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Influence of Pt, Fe/Ni/Cr–containing intermetallics and deuterium on the oxidation of Zr-based materials
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
2005 (English)In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 340, no 2-3, 271-283 p.Article in journal (Refereed) Published
Abstract [en]

An in situ gas phase analysis technique and the 18O-SIMS technique are used to evaluate the transport of oxygen and hydrogen in oxidation of Zr-based materials. At 400 °C, it is found that oxygen dissociation efficiency decreases in the order: Pt > Zr2Fe > Zr2Ni > ZrCr2 Zircaloy-2. Two Zr-plates partly coated with 200 Å porous Pt, with and respectively without D in the substrate, were oxidized in two stages at 400 °C. SIMS depth profiles in the Pt area show that an enhanced oxidation takes place mainly by inward oxygen transport. A minimum in the oxide thickness was found near the Pt area on both Zr plates. Two Ar-filled Zircaloy-2 tubes with ZrSn liner were exposed at 370 °C to 22 mbar water, filled in from one side. Our experimental results suggest that a proper choice of the SPP composition and size distribution can lead to reduced hydrogen uptake during oxidation of Zr-based materials in water.

Place, publisher, year, edition, pages
2005. Vol. 340, no 2-3, 271-283 p.
Keyword [en]
high-temperature oxidation, oxide-growth mechanisms, zirconium alloys, zircaloy-4 oxidation, scale adherence, hydrogen uptake, kinetics, oxygen, water, corrosion
National Category
Materials Engineering
Identifiers
URN: urn:nbn:se:kth:diva-6090DOI: 10.1016/j.jnucmat.2004.12.005ISI: 000228116500015Scopus ID: 2-s2.0-14844285777OAI: oai:DiVA.org:kth-6090DiVA: diva2:10701
Note
QC 20100629Available from: 2006-09-08 Created: 2006-09-08 Last updated: 2011-10-19Bibliographically 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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