Apparatus for High-Pressure High-Temperature X-Ray Powder Diffraction Studies

Abstract

A high‐pressure high‐temperature x‐ray powder diffraction apparatus has been developed based on a modification of the belt apparatus, which is an internally heated compressible gasket device. The unique feature of this device is that the die‐support ring assembly is fabricated in two parts which mate along a plane normal to the piston axis. The split‐die design permits entry of the x‐ray beam into the high‐pressure volume and egress of both the diffracted rays and the undeviated beam through suitable grooves and fan‐shaped slots ground in the mating surfaces. The high‐pressure x‐ray windows are either a beryllium ring with a wedge‐shaped cross section or epoxy resin stops at the bore of the die. The high‐pressure medium is ``amorphous'' boron, and the sample is in the form of a thin cylinder which is coaxial with the pistons and normal to the x‐ray beam. The compressible gaskets between the pistons and the die are made of pyrophyllite, as they are in conventional devices, inasmuch as they are not part of the x‐ray path. High sample temperatures are attained by resistance heating of carbon rods adjacent to the sample. Present limitations on pressure and temperature are 100 kilobars and 1000°C. High‐intensity Mo K_α radiation is employed. The apparatus is portable and may be positioned on a conventional x‐ray source.