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Modified oxygen and hydrogen transport in Zr-based oxides
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
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 [en]
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: urn:nbn:se:kth:diva-4095ISBN: 91-7178-429-2 (print)OAI: oai:DiVA.org:kth-4095DiVA: diva2:10706
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
List of papers
1. Gas phase analysis of CO interactions with solid surfaces at high temperatures
Open this publication in new window or tab >>Gas phase analysis of CO interactions with solid surfaces at high temperatures
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.

Keyword
CO; chromium; zirconium; zircaloy-2; adsorption; dissociation; high temperature; gas phase analysis
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-6089 (URN)10.1016/j.apsusc.2004.04.001 (DOI)000222497700050 ()2-s2.0-2942530929 (Scopus ID)
Note
QC 20100629 QC 20111101Available from: 2006-09-08 Created: 2006-09-08 Last updated: 2011-11-01Bibliographically approved
2. Influence of Pt, Fe/Ni/Cr–containing intermetallics and deuterium on the oxidation of Zr-based materials
Open this publication in new window or tab >>Influence of Pt, Fe/Ni/Cr–containing intermetallics and deuterium on the oxidation of Zr-based materials
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.

Keyword
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:nbn:se:kth:diva-6090 (URN)10.1016/j.jnucmat.2004.12.005 (DOI)000228116500015 ()2-s2.0-14844285777 (Scopus ID)
Note
QC 20100629Available from: 2006-09-08 Created: 2006-09-08 Last updated: 2011-10-19Bibliographically approved
3. Gas-tight oxides – Reality or just a Hope
Open this publication in new window or tab >>Gas-tight oxides – Reality or just a Hope
Show others...
2006 (English)In: Materials Science Forum, ISSN 0255-5476, Vol. 522-523, 93-101 p.Article in journal (Refereed) Published
Abstract [en]

A better understanding of the transport properties of gases in oxides is certainly very important in many applications. In the case of metals, a general protection measure against corrosion implies formation of a dense metal oxide scale. The scale should act as a barrier against gas transport and consequently it needs to be gas-tight. This is often assumed but rarely, if ever, confirmed. Hence there is a need for characterization of micro- and/or meso- pores formed especially during the early oxidation stage of metallic materials. This paper presents a novel and relatively straightforward method for characterization of gas release from an oxide previously equilibrated in a controlled atmosphere. The geometry of the sample is approximated to be a plate. The plate can be self-supporting or constitute a scale on a substrate. A mathematical model for calculation of diffusivity and gas content is given for this geometry. A desorption experiment, involving a mass spectrometer placed in ultra high vacuum, can be used to determine diffusivity and amount of gas released with aid of the mathematical model. The method is validated in measurements of diffusivity and solubility of He in quartz and applied in characterization of two Zr-oxides and one Fe oxide. From the outgassed amounts of water and nitrogen the H2O/N-2 molar ratio can be used to estimate an effective pore size in oxides.

Keyword
gas diffusion; porosity; gas content; gas phase analysis; zircaloy; iron; oxides
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-6091 (URN)000241416500011 ()2-s2.0-37848999932 (Scopus ID)
Note
QC 20100629Available from: 2006-09-08 Created: 2006-09-08 Last updated: 2010-06-29Bibliographically approved
4. Effects of hydrogen on the corrosion resistance of metallic materials and semiconductors
Open this publication in new window or tab >>Effects of hydrogen on the corrosion resistance of metallic materials and semiconductors
2006 (English)In: High-Temperature Oxidation And Corrosion 2005 / [ed] Taniguchi, S; Maruyama, T; Yoshiba, M; Otsuka, N; Kawahara, Y, 2006, Vol. 522-523, 139-146 p.Conference paper, Published paper (Refereed)
Abstract [en]

For long time it is known that protons in aqueous solutions have a detrimental effect on metallic materials. Relatively recently, it has also been observed in aqueous solution that the pitting corrosion resistance of Cr, stainless steel 304 and 310 decreases and the anodic dissolution rate increases due to the presence of hydrogen in the metal. In gas phase a high oxidation rate has been observed for hydrogen containing Cr and Fe. Hydrogen in the substrate can also enhance the oxidation of Fe in SS 316 and As in GaAs. All these results suggest enhanced dissolution in aqueous solution and enhanced oxide growth at the oxide/gas interface in gas phase oxidation due to hydrogen promoted outward-transport of substrate components. A possible mechanism for such out-transport is an increased metal ion diffusivity in the metal-oxide due to a high abundance of metal ion vacancies generated by hydrogen. In contrast to all the above examples, also positive effects of hydrogen have been identified under certain conditions. In an attempt to understand both the negative and the positive effects the concept of a beneficial, balanced oxide growth is used. In this concept a certain amount of hydrogen can be beneficial in the oxidation by improving the balance between oxygen-ion and metalion transport, leading to more dense and protective oxides. Depending on the temperature, H(2) in air is considered as either a sink or a source for hydrogen in materials.

Series
Materials Science Forum, ISSN 0255-5476 ; 522-523
Keyword
hydrogen, gas phase, water, metal diffusion, molecular dissociation, SIMS
National Category
Corrosion Engineering
Identifiers
urn:nbn:se:kth:diva-41990 (URN)000241416500016 ()2-s2.0-34548485611 (Scopus ID)0-87849-409-X (ISBN)
Conference
International Symposium on High-Temperature Oxidation and Corrosion 2005 (ISHOC 2005) Location: Nara, Japan, Date: NOV 30-DEC 02, 2005
Note
QC 20111005Available from: 2011-10-05 Created: 2011-10-05 Last updated: 2011-10-05Bibliographically approved
5. A gas phase analysis technique applied to in-situ studies of gas-solid interactions
Open this publication in new window or tab >>A gas phase analysis technique applied to in-situ studies of gas-solid interactions
2007 (English)In: Journal of materials science. Materials in electronics, ISSN 0957-4522, E-ISSN 1573-482X, Vol. 47, no 10, 3440-3453 p.Article in journal (Refereed) Published
Abstract [en]

An ultrahigh vacuum technique using mass spectrometry for in-situ investigations of gas-solid interactions is described in this paper. Examples of chemical reactions (oxidation, hydration) between solids and gas mixtures, dissociation of gases on solid surfaces, outgassing of solid materials and permeation of gases through membranes are discussed where the experimental arrangement is explained in detail. This Gas Phase Analysis (GPA) technique can be used at temperatures from room temperature to 1200 degrees C and at pressures up to 1 atm. Aspects related to sample preparation, isotopic gas mixture selection, data acquisition, calibration and interpretation of the experimental data are also addressed.

Keyword
temperature oxidation-kinetics, oxide-growth mechanisms, mass-spectrometry, scale adherence, metal-oxides, hydrogen, o-2, chromium, iron, dissociation
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-6093 (URN)10.1007/s10853-006-1023-6 (DOI)000246618700023 ()2-s2.0-34249057540 (Scopus ID)
Note
Conference: Workshop on Size-dependent Effects in Materials for Environmental Protection and Energy Application. Varna, BULGARIA. MAY 25-27, 2006 Available from: 2006-09-08 Created: 2006-09-08 Last updated: 2011-09-12Bibliographically approved
6. Isotopic investigation of the transport of oxygen species in Y-stabilized zirconia
Open this publication in new window or tab >>Isotopic investigation of the transport of oxygen species in Y-stabilized zirconia
(English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690Article in journal (Other academic) Submitted
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-6094 (URN)
Note
QC 20100629Available from: 2006-09-08 Created: 2006-09-08 Last updated: 2010-06-29Bibliographically approved

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