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  • 1
    Electronic Resource
    Electronic Resource
    Phase Relations and Volume Changes of Hafnia under High Pressure and High Temperature (2001)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 84 (2001), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Using multi-anvil high-pressure devices and synchrotron radiation, X-ray in situ observations of HfO2 under high pressure and high temperature have been performed to investigate its phase relations and compression behavior. An orthorhombic phase (orthoI) is stable from 4 to 14.5 GPa below 1250°–1400°C and transforms to a tetragonal phase, which is one of the high-temperature forms of HfO2, above these temperatures. Another orthorhombic phase (orthoII) with a cotunnite-type structure appears above 14.5 GPa. OrthoII is stable up to 1800°C at 21 GPa. OrthoII is quenchable to ambient conditions. The orthoI-to-orthoII transition is accompanied by ∼8 vol% decrease. The bulk moduli of orthoI and orthoII at room temperature are 220 and 312 GPa, respectively. This low compressibility of orthoII indicates that it is a potential candidate for very hard materials.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2001.tb00843.x
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  • 2
    Electronic Resource
    Electronic Resource
    Phase transformations in the earth's mantle and subducting slabs: Implications for their compositions, seismic velocity and density structures and dynamics (1993)
    Oxford, UK : Blackwell Publishing Ltd
    The @island arc 2 (1993), S. 0 
    Details
    ISSN: 1440-1738
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Abstract Phase transformations in model mantle compositions and those in subducting slabs have been reviewed to a depth of 800 km on the basis of recent high-pressure experimental data. Seismic velocity and density profiles in these compositions have also been calculated using these and other mineral physics data. The nature of the seismic velocity and density profiles calculated for a pyrolite composition was found to generally agree with those determined by seismic observations (e.g. PREM). The locations of the seismic discontinuities at 400 and 670 km correspond almost exactly to the depths where the transformations of the olivine component to denser phases take place. Moreover, the steep gradients in the seismic velocity/density profiles observed between these depths are qualitatively consistent with those expected from the successive transformations in the complementary pyroxene-garnet component in the pyrolite composition. Further, the calculated seismic velocity and density values agree well with those observed in the upper mantle and mantle transition region within the uncertainties attached to these calculations and observations. Pyrolite or peridotite compositions are thus most likely to represent the composition of the mantle above 670 km depth, although some degrees of chemical heterogeneity may exist in the transition region. The observed sharp discontinuous increases of seismic velocities and density at this depth may be attributed either to the phase transformation to a perovskite-bearing assemblage in pyrolite or to chemical composition changes. Density profiles in subducted slabs have been calculated along adequate geotherms assuming that the slabs are composed of the former oceanic crust underlain by a thicker harzburgitic layer. It is shown that the former oceanic crust is substantially less dense than the surrounding pyrolite mantle at depths below 670 km, while it is denser than pyrolite in the upper mantle and the transition region. The subducted former oceanic crust may be trapped in this region, forming a geochemically enriched layer at the upper mantle-lower mantle boundary. Thick and cool slabs may penetrate into the lower mantle, but the chemically derived buoyancy may result in strong deformation and formation of megalith structures around the 670 km seismic discontinuity. These structures are consistent with those detected by recent seismic tomography studies for subduction zones.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1440-1738.1993.tb00074.x
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  • 3
    Electronic Resource
    Electronic Resource
    Fusion of pyrope at high pressures and rapid crystal growth from the pyrope melt (1981)
    [s.l.] : Nature Publishing Group
    Nature 294 (1981), S. 62-64 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Pure pyrope synthesized at 6 GPa and 1, 250 C was used as the starting material. This powder was directly packed in a graphite capsule which is used as a heater. An MAS-type high-pressure apparatus3 was used. Pressure calibration was made at high temperature using the phase boundaries of ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/294062a0
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  • 4
    Electronic Resource
    Electronic Resource
    Stability of magnesite and its high-pressure form in the lowermost mantle (2004)
    [s.l.] : Macmillian Magazines Ltd.
    Nature 427 (2004), S. 60-63 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Carbonates are important constituents of marine sediments and play a fundamental role in the recycling of carbon into the Earth's deep interior via subduction of oceanic crust and sediments. Study of the stability of carbonates under high pressure and temperature is thus important for ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/nature02181
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  • 5
    Electronic Resource
    Electronic Resource
    Iron partitioning in a pyrolite mantle and the nature of the 410-km seismic discontinuity (1998)
    [s.l.] : Macmillan Magazines Ltd.
    Nature 392 (1998), S. 702-705 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Pyrolite is a hypothetical mixture of distinct minerals which iswidely believed to represent the composition of the Earth's mantle. The main pressure-induced phase transformations of the olivine component of pyrolite occur at about 13.5 GPa (α to β) and 24 GPa (γ ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/33663
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  • 6
    Electronic Resource
    Electronic Resource
    Absence of an aluminous phase in the upper part of the Earth's lower mantle (1994)
    [s.l.] : Nature Publishing Group
    Nature 370 (1994), S. 131-133 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Our high-pressure experiments were performed in a multianvil 6-8 type apparatus. Details of the experimental technique have been reported elsewhere8'9. Pyrolite10 was chosen as a representa-tive mantle composition. A starting material of this composition was prepared by intimately ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/370131a0
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  • 7
    Electronic Resource
    Electronic Resource
    Materials Ultrahard polycrystalline diamond from graphite (2003)
    [s.l.] : Nature Publishing Group
    Nature 421 (2003), S. 599-600 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Polycrystalline diamonds are harder and tougher than single-crystal diamonds and are therefore valuable for cutting and polishing other hard materials, but naturally occurring polycrystalline diamond is unusual and its production is slow. Here we describe the rapid synthesis of pure sintered ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/421599b
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  • 8
    Electronic Resource
    Electronic Resource
    Evaluation of the non-hydrostatic stress produced in a multi-anvil high pressure apparatus (1997)
    Springer
    Physics and chemistry of minerals 24 (1997), S. 139-148 
    Details
    ISSN: 1432-2021
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract  Olivine single crystals have been deformed under high confining pressure (P=5 GPa) and temperature (T=1400 °C) conditions in a multi-anvil high pressure apparatus. NaCl, diamond and NaCl+diamond (2:1 by volume) powders were encapsulated along with the olivine single crystals in order to produce a range of stress states. The change of the non-hydrostatic stress transmitted to the olivine samples, enclosed within these three different media, during heating has been evaluated by observation of dislocation microstructure and density. A higher differential stress can be generated with diamond powder (0.1 GPa) than with NaCl powder (0.02 GPa). Although an intermediate differential stress between 0.1 GPa and 0.02 GPa had been expected to be generated using NaCl+diamond powder, the generation of non-hydrostatic stress in the olivine sample was unsuccessful. This may be caused by the fact that compaction (or sintering) proceeded in the capsule throughout the experiments. The most important finding of these experiments is that a constant non-hydrostatic stress can be applied to a sample under very high pressure and temperature conditions within the multi-anvil high pressure apparatus for the duration of the experiment. This approach is therefore suitable for investigating the steady-state rheological properties of mantle minerals at near-mantle conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002690050027
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  • 9
    Electronic Resource
    Electronic Resource
    Compressibility of calcium ferrite-type MgAl2O4 (1997)
    Springer
    Physics and chemistry of minerals 24 (1997), S. 340-344 
    Details
    ISSN: 1432-2021
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract  In situ X-ray diffraction experiments of calcium ferrite-type MgAl2O4 have been carried out using a diamond anvil cell combined with synchrotron radiation and an imaging plate X-ray detector under hydrostatic pressures up to 9 GPa. The observed unit-cell volumes at various pressures were fitted to the Birch-Murnaghan equation of state, yielding a bulk modulus of K T 0= 241(3) GPa when K′ T 0=4 is assumed. This relatively large bulk modulus of calcium ferrite-type MgAl2O4 is consistent with that expected from the systematic relation between bulk modulus and molar volume for the most compounds possessing fcc oxygen packing.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002690050047
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