 kbar liquidi cross the 1 bar liquidus at a fairly constant temperature of 1630 K and with a deviation of no more than 3 wt% Fe. An asymmetric Margules equation for the liquid phase can describe the liquidus evolution given standard reference values for crystalline end member, iron. The calculated WG?s, which are the result of applying an asymmetric Margules formulation to the liquidus, for 1 bar are listed below. The WG?s are listed in their expanded form as WG= WH+PWV-TWS 1bar WG?s WHFe = 31 Kj/mole, WSFe = 0.012 Kj/mole K WHFeS = 29 Kj/mole, WSFeS =.000018 Kj/mole K Preliminary data for the 30 Kbar Liquidus is listed below. 30 Kbar WG?s WHFe = 31 Kj/mole, WSFe = -0.47 Kj/mole K, WVFe= -7.1 Kj/Kbar mole WHFeS= 27 Kj/mole, WSFeS=-1.2 Kj/mole K, WVFe= -62.8 Kj/Kbar mole These values work well for the Gamma phase of iron, which covers the temperature range up to around 1750 K. Above 1750 K the standard value for the delta phase requires a correction of roughly -.4 be added to the G of the crystalline phase of iron, this is less than .5% of the value, in order for the delta phase to be able to be fit. The change in the WG?s from 1 bar to 30 Kbar indicating more nearly ideal solution behavior requires a large negative excess volume which is in agreement with the WV?s listed. |
Pressure-volume-temperature studies of metal-oxide pairs |
| Andrew Campbell Dept. of Geology, University of Maryland ajc@umd.edu Lisa Danielson and Kevin Righter (Johnson Space Center, NASA); Christopher T. Seagle (Dept. of the Geophysical Sciences, University of Chicago); Yanbin Wang and Vitali Prakapenka (Center for Advanced Radiation Sources, University of Chicago) |
| Facility: APS-GSECARS Format: Poster |
| Pressure-volume-temperature relations for the Fe-FeO, Ni-NiO, and Re-ReO2 metal-oxide pairs were measured by synchrotron X-ray diffraction in both a multi-anvil press and a laser heated diamond anvil cell. The results offer several points of interest, including: (1) Simultaneous measurement of both the metal and its oxide provided a measure of the volume difference between the two phases that is more precise than comparisons between independently determined equations of state. This allows more precise evaluation of the thermodynamics of the metal-oxide system, for example oxygen fugacity buffer curves at high pressure. (2) Comparisons are made between results from different experimental methods, i.e. multi-anvil press and diamond cell. These can be made independent of the NaCl pressure standard when viewed as V(metal)-V(oxide)-T data. (3) Nonstoichiometric effects in wustite were eliminated by high-PT equilibration with Fe, allowing the equation of state of stoichiometric FeO to be measured. (4) Simultaneous measurement of three phases (metal, oxide, and NaCl) provided checks on the accuracy of previously determined equations of state, although high-PT data on some of these phases were scarce. (5) No new compounds were formed at high pressure by reaction between these metals and their oxides. |
Experimental investigation of the melting relations in the Fe-S system at high pressures and implications for planetary cores |
| Bin Chen University of Illinois at Urbana Champaign binchen2@uiuc.edu Jie Li |
| Facility: NSLS-U2A (DAC) Format: Poster |
| We have investigated melting relations in the Fe-S system at high pressures using a multi-anvil apparatus. Sulfur is believed to be one of the most likely alloying light elements in iron-rich planetary cores. Understanding the thermal and physical state as well as the evolution of planetary cores require detailed knowledge on the melting relations and sub-solidus mineralogy in the Fe-FeS system at high pressures. We have determined the liquidus curve of the iron-rich portion of the Fe-S binary system at 10 GPa and 14 GPa. Our data are applied to the current core of Mercury and proto-cores of Venus, Earth, and Mars. We will estimate the thermal profile of Mercuryâ??s core based on existing composition models. The contribution of latent heat to the energy budget of the cores of the terrestrial planets and its implications for the age of the Earthâ??s inner core will also be discussed. |
COMPRES Infrastructure Development Project Report: Monochromatic Side-Station at X17B2 of the NSLS |
| Jiuhua Chen Stony Brook University chenj@fiu.edu Liping Wang, Helene Couvy, Tony Yu, Hongbo Long, Li Li, Don Weidner, Mike Vaughan |
| Facility: NSLS-X17B2 (MAC) Format: Poster |
| Monochromatic beam from a single bounced monochromator has been delivered to the side station. The focusing Si(511) crystal provides photon flux of 1x10^10 ph/sec at energy = 55.3 keV and area of 0.2 mm x 0.2 mm. Preliminary experiments have been conducted using the monochromatic beam and a D-DIA (loan from main station). The poster will present the system feature of the side-station and some experimental data of shearing and compression deformation of olivine. A deformation Tcup apparatus (D-Tcup) purchased through the COMPRES infrastructure project fund is expected for delivery at the time of this COMPRES annual meeting. |
Experimental Petrology in the LHDAC |
| Elizabeth A Cottrell National Museum of Natural History, Smithsonian Institution cottrelle@si.edu Y. Fei, E. Hauri, A. Ricolleau, Carnegie Institution of Washington And V. Prakapenka GSECARS, Advanced Photon Source, Argonne National Laboratory |
| Facility: APS-GSECARS Format: Poster |
| Phase equilibrium and trace element partitioning between metal and silicate phases (Dmet/sil) can constrain ancient and modern interaction between planetary cores and mantles. Extension of the PT range beyond the reach of the multi-anvil (MA) presents an opportunity ? and a challenge - to access, recover, and analyze experiments in the PT space envisioned for an early terrestrial magma ocean as well as the modern CMB. The laser-heated diamond anvil cell (LHDAC) is the only static technique capable of achieving the desired pressures and temperatures, but LHDAC has not yet been systematically developed as a tool of experimental petrology. Our overarching strategy to develop this capability is to (1) start with systems that are well characterized at lower pressures and compare LHDAC results to MA for overlapping P, T, X and fO2 (2) test for equilibrium at all PT conditions by performing ?reversals? (3) test for reproducibility by performing replicates of each experiment (4) monitor phase assemblage and melting using X-ray diffraction (5) characterize products using our full analytical arsenal: electron micro-probe (EMP), nano scanning electron micro-probe (nanoSEM), and nano secondary ion mass spectrometry (nanoSIMS). We present the preliminary results of metal/silicate partitioning experiments from 2200-4000K and from 5-60 GPa in the LHDAC on the well-studied ?C1? chondrite composition. We chose to look at Ni, Co, and Fe in order to facilitate comparison with other multi-anvil (MA) and LHDAC partitioning data (e.g. Li and Agee, 1996; Chabot et al, 2005; Bouhifd and Jephcoat, 2003; Tschauner et al., 1999). We will present our advances in both experimental and analytical methodology. |
Diffusion of Trivalent Cations in MgO at 1 atm and High Temperature (1473-1783 K) |
| Katherine L Crispin Case Western Reserve University katherine.crispin@case.edu James A Van Orman, Chen Li |
| Facility: None Format: Poster |
| Trivalent impurities govern cation vacancy concentrations in most minerals, and thus play a central role in solid-state diffusion in the Earth. Periclase is the second most abundant mineral in Earth?s lower mantle and is a key to understanding creep and chemical exchange mechanisms. Although periclase is among the simplest of minerals, diffusion of trivalent cations is a complex process. Trivalent cations tend to bind to oppositely charged cation vacancies to form pairs, and in some cases higher-order complexes. Impurity-vacancy pairs are extremely mobile species; the continual presence of a vacancy adjacent to the trivalent impurity allows it to move through the lattice much more rapidly than it would in the absence of binding. We have performed experiments on diffusion of Al, Ga, Sc, Y and Cr in periclase, and developed a theoretical approach to extract the binding energy and impurity-vacancy pair diffusivity from the experimental diffusion profiles. Theoretical diffusion profiles were calculated numerically, and were fit to the experimental profiles through a chi-squared minimization scheme. Impurity-vacancy binding energies obtained from the fit are generally in good agreement with theoretical calculations. The diffusion coefficients generally decrease with ionic radius and preliminary results indicate that the activation energy for diffusion increases with ionic radius. Cr is an exception to the trend and diffuses more slowly than expected; it seems likely that this is due to the crystal field effect. |
Water in Subduction Zone Microdiamonds: Evidence from Synchrotron-Assisted Infrared Spectrometry |
| Larissa Dobrzhinetskaya University of California-Riverside larissa@ucr.edu Zhenxian Liu, Geophysical Laboratory, Carnegie Institution of Washington, Washington D.C., USA Junfeng Zhang & Harry W. Green Department of Earth Sciences, University of California, Riverside, CA 92521, USA |
| Facility: NSLS-U2A (DAC) Format: Poster |
| The Erzgebirge region of Saxony, Germany, records an ultrahigh pressure metamorphic event that occurred during Variscan continent-continent collision. Metamorphosed sediments within the Erzgebirge massif contain microdiamonds. The discussion of diamond origin is focused around their crystallization from a C-O-H supercritical fluid versus a silicate melt containing a suitable amount of dissolved carbon at high pressures and temperatures. According to geobarometry and finding of TiO2-II phase, the diamond-bearing felsic gneisses were recrystallized at T=1000oC and P=7-8GPa (Hwang et al., 2000, Massonne, 2003). To cast light on the diamond-forming medium, synchrotron radiation, a bright source of infrared photons, was used for infrared spectroscopy of the Erzgebirge diamonds at the National Synchrotron Light Source of the Brookhaven National Laboratory, USA. The optical layout of the beamline facility was described in detail earlier (Liu et al., 2002). The diamond IR spectra were collected with a Bruker IFS 66v/S vacuum Fourier transform interferometer interfaced with the synchrotron source and a modified Bruker IRscope-II microscope equipped with an HgCdTe type-A detector. The top aperture/field stop was set to 10´10 mm2, and the spectra were acquired in the range of 600?4000 cm-1 with a KBr beam splitter. A spectral resolution of 4 cm-1 was applied to all spectra. Infrared spectra were acquired from seven microdiamonds recovered from felsic gneiss by a microwave digestion method. The spectra show peaks for nitrogen impurities, molecular H2O, OH-stretching mode, and CO3 radicals. The presence of both nitrogen C- and A-defects classifies the studied diamonds as Type Ib-IaA, which is similar to other metamorphic diamonds from the Kokchetav massif (Kasakhstan) and from felsic gneisses of the Western Gneiss Region (Norway). The IR data are consistent with our studies of inclusions with the transmission electron microscope showing that these diamonds contain nanometric multicomponent inclusions consisting of both fluid and crystalline phases. The data strongly support the concept of diamond crystallization from a supercritical C-O-H fluid. |
Phase transitions and equations of state of alkaline earth fluorides CaF2 and SrF2 to 95 GPa |
| Susannah M Dorfman Princeton University dorfman@Princeton.EDU F. Jiang, Z. Mao, A. Kubo (now at GSECARS, Advanced Photon Source), and T. Duffy |
| Facility: APS-GSECARS Format: Poster |
| The high-pressure behavior of AX2 compounds is of broad interest in materials science and chemistry. In this study we examine phase transitions and equations of state of the alkaline earth fluorides CaF2 and SrF2 to 95 GPa. Angle-dispersive x-ray diffraction experiments were performed on CaF2 and SrF2 samples in laser-heated diamond anvil cells at beamlines X17B3 of the National Synchrotron Light Source and 13-ID-D of the GSECARS sector at the Advanced Photon Source. We confirmed that both materials undergo a phase transition from the cubic fluorite structure to the orthorhombic cotunnite structure at pressures less than 10 GPa. Both materials further transform to a hexagonal Ni2In-type structure at 84 and 40 GPa, respectively, following laser heating. This finding is consistent with theoretical calculations and the behavior of the analog compound BaF2. For SrF2, the Ni2In-type phase was confirmed by Rietveld refinement. Unit cell parameters and volumes were determined as a function of pressure for the new phase. We also constrained the equation of state of the cotunnite phase of CaF2 to 82 GPa. Fitting the data to a Birch-Murnaghan equation of state yields a zero-pressure bulk modulus of 97.9 GPa with a pressure derivative of 5.6 for cotunnite-type CaF2. This work represents the first synthesis and characterization of the Ni2In-type phase for these compositions. |
Large excess volumes and thermal expansions in pyrope-grossular garnet series |
| Wei Du Columbia University in the city of New York Lamont-Doherty Earth Observatory weidu@ldeo.columbia.edu Dave Walker Columbia University in the city of New York Lamont-Doherty Earth Observatory Simon Clark,Martin Kunz,Wendel A. Caldwell Advanced Light Source, Lawrence Berkeley National Laboratory |
| Facility: ALS Format: Poster |
| Multi-anvil synthesis techniques and XRD were used to measure the unit cell parameters of six garnet compositions on the join pyrope-grossular between 298K and ~870K. The pyrope-gossular garnet series has positive excess volumes at all temperatures that are close to unpublished data from measurements of garnets also synthesized by MA techniques at Daresbury, UK. Present excess volumes are locally greater than those literature data from piston/cylinder synthesis, and smaller than garnets synthesized from diamond anvil cells. Intermediate garnets show excess volumes approaching 0.9 cm3/mol, which are ~3 times those previously reported. The excess volume pattern at room temperature is asymmetric leaning toward grossular. A two-parameter Margules equation fitted to the data gives = 4.9+-0.7 cm3/mol, = 1.1+-0.8 cm3/mol at 298K, showing the same sense of asymmetry as Boseneck and Geigerâ??s (1997) study but are ~3 times larger. The estimate of garnet solvus crest rise in T with increasing P is significantly enhanced compared to that given by Haselton and Newton (1980). Thermal expansions of garnets in this series range from 1.9-3.0e-5/K and uniformly increase with temparture at rates that differ with garnet composition. The values for pyrope and grossular closely follow those given by Skinner (1956). The values for thermal expansion at high temperature converge to ~1/2 the range shown at room temperature. The dependence of garnet volume on composition and temperature shows that at room temperature, the thermal expansions of garnet compositions with larger excess volume are relatively smaller. The reason for the large range in excess volumes observed along pyrope-grossular garnet series need to be unraveled before any meaningful equation of state work can be undertaken. Different grain sizes caused by different annealing and synthesis P-T routes may be the reason for the difference between these three series of excess volume values from piston/cylinder, multi-anvil, and diamond anvil cell techniques. Peak broadening in DAC synthesis of garnets is consistent with diminished grain size compared to MA synthesis. |
A hybrid self-gasketing "dry" DIA cell |
| William B. Durham Massachusetts Institute of Technology wbdurham@mit.edu Kurt Leinenweber (Arizona State University) Shenghua Mei (University of Minnesota) |
| Facility: NSLS-X17B2 (MAC) Format: Poster |
| The cubic medium that is the basis of the self-gasketing DIA pressure assembly must have sufficient strength to achieve good pressure efficiency and sufficient ductility to form competent gaskets bounding the six anvils. Few materials outside of boron-epoxy and unfired pyrophyllite meet these criteria. Both materials contain considerable water, and it is often problematic in the DIA to measure material properties that are affected by water. In order to measure the rheology of olivine--a material that is known to water weaken--in the Deformation-DIA, we have developed and successfully tested a hybrid cell that combines the dryness and strength of mullite with the self-gasketing properties of unfired pyrophyllite. Conceptually, the cell is a cube of pyrophyllite with a spherical cavity of diameter equal to the edge length of the cube, with a sphere of mullite exactly filling the cavity. Machining and assembly of the pyrophyllite "web" and the mullite sphere (which can also be made as half-spheres if desired) is not complex. We have carried out over a dozen runs with the hybrid cell, both on- and off-(synchrotron) line, and have been able to achieve significantly higher pressures and incur fewer blowouts, than with an earlier version of the anhydrous cell made only of mullite. The performance is comparable to that of boron-epoxy, but without the water. |
Magnetic transition and sound velocities of Fe3C at high pressure: implications for the Earth?s core |
| Lili Gao Department of Geology, University of Illinois at Urbana-Champaign liligao2@uiuc.edu Bin Chen, Jingyun Wang, Jie Li, Michael Lerche, Sector 3 of Advanced Phonon Source (APS), Argonne National Laboratory Jiyong Zhao, Sector 3 of Advanced Phonon Source (APS), Argonne National Laboratory Wolfgang Sturhahn, Sector 3 of Advanced Phonon Source (APS), Argonne National Laboratory |
| Facility: Other Format: Poster |
| Carbon has long been considered a candidate light element in the Earth?s core. Fe3C (cementite) has the highest C content among all known Fe-C compounds. Under ambient condition, Fe3C is ferromagnetic. At room temperature, a pressure-induced magnetic transition from ferromagnetic phase to paramagnetic phase has been found in previous studies; however, there is controversy in the transition pressure. In this study, we carried out nuclear forward scattering (synchrotron Mössbauer spectroscopy) and nuclear resonance inelastic x-ray scattering on Fe3C up to 28 GPa at room temperature in Sector 3 of the Advanced Photon Source (APS), Argonne National Laboratory. The magnetic transition pressure was found to be between 9 GPa and 20 GPa in this study, lower than the previously reported transition pressure of 25 GPa from an x-ray emission spectroscopy study (Lin et al., 2004), but consistent with changes in linear compressibility in an x-ray diffraction study (Li et al., 2002). The ferromagnetic to paramagnetic phase transition is also observed at 483 K under room pressure (Wood et al., 2004). The observed magnetic collapse under high pressure and high temperature indicates that the ferromagnetic phase is not stable under the Earth?s core condition, and that the paramagnetic phase of Fe3C is more applicable to the Earth?s core. Hyperfine filed parameters can be derived from our nuclear forward scattering spectra as well. These parameters can be compared with theoretical results for an improved understanding of the electronic structure of iron as a function of pressure. We have also derived Debye velocities of Fe3C from parabolic fitting to the low-energy range of the nuclear resonance inelastic x-ray scattering spectra. Combined with equation of state of Fe3C (Li et al., 2002), the compressional and shear wave velocities of Fe3C have been derived. |
Progress toward linking the structure and properties of MgSiO3 glasses with complementary liquids? |
| Sarah J Gaudio University of California, Davis Gaudio@geology.ucdavis.edu C.E. Lesher1, and S. Sen2 1 Department of Geology, University of California, Davis, California 95616, USA 2 Department of Chemical Engineering and Material Science, University of California, Davis, California 95616, USA |
| Facility: Other Format: Poster |
| Determining the structure and densification mechanisms of amorphous mantle melt analogues is essential for constraining extrapolations of thermodynamic and rheological properties of magmatic liquids to experimentally and computationally inaccessible conditions relevant to the Earthâ??s mantle. MgSiO3 is an appropriate proxy for a partially depolymerized mantle melt composition. However, the refractory and fragile nature of MgSiO3 and other alkaline earth metasilicate compositions present several analytical challenges under high pressure and temperature, in spite of their compositional simplicity. This work is focused on bridging the gap in our understanding of glass and melt structure and properties from 300 K to liquidus temperatures under high-pressure. We report the results of density measurements, 29Si MAS NMR spectroscopy, and ab initio simulation studies of pressure-induced structural rearrangement in recovered MgSiO3 glasses. Experiments were performed below Tg at atmospheric pressure (1039 K). Ab initio simulations were performed to support structural interpretations of the spectroscopic data, and suggest possible densification mechanisms producing high-coordinated Si identified in our experiments. Results from density measurements, 29Si MAS NMR spectra, and the ab initio simulation are used to explore the sub-Tg relaxation of MgSiO3 glass and associated densification, recoverable from high-pressure conditions. More work is required to understand sub-Tg reorganization in glassy materials under high-pressure conditions; however, if this process occurs in mantle melt analogues at experimentally accessible temperatures, then these data will be useful in developing a theoretical relationship that links pressure-induced structural configurations and properties of glassy-state silicates to their molten-state complements. |
Viscosity measurements of liquid water to 4 GPa and 500 Kelvin |
| Brent Grocholski University of California-Berkeley b.grocholski@gmail.com Raymond Jeanloz |
| Facility: ALS Format: Poster |
| We have measured viscosity of pure water from 0.1 GPa to 4.0 GPa from room temperature to 500 Kelvin using an externally-heated, rolling-sphere diamond-cell viscometer. While this represents a change in density of up to 40%, viscosity values only vary between 0.5 to 2 times the value at room temperature and pressure. Given the importance of water in planetary geophysics, it is surprising that almost no measurements of viscosity are available above 1 GPa until now. This is at least in part due to the difficulty in reliably measuring the rapid fall-times of spheres used to determine viscosities in fluids. This problem has been eliminated by using a strobed light-emitting diode, allowing us to calibrate to ambient-condition viscosities and obtain high-pressure viscosities consistent with accurate values given in the literature for water to 1 GPa. In principle, our approach can be extended to over 30 GPa and 1000 K, thereby providing significant tests of theoretical models of fluid-transport properties at conditions existing deep inside planets. |
The development of sagittal-Laue monochromator at X17B3 in 2006 |
| Quanzhong Guo University of Chicago qguo@bnl.gov Jingzhu Hu, University of Chicago; Zhong Zhong, NSLS-BNL |
| Facility: NSLS-X17B3 (DAC) Format: Poster |
| A prototype 4-crystal sagittal-Laue monochromator was designed, assembled, has and tested at X17B3 beam line successfully. The x-ray flux provided by such four-crystal monochromator system is one order of magnitude less than that provided by two-crystal sagittal-focusing Laue monochromators, currently in use at X17C and X17B3 beamlines. The thickness of the Si crystals was selected to be 0.6 mm to provide design energy 30keV. In order to increase the x-ray flux, we optimized the thickness of Si Laue crystals in 2006. The experimental results show that the three pieces of 0.6 mm crystals provided the strongest diffraction intensity, compared with 1, 2 and 4 pieces of 0.6 mm Si crystals. Moreover, the results also show that it is possible to align multiple crystals, cut from the same wafer, to provide one single x-ray energy from the 111 diffraction. Such arrangement is also compatible with two-crystal Laue monochromators. |
Pressure and Temperature Dependence of the Elasticity of Pyrope (Py) ?Majorite (Mj) Garnets measured by Ultrasonic Interferometry Technique. |
| Gabriel D Gwanmesia Department of Physics & Pre-Engineering, Delaware State University, Dover, DE 19901, USA ggwanmesia@desu.edu L. Wang (2, 3), R. Triplett (1), R. C. Liebermann (2, 3) (1) Department of Physics & Pre-Engineering, Delaware State University, Dover, DE 19901, USA (2) Mineral Physics Institute, Stony Brook University, Stony Brook, New York 11974-2100, USA. (3) Department of Geosciences, Stony Brook University, Stony Brook, New York 11974-2100, USA. |
| Facility: NSLS-X17B2 (MAC) Format: Poster |
| Velocities of acoustic compressional (P) and shear (S) waves have been measured for dense (>99.5% of theoretical density) isotropic polycrystalline Pyrope (Py) ? Majorite (Mj) garnets (Py100, Mj50Py50 and Py40Mj40) at simultaneous high pressures and high temperatures using ultrasonic interferometry, in conjunction with in-situ synchrotron x-ray diffraction and imaging techniques. Fine-grained elastically isotropic polycrystalline garnet specimens were synthesized from homogeneous glass starting materials at high pressures and temperatures in the Kawai-type multi-anvil apparatus. The physical properties of the recovered specimens have been characterized with density measurements, microprobe analysis, scanning electron (SEM) microscopy and by synchrotron x-ray diffraction. The elasticity of synthetic polycrystalline pyrope (Py100) were also measured to 1000K at 300 MPa in an internally heated gas-medium apparatus using phase comparison ultrasonic Interferometry technique. We compare the elasticity data from the two studies to data from Brillouin spectroscopy and to those of other previous investigators, and illustrate the effect on the pressure and temperature dependence of the elastic properties due to substitution of Si for Al and Mg in the garnet structure along the pyrope-majorite join. We also compare our data with the seismic velocity gradients in the Earth?s transition zone. |
The Equation of State and Phase Boundary of Post-Perovskite in (Mg,Fe)SiO3 and NaMgF3 |
| Justin W Hustoft Massachusetts Institute of Technology justin.hustoft@yale.edu S.-H. Shim, Massachusetts Institute of Technology K. C. Catalli, Massachusetts Institute of Technology A. Kubo, GSECARS, University of Chicago V. Prakapenka, GSECARS, University of Chicago W. A. Caldwell, Advanced Light Source, Lawrence Berkeley National Laboratory M. Kunz, Advanced Light Source, Lawrence Berkeley National Laboratory |
| Facility: APS-GSECARS Format: Poster |
| We have measured the equation of state and phase boundary of post-perovskite in (Mg0.9Fe0.1)SiO3 and NaMgF3 using an Ar pressure medium over wide pressure ranges at the GSECARS sector of APS and beamline 12.2.2 of ALS. In our in situ measurements, we found that Pv + PPv mixture transforms completely to pure PPv at 2500 K and 135 GPa. We used the same gold scale (Tsuchiya et al. 2003) as the measurements without a pressure medium by Hirose et al. (2006) which suggested much lower pressure for the boundary, 113 GPa. Previous studies of NaMgF3 using NaCl and MgO pressure media reported a complete transformation to PPv at 28-30 GPa at room temperature (Martin et al. 2006). However, we observe the first appearance of PPv occurring between 36 and 41 GPa in an Ar pressure medium. After complete transformation, we decompressed pure (Mg0.9Fe0.1)SiO3-PPv to measure the equation of state. We found changes in the compressional behavior of PPv at 110 GPa and 80 GPa due to its metastability. If only the data points above 110 GPa are included, a fit to the second order Birch-Murnaghan equation yields K(125GPa) = 657(8) GPa [K0 = 221 GPa] which is in excellent agreement with first-principles predictions and Shieh et al. (2006)'s measurements. If all the data points above 80 GPa are included, ignoring the change at 110 GPa, we find K(125GPa) = 833(8) GPa which is consistent with Mao et al (2006). The volumes of NaMgF3-Pv and PPv measured during decompression show good agreement with those reported by Martin et al. (2006) who report an 80% higher bulk modulus of PPv than Pv, which is not consistent with the first-principles result (Umemoto et al. 2006). |
Melting investigations of iron at high-pressure using synchrotron Moessbauer spectroscopy |
| Jennifer M Jackson California Institute of Technology jackson@gps.caltech.edu Wolfgang Sturhahn, Michael Lerche, Jiyong Zhao, Stanislav V. Sinogeikin (Advanced Photon Source, Argonne National Laboratory, IL), Dmitry L. Lakshtanov, and Jay D. Bass (Department of Geology, University of Illinois, Urbana, IL) |
| Facility: Other Format: Poster |
| Seismological observations indicate that Earth's iron-dominated core consists of a solid inner region surrounded by a liquid outer core. The melting temperature of iron at high-pressure therefore provides a bound on the temperature regime of the core. Previously, melting studies of iron metal at high-pressures and temperatures were performed by shock-compression, resistive- and laser-heating in diamond anvil cells using visual observations or synchrotron x-ray diffraction and theoretical methods. However, the melting curve of iron is still controversial, especially at very high pressure, where experiments are extremely challenging. Here, we will present a new method of detecting the solid-liquid phase boundary of iron at high-pressure using 57^Fe synchrotron Moessbauer spectroscopy (SMS). Such a method has become possible with the development of third generation synchrotron sources in conjunction with laser-heated diamond anvil cells. Specifically, focused synchrotron radiation with 1 meV bandwidth passes through a laser-heated sample inside a diamond anvil cell. The characteristic SMS time signature is observed by fast detectors and vanishes suddenly when melting occurs. In addition to presenting our results on iron at high-pressures, future applications of this method to the study of melting under pressure will be discussed. |
Elasticity of Stishovite by Brillouin Scattering to 22 GPa |
| Fuming Jiang Department of Geosciences, Princeton University, Princeton, NJ 08540 fumingj@princeton.edu Gabriel D. Gwanmesia*, and Thomas S Duffy *Physics Department, Delaware State University |
| Facility: Other Format: Poster |
| Detailed Brillouin scattering measurements of the complete set of elastic constants of stishovite have been carried out over 12 GPa and partial measurements up to 22 GPa. Brillouin experiment on stishovite at high-pressures in a diamond anvil cell is technically challenging because of the overlapping of stishovite P-wave with the diamond S-wave. Three random crystal platelets were polished to about 30 µm thick from as-grown crystals and measured in a symmetric forward scattering geometry with a 50 step in a range of 1800. For each platelet, one P-wave and two S-waves were observed. The measured velocity data of three platelets were fit together to the Christoffel?s equation. The fit yielded the full elastic constants of C11 = 454.8(12) GPa, C33 = 761.7(13) GPa, C12 = 199.2(17) GPa, C13 = 192.0(12) GPa, C44 = 257.5(6) GPa, C66 = 320.5(9) GPa. The Voigt and Reuss bounds on the aggregate bulk and shear moduli are KV = 315(1) GPa, GV = 240(1) GPa for Voigt, KR = 301(1) GPa, GR = 216(1) GPa for Reuss. For one crystal-platelet, the slow shear wave velocity decreased by 11% from ambient condition to 22 GPa in a specific direction, indicating acoustic mode softening. According to theory, the combined elastic constant (C11-C12)/2 is related to a transverse acoustic mode which triggers phase transition of stishovite to CaCl2-type at high pressure. Our results show that (C11-C12)/2 has a negative slope with increase of pressure in agreement with theoretical models. The isothermal compression curve constructed from this study is also in close agreement with previous static compression studies. |
A computational study of ionic vacancies and diffusion in MgSiO3 perovskite and post-perovskite |
| Bijaya B Karki Department of Computer Science, Department of Geology and Geophysics, Louisiana State University, Ba karki@csc.lsu.edu Gaurav Khanduja Department of Computer Science, Louisiana State University, Baton Rouge, Louisiana, USA |
| Facility: None Format: Poster |
| We have performed first-principles simulations within density functional theory to investigate the effects of pressure on the formation of defects (ionic vacancies) and ionic diffusion in the perovskite (pv) and post-perovskite (ppv) phases of MgSiO3. Our results show that the predicted formation enthalpies of three Schottky (MgO, SiO2 and MgSiO3) defects are similar between the two phases at high pressures (100 to 150 GPa) with MgO Schottky defect being the most favorable. However, the calculated activation enthalpies and activation volumes of diffusion are shown to differ substantially between them. In particular, the activation enthalpies for Mg and Si diffusion in ppv are smaller than the corresponding values for pv, for example, by factors of 2.2 and 3.4, respectively, at 120 GPa, whereas the O migration enthalpy of ppv is only slightly larger than that of pv. The easy migration paths of the cations in ppv are shown to take place along the <100> direction in which Si-O octahedra share the edges. Visualization of the simulation data reveals that the vacancy defects and migrating ions induce substantial distortions in the atomic and electronic structures around them. It is suggested that diffusion is equally easy for all three species in ppv and is likely to occur through extrinsic processes near the bottom of the lower mantle. |
A computational study of ionic vacancies and diffusion in MgSiO3 perovskite and post-perovskite |
| Bijaya B Karki Department of Computer Science, Department of Geology and Geophysics, Louisiana State University, Ba karki@csc.lsu.edu Gaurav Khanduja Department of Computer Science, Louisiana State University, Baton Rouge, Louisiana, USA |
| Facility: None Format: Poster |
| We have performed first-principles simulations within density functional theory to investigate the effects of pressure on the formation of defects (ionic vacancies) and ionic diffusion in the perovskite (pv) and post-perovskite (ppv) phases of MgSiO3. Our results show that the predicted formation enthalpies of three Schottky (MgO, SiO2 and MgSiO3) defects are similar between the two phases at high pressures (100 to 150 GPa) with MgO Schottky defect being the most favorable. However, the calculated activation enthalpies and activation volumes of diffusion are shown to differ substantially between them. In particular, the activation enthalpies for Mg and Si diffusion in ppv are smaller than the corresponding values for pv, for example, by factors of 2.2 and 3.4, respectively, at 120 GPa, whereas the O migration enthalpy of ppv is only slightly larger than that of pv. The easy migration paths of the cations in ppv are shown to take place along the <100> direction in which Si-O octahedra share the edges. Visualization of the simulation data reveals that the vacancy defects and migrating ions induce substantial distortions in the atomic and electronic structures around them. It is suggested that diffusion is equally easy for all three species in ppv and is likely to occur through extrinsic processes near the bottom of the lower mantle. |
The High Pressure, Temperature Phase Diagram of Silver Iodide |
| Abby Kavner UCLA Earth&Space Science Department akavner@igpp.ucla.edu Kelly Havens UCLA Matthew Armentrout UCLA Martin Kunz, Advanced Light Source, LBNL W. A. Caldwell, Advanced Light Source, LBNL |
| Facility: ALS Format: Poster |
| Silver iodide (AgI) is a model system in solid state physics and an industrially important ionic conductor, which undergoes a series of phase transformations at high pressures and temperatures. We studied the high-pressure, high-temperature phase stability of AgI using synchrotron X-ray diffraction in conjunction with in situ laser heating at beamline 12.2.2 at the Advanced Light Source in Berkeley, CA. The room pressure phase transformation from fcc phase III to a high pressure phase V was bracketed to be between 11.0 and 11.4 GPa. The AgI undergoes an additional phase transformation as it is heated to ~1400 K with an infrared laser, phase VI, which is optically observable in the diamond cell sample, and is quenchable upon return to ambient temperature. Upon further heating (above 1400 K), phase III reappears; however the reappearance is only observed during high temperatures--the sample reverts to phase VI as soon as the temperature returns to room temperature (See Fig. 1). This experiment provides a demonstration of the importance of an in situ measurement at both high pressures and high temperatures, in which it is assured that the X-ray beam is in complete collinear alignment with the laser-heated spot. In this poster, we present the new high pressure and temperature phase diagram of silver iodide, and provide constraints on the equations of state of the stable high pressure phases. |
Structure of high pressure La- and Li-containing aluminosilicate glasses |
| Kimberly Kelsey Stanford University kkelsey@stanford.edu Jonathan F. Stebbins - Stanford University Paul D. Asimow - California Institute of Technology Jed L. Mosenfelder - California Institute of Technology |
| Facility: Other Format: Poster |
| Understanding the structure of high pressure aluminosilicate glasses is important to better constrain the macroscopic properties and igneous processes in the upper mantle. As melts densify, bond angles and distances change and the average coordination number for the cations increases. It has been shown that the type and amount of network modifying cation (i.e. Ca, Mg, Na, K, etc?) present will dramatically affect the generation of high coordination aluminum as well as the density of the resulting melt (Allwardt et al. 2005). This study uses nuclear magnetic resonance (NMR) spectroscopy to study Li3AlSi3O9 and LaAlSi3O9 glasses quenched from liquids at pressures up to 8 GPa to better understand the effect of modifier cation on pressure-induced structural changes. 27-Al MAS NMR spectra show that the La-containing glasses have a substantial increase in average aluminum coordination number, from approximately 4.21 to 5.07 from ambient pressure to 8GPa, while the Li-containing glasses have consistently lower average aluminum coordination number, increasing from 4.02 to 4.48 from ambient pressure to 6GPa. This is consistent with previous results indicating an increase in 5,6Al with increasing modifier cation field strength. At 6 and 8GPa the La-containing glasses the average aluminum coordination number is less than expected, suggesting additional cations present in the glasses may be undergoing significant structural changes. La XANES confirmed an increase in average La coordination, however 29-Si MAS NMR spectra do not detect any 5,6Si (5% detection limit). 17-O 3QMAS NMR spectra of the Li-containing glasses are consistent with the previously proposed mechanisms for the generation of 5,6Al at the expense of non-bridging oxygen (Allwardt et al. 2005), however the La-containing glasses have nearly no change in oxygen environments with increasing pressure. |
Mechanism for Pressure Induced Amorphization in Ca(OH)2 Portlandite |
| Boris Kiefer New Mexico State University bkiefer@physics.nmsu.edu Megan Lockwood |
| Facility: None Format: Poster |
| Hydroxides have attracted significant scientific interest for several decades. Some hydroxides such as Ca(OH)2 - portlandite show pressure induced reversible solid state amorphization at room temperature. This process has been observed in X-ray diffraction experiments as well as Raman spectroscopy. For fine grained powders the transition occurs between ~11-12 GPa during compression and long-range order re-appears during decompression between 2-3 GPa. In contrast single crystals first undergo a phase transition from Ca(OH)2-I to Ca(OH)2-II at 4.5 GPa and amorphize at a pressure between ~18-22 GPa with a small hysteresis of ~1 GPa. However, the mechanism for pressure induced amorphization in portalandite remains unknown We use first-principle calculations to investigate Ca(OH)2 up to 30 GPa. Our results confirm the phase transition from Ca(OH)2-I to Ca(OH)2-II at 4.5 GPa consistent with previous experimental and theoretical studies. We find that pressure induced changes in Ca(OH)2-I are largely limited to the hydrogen sublattice, consistent with neutron diffraction experiments. This indicates that a disordered hydrogen array can coexist with ordered octahedral sheets in portlandite, similiarily to Mg(OH)2. However, amorphization requires the absence of long-range order on a length scale that is short compared to the coherence length of the experiments. Our simulations show the existence of a new structure that becomes more stable than Ca(OH)2-I above ~13 GPa, a pressure comparable to the experimental amorphization pressure in powders. In this new structure the Ca-octahedra are separated by calcium in trigonal prismatic coordination. Furthermore this new structure reverts back to Ca(OH)2-I at ~1 GPa upon decompression Thus our predicted hysteresis is very similar to experimental observations in Ca(OH)2 powders. These findings suggest that amorphization in portlandite powders is related to the appearance of this new structure and due to interface formation. The enthalpy of the new structure is always higher as compared to Ca(OH)2-II but the difference decreases rapidly, approaching ~30 meV/atom (~350 K, at 20 GPa). Thus the new structure and interface formation may also explain the reversible amorphization of Ca(OH)2-II and its small hysteresis. Therefore our findings suggest that amorphization in portlandite proceeds by formation of an intermediate structure, a pathway that has also been found in α-quartz. |
Elasticity of pyroxene at high pressure and temperature |
| Jennifer kung National Cheng Kung University, Taiwan jkung@mail.ncku.edu.tw Baosheng Li, Mineral Physics Institute, Stony Brook University. Robert C. Liebermann, Department of Geosciences and Mineral Physics Institute, Stony Brook University |
| Facility: NSLS-X17B2 (MAC) Format: Poster |
| Elastic wave velocity measurements on mantle minerals provide the data for direct comparison with seismic observations and deductions about the structure and composition of the Earth's interior. Major mineralogical constituents of petrological models of the Earth?s upper mantle include the olivine, pyroxene (Mg-rich orthopyroxene and Ca-rich clinopyroxene) and garnet phases. To date, the elasticity of the olivine and garnet phases have been measured under different experimental conditions: at high pressures and room T, at high temperatures at ambient P, and at simultaneous at high pressures and temperatures. In recent studies on Mg-rich pyroxene (i.e. orthoenstatite) at high pressure and high temperature regimes, the velocities have exhibited anomalous behavior the along both the high T and high P paths (Jackson et al., 2004; Kung et al., 2004); such behavior has not been observed in the olivine or garnet phases. Thus, the question arises whether the pressure derivatives of the velocities measured at room temperature or the temperature derivatives at room pressure for orthoenstatite can be can used for exploring the physical state of upper mantle. To obtain the pressure and temperature derivatives under mantle conditions, we, therefore, conducted elasticity measurement of orthoenstatite at simultaneous at high pressures and temperatures. In this meeting, we will present the results and compare with those measured at different experimental conditions. |
Water nanostructures confined inside the quasi-1D channels of LTL zeolite |
| Yongjae Lee Yonsei University yongjaelee@yonsei.ac.kr Yongjae Lee,1,* Chi-Chang Kao,2 Sun Jin Kim,3 Hyun-Hwi Lee,4 Dong Ryeol Lee,4 Tae Joo Shin,4 and Jae-Young Choi4 1Department of Earth System Sciences, Yonsei University, Seoul 120-749, Korea 2National Synchrotron Light Source, Brookhaven National Laboratory, Upton, NY, 11973, USA. 3Nano-Materials Research Center, Korea Institute of Science and Technology, Seoul 136-791, Korea 4Pohang Accelerator Laboratory, POSTECH, Pohang, 790-784, Korea. |
| Facility: Other Format: Poster |
| Understanding the formation and evolution of confined water molecules is critical in understanding many chemical and biological processes as well as the water transport inside the Earth. It is often difficult, however, to probe such processes since the host-guest interactions are dynamic in nature. Using a well-defined zeolitic channel as an ideal host and hydrostatic pressure as a driving force, we show how water molecules are introduced and evolve into various confined nano-structures up to 3.37 GPa. In the initial stage of pressure-induced hydration (PIH) occurring inside the undulating 12-ring channels of a synthetic potassium gallosilicate with zeolite LTL topology, water molecules preferentially assemble into hydrogen-bonded clusters, which alternate with water layers. With increasing PIH (by ~50%) at higher pressures, the interaction between the confined water molecules increases, and the water clusters and layers are interconnected to form hydrogen bonded water nanotubes inside the zeolitic channels. The confined water nanotube closes its maximum access diameter at further increasing pressures and gradually transform into isolated species interacting with the zeolitic host framework. The evolution of the confined water nano-structures is well coordinated by the concerted changes in the framework distortion and the reentrant cation migration, which appear to be driven by the gradual ¡®flattening¡¯ of the host 12-ring channels. |
The High Pressure Synergetic Center at APS: a new approach to High Pressure Physics |
| Michael Lerche High Pressure Synergetic Center, Carnegie Institution of Washington lerche@aps.anl.gov Yang Ding, Lin Wang, Guoyin Shen, Russell J. Hemley and Ho-kwang Mao |
| Facility: Other Format: Poster |
| Very recently a new group promoting High Pressure (HP) research started at the Advanced Photon Source (APS), the High Pressure Synergetic Center (HPSynC). The HPSynC mission is to establish high-pressure environments at many APS beamlines for the users community. This group will be equivalent to a full beamline team of eight scientists/engineers who, working with HP researchers and beamline scientists, are focusing on the integration of novel high-pressure synchrotron techniques at all specialized beamlines. The HPsynC concept is beyond the normal "extreme environment" infrastructure that is limited to sharing gas-filling equipment, sample preparation laboratory, diamond cells, etc. In addition to these functions, the main role of HPSynC is to facilitate the next level of scientific and technical integration. The HPSynC staff who have the scientific agendas and technical know-how will improve both high-pressure apparati and beamline parameters interactively to optimize the extraordinary capabilities and resource of the synchrotron facility for novel high-pressure experimentation. This new approach is designed to solve the most prominent problem in High Pressure physics using synchrotron radiation. To satisfy the growing demand of beamtime for HP experiments many beamlines have been dedicated to HP research. This allows experienced support of HP experiments, but leaves almost no time for the beamline staff to implement and/or to develop new promissing x-ray techniques to be used at those beamlines. The HP researchers on the other hand are facing the problem of how to actually implement new techniques at these highly sophisticated and specialized beamlines. HPSynC wants to overcome this problem by promoting and developing new techniques together with both groups, the beamline staff and the research team. |
Energy dissipation of minerals at mantle P-T and seismic frequency |
| Li Li Stony Brook University lilli@ic.sunysb.edu Donald J. Weidner, Michael Vaughan, Liping Wang |
| Facility: NSLS-X17B2 (MAC) Format: Poster |
| The dynamic response of materials to an applied stress, especially a cyclic loading force, bears fundamental information about their physical properties. The mechanical properties such as the creep in the transition creep regime can be studied by applying a cyclic force at frequencies corresponding to the characteristic time period of the transient (Jackson and Paterson 1993; Gribb and Cooper 1998); the anelastic response of materials caused by the motion of the ferroelastic domain wall can be studied by dynamic mechanical analysis method (Harrison, Redfern, Buckley and Salje 2004); the nature of the material fatigue damage and ultimate failure can be studies by when the material is subject to cyclic loading (Frost, Marsh and Pook 1999). A very important connection exists between these dynamic properties of minerals with the dynamics of the earth, which are manifested as the attenuation and dispersion of seismic waves (Karato 1993). The viscoelastic or anelastic features of the mantle minerals at deep earth may be caused by the viscous motion of defects (Karato 1998); may be caused by the presence of certain ferroelastic minerals (Carpenter 2000). The challenge is how to detect the energy dissipation at high pressure/temperature and seismic frequencies in the laboratory. Here we demonstrate a methodology to study the anelastic properties of materials at high pressure and high temperature. We use multi-anvil high pressure deformation apparatus coupled with synchrotron X-ray radiation. A cyclical loading force (mHz-Hz frequency) can be applied to the sample at mantle pressure and temperature. Stress and strain relation as a function of time can be resolved during the deformation. The experimental protocol has been tested by applying a sinusoidal stress on a San Carlos olivine specimen. We have obtained experimental results which exhibits resolvable attenuation factors at mantle conditions and are in agreement with pervious reported data. In this paper, we will describe the method and use the available data to demonstrate the frequency range (mHz-Hz frequency) and strain resolution (10-4 to 10-5). |
New density measurements on fayalite liquid: test on new method for Fe2+-rich silicate liquids |
| Qiong Liu University of Michigan, Stony Brook University qioliu@notes.cc.sunysb.edu Rebecca A. Lange University of Michigan, Department of Geological Sciences |
| Facility: NSLS-U2A (DAC) Format: Poster |
| An equation of state for the Fe2SiO4 liquid is important to model the thermodynamic and dynamic behavior of the Earth at depth in which olivine (Mg,Fe)2SiO4 or its high pressure polymorphs are predominant phases. Although iron-rich olivine is unlikely to be present in the Earth?s mantle, data on molten Fe2SiO4 provide useful information about the properties of the Mg-rich (Mg,Fe)2SiO4 liquid at pressures beyond the range of currently available experimental techniques. Furthermore, the one-bar thermodynamic properties are fundamental to model the magmatic liquids at depth, whereas the one-bar volumetric data on Fe2+-rich silicate liquid are very sparse, the study of properties of Fe2SiO4 liquid helps to better constrain the partial molar properties of the FeO component, which are required in thermodynamic modeling. Density measurements on fayalite liquid were performed at one bar between 1278 and 1545 ºC using molybdenum double-bob Archimedean method in a molybdenum crucible under a stream of 99%Ar-1%Co gas mixture. A check on the accuracy of this new method was obtained by measurements of the density of molten NaCl at 1094, 1188, and 1286 K. In addition, platinum bobs are used to measure the density of NaCl liquid under the same reducing condition at 1094 K. Our density measurements by molybdenum bobs are within 0.06 - 0.47%, 0.01 - 0.28%, and 0.11 - 0.46% of the fit to the NaCl density data of Stein et al. (1986), Lange and Carmichael (1987), and Liu and Lange (2001), respectively. The density value with platinum bobs vary by -0.03%, -0.38%, and - 0.09% from the three literature data respectively. The consistency of our results using the new method with other density data on NaCl liquid from the literature proves that our method is convincing and can be used with confidence to the study of Fe2+-rich silicate liquids. |
Measurement of Elasticity at High Pressure and High Temperature with a Self-calibrated Pressure Scale |
| Wei Liu MPI, Stony Brook University weiliu3@notes.cc.sunysb.edu Jennifer Kung, Department of Earth Sciences, National Cheng Kung University, Taiwan Baosheng Li MPI, Stony Brook University |
| Facility: APS-GSECARS Format: Poster |
| The effect of P and T on the propagation of elastic waves in materials is essential for understanding elasticity, mechanical stability of solids, phase transition mechanism, material strength, and the internal structure of the Earth and other planets. The state-of-the-art ultrasonic measurement using multianvil apparatus utilizes a combination of ultrasonic interferometry, x-ray diffraction, and x-ray radiography techniques, allowing for simultaneous measurements of P and S-wave travel times, specific volume (density), and sample length on either single-crystal or polycrystalline specimens. A combined analysis of ultrasonic velocities and density using finite strain theory provides not only the determination of the elastic moduli and their pressure and temperature dependence without pressure calibrant, but also the absolute pressure. In this poster, we will present the analysis procedure and the available data on San Carlos olivine and wadsleyite measured at simultaneously high pressure and high temperature. |
Single-crystal elasticity of hydrous wadsleyite at high pressures and its implication for the earth?s transition zone |
| Zhu Mao Princeton University zhu.mao@jsg.utexas.edu Steven D. Jacobsen2, Fuming Jiang1, Joseph R. Smyth3, Christopher M. Holl3, Thomas S. Duffy1, Daniel J. Frost4 1Princeton University, Department of Geosciences, Princeton, NJ, 08540; 2Northwestern University, Department of Geological Sciences, Evanston, IL 60208; 3University of Colorado, Department of Geological Sciences, Boulder, CO 80309; 4Bayerisches Geoinstitut, Universität Bayreuth, 95440 Bayreuth, Germany |
| Facility: None Format: Poster |
| Wadsleyite is expected to be the dominant phase in the transition zone from 410 to 520 km depth. Previous studies have shown that wadsleyite could theoretically incorporate as much as 3.3 wt% water as structurally bond hydroxyl (e.g. Smyth et al., 1987; Kohlstedt et al., 1996). Even under transition zone conditions, wadsleyite could contain up to 0.9 wt% H2O (Demouchy et al., 2005). We recently showed that the incorporation of water strongly decreases the bulk and shear moduli of wadsleyite (Mao et al., 2007). Here, we present new results on the single-crystal elasticity of wadsleyite with 0.84 wt% H2O to 12 GPa measured by Brillouin scattering. Pressure derivatives of bulk and shear moduli of hydrous wadsleyite are similar to the anhydrous phase: KS0?=4.2(1), G0?=1.4(1). To quantify the effect of H2O on the 410-km discontinuity, we calculate the velocity contrast at 13.7 GPa along 1400oC adiabatic. 10 mol% iron is assumed. We assume the pressure derivatives of aggregate elastic moduli of hydrous olivine are the same as anhydrous phase. We also assume the temperature derivatives of the bulk and shear moduli of hydrous wadsleyite and olivine are the same. The H2O partition coefficient between olivine and wadsleyite is taken to be 2 (Frost and Dolej? 2007). Compared with a dry transition zone, 0.9 wt% H2O in wadsleyite decreases the velocity contrast between wadsleyite and olivine from 10.4% to 8.5% for P wave velocity and from 11.9% to 9.3% for S wave velocity. Thus, 0.9 wt% H2O in wadsleyite could decrease the velocity contrast by ~20%. For a pyrolite upper mantle (60 vol% olivine), 1.3 wt% (or 1.5 wt% determined by S wave) H2O in wadsleyite is required to match the velocity contrast given by seismic model AK135. On the other hand, if the transition zone is considered to be water saturated which corresponds to 0.9 wt% H2O in wadsleyite, 45-49 vol% olivine is needed to explain the magnitude of the 410-km discontinuity. |
On the phase transition between perovskite and post-perovskite structure |
| Charles Martin Geosciences Department, 255 Earth and Space Sciences Building, Stony Brook University, Stony Brook, Ph_d_@hotmail.com John B. Parise |
| Facility: APS-GSECARS Format: Poster |
| We present structure models of MgGeO3 post-perovskite and a structure survey, showing that all known perovskite, post-perovskite and CaIrO3-type structures (ABX3) have specific ranges of the volume-ratio between cation-centered polyhedra (VA:VB). The pressure-temperature conditions (i.e. Clapeyron slope) where the perovskite/post-perovskite phase transition occurs can be estimated by extrapolating the change in VA:VB to ~4.0?a value corresponding to tilt of BX6 octahedra in the perovskite structure where extra-octahedral anion-anion distances match the average intra-octahedral anion-anion distance. We suggest that repulsion between ions, separated by these short distances between octahedra corners, prevents further tilting of octahedra in the perovskite structure and decrease in the VA:VB ratio. Obtaining data of sufficient quality at close to 100 GPa to allow accurate characterization of these structural changes in MgGeO3 is facilitated by construction of a graphite gasket-insert for the diamond anvil cell, which stabilizes a concave anvil culet surface and a larger sample volume, providing better powder statistics and structural models less dependent on corrections for preferred orientation during Rietveld refinement. |
Pressure Dependence of Liquid Komatiite Viscosity |
| Lara O'Dwyer Brown University of California at Davis lodwyer@ucdavis.edu Charles E. Lesher (UC Davis) Yanbin Wang (APS-GSECARS) |
| Facility: APS-GSECARS Format: Poster |
| We have measured the viscosity of komatiite liquids from Gorgona Island (MgO = 17.8 wt.%; NBO/T = 1.6) up to 10 GPa and 2100 K, and from Belingwe, Zimbabwe (MgO = 28.14 wt.%; NBO/T = 2.1) up to 11 GPa and 2100 K, using the in-situ falling sphere technique, at the GSECARS 13 ID-D beamline at the Advanced Photon Source, ANL. Under isothermal conditions viscosity increases with pressure. For Gorgona Island komatiite at 1900 K, viscosity increases from 1.5 (± 0.3) Pa s at 3.5 GPa to 3.4 (± 0.3) Pa s at 6 GPa, corresponding to an activation volume of 5 cm3/mol. Belingwe komatiite viscosity at 2100 K increases from 0.08 (± 0.02) Pa s at 3.7 GPa to 0.13 (± 0.03) Pa s at 7.6 GPa, corresponding to an activation volume of 2.4 cm3/mol. At high pressures, the viscosity of komatiite liquid is an order of magnitude higher than peridotite melt (MgO = 37.1 wt.%; NBO/T = 2.5) (Liebske et al. 2005, EPSL, v. 240), but similar in magnitude to molten diopside (NBO/T = 2) (Reid et al. 2003, PEPI, v. 139). The positive pressure dependence is attributed to a reduction in interatomic space that diminishes the free volume of the liquid as it is compressed. Our data on komatiite liquid preclude a maximum in viscosity below 11 GPa in contrast to the reversal of the pressure dependence of peridotite and diopside melt viscosities at ~8.5 GPa and ~10 GPa, respectively, that has been reported. This work contributes to our understanding of the fundamental properties governing viscous flow in compositions relevant to the Earth?s mantle. |
Determination of Wavelength- and Temperature-Dependent Emissivity |
| Wendy R Panero Ohio State University panero.1@osu.edu Abby Kavner University of California, Los Angeles Sander Caldwell Lawrence Berkeley National Laboratory Carolyn Nugent University of California, Los Angeles Daniel Reaman, Wes Clary Ohio State University |
| Facility: Other Format: Poster |
| Measuring the properties of deep Earth materials requires that we subject them to high temperatures, and measure those high temperatures precisely and accurately. We present an analysis of grey-body emission from several metal wires at ambient pressure to test methods for the determination of wavelength- and temperature-dependent emissivity of materials in the laser-heated diamond anvil cell. The total intensity of light emitted is relatively insensitive to wavelength-dependent emissivity, but becomes quite apparent in measurements comparing the ratios of intensity at two wavelengths. Temperature-dependent emissivity is apparent when comparing the total intensity of light using a modified Stephan-Boltzman law to the Planck spectrum. Tungsten is observed to have a temperature-dependent emissivity that decreases exponentially as a function of temperature, decreasing a factor of 50 between 1100 K and 2800 K, and a wavelength-dependent emissivity decreasing by 45% between 400 and 800 nm. The wavelength-dependent emissivities will cause an underestimate of ~200 K using standard spectral measurements in the laser-heated diamond anvil cell. The temperature-dependent emissivities will cause an overestimate of 50% at 1500 K when temperature is based only on the total intensity of the hotspot and a modified-Stephan Boltzmann law, but errors decrease with increasing temperature. These measurements illustrate the need to collect both spectral data and total intensity data for accurate temperature measurements. We report emissivities relative to tungsten for molybdenum, platinum, iron and nickel and propose methods to measure relative emissivities at high pressures in the laser-heated diamond anvil cell. |
Micro-fabrication of Controlled Geometry Samples for use in the Laser-Heated Diamond Anvil Cell |
| Daniel M Reaman The Ohio State University reaman.5@geology.ohio-state.edu Wendy Panero Derek Ditmer Robert Davis |
| Facility: Other Format: Poster |
| Micro-fabrication of multi-layered, controlled-geometry samples for use in the diamond anvil cell is now possible and somewhat routine. Micro-fabrication of samples at Ohio State University?s Nanotech West Laboratory is accomplished using an ultra-high vacuum fabrication technique, pre cleaning both the target and substrate surface to remove oxidation. 3-D structures are created using photolithography and a 5x5 or 10x10 micron negative grid mask, and then etched at a pre-calibrated rate, exposing the original substrate. Such fabrication techniques can produce chemically- or isotopically marked crystalline layers 0.1-1 micron thick; thereby allowing for vertical and lateral discontinuities in the concentration of elements to be created. These features are less than the size of typical laser-heated spots in the diamond anvil cell, allowing for the measurement of transport properties with modest temperature gradients. Beginning with an established discontinuity in the concentration of elements in the material, the change in compositional gradients due to heating for a fixed time can be related to diffusivity in the solid state or a marker for melting. |
Johnson Noise Thermometry at high pressure |
| Takeshi Sanehira GeoSoilEnviroCARS, the University of Chicago sanehira@cars.uchicago.edu Yanbin Wang, Mark L. Rivers, Steve R. Sutton, GeoSoilEnviroCARS, the University of Chicago, Ivan C. Getting, University of Colorado-Boulder, John Labenski, NIST |
| Facility: APS-GSECARS Format: Poster |
| We report the first Johnson Noise Thermometry (JNT) measurements at pressure and temperature at Sector 13 of the GeoSoilEnviroCARS IDD beamline, the Advanced Photon Source. A DIA-type, cubic anvil apparatus was used in this test. A 16 mm cubic cell assembly was developed specifically for this work. The cell consists of a soft-fired pyrophyllite pressure medium and graphite furnace, along with MgO and BN disks and sleeves. The MgO and BN components were fired at 900-1100 oC overnight to remove volatiles from moisture and adhesives used to mount them before assembling these parts. In previous tests we determined that these volatiles contaminated the cell and corrupted the electronic signals at high temperature. Probe resistors were built on polished faces of sapphire disks 5 mm in diameter and 1 mm thick by vapor deposition of metals (Ti and Pt). A mask was used to produce a serpentine-like metal ribbon 400 nm thick. Two pairs of thermocouples (WRe26%-WRe5%) were used to make four-wire probe resistance measurements and to obtain temperature measurements at each end of the probe resistor. All unused electronics inside the experimental station were turned off to avoid signal contamination for the JNT measurements. Harmonics of the 60 Hz sinusoidal heater power source were present in the JNT signals, however. They occurred at frequencies below about 20 kHz. The contamination increased with increasing electrical power during heating. A numerical notch filter was used to reduce these harmonics from 600 to 9000 Hz with notch bandwidths of 5 or 10. The original time series also passed through a second numerical filter, which is a 4th or 10th order high pass filter with a corner frequency of 20 kHz. In the first high pressure run, a load up to 20 tons was applied prior to the first temperature excursion. A total of four heating cycles were made with Johnson Noise observations during both increasing and decreasing temperatures. After the first heating cycle, we increased the load to 25 tons for the 2nd and 3rd heating cycles to obtain a better furnace contact between the upper and lower guide block of the DIA apparatus. The final heating cycle was made at a load of 35 tons. Because of the large cell used, pressures were estimated to be 0.1 ? 0.2 GPa at these loads. Using the filtering described above we obtained the measurements of Johnson Noise without significant contamination to ~600 K. Above this temperature, the apparent probe resistor resistance decreased noticeably over a temperature range of about 100 K and then increased again. This behavior is physically unrealistic and resulted in a non-linear relationship between the output of Johnson Noise measurements and the product of resistance times temperature. These anomalous results were reproducible in all four heating cycles. Further refinement of the cell will be required to assure realistic determination of the probe resistance and to reduce pick up from the heater current, before moving to higher pressures. |
Distinct thermal behavior of GeO2 glass in tetrahedral, octahedral and their intermediate forms |
| Guoyin Shen G. Shen, HPCAT, Carnegie Institution of Washington gshen@hpcat.aps.anl.gov H.P. Liermann S. Sinogeikin W. Yang X. Hong, GSECARS, The University of Chicago C.S. Yoo, Lawrence Livermore National Lab H. Cynn, Lawrence Livermore National Lab |
| Facility: APS-HPCAT Format: Poster |
| One fascinating high pressure behavior of tetrahedral glasses and melts is the local coordination change with increasing pressure, which provides a microscopic basis for understanding numerous anomalies in their high pressure properties. Because the coordination change is often not retained upon decompression, studies must be conducted in situ. Previous in situ studies have revealed that tetrahedral structured glasses and melts display short range order change above a threshold pressure, and gradually transform to octahedral form with further pressure increase. We report thermal effect associated with the coordination change at given pressures and demonstrate distinct thermal behavior of GeO2 glass in tetrahedral, octahedral and their intermediate forms. An unusual thermal induced densification, as large as 16%, was observed on GeO2 glass at a pressure of 5.5 GPa, based on in situ density and x-ray diffraction measurements at high pressures and high temperatures. The large thermal densification under pressure was found to be associated with the 4-fold to 6-fold coordination increase. Experiments at other pressures show that the tetrahedral GeO2 glass displayed small thermal densification at 3.3 GPa due to the relaxation of intermediate range structure, while the octahedral glass at 12.3 GPa did not show any detectable thermal effects. |
Development of an X-ray Diffraction Analysis Program Suite for Large Data Sets |
| Sang-Heon Shim Massachusetts Institute of Technology sangshim@MIT.EDU |
| Facility: None Format: Poster |
| In recent years, X-ray diffraction techniques have become mature and popular in mineral physics. Often hundreds to even thousands of data files are obtained from one synchrotron run. Most of existing diffraction data analysis programs are designed for handling individual patterns. Furthermore, high-pressure diffraction patterns tend to have peaks from many different phases, including sample, pressure medium, internal pressure calibrant, and gasket material. We have been developing a computer program suite for the calibration, background fitting and subtraction, correction for the absorption from backing plates, phase identifications at high pressure, and peak fitting of diffraction patterns. An emphasis in this development is to allow users to conduct rapid yet accurate data analysis of large diffraction datasets obtained from typical in situ high pressure measurements. |
First-principles calculation of lattice thermal conductivity of MgO at high pressure and high temperature |
| Xiaoli Tang Physics Department, Auburn University tangxia@auburn.edu Jianjun Dong |
| Facility: None Format: Poster |
| Detailed knowledge on thermal conductivity of minerals under high-pressure and high-temperature conditions is crucial to understand the heat flow inside the Earth. Here we report our recent ab initio calculations of lattice thermal conductivity of MgO at high-pressures and high-temperatures. In the current study, we only consider the phonon-phonon scattering due to the lowest order lattice anharmonicity, i.e. the three phonon processes. We have implemented an efficient real-space, finite difference algorithm to directly calculate the irreducible set of elements for a third-order anharmonicity tensor (the 3rd order energy derivatives) using the first-principles density functional theory methods, and then reconstruct the full 3rd-order anharmonicity tenor based on the theoretical group theory. The phonon-phonon scattering is then evaluated based on the linearized Boltzmann equation. Our preliminary calculations predict the phonon life times of the optic phonon modes are 3.22 and 0.55 ps respectively at the ambient conditions, which is consistent with the estimation from experiment. |
Velocity and anisotropy structures and thermal and compositional models beneath Eastern Asia |
| Yi Wang Department of Geosciences, State University of New York at Stony Brook yiwang1@ic.sunysb.edu Lianxing Wen, Department of Geosciences, State University of New York at Stony Brook Donald Weidner Department of Geosciences, State University of New York at Stony Brook Yumei He Institute of Geology and Geophysics, Chinese Academy of Sciences |
| Facility: None Format: Poster |
| The upper mantle velocity and anisotropy structures and thermal and compositional models are important for understanding mantle dynamics. There are several phase transformations in the upper mantle, and the stable phase assemblages in the upper mantle are sensitive to mantle composition, temperature and chemical interactions between the olivine- and pyroxene-normative components. With the accumulation of in-situ measurements of elastic properties and accurate determination of phase equilibria data, we can now explore various chemical interactions and quantitatively calculate seismic velocity and anisotropy profiles for various mantle temperature and composition. Mantle compositional and thermal models can thus be quantitatively constrained by jointly modeling mineral physics data and seismic observations. In this study, we constrain fine seismic P, SH and SV velocity and anisotropy structures in the upper mantle beneath eastern Asia, and explore thermal and compositional models based on mineral physics modeling. We use the triplicated phases recorded in the epicentral distance range of 13-40 degree for three events occurring in eastern Asia. These three events have large signal to noise ratios for P, SH and SV data. The epicenters of them are close, and the seismic data sample the same region of the upper mantle. Seismic observations allow us to constrain the P, SH and SV velocity gradients in the uppermost mantle, the velocities in the transition zone, the velocity gradients above the 660-km discontinuity and the velocity gradients below the 660-km discontinuity. For example, the seismic data indicates a larger S wave velocity gradient above the 660-km discontinuity. Based on comparisons between the SH and SV data, the upper mantle and the transition zone in this region are almost isotropic, while the uppermost lower mantle is anisotropic, with a SH velocity larger than SV velocity. In joint modeling of the mineral physics and seismic data, we explore a variety of compositional and thermal models by comparing their predicted velocity and anisotropy profiles using the mineral physics modeling program developed by Weidner and Wang (1998) with the seismic velocity and anisotropy structures inferred from the seismic data. We will present the best-fitting thermal and compositional model with its predicted velocity and anisotropy structure best explaining the seismic data. |
Room Temperature Equation of State for Fe3P - Schreibersite |
| Sabrina ARA Whitaker The Ohio State University huggins.43@osu.edu Henry P. Scott1, Javier Santillan2, Quentin Williams3, Charles D. Martin4, Steven J. Maglio5 1Department of Physics and Astronomy, Indiana University South Bend, South Bend, IN 46634. 2Department of Earth Sciences, Massachusetts Institution of Technology 3Department of Earth Sciences, University of California Santa Cruz 4Department of Geological Sciences, SUNY Stony Brook 5Department of Geology and Environmental Geosciences, Northern Illinois University |
| Facility: APS-GSECARS Format: Poster |
| Fe3P â?? schreibersite is commonly found in iron meteorite inclusions, which makes schreibersite the most likely phase that would allow phosphorus to be incorporated in planetary interiors. In order to determine the likelihood that phosphorus is a light alloying element in planetary cores and whether Fe3P schreibersite is the phase in which phosphorus would be found, the room temperature equation of state for Fe3P â?? schreibersite was determined. To obtain the equation of state we collected in situ diffraction patterns using a diamond anvil cell and two different synchrotron X-ray beamlines at Argonne National Laboratory. The two beamlines are HP-CAT (16ID-B) and GSECARS (13BM-D). Using a hydrostatic pressure medium, methanol-ethanol-water in a volumetric ratio of 16:3:1 for pressures less than 8 GPa and NaCl for greater pressures, we measured the lattice parameters and the unit cell volume from ambient pressure to 8 GPa. Our zero-pressure lattice parameters and unit cell volume are the following: a= 9.099(2)Ã?, c=4.463(2)Ã?, and V=369.5(2)Ã?^3. A second order Burch-Murnaghan equation of state produces an isothermal bulk modulus, K of 160+/- 3GPa, with a pressure derivative, dK/dP, defined as 4. Due to this instability, it is unlikely that Fe3P-schreibersite is the stable structure for phosphorus that would be found in planetary cores. |
The H2O Storage Capacity of the Upper Mantle |
| Tony Withers University of Minnesota withe012@umn.edu Marc M Hirschmann |
| Facility: Other Format: Poster |
| We have investigated the effect of temperature on the water storage capacity of olivine and pyroxene in order to constrain the bulk water storage capacity of the upper mantle along the geotherm. At mantle temperatures, nominally anhydrous minerals can never coexist with a pure hydrous fluid. Rather, the coexisting fluid/melt has a significant silicate component at realistic mantle temperatures. The effect of this dilution of the hydrous component of the fluid is to reduce the storage capacity of the minerals with increasing temperature, thus the storage capacity of olivine is reduced from >1000 ppm at 1000 °C and 8 GPa to <330ppm H2O at 1600 °C. A similar effect is seen for clinoenstatite, but is offset by very large storage capacities at high pressure (6500 ppm H2O at 13 GPa and 1300 °C). The high H2O content of clinopyroxene suggests that more water may in fact be stored in clinopyroxene than in olivine in the mantle overlying the transition zone, despite the lower relative abundance of clinopyroxene. |
First-Principles study of high-pressure phase transition and thermal properties of Al2O3 |
| Bin Xu Bin Xu xubin01@auburn.edu Jianjun Dong |
| Facility: None Format: Poster |
| Using ab initio density functional theory and statistical quasi-harmonic approximation theory, we have performed a systematic theoretical calculation of equilibrium phase diagrams of Al2O3 at high-pressure and high-temperature conditions. We further predicted the pressure dependences of Raman and IR modes in the trigonal corundum, orthorhombic Rh2O3(II), and the post-perovskite phases of Al2O3. In addition, we have derived measurable thermal properties, such as lattice thermal expansion, heat capacity, and isothermal compressibility, and our predictions are in excellent agreement with available experimental data. |
Anharmonic correction to the free energy of solids at high temperature |
| Bin Xu Bin Xu xubin01@auburn.edu Jianjun Dong |
| Facility: None Format: Poster |
| We have recently implemented an algorithm based on the perturbation theory to include anharmonic interatomic interactions in our calculations of free energy of solids at high temperature. At the first step, we studied two relative simple systems, diamond-structured Si and MgO, which both contain only 2 atoms per primitive unit cell. We have calculated the anharmonicity using both empirical potentials and the first-principles LDA theory. Our results will be discussed in comparison with the previous quasi-harmonic calculations and the available experimental data. |
The Development of the automated data analysis system (CEAD) |
| Jinyuan Yan Virginia Polytechnic Institute and State University jyan@lbl.gov Simon Clark, Paul Adams, Nancy Ross, Ross Angel, Mark Rivers, John Parise, Martin Kunz, Nigel Moriarty |
| Facility: ALS Format: Poster |
| Currently in the COMPRES community, most crystallography projects require the application of different and incompatible software packages for various steps in the calculation of the diffraction data from modern synchrotron and neutron sources. Therefore, the automation of these existing programs is of great significance. Fortunately, the automated data analysis environment for reuse of the existing software packages has been found. The automation of two popular programs, fit2d and GSAS, has been completed and tests of the automation program shows that multiple datasets collected from the same sample at many different pressures or temperatures can be analyzed automatically without manual intervention. |
High Pressure and High Temperature Pair Distribution Function Study of Liquid Gallium: Clusters in Liquid |
| Tony Yu Stony Brook University tyu@cars.uchicago.edu Lars Ehm Department of Geosciences/ Mineral Physics Institute, Stony Brook University, Stony Brook, NY 11794-2100, USA. Jiuhua Chen Department of Geosciences/ Mineral Physics Institute, Stony Brook University, Stony Brook, NY 11794-2100, USA. Quanzhong Guo X17B3, National Synchrotron Light Source, Brookhaven National Laboratory, Upton, NY, 11973-5000, USA. Shengnian Luo Physics Division, Los Alamos National Laboratory, Los Alamos, NM 87545, USA. John Parise Department of Geosciences/ Mineral Physics Institute, Stony Brook University, Stony Brook, NY 11794-2100, USA. |
| Facility: NSLS-X17B3 (DAC) Format: Poster |
| Integrating a hydrothermal diamond anvil cell (HDAC) and focused high energy x-ray from the superconductor wiggler X17, we have successfully collected high quality total x-ray scattering data of liquid gallium. To ensure the enough statistic of the weak diffuse scattering signal from the liquid and meanwhile avoid overexposure of Bragg peaks from the diamond anvil, we collected 20 5-min. spectra using an imaging plate for each data point. For the first time, pair distribution functions (PDF) for liquid gallium at high pressure and high temperature were derived up to 10 Å. Observed compressibility of the first two nearest neighbor distances (first G(r) peak and its shoulder) are consistent with previous observation by x-ray absorption. However, combination of this information with newly obtained data on compressibility for farther interatomic distances lead to a conclusion of the existence of clusters in the liquid. The experiments were conducted at pressures up to 5.28 GPa and temperatures up to 200°C. An icosahedral-like cluster structure is suggested for the short range ordering. |
Diamond Nucleation from Amorphous Carbon and Graphite with COH Fluids: an in Situ High Pressure and Temperature Laser-Heated Diamond Anvil Cell Experimental Study |
| Junfeng Zhang University of California-Riverside jfzhang@cug.edu.cn Vitali Prakapenka, Atsushi Kubo, GSECARS, Argonne National Laboratory, Abby Kavner, University of California Los Angeles Harry W. Green, Larissa F. Dobrzhinetskaya, University of California Riverside |
| Facility: APS-GSECARS Format: Poster |
| Microdiamonds from orogenic belts contain nanometer size fluid inclusions suggesting diamond formation from supercritical COH fluids. Previous studies have shown that diamonds synthesized from high pressure and temperature experiments with supercritical COH fluids are characterized by skeletal morphology and solid oxide inclusions. However, mechanism and kinetics of graphite/carbon-to-diamond transformation promoted by COH fluids at high pressure and high temperature conditions are not well understood. Here we report in situ observations of diamond nucleation from COH fluids in laser-heated diamond anvil cell. Our experimental starting materials were amorphous carbon (impurity < 2ppm) and graphite (99.9% pure). Oxalic acid dihydrate (COOH)22H2O) was added to amorphous carbon and glucose (C6H12O6) was added to both amorphous carbon and graphite. The organic compounds (3 wt.% ) provide CO2- and CH4-rich fluid environments respectively during their breakdown at high pressure and temperature. The mixtures were kept at temperature of 1400-1700 ºC and pressure of 8-10 GPa for 10-30 minutes. Experiments show that only nanocrystals of diamond were nucleated from amorphous carbon in CO2-rich fluid environment. The fastest rate of diamond nucleation and growth of ~15 micron size crystals was found in the mixture of amorphous carbon with glucose (CH4-rich environment), whereas only nanocrystalline nuclei were produced in the mixture of graphite with glucose. We have also established that under anhydrous conditions, no diamond nucleation occurred in pure graphite, and only nanocrystals of diamond were observed in the amorphous carbon starting material at temperatures 1700-1900 ºC. Our results revealed that the kinetics of diamond nucleation depend on the ¡°precursor¡±: diamond nucleates and grows faster from amorphous carbon than from graphite in the presence of COH fluid; in our anhydrous experiments diamond nucleates only from amorphous carbon. These results demonstrate: (1) diamond nucleation from anhydrous graphite starting material is hampered because of the well-known kinetic barrier that requires a huge amount of energy to convert sp2-bonding to sp3-bonding, whereas there is no difficulty for diamond nucleation in amorphous carbon material; (2) the critical role of supercritical COH fluid for promoting the graphite-to-diamond transformation. |