OHFUJI, Hiroaki

Faculty
Geodynamics Research Center
PositionProfessor
Mail
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Birthday
Last Updated :2017/11/08

Researcher Profile and Settings

Academic & Professional Experience

  •   2016 04 ,  - 現在, Ehime University, Geodynamics Research Center, Professor
  •   2012 04 ,  - 2016 03 , Ehime University, Geodynamics Reserch Center, Associate Professor
  •   2007 04 ,  - 2012 03 , Ehime University, Geodynamics Research Center, Assistant Professor
  •   2005 10 ,  - 2007 03 , Ehime University, Geodynamics Research Center , Assistant Professor
  •   2004 11 ,  - 2005 09 , Ehime University, Geodynamics Research Center, Postdoctoral Fellow

Association Memberships

  • The Mineralogical Society of Japan
  • The Japan Society of High Pressure Science and Technology
  • American Geophysical Union
  • Mineralogical Society of America

Research Activities

Research Interests

    High-Pressure Experiment, Diamond Anvil Cell, Electron Microscopy

Published Papers

Patents

  • 特願2013-168004, 特開2014-055099

Awards & Honors

  •   2017 09 , Japan Association of Mineralogical Sciences, Award of Japan Association of Mineralogical Sciences
  •   2002 09 , Universities UK, Overseas Research Student Award

Research Grants & Projects

  • Dislocation structure around fluid inclusions in olivine and orthopyroxene
    Ministry of Education, Culture, Sports, Science and Technology, Grants-in-Aid for Scientific Research(挑戦的萌芽研究), Junji YAMAMOTO, Dislocations provide a direct proof of plastic deformation of minerals. We observed dislocation structure around fluid inclusions in olivine and orthopyroxene. For olivine, development of edge dislocations with loop shape whose size is analogous to that of an adjacent fluid inclusion indicate that the dislocations result from excess pressure of the fluid inclusion. The generation of loop dislocations would be controlled by yield strength of slip systems of olivine. For orthopyroxene, a few screw dislocations are identified in c-axis. The difference in dislocation density between both minerals suggests the higher yield strength of orthopyroxene. This is verified by the fact that expansion of a fluid inclusion in olivine estimated by dislocation structure can well explain difference in CO2 fluid density between the minerals. The observation of dislocation structure around fluid inclusions in xenoliths is useful to assess relative strength of slip systems among minerals.
  • Synthesis of pure sintered body of hexagonal diamond and its characterization
    Ministry of Education, Culture, Sports, Science and Technology, Grants-in-Aid for Scientific Research(若手研究(B)), Hiroaki OHFUJI, We performed a series of high pressure and high temperature experiments using a large-volume press to synthesize a pure, single-phase hexagonal diamond sintered body. Our study demonstrated that single-phase hexagonal diamond, which includes neither traces of unreacted graphite starting material nor cubic diamond, can be obtained at 25 GPa and 1100-1500C through direct conversion of highly-oriented, highly-crystalline graphite. The sample consists of extremely thin layered units (a few to several tens of nm) and is as dense as cubic diamond. Since our preliminary hardness measurements provided very high indentation hardness values comparable to or exceeding that of cubic diamond, this nano-sintered body of pure hexagonal diamond would have potential application as a novel ultra-hard material.
  • Verification of ultra-low strain rate effect on olivine rheology
    Ministry of Education, Culture, Sports, Science and Technology, Grants-in-Aid for Scientific Research(基盤研究(B)), Jun-ichi ANDO, In this research, we observed the microstructures of both alpine-type peridotites and peridotite xenoliths in basalt, and analyzed the microchemistry around the dislocations developed in the olivine grains of the studied samples, using optical microscopy, EPMA, EBSD, TEM and ATEM techniques to clarify if the ultra-low strain rate has any effect on the olivine plasticity. We detected Fe-concentration along dislocation line in all observed samples, which was probably caused by Cottrell atmosphere. This result strongly suggests that the effect of ultra-low strain rate on olivine plasticity is very important to understand the dynamics of the upper mantle, which has not been studied so far. In addition, we tried to do the deformation experiments of olivine to support the above conclusion, which has yet to produce any confirming results.
  • Behavior ofFe-bearing materials under very high pressure and mineralogy of the lowermost mantle and the inner core
    Ministry of Education, Culture, Sports, Science and Technology, Grants-in-Aid for Scientific Research(特別推進研究), Tetsuo IRIFUNE, Behaviors of iron and iron-bearing minerals have been studiedby both multianvil and diamond anvil cell experiments, in conjunction with ab initio calculations, under the pressure and temperature conditions from the deep lower mantle to the inner core of the Earth. A number of important results such as relevant to the partitioning of iron in the lower mantle and the phase relations of iron in the inner core, as well as technological developments in applying nano-polycrystalline diamond (NPD or HIME-diamond) to various high-pressure apparatus, have been obtained in this study.
  • The behavior and distribution of water and carbon dioxide in the Earth's interior
    Ministry of Education, Culture, Sports, Science and Technology, Grants-in-Aid for Scientific Research(基盤研究(A)), Toru INOUE, Distribution of water in the Earth’s interiors and the effect of water for phase transition boundaries were clarified, and the water content in the Earth’s interior s was estimated by combining with the seismic data. Moreover, the studies for the dehydration reaction and the equation of state of the slab constituent minerals, and also the study for the effect of water to the mantle mineralogy were carried out. In addition, the study of the compositional dependence for the water content in mantle minerals was carried out. We also tried to determine the water content of magma as a function of pressure and temperature.
  • Material sciences at ultra-high pressure using the strongest spallation neutron source
    Ministry of Education, Culture, Sports, Science and Technology, Grants-in-Aid for Scientific Research(学術創成研究費), Hiroyuki KAGI, This research project aimed at developing neutron diffraction measurements at high pressure using a intense spallation neutron source at J-PARC and clarifying crystal structures of hydrogen-bearing materials in the deep earth, interior of planets, and so on. We have developed novel neutron-focusing device for small samples under high pressure, new high-pressure instruments optimized for the intense neutron source. We have opened a new horizon for sciences on earth and planetary materials at high pressure.
  • High pressure and temperature generation using nano-polycrystalline diamond for diamond anvil cell-Application for melting experiments of pure iron-
    Ministry of Education, Culture, Sports, Science and Technology, Grants-in-Aid for Scientific Research(若手研究(B)), Hiroaki OHFUJI, Laser heating in diamond anvil cell (DAC) equipped with nano-polycrystalline diamond (NPD) anvils was tested for the first time using various types of lasers. NPD-based DAC was found to provide better heating efficiency than a standard DAC with single-crystal anvils. We observed high-temperature generation exceeding 5000 K and 3500 K during laser heating of hcp-Fe sample at pressures of ~100 and 170 GPa, respectively.
  • Two-phase rheology of earth's lower mantle
    Ministry of Education, Culture, Sports, Science and Technology, Grants-in-Aid for Scientific Research(基盤研究(B)), Daisuke YAMAZAKI
  • Modeling of slab penetration and stagnation processes
    Ministry of Education, Culture, Sports, Science and Technology, Grants-in-Aid for Scientific Research(特定領域研究), 入舩 徹男, Norimasa NISHIYAMA
  • Searching mineralogy of the Earth's deep interior using a combination of synchrotron radiation and high-pressure technology
    Ministry of Education, Culture, Sports, Science and Technology, Grants-in-Aid for Scientific Research(学術創成研究費), Tetsuo IRIFUNE, Technical developments have been made in producing higher pressures in multianvil apparatus using sintered diamond (SD) anvils and also for precise measurements of sound velocities of high-pressure phases under the P/T conditions of the mantle transition region. We succeeded to produce pressures as high as〜80 GPa at room temperature using SD anvils, while pressures have been limited to〜60 GPa at the high temperatures relevant to the Earth's mantle. Some new phase transitions have been found in mantle minerals under the conditions of the lower mantle, and precise determination of the P-V-T relations of these and other high-pressure phases have been conducted under the corresponding P, T conditions. On the other hand, precise measurements of sound velocities have been made at pressures to〜20GPa and temperatures to〜1700K, equivalent to those of the depths of the middle part of the mantle transition region. Using this technique; measurements on ringwoodite and majorite in a pyrolite composition, polycrystalline MgO, and the garnetite (majorite + stishovite) in a basaltic composition have been made, which provided important data sets to constrain the mineralogy of the mantle transition region and to provide a new self-consistent pressure scale. In addition to these studies, we have tested the performance of the newly produced nano-polycrystalline diamond (HIME-DIA) for high-pressure devices, and found the great potential of this novel material for anvils for both multianvil apparatus and diamond anvil cell, which yielded the highest pressures of〜110 Gpa and〜20 Gpa, respectively.
  • Physical properties of deep Earth minerals and the effect of water
    Ministry of Education, Culture, Sports, Science and Technology, Grants-in-Aid for Scientific Research(基盤研究(B)), Toru INOUE, We have clarified the physical properties of deep Earth mantle minerals and the effect of water. Experiments were conducted by in situ X-ray measurements in addition to quench experiments.From our previous studies, it has been clarified that high pressure polymorphs of olivine, wadsleyite and ringwoodite, can contain 2-3 wt% of H_2O in their crystal structures, but the partitioning of H_2O among these minerals has not been clarified yet. In the present study, we have clarified the partitioning of H_2O to synthesize these coexisting phases, and found that mantle transition zone should be a strong water reservoir in the Earth's interior.In addition, the measurements of thermal expansion and elastic properties of hydrous wadsleyite and hydrous ringwoodite were conducted to clarify the H_2O content in the mantle. Combined these results with seismic observation, we estimated the H_2O content in the mantle. Further extensive studies have been conducted with seismologist.We also tried to observe dehydration and physical properties of high pressure hydrous phase with capsulation using relatively light metal capsule by in situ X-ray observation. We succeeded to get X-ray spectra of superhydrous phase B using AgPd capsule, and further improved capsule, which were made by a single crystal diamond sleeve and metal caps, were designed for in situ X-ray experiment. The capsule is quite successful, and the effective acquisition of X-ray spectra under high pressure has been achieved by in situ X-ray experiment. This technique has been adopted to determine hydrous melt structure and time-resolved experiment of dehydration.


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