THE SELECTIVE REMOVAL OF OXYGEN FROM RARE-EARTH AND THORIUM METALS THROUGH OXYHALIDE FORMATION

The reactions of yttrium, lanthanum, neodymium and gadolinium metals containing 1-5 at. % dissolved oxygen with the respective trichlorides RCl//3 to produce ROCl as well as the reverse reactions of ROCl with pure lanthanum and gadolinium in the presence of RCl//3 have been studied in sealed niobium or tantalum containers. Such reactions at 730-850 degree C for 1-2 weeks duration yield metal containing 0. 1-0. 2 at. % oxygen, consistent with thermodynamic estimates for the reaction limits. Precipitation of LaOCl within the low-melting lanthanum metal limits the removal of 2-5 at. % oxygen at 850 degree C to about 0. 5 at. % but this limit can be decreased to about 0. 27% by longer reactions at 760-775 degree C. These types of reactions appear general for the selective removal of oxygen from nearly all the rare earth metals.