Investigation of sintered tungsten rhenium additive alloys for high temperature space application

In the quest to obtain enhanced bare work functions and increase their utility for thermionic energy conversion in future space applications, four tungsten rhenium alloys (W-3%Re, W-10%Re, W-25%Re, W-30%Re) were tested and found to have effective work functions of 4.87 +/- 0.04 eV, 4.80 +/- 0.04 eV, 4.94 +/- 0.04 eV, and 5.04 +/- 0.04 eV, respectively at an operating temperature of 1950 K. Tests were conducted at progressively increasing temperatures up to 2350 K and the effective work functions were found to increase uniformly with temperature. The effect of adding 1% ThO2, to each one of the above mentioned alloys was to marginally increase the work functions to 4.83 +/- 0.04 eV, 4.82 +/- 0.04 eV, 4.96 +/- 0.04 eV and 5.06 +/- 0.04 eV, respectively. The work functions exhibited trends similar to that of the W, Re alloys, with increase in temperature and rhenium content. Normal spectral emissivities of W, W-3%Re, W-25%Re and W-30%Re were evaluated with a sophisticated photon-counting pyrometer. At 1400 K these alloys were found to have emissivities of 0.599, 0.521, 0.476, and 0.610, respectively, and in each case the values decreased with increase in operating temperature. W, 25%Re had the lowest and most stable values in the range of temperatures (1400 K to 2500 K) tested. The thoriated samples exhibited the same behavior as the W, Re samples but were observed to be more stable