六面顶压机立方压腔内压强的定量测量及受力分析

将六面顶压机立方压腔内置入电路,采用原位电阻测量确定Bi,Tl,Ba相变的方法,标定了压腔内不同位置的压力(强).通过标定立方压腔顶锤表面的压力并结合计算,分别得到了外部加载与压腔密封边受力以及合成腔体受力的对应关系.实验分析结果表明,随着外部加载的增加,当腔体压力达到5 GPa时,消耗在压腔密封边上的加载急剧上升,消耗在合成腔体的加载趋于不变,从而导致立方压腔压力达到上限.利用实验结果,分析了立方压腔在高压下的受力状态,解释了立方压腔的压力难以超过7 GPa的原因.结合立方压腔的几何结构,通过理论分析,提出了采用高体弹模量的物质作为传压介质,同时采用低体弹模量的物质作为密封边提高立方压腔压力上限的可行方案.通过定量标定叶腊石压腔轴向的压力梯度,给出了压腔内沿对称轴不同位置压力值的计算方法,此方法可为高压实验提供更精确的压力数据.     

Effect of precompression on pressure-transmitting efficiency of pyrophyllite gaskets

Pyrophyllite is widely used both as a gasket material and as a pressure-transmitting medium, especially for a large-volume press. Its pressure-transmitting efficiency mainly depends on the following factors: geometry of anvil and pyrophyllite block, chemical composition, density and strength. For a long time, most studies have been devoted to the first two factors, whereas the third one has been studied less. In this work, we report that the pressure-transmitting efficiency of pyrophyllite is improved by precompressing. The results show that pyrophyllite was fully densified when the pressure reached about 1 GPa. The press load for Ba I–II transition in the cubic large-volume pressure cell is reduced more than 8×10⁵ N by using the densified pyrophyllite, compared with the unprecompressed pyrophyllite. Namely, the press-load utilization efficiency was improved above 15% when the precompressed pyrophyllite is used as a pressure-transmitting medium.     

Finite-element analysis on pressure transfer mechanism in large-volume cubic press

Pressure transmission inside a large-volume cubic press was examined using finite-element (FE) simulations. Calculations were carried out for the pyrophyllite P-transmitting mediums (32.5?×?32.5?×?32.5?mm³). The cell pressures of the simulations were chosen as representative values, including 3.75 and 5.5?GPa. A modified constitutive model for pyrophyllite and more realistic modelling were proposed. The global pressure fields were displayed using the contour plots. The results reveal that (1) at the centre of the pyrophyllite cube exists a region of constant quasi-hydrostatic pressure (RoCQHyP) where the pressure drop is less than 50?MPa; (2) how mechanical property (e.g. bulk modulus) of the P-transmitting medium affects cubic press P-transmitting performance. The simulated results were corroborated by high pressure experiments.     

High pressure behavior of nano-crystalline CeO2 up to 35 GPa: a Raman investigation

The present paper reports the results of in situ Raman studies carried out on nano-crystalline CeO₂ up to a pressure of 35 GPa at room temperature. The material was characterized at ambient conditions using X-ray diffraction and Raman spectroscopy and was found to have a cubic structure. We observed the Raman peak at ambient at 465 cm^?1, which is characteristic of the cubic structure of the material. The sample was pressurized using a diamond anvil cell using ruby fluorescence as the pressure monitor, and the phase evolution was tracked by Raman spectroscopy. With an increase in the applied pressure, the cubic band was seen to steadily shift to higher wavenumbers. However, we observed the appearance of a number of new peaks around a pressure of about 34.7 GPa. CeO₂ was found to undergo a phase transition to an orthorhombic α -PbCl₂-type structure at this pressure. With the release of the applied pressure, the observed peaks steadily shift to lower wavenumbers. On decompression, the high pressure phase existed down to a total release of pressure.     

New techniques for high pressure falling sphere viscosimetry in DIA-type large volume presses

Here we report recent technical advances that enable viscosity measurements in two DIA-type multi-anvil apparatus with a maximum of 250 tons and 1750 tons. We anticipate that this system will enable viscosity measurements for the pressures up to about 30 GPa. The deformation of the cell assemblies were analyzed by X-ray absorption tomography at beamline W II at DESY/HASYLAB after the high pressure runs. This analysis gave considerable insights into strategies for improving the cell assembly with the result that the optimized assemblies could be used at much higher pressures without blow-outs. We demonstrate using of X-ray transparent cubic boron nitride-anvils (single-stage DIA) and slotted carbide anvils (double-stage DIA) to make the whole melting chamber accessible for the high pressure X-radiography system. Results are demonstrated with viscosity measurements following Stokes’ Law by evaluation of X-radiography sequences taken by a camera equipped with a charge-coupled device sensor (CCD-camera) at pressures of 5 GPa as well as 10 GPa and temperatures of 1890 K.     

复合型多晶金刚石末级压砧的制备并标定六面顶压机6-8型压腔压力至35GPa

通过分析二级6-8型大腔体静高压装置八面体压腔的受力状况, 研制了一种使用成本低、尺寸大且易于加工的多晶金刚石-硬质合金复合二级(末级)顶锤(压砧). 采用原位电阻测量观测Zr在高压下相变(α-ω, 7.96 GPa; ω-β, 34.5 GPa)的方法, 标定了由多晶金刚石-硬质合金复合末级压砧构建的5.5/1.5(传压介质边长/二级顶锤锤面边长, 单位: mm)组装的腔体压力. 实验表明, 自行研制的多晶金刚石-硬质合金复合末级压砧可使基于国产六面顶压机构架的二级加压系统的压力产生上限从约20 GPa提高到35 GPa以上, 拓展了国内大腔体静高压技术的压力产生范围. 应用这一技术, 我们期望经过末级压砧材料与压腔设计的进一步优化, 在基于国产六面顶压机的二级6-8 型大腔体静高压装置压腔中产生超过50 GPa的高压. 关键词： 二级6-8型大腔体静高压装置 多晶金刚石-硬质合金复合末级压砧 压力标定     

FEM study on a double-beveled anvil and its application to synthetic diamonds

A new double-beveled anvil for the synthesis of high-quality diamonds has been described, which is used in a China-type large-volume, cubic-anvil, high-pressure apparatus (LV-CHPA, SPD-6X2000). Our results indicate that the pressure generation of a double-beveled anvil is more efficient than that of a single-beveled anvil. To gain the same cell pressure (5.5 GPa), the oil pressure of LV-CHPA using double-beveled anvils decreased by about 10%, compared to using single-beveled anvils. Furthermore, a double-beveled anvil can pressurize a cubic cell of 36 mm³ up to about 6.0 GPa, and simultaneously can increase the temperature up to 1360°C for routine operation. This provides considerable advantages to the synthesis of high-quality diamonds under ultra-high-pressure conditions with the same hydraulic rams.     

A large volume cubic press with a pressure-generating capability up to about 10 GPa

A massive cubic press, with a maximum load of 1400 tons on every WC anvil, has been installed at the High Pressure Laboratory of Peking University. High-P experiments have been conducted to examine the performance of the conventional experimental setup and some newly developed assemblies adopting the anvil-preformed gasket system. The experimental results suggest that (1) the conventional experimental setup (assembly BJC2-0) can reach pressures up to about 6 GPa with a large cell volume of 34.33 cm³; (2) the anvil-preformed gasket system, despite decreasing the P-generating efficiency, extends the P-generating capability up to about 8 GPa at the expense of reducing the cell volume down to 8.62 cm³ (assembly BJC2-6); (3) due to the large cell volume, it is possible to make further modifications to extend the pressure range, as readily demonstrated, to about 10 GPa (assembly BJC5-7); (4) the effect of high temperature on the pressure generation of the press is not significant. It follows that this cubic press can be very useful in synthesizing materials of large volume at high pressures and to the studies such as high-P phase equilibrium, trace element partitioning and isotope fractionation in the research fields of Earth and planetary sciences.     

基于铰链式六面顶压机的二级6-8型大腔体静高压装置

报道了一种新型二级6-8型大腔体静高压装置.该装置是以国产DS6×800T铰链式六面顶压机为构架,在其六面体压腔中直接放入二级6-8模(球分割)增压装置以产生10GPa以上的压力,还实验了不同规格的预密封边和不同密度的叶蜡石对压力产生效率的影响,在室温下用BiⅠ-Ⅱ(2.55GPa),Ⅲ-Ⅴ(7.7GPa)和SnⅠ-Ⅱ(9.4GPa)在高压下的相变对14／8(8面体传压介质边长／8面体压腔边长)规格压腔进行了压力标定.实验结果表明,该系统可以在加载压力(油压)约为3×10⁶N(～42 关键词： 铰链式六面顶压机 6-8型球分割大腔体静高压装置 压力标定     

Powder neutron diffraction of wüstite (Fe0.93O) to 12 GPa using large moissanite anvils

High-pressure powder neutron diffraction of wüstite-Fe_0.93O has been achieved to 12 GPa using a large gem-moissanite (SiC) anvil cell. The moissanite anvils are weakly absorbing and provide greater neutron fluxes to the sample than is possible with tungsten carbide anvils. There is minimal diffraction overlap from the single-crystal moissanite anvils compared to tungsten carbide or synthetic diamond anvils, providing cleaner background profiles. The required sample volume for high-pressure neutron diffraction is dramatically reduced to several cubic millimeters. High-quality powder diffraction patterns of wüstite were recorded at 90 min exposure times on the HIPPO diffractometer at LANSCE when the sample volume was in the range of ～10 mm³. This is about two orders of magnitude smaller than the necessary sample volume (～1.0 cm³) for the same kind of experiment with other high-pressure cells and nominal neutron fluxes.     

High pressure synthesis at 10 GPa and 1400 K using a small cubic anvil apparatus with a multi-anvil 6-6 system

In the present study, high pressure synthesis up to 10 GPa was done using a small cubic anvil apparatus (W45×D52×H92 cm³, load capacity of 1.80 MN) with a multi-anvil 6-6 system. Its performance was demonstrated by synthesizing a ferromagnetic perovskite oxide, CaCu₃Fe₄O₁₂, at pressure–temperature conditions of 10 GPa and 1400 K. The synthesized CaCu₃Fe₄O₁₂ perovskite was ～1 mm in diameter and ～2 mm in height and its size was large enough for performing magnetic susceptibility measurements at 5–300 K using a superconducting quantum interference device magnetometer and phase identification by X-ray diffraction. The experimental system developed in the present study has many advantages when used in high pressure synthesis experiments, and the technical development of a small cubic anvil apparatus will greatly contribute to the advancement of high pressure synthesis of novel materials.     

Ab initio study of the structural,electronic, elastic and thermal conductivity properties of SrClF with pressure effects

Abstract

SrClF is an important optical crystal and can be used as pressure gauge in diamond anvil cell at high pressure. In this work, we performed a systematic study on the structural, electronic and elastic properties of SrClF under pressure, as well as its thermal conductivity, by first-principles calculation. Different exchange-correlation functionals were tested and PBESOL was finally chosen to study these properties of SrClF. Studies reveal that SrClF has a bulk modulus of about 56.2 GPa (by fitting equation of states) or 54.3 GPa (derived from elastic constants), which agree well with the experimental result. SrClF is mechanically and dynamically stable up to 50 GPa. Its elastic constants increase with the applied pressure, but its mechanical anisotropy deteriorates as the pressure increases. Investigation of its electronic properties reveals that SrClF is a direct band-gap insulator with a gap value of 5.73 eV at 0 GPa, which decreases with the increasing pressure and the reason is found by analysing the partial density of states. Based on the calculated phonon dispersion curves, thermal conductivity of SrClF is predicated. At ambient conditions, the predicted thermal conductivity is about 3.74 Wm^?1 K^?1, while that obtained using the simplified Slack model give a slightly larger value of 4.62 Wm^?1 K^?1.     

Distortion of spores of moss Venturiella under ultra high pressure

In our previous studies on the tolerance of living organisms such as planktons and spores of mosses to the high hydrostatic pressure of 7.5 GPa, we showed that all the samples could be borne at this high pressure. These studies have been extended to the extreme high pressure of 20 GPa by using a Kawai-type octahedral anvil press. It was found that the average diameter of the spores of Venturiella exposed to 20 GPa for 30 min was 25.5 μm, which is 16.5% smaller (40.0% smaller in volume) than that of the control group which was not exposed to high pressure. The inner organisms showed a further extent of plastic deformation. As a result, a gap appeared between the outer cover and the cytoplasm. A relationship has been obtained between the survival ratio and plastic deformation of spores of moss Venturiella caused by the application of ultra high pressure.     

Diamond anvil cell syntheses and compressibility studies of the spinel-structured gallium oxonitride

The formation conditions of cubic spinel-structured gallium oxonitride have been investigated in situ under high-pressure/high-temperature conditions using a laser-heated diamond anvil cell. As starting materials, a mixture of the end members w-GaN/β-Ga₂O₃ in a molar ratio of 3:2 and a gallium oxonitride ceramic derived during pyrolysis from the metallo-organic precursor (Ga(O^tBu)₂NMe₂)₂ were used. In the mixture of the end members, spinel-structured gallium oxonitride starts crystallizing at a pressure of 3 GPa and at a temperature of about 1300 °C. The precursor-derived ceramic with predefined bondings reacted completely to the spinel phase, without by-products, at a pressure of 0.7 GPa. For the spinel-structured gallium oxonitride we determined a bulk modulus K of 216(7) GPa using a fixed value of 4 for K′. The spinel-structured gallium oxonitride exhibits a cell volume of 552.9(5) ų at ambient pressure.     

A new multi-anvil press employing six independently acting 8 MN hydraulic rams

A new large volume multi-anvil system which employs six independently acting hydraulic rams with independent oil pressurization systems has been developed for high pressure and temperature experiments. The six 8 MN hydraulic rams approach at right angles inside a composite steel plate frame and can each advance a square faceted anvil of either hardened steel or tungsten carbide. The position of each anvil can be measured relative to the frame of the press to a precision of 0.1 μ m. The press is designed to perform both deformation experiments using cubic ceramic pressure media and experiments employing eight inner cubic anvils to compress an octahedral pressure medium. During compression, the position of each anvil relative to the press frame can be precisely measured and controlled independently, thus ensuring a high level of symmetry in the compressive stress environment. The highly cubic compressive regime provides an optimal environment for the use of inner sintered diamond cubic anvils, which can potentially obtain pressures above 50 GPa. The large loading capacity (24 MN) allows larger cubic pressure media to be used at higher pressures than conventional systems.     

一套基于六面顶高压装置的静水压高频介电测试系统

 以一套6×14 400 kN六面顶高压装置和一台Agilent 4294A精密阻抗分析仪为主体,建立了一套静水压高频介电实时测试系统。通过固体传压介质预成型方法,解决了液体测试腔在固体传压介质中的密封以及包括4根微同轴电缆在内的多根测量导线引出密封边问题,将常压下通用的四同轴阻抗谱测试技术引入了高压研究。液体测试腔容积可达(Φ13×15) mm³,可同时容纳10 mm×10 mm样品、高频测试夹具、温度与压力传感器、加热装置,以及包括4根外径为1.6 mm、特性阻抗为50 Ω微同轴电缆在内的16根引线,进行室温至300 ℃、常压至3 GPa 静水压力、测试频率40 Hz~5 MHz范围材料的四线阻抗谱测量,实验误差小于3%。利用这套装置观察了室温下,BaTiO₃单晶在约2.6 GPa静水压力下的压致铁电-顺电相变。     

High pressure X-ray diffraction and Raman spectroscopic studies of the phase change of D2O ice VII at approximately 11 GPa

High pressure experiments were performed on D₂O ice VII using a diamond anvil cell in a pressure range of 2.0–60 GPa at room temperature. In situ X-ray diffractometry revealed that the structure changed from cubic to a low symmetry phase at approximately 11 GPa, based on the observed splitting of the cubic structure's diffraction lines. Heating treatments were added for the samples to reduce the effect of non-hydrostatic stress. After heating, splitting diffraction lines became sharp and the splitting was clearly retained. Although symmetry and structure of the transformed phase have not been determined, change in volumes vs. pressure was calculated, assuming that the low-symmetry phase had a tetragonal structure. The bulk modulus calculated for the low-symmetry phase was slightly larger than that for the cubic structure. In Raman spectroscopy, the squared vibrational frequencies of ν₁ (A_1g), as a function of pressure, showed a clear change in the slope at 11–13 GPa. The full width at half maxima of the O-D modes decreased with increasing pressure, reaching a minimum at approximately 11 GPa, and increased again above 11 GPa. These results evidently support the existence of phase change at approximately 11 GPa for D₂O ice VII.     

A simple opposed-anvil apparatus for high pressure and temperature experiments above 10 GPa

A new opposed-anvil high pressure and temperature apparatus was developed based on the Drickamer-type apparatus. Various improvements were made to increase the sample volume and to generate high pressure and temperature stably and easily. By optimizing components such as the anvil, heater, and gasket, large sample volumes of about 4?mm³ (～10³ times more than that previously obtained with our previous apparatus) were achieved, with compact and light apparatus (outer diameter ? 40?mm; height 31?mm; weight 300?g). Pressures and temperatures up to about 15?GPa and 1700?K can routinely and stably be achieved by using this assembly. In order to extend the pressure range further, sintered diamond was used as an anvil material. As a result, pressures and temperatures of around 38?GPa and 1400?K were achieved, although the sample volume was decreased to about 1.3×10^?1?mm³.     

Resonance Raman spectroscopy of carbon nanotubes: pressure effects on G-mode

We use 488 and 568 nm laser Raman spectroscopy under high pressure to selectively follow evolution of Raman G-mode signals of single-walled carbon nanotubes (SWCNTs) of selected diameters and chiralities ((6, 5) and (6, 4)). The G-mode pressure coefficients of tubes from our previous work are consistent with the thick-wall tube model. Here we report the observation of well-resolved G-minus peaks in the Raman spectrum of SWCNTs in a diamond-anvil cell. The pressure coefficients of these identified tubes in water, however, are unexpected, having the high value of over 9 cm^?1 GPa^?1 for the G-plus and the G-minus, and surprisingly the shift rates of the same tubes in hexane have clearly lower values. We also report an abrupt increase of G-minus peak width at about 4 GPa superposed on a continuous peak broadening with pressure.     

Structural phase transition in Bi2Te3 under high pressure

Structural change in Bi₂Te₃ under high pressure up to 16.6 GPa has been studied by powder x-ray diffraction. We observed two times of phase transitions at room temperature at the pressures of 8 and 14 GPa, respectively. According to our preliminary result on electrical resistance, it is reasonable to suppose that superconducting transition with T _c =2.8 K at the pressures of 10.2 GPa is observed in phase II. On the other hand, we found anomalies of the pressure dependences of lattice parameters and volume at around 2 GPa, which probably means the change in electrical structure on the Fermi surface.