The Chemistry of Non-Sag Tungsten

Non-sag (NS) tungsten is a dispersion-strengthened microalloy with elemental potassium, which is contained as microscopic bubbles in the tungsten lattice. Under working conditions in an incandescent lamp the potassium is a gas under high pressure. These gas bubbles essentially prevent the recrystallization of the tungsten wire and are responsible for the outstanding creep resistance of NS tungsten at the extremely high temperatures of a glowing lamp filament. More than 90% of NS tungsten is used for incandescent lamps. In addition, small amounts are used as defroster heating wires in automobile windshields and as heating wire coils for aluminium evaporation in metallization applications. The presented papers deal with the chemical reactions and the chemical compounds occurring along the path from tungsten raw materials to the final NS tungsten filament; a compendium of present knowledge on the different chemical aspects of NS tungsten manufacture is presented. It is composed of nine individual papers, each of them written by experts working in the field.