Formation of Oxides on Tungsten Conductors Heated by Electric Current

Abstract

Peculiarities of high temperature tungsten oxidation were studied experimentally by hot-filament method. Steady-state oxidation process of tungsten filaments (d = 300 mcm, L=0,1 m) heated electrically were investigated by optical pyrometry and electrothermography. Temperature profiles along the filament and its mean steady-state temperatures were measured for different values of heating current. It was found that tungsten trioxide whiskers appeared on the surface at 800 K. They grew up and gradually transformed to plate-like crystals. Their size, morphology and surface density depended on oxidation temperature, duration, gas phase pressure and composition. In case tungsten filament was oxidized in air at atmospheric pressure (T = 1400 K) during 30 minutes the mean oxide plates diameter was 60 mcm and the largest crystals mounted to 320 mcm.