Elastic and plastic deformation of NaCl and Ni3Al polycrystals during compression in a multi-anvil apparatus

Abstract

The compression behaviour in a multi-anvil apparatus of pure NaCl and of a foil of Ni₃Al embedded in a pressure medium of NaCl has been studied by energy-dispersive X-ray diffraction. At ambient temperature, the pressure and stresses, determined from line positions of NaCl, were constant throughout the sample chamber. Line positions and line widths of NaCl reflections were reversible on pressure release. A saturation of microstrains observed in NaCl at 2 GPa is thus attributed to brittle fracture setting in at uniaxial stresses of around 0.3 GPa. Ni₃Al polycrystals, in contrast, undergo extensive (ductile) plastic deformation above 4 GPa. The compression behaviour of both Ni₃Al and NaCl is identical to that previously determined in a diamond anvil cell. While a multi-anvil device thus has the advantage, compared with a diamond anvil cell, of constant pressure and stress throughout the sample chamber, microstrains in poly-crystalline samples arise in both devices. Samples in a multi-anvil apparatus thus need to be mixed with a pressure medium and to consist of essentially single crystals just as in a diamond anvil cell. Annealing experiments at high pressures confirm that the release of the uniaxial stress component in the pressure medium does not cause a release of microstrains in the embedded sample if the latter has been plastically deformed. Annealing for the purpose of attaining hydrostatic conditions in compression studies thus has to be carried out with care.     

Effects of pressure on the structure and the thermal decomposition kinetics of RDX

Abstract

High pressure and temperature structural changes for RDX were investigated to 7.0 GPa and 570 K in a diamond anvil cell apparatus using FTIR absorption, optical microscopy, and energy-dispersive powder x-ray diffraction techniques. Three distinct solid phases were observed. The effects of pressure on the thermal decomposition kinetics as a function of RDX pressure were investigated using an infrared absorption technique. Solid phase I was found to have a pressure enhanced reaction rate with an energy and volume of activation of 51 Kcal/mole and -5.6 cc/mole respectively. Solid II was not observed to react and the observed reaction rate of Solid III decreased with increasing pressure.     

High pressure generation in the Kawai-type multianvil apparatus equipped with sintered diamond anvils

ABSTRACT

Generation of high pressure is a key to the investigation of the interior of the Earth. The Kawai-type multianvil apparatus (KMA) has been widely used in the fields of Earth science and material science. In conventional KMA, tungsten carbide (WC) has been used as the second stage anvil material. However, attainable pressure is limited to ～70?GPa even if newly developed WC is used. Recently, on the other hand, second stage anvils of sintered diamond that is much harder than WC have enabled us to extend the pressure range of KMA up to 120?GPa, corresponding to the pressure of the D” layer in the Earth’s mantle. It is evident that our development of pressure generation facilitates the investigation of the structure and dynamics of the deep mantle of the Earth.     

Bulk diamond formation from graphite in the presence of C-O-H fluid under high pressure

Abstract

C-O-H fluids have been successfully applied as catalysts for bulk diamond formation under high pressure. New insight into C-O-H fluids extends the understanding of the origin of natural diamond, which is presently of interest in materials and geological sciences. This review presents current literature data concerning the synthesis and characterization of bulk diamond formation assisted by C-O-H fluids at high pressure and high temperature. Based on a general survey of this subject, the pressure-temperature regime for diamonds formed in these fluids was established and the mechanism of conversion from graphite to diamond is discussed. Finally, a few questions are put forward that may be useful for the continued development of this research area.     

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.     

Synthesis experiments on B-Sb,Ge-Sb,and Xe-Pd systems using a laser heated diamond anvil cell

Abstract

In an effort to synthesize B-Sb, Ge-Sb and Xe-Pd compounds under high pressure, the respective system was laser-heated in a diamond anvil cell at temperatures above 2500 K and up to a maximum pressure of 51 GPa. The product was characterized by X-ray diffraction using rotating anode and synchrotron radiation X-ray sources. No reaction was observed in any of these systems up to pressures of 32, 20 and 51 GPa, respectively. In the case of Ge-Sb, new peaks were observed in the pressurequenched samples, but they were identified with the known metastable phases of Ge. In this regard our results are contrary to the earlier work on Ge-Sb.     

High pressures: Recent trends in materials science

Abstract

Pressure was developed during the 20th century. The most important illustration of the use of high pressure in Materials Science was the synthesis of diamond at the beginning of the fifties.

This contribution will describe the main scientific research axis developed these last years and based on high pressure (synthesis of new materials, stabilization of specific structures, crystal-growth, preparation of finely divided materials…).

In parallel some industrial developments will be analyzed.

In conclusion, the potential of high pressure will be sketched for the near future.     

High pressure assisted 1,3-dipolar cycloadditions: Synthesis of silylated triazoles from heteroaryl azides

Abstract

The 1,3-dipolar cycloaddition of 2- and 3-benzothiopheneazide with (trimethyl-sily1)acetylene to yield 1,2,3-triazoles has been studied at pressures up to 1GPa. The kinetics as a function of pressure was followed interfacing a diamond anvil cell to a FTIR spectrometer. Alike with aryl azides, the rate of reaction was found to increase logarithmically with pressure with a yield close to quantitative.     

高温高压下纳米金刚石粉的特性研究

 研究了炸药爆轰合成的纳米金刚石粉在高温（约1 600 K）、高压（5.2 GPa）条件下的行为。将纳米金刚石粉与粉末合金（Ni₇₀Mn₂₅Co₅、100^#）混合、压制成圆片,与合金片 （Ni₇₀Mn₂₅Co₅）和人造石墨片一起交替放入高温高压合成腔体内,进行高温高压实验。实验结果表明：在高温高压条件下,纳米金刚石粉不能长大,反而石墨化了;在相同的高压和保温时间条件下,随着温度的降低,纳米金刚石粉的石墨化程度减弱,纳米金刚石粉的纳米颗粒长大,可长成0.1 mm尺寸的金刚石颗粒（温度为1 070 K左右）。而在此条件下,人造石墨不能合成金刚石,一般金刚石晶体要变成石墨相。这进一步表明,纳米金刚石颗粒表面的活性使得它可以在较低的温度下长成较大颗粒的金刚石。     

Melting behaviors of carbon underhigh pressures

Abstract

The melting behaviors of graphite and diamond were investigated at pressures up to 25 GPa using flash-heating method. By rapid heating, the metastable graphite was melted in the diamond stable P-T field, competing with its conversion to diamond in the rate of reaction. For the diamond the pressure dependence of inserted energy required to reach the molten state suggested that the melting temperature of diamond increases with pressure.     

Diamond Composites with TiC,SiC and Ti 3 SiC 2 Bonding Phase

The problems connected with producing diamond composites with 30 wt.% of bonding phase in form of: SiC, TiC, and Ti 3 SiC 2 are presented in the paper. Increasing the fraction of the bonding phase within the composite generally helps to reduce internal stresses. Composites were sintered at pressure 8.0 - 0.2 GPa and temperature of 2070 - 50 K using the Bridgman type high pressure apparatus. Interactions in the diamond-SiC, the diamond-TiC, and the diamond-Ti 3 SiC 2 systems were studied by means of transmission electron microscope (TEM) and X-ray diffraction. Density was measured pycnometrically. The wear resistance studies of these composites were carried out using pin - on disc type laboratory equipment. Hardness was measured with Vickers apparatus. Results of measurements of physical and mechanical properties are reported.     

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     

Melting of B12P2 boron subphosphide under pressure

Melting of boron subphosphide (B₁₂P₂) to 26?GPa has been studied by in situ synchrotron X-ray powder diffraction in a laser-heated diamond anvil cell, and by quenching and electrical resistance measurements in a toroid-type high pressure apparatus. B₁₂P₂ melts congruently, and the melting curve has a positive slope of 23(6)?K/GPa. No solid-state phase transition was observed up to the melting in the whole pressure range under study.     

Exploiting optical properties of nanopolycrystalline diamond in high pressure experiments

ABSTRACT

We investigated the optical properties (absorption, luminescence and Raman spectra) of nanopolycrystalline diamond (NPD) aiming at exploring its capabilities as a pressure sensor and as a pressure-cell anvil for combined X-ray/neutron and optical studies. Notably, we analysed the Raman peak shift and broadening with pressure using a Moissanite Anvil Cell (MAC). The results are compared with those obtained in a DAC, where Raman signals from NPD chips and diamond anvils strongly overlap. Its pressure behaviour in the hydrostatic and non-hydrostatic regimes were investigated. We showed that the nanopolycrystalline structure induces remarkable differences in the peak shift and broadening between NPD and natural type IIa single-crystal diamond, making NPD suitable as pressure gauge for pressure determination and testing hydrostaticity of pressure transmitting medium.     

Single crystal EXAFS at high pressure

Abstract

We present a new technique for structure characterization under high pressure conditions. The use of an undulator beam of the third-generation ESRF source of synchrotron radiation has enabled the first single crystal EXAFS experiments at high pressure using a diamond anvil cell as pressure generator. Taking advantage of the linear polarization of X-rays the technique becomes an orientation-selective probe of the local structure of materials. We describe the principle of the technique and some applications.     

Nano-polycrystalline diamond synthesized through the decomposition of stearic acid

ABSTRACT

Here we report a novel route for synthesizing nano-polycrystalline diamond (NPD) using stearic acid (C₁₈H₃₆O₂) as a starting material under high pressure and high temperature. The obtained NPD shows a transparent dark-yellowish color similar to the standard NPD synthesized from graphite and consists of extremely fine diamond grains (～10?nm). The temperature required for the present synthesis of pure transparent NPD is as low as 1000°C at 13 and 17?GPa, which is surprisingly lower than that for conventional NPD synthesis (1800–2000°C). The amorphous-like, extremely poorly crystalline graphite produced by the thermal decomposition of stearic acid likely provides preferential nucleation sites for diamond and significantly lower the activation energy. The removal of volatile components such as H₂O generated through the decomposition from the system is a key to obtain pore-free transparent NPD. Magnesite, MgCO₃ and periclase, MgO can be used as an efficient H₂O remover through the hydration reaction.     

Growth of gem-grade nitrogen-doped diamond crystals heavily doped with the addition of Ba（N3）2

Additive Ba(N 3) 2 as a source of nitrogen is heavily doped into the graphite-Fe-based alloy system to grow nitrogendoped diamond crystals under a relatively high pressure (about 6.0 GPa) by employing the temperature gradient method.Gem-grade diamond crystal with a size of around 5 mm and a nitrogen concentration of about 1173 ppm is successfully synthesised for the first time under high pressure and high temperature in a China-type cubic anvil highpressure apparatus.The growth habit of diamond crystal under the environment with high degree of nitrogen doping is investigated.It is found that the morphologies of heavily nitrogen-doped diamond crystals are all of octahedral shape dominated by {111} facets.The effects of temperature and duration on nitrogen concentration and form are explored by infrared absorption spectra.The results indicate that nitrogen impurity is present in diamond predominantly in the dispersed form accompanied by aggregated form,and the aggregated nitrogen concentration in diamond increases with temperature and duration.In addition,it is indicated that nitrogen donors are more easily incorporated into growing crystals at higher temperature.Strains in nitrogen-doped diamond crystal are characterized by micro-Raman spectroscopy.Measurement results demonstrate that the undoped diamond crystals exhibit the compressive stress,whereas diamond crystals heavily doped with the addition of Ba(N 3) 2 display the tensile stress.     

Volume compression of thallium to 45 GPa

Abstract

High-pressure structural transition and volume compression for thallium were investigated to 45 GPa in a diamond anvil cell using the angular dispersive X-ray diffraction technique. Except for the known polymorphic transition at 3.7 GPa, no other structural change was observed in this pressure range. The equation of state of the high pressure phase has been obtained: its initial bulk modulus, B₀ = 33.1 GPa, is lower by 10% than that of the hexagonal phase at normal pressure.