Chemical vapor deposition of thoriated tungsten protective cups Page: 19 of 45
This report is part of the collection entitled: Office of Scientific & Technical Information Technical Reports and was provided to Digital Library by the UNT Libraries Government Documents Department.
The following text was automatically extracted from the image on this page using optical character recognition software:
Of course, the major portion of the tungsten comes from reaction (1). In addition, an
oxidizer must be used to simultaneously oxidize the reduced thorium metal to thoria in the
reaction chamber during the deposition of the tungsten. The oxidizers which were tested in
this system were pure oxygen, air, water vapor, and carbon dioxide. Of these, carbon
dioxide was chosen because of its relatively constant free energy of formation as a function
of increasing temperature. The chemical reaction is:
(3) Th + 2CO2 2CO + ThO2
The oxidation potential of the carbon dioxide in this system can be adjusted by
varying the temperature which allows the adjustment of the net free energy change between
carbon monoxide and carbon dioxide to drive the reaction. The carbon monoxide becomes
increasingly more stable with increasing temperature as does carbon dioxide, though to a
lesser degree. It was found that the thorium metal was oxidized in the gas stream and apparently
disperses uniformly in the deposited tungsten metal. The oxidation is indicated by the
recrystallized grain structure of the tungsten which is super fine, uniform, and equiaxed as
shown in Figure 3. Possibly the super fine thoria is molecular in size as it could not be
identified or resolved metallographically at 1000X. The unquestionable presence of thoria
was manifest by the resistance of the material to grain growth at elevated temperatures.
Temperature and Pressure
A chamber pressure of 225 to 275 millimeters of mercury absolute and a substrate
temperature of 11200 +450F were maintained during the deposition cycle. The chamber
pressure was the same as that used for the deposition of pure tungsten, but it was necessary to
increase the temperature from 10500F (that used for pure tungsten) to 11200F for the thoriated
Here’s what’s next.
This report can be searched. Note: Results may vary based on the legibility of text within the document.
Tools / Downloads
Get a copy of this page or view the extracted text.
Citing and Sharing
Basic information for referencing this web page. We also provide extended guidance on usage rights, references, copying or embedding.
Reference the current page of this Report.
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/m1/19/: accessed March 23, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.