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Compositional dependence of crystallization and chemical durability in nepheline (Na2O•Al2O3•2SiO2) based glasses

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Title
Compositional dependence of crystallization and chemical durability in nepheline (Na<sub>2</sub>O•Al<sub>2</sub>O<sub>3</sub>•2SiO<sub>2</sub>) based glasses
Name (type = personal)
NamePart (type = family)
Deshkar
NamePart (type = given)
Ambar
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Ambar Deshkar
Role
RoleTerm (authority = RULIB)
author
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Goel
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Ashutosh
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Ashutosh Goel
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Advisory Committee
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chair
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Klein
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Lisa
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Lisa Klein
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Advisory Committee
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internal member
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Lehman
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Richard
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Richard Lehman
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Advisory Committee
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Mauro
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John
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John Mauro
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Advisory Committee
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outside member
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Rutgers University
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degree grantor
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School of Graduate Studies
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Text
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theses
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2019
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2019-10
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2019
Language
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English
Abstract (type = abstract)
Vitrification of sodium and alumina-rich high-level radioactive waste (HLW) into borosilicate glasses faces the problem of nepheline (NaAlSiO4) crystallization during canister-centerline cooling (CCC), which is potentially detrimental to the durability and long-term stability of the final waste form. Some components within the nuclear waste – such as CaO, B2O3, Li2O, Fe2O3, etc. – have been shown to have a profound influence on the propensity of nepheline formation, but the compositionally complex nature of HLW waste makes it difficult to ascertain the mechanisms behind crystallization in the HLW melt during cooling. Hence, this research aims to elucidate the compositional dependence on the structure, crystallization kinetics and chemical durability of simplified HLW glasses designed in the crystallization phase field of nepheline (NaAlSiO4), with an emphasis on understanding the effect of oxides namely CaO, B2O3, Li2O, and Fe2O3. Accordingly, glasses designed in the CaO-Na2O-Al2O3-SiO2, Na2O-Al2O3-B2O3-SiO2, Li2O-Na2O-Al2O3-B2O3-SiO2, and Na2O-Fe2O3-Al2O3-B2O3-SiO2 systems have been the subject of this research.
Crystallization studies on glasses in the Na2O–CaO–Al2O3–SiO2 system indicate that the sequence of polymorphic phase transformations in these glass-ceramics is dictated by the compositional chemistry of parent glasses and local environments of different species in the glass structure, for example, sodium environment in glasses becomes highly ordered with decreasing Na2O/CaO ratio, thus favoring the formation of hexagonal nepheline, while cubic polymorph is the stable phase in SiO2–poor glass-ceramics with (Na2O+CaO)/Al2O3 > 1. In the Na2O–Al2O3–B2O3–SiO2 system, crystallization studies indicate that boron suppresses crystallization by staying in the glassy phase and not entering the nepheline crystal. It is found that nepheline crystallization is more strongly suppressed when B2O3 is substituted against Al2O3 than when substituted against SiO2. With increasing B2O3, there is a decrease in the liquidus temperature of the melts along with an increase in viscosity at the liquidus temperature. The increase in viscosity at the liquidus is likely to be the main reason behind suppression in the extent of crystallization in these glasses. Furthermore, the compositional dependence on crystallization and chemical durability is determined in Li2O–Na2O–Al2O3–B2O3–SiO2 glasses by performing Canister Centerline Cooling (CCC) treatments and Product Consistency Tests (PCT). It is found that a direct correlation exists between the extent of nepheline formation and the increase in dissolution of B, Na and Li elements in an aqueous environment. The change in the thermal history of glasses due to different cooling rates is found to have a profound impact on dissolution.
Lastly, heat treatments conducted have been conducted as a function of heating atmosphere on glasses in the Na2O–Fe2O3–Al2O3–B2O3–SiO2 system. It is found that while iron coordination in glasses and glass-ceramics changes as a function of glass chemistry, the heating atmosphere during crystallization exhibits a minimal effect on iron redox. The change in the heating atmosphere does not affect the phase assemblage but does affect the microstructural evolution. For future work, it is recommended that more complex compositions be explored in the 7-component Li2O-Na2O-CaO-Fe2O3-Al2O3-B2O3-SiO2 system to understand the combined effect of the species studied in this thesis on crystallization and chemical durability of model HLW glasses.
Subject (authority = RUETD)
Topic
Materials Science and Engineering
Subject (authority = local)
Topic
Nepheline
Subject (authority = local)
Topic
Crystallization
Subject (authority = local)
Topic
Glasses
Subject (authority = local)
Topic
Glass-ceramics
Subject (authority = local)
Topic
Chemical durability
Subject (authority = local)
Topic
Polymorphism
Subject (authority = local)
Topic
Structure
Subject (authority = local)
Topic
Viscosity
Subject (authority = local)
Topic
Liquidus
Subject (authority = local)
Topic
Iron redox
Subject (authority = local)
Topic
Heating atmosphere
Subject (authority = local)
Topic
Dissolution
Subject (authority = LCSH)
Topic
Nephelite
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Title
Rutgers University Electronic Theses and Dissertations
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ETD_10181
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1 online resource (xxiv, 250 pages) : illustrations
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Ph.D.
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Includes bibliographical references
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School of Graduate Studies Electronic Theses and Dissertations
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rucore10001600001
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Identifier (type = doi)
doi:10.7282/t3-waxs-bt57
Genre (authority = ExL-Esploro)
ETD doctoral
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The author owns the copyright to this work.
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Deshkar
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Ambar
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2019-08-24 00:41:15
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Ambar Deshkar
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Rutgers University. School of Graduate Studies
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I hereby grant to the Rutgers University Libraries and to my school the non-exclusive right to archive, reproduce and distribute my thesis or dissertation, in whole or in part, and/or my abstract, in whole or in part, in and from an electronic format, subject to the release date subsequently stipulated in this submittal form and approved by my school. I represent and stipulate that the thesis or dissertation and its abstract are my original work, that they do not infringe or violate any rights of others, and that I make these grants as the sole owner of the rights to my thesis or dissertation and its abstract. I represent that I have obtained written permissions, when necessary, from the owner(s) of each third party copyrighted matter to be included in my thesis or dissertation and will supply copies of such upon request by my school. I acknowledge that RU ETD and my school will not distribute my thesis or dissertation or its abstract if, in their reasonable judgment, they believe all such rights have not been secured. I acknowledge that I retain ownership rights to the copyright of my work. I also retain the right to use all or part of this thesis or dissertation in future works, such as articles or books.
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2019-09-30T11:13:29
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