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 Kα radiation is employed. The apparatus is portable and may be positioned on a conventional x-ray source.