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Zirconolite Ceramic and Glass-Ceramic Wasteforms

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A special issue of Ceramics (ISSN 2571-6131).

Deadline for manuscript submissions: closed (31 October 2023) | Viewed by 12715

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Special Issue Editors

Dr. Lewis R Blackburn

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Guest Editor

Immobilisation Science Laboratory, Department of Materials Science and Engineering, University of Sheffield, Sheffield S1 3JD, UK
Interests: ceramic wasteform design and synthesis; crystalline materials for actinide disposition; zirconolite, pyrochlore and related titanate/zirconates; SYNROC; advanced materials characterisation

Prof. Dr. Michael I. Ojovan

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Guest Editor

Department of Materials, Imperial College London, South Kensington Campus, Exhibition Road, London SW7 2AZ, UK
Interests: amorphous and crystalline materials; glass transition; vitrification; nuclear waste management; immobilisation; radiation effects
Special Issues, Collections and Topics in MDPI journals

Dr. Daniel Gregg

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Guest Editor

Australian Nuclear Science and Technology Organisation (ANSTO), Lucas Heights, NSW 2232, Australia
Interests: 99Mo production waste treatment; hot isostatic pressing for waste immobilisation; pyroprocessing waste treatment; SYNROC wasteform development for challenging nuclear wastes

Special Issue Information

Dear Colleagues,

As nuclear power continues to contribute significantly to the international energy portfolio, there remains a pressing need to develop advanced materials capable of facilitating the safe immobilisation, storage, and final disposal of highly radioactive nuclear waste streams. Several decades of continued wasteform development has identified a number of glass and ceramic compositions that could feasibly immobilise actinide-rich wastes, whilst conferring passive safety that is compatible with geological disposal. In particular, single-phase ceramic wasteform compositions are a feasible pathway towards the ultimate disposition of stockpiled actinides, such as Pu. One such phase, zirconolite (CaZrTi₂O₇) has attracted significant attention on the basis of high chemical durability, chemical flexibility, radiation stability and relative ease of processing.

Accordingly, this Special Issue of ‘Ceramics’ is focussed on the properties of zirconolite and related titanate/zirconate wasteform materials. The aim of this issue is to connect scientists around the globe with interests in the synthesis and processing optimisation; mechanical, thermal and electronic properties; and durability and radiation stability of zirconolite single/polyphase ceramics and glass-ceramic composites, alongside related wasteform materials. The guest editors kindly encourage submissions from researchers internationally to contribute original work, both experimental and theoretical, and review articles conveying recent advances.

Dr. Lewis R Blackburn
Prof. Dr. Michael I. Ojovan
Dr. Daniel Gregg
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Ceramics is an international peer-reviewed open access quarterly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

ceramic wasteforms
glass-ceramic wasteforms
zirconolite
pyrochlore
actinide immobilisation
SYNROC

Published Papers (6 papers)

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Research

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10 pages, 2143 KiB

Open AccessArticle

Investigation of the Effect of Milling Duration on a Ce-Gd Doped Zirconolite Phase Assemblage Synthesised by Hot Isostatic Pressing

by Merve Kuman, Laura J. Gardner, Lewis R. Blackburn, Martin C. Stennett, Neil C. Hyatt and Claire L. Corkhill

Ceramics 2023, 6(1), 707-716; https://doi.org/10.3390/ceramics6010043 - 11 Mar 2023

Viewed by 1983

Abstract

Zirconolite is a candidate ceramic wasteform under consideration for the immobilisation of the UK civil PuO₂ inventory. In the present work, a baseline dual-substituted zirconolite with the target composition (Ca_0.783Gd_0.017Ce_0.2)(Zr_0.883Gd_0.017Ce_0.1)(Ti_1.6Al_0.4)O₇ was fabricated by hot isostatic pressing (HIPing). In order to optimise the microstructure properties and improve the obtained yield of the zirconolite phase, a range of planetary ball milling parameters were investigated prior to consolidation by HIP. This included milling the batched oxide precursors at 400 rpm for up to 120 min, the pre-milling of CeO₂ (PuO₂ surrogate) to reduce the particle size and using a CeO₂ source with finer particle size (<5 µm). The HIPed zirconolite product consisted of both zirconolite-2M and zirconolite-3T polytypes in varying proportions; however, an additional perovskite phase was obtained in varying quantities as a secondary phase. Ce L₃-edge X-ray absorption spectroscopy was utilised to determine the Ce oxidation state. In this study, the ideal milling parameter for the fabrication of zirconolite waste forms was defined as 60 min at 400 rpm. Full article

(This article belongs to the Special Issue Zirconolite Ceramic and Glass-Ceramic Wasteforms)

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8 pages, 2896 KiB

Open AccessCommunication

Process Development of Zirconolite Ceramics for Pu Disposition: Use of a CuO Sintering Aid

by Aidan A. Friskney, Ismail Aldean, Claire L. Corkhill and Lewis R. Blackburn

Ceramics 2023, 6(1), 678-685; https://doi.org/10.3390/ceramics6010041 - 08 Mar 2023

Viewed by 1358

Abstract

Zirconolite-structured ceramics are candidate wasteform materials for the immobilisation of separated Pu. Due to the refractory properties of zirconolite and other titanates, removing residual porosity remains challenging in the final wasteform product when utilising a conventional solid state sintering route. Herein, we demonstrate that the addition of CuO as a sintering aid increases densification and promotes grain growth. Moreover, zirconolite phase formation was enhanced at lower process temperatures than typically required (≥1350 °C). CuO addition allowed an equivalent density to be reached using process temperatures of 250 °C lower than the undoped composition. At 150 °C lower than the undoped zirconolite, the addition of CuO resulted in a favourable microstructure and phase assemblage, as confirmed via X-ray diffraction and scanning electron microscopy. Secondary phases of CaTiO₃ and Ca_0.25Cu_0.75TiO₃ were observed at some processing temperatures, which may prove deleterious to wasteform performance. The use of a CuO sintering aid provides an avenue for the further development of the thermal processing of ceramic wasteform materials. Full article

(This article belongs to the Special Issue Zirconolite Ceramic and Glass-Ceramic Wasteforms)

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16 pages, 4827 KiB

Open AccessArticle

Characterisation of a Complex CaZr_0.9Ce_0.1Ti₂O₇ Glass–Ceramic Produced by Hot Isostatic Pressing

by Malin C. J. Dixon Wilkins, Clémence Gausse, Luke T. Townsend, Laura J. Gardner and Claire L. Corkhill

Ceramics 2022, 5(4), 1035-1050; https://doi.org/10.3390/ceramics5040074 - 19 Nov 2022

Cited by 2 | Viewed by 2047

Abstract

The behaviour of Ce-containing zirconolites in hot isostatically pressed (HIPed) materials is complex, characterised by redox interactions between the metallic HIP canister that result in reduction of Ce⁴⁺ to Ce³⁺. In this work, a glass–ceramic of composition 70 wt.% CaZr_0.9Ce_0.1Ti₂O₇ ceramic in 30 wt.% Na₂Al₂Si₆O₁₆ glass was produced by HIP (approx. 170 cm³ canister) to examine the extent of the material–canister interaction. A complex material with six distinct regions was produced, with the extent of Ce reduction varying depending on the distance from the canister. Notably, the innermost bulk regions (those approximately 7 mm from the canister) contained only Ce⁴⁺, demonstrating that a production-scale HIPed glass–ceramic would indeed have a bulk region unaffected by the reducing environment induced by a ferrous HIP canister despite the flow of glass at the HIP temperature. Each of the six regions was characterised by XRD (including Rietveld method refinements), SEM/EDX and linear combination fitting of Ce L₃-edge XANES spectra. Regions in the lower part of the canister were found to contain a significantly higher fraction of Ce⁴⁺ compared to the upper regions. Though zirconolite-2M was the major crystalline phase observed in all regions, the relative abundances of minor phases (including sphene, baddeleyite, rutile and perovskite) were higher in the outermost regions, which comprised a significantly reduced Ce inventory. Full article

(This article belongs to the Special Issue Zirconolite Ceramic and Glass-Ceramic Wasteforms)

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16 pages, 11373 KiB

Open AccessArticle

Investigation of the Microstructure of Fine-Grained YPO₄:Gd Ceramics with Xenotime Structure after Xe Irradiation

by Dmitriy A. Mikhaylov, Ekaterina A. Potanina, Aleksey V. Nokhrin, Albina I. Orlova, Pavel A. Yunin, Nikita V. Sakharov, Maksim S. Boldin, Oleg A. Belkin, Vladimir A. Skuratov, Askar T. Issatov, Vladimir N. Chuvil’deev and Nataliya Y. Tabachkova

Ceramics 2022, 5(2), 237-252; https://doi.org/10.3390/ceramics5020019 - 13 Jun 2022

Cited by 8 | Viewed by 2197

Abstract

This paper reports on the preparation of xenotime-structured ceramics using the Spark Plasma Sintering (SPS) method. Y_0.95Gd_0.05PO₄ (YPO₄:Gd) phosphates were obtained using the sol-gel method. The synthesized powders were nanodispersed and were agglomerated (the agglomerates sizes were 10–50 µm). The ceramics had a fine-grained microstructure and a high relative density (98.67 ± 0.18%). The total time of the SPS process was approximately 18 min. The sintered high-density YPO₄:Gd ceramics with a xenotime structure were irradiated with ¹³²Xe⁺²⁶ ions with 167 MeV of energy and fluences in the range of 1 × 10¹²–3 × 10¹³ cm⁻². Complete amorphization was not achieved even at the maximum fluence. The calculated value of the critical fluence was (9.2 ± 0.1) × 10¹⁴ cm⁻². According to the results of grazing incidence X-ray diffraction (GIXRD), the volume fraction of the amorphous structure increased from 20 to 70% with increasing fluence from 1 × 10¹² up to 3 × 10¹³ cm⁻². The intensity of the 200 YPO₄:Gd XRD peak reached ~80% of the initial intensity after recovery annealing (700 °C, 18 h). Full article

(This article belongs to the Special Issue Zirconolite Ceramic and Glass-Ceramic Wasteforms)

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Review

Jump to: Research

50 pages, 8002 KiB

Open AccessReview

Zirconolite Matrices for the Immobilization of REE–Actinide Wastes

by Sergey V. Yudintsev, Maximilian S. Nickolsky, Michael I. Ojovan, Olga I. Stefanovsky, Victor I. Malkovsky, Amina S. Ulanova and Lewis R. Blackburn

Ceramics 2023, 6(3), 1573-1622; https://doi.org/10.3390/ceramics6030098 - 15 Jul 2023

Cited by 4 | Viewed by 1500

Abstract

The structural and chemical properties of zirconolite (ideally CaZrTi₂O₇) as a host phase for separated REE–actinide-rich wastes are considered. Detailed analysis of both natural and synthetic zirconolite-structured phases confirms that a selection of zirconolite polytype structures may be obtained, determined by the provenance, crystal chemistry, and/or synthesis route. The production of zirconolite ceramic and glass–ceramic composites at an industrial scale appears most feasible by cold pressing and sintering (CPS), pressure-assisted sintering techniques such as hot isostatic pressing (HIP), or a melt crystallization route. Moreover, we discuss the synthesis of zirconolite glass ceramics by the crystallization of B–Si–Ca–Zr–Ti glasses containing actinides in conditions of increased temperatures relevant to deep borehole disposal (DBD). Full article

(This article belongs to the Special Issue Zirconolite Ceramic and Glass-Ceramic Wasteforms)

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18 pages, 1194 KiB

Open AccessReview

A Review of Zirconolite Solid Solution Regimes for Plutonium and Candidate Neutron Absorbing Additives

by Lewis R. Blackburn, Claire L. Corkhill and Neil C. Hyatt

Ceramics 2023, 6(3), 1330-1347; https://doi.org/10.3390/ceramics6030082 - 22 Jun 2023

Viewed by 1922

Abstract

Should the decision be made to immobilise the UK Pu inventory through a campaign of Hot Isostatic Pressing (HIP) in a zirconolite matrix, prior to placement in a geological disposal facility (GDF), a suite of disposability criteria must be satisfied. A GDF safety case should be able to demonstrate that post-closure criticality is not a significant concern by demonstrating that such an event would have a low likelihood of occurring and low consequence if it were to occur. In the case of ceramic wasteforms, an effective means of criticality control may be the co-incorporation of a requisite quantity of a suitable neutron absorbing additive, either through co-immobilisation within the host structure or the encapsulation of discrete particles within the grain structure. Following an initial screening of a range of potential neutron absorbing additives, a literature-based assessment of the solid solution limits of a number of potential additives (Gd, Hf, Sm, In, Cd, B) in the candidate zirconolite (CaZrTi₂O₇) wasteform is presented. Key areas of research that are in need of development to further support the safety case for nuclearised HIP for Pu inventories are discussed. Full article

(This article belongs to the Special Issue Zirconolite Ceramic and Glass-Ceramic Wasteforms)

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