ABSTRACT
By the early 1900s, the carbon-filament lamp had reached its peak of luminous efficicacy with 3.5 to 4.3 lumens per watt. Production of wires for filaments was nearly impossible, however; tungsten was found intractable, either as a brittle mass or as a fine crystalline powder, that resisted being worked into a coherent form. This chapter deals with the kinetic effects which made the doping of “blue oxide” so successful compared to the same process step with “Yellow Oxide”. It describes the technology of converting blended doped tungsten powders into bars of rectangular, hexagonal or circular cross sections weighing 1—6 kilograms and being 80—120 cm long. The chapter suggests that silicon is essential for the doping process in that it “mobilizes” potassium in the salt melt at moderate temperatures, whereas aluminum secures the stability of β-tungsten over a wider range at temperatures, where the incorporation of potassium becomes possible.
