Washing Treatment to Doped Tungsten Powder by Hydrofluoric Acid

Abstract

A tungsten filament of incandescent lamp recrystallizes and becomes brittle when the lamp is first lighted. It has been desired to prevent the filament to become brittle. In order to find the desirable process, effects of the dopant added to tungsten oxide on tungsten powder and the washing treatment of doped or undoped tungsten powder were investigated in the present study.
This study revealed the following facts. (1) Dopant rich layers were deposited on the surfaces of tungsten perticles produced through the reduction process of doped tungsten oxide by hydrogen. (2) These dopant rich layers played a role as adhesive and joined primary particles into coalescences. (3) The washing treatment by dilute hydrofluoric acid removed these dopant rich layers, and therefore broke the coalescences into smaller particles. (4) This washing treatment by hydrofluoric acid increased the apparent densitys of both of green compact and sintered body, and increased the ductility of recrystallized filament.
Furthermore, the effects of the doping and the washing treatment on the ductility of recrystallized filament were discussed.