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 arc-welding. A subsecond pulse-heating technique was applied to rod specimens; radiance temperature was measured by high-speed pyrometry. Literature values of the temperature dependence of the normal spectral emissivity of tungsten were used to obtain 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 discussed, along with data obtained during the initial part of the free cooling period. The electrical resistivity results show a regular behavior up to the melting point, indicating that thoria remains an insulator up to 3680 K. During heating, a heat capacity anomaly is found near 3666 K, interpreted as the melting point of thoria. During cooling, two anomalies are found, the first one with a peak near 3660 K and a second one (possibly a Frenkel disorder) with a peak near 3148 K.