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Gas phase analysis of CO interactions with solid surfaces at high temperatures
KTH, Superseded Departments, Materials Science and Engineering.
KTH, Superseded Departments, Materials Science and Engineering.
KTH, Superseded Departments, Materials Science and Engineering.
2004 (English)In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 233, no 1-4, 392-401 p.Article in journal (Refereed) Published
Abstract [en]

An in situ method including mass spectrometry and labeled gases is presented and used to gain information on adsorption of molecules at high temperatures (>300 degreesC). Isotopic exchange rate in H-2 upon exposure to an oxidized zicaloy-2 sample and exchange rate in CO upon exposure to various materials have been measured. From these measurements, molecular dissociation rates in respective system have been calculated. The influence of CO and N-2 on the uptake rate of H-2 in zirconium and oxidized zicaloy-2 is discussed in terms of tendency for adsorption at high temperatures. In the case of oxidized Cr exposed to CO gas With C-12, C-13, O-16 and O-18, the influence of H2O is investigated with respect to dissociation of CO molecules. The presented data supports a view of different tendencies for molecular adsorption of H2O, CO, N-2, and H-2 molecules on surfaces at high temperatures.

Place, publisher, year, edition, pages
2004. Vol. 233, no 1-4, 392-401 p.
Keyword [en]
CO; chromium; zirconium; zircaloy-2; adsorption; dissociation; high temperature; gas phase analysis
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:kth:diva-6089DOI: 10.1016/j.apsusc.2004.04.001ISI: 000222497700050Scopus ID: 2-s2.0-2942530929OAI: oai:DiVA.org:kth-6089DiVA: diva2:10700
Note
QC 20100629 QC 20111101Available from: 2006-09-08 Created: 2006-09-08 Last updated: 2017-12-14Bibliographically approved
In thesis
1. Modified oxygen and hydrogen transport in Zr-based oxides
Open this publication in new window or tab >>Modified oxygen and hydrogen transport in Zr-based oxides
2006 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

Most metals and alloys in the presence of oxygen and moisture will instantaneously react and form a thin (2-5 nm) surface oxide layer. For further reaction to occur, oxygen ions and/or metal cations often diffuse through the already formed oxide layer. The corrosion resistance of a metal in aggressive environments at high temperatures depends on the properties of the surface oxide scale.

Zirconium-based alloys represent the main structural materials used in water-cooled nuclear reactors. For these materials, the formation of a thin, adherent oxide scale with long-term stability in high temperature water/steam under irradiation conditions, is crucial. In this thesis, the transport of oxygen and hydrogen through Zr-based oxide scales at relevant temperatures for the nuclear industry is investigated using isotopic gas mixtures and isotope-monitoring techniques such as Gas Phase Analysis and Secondary Ion Mass Spectrometry.

Porosity development in the oxide scales generates easy diffusion pathways for molecules across the oxide layer during oxidation. A considerable contribution of molecular oxygen to total oxygen transport in zirconia has been observed at temperatures up to 800°C. A novel method for evaluation of the gas diffusion, gas concentration and effective pore size of oxide scales is presented in this thesis. Effective pore sizes in the nanometer range were found for pretransition oxides on Zircaloy-2. A mechanism for densification of oxide scales by obtaining a better balance between inward oxygen and outward metal transport is suggested. Outward Zr transport can be influenced by the presence of hydrogen in the oxide and/or metal substrate. Inward oxygen transport can be promoted by oxygen dissociating elements such as Fe-containing second phase particles. The results suggest furthermore that a proper choice of the second-phase particles composition and size distribution can lead to the formation of dense oxides, which are characterized by low oxygen and hydrogen uptake rates during oxidation.

Hydrogen uptake in Zr-based materials during oxidation in high temperature water/steam can generate degradation due to the formation of brittle hydrides in the metal substrate. A promising method for the suppression of hydrogen uptake has been developed and is presented in this thesis.

Place, publisher, year, edition, pages
Stockholm: KTH, 2006. 48 p.
Keyword
Zirconia, Zirconium, Zircaloy, hydrogen and oxygen diffusion, SPP, oxygen dissociating elements, oxidation, dissociation, hydration, CO adsorption, molecular transport, porosity.
National Category
Materials Engineering
Identifiers
urn:nbn:se:kth:diva-4095 (URN)91-7178-429-2 (ISBN)
Public defence
2006-09-22, F3, Lindstedtsvägen 26, Stockholm, 10:00
Opponent
Supervisors
Note
QC 20100629Available from: 2006-09-08 Created: 2006-09-08 Last updated: 2011-10-05Bibliographically approved

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