Large-volume High-pressure Apparatus Research Articles

In situ EXAFS study on GeS 2 glass under high-pressure

A GeS 2 glass was compressed up to 8 GPa at room temperature, heated up to 270 °C under 8 GPa and then decompressed to ambient pressure at room temperature, using a large volume high-pressure apparatus. The local structural-changes around Ge were examined by means of an in situ EXAFS method. The Ge–S bond length became monotonously short with increasing applied-pressure up to 8 GPa at room temperature. When the specimen was heated to 270 °C under 8 GPa, however, the bond length became slightly long. The elongated bond length was almost kept even after the temperature was descended to room temperature. In decompression process, the bond length became gradually long with releasing applied-pressure down to 2 GPa, following a change in compression process. Below 2 GPa, however, the Ge–S bond length was largely elongated, being longer than the initial one. No significant change of coordination number was found in the compression and decompression processes up to 8 GPa. This change can be explained by a combined effect of elastic and inelastic structural-changes.

Heater cell for materials synthesis and crystal growth in the large volume high pressure apparatus at 10 GPa

To realize materials synthesis and crystal growth in a large volume of high pressure apparatus in the region of 10 GPa, a heater cell was developed for a belt-type high pressure apparatus with a bore diameter of 32 mm. The cell consists of a cylindrical electrode made of TiC powders located between a pair of graphite heaters with a disk shape. High temperature of 1500 °C at nominal pressure of 9.7 GPa (9.35 GPa corrected) was successfully generated for 1 h using the cell. Synthesis and growth of stishovite was performed at high pressure and high temperature conditions based on their calibrations. Experimental results suggest that the materials synthesis and crystal growth above 10 GPa can be realized in a large volume of belt-type apparatus using the heater cell.

High-Pressure Phase Relationships for FeS

Phase relationships for FeS polymorph have been studied at the pressure of 16-20 GPa and temperature of 300-1350 K by in situ X-ray observation using a large volume high-pressure apparatus and a synchrotron radiation. Contrary to Fei's prediction [1], we found the stability field of NiAs-type phase of FeS extending at least to 18 GPa. Results of in situ X-ray observation correspond with the NiAs-hexagonal phase boundary determined by Kusaba et al . [2, 3]. Assuming the straight NiAs-hexagonal phase boundary, we estimate that the NiAs-hexagonal-liquid triple junction is located at 39.5 GPa and 2300 K.

Structural changes of quartz-type crystalline and vitreous GeO2 under pressure.

Using a large volume high pressure apparatus, quartz-type crystalline GeO2 and Li2O-4GeO2 glass have been compressed up to 14 GPa at room temperature and their local structural changes have been investigated by an in-situ XAFS method. In quartz-type crystalline GeO2, the change of the coordination number from 4 to 6 begins above 8 GPa and finishes below 12 GPa. On decompression, reversal transition begins below 8 GPa and there is a large hysteresis. Almost no sixfold coordination of Ge is preserved after releasing pressure. Change of coordination number in vitreous Li2O-4GeO2 begins above 6 GPa and is completed below 10 GPa. Reversal transition begins below 10 GPa and the hysteresis is smaller than that of quartz-type GeO2. Change of coordination number in vitreous Li2O-4GeO2 is also reversal.

SPring-8 Beamlines for High Pressure Science with Multi-Anvil Apparatus.

The SPring-8 will open for public use in October, 1997. Three beamlines are now under construction for high pressure research with large volume high pressure apparatus. Two multi-anvil apparatus will be installed on these beamlines. One is a 1500 ton press with a big DIA type guide-block for two stage compression, which is used for the energy dispersive x-ray diffraction study. The other is a 180 ton small DIA press similar to MAX90 at the Photon Factory, which is used for both energy and angle dispersive diffraction as well as an x-ray absorption study.

高温高圧鉱物物性 ＳＰｒｉｎｇ‐８ビームラインでの高温高圧Ｘ線回折実験

SPring-8 is a third-generation synchrotron radiation facility that provides super-intense X-rays for basic and applied research in materials science. The bending magnet beamline, BL04B1 is one of the beamlines open for high-pressure and high-temperature research. A newly large volume high-pressure apparatus (SPEED-1500) was installed at BL04B1. This apparatus has a capability of generating pressures up to 40 GPa and a temperature of 3000 K by using a double-stage multi-anvil system with the sintered diamond anvils. High-pressure and high-temperature X-ray diffraction measurement using a combination of synchrotron radiation and SPEED-1500 makes it possible to investigate the constituent materials of the Earth's interior in the lower mantle.

A study of the polymorphic transformations in Co2SiO4

The olivine-beta phase transformation in Co2SiO4 has been studied in a large-volume high-pressure apparatus (USSA-2000). The experimental conditions straddle the univariant phase boundaries due to the presence of a substantial temperature gradient (150–200° C over the 3-mm length of the sample). At conditions close to equilibrium, the transformation mechanism is one of limited nucleation with rapid growth of large crystals of the beta phase. Transmission electron microscopy (TEM) analysis shows that the cation stacking faults in Co2SiO4-spinel are identical to those seen in numerous spinels. The 010 faults in beta-Co2SiO4 are found to be identical to those seen in beta-(Mg,Fe)2SiO4 found in shocked veins in meteorites.

Kinetics measurement of the phase transformation in Ni2SiO4 under high pressure and temperature (abstract)

The kinetics of the pressure-induced phase transformations in minerals are of considerable importance in affecting the dynamics of convection in the Earth. Because of the long exposure time of the high pressure in situ x-ray observations, however, it was very difficult to study the kinetics of such transformations. Combination of the synchrotron radiation and a large-volume high-pressure and high-temperature apparatus made it possible to perform such a study. The kinetics of the olivine-spinel transformation in Ni2SiO4 have been studied at conditions of 3.6–4.8 GPa and 765–980 °C. X-ray diffraction experiments were carried out using the MAX-80 high-pressure, high-temperature cubic-anvil apparatus at the National Laboratory for High Energy Physics, Japan. Synchrotron radiation was supplied by an accumulator ring operating at 6.5 GeV and between 15 and 5 mA. Ni2SiO4 olivine powder was hot pressed in the olivine stability field and then the pressure-temperature conditions were changed to initiate the transformation to spinel. Reaction progress was monitored by collecting x-ray diffraction patterns at intervals of either 30 or 100 s. The extent of transformation was estimated as a function of time and the data were analyzed on the basis of a nucleation and growth model. Pressure and temperature dependence of the transformation rate were determined from the present study.

Construction of liter-class large volume high pressure apparatus for materials synthesis

A belt type high pressure apparatus was constructed with a chamber volume of about 1000 cc and an hydraulic press to operate the apparatus. The maximum pressure generated in the chamber is 6 GPa for a first step and 10 GPa for the final goal. The 6 GPa apparatus (FB120) was designed by the use of high speed steel anvils and a cylinder core. To prevent plastic deformation of the inner wall of the core special cell and inner sleeve materials of smaller thermal conductivity were adopted. A 30 000 ton wire winding frame type press was constructed for this purpose. The design and analysis of the press frame deformation during wire winding is presented.