George Amulele

Laser generation and detection of longitudinal and shear acoustic waves in a diamond anvil cell

Laser ultrasonics in a point-source-point-receiver configuration is applied for the evaluation of elastic properties of nontransparent materials in a diamond anvil cell at high pressures. Measurement of both longitudinal and shear acoustic wave velocities in an iron foil at pressures up to 23 GPa does not require any information in addition to the one obtained by all-optical pump-probe technique.

Equation of state of hydrous Fo90 ringwoodite to 45 GPa by synchrotron powder diffraction

Abstract The equation of state of Fo90 hydrous ringwoodite has been measured using X-ray powder diffraction to 45 GPa at the GSECARS beam line at the Advanced Photon Source synchrotron at Argonne National Laboratory. The sample was synthesized at 1400°C and 20 GPa in the 5000 ton multi anvil press at Bayerisches Geoinstitut in Bayreuth. The sample has the formula Mg1.70Fe0.192+Fe0.023+H0.13-Si1.00O4 as determined by electron microprobe, Fourier transform infrared and Mössbauer spectro-scopies, and contains ~0.79% H2O by weight. Compression of the sample had been been measured previously to 11 GPa by single crystal X-ray diffraction. A third-order Birch-Murnaghan equation of state fit to all of the data gives V0 = 530.49±0.07 Å3, K0 = 174.6±2.7 GPa and Kʹ = 6.2±0.6. The effect of 1% H incorporation in the structure on the bulk modulus is large and roughly equivalent to an increase in the temperature of ~600°C at low pressure. The large value of Kʹ indicates significant stiffening of the sample with pressure so that the effect of hydration decreases with pressure.

Mapping temperatures and temperature gradients during flash heating in a diamond-anvil cell

Here, we couple two-dimensional, 4-color multi-wavelength imaging radiometry with laser flash heating to determine temperature profiles and melting temperatures under high pressures in a diamond-anvil cell. This technique combines the attributes of flash heating (e.g., minimal chemical reactions, thermal runaway, and sample instability), with those of multi-wavelength imaging radiometry (e.g., 2D temperature mapping and reduction of chromatic aberrations). Using this new technique in conjunction with electron microscopy makes a powerful tool to determine melting temperatures at high pressures generated by a diamond-anvil cell.

Compression behavior of WC and WC-6%Co up to 50 GPa determined by synchrotron x-ray diffraction and ultrasonic techniques

The equations of state (pressure-volume relations) for WC and WC-6%Co have been determined by synchrotron x-ray diffraction measurements on polycrystalline powder samples loaded in a diamond anvil cell as well as by ultrasonic measurements on hot-pressed polycrystalline, cylindrical samples loaded in a multianvil high-pressure apparatus. The third-order Birch–Murnaghan equation of state fitted to the x-ray diffraction pressure-density sets of data, collected up to 50 GPa, yields ambient pressure isothermal bulk moduli of KoT=411.8±12.1 GPa and KoT=402.4±14.1 GPa, with pressure derivatives of KoT′=5.45±0.73 and KoT′=7.50±0.86 for WC and WC-6%Co, respectively. The ultrasonic measurements, conducted up to 14 GPa, enabled the determination of the pressure dependences of both bulk and shear moduli. Using Eulerian finite strain equations to fit the ultrasonic data, we obtain for WC an ambient pressure adiabatic bulk modulus of Kos=383.8±0.8 GPa, and Kos′=2.61±0.07 for its pressure derivative, while values of Go...

Compression studies of TiB2 using synchrotron x-ray diffraction and ultrasonic techniques

The compressibility of TiB2 has been determined separately by synchrotron x-ray diffraction and ultrasonic measurements on samples loaded in diamond-anvil cells and in multianvil high-pressure apparatus up to pressures of 65.9GPa and 13.9GPa, respectively, at ambient temperature. The high-pressure x-ray diffraction measurements, carried out on a pure polycrystalline sample, show a monotonic decrease of the lattice parameters with pressure, with the c∕a ratio variation suggesting an increase in the structural rigidity along the c direction. No structural transition is observed even after laser heating of the sample up to 2200K at 40GPa, indicating a phase stability of TiB2 in this pressure range. The ultrasonic measurements of compressional Vp and shear Vs velocities on a cylindrical specimen show linear pressure dependencies. Using the third-order Eulerian finite strain equation to fit the pressure-volume x-ray data, we obtain an isothermal bulk modulus of KTo=232.9±4.2GPa and its pressure derivative KTo′...

High pressure ultrasonic and x-ray studies on monolithic SiC composite

The equation of state (pressure-volume relationship) of a monolithic SiC composite has been determined separately by high pressure ultrasonic and x-ray techniques. The ultrasonic measurements were performed on a cylindrical specimen, 2.2 mm in diameter and 2.2 mm in length, in a large-volume uniaxial split cylinder press to 13.6 GPa. The synchrotron measurements were carried out on the polycrystalline sample loaded in a diamond anvil cell up to a pressure of 27 GPa. The room temperature bulk modulus obtained from the ultrasonic measurements is K0=216.5±1.1 GPa and the pressure derivative is K0′=4.19±0.09. The shear modulus obtained is G0=196.7±0.7 GPa with its pressure derivative G0′=0.95±0.03. Using K0′ obtained from the ultrasonic measurements in the Birch–Murnaghan equation to fit the synchrotron x-ray data, we obtain a bulk modulus of K0=218.4±4.9 GPa for the composite.

Application of radial x-ray diffraction to determine the hydrostatic equation of state and strength of TiB2 up to 60GPa

Room temperature investigations of the shear strength of hexagonal TiB2 have been performed in order to determine the hydrostatic equation of state of the material up to 60GPa using radial x-ray diffraction in a diamond anvil cell. We have analyzed the deformation mechanisms under pressure by analyzing the (001) and (100) peaks in the powder diffraction data, and we have deduced the hydrostatic equation of state of TiB2. The uniaxial stresses in the (100), (001), and (101) diffraction planes show a large pressure dependence, indicating a significantly large anisotropy in the material. The stress in the (001) plane shows the largest increase with pressure and reaches a maximum value before the other planes, indicating an initial activation of slip in the (001) plane at the onset of plastic deformation. Compared to gold, the averaged uniaxial stress component in TiB2 is almost 27 times as large at the maximum loading pressure, 60GPa, achieved in the experiment.

Efficient graphite ring heater suitable for diamond-anvil cells to 1300 K

In order to generate homogeneous high temperatures at high pressures, a ring-shaped graphite heater has been developed to resistively heat diamond-anvil cell (DAC) samples up to 1300 K. By putting the heater in direct contact with the diamond anvils, this graphite heater design features the following advantages: (1) efficient heating: sample can be heated to 1300 K while the DAC body temperature remains less than 800 K, eliminating the requirement of a special alloy for the DAC; (2) compact design: the sample can be analyzed with in situ measurements, e.g., x-ray, optical, and electrical probes are possible. In particular, the side access of the heater allows for radial x-ray diffraction (XRD) measurements in addition to traditional axial XRD.

Compressibility and structural stability of two variably hydrated olivine samples (Fo97Fa3) to 34 GPa by X-ray diffraction and Raman spectroscopy

Abstract The content and transport of fluid phases such as water into the deep Earth is of great importance not only to correlate seismological models of the planet’s interior with mineralogical models, but also for the understanding of the evolution of the solid Earth as well as the Earth’s atmosphere. This study reports on the influence of water on the structural and physical properties of olivine, which is known to be the main constituent of the upper mantle. Two hydrous olivines of composition Fo97Fa3 with water content of 4883 parts per million by weight (ppmw) (SZ0407A) and 8000 ppmw (SZ0407B) were synthesized at 1250 °C and 12 GPa. Single-crystal X‑ray diffraction was used to determine unit-cell parameters of SZ0407A and SZ0407B at pressures up to 7.1 GPa at room temperature. Synchrotron powder X‑ray diffraction and Raman scattering experiments were performed on sample SZ0407A in a diamond-anvil cell to 34 GPa at room temperature. For both samples, the compressibility is the largest along the b-axis and smallest along the a-axis. Using the compression (V/Vo) vs. pressure data for sample SZ0407A to 29 GPa, in conjunction with the third-order Birch-Murnaghan equation of state, we calculate the isothermal bulk modulus and its pressure derivative as K0 = 119.2(12) GPa and K′o = 6.6(4). Single-crystal compression data for sample SZ0407A to 7 GPa give Ko = 121.5(6) GPa and K′o = 5.7(2); and for sample SZ0407B Ko = 122.2(12) GPa and K′o = 6.2(4). High-pressure Raman spectra for SZ0407A up to 34 GPa show a continuous shift of all the observed bands to higher frequency with increasing pressure; there is no indication of any first-order phase transition. However, the Raman spectra indicate subtle discontinuous changes around 22 GPa, unobserved in previously reported studies on anhydrous olivines.