THERMOPHYSICAL PROPERTIES OF THORIATED TUNGSTEN ABOVE 3600 K BY A PULSE-HEATING METHOD

Thoriated tungsten (tungsten, 98% thorium oxide, 2%) is a widely used electrode material for inert-gas are-welding. A subsecond pulse-heatin g technique was applied to rod specimens; radiance temperature was mea sured by highspeed pyrometry. Literature values of the temperature dep endence of the normal spectral emissivity of tungsten were used to obt ain true temperatures, with the melting point of thoriated tungsten as a calibration point. Experimental results obtained in the temperature range from 3600 K to the melting point (3693 K) are presented and dis cussed, along with data obtained during the initial part of the free c ooling period. The electrical resistivity results show a regular behav ior up to the melting point, indicating that thoria remains an insulat or up to 3680 K. During heating, a heat capacity anomaly is found near 3666 K, interpreted as the melting point of thoria. During cooling, t wo anomalies are found, the first one with a peak near 3660 K and a se cond one (possibly a Frenkel disorder) with a peak near 3148 K.