The solubility of tantalum and tungsten in liquid rare-earth metals

Abstract

The solubilities of tantalum in eight liquid rare-earth metals (Y, La, Ce, Pr, Nd, Sm, Eu and Yb) and of tungsten in all the liquid rare-earth metals (except Pm) have been measured from 1325° to 2150°C. These data show that tungsten is a much better crucible material for the rare-earth metals than tantalum, since tungsten is less soluble than tantalum in the liquid rare-earth metals by a factor ranging from 2 for Sc and the heavy lanthanides to 10 or greater for the light lanthanides. The solubilities of both tantalum and tungsten at a given temperature vary inversely with the atom sizes of the rare-earth solvents. Furthermore, it was found that the solubility change for a given size increment is much larger if the size factor is less than a critical value (about 17.5% for the Ta alloys and 20% for the W alloys), than if the size factor were larger than the critical value. The heats of solutions were calculated from the liquidus data and were found to support the size correlation proposed by Strauss, White and Brown for liquid alloys.