Techniques for Evaporation of Metals

Abstract

Thirty-four elements have been observed for evaporation behavior, the results being summarized for each element and the best techniques then listed in Table I. Heaters studied fall into two general classes, wires and crucibles. Tungsten, iron, nickel, and chromel wires were used and these were formed into close wound conical baskets and helical coils. Each element was studied for evaporation behavior from as many of these forms as was possible. Alundum and BeO crucibles formed by painting suspensions of these materials on a tungsten conical basket followed by baking at a high temperature were exceptionally satisfactory heaters for almost all of the elements studied. These crucibles served well for the evaporation of metals whose evaporation temperatures approached 2000°C as well as for those with lower evaporation temperatures. The 18-inch evaporation system was designed and constructed along fairly standard lines. An externally operated, four-inch vacuum valve between the diffusion pump and the bell jar allowed air to be admitted to the bell jar without cooling the diffusion pump. This valve was an especially useful feature of the equipment.