Physical changes in tungsten and thoriated tungsten electrodes after subsecond heating

Abstract

s-t '.r,,ugsten and thoriated tungsten rods are commonly used as cathodes for arcs operating in argon. Thoriated tungsten electrodes (2 wt% thorium oxide) have significantly longer lifetimes than pure tungsten electrodes, though the reason for this is not well understood. Samples of both types of electrode were heated to the melting point of tungsten using a subsecond pulse heating technique. The samples were then examined using electron microscopy and X-ray analysis and the results compared with similar examinations of unheated electrodes. There were definite physical changes apparent in the shape of the thoria particles, but no evidence of any reduction of the thoria.

Thermophysical properties of thoriated tungsten above 3600 K by a pulse-heating method

“…The thoriated tungsten rods are made of 98 % tungsten with thoria (ThO2) particles finely dispersed in the tungsten matrix [ 7 ]. The temperature measurements are performed over a relatively large target area (circle of diameter, 300/Lm) with respect to the typical size of the thoria particles (spheres of diameter, 1 #m).…”