Kinetic Studies of the Reactions Occurring Between Tungsten and Gases at Low Pressure and High Temperatures

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Oxygen, nitrogen, and nitric oxide gases were passed through a system consisting of a tungsten filament, an ion gauge, and a mass spectrometer. The ion gauge recorded total pressures and the spectrometer recorded partlal pressures of O/sub 2/, N/sub 2/, NO, CO, COa, and H/sub 2/O. From the way these pressures changed with filamert temperature, the rates of conversion of O/sub 2/ to volatile tungsten oxides and O, and of NO to volatile tungsten oxides N/sub 2/ , O/sub 2/, and O were computed. The time rate of resistance change in the filament was used to compute the rate of ... continued below

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Pages: 141

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Anderson, H. U. April 1, 1962.

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  • Lawrence Berkeley Laboratory
    Publisher Info: California Univ., Berkeley, CA (United States). Lawrence Radiation Lab.
    Place of Publication: Berkeley, California

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Oxygen, nitrogen, and nitric oxide gases were passed through a system consisting of a tungsten filament, an ion gauge, and a mass spectrometer. The ion gauge recorded total pressures and the spectrometer recorded partlal pressures of O/sub 2/, N/sub 2/, NO, CO, COa, and H/sub 2/O. From the way these pressures changed with filamert temperature, the rates of conversion of O/sub 2/ to volatile tungsten oxides and O, and of NO to volatile tungsten oxides N/sub 2/ , O/sub 2/, and O were computed. The time rate of resistance change in the filament was used to compute the rate of conversion of tungsten to tungsten oxides. The filament temperatures ranged from 1950 through 2600 deg K and gas pressures ranged from 10/sup -8/ to 10/sup -6/ atm. For the tungsten-oxygen reaction, the rates of tungsten and oxygen loss were found to depend upon oxygen atom concentration on the surface. The rate of oxide power, depending upon the concentration of oxygen atoms on the surface. The reaction rate at constant oxygen pressure decreases with increasing temperature. For calculational purposes, the tungsten oxygen gas moleeules were assumed to be WO/sub 3/ only, though WO/sub 2/ and WO are other possible products. The apparent activation energy for the formation of WO/sub 3/ decreases from 14to -20 kcal./mole as the concentratlon of oxygen atoms decreases, because of the competing processes of oxygen molecule desorption from the surface. The rate of reaction of nitrogen with tungsten was found to be less than could be measured under the conditions of this study. The rate of decomposition of nitric oxide was found to depend upon the number of adsorption sites available on the surface, and the rate is controlled by the adsorption of a molecule on a site. The over-all rate decreased with increasing pressure and had an activation energy of 35.2 kcal/mole. The rate of tungsten loss at constant nltric oxide pressure was found to increase wlth increased temperature. The apparent activation energy for the process increased from 0 to about 50 kcal/mole as pressure decreased. Atomic oxygen was evolved from the tungsten filaments at measurable rates above 2000 deg K for both the O/sub 2/ and the NO reactions. Tungsten can be made carbon-free by heatlng it in pressures of oxygen near 10/sup -8/ atm for 20 to 50 hours. Equations were derived to descrlbe the rates of tungsten oxide evolution and monatomic oxygen formation as functions of temperature and of pressure of O/sub 2/ or of NO. (auth)

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Pages: 141

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  • Other Information: Orig. Receipt Date: 31-DEC-62

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  • Report No.: UCRL-10135
  • Grant Number: W-7405-ENG-48
  • DOI: 10.2172/4827540 | External Link
  • Office of Scientific & Technical Information Report Number: 4827540
  • Archival Resource Key: ark:/67531/metadc1060936

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  • April 1, 1962

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  • Jan. 22, 2018, 7:23 a.m.

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  • April 24, 2018, 5:20 p.m.

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Anderson, H. U. Kinetic Studies of the Reactions Occurring Between Tungsten and Gases at Low Pressure and High Temperatures, thesis or dissertation, April 1, 1962; Berkeley, California. (digital.library.unt.edu/ark:/67531/metadc1060936/: accessed May 25, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.