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We investigated phase relations in pyrolite at ∼33-40 GPa and ∼1800-2150 K by in situ X-ray diffraction using Kawai-type apparatus with sintered diamond anvils. The results demonstrated that MgSiO3-rich orthorhombic perovskite (mpv), CaSiO3-rich cubic perovskite (cpv) and (Mg,Fe)O ferropericlase (fp) are the stable phases in pyrolite bulk composition at the conditions corresponding to the lower mantle. However, chemical analyses of a run product recovered from ∼ 34 GPa by an analytical transmission electron microscope showed the coexistence of metallic iron particles with mpv, fp, and SiO2-rich amorphous phase. Also, Fe/Mg partitioning coefficient between mpv and fp was found to be 0.66(31), which is consistent with previous results for pyrolite bulk composition at 26-30 GPa and ∼1900 K. These results indicate that iron-rich metallic particles can exist in the lower mantle as a stable phase to the depth of at least ∼900 km. [ABSTRACT FROM AUTHOR]

We tested boron-doped diamond (BDD) synthesized by chemical vapor deposition (CVD) as a heating element in a multi-anvil apparatus. We succeeded in manufacturing BDD into a tubular shape by laser cutting and electric discharging machining. The BDD tube shaped by the electric discharging machining was contaminated by discharging electrode materials (Mo and W), which affected the heating performance. The laser-cut BDD tube has a clean surface and, therefore, had a good heating performance. We succeeded in generating temperature as high as 2670 K at a pressure around 30 GPa with laser-cut heater. Heating reproducibility was confirmed through repeated heating and cooling cycles. The recovered sample shows that a higher temperature generation above 2670 K was prevented by eutectic melting of ZrO2 thermal insulator and Al2O3 sample. Owing to the commercial availability with a reasonable price, CVD–BDD heaters are more practical than a high-pressure synthesized BDD heaters for wide applications. [ABSTRACT FROM AUTHOR]

A new furnace system with an almost zero temperature gradient throughout the sample area was designed for multi-anvil high pressure experiments. Test experiments of the new design were performed using 18/11 and 25/15 cell assemblies at 4 GPa, 1400°C and 1500°C, respectively. The temperature field within the sample capsules appeared to be very homogenous as indicated by Mg2Si2O6-MgCaSi2O6 two-pyroxene thermometry, by direct temperature measurements using two thermocouples within the same assembly, and by distribution of solid and liquid phases in the sample capsule. The temperature gradient is estimated to be <2.4°C/mm over an area of 4 × 5 mm2 within the furnace. It is significantly lower than standard multi-anvil experiments with straight or stepped furnace systems, which are at the levels of 20-200°C/mm. [ABSTRACT FROM AUTHOR]

We have expanded the pressure ranges at room and high temperatures generated in a Kawai-type multi-anvil apparatus (KMA) using tungsten carbide (WC) anvils with a high hardness ofHv = 2700 and a Young’s modulus of 660 GPa. At room temperature, a pressure of 64 GPa, which is the highest pressure generated with KMA using WC anvils in the world, was achieved using 1°-tapered anvils with a 1.5-mm truncation. Pressures of 48–50 GPa were generated at high temperatures of 1600–2000 K, which are also higher than previously achieved. Tapered anvils make wide anvil gaps enabling efficient X-ray diffraction. The present pressure generation technique can be used for studying the upper part of the Earth’s lower mantle down to 1200 km depth without sintered diamond anvils. [ABSTRACT FROM PUBLISHER]

Semi-sintered MgO- and ZrO2-based ceramics are the conventional materials used as a pressure-transmitting medium (PM) for large-volume high-pressure experiments. Our experimental data for both MgO and ZrO2 provide similar pressure generation efficiency. The major requirement for a PM material is low compressibility. However, our experimental data suggest that semi-sintered types of these ceramics are more compressible than can be expected. For instance, the apparent compressibility of semi-sintered magnesia is 35% and 60% higher than the lattice compressibility of MgO at 15 and 30 GPa, respectively. The difference in lattice and apparent compressibilities of semi-sintered ceramics is most probably caused by a residual porosity. The use of a low-porous pressure medium should be considered as an improvement of pressure generation efficiency of high-pressure apparatuses. [ABSTRACT FROM AUTHOR]