MR13A-01 INVITED 13:40h
Nuclear Resonant Scattering Studies Under High Pressure and HighTtemperature
Nuclear resonant scattering techniques have been applied very successfully to iron-bearing alloys [1-3] and silicates [4] under pressures in the Mbar regime using diamond anvil cells. The two main methods, nuclear resonant inelastic x-ray scattering (NRIXS) and synchrotron M\"ossbauer spectroscopy (SMS), will be discussed in their potential for the geophysical problem area. In general, NRIXS provides the phonon density of states [5] and sound velocities [6], whereas SMS gives access to the abundance of ferric iron and the spin state of iron in minerals and their polymorphs. % The introduction of Laser heating in combination with NRIXS and SMS at sector 3-ID of the Advanced Photon Source permits us now to conduct these studies under high pressure \textit{and} high temperature. Here we will address two examples of this powerful, new opportunity. The reduction of sound velocities with increasing temperature, in particular for the shear wave, observed from NRIXS on hot, compressed iron metal in a pressure range of 40\,GPa to 60\,GPa. We find that the sound velocities do not depend on density alone but show an explicit temperature dependence. In a second experiment, we analyzed valence and spin state of iron in magnesium silicates. The starting material, orthoenstatite $^{57}$Fe$_{0.1}$Mg$_{0.9}$SiO$_3$, was compressed in several steps up to 31\,GPa in a diamond anvil cell. Each step involved laser annealing and the collection of SMS spectra at several temperatures. With x-ray diffraction we confirmed the creation of high-clinoenstatite, ringwoodite, ilmenite, and perovskite structures. Unique data on the iron behavior in each polymorph was obtained. % This work is supported by the U.S. DOE-BES, Office of Science, under Contract No. W-31-109-Eng-38 and by NSF through COMPRESS. % {}[1] H.K.Mao et al., Science \textbf{292}, 914 (2001) [1mm] % {}[2] J.-F.Lin et al., Geophysical Research Letters \textbf{30}, 2112 (2003) [1mm] % {}[3] W.L.Mao et al., Geophysical Research Letters \textbf{31}, L15618 (2004) [1mm] % {}[4] J.M.Jackson et al., American Mineralogist, (in press) [1mm] % {}[5] W.Sturhahn et al., Phys.Rev.Lett. \textbf{79}, 3832 (1995) [1mm] % {}[6] M.Y.Hu et al., Phys.Rev. B \textbf{67}, 094304 (2003)
MR13A-02 INVITED 13:55h
LAPTRON : Los Alamos Pressure-Temperature Researches Online Neutron
We propose to build a dedicated high-pressure (P) and high-temperature (T) neutron beamline at Los Alamos Neutron Science Center (LANSCE) to perform state-of-the-art simultaneous neutron diffraction and neutron tomography experiments at high P-T conditions for the characterization of material properties in a wide range of scientific and technological disciplines. A large volume 2000-tone press, TAPLUS-2000, will be the central apparatus mounted permanently in the instrument hutch and advanced beamline equipments will be built around the press. The proposed high-pressure neutron beamline will integrate diffraction, radiography, tomography, and ultrasonic interferometry techniques so that the instrument can profoundly focus on materials property characterization. It will be particularly valuable for the engineering aspects of the materials study such as deformation mechanism, yield strength, constitutive equation, acoustic elasticity, and flow law under high P-T conditions. The integrations with in-situ neutron diffraction, radiography, and tomography will greatly enhance instrument performances and achieve significantly in multidiscipline sciences. For MR01: The Laboratory Prospect to the Earth: Advances in Mineral and Rock Physics
MR13A-03 14:10h
A New Technique for High-Pressure Angle-Dispersive Powder Diffraction Using an Energy-Dispersive Setup and White Synchrotron Radiation
We introduce a new step-scan diffraction technique, which collects angle-dispersive data using a solid-state detector (SSD) and white synchrotron radiation. By step-scanning a well-calibrated SSD over a limited 2$\theta$ range, a series of 1-dimensional energy dispersive data (intensity vs. energy) are obtained as a function of 2$\theta$. The entire intensity (Int) dataset consists of several thousand channels covering a range of photon energies, E, (up to ~150 keV) at each of the ~1000 2$\theta$ steps, forming a 2-4 mega-element two-dimensional array, Int(E, 2$\theta$). These intensity data are then regrouped according to photon energies, which are defined in the multichannel SSD as individual channels, yielding a large number of intensity versus 2$\theta$ (angle-dispersive) datasets, Int(E=const., 2$\theta$), each of which corresponds to a given photon energy or wavelength. The entire dataset, selected subsets or composite scans can be used for multiple dataset Rietveld refinement. Data collected on $\alpha$-Al2O3 (a NIST diffraction standard) at ambient conditions, from both the tapered undulator at 13-ID-D, APS and the bending magnet beamline BL04B1, SPring-8, were analyzed using the Rietveld technique, with varying schemes of data treatment. We demonstrate that data within certain energy bands ($\Delta$E/E=$\pm$10 percent) may be binned together to improve counting statistics in a composite angle dispersive scan, so that data can be collected with much coarser scan steps of 0.1$\deg$ or 0.2$\deg$. This technique has been used to collect high-pressure angle-dispersive data at the BL04 bending magnet beamline at SPring-8, with the multianvil apparatus SPEED-1500, up to 20 GPa and 1100 K. Data obtained on several materials will be shown to demonstrate the feasibility of simultaneous high pressure and temperature Rietveld refinement.
MR13A-04 14:25h
Transient Measurements Under Simulated Mantle Conditions - Simultaneous DTF-Ultrasonic Interferometry, X-Radiography, XRD
The interpretation of seismic data from the Earth's deep interior requires measurements of the physical properties of Earth materials under experimental simulated mantle conditions. Elastic wave velocity measurement by ultrasonic interferometry is an important tool for the determination of the elastic properties in multi-anvil devices. Whereas the classical sweep method is very time-consuming, the ultrasonic data transfer function technique (DTF), simultaneously generating all the frequencies used in the experiment, first described by Li et al. (2002), requires just few seconds to save the response of the system. The success of the technique substantially depends on the excitation function and the resolution used for saving the DTF (Mueller et al., 2004a). Background discussion as well as high pressure, high temperature results demonstrate how to optimize the technique. All Ultrasonic interferometry allows highly precise travel time measurement at a sample enclosed in a high-pressure multi-anvil device. But under high pressure conditions the influence of sample deformation on the frequencies for destructive and constructive interference used for the evaluation of the elastic properties might be stronger than that from the shift of the elastic moduli. Consequently ultrasonic interferometry requires the exact sample length measurement under in situ conditions. X-ray imaging using brillant synchrotron radiation, called X-radiography, produces grey-scale images of the sample under in situ conditions by converting the X-ray image to an optical one by a CE-YAG-crystal. Saving the optical image by a CCD-camera after redirection by a mirrow, also requires few seconds. To derive the sample length, the different brightness of sample, buffer rod and reflector at the electronic image is evaluated (Mueller et al., 2004b). Contrary to XRD measurements, imaging the sample by X-rays requires a beam diameter larger than the sample length. Therefore the fixed primary slits of Max80 were exchanged by 4-blade high precision slits of Advanced Design Consulting, Inc. Some recent results on the non-quenchable high-P, low-P clinoenstatite transition and to the quartz-coesite transition will be given to discuss the different interferometric techniques, including the XRD-data and X-radiography results, necessary to detect the phase transitions under in situ conditions and to measure the sample deformation. Li, B.; Chen, K.; Kung, J.; Liebermann, R.C.; Weidner, D.J., J. Phys.: Condens. Matter 14, 11337-11342, (2002). Mueller, H.J.; Lathe, C.; Wunder, B., In: J. Chen, Y. Wang, T. Duffy, G. Shen, L. Dobrzhinetskaya (eds.), Frontiers in High Pressure Research, Elsevier Science, submitted, (2004a). Mueller, H.J.; Schilling, F.R.; Lathe, C.; Lauterjung, J., In: J. Chen, Y. Wang, T. Duffy, G. Shen, L. Dobrzhinetskaya (eds.), Frontiers in High Pressure Research, Elsevier Science, in press, (2004b).
MR13A-05 14:40h
Synchrotron Radiation High Pressure Systems for Mineral Physics at Spring-8
Synchrotron radiation (SR) has been recognized as an indispensable tool for the in-situ structural study at high pressure for mineral physics, and high pressure SR experiments are conducting at various SR facilities over the world. At SPring-8, there are two kinds of high pressure and high temperature systems with SR for mineral physics. One is a multi-anvil system, and the other is a laser heated DAC system. Kawai-type double stage press with a thrust of 1500 ton, named SPEED1500, was one of the first apparatuses installed at SPring-8 in 1997. In situ observation of olivine-spinel transition boundary became a sensational problem for the determination of transition zone boundary. In addition to the diffraction experiments, viscosity measurement technique has successfully been developed. A trial of topography experiment to reveal the transition mechanism was conducted, and the simultaneous measurement of diffraction and ultrasonic velocity is now underway. In order to perform the experiment at higher pressures, a new double-stage system named SPEED MkII was installed in tandem with SPEED1500. SPEED MKII can generate pressures higher than 50 GPa with sintered diamond anvils. Press oscillation mechanism can give better quality of powder diffraction data. A typical example is the precise determination of the B1-B2 transition of NaCl. The laser heated DAC system consists of a YLF laser and X-ray lens to focus both laser and X-ray in a few tens of a micrometer region, and can achieve 200 GPa and 2500K. Recent observation of the post-spinel transition is an excellent topic. Further interesting results obtained with these high pressure systems will be presented in more detail.
MR13A-06 INVITED 14:55h
Use of Kawai-type Apparatus Combined with Synchrotron X-ray Radiation for Study of Kinetics of Phase Transformations in Mantle Minerals
Kawai type multianvil apparatus combined with the intense X-ray from synchrotron radiation is a useful tool for study of the reaction kinetics of the phase transformations of mantle minerals. MAX-III installed at Photon Factory and SPEED 1500 at SPring-8 are used for the experiments. We used sintered diamond composites of 10mm or 14 mm cubes with a 2 mm truncation for the experiments made above 30 GPa. We conducted studies on reaction kinetics of several phase transformations of mantle minerals. Decomposition of ringwoodite is the most important phase transformation which corresponds to the 660 km discontinuity. Metastable coexistence of periclase + stishovite, or periclase + ilmenite was observed in the initial stage of the transformation in the low temperature range. The metastable assembly disappears eventually after about 10 minutes. A kinetics study of the post-garnet transformation revealed that the post-garnet transformation is significantly sluggish compared to the decomposition reaction of ringwoodite. The reaction kinetics of the transformation of MgSiO3 from enstatite to wadsleyite + stishovite, ringwoodite + stishovite, and to ilmenite were studied. The enstatite-ilmenite phase transformation is much faster than the decomposition reactions. This suggests that a decomposition of enstatite may not occur but enstatite transforms directly to ilmentite in the cold subducting slabs. The experiments on the olivine-wadsleyite transformation kinetics in Mg2SiO4 under the dry and wet conditions with 0.5 wt. % water indicate remarkable enhancement of the phase transformation kinetics by existence of water. Seismic observations indicate that metastable olivine regions are not detected in the slabs, rather the elevation of the 410 km discontinuity, which is consistent with the equilibrium boundary, has been observed. The seismic reflectors, which were reported in the lower mantle, imply a density increase associated with the anomaly (e.g., Niu et al., 2003), suggesting existence of the basaltic crust with a perovskite assemblage in the lower mantle. These seismic data imply existence of equilibrium assemblies even in the cold slabs in the transition zone and lower mantle, which may be consistent with the wet slabs where the phase transformation kinetics are enhanced under the wet conditions.
MR13A-07 15:10h
Laser-induced shock waves in condensed matter, and their geophysical applications*
Laser-induced shock-wave techniques complement conventional shock-wave and static loading techniques in the study of equation of state, phase transitions, high-pressure physics and chemistry, and mechanical properties of condensed matter under extreme pressure and temperature conditions. Furthermore, the strain rates in laser experiments can be varied over a wide range, thus making them suitable for geophysical research in Earth and planetary materials, and impact behavior. We review some techniques in laser-induced shock waves and commonly-associated diagnostics, including direct laser drive, laser-launched flyer plate, quasi-isentropic loading, point and line imaging velocity interferometry, transient x-ray diffraction, spectroscopy and shock recovery. We will also show exemples of measurements from studies of equations of state, spall, and phase transitions. *Work performed under the auspices of the US Department of Energy under contract No. W-7405-ENG-36.
MR13A-08 15:25h
Diamond-Cell Measurements of Fluid Viscosity and Activation Energy at High Pressures
Significant advances in high pressure-temperature experiments now make it possible to measure the viscosity of fluids at deep-planetary conditions. This is important because viscosity is often the rate-limiting factor for internal planetary dynamics, yet it is poorly understood from a theoretical perspective. New rolling-sphere measurements on methanol and a 4:1 methanol:ethanol mixture, using a resistance-heated diamond-cell, yield an activation energy and volume of 18 to 99 ($\pm$ 5) kJ/mol and 4.5 to 3.2 ($\pm$ 0.4) cm$^{3}$/mol over the pressure-temperature range of 0 to 6.5 GPa and 298 to 338 K. These alcohols are potential analogs for structured liquids, such as the silicate melts of the Earth's interior, and are also important as pressure transmitting media in diamond-cell experiments. Our data are in good agreement with previous measurements at room temperature, and we find that both activated-state (Arrhenius) and free-volume models fit the data within our uncertainties. Extrapolation based on these models yields glass-transition pressures (10$^{12}$ Pa s) of 19.7 ($\pm$ 0.5) GPa and 11.0 ($\pm$ 0.8) GPa at room temperature. Note that our measurements extend beyond the equilibrium crystallization pressure of methanol, 3.6 GPa at 300 K, so provide information about viscous relaxation of the metastable liquid state.