Influence of Inert Gas Atmosphere on the Evaporation Loss of Refractory Metals.

The evaporation of tungsten, molybdenum, tantalum, and niobium has been studied as a function of inert gas pressure at high temperatures in the range of 10** minus **2 to 100 Torr. The metal losses are markedly reduced by the gas atmosphere. Gases with heavier atomic or molecular weight are slightly more effective, eg in the sequence: helium, argon, nitrogen. At atmospheric pressure the metal losses are reduced at least by two orders of magnitude. For a rough estimation one can take K equals 1. 5 and n equals 0. 9. In the presence of oxygen impurities in the inert gas atmosphere the evaporation rates may go up again owing to additional metal losses caused by the formation of volatile oxides. Refs.