An apparatus has been developed which permits x-ray powder patterns to be obtained to over 500 kilobars presure. The apparatus is derived in part from the supported tapered piston electrical resistance apparatus in use in this laboratory, but the x rays are transmitted through a thin layer of LiH with suitable platinum collimation. The pressures are established by measuring the change of lattice parameter of a suitable marker mixed with the sample. These changes are then compared with volume changes obtained in shock wave work. Usual markers used to date include silver, rhodium, and palladium. Typical data for sample pressure versus average applied pressure for these metals are given. Also included is the change in lattice parameter with pressure for CsCl to 500 kilobars. The results are compared with the extrapolation of Bridgman's data.

A systematic investigation of the design variables for a high pressure cell with supported taper pistons has been undertaken. The variables studied include: the effect of center thickness, the effect of flat diameter and piston diameter, the pressure gradient across the flat, the pressure gradient on the taper, and the effect of different materials supporting the center. It is concluded that any scaling up in size from the dimensions used in the electrical resistance cell previously described in the literature (2.29 mm diam flat and 0.33 mm center thickness) results in a drastic reduction in pressure range. Scaling down the flat size results in a modest increase in pressure range. The pressure is remarkably independent of radius in the region of the flat which contains the electrical resistance sample. A piston with a double taper might suppy a greater degree of support for the piston tip.

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