The maximum attainable pressure in a Kawai-type of high-pressure apparatus (KHA) is limited to about 27 GPa when using tungsten carbide (WC) as the anvil material. Recently a remarkable innovation has been made for the KHA by adopting sintered diamond (SD) as the anvil material. So far pressures up to 50 GPa have been confirmed in SD anvil assemblies without any reduction of the specimen volume. Therefore, phase equilibrium and melting experiments of Earth materials have been extended to conditions deep into the lower mantle. The results will substantially advance our understanding of the structure of the lower mantle and the state of the Earth early in its history.
A laser heated diamond anvil cell (LHDAC) is a powerful tool to investigate the Earth's deep interior. Recent advances and problems of synchrotron experiments are reviewed in this paper. An on-line temperature and pressure measurement system was developed for effective laser heating experiments. High temperature reduction of iron bearing material was discussed also. The results of an in-situ powder X-ray diffraction experiment are shown for SiO2 and (Mg, Fe)O. Stishovite transforms to a CaCl2-structured phase at about 55 GPa and the phase was stable up to 80 GPa and 2000°C. A rhombohedral distortion of magnesiowüsutite was observed for (Mg, Fe)O. The positive phase boundary between rocksalt and the rhombohedral phase continues over 100 GPa.
Molecular dynamics (MD) simulation with a realistic and precise potential model is found to be very successful in accurately reproducing the observed molar volume and the measured elastic constants of MgO at ambient conditions, and their temperature and pressure dependencies over wide temperature and pressure ranges. We present the MD simulated temperature-pressure-volume equation of state for MgO as a reliable internal pressure calibration standard at high temperatures and high pressures.
Recent high-pressure and high-temperature experiments strongly imply the possibility of non-stoichiometry for Al, Fe3+ containing MgSiO3 perovskite and the related Al-phases. Therefore, the non-stoichiometric behavior of perovskites in the MgSiO3-MgAlO2.5 system and also in the multi-component system which are similar to natural mantle minerals and rocks was discussed by considering the trivalent cation substitution mechanism: 2VI Si4+ ⇔ 2VI (Al3+, Fe3+) + VO••. Since the behavior of Al coupled with iron in the MgSiO3 perovskite is much more complicated because of the issue of fO2 conditions, it is still under discussion. For dealing with the chemical behavior of Fe3+ in the perovskite, the electron energy-loss spectroscopy (EELS) in transmission electron microscopy (TEM) is becoming a powerful tool by which we can determine the Fe3+ / ΣFe ratio of coexisting phases separately on a nanometer order of resolution. It is expected that the EELS method combined with TEM techniques will be very useful to characterize synthetic high-pressure mantle minerals.
In order to understand the formation, evolution and dynamic processes of the molten core of the terrestrial planets, knowledge of the physical properties, such as viscosity and density, of the molten iron alloy is required. Recent progress in the high-pressure technology combined with synchrotron radiation allows us to measure such properties at high-temperature and high-pressure. In this article, recent advances in the high-pressure research of molten iron alloys are reviewed.
A high temperature diamond anvil cell (HTDAC) was installed in an infrared (IR) microscope at BL43IR of the synchrotron radiation (SR) facility SPring8 to investigate the behavior of “water” in minerals. Since IRSR as an IR light source is more brilliant than a conventional IR source, the IRSR is useful for IR measurements under experimentally difficult conditions such as in a DAC study. In this text, IR microspectroscopy of BL43IR at SPring8, the HTDAC for IR study and the behavior of the proton in brucite (Mg(OH)2) under high temperature and high pressure revealed by IR absorption spectra with IRSR and HTDAC are introduced.
Accurate measurement of pressure is fundamental in high-pressure and high-temperature research. To make better measurements, it is important to identify error sources and their seriousness. Error sources in synchrotron X-ray-diffraction multi-anvil experiments, such as non-hydrostatic stresses, pressure effects on e.m.f. of thermocouples, uncertainties in pressure scales, etc. are reviewed.
The hydrogen bonding structure and dynamics of supercritical water is studied by means of high-temperature and high-pressure NMR. The proton chemical shift is measured over a wide range of thermodynamic conditions and is related to the number of hydrogen bonds in supercritical water with the help of computer simulations. It is found that the hydrogen bonding persists at supercritical temperatures and that the average number of hydrogen bonds is at least one in the supercritical densities. The spin-lattice relaxation time is further measured to determine the reorientational correlation time. It is shown that while the reorientational relaxation proceeds on the order of picosecond in ambient water, it does on the order of several tens of femtoseconds in supercritical water. The role of water in noncatalytic reactions in hydrothermal conditions is also examined by focusing on the dehydration of 1, 4-butanediol into tetrahydrofuran, which proceeds under the presence of a strong acid at ambient conditions. The water-induced and acid-catalyzed rate constants are separately determined, and water is proven to promote the reaction in its undissociated form.