Stress Distribution During Cold Compression of Rocks and Mineral Aggregates Using Synchrotron-based X-Ray Diffraction.

We report detailed procedures for performing compression experiments on rocks and mineral aggregates within a multi-anvil deformation apparatus (D-DIA) coupled with synchrotron X-radiation. A cube-shaped sample assembly is prepared and compressed, at room temperature, by a set of four X-ray transparent sintered diamond anvils and two tungsten carbide anvils, in the lateral and the vertical planes, respectively. All six anvils are housed within a 250-ton hydraulic press and driven inward simultaneously by two wedged guide blocks.

High-energy X-ray focusing and applications to pair distribution function investigation of Pt and Au nanoparticles at high pressures.

We report development of micro-focusing optics for high-energy x-rays by combining a sagittally bent Laue crystal monchromator with Kirkpatrick-Baez (K-B) X-ray focusing mirrors. The optical system is able to provide a clean, high-flux X-ray beam suitable for pair distribution function (PDF) measurements at high pressure using a diamond anvil cell (DAC). A focused beam of moderate size (10-15 μm) has been achieved at energies of 66 and 81 keV.

In situ analysis of texture development from sinusoidal stress at high pressure and temperature.

Here, we present a new experimental protocol to investigate the relationship between texture, plastic strain, and the mechanisms of plastic deformation at high pressure and temperature. The method utilizes synchrotron X-ray radiation as the probing tool, coupled with a large-volume high pressure deformation device (D-DIA). The intensity of X-ray diffraction peaks within the spectrum of the sample is used for sampling texture development in situ.

Pressure-induced stiffness of Au nanoparticles to 71 GPa under quasi-hydrostatic loading.

The compressibility of nanocrystalline gold (n-Au, 20 nm) has been studied by x-ray total scattering using high-energy monochromatic x-rays in the diamond anvil cell under quasi-hydrostatic conditions up to 71 GPa. The bulk modulus, K0, of the n-Au obtained from fitting to a Vinet equation of state is ~196(3) GPa, which is about 17% higher than for the corresponding bulk materials (K0: 167 GPa). At low pressures (<7 GPa), the compression behavior of n-Au shows little difference from that of bulk Au.

Deformation T-Cup: a new multi-anvil apparatus for controlled strain-rate deformation experiments at pressures above 18 GPa.

A new multi-anvil deformation apparatus, based on the widely used 6-8 split-cylinder, geometry, has been developed which is capable of deformation experiments at pressures in excess of 18 GPa at room temperature. In 6-8 (Kawai-type) devices eight cubic anvils are used to compress the sample assembly. In our new apparatus two of the eight cubes which sit along the split-cylinder axis have been replaced by hexagonal cross section anvils.

Detection of melting by X-ray imaging at high pressure.

The occurrence of partial melting at elevated pressure and temperature is documented in real time through measurement of volume strain induced by a fixed temperature change. Here we present the methodology for measuring volume strains to one part in 10(-4) for mm(3) sized samples in situ as a function of time during a step in temperature. By calibrating the system for sample thermal expansion at temperatures lower than the solidus, the onset of melting can be detected when the melting volume increase is of comparable size to the thermal expansion induced volume change.

Note: Synchronized stress-strain measurements in dynamic loading at high pressure using D-DIA.

A new data collection protocol for forced oscillation experiments using a multianvil high pressure device is reported. We derive the stress of the sample at high pressure and temperature from synchrotron x-ray diffraction that is synchronized with sample strain measurements from x-ray radiographs. This method yields stress directly from the sample rather than a stress proxy.

Precise stress measurements with white synchrotron x rays.

In situ measurement of stress in polycrystalline samples forms the basis for studies of the mechanical properties of materials with very broad earth science and materials science applications. Synchrotron x rays have been used to define the local elastic strain in these samples, which in turn define stress. Experimental work to date has been carried out on a prototype detection system that provided a strain measurement precision >10(-4), which corresponds to a stress resolution >50 MPa for silicate minerals.

Effect of phase transitions on compressional-wave velocities in the Earth's mantle.

The velocities of seismic waves in the Earth are governed by the response of the constituent mineral assemblage to perturbations in pressure and stress. The effective bulk modulus is significantly lowered if the pressure of the seismic wave drives a volume-reducing phase transformation. A comparison between the amount of time required by phase transitions to reach equilibrium and the sampling period thus becomes crucial in defining the softening and attenuation of compressional waves within such a two-phase zone.

Energy dissipation of materials at high pressure and high temperature.

We report an experimental method to study the anelastic properties of materials at high pressure and high temperature. The multianvil high pressure deformation device, used to apply a cyclic loading force onto the sample, can reach 15 GPa and 2000 K. A synchrotron x-ray radiation source provides time resolved images of the sample and reference material.

Measurement of stress using synchrotron x-rays.

Stress analysis in polycrystalline materials reveals that stress can vary considerably among different subpopulations of grains. Samples of MgO and mixtures of MgO and spinel have been studied. After the onset of plastic flow, stronger grains or orientations will support more stress than the weaker grains.

Do Reuss and Voigt bounds really bound in high-pressure rheology experiments?

Energy dispersive synchrotron x-ray diffraction is carried out to measure differential lattice strains in polycrystalline Fe(2)SiO(4) (fayalite) and MgO samples using a multi-element solid state detector during high-pressure deformation. The theory of elastic modelling with Reuss (iso-stress) and Voigt (iso-strain) bounds is used to evaluate the aggregate stress and weight parameter, α (0≤α≤1), of the two bounds. Results under the elastic assumption quantitatively demonstrate that a highly stressed sample in high-pressure experiments reasonably approximates to an iso-stress state.

The strength of Mg(0.9)Fe(0.1)SiO3 perovskite at high pressure and temperature.

The Earth's lower mantle consists mainly of (Mg,Fe)SiO3 perovskite and (Mg,Fe)O magnesiowüstite, with the perovskite taking up at least 70 per cent of the total volume. Although the rheology of olivine, the dominant upper-mantle mineral, has been extensively studied, knowledge about the rheological behaviour of perovskite is limited. Seismological studies indicate that slabs of subducting oceanic lithosphere are often deflected horizontally at the perovskite-forming depth, and changes in the Earth's shape and gravity field during glacial rebound indicate that viscosity increases in the lower part of the mantle.