The effect of Niobium on the defect chemistry and corrosion kinetics of tetragonal ZrO₂ : a density functional theory study
Thesis (S.M. and S.B.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2013.
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| Format: | Thesis |
| Language: | eng |
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Massachusetts Institute of Technology
2013
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| Online Access: | http://hdl.handle.net/1721.1/82458 |
| _version_ | 1826199906713337856 |
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| author | Otgonbaatar, Uuganbayar |
| author2 | Bilge Yildiz. |
| author_facet | Bilge Yildiz. Otgonbaatar, Uuganbayar |
| author_sort | Otgonbaatar, Uuganbayar |
| collection | MIT |
| description | Thesis (S.M. and S.B.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2013. |
| first_indexed | 2024-09-23T11:28:01Z |
| format | Thesis |
| id | mit-1721.1/82458 |
| institution | Massachusetts Institute of Technology |
| language | eng |
| last_indexed | 2024-09-23T11:28:01Z |
| publishDate | 2013 |
| publisher | Massachusetts Institute of Technology |
| record_format | dspace |
| spelling | mit-1721.1/824582019-04-12T20:29:39Z The effect of Niobium on the defect chemistry and corrosion kinetics of tetragonal ZrO₂ : a density functional theory study Otgonbaatar, Uuganbayar Bilge Yildiz. Massachusetts Institute of Technology. Department of Nuclear Science and Engineering. Massachusetts Institute of Technology. Department of Nuclear Science and Engineering. Nuclear Science and Engineering. Thesis (S.M. and S.B.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2013. Cataloged from PDF version of thesis. Includes bibliographical references (pages 57-60). Abstract Advanced Zirconium based alloys used in the nuclear industry today, such as ZIRLOTM , M5 contain up to wt 1.2% Niobium [8]. Experimental effort to determine the effect of Nb on corrosion behaviour of these alloys has no clear answer to whether Nb improves or degrades the corrosion resistance[8, 48, 201. Even the charge state of Nb as a defect in zirconia is debated. Experimental findings of Froideval et al [5] indicate charge state between +2 and +4 whereas other authors assume it to be +5 [21, 31, 34]. In order to uncover the role of Nb on the local oxide protectiveness we employed ab initio Density Functional Theory (DFT) calculations, and assessed the effect of Niobium on the point defect equilibria in tetragonal zirconia which is critical in the oxide protectiveness [81 among other phases of zirconia. DFT calculated defect formation energies are adjusted for finite temperature effects by accounting for thermal vibrations. Adjusted defect formation energies are then used to construct Kroger-Vink diagram for defect equilibrium concentrations at applicable p02 levels. The Kr6ger-Vink diagrams for Nb containing zirconia was compared to that of pure t-Zirconia in order to isolate the changes due to Nb. Nb is treated as point defect in the oxide. Among the considered point defects and defect complexes of Nbzr ,Nbi, Nbzr - Vo and Nbzr - Oi, the substitutional point defect Nbzr was found to have the lowest free energy of formation, and the highest equilibrium concentration. Nb substitutional point defect, Nbzr, is found to be stable for Nb+3, Nb+4, Nb+5 charge states while Nb+5 has the highest concentration. The effect of applied external compressive strain on the energetics and stress of different types of defects, and formation energy is quantified as a function of strain. It is observed that the more positively charged the defect, the formation energy increases less as compressive strain is applied. Compared to pure T-ZrO2, ~100 times increase in Zirconium vacancy concentration accompanied by a ~5 times decrease in the doubly charged oxygen vacancy concentration was found due to the presence of Niobium in the high oxygen partial pressure (p02) regime corresponding to oxide/water interface. This change implies slowing down of oxygen diffusion from surface to bulk, while accelerating oxygen exchange on the surface. Diffusion of zirconium ion to the surface will also accelerate as available point defect concentration increases due to Nb. The increased concentration of Nbzr defect with increasing oxygen partial pressure is consistent with our experimental findings in a parallel work in our group[47]. by Uuganbayar Otgonbaatar. S.M.and S.B. 2013-11-18T19:25:44Z 2013-11-18T19:25:44Z 2013 Thesis http://hdl.handle.net/1721.1/82458 863063609 eng M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission. http://dspace.mit.edu/handle/1721.1/7582 80 pages application/pdf Massachusetts Institute of Technology |
| spellingShingle | Nuclear Science and Engineering. Otgonbaatar, Uuganbayar The effect of Niobium on the defect chemistry and corrosion kinetics of tetragonal ZrO₂ : a density functional theory study |
| title | The effect of Niobium on the defect chemistry and corrosion kinetics of tetragonal ZrO₂ : a density functional theory study |
| title_full | The effect of Niobium on the defect chemistry and corrosion kinetics of tetragonal ZrO₂ : a density functional theory study |
| title_fullStr | The effect of Niobium on the defect chemistry and corrosion kinetics of tetragonal ZrO₂ : a density functional theory study |
| title_full_unstemmed | The effect of Niobium on the defect chemistry and corrosion kinetics of tetragonal ZrO₂ : a density functional theory study |
| title_short | The effect of Niobium on the defect chemistry and corrosion kinetics of tetragonal ZrO₂ : a density functional theory study |
| title_sort | effect of niobium on the defect chemistry and corrosion kinetics of tetragonal zro₂ a density functional theory study |
| topic | Nuclear Science and Engineering. |
| url | http://hdl.handle.net/1721.1/82458 |
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