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Formation of oxide layers on tungsten at low oxygen partial pressures
Dalarna University, School of Technology and Business Studies, Materials Technology.ORCID iD: 0000-0001-7938-9909
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2018 (English)In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 506, no SI, p. 26-34Article in journal (Refereed) Published
Abstract [en]

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" role="presentation" style="box-sizing: border-box; margin: 0px; padding: 0px; display: inline-block; line-height: normal; font-size: 14.4px; word-spacing: normal; word-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; position: relative;">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 alloysin 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.

Place, publisher, year, edition, pages
2018. Vol. 506, no SI, p. 26-34
Keywords [en]
Tungsten, Oxidation, Spallation target
National Category
Materials Engineering
Research subject
Steel Forming and Surface Engineering
Identifiers
URN: urn:nbn:se:du-26922DOI: 10.1016/j.jnucmat.2017.12.018ISI: 000432848200005Scopus ID: 2-s2.0-85038857400OAI: oai:DiVA.org:du-26922DiVA, id: diva2:1172214
Conference
13th International Workshop on Spallation Materials Technology (IWSMT), Chattanooga, USA, 2016
Available from: 2018-01-09 Created: 2018-01-09 Last updated: 2018-06-07Bibliographically approved

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Surreddi, Kumar Babu

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