In-situ high temperature spatially resolved X-ray diffraction of TiB2 up to ~3250 ˚C

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Environmental conical nozzle levitator equipped with dual lasers

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From the atomic scale to the bulk: Ultra high temperature evaluation of metal diborides MB2 (M = Ta, Ti, Hf, Zr, Nb)

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Direct ink writing of ultra-high temperature ceramics

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Electrical properties of methane hydrate + sediment mixtures

Knowledge of the electrical properties of multicomponent systems with gas hydrate, sediments, and pore water is needed to help relate electromagnetic (EM) measurements to specific gas hydrate concentration and distribution patterns in nature. Toward this goal, we built a pressure cell capable of measuring in situ electrical properties of multicomponent systems such that the effects of individual components and mixing relations can be assessed. We first established the temperature-dependent electrical conductivity (?) of pure, single-phase methane hydrate to be ~5 orders of magnitude lower than seawater, a substantial contrast that can help differentiate hydrate deposits from significantly more conductive water-saturated sediments in EM field surveys. Here we report ? measurements of two-component systems in which methane hydrate is mixed with variable amounts of quartz sand or glass beads. Sand by itself has low ? but is found to increase the overall ? of mixtures with well-connected methane hydrate. Alternatively, the overall ? decreases when sand concentrations are high enough to cause gas hydrate to be poorly connected, indicating that hydrate grains provide the primary conduction path. Our measurements suggest that impurities from sand induce chemical interactions and/or doping effects that result in higher electrical conductivity with lower temperature dependence. These results can be used in the modeling of massive or two-phase gas-hydrate-bearing systems devoid of conductive pore water. Further experiments that include a free water phase are the necessary next steps toward developing complex models relevant to most natural systems

Water in cratonic lithosphere : calibrating laboratory-determined models of electrical conductivity of mantle minerals using geophysical and petrological observations

Author Posting. © American Geophysical Union, 2012. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry Geophysics Geosystems 13 (2012): Q06010, doi:10.1029/2012GC004055.Measurements of electrical conductivity of “slightly damp” mantle minerals from different laboratories are inconsistent, requiring geophysicists to make choices between them when interpreting their electrical observations. These choices lead to dramatically different conclusions about the amount of water in the mantle, resulting in conflicting conclusions regarding rheological conditions; this impacts on our understanding of mantle convection, among other processes. To attempt to reconcile these differences, we test the laboratory-derived proton conduction models by choosing the simplest petrological scenario possible – cratonic lithosphere – from two locations in southern Africa where we have the most complete knowledge. We compare and contrast the models with field observations of electrical conductivity and of the amount of water in olivine and show that none of the models for proton conduction in olivine proposed by three laboratories are consistent with the field observations. We derive statistically model parameters of the general proton conduction equation that satisfy the observations. The pre-exponent dry proton conduction term (σ0) and the activation enthalpy (ΔHwet) are derived with tight bounds, and are both within the broader 2σ errors of the different laboratory measurements. The two other terms used by the experimentalists, one to describe proton hopping (exponent r on pre-exponent water content Cw) and the other to describe H2O concentration-dependent activation enthalpy (term αCw1/3 added to the activation energy), are less well defined and further field geophysical and petrological observations are required, especially in regions of higher temperature and higher water content.The SAMTEX data were acquired through funding provided by the Continental Dynamics program of the U.S. National Science Foundation (grant EAR0455242 to RLE), the South African Department of Science and Technology (grant to South African Council for Geoscience), and Science Foundation Ireland (grant 05/RGP/GEO001 to AGJ) plus financial and/or logistical support provided by all members of the SAMTEX consortium. JF was initially supported by an IRCSET grant to AGJ for the TopoMed project (TopoMed: Plate reorganization in the western Mediterranean: Lithospheric causes and topographic consequences) within the European Science Foundation’s TOPOEUROPE EUROCORES (http://www.esf.org/activities/eurocores/ running-programmes/topo-europe.html), and subsequently by an SFI PI grant (10/IN.1/I3022) to AGJ for IRETHERM (www.iretherm.ie).2012-12-1

Velocity–conductivity relationships for mantle mineral assemblages in Archean cratonic lithosphere based on a review of laboratory data and Hashin–Shtrikman extremal bounds

Author Posting. © Elsevier B.V., 2009. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Lithos 109 (2009): 131-143, doi:10.1016/j.lithos.2008.10.014.Can mineral physics and mixing theories explain field observations of seismic velocity and electrical conductivity, and is there an advantage to combining seismological and electromagnetic techniques? These two questions are at the heart of this paper. Using phenomologically-derived state equations for individual minerals coupled with multi-phase, Hashin-Shtrikman extremal-bound theory we derive the likely shear and compressional velocities and electrical conductivity at three depths, 100 km, 150 km and 200 km, beneath the central part of the Slave craton and beneath the Kimberley region of the Kaapvaal craton based on known petrologically-observed mineral abundances and magnesium numbers, combined with estimates of temperatures and pressures. We demonstrate that there are measurable differences between the physical properties of the two lithospheres for the upper depths, primarily due to the different ambient temperature, but that differences in velocity are negligibly small at 200 km. We also show that there is an advantage to combining seismic and electromagnetic data, given that conductivity is exponentially dependent on temperature whereas the shear and bulk moduli have only a linear dependence in cratonic lithospheric rocks. Focussing on a known discontinuity between harzburgite-dominated and lherzolitic mantle in the Slave craton at a depth of about 160 km, we demonstrate that the amplitude of compressional (P) wave to shear (S) wave conversions would be very weak, and so explanations for the seismological (receiver function) observations must either appeal to effects we have not considered (perhaps anisotropy), or imply that the laboratory data require further refinement

Crustal imaging of a mobile belt using magnetotellurics: An example of the Fowler Domain in South Australia

Extent: 18p.A long-period magnetotelluric data set was obtained in 2005 along a two-dimensional profile across the western part of the late Archaean-early Proterozoic Gawler Craton, South Australia. The study is aimed at delineating the electrical conductivity structure of the crust and upper mantle underneath an east-west trending profile extending from the Gawler Range Volcanics in the east, crossing the Nuyts Domain and the highly prospective Meso-Proterozoic Fowler Domain, and terminating in the Eucla Basin to the west. The resistivity model shows a very electrically resistive crust and upper mantle underneath the Nuyts and Fowler Domain, possibly representing the cratonic root of the Gawler Craton extending to depths of ∼160 km. The resistive cratonic root is closer to the surface underneath the Fowler Domain compared to the Nuyts Domain which supports findings from outcrops of metasediments of higher metamorphic grade in the Fowler Domain. A subvertical conductor marks the western terminus of the Fowler Domain and is imaged to upper mantle depths. On the eastern side of the Fowler Domain, another subvertical conductor extends to similar depths. These features spatially coincide with the Tallacootra and Coorabie shear zone at the surface, respectively, and their higher conductivity is likely due to a reduction in grain size of olivine associated with an increase in influence of grain boundary diffusion and thus enhanced conductivity. A comparison of the results with other surveys across mobile belts worldwide shows a more resistive response of the interpreted mobile belt of the Fowler Domain raising questions as to the nature of the domain.Stephan Thiel and Graham Heinso