Toroidal Anvil Research Articles

Performance of ceramic anvils for high pressure neutron scattering

Three kinds of ceramics, zirconia-toughened alumina (ZTA), alumina-toughened zirconia (ATZ) and yttria-stabilized zirconia (YSZ), were tested as anvil materials, mainly for the purpose of neutron scattering study under high pressure. ZTA with non-toroidal anvil profile, having the same sample volume as conventionally used double toroidal anvils, sustained pressures up to 11.9 GPa. This is comparable to anvils made of tungsten carbide (TC) with Ni binder with the same dimensions. ATZ would also be an alternative material to TC with pressure performance comparable to ZTA, whereas YSZ is much weaker than the other two ceramics. The attenuation coefficient for YSZ is significantly smaller than that of TC and similar to ZTA and ATZ, the latter being estimated by attenuation calculations. Neutron diffraction on a sample of lead in YSZ anvils as well as quasi-elastic neutron scattering on liquid water in ZTA also demonstrate the outstanding neutron transparency of these ceramics. The gain factor in count rate is up to one order of magnitude.

Density-driven structural transformations in network forming glasses: a high-pressure neutron diffraction study of GeO2 glass up to 17.5 GPa

The structure of GeO2 glass was investigated at pressures up to 17.5(5) GPa using in situ time-of-flight neutron diffraction with a Paris–Edinburgh press employing sintered diamond anvils. A new methodology and data correction procedure were developed, enabling a reliable measurement of structure factors that are largely free from diamond Bragg peaks. Calibration curves, which are important for neutron diffraction work on disordered materials, were constructed for pressure as a function of applied load for both single and double toroid anvil geometries. The diffraction data are compared to new molecular-dynamics simulations made using transferrable interaction potentials that include dipole-polarization effects. The results, when taken together with those from other experimental methods, are consistent with four densification mechanisms. The first, at pressures up to ≃ 5 GPa, is associated with a reorganization of GeO4 units. The second, extending over the range from ≃ 5 to 10 GPa, corresponds to a regime where GeO4 units are replaced predominantly by GeO5 units. In the third, as the pressure increases beyond ∼10 GPa, appreciable concentrations of GeO6 units begin to form and there is a decrease in the rate of change of the intermediate-range order as measured by the pressure dependence of the position of the first sharp diffraction peak. In the fourth, at about 30 GPa, the transformation to a predominantly octahedral glass is achieved and further densification proceeds via compression of the Ge–O bonds. The observed changes in the measured diffraction patterns for GeO2 occur at similar dimensionless number densities to those found for SiO2, indicating similar densification mechanisms for both glasses. This implies a regime from about 15 to 24 GPa where SiO4 units are replaced predominantly by SiO5 units, and a regime beyond ∼24 GPa where appreciable concentrations of SiO6 units begin to form.

An opposed-anvil-type apparatus with an optical window and a wide-angle aperture for neutron diffraction

We designed new anvil assemblies for acquiring high-quality neutron diffraction data and ruby fluorescence spectra inside a sample chamber. The conical aperture of Ni-binded WC anvils was expanded by a factor of two. A hybrid gasket made of TiZr- and Al-alloy was developed to prevent outward extrusion. A small and optically transparent window of moissanite was introduced to allow for the determination of pressure and hydrostaticity by measurement of ruby fluorescence spectra. High pressure-generation tests that make use of Bi electrical conductivity and ruby pressure markers revealed that pressure could be determined over 10 GPa. In situ synchrotron X-ray diffraction experiments were also carried out using NaCl as the pressure calibrants. The maximum pressure achieved was approximately 13 GPa. The neutron diffraction intensity from the newly generated anvil assemblies was 2.5–3.0 times greater than that using the standard toroidal anvil assemblies used previously.

Technical Performance of High Pressure and High Temperature Processed TiC Ceramic Tools

Non-oxide covalent ceramics such as TiC and TiN display hardness and thermal stability that favor their use as cermet insert for high speed turning operations. The objective of this work was to assess the properties of the TiC combined with W-Mo as binding matrix. The cermet sintering was carried out inside a toroidal anvil type of high pressure device up to 1.0 GPa of pressure and temperatures up to 1800°C. It was found that at 1400°C the Mo reacts with TiC forming Mo2C while at 1800°C the reaction with W forms WC. Moreover, the cermets density reaches 98% of the theoretically calculated value with strength of 942 MPa and Rockwell A hardness of 94. Efficient turning parameters are reported for machining operation using these cermets as tools insert.

Note: Achieving quasi-hydrostatic conditions in large-volume toroidal anvils for neutron scattering to pressures of up to 18 GPa

We present developments that allow neutron-scattering experiments to be performed, with both single-crystal and powder samples, under quasi-hydrostatic conditions to pressures beyond previous limits. Samples of sodium chloride and squaric acid (H(2)C(4)O(4)) have been loaded with argon as the pressure-transmitting medium in encapsulated gaskets redesigned for double-toroidal anvils, using a gas-loading method at ambient temperature. These samples have been compressed up to 18 GPa in a Paris-Edinburgh press, and no evidence of peak broadening in either the single-crystal or the powder experiments was observed.

The large-volume high-pressure facility at GSECARS: A “Swiss-army-knife” approach to synchrotron-based experimental studies

A number of new techniques have been developed at the large-volume press (LVP) high-pressure facility at the GeoSoilEnviroCARS (GSECARS) sector of the advanced photon source (APS). This article describes the 10 MN (1000 T) and 2.5 MN (250 T) hydraulic presses in the insertion device (ID) and bending magnet (BM) beamlines, respectively, with several apparatus and various diffraction and imaging techniques developed since the inception of the facility. Several Kawai-type high-pressure modules, whose second-stage anvils range from 10 mm to 25.4 mm in edge lengths, are used in the hydraulic presses, with pressure ( P) and temperature ( T) capabilities up to 30 GPa and 3000 K. A DIA-type apparatus can be compressed in both presses for studies requiring large sample volumes. A deformation DIA (D-DIA) has been developed to allow controlled deformation studies on both crystalline and glass materials, using monochromatic diffraction and imaging, up to 20 GPa and 1800 K. A high-pressure tomography apparatus is available for conducting tomography studies at high P and T, with a typical spatial resolution of a few micrometers. Toroidal anvil modules provide large 2 θ angles for studies of non-crystalline materials, and a new large D-DIA module is under construction for double-stage megabar pressure generation as well as deformation on large samples with the capability of acoustic emission detection. The flexible design of the monochromator at the BM beamline makes it feasible to switch between monochromatic and white-beam mode during an experiment, ideal for monochromatic imaging studies (e.g., high- P tomography) with energy-dispersive diffraction for pressure measurements. A new angle-dispersive diffraction technique has been developed for high P– T crystallography studies, where a solid-state detector is step-scanned, thereby collecting a large number of angle-dispersive spectra over a wide range of photon energies recorded in the multi-channel analyzer. An ultrasonic interferometer is available and has been used in several high-pressure modules for acoustic velocity measurements. These unique features allow world-wide users to select the best experimental techniques for tackling a wide range of problems relevant to earth and planetary science, materials science, physics, and chemistry. Scientific highlights are provided and future improvements and prospects are discussed.

Pressure distribution in solid samples compressed by toroidal anvils

We report the measurements of the three-dimensional pressure distribution in a sample of NaCl compressed to 6 GPa by apposed anvils with toroidal geometry. The results were obtained by energy-dispersive synchrotron X-ray diffraction using a V4-Paris-Edinburgh (PE) press with sintered diamond anvils and the incident beam directed along the thrust axis. This particular scattering geometry may be useful for other types of diffraction experiments using the PE press at synchrotron sources.

Pressure evolution of resistance in framework structured materials α-ZrMo2O8 and α-HfMo2O8

The ac resistance measurements on the trigonal (α-) phase of ZrMo2O8 and HfMo2O8 carried out up to 5GPa using the toroid anvil apparatus are reported. The ac resistance data in both the materials are found to be strongly frequency dependent and show a transition between two power law regimes with a crossover frequency (ωc) near 1kHz. For both the compounds slope changes and anomalies are observed in the ac resistance data at the structural transition pressures. The activation volumes at room temperature are obtained by analyzing the ac conductance data in terms of the pressure dependent activation volume model. The main conduction mechanism at 12Hz is believed to be the diffusion of oxygens ions, whereas hopping of point defects is responsible for ac conductuance above 33kHz. At 1KHz, a crossover from hopping to diffusion of point defects is observed at the α-δ (monoclinic) phase transition pressure.

Thermoelastic and texture behavior of aluminum at high pressure and high temperature investigated by in situ neutron diffraction

The behavior of aluminum under high pressures and temperatures was investigated by in situ time-of-flight neutron diffraction with a developed Toroidal Anvil Press (TAP-98). The effect of the displacement of the center of diffraction, which is caused by sample movement during compression, is corrected by an additional calibration. Unit-cell dimensions, measured up to P=5.7 GPa and T=900 K, were derived from the refinement results and fitted to the high-temperature Birch–Murnaghan equation of state. With (∂KT/∂P)T fixed at 4, we obtained K0=72.8(±2.4) GPa, (∂KT/∂T)P=−0.04(±0.01) GPa K−1, and αT (K−1)=3.7(±1.6)×10−5+9.7(±3.5)×10−8T. Our data are compared with previous experimental data involving shock wave, static compression, ultrasonic, and thermal-expansion measurements and with theoretical predictions. The results demonstrate that the newly developed high-pressure high-temperature system for in situ neutron diffraction is reliable. It was also found that the crystalline orientation of Al grains became highly preferred when the sample was heated to 900 K at ∼4 GPa.

Preparation, thermal expansion, high pressure and high temperature behavior of Al2(WO4)3

The titled compound Al2(WO4)3 was synthesized by a conventional solid state reaction and characterized by powder XRD. It crystallizes in an orthorhombic (Pbcn, No. 60) lattice, with unit cell parameters as 12.582(2), 9.051(1), 9.128(2) A, and V = 1039.5(3) (A)3. The compound was found to show negative thermal expansion (NTE) behavior in the temperature range of 25 to 850°C. The average linear NTE coefficient (α1), in this temperature range, was −1.5 × 10−6 K−1. The effect of pressure at ambient temperature, was studied by a Bridgman Anvil (BA) apparatus, to reveal that there is no irreversible phase transition up to 8 GPa. The effect of high pressure and high temperature on this compound was studied by a Toroid Anvil (TA) apparatus. This compound has a limited stability under high pressure and temperature, as it undergoes a decomposition to AlWO4 and WO3−x with a partial oxygen loss. As an off-shoot of this work, certain new modifications of WO3−x under pressure and temperature were observed, viz., monoclinic, tetragonal and an orthorhombic modifications at 5 GPa/1400°C, 3 GPa/900°C and 1.8 GPa/1030°C, respectively. The detailed XRD studies of the products are presented here.

Effect of high pressure and temperature on nanocrystalline Fe2O3 and TiO2

Nanocrystalline (n) γ Fe2O3 and n TiO2 (anatase) prepared by gel combustion technique and n TiO2 (rutile) prepared by sol-gel technique were subjected to high pressures and high temperatures in a toroid anvil aparatus. A new polymorph of Fe2O3 belonging to hexagonal system, with a= 10.752Å and c= 17.806Å, was found in the material quenched from 5.2 GPa and 900°C. n TiO2 (anatase) sintered at 5.2 GPa pressure and 700°C temperature transformed to rutile structure, as expected. However, n TiO2 (rutile) did not show any phase changes. At 27°C, n 7 Fe2O3 and n TiO2 (anatase) showed transition to an apparently amorphous state above 8 GPa.

Uniaxial Stress Component in WC Toroidal Anvils under High Pressure and Temperature

The uniaxial stress components (USC), t, have been measured in NaCI samples, under variable pressure and temperature, in tungsten carbide (WC) toroidal anvils by energy dispersive X-ray diffraction under synchrotron radiation in a large volume Paris-Edinburgh cell. It was observed that t increases with load and at p = 4.6 GPa, t = -0.6 GPa (measured from the mean value of the lattice parameter of NaCl). When heating is applied (under load), t decreases, and becomes zero for T > 600 K. On cooling at constant load, t remains negligible (t = 0.01 GPa) down to room temperature. After loading again (p = 3.8 GPa) at room temperature, t remains small (t = -0.07 GPa). A measurement of the FWHM of the diffraction peaks verifies the improvement in hydrostaticity after heating.

Manufacture of gem quality diamonds: a review

Gem quality diamonds have been grown using high temperature, high pressure processes like the solvent catalyst method and the temperature gradient method. This review with 64 references focuses on the thermodynamics, kinetics of the growth processes and the apparatus used to grow diamonds. Gem quality diamonds can be synthesized by the high pressure, high temperature process, either by the solvent catalyst method or the reconstitution technique. The Hall belt apparatus and the toroid anvil are the commonly used equipment to generate high pressures. In the high pressure, high temperature processes a catalyst is essential for synthesis. The commonly used catalysts are Fe, Co and Ni whereas recently hydroxides and carbonates have also been used to synthesize diamond. Surface chemistry plays an important role in determining the quality of the crystal. If the carbon flux to the nucleating diamond exceeds a certain limit, graphite nucleates instead of diamond. Temperature, pressure and impurities like nitrogen and boron also affect the quality and growth rates of the synthesized diamond. High growth rates have also been observed if substantial amount of paramagnetic nitrogen is dispersed in the reaction bath. Recent developments of growing diamond by chemical vapour deposition techniques like microwave plasma and hot filament technique have been reviewed. Non-destructive, optical methods to characterize diamonds have been briefly described. ©

A high P–T cell assembly for neutron diffraction up to 10GPa and 1500 K

We present the design of a cell assembly for neutron diffraction experiments capable of performing simultaneous high-pressure (P) and high-temperature (T) conditions up to 10GPa and 1500 K. The high P-T cell assembly, designed for a Paris-Edinburgh (PE) toroidal anvil press, consists of a ceramic gasket, a cylinder/disk furnace, a confining ring, two thermocouples, and platinum wires which serve as electrodes for ohmic heating of the sample. The properties of mechanical strength, yield strength for plastic deformation, thermal/electric insulation, and neutron transparency of the gasket materials are the keys to the success of the cell assembly. The high P-T neutron diffraction experiments conducted at the HIPD beam-line at LANSCE using this cell assembly have produced high quality data and with stable, uniform temperature and sustained hydrostatic pressure.

EDX station for high pressure at lure (DCI)

Abstract A new station is being built at LURE (Orsay, France) for high pressure x-ray diffraction on powders, in the energy dispersive mode. It will be suitable both for diamond anvil cell work and large volume toroidal anvils setups. Presented at the IUCr Workshop on ‘Synchrotron Radiation Instrumentation for HighPressure Crystallography’. Daresbury Laboratory 20-21 July 1991

A large volume pressure cell for high temperatures

Abstract Studies of matter under very high pressure at synchrotron radiation sources are mostly done using pressure cells with single-crystal diamond anvils. In some cases the available volume (≤ 10−3mm3)in such cells causes problems especially at high temperature and for crystal synthesis. To ensure sufficient homogeneity of pressure and temperature, the use of cells with large sample volumes (≥ 1 mm3) is necessary. Existing devices for such measurements are compared with a novel setup which consists of a toroidal anvil arrangement and a lightweight (50 kg) press with 250 tonnes (2.5 MN) capacity. Preliminary tests of this instrument with synchrotron radiation are reported. Presented at the IUCr Workshop on ‘Synchrotron Radiation Instrumentation for HighPressure Crystallography’. Daresbury Laboratory 20-21 July 1991

Equation of state of lithium deuteride from neutron diffraction under high pressure.

Time-of-flight neutron-diffraction spectra of powder samples of $^{7}\mathrm{LiD}$ have been recorded at 300 K, up to 10 GPa at the ISIS spallation source. The experimental setup consists of a 2.5-MN hydraulic press, 50 kg in mass, acting on a toroidal anvil cell. This allows compression of 100-${\mathrm{mm}}^{3}$ samples to over 10 GPa, with better stress homogeneity than flat-anvil devices. The equation of state of $^{7}\mathrm{LiD}$ has been related to the NaCl pressure scale with a precision of 1.5\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}3}$ on the volume variation under pressure. Comparison of existing calculations with the present data shows variable agreement, depending on the calculational hypotheses. Reassessment of the divergent theoretical estimates for the pressure of band crossing in lithium hydrides reconciles them to a common prediction of about 180 GPa for the pressure of semi- metallization. However, the present work cannot reduce the wide separation of the estimates for the B1\ensuremath{\rightarrow}B2 structural-transition pressure.