High Temperature Structure of Plutonium Dicarbide

Abstract

THE presence of a dicarbide in the Pu–C system was originally reported by Drummond¹. Mulford and Ellinger² showed that the compound was unstable below ∼ 1,750° C, and that it decomposed to form PuC₂ and carbon. These workers were unable to index the X-ray diffraction pattern obtained at room temperature from alloys quenched from the molten state. Chackraburtty and Jayadevan³ indexed diffraction lines from a sample of PuO₂ and carbon quenched from the reaction temperature of 2,200° C as arising from a body centred tetragonal phase isomorphous with UC₂ and deduced that this was also the high temperature structure. Tetragonal structures have also been found in quenched materials by J. A. Leary and J. G. Reavis (private communication), who also reported that the formation temperature of PuC₂ was 1,650° C. As part of a study of the phase relationships in the UC₂–PuC₂ system it was necessary to determine the high temperature structure of PuC₂. The apparatus used was a high temperature diffractometer⁴ attached to a conventional Philips X-ray goniometer using Cu Ka radiation.