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The solubility of NaCl in water is one of the most important thermo-physical properties. However, the solubility behavior of NaCl in water is poorly understood at high pressure and low temperature. Herein, we performed high pressure neutron diffraction and Raman scattering to investigate the solubility of NaCl in water and the corresponding structural change, respectively. With the pressure increasing, the solubility almost increases linearly below 0.2 GPa, beyond which it starts to level off and reaches its maximum at about 0.61 GPa. The Raman spectra suggested that the deformation of the hydrogen-bonded network in the NaCl aqueous solution promotes the formation of ions pairing and is responsible for the solubility increase of NaCl in water. Finally, we used a two-dimensional Mercedes-Benz model to descript the picture of solubility behavior of NaCl in water at high pressure. [ABSTRACT FROM AUTHOR]

We report experimental determination of compressibility and thermoelasticity for CrN based on in situ high pressure/high temperature synchrotron x-ray diffraction measurements. The pressure-induced cubic-to-orthorhombic phase transition is observed at ∼ 5 GPa in high-quality CrN samples synthesized using a high pressure reaction route. Equation of state, bulk modulus and axial compressibility of this material are obtained by analysis of high pressure x-ray diffraction data collected at room temperature. Both cubic and orthorhombic phases have a similar bulk modulus value of 257 (5) and 262 (6) GPa, respectively. For orthorhombic CrN, the b-axis has the most axial incompressibility, which should be associated with magnetic properties. In addition, the isothermal equation of states is also determined at different temperatures of 300, 400, 600, 800, 1000, and 1200 K, respectively. Some of the important thermoelastic properties of cubic CrN are thus derived, including temperature derivative of bulk modulus ∂ K T / ∂ T = − 2.95 (5) × 10 − 2 G P a ⋅ K − 1 and volumetric thermal expansivity a T ≈ a 0 + a 1 ⋅ T where a0 = 1.95 (16)×10−5 K−1 and a1 = 4.39 (3)×10−9 K−1. [ABSTRACT FROM AUTHOR]

We analyzed the compression process of the centrally caved Bridgman-anvil cell by a simplified mechanics model and proposed that the pressure limitation for a given configuration is governed by the compressibility and compression ratios (V0/V) of the gasket and sample. Then we replaced the middle part of the sample that is prone to undergo plastic deformation with a diamond plate, which will obviously change the stress state of the sample and gasket. The results of ex situ and in situ pressure testing experiments show that this way doubles the efficiency of the pressure generation and largely expands the pressure limitation. The pressure of sample Ni can reach 29.4 GPa in the double toroidal sintered-diamond anvil cell with a sample volume of 17 mm3 even at the loading force of 1500 kN. [ABSTRACT FROM AUTHOR]

The thermal insulation performance of cubic ZrO2-CaO solid solution (CSZ) (16 mol % CaO) and monoclinic ZrO2 (MZ) was investigated in a two-stage multi-anvil press under a pressure of 10 GPa and temperatures up to 1800°C through in situ temperature measurements with the same cell assembly. The results show that the cell temperatures with CSZ as the thermal insulator were always higher than that when thermal insulator was MZ at the same heating power, and the maximum deviation value was 600°C (50% higher) within the measurable range. These two materials were analyzed using X-ray diffraction (XRD), thermal conductivity measurement and scanning electron microscopy. It revealed that the point defects existed in CSZ dominated the thermal insulation performance at high pressure, the same as what at normal pressure. It was also found that the heating process was more controllable when using CSZ as thermal insulator under high pressure. [ABSTRACT FROM AUTHOR]

Magnesium oxide (MgO) doped with cobalt (Co) semi-sintered pressure-transmitting medium (MCOPM) was prepared at 1200°C in air, starting with a pre-compressed mixture of MgO and cobalt oxide (CoO). The samples were characterized using powder X-ray diffraction, scanning electron microscopy, and thermal conductivity measurements. The results demonstrate that during the sintering process, the exchange of metal ions between the mixture powders introduced lattice defects into the MgO lattice structure, and an MgO-CoO solid solution was formed. Compared to commercial semi-sintered MgO pressure-transmitting medium (SSMPM), the temperature-generation efficiency of MCOPM-17 (MgO + 17 mol% CoO) improved by about 220% at the high pressure of 12 GPa with a cell assembly in a two-stage multi-anvil large volume press. Moreover, the thermal conductivity of CoO-doped MgO decreased with increasing CoO doping. [ABSTRACT FROM AUTHOR]

As a new member in the family of Mott system, perovskite PbCrO3 has recently been uncovered to exhibit fantastic structural transition under pressure, coupled with magnetic, electronic, and ferromagnetic transitions, which provide many opportunities for understanding of correlated system. However, it is still challenging to synthesize high-quality single-crystal PbCrO3, leading to the limited exploration of this Mott compound. In this work, we formulate a new high-pressure reaction route for preparation of high-quality PbCrO3 crystals between PbCl2 and Na2CrO4 at high pressure of 5-10 GPa and at high temperature of 750-1500°C. Because of the formation of reaction byproduct NaCl, the final product can readily be separated by washing with water. The obtained sample is in the form of single crystal with crystallite size up to 200 μm. In addition, combined with X-ray diffraction measurement, a tentative pressure-temperature synthesis diagram of PbCrO3 is mapped out from the reaction between PbCl2 and Na2CrO4 and the reaction mechanism is also explored in detail. [ABSTRACT FROM AUTHOR]

We report the combined experimental and theoretical investigations on high pressure structural stability of niobium carbide (NbC). The compressibility of NbC has been measured using angle-dispersive synchrotron X-ray diffraction in a diamond anvil cell (DAC) at room temperature and high pressure (up to 38.0 GPa), complemented with first-principles density-function theory calculations. The results imply that NbC shows bulk modulus of = 281 (6) GPa with a pressure derivative = 6.2 (1.5) for its strong covalent bonding. In addition, indentation testing on the well-sintered bulk NbC obtained at 5.0 GPa/1400°C yielded a Vickers hardness of 19.2 GPa and fracture toughness of 7.7 MPa m1/2at applied load of 10 kgf, demonstrating that binderless NbC prepared under high pressure should be a prospective hard material. [ABSTRACT FROM PUBLISHER]

In this paper, two average tungsten carbide particle sizes of 2, 0.5 μm are placed respectively, in contact with a WC-16Co substrate, pressed at the pressure of 4.5–5.5 GPa, and heated to temperatures ranging from 1350°C to 1500°C in a large-volume cubic press. During the process Co was forced out of the WC-16Co substrate into the compressed powder. The resulting infiltrated samples were characterized using X-ray diffraction (XRD), scanning electron microscope (SEM), Vickers hardness and cutting performance tests. The results of XRD confirmed that the sintered bulks have WC and Co phases. The scanning electron microscopy (SEM) analysis reveals that the WC grains in well-sintered alloys are round in shape and cobalt with lower content is uniformly dispersed in the WC grain boundaries. The sintered sub-micron WC-Co alloy with a cobalt content of 3.8 wt% exhibits a prominent combination of high hardness value of 23.1 GPa and a large fracture toughness value of 8.6 MPa m½. The high-speed cutting tests indicating its cutting performance is significantly superior to the commercial YG6X (WC-6 wt%Co with WC grain size of 0.5 μm). [ABSTRACT FROM AUTHOR]

The diamond thick layers prepared using chemical vapor deposition (CVD) methods have been treated at high pressures and high temperatures (HP-HT). It was found that the Vickers hardness of the HP-HT treated bulks was nearly two times as high as that of the starting CVD diamond samples. The hardness of the samples treated at 8 GPa and 1800°C is ∼80 GPa at a loading force of 49 N, close to that of the single-crystal diamond (∼100 GPa). In addition, the oxidation resistance of CVD diamond samples was also enhanced greatly after HP-HT treatments, and the diamondization of sp2bonded carbon in the CVD diamond samples could occur at 7–8 GPa and 1600–1800°C. The HP-HT conditions of diamondization in our works are much lower than the case of the graphite-to-diamond direct transformation without the presence of catalyst (>15 GPa and 2000°C). [ABSTRACT FROM PUBLISHER]

Spherical iron nitride (ϵ-Fe3N) of 4 mm in diameter was synthesized by a high pressure solid-state metathesis reaction between alkaline or alkaline-earth metal ferrite (NaFeO2, MgFe2O4, and Ca2Fe2O5) and boron nitride. The Fe/N atomic ratio of the obtained crystals is close to 3:1 by means of energy-dispersive X-ray analysis, X-ray photoelectron spectroscopy, and chemical reaction analysis. Bulk modulusB0= 154(2) GPa with a fixed pressure derivativeis determined by high pressure synchrotron axial X-ray diffraction measurement. ϵ-Fe3N is thermally stable in the air below 500°C byin situhigh-temperature Raman spectroscopy. Vickers hardness tests show that theHvis 5.9 GPa with a load of 5 N, and vibrating sample magnetometer measurements show that saturation magnetization (σs) is 88.53 emu/g and coercivity value (Hc) is 466.67 Oe. [ABSTRACT FROM PUBLISHER]

The pressure transmitting medium (PTM)-dependent structure stability of ∼12 nm nanoanatase TiO2under high pressure has been investigated usingin situsynchrotron X-ray powder diffraction techniques at room temperature. We found that the starting anatase phase (I41/amd) transforms into the monoclinic baddeleyite phase (P21/c) regardless of embedded in PTM or not. However, the beginning and ending pressure for the transformation under quasihydrostatic compression is found to be ∼7 GPa higher than that of under nonhydrostatic compression, and amorphization of sample occurs more easily during the former condition. This result indicates that the interface energy between the PTM and nanoparticles undoubtedly modifies the phase stability during high pressure experiments. [ABSTRACT FROM PUBLISHER]

The equation of state and compression behavior of lithium fluoride, LiF, have been determined to 92 GPa by X-ray diffraction in a diamond anvil cell. A neon pressure-transmitting medium was used to minimize the effect of differential stress on the sample. Consistent results using multiple pressure standards were obtained. By fitting the pressure–volume data to a Birch–Murnaghan equation of state, the isothermal bulk modulus and its corresponding pressure derivative at zero pressure were determined to beK0=70.1±0.7 GPa, andK′0=4.3±0.1. If the bulk modulus is fixed at 66.2 GPa, a value well constrained by independent elasticity measurements, we obtainK′0=4.6±0.1. The bulk modulus and its pressure derivative obtained from this work resolve the large discrepancy in previously reported values ofK0andK′0for this material. Consequently, the equation of state of LiF is now sufficiently well constrained to allow its use as a pressure calibrant in high pressure experiments. [ABSTRACT FROM AUTHOR]

Nanophase materials have novel physical and chemical properties, differing from bulk materials. It is of exceptional interest to investigate the size effect on structural stability in nanocrystals. Here, we investigated pressure-induced phase transitions in nanosized Er2O3using angle-dispersive synchrotron X-ray diffraction up to 40.6 GPa. Nano-Er2O3has enhanced transition pressure and higher bulk modulus (K0) than its bulk counterparts. Amorphous Er2O3nanoclusters with traces of monoclinic phase are obtained upon compression. This is the first time that partial amorphous structure under compression was observed in nano-Er2O3, indicating a kinetic trapping of partial amorphous Er2O3on pressurizing. [ABSTRACT FROM AUTHOR]

High pressure and high temperature synthesized MoB2and WB2compacts were investigated using X-ray diffraction, energy dispersive spectroscope, scanning electron microscope, Vickers indentation test and ultrasonic measurements. Experiments showed that both MoB2and WB2compacts are phase pure and with a grain size of 100–200 nm. Vickers indentation test under a large loading force of 49 N showed that the Vickers hardness of MoB2and WB2are about 21 and 22 GPa, respectively. The bulk modulus and shear modulus are about 296 GPa, and 190 GPa for MoB2and 349 and 200 GPa for WB2through ultrasonic measurements. Our results indicate that MoB2and WB2are both hard materials with a hardness similar to that of tungsten carbide, which is widely used in industry. [ABSTRACT FROM PUBLISHER]

A new method is introduced for investigating the compressibility of solids under high pressure by in situ electrical resistance measurement of a manganin wire, which is wrapped around the sample. This method does not rely on the lattice parameters measurement, and the continuous volume change of the sample versus pressure can be obtained. Therefore, it is convenient to look at the compressibility of solids, especially for the X-ray diffraction amorphous materials. The I–II and II–III phase transition of Bi accompanying with volume change of 4.5% and 3.5% has been detected using the method, respectively, while the volume change for the phase transition of Tl occurring at 3.67 GPa is determined as 0.5%. The fit of the third-order Birch–Murnaghan equation of state to our data yields a zero-pressure bulk modulus K 0=28.98±0.03 GPa for NaCl and 6.97±0.02 GPa for amorphous red phosphorus. [ABSTRACT FROM AUTHOR]

A hybrid pressure cell of pyrophyllite and magnesium oxide (HPCPM) used in large volume cubic presses is presented. In the HPCPM, a cubic frame which is made of pyrophyllite with face-centered square holes works as gaskets, and a heteromorphosis magnesium oxide works as the pressure-transmitting medium. Our experimental results indicated that the pressure-generation efficiency using the HPCPM was improved by about 40% than that using the traditional pyrophyllite pressure cell without decreasing the anvil truncation size (without sacrificing the sample volume). The HPCPM could pressurize samples of 1000 mm3 volume up to about 8 GPa, which is significantly higher than that available using the traditional pressure cell, which reports a highest pressure of about 6 GPa. [ABSTRACT FROM AUTHOR]

In this study, pure-phase Cd7P10 crystals are prepared by the reaction of elements at high pressures in a large-volume cubic press. The synthetic Cd7P10 samples are characterized by powder X-ray diffraction, scanning electron microscopy and diamond indentation method. The results show that orthorhombic Cd7P10 grains with a size of over 70 μm could be obtained and that the high pressure well-sintered Cd7P10 compacts have a Vickers hardness value of 8.9 GPa under a load of 49 N. The pressure–temperature formation region of Cd7P10 is determined up to 5 GPa and 1500°C, and the formative mechanism under high pressures is discussed. Our results exhibit a novel route for synthesizing bulk semiconductor polystalline Cd7P10 compacts. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Quantitative measurements of pressure gradients have been made in the pyrophyllite and magnesium oxide (MgO) pressure-transmitting mediums using large-volume cubic apparatus. The relationships of pressure gradients along the axis of symmetry of the pyrophyllite and MgO cubes versus corresponding cell pressures have been established at room temperature. Our experimental results indicated that the pressure gradients increase as the cell pressure increases and that the pressure gradient in the MgO pressure-transmitting medium is about twice as high as that in the pyrophyllite pressure-transmitting medium at the same cell pressure. When the cell pressure reaches 5.5 GPa, the pressure gradient along the axis of symmetry of the pyrophyllite cube is about 50 MPa/mm. When the cell pressure reaches 7.7 GPa, the pressure gradient along the axis of symmetry of the MgO cube is about 140 MPa/mm. The experimental data obtained in the present work not only adapt to the cubic apparatus but also provide reference for the tetrahedral press and the double-stage multi-anvil apparatus (the octahedral compression). [ABSTRACT FROM PUBLISHER]

Diamond anvil cell synchrotron X-ray diffraction (XRD) experiments have been carried out on submicron-sized tungsten tetraboride (WB4) at room temperature up to 50.8 GPa with a silicone oil pressure medium. The crystal structure of WB4 remains unchanged up to the highest pressure. The isothermal bulk modulus K0 and its pressure derivative, [image omitted] , have been determined from the present compression by fitting the third-order Birch-Murnaghan equation of state: K0=325±9 GPa and [image omitted] . The high value of the bulk modulus shows that WB4 has high stiffness and/or low-compressibility. Moreover, we also found that the compression behavior of the unit cell axes (a- and c-axes) of WB4 demonstrates an anisotropic nature of compressibility. [ABSTRACT FROM AUTHOR]

Cell pressures in the cubic press have been determined by means of differential thermal analysis (DTA) based on the known fusion curve of aluminum. The results compared favorably with those of the well-known fixed-point method, based on pressure-induced phase transitions in bismuth (I-II, 2.55 GPa) and thallium (II-III, 3.68 GPa). The high-pressure fusion curve of lead was measured using our calibrated results, which agreed well with those of the previous work. All of this was made possible by the development of a successful cell assembly for the DTA analyses in the cubic press. Details of the design are described in the present work. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]