Naoto Kawai

The Generation of Ultrahigh Hydrostatic Pressures by a Split Sphere Apparatus

A split sphere apparatus has been developed to generate exceedingly high hydrostatic pressures more than 300 kilobars at temperatures over 1500°C in a sample chamber of ample volume. The calibration of pressures is made by the use of known phase transition points in Bi, Fe, and Pb. The calibration above the Pb point (161 kilobars) is discussed in terms of resistance changes for In and CdS previously reported by Drickamer et al.

Synthesis of γ-Mg2SiO4

Abstract Magnesium orthosilicate with spinel structure (γ-Mg2SiO4) was synthesized at about 250 kbar and 1000°C. Unit cell dimension was established to be 8.076 ± 0.001A. X-ray powder diffraction pattern revealed a significant difference between γ-Mg2SiO4 and other γ-M2SiO4 spinels (M = Fe, Co, and Ni) in the intensities of (111) and (331) reflections, both of which are virtually absent in the Mg2SiO4 spinel. This feature could be thoroughly understood by the calculation of the intensities for several silicate spinels.

Split sphere high pressure vessel and phase equilibrium relation in the system Mg2SiO4Fe2SiO4

Abstract In part 1 of this paper a split sphere multipiston assemblage is introduced with which it is possible to produce ultra high pressure and temperature for synthetic experiments. The second part of this paper reports a study on high pressure and temperature stability relation in Mg-rich mineral olivine, i.e. the most occurring mineral in the earths mantle. Then, a phase diagram in the system Mg 2 SiO 4 and Fe 2 SiO 4 is shown together with some technical remarks.

High-pressure X-ray diffraction studies on β- and γ-Mg2SiO4

Abstract Pressure effects on the lattice parameters of β- and γ-Mg 2 SiO 4 have been measured at room temperature and at pressures up to 100 kbar using a multi-anvil high-pressure X-ray diffraction apparatus. The volume changes ( ΔV / V 0 ) at 90 kbar are 5.4 · 10 −2 and 4.2 · 10 −2 for β- and γ-Mg 2 SiO 4 , respectively. Isothermal bulk moduli at zero pressure have been calculated from least-square fits of the data to straight lines. They turn out to be 1.66 ± 0.4 and 2.13 ± 0.1 Mbar for β- and γ-Mg 2 SiO 4 , respectively. The α → γ transition obeys Wangs linear V φ − ρ relation but the α → β transition does not.

Olivine-Spinel transformation in a natural forsterite

Abstract The olivine-spinel transformation in a natural forsterite is studied in the pressure range 98–130 kb and the temperature range 700–1100 °C. The reaction boundary at which olivine solid solution of 93% Mg 2 SiO 4 and 7% Fe 2 SiO 4 breaks down to spinel solid solution and olivine solid solution is determined as P (kb) = 0.054 T (°C)+61. The entropy change of the metastable olivine-spinel transformation in pure Mg 2 SiO 4 is calculated to be − 4.4 cal/° · mole at 100 kb and 1000 °C.

Semiconductor-to-metal transition in GaP under high pressure

Abstract The semiconductor-to-metal transition was observed in GaP under very high pressure exceeding 500 kbar. At the transition the electrical resistance decreased almost instantaneously by five orders of magnitude. This study was also carried out on BP and SiC and no drastic change was observed in their electrical resistance.

Palaeomagnetic and potassium-argon age informations supporting cretaceous-tertiary hypothetic bend of the main island Japan

Abstract Summarizing the data of Cretaceous palaeomagnetic investigation and KAr age determination so far obtained, a hypothetic bend of the main island Japan was examined in detail in this paper. From the analysis it was found first that the bending motion initiated from the beginning of Cretaceous time about 120 m.y. ago, secondly that Japanese Island had been a comparatively straight land mass before this bending occurred, and thirdly that the active period of this motion had continued at least up to 80 m. y. ago. Rate of the rotation of northern Japan relative to southern Japan was also estimated to be 2.9°/m.y. in that active period.

Low Temperature Melting of Elements under High Pressure and Its Progression in the Periodic Table

Data Obtained and gathered to data regarding melting phenomena in elements and compounds have been both reviewed and summarized in this paper. The result has yielded information concerning a new melting relation for materials, the characteristics of which are described in the following three items. 1) Any solid possesses a maximum melting point at a characteristic applied hydrostatic pressure. 2) At any temperature below the maximum melting point the solid melts at two characteristic pressures. 3) The pressure corresponding to the maximum melting point is lower in a solid composed of elements having a larger mass number; the progression of pressure for the maximum melting point is evident in each group elements in the periodic table.

Lattice vibrational spectra of vitreous silica densified by pressure

Abstract The results of the measurement of Raman scattering spectra and infra-red absorption spectra of densified vitreous silica are reported. Raman active-low frequency vibrations are largely changed by compression.

High-pressure decompositions in manganese silicates and their geophysical implications

Abstract High-pressure experiments on manganese silicates at a temperature of about 1000°C have shown the following reactions: 1. (1) Mn2SiO4 → MnO + MNSiO3 ∼ 140 kbar (olivine) (rock (tetragonal salt) “garnet”) 2. (2) Mn2SiO4 → 2MnO + SiO2 ∼ 300(±50)kbar (olivine (rock (stishovite) salt) and, by inference: 3. (3) MnSiO3 → MnO + SiO2 ∼ 300(±50)kbar (tetragonal (rock (stishovite) “garnet”) salt) This work supports earlier suggestions that ferromagnesian silicates in the earths mantle transform to spinel-like and garnet-like phases in the transition zone, but disproportionate to dense oxides in the lower mantle.