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Formation of oxide layers on tungsten at low oxygen partial pressures

Habainy, Jemila LU ; Iyengar, Srinivasan LU ; Surreddi, Kumar Babu LU ; Lee, Yongjoong and Dai, Yong (2017) In Journal of Nuclear Materials
Abstract

This work focuses on the oxidation of tungsten in inert gas atmospheres containing oxygen and moisture. It is particularly relevant for the European Spallation Source where the tungsten target is cooled by purified helium gas and the 5 MW proton beam can raise the maximum target temperature beyond the threshold for oxidation. Tungsten discs were oxidized isothermally at 400° to 900 °C for 2 h in pure helium and helium mixed with oxygen and water vapor, with varying partial pressures up to 500 Pa. Tungsten was oxidized even with a small amount of oxygen (≤5 ppm) present in industrially pure helium. Non-isothermal oxidation of tungsten foils was carried out in water vapor (~100 Pa), in situ in an environmental scanning electron... (More)

This work focuses on the oxidation of tungsten in inert gas atmospheres containing oxygen and moisture. It is particularly relevant for the European Spallation Source where the tungsten target is cooled by purified helium gas and the 5 MW proton beam can raise the maximum target temperature beyond the threshold for oxidation. Tungsten discs were oxidized isothermally at 400° to 900 °C for 2 h in pure helium and helium mixed with oxygen and water vapor, with varying partial pressures up to 500 Pa. Tungsten was oxidized even with a small amount of oxygen (≤5 ppm) present in industrially pure helium. Non-isothermal oxidation of tungsten foils was carried out in water vapor (~100 Pa), in situ in an environmental scanning electron microscope. On specimens oxidized in inert gas containing water vapor (2 h, pH2O ~790 Pa), Auger electron spectroscopy studies confirmed the presence of a thin oxide layer (40 nm) at 400 °C. At 500 °C the oxide layer was 10 times thicker. A dark, thin and adherent oxide layer was observed below 600 °C. Above this temperature, the growth rate increased substantially and the oxide layer was greenish, thick and porous. Oxide layers with varying stoichiometry were observed, ranging from WO3 at the surface to WO2 at the metal-oxide interface. For comparison, oxidation of tungsten alloys in He-5%O2 was studied. The implications of this work on the design and operation of the helium loop for cooling the target are discussed.

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author
organization
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type
Contribution to journal
publication status
epub
subject
keywords
Oxidation, Spallation target, Tungsten
in
Journal of Nuclear Materials
publisher
Elsevier
external identifiers
  • scopus:85038857400
ISSN
0022-3115
DOI
10.1016/j.jnucmat.2017.12.018
language
English
LU publication?
yes
id
dc2cea92-ff56-4fc5-ab8a-14ad247a5038
date added to LUP
2018-01-04 13:59:44
date last changed
2018-01-04 13:59:44
@article{dc2cea92-ff56-4fc5-ab8a-14ad247a5038,
  abstract     = {<p>This work focuses on the oxidation of tungsten in inert gas atmospheres containing oxygen and moisture. It is particularly relevant for the European Spallation Source where the tungsten target is cooled by purified helium gas and the 5 MW proton beam can raise the maximum target temperature beyond the threshold for oxidation. Tungsten discs were oxidized isothermally at 400° to 900 °C for 2 h in pure helium and helium mixed with oxygen and water vapor, with varying partial pressures up to 500 Pa. Tungsten was oxidized even with a small amount of oxygen (≤5 ppm) present in industrially pure helium. Non-isothermal oxidation of tungsten foils was carried out in water vapor (~100 Pa), in situ in an environmental scanning electron microscope. On specimens oxidized in inert gas containing water vapor (2 h, pH2O ~790 Pa), Auger electron spectroscopy studies confirmed the presence of a thin oxide layer (40 nm) at 400 °C. At 500 °C the oxide layer was 10 times thicker. A dark, thin and adherent oxide layer was observed below 600 °C. Above this temperature, the growth rate increased substantially and the oxide layer was greenish, thick and porous. Oxide layers with varying stoichiometry were observed, ranging from WO<sub>3</sub> at the surface to WO<sub>2</sub> at the metal-oxide interface. For comparison, oxidation of tungsten alloys in He-5%O<sub>2</sub> was studied. The implications of this work on the design and operation of the helium loop for cooling the target are discussed.</p>},
  author       = {Habainy, Jemila and Iyengar, Srinivasan and Surreddi, Kumar Babu and Lee, Yongjoong and Dai, Yong},
  issn         = {0022-3115},
  keyword      = {Oxidation,Spallation target,Tungsten},
  language     = {eng},
  month        = {12},
  publisher    = {Elsevier},
  series       = {Journal of Nuclear Materials},
  title        = {Formation of oxide layers on tungsten at low oxygen partial pressures},
  url          = {http://dx.doi.org/10.1016/j.jnucmat.2017.12.018},
  year         = {2017},
}