⇦Chinese Physics Letters, 2020, Vol. 37, No. 8, Article code 080701 Pressure Generation above 35 GPa in a Walker-Type Large-Volume Press Yu-Chen Shang (尚宇琛)1†, Fang-Ren Shen (沈方韧)1†, Xu-Yuan Hou (侯旭远)1, Lu-Yao Chen (陈璐瑶)1, Kuo Hu (胡阔)1, Xin Li (李鑫)2, Ran Liu (刘然)1,2, Qiang Tao (陶强)1, Pin-Wen Zhu (朱品文)1,2, Zhao-Dong Liu (刘兆东)1,2*, Ming-Guang Yao (姚明光)1*, Qiang Zhou (周强)1,2, Tian Cui (崔田)1,2, and Bing-Bing Liu (刘冰冰)1,2* Affiliations 1State Key Laboratory of Superhard Materials, Jilin University, Changchun 130012, China 2Synergetic Extreme Condition User Facility, Jilin University, Changchun 130012, China Received 29 April 2020; accepted 14 June 2020; published online 28 July 2020 Supported by the National Natural Science Foundation of China (Grant Nos. 51320105007, 11634004 and 41902034), the Fundamental Research Funds for the Central Universities of China (Grant No. 45119031C037), and the Program for Changjiang Scholars and Innovative Research Team in University (Grant No. IRT1132).
†These authors contributed equally to this work.
*Corresponding authors. Email: liubb@jlu.edu.cn; yaomg@jlu.edu.cn; liu_zhaodong@jlu.edu.cn Citation Text: Shang Y C, Chen F R, Hou X Y, Chen L Y and Hu K et al. 2020 Chin. Phys. Lett. 37 080701    Abstract Pressure generation to a higher pressure range in a large-volume press (LVP) denotes our ability to explore more functional materials and deeper Earth's interior. Pressure generated by normal tungsten carbide (WC) anvils in a commercial way is mostly limited to 25 GPa in LVPs due to the limitation of their hardness and design of cell assemblies. We adopt three newly developed WC anvils for ultrahigh pressure generation in a Walker-type LVP with a maximum press load of 1000 ton. The hardest ZK01F WC anvils exhibit the highest efficiency of pressure generation than ZK10F and ZK20F WC anvils, which is related to their performances of plastic deformations. Pressure up to 35 GPa at room temperature is achieved at a relatively low press load of 4.5 MN by adopting the hardest ZK01F WC anvils with three tapering surfaces in conjunction with an optimized cell assembly, while pressure above 35 GPa at 1700 K is achieved at a higher press load of 7.5 MN. Temperature above 2000 K can be generated by our cell assemblies at pressure below 30 GPa. We adopt such high-pressure and high-temperature techniques to fabricate several high-quality and well-sintered polycrystalline minerals for practical use. The present development of high-pressure techniques expands the pressure and temperature ranges in Walker-type LVPs and has wide applications in physics, materials, chemistry, and Earth science. DOI:10.1088/0256-307X/37/8/080701 PACS:07.35.+k, 62.50.-p, 81.40.Vw © 2020 Chinese Physics Society Article Text The large-volume press (LVP) has been widely used in materials, physics, chemistry, and Earth science because of well-controlled pressure and temperature in a larger sample chamber compared with that available in a laser-heated diamond anvil cell.[1–6] A large sample volume in LVPs enables us to measure physical and chemical properties of materials under precise high pressure and high temperature (HPHT). Among various types of LVPs, the Walker-type LVP has an advantage of self-organization in alignment of six independent first-stage anvils upon compression.[7] Its main feature is constructed on the geometry of well-established octahedron-within-eight cubes in the Kawai-type LVP.[1] The Walker-type LVP finds its unique, versatile, and user-friendly way in experimental laboratories and is routinely used for fabrication of novel functional materials.[3,5,6] Pressure generation in a confined and large space is vital for the applications of LVPs.[3–6] Pressure generated by LVPs is generally determined by the materials of second-stage anvils since the press load is applied on the second-stage anvils.[8–16] Both tungsten carbide (WC) and sintered diamond (SD) have been used as the second-stage anvil materials.[8–16] Although SD anvils with hardness of two times higher than WC anvils can generate pressure above 60 GPa in LVPs,[12–14] the limited size and poor electronic conductivity of SD anvils hinder the synthesis of a large-sized sample at HPHT.[12] In contrast, WC anvils are relatively practical and easily produced.[8–11] Pressure generation by conventional WC in a commercial way is basically limited to 25 GPa,[8–10] especially at high temperature, due to their limited hardness. Recently, Ishii et al.[17,18] and Kunimoto et al.[19] adopted new types of ultrahard TF05 and TJS01 WC anvils to generate pressure above 40 GPa in a DIA-type LVP with a good guide-block system. However, these ultrahard WC anvils are fragile and easily broken upon compression that can only be used several times (TF05: 5–8 times; TJS01: 1 time). Ultrahigh pressure generation in LVP experiments remains challenging and it is thus important to develop related techniques for LVPs. In this letter, we adopt three new types of hard WC anvils with different cobalt contents to examine their efficiencies of pressure generations in a Walker-type LVP. The hardest WC anvils can generate pressure exceeding 35 GPa even at high temperatures, which breaks its pressure limitation and reaches the available pressure range generated by TF05 and TJS01 WC anvils in a DIA-type LVP. Physical, chemical, and mechanical properties are examined to illustrate their efficiencies of pressure generation. The designed cell assemblies can stably generate pressures above 35 GPa and temperatures above 2000 K, which is important for syntheses of novel functional materials under extreme conditions and for understanding the deep Earth's interior.
cpl-37-8-080701-fig1.png
Fig. 1. Schematic drawing (a) and photograph (b) of the JLUHC-1000 LVP. Images surrounded by white dashed lines are the overviews of Walker module with three first-stage anvils in the bottom and cell assemblies in WC anvils.
A Walker-type JLUHC-1000 LVP with a maximum press load of 1000 tons was installed at the State Key laboratory of Superhard Materials (SKLSHM), Jilin University, China. The concept of this LVP is almost the same as the design by Walker et al.[7] Its schematic drawing and photograph are displayed in Fig. 1. The Walker-type module is located on a horizontally traveling carriage, which allows a manual manipulation of its position (Fig. 1(a)). It consists of six removable split cylinder anvils inside a cylindrical containment ring (Fig. 1(b)). The out part of first stage anvils is made of hardened tungsten carbide steel with a truncated edge length of 50 mm. The inner cubic WC anvils have an edge length of 25.4 mm. The upper and lower guide blocks are equipped with three first-stage anvils, respectively. The second-stage anvil assembly composed by eight cubic WC anvils and an octahedral pressure medium is vertically placed in the [111] direction and compressed uniaxially (Fig. 1(b)). A double plastic sheet was put on the interface between the first-stage and second-stage anvils to provide lubrication for experiments. Wedges of first-stage anvils converge on the cubic cavity and are consequently forced outward against the bore of the ring. Compression will allow a good self-organization for alignment of the assembly between these first- and second-stage anvils. Electric power is supplied by a power source with a capacity of 6 kW, which is connected to the guide blocks using a power cable with the electric current capacity of up to 500 A. Temperature at high pressure is controlled and maintained automatically by computers.
Table 1. Mechanical properties of our used new types of WC anvils compared with other types of anvils.
Company Grade Rockwell Vickers Transverse rupture
hardness (HRA) hardness (HV) strength (GPa)
Heyuan ZK01F 93.5 1900 $\ge$ 1.9
ZK10F 93.0 1800 $\ge$ 2.2
ZK20F 92.5 1700 $\ge$ 2.6
Fuji TJS01 98.0 2700 2.6
TF05 95.0 2400 1.5
F09 93.0 1800 4.4
Hawedia HA-6%Co 93.0 1770
cpl-37-8-080701-fig2.png
Fig. 2. SEM images and distributions of grain sizes of ZK01F, ZK10F, and ZK20F WC anvils.
Three new types of WC anvils with different compositions (ZK01F, ZK10F, and ZK20F; supplied by Heyuan Zhenxin Hardmetal Carbide Pte Co. Ltd, China) were adopted for high pressure generation in JLUHC-1000 LVP. Table 1 lists their mechanical properties compared with other kinds of WC anvils. Among new types of WC anvils, ZK01F is the hardest anvil, which is comparable to that of F09 but lower than that of TJS01 and TF05 types. Their microstructures and compositions are analyzed by a field emission scanning electron microscope (FE-SEM Magellan 400) combined with one energy dispersive spectrometer (EDS, Oxford-X Max 150) at the State Key Laboratory of Superhard Materials, Jilin University, China. Scanning electron microscope (SEM) observations show that ZK01F, ZK10F, and ZK20F anvils have an average grain size of 0.6, 0.8, and 0.9 µm, respectively (Fig. 2). The contents of cobalt (Co) binder in ZK01F, ZK10F and ZK20F anvils are 4, 6, and 8 wt%, respectively. Note that ZK01F anvils have the smallest grain size and the least Co contents, which are comparable with those of TF05 anvils. This variation of Co content and sintered grain size can well explain the variation of their hardness that harder anvils generally consist of smaller particles and contain a lesser amount of the Co binder. Tapering of anvil surfaces has been adopted by several studies to increase the efficiency of pressure generation.[17,20,21] Here a 1$^{\circ}$ tapering to three surfaces in the direction of (111) of each hardest ZK01F anvils has been introduced for examination (Fig. 3). These tapered surfaces provide lateral supports according to an elastic or plastic design and hence are expected to increase the efficiency of pressure generation.[22]
cpl-37-8-080701-fig3.png
Fig. 3. Schematic drawing of the assembly of flat (a) and 1$^{{^{\circ}}}$ tapering (b) WC anvils. Small squares are the drawing of gaskets, and dashed arrows represent the sliding directions of gaskets upon compression.
Pressure generation in LVPs is also dependent on the truncated edge length (TEL) of second-stage WC anvils as well as materials and sizes of pressure medium and gasket. In the present study, TELs of WC anvils are cut into 1.5, 3, 4, 5, and 8 mm according to the target sample volume and pressure generation. For the pressure medium, we mainly used the semi-sintered Cr-doped MgO octahedra (5 wt% Cr$_{2}$O$_{3}$, supplied from Mino Ceramic Co., Ltd.). An Al$_{2}$O$_{3}$-doped MgO octahedron (Supplied from COMPRES) was also used in one experiment for comparison. Pyrophyllite was used as the gasket to confine pressure into the pressure medium and laterally support anvils. The gaskets were dried at 500 K to avoid a pressure drop at high temperature.[23] As shown in Figs. 4(a) and 4(b), a two-wire method was used for the phase transition of standards from covalent to metallic phases such as ZnTe (6.6, 8.9, and 12.9 GPa), ZnS (15.6 GPa), GaAs (18.7 GPa), and GaP (23.0 GPa) from semiconductor to metal, while a four-wire method was used for the phase transition of Zr ($\alpha$–$\omega$, 8.0 GPa; $\omega$–$\beta$, 34.5 GPa).[9,12] We also calibrated the pressure at high temperatures of 1700–2000 K using the Al$_{2}$O$_{3}$ content in perovskite.[14,15] Starting materials are MgSiO$_{3}$ and Mg$_{0.875}$Al$_{0.25}$Si$_{0.875}$O$_{3}$ glass and Mg$_{0.5}$AlSi$_{0.5}$O$_{3}$ oxide-mixture, which were described in our earlier studies.[14,15] Figure 4(c) shows our pressure calibration for the 7/3 (the edge length of octahedral pressure medium/TEL of WC anvils) assembly using three new types of WC anvils at room temperature. For the occurrence of phase transition of GaP at 23 GPa in a pressure medium of Cr-doped MgO octahedron, the corresponding press load is around 4.4 MN for ZK01F anvils, which is higher than that for ZK10F (4.7 MN) and ZK20F (7.9 MN). Thus, ZK01F anvils have the highest efficiency for the pressure generation compared with ZK10F and ZK20F anvils because of its higher hardness. If we used the Al-doped MgO pressure medium for the assembly in ZK01F anvils, the pressure generation would be slightly lower than that for the Cr-doped pressure medium because of its lower hardness. The efficiency of pressure generation of ZK01F anvils is almost consistent with that of TF05 anvils as obtained by Ishii et al.,[17] which is significantly higher than that for the F09 and Hawadia 6% anvils in a later study. The reported hardness of TF05 from Fuji Die Co. Ltd. has a higher Co content (5 wt%) and hardness than those of ZK01F supplied by Heyuan Zhenxin Pte Co. Ltd., but their pressure generations are almost the same within uncertainties. This fact suggests that ZK01F and TF05 anvils actually have similar hardness, although their reported hardness is slightly different. At pressure above 30 GPa, we adopted a small assembly of 6/1.5 using both flat and 1$^{\circ}$ tapering ZK01F anvils. As shown in Fig. 4(d), the pressure generation efficiency by 1$^{\circ}$ tapering ZK01F anvils is significantly higher than flat anvils. At room temperature, we generated a pressure of 34.5 GPa by the resistance change of Zr associated with phase transitions for 1$^{\circ}$ tapering ZK01F anvils at a low press load of 4.5 MN. We did not observe this phase transition of Zr using the flat anvils at a press load even up to 7.5 MN, suggesting that these anvils cannot reach 34.5 GPa at this high press load and a higher load is thus required. This fact clearly shows that the tapering of anvil surfaces significantly increases the efficiency of pressure generation.[17,21,23] As illustrated in Fig. 3, gaskets between 1$^{\circ}$ tapering WC anvils are easily sliding upon compression compared with flat anvils. Therefore, press loading is not dispersed by the deformation of anvil top and hence applied on the pressure medium, which will significantly increase pressure generation efficiency.
cpl-37-8-080701-fig4.png
Fig. 4. Representative recorded resistances of GaP (a) and Zr (b), respectively, as a function of press load. (c) Pressure generation at room temperature using three new types of WC anvils with TEL = 3 mm and Cr- and Al-doped semi-sintered MgO pressure medium with an edge length of 7 mm. Dashed lines are the results from Ishii et al.[17] (d) Pressure generation for the 6/1.5 cell assembly using flat and 1$^{\circ}$ tapering ZK01F WC anvils. Squares represent the estimated pressure at high temperatures using the Al$_{2}$O$_{3}$ content in perovskites.
cpl-37-8-080701-fig5.png
Fig. 5. Magnitudes of the plastic deformation of flat WC anvils with 3 mm TEL decompressed from 23 GPa as a function of the distance from the top to end of the anvil cube, as shown in the inset figure.
To further illustrate the efficiencies of pressure generation of these new WC anvils, plastic deformation of WC anvils was measured. Earlier studies showed that plastic deformation of WC anvils occurs at pressure above 10 GPa.[24] Figure 5 shows plastic deformations of flat WC anvils with 3 mm TEL when compressed to 23 GPa using the present new types of anvils. We found that top regions of the anvils are depressed within the distance of 5 mm, while out regions are slightly swelling above 5 mm. The hardest ZK01F anvils have a slightly smaller plastic deformation than that of ZK10F but a much smaller plastic deformation than that of ZK20F anvils, suggesting that the hardest ZK01F anvils suffer a smaller stress than other two types of anvils. This fact is also consistent with pressure generation behavior in Fig. 4(c). Further studies on the deformation and yielding properties of WC anvils are required. Stable temperature generation has been achieved by the present high temperature cell assemblies. We modified several high temperature cell assemblies according to some early studies.[17–22] A double-rolled Re foil with a thickness of 25 µm was used as the heater (Figs. 6(a) and 6(b)). ZrO$_{2}$ sleeves are used as the thermal insulator to keep high temperatures in the samples. MgO sleeves are used as thermal conduction materials. A high temperature of 2000 K was achieved for the 7/3 cell assembly, while temperatures above 2500 K can be stably generated by the 10/4 and 10/5 cell assemblies. We have synthesized two MgSiO$_{3}$ perovskites at 5 and 8 MN, respectively, by using 7/3 and 10/4 cell assemblies under 2000 K, suggesting that pressure is above 23 GPa at these press loads under this temperature based on the phase transition of MgSiO$_{3}$ (Figs. 7(a) and 8(a)).[15] Their back-scattered electron (BSE) images were made by FE-SEM with a backscattering detector with an acceleration voltage of 10–15 kV. In addition, Mg$_{0.875}$Al$_{0.25}$Si$_{0.875}$O$_{3}$ perovskite was fabricated at 8 MN under 2000 K using the 7/3 assembly (Figs. 7(b) and 8(b)), suggesting that the corresponding pressure is around 27 GPa at 8 MN under 2000 K from the relationship of Al$_{2}$O$_{3}$ content in perovskite with pressure and temperature.[15,16] For the 6/1.5 cell assembly, we synthesized two aluminous perovskite samples with 13 and 12 mol% Al$_{2}$O$_{3}$ at 1700 and 1800 K, respectively (Figs. 7(c) and 7(d)). This fact suggests that pressure at 1700 K should be around 36 GPa, while it is around 32 GPa at 1800 K.
cpl-37-8-080701-fig6.png
Fig. 6. High temperature generation by Re heaters for 7/3 (a) and 6/1.5 (b) cell assemblies, respectively, at around 27 and 36 GPa.
cpl-37-8-080701-fig7.png
Fig. 7. Back-scattered electron (BSE) images of the synthesized samples at high pressure and high temperature from starting materials of MgSiO$_{3}$ (a) and Mg$_{0.875}$Al$_{0.25}$Si$_{0.875}$O$_{3}$ glass (b) and Mg$_{0.5}$AlSi$_{0.5}$O$_{3}$ oxide-mixture [(c), (d)].
We have fabricated several high-quality polycrystalline minerals such as the above MgSiO$_{3}$ and Mg$_{0.875}$Al$_{0.25}$Si$_{0.875}$O$_{3}$ perovskite (Figs. 8(a) and 8(b)) and Mg$_{0.9}$Al$_{0.2}$Si$_{0.9}$O$_{3}$ garnet (Fig. 8(c)) using high-pressure hot pressing techniques. These samples have a diameter of 1–2 mm and a height of 1–2 mm. They are well-sintered, free of micro-cracks, and milky or transparent synthesized at pressures of 15–27 GPa and temperatures of 1900–2300 K. These well-sintered samples are good specimens for sound velocity measurements with either ultrasonic interferometry or Brillouin scattering methods.
cpl-37-8-080701-fig8.png
Fig. 8. Hot pressing of polycrystalline high-pressure minerals of (a) MgSiO$_{3}$ and (b) Mg$_{0.875}$Al$_{0.25}$Si$_{0.875}$O$_{3}$ perovskite and (c) Mg$_{0.9}$Al$_{0.2}$Si$_{0.9}$O$_{3}$ garnet.
cpl-37-8-080701-fig9.png
Fig. 9. (a) High pressure generation of various cell assemblies using ZK01F WC anvils in JLUHC-1000 LVP. (b) Available pressure and temperature range achieved in Kawai- and Walker-type LVPs using various types of WC anvils in this and earlier studies.[8–10,17,19,25]
In summary, five types of cell assemblies (14/8, 10/5, 10/4, 7/3, and 6/1.5) for different sample sizes from 1 to 4 mm in diameter have been tested to generate pressure in a Walker-type LVP (Fig. 9(a)). The ultrahard ZK01F anvils with taping surfaces used here have generated pressure as high as 36 GPa at 1700 K, which breaks the pressure limitation generated in Walker- and Kawai-type LVPs (25–27 GPa at high temperatures) (Fig. 9(b)). Currently, ZK01F anvils can be repeatedly used 3–5 times depending on the pressure and temperature conditions, while the number of repeated use of ZK10F anvils is more than the former. However, the present number of repeated use of anvils is a tentative measurement of the performance of anvils according to our current experiments, and further more meaningful performance tests are needed to examine the feasibility of WC anvils in LVPs. Considering similar mechanical properties of ZK01F anvils to those of ultrahard TF05 anvils, we believe that the present newly developed ZK01F anvils could reach a higher pressure of 45 GPa at high temperature under a higher press load in a DIA-type LVP with a good guide-block system. The present high pressure techniques in Walker-type LVPs, by adopting new types of WC anvils, will contribute to the exploration of more novel functional materials and their physical properties, as well as the study on the deep Earth's interior. References The Generation of Ultrahigh Hydrostatic Pressures by a Split Sphere ApparatusWide-Temperature-Range Dielectric Permittivity Measurement under High PressureUltrahard polycrystalline diamond from graphiteCharacteristics of urea under high pressure and high temperatureSlater Insulator in Iridate Perovskites with Strong Spin-Orbit CouplingNanotwinned diamond with unprecedented hardness and stabilityA novel large-volume Kawai-type apparatus and its application to the synthesis of sintered bodies of nano-polycrystalline diamondFrontier of High-Pressure Earth Science. Sintered Diamond and Research of the Earth's Interior.Pressure generation to 80 GPa using multianvil apparatus with sintered diamond anvilsP - V - T equation of state of MgSiO 3 perovskite based on the MgO pressure scale: A comprehensive reference for mineralogy of the lower mantleOver 1Mbar generation in the Kawai-type multianvil apparatus and its application to compression of (Mg0.92Fe0.08)SiO3 perovskite and stishovitePhase relations in the system MgSiO 3 –Al 2 O 3 up to 52 GPa and 2000 KPhase Relations in the System MgSiO 3 -Al 2 O 3 up to 2300 K at Lower Mantle PressuresGeneration of pressures over 40 GPa using Kawai-type multi-anvil press with tungsten carbide anvilsPressure generation to 65 GPa in a Kawai-type multi-anvil apparatus with tungsten carbide anvilsPressure-induced phase transformations of PbCO 3 by X-ray diffraction and Raman spectroscopyThe absence of oxide mixture in high-pressure phases of Mg-silicatesRapid decrease of MgAlO2.5 component in bridgmanite with pressureEffects of pre-heated pyrophyllite gaskets on high-pressure generation in the Kawai-type multi-anvil experimentsSubsolidus and melting phase relations of basaltic composition in the uppermostlower mantle
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