LVP/Multi-Anvil (MAC)

The large volume press (LVP) has been widely used for high-pressure research in Earth science during last 50 years, and recently has increasingly been employed in other branches of science, such as physics, chemistry and material sciences. The multi-anvil apparatus can provide well-controlled pressure (P) – temperature (T) – stress (s) environment for probing material properties, and is indispensable in synthesizing novel materials under extreme conditions. Some of the advanced techniques in association of LVP include synchrotron- and neutron-based methods for in-situ and real-time studies, rheological and deformational investigations, acoustic velocity measurements, and thermal and electric conductivity measurements. It’s also been done routinely to combine two or more techniques in a single experiment to study multiple properties simultaneously.

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The LVP laboratory in HiPSEC/UNLV houses a 2000-ton hydraulic press and its pumping, heating and computerized controlling systems. The entire unit is on loan from the Los Alamos National Laboratory (LANL). In conjunction with a large deformational DIA-type (DDIA) cubic tooling, the multi-anvil apparatus having single ram of 12 inches in diameter can generate a quasi-hydrostatic pressure via uniaxial compression. The first-stage anvils of the DDIA module are made of WC with 1.5” square truncations. This design meets the requirements (e.g., sample size and diffraction geometry) of in-situ study at a neutron beam line for which the LVP system was originally intended. Due to the large truncation size of the DDIA’s first-stage anvils, limited pressure (< 5 GPa) can be achieved by this system as designed.

We have adopted Kawai-type cell assembly for the second stage compression to achieve higher pressures, and the DDIA was modified accordingly to accommodate this addition. The second-stage anvils consist of eight one-inch WC cubes with their corners truncated to form equilateral triangles. The smaller the truncation, the higher the pressure can be generated. The common edge-lengths for the truncation are 12, 8, 5 and 3 mm. The common edge-lengths for coupling MgO octahedron (pressure medium) are 18, 14, 10 and 8 mm, respectively. High temperature is achieved through resistive heating. The common materials for the heater are graphite, rhenium, platinum, and TiC + diamond mixture. Type-C thermocouple is generally used to measure temperature. With this set-up, a peak condition of about 30 GPa and 2500 K can be reached by using 8/3 assembly. The sample size ranges from ~ 1.5 (8/3) to ~ 65 (18/12) mm3. All cell parts are acquired from Arizona State University (Dr. K. Leinenweber). Once assembled, the assembly is then transferred into DDIA, which is then rolled into TAPLUS-2000 for compression after the half with the top anvil is in place.

The pressure inserted on the sample at any given load (oil pressure) has been calibrated against the known phase transitions at both room (25 oC left top) and high (1200 oC; left bottom) temperatures for 14/8 and 18/12 assemblies. In-situ measurements of the electric resistance for Bi, PbS, PbTe and ZnTe were conducted to determine the Pressure vs Load at room temperature. The following phase equilibria were reversed/bracketed at 1200 oC: quartz (Qz) – coesite (Coe) in SiO2, coesite – stishovite (St) in SiO2, and garnet (Gt) -perovskite (Pv) in CaGeO3. The average of pressures for forward and backward transition is used for the calibration. Similar procedures are underway for 10/4 and 8/3 assemblies.

It’s expected that the LVP facility will be mainly involved in student training and their thesis research within HiPSEC. Since being on-line in late 2016, the lab has welcomed students and junior researchers who are synthesizing new materials. Other in-situ techniques, such as electric/thermal conductivity and acoustic velocity measurements at simultaneous high P & T, are under development. We also anticipate to collaborate with scientists from outside of UNLV, especially those from NNSA laboratories. Please contact Dr. Liping Wang (liping.wang@unlv.edu) for all inquiries related to this facility.