| The ductile metallic tungsten was obtained at low temperature (1000-1300℃), using the metallic activator and the so called "chemical agitation" to facilitate the sintering effects. About 0.3 w/o Ni was impregnated into W as activator and the sintering atmosphere was chemically activated in the atmosphere of the mixture of H₂ and H₂O vapor saturated at 30℃. With this atmospheric control the activated sinterings effect was improved by 30%. With this double activation method, the sintered tungsten of the density 17.1 g/㏄ and that of 16.3 could be obtained by the sintering at 1300℃ for 1 hour and at 1200℃ for 1 hour, respectively. The mechanical-and physical properties of the ductile tungsten metal obtained by this method were superior compared to those obtained from the traditional "coolidge method", except their electrical conductivity. The activation energy E for the sintering was calculated with the temperature range of 850℃ to 1300℃. E for the double activated sintering was 43 ㎉/mole above 1000℃ and 57 ㎉/mole under 1000℃, and E for the activated sintering with 0.3% Ni-activator was 52 ㎉/mole above 1000℃ and 75 ㎉/mole under 1000℃. The microstructural observation and the study of sintering mechanism were also performed and discussed. |
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