Chemical vapor deposition of thoriated tungsten protective cups Page: 14 of 45
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The NRX-A6 reactor design defined a requirement for a cup to protect the pyrolytic
graphite insulating cups from the hot, high velocity hydrogen gas exiting from the
support blocks. Requirements of the application involved:
1) a complete range of temperatures from 2000 to 50000R,
2) appreciable time of operation at about 45000R in a hydrogen environment, and
3) repeated thermal cycling to the operating temperature.
A prime material candidate for this high temperature application was thoriated
tungsten, an alloy developed by the electric filament industry for resisting grain growth after
many thermal cycles and long exposures at elevated temperatures.
The feasibility of manufacturing the thoriated tungsten cup by the following six
proposed methods were investigated:
1) Multi-sintering of blended thoria and tungsten powders hydrostatically pressed
into a cup configuration
2) Plasma sprayed cups
3) Cups machined from commercially available 3-inch round barstock extruded from
powder metallurgy billets
4) Cups machined from 1 -1/8 inch round barstock, extruded from Westinghouse
W-Special powder metallurgy billets, a super fine dispersion of co-reduced thoria in tungsten
5) Cups hot spun from special cross-rolled sheet
6) Chemical vapor deposited cups
Experiments were conducted utilizing each of the six fabricating methods with special
emphasis placed on the Westinghouse W-Special alloy. This alloy developed by the Westinghouse
Lamp Division, possesses superior engineering properties in addition to resisting recrystallization
and degradation of mechanical properties after exposure to elevated temperatures. This unique
alloy is manufactured by powder metallurgy techniques from powder in which the thoria exists
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Blay, J.S. Chemical vapor deposition of thoriated tungsten protective cups, report, January 1, 1968; Pittsburgh, Pennsylvania. (https://digital.library.unt.edu/ark:/67531/metadc1026564/m1/14/: accessed March 24, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.