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     

超高压装置中的封垫问题

 本文就年轮型高压装置,对福长修的平板模型作了改进,即在式中引入了压砧的半顶角θ,计算了封垫中的压力及封垫对于压砧的支撑力,计算结果基本上和实验结果符合。就年轮型及立方六面顶型高压装置讨论了高压室和封垫的压力增量之间的匹配问题,还就卸压问题介绍了Murnaghan方程的应用。     

不同加载压力下平面对顶砧间叶蜡石封垫力学状态的演变

以Wakatsuki提出的恒定加载压力下封垫的压缩模型为基础,采用直径20mm的硬质合金平面对顶压砧,测量了不同外部加载压力下叶蜡石封垫的临界厚度、弹性区半径以及回弹率等数据;结合对中心压力的标定,以及对回收封垫的图像处理分析和相关计算,给出了封垫内弹性区和塑性区的压力分布随外加压力变化的规律,并估算了准静水压区范围。实验表明:平面对顶压砧间封垫塑性区内的剪切强度随压力提高而增加,中心的压力随外加压力的提高而增加,其增加的比率具有逐渐上升的特点。     

滑块式六含八超高压实验装置及其压力温度标定

报道了一种新型六含八超高压实验装置.三柱式的机体框架与滑块式上三下三模具同为三次对称结构,在力学上较为合理.该装置加压时具有自动校准位置能力,同步性和重复性好.模具推动八块硬质合金压砧在叶腊石八面体中产生高压.分别采用Bi丝和ZnTe晶体的压致相变点255,77,96,12 GPa,对截角边长8 mm压砧和125 mm边长叶腊石块组合的实验体系进行了室温下的压力标定,结果表明压力可达12 GPa以上.在10 GPa压力下,用WRe3-WRe25热电偶将温度标定到1560 ℃,并结合铁碳二元相图和钢 关键词： 压力标定 温度标定 六含八多压砧模具 高压装置     

用于高压原位中子衍射的PCBN压腔

基于多晶立方氮化硼(PCBN)的高硬度以及对中子良好的吸收性,选用PCBN作为压砧材料,设计了一种新型外凹式平面压砧以及由钛锆合金、碳纤维管、聚四氟乙烯组成的复合封垫。使用该PCBN压腔,分别利用ZnTe和ZrW2O8的相变点对腔体压力进行标定。结果表明:当样品腔体积为9mm3、负载压力为260kN时,腔内压力达到9GPa。高压原位中子衍射实验显示,采用外凹式PCBN压腔得到了无压砧背底信号的铁的高压中子衍射谱。预计通过进一步优化,利用PCBN压腔可获得更高压力(10GPa以上)下高质量高压中子衍射谱。     

高压下锗化镁的金属化相变研究

锗化镁是一种窄带半导体,压力作用可以使锗化镁导带底与价带顶的能隙变小.本文基于第一性原理计算了锗化镁在高压下的能带结构以及反萤石相(常压稳定相)和反氯铅矿相(高压相)的焓值,发现在7.5 GPa时反萤石结构锗化镁导带底与价带顶的能隙闭合,预示着半导体相转变为金属相,计算结果还预测在11.0 GPa时锗化镁发生从反萤石结构到反氯铅矿结构的相变.实验研究方面,本文采用长条形压砧在连续加压条件下测量了锗化镁高压下的电阻变化,采用金刚石对顶压砧测量了锗化镁的高压原位拉曼光谱,发现在8.7 GPa锗化镁的电阻出现不连续变化,9.8 GPa以上锗化镁的拉曼振动峰消失.由于金属相的自由电子浓度高会阻碍激发光进入样品,进而引起拉曼振动峰消失,因此我们推测锗化镁在9.8 GPa转变为金属相.     

基于集成技术的金刚石对顶砧原位电学量测量

 金刚石对顶砧是应用最多的高压装置,能够产生超过400 GPa的超高压力,借助激光加温,还可以加载6 000 K的高温。近20年来,基于金刚石对顶砧的微小测量电路集成技术的突破,带动了高压原位电学量测量技术的发展,使常压下能够测量的电学量大部分都能在金刚石对顶砧中的高压环境下实现。全面回顾了基于集成技术的金刚石对顶砧高压原位电学量测量技术的发展历程,介绍了最新的技术进展。     

Bridgman压砧上叶蜡石封垫预烧工艺与内加热方式的改进北大核心CSCD

在Bridgman压砧上研究了不同预烧工艺对叶蜡石封垫高压性能的影响,发现提高焙烧温度有助于提高叶蜡石封垫的临界厚度和中心弹性区面积,能有效扩大样品腔尺寸,并对高温焙烧(最高900℃)的叶蜡石封垫进行了压力标定。在此基础上,对叶蜡石封垫的内加热组装方式进行了改进,并在常压和高压下分别测试了新组装方式的加热性能,实现了4.0GPa高压下1 300℃温度范围内的加热。这些实验工作为进一步开展在Bridgman压砧上制备大尺寸亚稳材料提供了实验条件。     

二级6-8型静高压装置厘米级腔体的设计原理与实验研究

利用大腔体静高压装置的实验数据,提出了"极限压缩体积比"的概念以及腔体与组装设计的一般性原理。通过对极限压缩体积比的分析,设计出了样品腔体达到厘米级的36/20(正八面体传压介质边长为36mm/末级压砧正三角形截角边长为20mm)组装。采用原位电阻观测Bi(Ⅲ-Ⅴ,7.7GPa),ZnTe(Ⅰ-Ⅱ,5GPa;Ⅱ-Ⅲ,8.9~9.5GPa;半导体-金属,11.5~13.0GPa)和ZnS(半导体-金属,15.6GPa)在高压下相变的方法,标定了36/20组装的腔体压力。实验结果表明所设计样品腔的尺寸大于10mm,压力可以达到15GPa以上。本工作使得基于国产6×2 500t(吨)铰链式六面顶压机的二级6-8型静高压装置在高压实验研究中具有更加广阔的应用前景。     

1 000 t Walker型高温高压装置的使用与压力标定

 介绍了一种6-8型二级加压装置——1 000 t Walker型大腔体高温高压装置中样品的组装方式、组装件材料和压力标定方法。采用碳化钨作为压砧时,获得的最高压力超过20 GPa。压力标定方法采用相变点法,即利用Bi、Tl、ZnTe、Pb、SnS、GaAs等标准压力标定物质,通过测量其在室温高压下的电阻变化,确定相变点,进而获得高压腔体内的压力与外加载荷的关系。对具有不同二级压砧截角边长（4、6、8、12 mm）组装的内部实际压力进行标定,得到了外加载荷与内部压力的关系曲线,为今后在该装置上的实验样品组装及样品实际压力确定提供了准确的数据。     

Pressure generation to 50 GPa in Kawai-type multianvil apparatus using newly developed tungsten carbide anvils

A pressure generation test for Kawai-type multianvil apparatus (KMA) has been made using second-stage anvils of a newly developed ultra-hard tungsten carbide composite. Superb performance of the new anvil with significantly less plastic deformation was confirmed as compared to those commonly used for the KMA experiments. A maximum pressure of ～48?GPa was achieved using the new anvils with a truncation edge length (TEL) of 1.5?mm, based on in situ X-ray diffraction measurements. Further optimization of materials and sizes of the pressure medium/gasket should lead to pressures even higher than 50?GPa in KMA using this novel tungsten carbide composite, which may also be used for expansion of the pressure ranges in other types of high pressure apparatus operated in large volume press.     

A portable high-pressure stress cell based on the V7 Paris–Edinburgh apparatus

We describe a new device, based on a V7 Paris–Edinburgh press, for torsional testing of material at pressures up to 7 GPa (extendable to 15 GPa). Samples are deformed using a simple shear geometry between opposed anvils by rotating the lower anvil, via a rotational actuator, with respect to an upper, stationary, anvil. Use of conical anvil profiles greatly increases sample dimensions more than other high-pressure torsional apparatus did. Samples of polycrystalline Zr (2 mm thick, 3.5 mm diameter) have been sheared at strains exceeding γ ～1.5 at constant strain rate and at pressures from 1.8 to 5 GPa, and textural development has been studied by electron microscopy. Use of amorphous-boron-epoxy gaskets means that nearly simple shear of samples can be routinely achieved. This apparatus allows study of the plastic and anelastic behaviour of materials under high pressure, and is particularly suited for performing in situ investigations using synchrotron or neutron radiation.     

The numerical modelling of the stress-strained state of diamond anvil cell components

Abstract

The method of numerical modelling of the behaviour of main components (anvils and deformable gasket) in diamond anvil cells (DAC) in the process of pressure generation has been developed and realized in the form of programs packages. The optimization of the geometry and loading conditions for an anvil was conducted in line with the multilevel factor plan of major effects (MFPME). A combination of optimizing factors allowing to obtain the theoretically predicted pressure of 465 GPa has been found, the value that by 2.7 times higher than that obtained on anvils at an analogous external pressure distribution [1] and the same diamond strength.

FEM     

New anvil designs in diamond-cells

New diamond anvils with conical support are introduced. Compared to conventional anvils the new design offers superior alignment stability, larger aperture, and reduced cost owing to significantly smaller anvil diameters. Except for table and culet, all surfaces are precision ground on a lathe, which lowers cost compared to faceted anvils. The conical design allows for steel supports, which are significantly easier and cheaper to manufacture than tungsten carbide supports. Conical support also prevents seat damage upon diamond failure. An additional new feature of the anvils is the roughened outer portion of the culet, which increases friction between the anvils and the gasket. This increases the height to diameter ratio of the pressure cell and prevents bonding between gasket and diamond, which causes ring cracks during pressure release. This technique replaces complicated diamond coating procedures. The anvils have been extensively tested for culets ranging from 0.1 to 1 mm diameter up to megabar pressures. A new anvil shape with cup-shaped culets to further increase the cell volume and gasket stability is also introduced.     

High pressure studies using two-stage diamond micro-anvils grown by chemical vapor deposition

Ultra-high static pressures have been achieved in the laboratory using a two-stage micro-ball nanodiamond anvils as well as a two-stage micro-paired diamond anvils machined using a focused ion-beam system. The two-stage diamond anvils’ designs implemented thus far suffer from a limitation of one diamond anvil sliding past another anvil at extreme conditions. We describe a new method of fabricating two-stage diamond micro-anvils using a tungsten mask on a standard diamond anvil followed by microwave plasma chemical vapor deposition (CVD) homoepitaxial diamond growth. A prototype two-stage diamond anvil with 300?µm culet and with a CVD diamond second stage of 50?µm in diameter was fabricated. We have carried out preliminary high pressure X-ray diffraction studies on a sample of rare-earth metal lutetium sample with a copper pressure standard to 86?GPa. The micro-anvil grown by CVD remained intact during indentation of gasket as well as on decompression from the highest pressure of 86?GPa.     

Toroidal anvils for single-crystal neutron studies

The standard design of single-toroid anvil and gasket used in Paris-Edinburgh cells has been modified to achieve greater angular access for neutron scattering. These anvils have potential uses for single-crystal studies and phonon measurements at high pressure. To date, they have been used successfully to 8 GPa.     

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.