There are a variety of different pressure assemblies used in the High Pressure Laboratory that conform to both the needs of the specific experiment being conducted and the device in which the experiment is being carried out. The cell assemblies used in a given experiment also vary depending on whether it is a simple synthesis, a hot-pressing, an ultrasonics experiment, or other type of experiment, as well as which press is used to conduct the study. The information on this page describes in detail the specifics of the pressure and cell assemblies used most commonly in the High Pressure Laboratory. Please note that, as the Girdle is in the process of being refurbished, information on the cell assemblies used in that apparatus will be witheld until the device is once again operational.
The pressure assembly used in the Sumitomo Press consists of eight individual Tungsten Carbide cubes with truncated corners. The size of the cubes and their truncations vary depending on the desired pressure and sample volume of the experiment (generally designated as 8/3 and 14/8), though the basic assembly is the same regardless of size, and is shown at right in the form of a wooden block model (for a larger picture, click the image). The truncated corners of the eight cubes for an octahedral space at the center, which is where the cell assembly containing the sample material is placed. Pressure is applied vertically by the press, and as pressure is increased, the cubes are squeezed together, applying directionally-uniform pressure to the sample inside.
The octahedral pressure medium used in this split-sphere apparatus is made of either MgO or MgO + spinel and has the center drilled out to accomodate the cell assembly. A diagram of the cell assembly and all of its parts can be found at the left (for a larger diagram, simply click on the image). This diagram is specifically of the 14/8 cell assembly, though the 8/3 assembly is similar in nature, and was provided by Kurt Leinenweber at Arizona State University. The gray area at the center that is labeled "sample configuration" varies depending on the experimental sample material and the type of capsule used to house the sample.
The pressure assembly used in the Kennedy Press is similar to that used in the Sumitomo Press. The cubes used in the Kennedy Press most often conform to the 14/8 truncation scheme, shown in the large image at the top of this page with the sample and thermocouple assembly visible. Pressure is again applied vertically by the press, and as pressure is increased, the cubes are squeezed together, applying pressure to the sample inside that is uniform in all directions.
For a PDF file with more detailed information about the pressure assembly used in these presses, as well as specific instructions on how to put together the cell assembly, CLICK HERE
. This PDF file depicts the pressure and cell assemblies used in experiments conducted with the 10/5 truncation scheme, but is largely the same as those used in the 8/3 and 14/8 assemblies. There are subtle differences, however, such as the use of a graphite furnace instead of rhenium in most Kennedy experiments. For a PDF file furnished by Kurt Leinenweber at Arizona State University that shows detailed diagrams of the 14/8 cell assembly and how it is put together, please CLICK HERE
The Kennedy Press is also used for conducting in situ ultrasonic interferometry experiments on large-volume samples that have been synthesized in either the Kennedy or Sumitomo presses. Shown at right is a schematic cross-section of an octahedral semi-sintered MgO cell assembly used for acoustic measurements in the Kennedy press. This figure was taken from Kung et al., 2004 in Physics of the Earth and Planetary Interiors, and for a larger view, simply click the figure at right. A cylindrical graphite furnace with end disk was inserted into MgO octahedron, with salt (NaCl + 10 vol.% of BN) and MgO cups filling the space between the specimen and the furnace. On one end of the cell assembly, an alumina rod served as an acoustic buffer rod, located between the tungsten-carbide cube and specimen; this buffer rod was surrounded by brass foil to provide electrical contact between the WC cube and the graphite furnace. On the other end of the cell, a Mo-alloy ring provided the other furnace electrode. The remaining space inside the MgO octahedron was filled with a zirconia sleeve and rings. The temperature was measured by a thermocouple, which was inserted from the edge of the MgO octahedron and located at the bottom of the specimen, inside of the NaCl cup. Two gold foils (2-microns thick, not shown in the diagram) were inserted at both ends of the specimen as the image markers; the foil between the Al2
and specimen was also used to improve the mechanical coupling.
Information of the cell assemblies used in the Girdle will be added to this page once the apparatus is once again operational.