Measurement of thermophysical properties by a pulse-heating method: Thoriated tungsten in the range 1200 to 3600 K

Abstract

Thoriated tungsten {tungsten, 98 %; thorium oxide. 2 %) is a widely used electrode material for inert-gas arc-v.,elding. Data for the hc~,t capacity, electrical resistivity, and hemispherical total emissivity of this material are reported for the temperature range 1200-3600 K. 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, using the melting point of thoriated tungsten as a calibration point. Reported uncertaintics for the properties are 4% for heat capacity, 1.5 % for electrical resistivity, and 7% for hemispherical total emissivity. KEY WORDS: electrical resistivity: heat capacity: hemispherical total emissivity: high temperature: tungsten: welding electrodes.

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

“…It should be noted that, throughout the entire temperature range 1500-3680 K, the experimentally measured electrical resistivity of thoriated tungsten remains approximately 4% above the electrical resistivity of tungsten. Below 1500 K this difference percentage tends to increase [4], reaching about 5 % at 1200 K (lowest temperature of measurements). No significant changes in electrical resistivity are seen in the range 3600-3680 K, with sharp increases after that temperature due to the onset of melting.…”

“…Complete technical details on the apparatus and on the measuring technique are given in earlier publications [1][2][3]. Thermophysical properties of thoriated tungsten were measured from 1200 K to the melting point [4]; this work describes the experimental results above 3600 K and specific phenomena occurring after the material has reached those temperatures.…”

A Study on the Feasibility of Measuring the Emissivity with the Laser-Flash Method

“…To get realistic data typical parameters of the setup are used: a laser pulse energy of 5 J at a wavelength of 1064 nm and a tungsten sample with a mass of 5 g. The values for the temperature-dependent specific heat capacity were taken from the literature [21], and the emissivity values are taken from Latyev et al [22] and interpolated. According to this literature, for example, at a temperature of 2000 K, the emissivity at the desired wavelength of 1064 nm is ε = 0.36 and the specific heat capacity is c p = 175 J · kg −1 · K −1 for the hypothetic tungsten sample.…”

Physical changes in tungsten and thoriated tungsten electrodes after subsecond heating

“…The samples were resistively heated to the tungsten melting point very quickly (times in the order of 1 s), but heating was stopped before fusion was complete and the samples remained intact. Technical details of the equipment used have been given elsewhere [9][10][11] and the results of the thermophysical measurements in tungsten [ 12,13] and thoriated tungsten [ 14,15] are given in complementary publications. The physical changes caused by the rapid heating were examined using electron microscopy and X-ray microanalysis.…”