The Kennedy Press

The so-called "Kennedy Press" is a 1000-ton uniaxial split-cylinder apparatus (USCA-1000). This apparatus is similar in nature to the Sumitomo Press, but has a smaller-capacity press and high pressure module. The high-pressure module within the Kennedy is a Walker device. This apparatus is used for synthesis experiments that require extended durations of high temperatures and pressures in large-volume samples, but is not capable of achieving pressures quite as high as the Sumitomo (~16 GPa at maximum). The samples synthesized in this press are then analyzed and characterized using a variety of different methods in various MPI-affiliated facilities.

The pressure assembly used in the Kennedy Press is similar to that used in the Sumitomo Press. The assembly consists of eight individual Tungsten Carbide cubes with truncated corners. The cubes used in the Kennedy Press most often conform to the 14/8 truncation scheme, shown at the right with the sample and thermocouple assembly visible (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, as seen in the image at the right. 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.

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, 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 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 Al2O3 and specimen was also used to improve the mechanical coupling.

For more information on the cell assemblies used in these experiments conducted in the Kennedy Press, see the Cell Assemblies page.

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Page Last Modified June 1, 2008