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    Rights statement: This is the author’s version of a work that was accepted for publication in Acta Materialia. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Acta Materialia, 132, 2017 DOI: 10.1016/j.actamat.2017.04.063

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The effect of Nb on the corrosion and hydrogen pick-up of Zr alloys

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The effect of Nb on the corrosion and hydrogen pick-up of Zr alloys. / Bell, B.D.C.; Murphy, S.T.; Grimes, R.W.; Wenman, M.R.

In: Acta Materialia, Vol. 132, 15.06.2017, p. 425-431.

Research output: Contribution to Journal/MagazineJournal articlepeer-review

Harvard

Bell, BDC, Murphy, ST, Grimes, RW & Wenman, MR 2017, 'The effect of Nb on the corrosion and hydrogen pick-up of Zr alloys', Acta Materialia, vol. 132, pp. 425-431. https://doi.org/10.1016/j.actamat.2017.04.063

APA

Bell, B. D. C., Murphy, S. T., Grimes, R. W., & Wenman, M. R. (2017). The effect of Nb on the corrosion and hydrogen pick-up of Zr alloys. Acta Materialia, 132, 425-431. https://doi.org/10.1016/j.actamat.2017.04.063

Vancouver

Author

Bell, B.D.C. ; Murphy, S.T. ; Grimes, R.W. ; Wenman, M.R. / The effect of Nb on the corrosion and hydrogen pick-up of Zr alloys. In: Acta Materialia. 2017 ; Vol. 132. pp. 425-431.

Bibtex

@article{4a99ab6551464d0886830d53a6d2cfb6,
title = "The effect of Nb on the corrosion and hydrogen pick-up of Zr alloys",
abstract = "Abstract Zr-Nb alloys are known to perform better in corrosion and hydrogen pick-up than other Zr alloys but the mechanism by which this happens is not well understood. Atomistic simulations using density functional theory of both tetragonal and monoclinic ZrO2 were performed, with intrinsic defects and Nb dopants. The overall defect populations with respect to oxygen partial pressure were calculated and presented in the form of Brouwer diagrams. Nb is found to favour 5 + in monoclinic ZrO2 at all partial pressures, but can exist in oxidation states ranging from 5 + to 3 + in the tetragonal phase. Nb5+ is charge balanced by Zr vacancies in both phases, suggesting that contrary to previous assumptions, Nb does not act as an n-type dopant in the oxide layer. Clusters containing oxygen vacancies were considered, Nb2+ was shown to exist in the tetragonal phase with a binding energy of 2.4 eV. This supports the proposed mechanism whereby low oxidation state Nb ions (2 + or 3+) charge balance the build-up of positive space-charge in the oxide layer, increasing oxygen vacancy and electron mobility, leading to near-parabolic corrosion kinetics and a reduced hydrogen pick-up. Previous experimental work has shown that tetragonal ZrO2 transforms to the monoclinic phase during transition, and that during transition a sharp drop in the instantaneous hydrogen pick-up fraction occurs. The oxidation of lower charge state Nb defects to Nb5+ during this phase change, and the consequent temporary n-doping of the oxide layer, is proposed as an explanation for the drop in hydrogen pick-up during transition.",
keywords = "Density functional theory, Zirconium, Niobium, Corrosion, Hydrogen pick-up",
author = "B.D.C. Bell and S.T. Murphy and R.W. Grimes and M.R. Wenman",
note = "This is the author{\textquoteright}s version of a work that was accepted for publication in Acta Materialia. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Acta Materialia, 132, 2017 DOI: 10.1016/j.actamat.2017.04.063",
year = "2017",
month = jun,
day = "15",
doi = "10.1016/j.actamat.2017.04.063",
language = "English",
volume = "132",
pages = "425--431",
journal = "Acta Materialia",
issn = "1359-6454",
publisher = "PERGAMON-ELSEVIER SCIENCE LTD",

}

RIS

TY - JOUR

T1 - The effect of Nb on the corrosion and hydrogen pick-up of Zr alloys

AU - Bell, B.D.C.

AU - Murphy, S.T.

AU - Grimes, R.W.

AU - Wenman, M.R.

N1 - This is the author’s version of a work that was accepted for publication in Acta Materialia. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Acta Materialia, 132, 2017 DOI: 10.1016/j.actamat.2017.04.063

PY - 2017/6/15

Y1 - 2017/6/15

N2 - Abstract Zr-Nb alloys are known to perform better in corrosion and hydrogen pick-up than other Zr alloys but the mechanism by which this happens is not well understood. Atomistic simulations using density functional theory of both tetragonal and monoclinic ZrO2 were performed, with intrinsic defects and Nb dopants. The overall defect populations with respect to oxygen partial pressure were calculated and presented in the form of Brouwer diagrams. Nb is found to favour 5 + in monoclinic ZrO2 at all partial pressures, but can exist in oxidation states ranging from 5 + to 3 + in the tetragonal phase. Nb5+ is charge balanced by Zr vacancies in both phases, suggesting that contrary to previous assumptions, Nb does not act as an n-type dopant in the oxide layer. Clusters containing oxygen vacancies were considered, Nb2+ was shown to exist in the tetragonal phase with a binding energy of 2.4 eV. This supports the proposed mechanism whereby low oxidation state Nb ions (2 + or 3+) charge balance the build-up of positive space-charge in the oxide layer, increasing oxygen vacancy and electron mobility, leading to near-parabolic corrosion kinetics and a reduced hydrogen pick-up. Previous experimental work has shown that tetragonal ZrO2 transforms to the monoclinic phase during transition, and that during transition a sharp drop in the instantaneous hydrogen pick-up fraction occurs. The oxidation of lower charge state Nb defects to Nb5+ during this phase change, and the consequent temporary n-doping of the oxide layer, is proposed as an explanation for the drop in hydrogen pick-up during transition.

AB - Abstract Zr-Nb alloys are known to perform better in corrosion and hydrogen pick-up than other Zr alloys but the mechanism by which this happens is not well understood. Atomistic simulations using density functional theory of both tetragonal and monoclinic ZrO2 were performed, with intrinsic defects and Nb dopants. The overall defect populations with respect to oxygen partial pressure were calculated and presented in the form of Brouwer diagrams. Nb is found to favour 5 + in monoclinic ZrO2 at all partial pressures, but can exist in oxidation states ranging from 5 + to 3 + in the tetragonal phase. Nb5+ is charge balanced by Zr vacancies in both phases, suggesting that contrary to previous assumptions, Nb does not act as an n-type dopant in the oxide layer. Clusters containing oxygen vacancies were considered, Nb2+ was shown to exist in the tetragonal phase with a binding energy of 2.4 eV. This supports the proposed mechanism whereby low oxidation state Nb ions (2 + or 3+) charge balance the build-up of positive space-charge in the oxide layer, increasing oxygen vacancy and electron mobility, leading to near-parabolic corrosion kinetics and a reduced hydrogen pick-up. Previous experimental work has shown that tetragonal ZrO2 transforms to the monoclinic phase during transition, and that during transition a sharp drop in the instantaneous hydrogen pick-up fraction occurs. The oxidation of lower charge state Nb defects to Nb5+ during this phase change, and the consequent temporary n-doping of the oxide layer, is proposed as an explanation for the drop in hydrogen pick-up during transition.

KW - Density functional theory

KW - Zirconium

KW - Niobium

KW - Corrosion

KW - Hydrogen pick-up

U2 - 10.1016/j.actamat.2017.04.063

DO - 10.1016/j.actamat.2017.04.063

M3 - Journal article

VL - 132

SP - 425

EP - 431

JO - Acta Materialia

JF - Acta Materialia

SN - 1359-6454

ER -