HISAKI Project Team

Takehiko Ishikawa

  (石川 毅彦)

Profile Information

Affiliation
Professor, Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency

J-GLOBAL ID
201901019246827999
researchmap Member ID
B000358321

External link

Papers

 199
  • Manabu Watanabe, Yuki Watanabe, Takehiko Ishikawa, Chihiro Koyama
    Thermochimica Acta, 747 179976-179976, May, 2025  Peer-reviewed
  • Stephen K. Wilke, Abdulrahman Al-Rubkhi, Chris J. Benmore, Jörg Neuefeind, Chihiro Koyama, Takehiko Ishikawa, Rina Shimonishi, Richard Weber
    The Journal of Chemical Physics, 162(12), Mar 24, 2025  Peer-reviewed
    Rare earth aluminum garnets are important materials in optical, dielectric, and thermal barrier applications. To advance the understanding of their melt processing and glass forming ability, we report the atomic structure of molten Yb3Al5O12 over 1770–2630 K, which spans the equilibrium and supercooled liquid regimes. The melt density at Tm = 2283 K is 5.50 g cm−3, measured via silhouette imaging of electrostatically levitated drops over 1010–2420 K. Four separate structure measurements were made with aerodynamically levitated melts using x-ray and neutron diffraction with isotope substitution of Yb (172Yb, 174Yb, or natYb). Empirical potential structure refinement models were developed, which are in excellent agreement with the experiments. Coordination environments for Al–O are predominantly 4- and 5-coordinate, with a mean coordination of nAlO = 4.43(8), while Yb–O environments mostly range from 5- to 8-coordinate, with nYbO = 6.26(8). The cation–oxygen polyhedra are connected primarily by corner-sharing, with edge-sharing constituting up to ∼1/3 of the connectivity among polyhedra with Yb or higher-coordinated Al–O. Structurally, the –Al–O– network in molten Yb3Al5O12 appears conducive to glass formation: nOAl = 1.85(3), there are 1.86 AlOx–AlOx connections per Al atom (e.g., a mixture of Q3 and Q4 units), and the modal ring size is six cations. These characterize a network that is somewhat less constrained compared to SiO2 glass, yet Yb3Al5O12 cannot be quenched into crystal-free glass. Aluminum garnet compositions with larger rare earth cations do form glass, so these characterizations help reveal the structural characteristics corresponding to the limit of glass forming ability in rare earth aluminates.
  • Yoshio Kono, Chihiro Koyama, Nozomi M. Kondo, Koji Ohara, Hideharu Kuwahara, Ryoichi Nakada, Yuki Watanabe, Hirohisa Oda, Takehiko Ishikawa
    Communications Earth & Environment, 6(1) 148, Mar 3, 2025  Peer-reviewed
    Abstract Possible existence of dense iron-rich silicate melt layer above Mars’ core is important in understanding the nature and evolution of Mars. However, gravitational stability of iron-rich silicate melt in the Mars’ interior has not been well constrained, due to experimental difficulties in measuring density of iron-rich peridotitic melt. Here we report density measurements of iron-rich peridotitic melts up to 2465 K by using electrostatic levitation furnace at the International Space Station. Our experimentally obtained densities of iron-rich peridotitic melts are markedly higher than those calculated by first principles simulation, and are distinct from those estimated by extrapolating a density model for SiO2-rich basaltic melts. Our determined density model suggests that peridotitic melt with the Fe/(Mg+Fe) ratio more than 0.4-0.5 has higher density than that at the base of the Mars’ mantle, which indicates gravitational stability of the iron-rich peridotitic melt at the core-mantle boundary in Mars.
  • Y. Watanabe, C. Koyama, T. Ishikawa, P.-F. Paradis
    International Journal of Microgravity Science and Applicaiton, 42(1) 420101, Jan, 2025  Peer-reviewed
  • Yusaku Seimiya, Hidekazu Kobatake, Kazuki Tono-oka, Riku Sugahara, Shuya Kurosawa, Suguru Shiratori, Ken-ichi Sugioka, Takehiko Ishikawa, Chihiro Koyama, Yuki Watanabe, Rina Shimonishi, Shumpei Ozawa
    ISIJ International, 64(15) 2253-2261, Dec 30, 2024  Peer-reviewed

Misc.

 135

Presentations

 63

Research Projects

 13

● 専任大学名

 1
  • Affiliation (university)
    総合研究大学院大学(SOKENDAI)

● 所属する所内委員会

 4
  • ISAS Committee
    安全委員会
  • ISAS Committee
    ISASニュース編集委員会
  • ISAS Committee
    宇宙環境利用専門委員会
  • ISAS Committee
    大気球専門委員会