A5027418902- Nuclear materials and radiation effects
- Radioactive element chemistry and processing
- Nuclear Materials and Properties
- Ferroelectric and Piezoelectric Materials
- Advanced Condensed Matter Physics
- Microwave Dielectric Ceramics Synthesis
- Luminescence Properties of Advanced Materials
- Glass properties and applications
- Advanced materials and composites
- MXene and MAX Phase Materials
- High-pressure geophysics and materials
- Recycling and utilization of industrial and municipal waste in materials production
- Infectious Diseases and Tuberculosis
- Electronic and Structural Properties of Oxides
- Advanced ceramic materials synthesis
- Hydrocarbon exploration and reservoir analysis
University of Sheffield
2020-2024
Zirconolite (CaZrTi2O7) has been identified as a candidate ceramic wasteform for the immobilisation and disposal of Pu inventories, which there is no foreseen future use. Here, we provide an overview relevant zirconolite solid solution chemistry with respect to Ce, U incorporation, alongside summary available literature on aqueous durability. The phase may accommodate wide variety tri- tetravalent actinide rare-earth dopants through isovalent heterovalent solution, e.g. CaZr1–xPuxTi2O7 or...
A series of Ca1-xCexZrTi2-2xCr2xO7 zirconolite ceramics (0 ≤ x 0.35) were reactively sintered in air at 1350 °C for 20 h. Single phase zirconolite-2M was formed 0.15, with Cr2O3 and an undesirable Ce-bearing perovskite present above = 0.20. Electron diffraction analysis confirmed that the polytype maintained over solid solution. X-ray absorption near edge structure (XANES) data determined between 10–20% Ce speciated as Ce3+, Cr uniformly Cr3+ features consistent occupation octahedral sites...
A series of zirconolite ceramics with nominal stoichiometry CaZr1-xCexTi2O7 (0.0 ≤ x 0.4) were synthesised under oxidizing, inert and reducing conditions, by a conventional solid-state cold press sinter method. The evolution phase assemblage microstructure characterized XRD, SEM-EDS, Ce-L3 XANES Raman spectroscopy techniques. It was determined that the relative yield zirconolite-2M zirconolite-4M polytypes, alongside secondary perovskite phases, influenced processing environment via control...
Zirconolite is considered to be a suitable wasteform material for the immobilization of Pu and other minor actinide species produced through advanced nuclear separations. Here, we present comprehensive investigation Dy3+ incorporation within self-charge balancing zirconolite Ca1-xZr1-xDy2xTi2O7 solid solution, with view simulate trivalent immobilization. Compositions in substitution range 0.10 ≤ x 1.00 (Δx = 0.10) were fabricated by conventional mixed oxide synthesis, two-step sintering...
The structural and chemical properties of zirconolite (ideally CaZrTi2O7) as a host phase for separated REE–actinide-rich wastes are considered. Detailed analysis both natural synthetic zirconolite-structured phases confirms that selection polytype structures may be obtained, determined by the provenance, crystal chemistry, and/or synthesis route. production ceramic glass–ceramic composites at an industrial scale appears most feasible cold pressing sintering (CPS), pressure-assisted...
A series of zirconolite ceramics with stoichiometry Ca1-xCexZrTi2-2xAl2xO7 (x = 0–0.35), considered as a host phase for the immobilisation separated plutonium, were prepared from mixture oxide precursors by sintering in air at 1450 °C. Ce was utilised structural surrogate Pu, Al added to provide charge compensation. XRD and electron diffraction analyses indicated crystallisation zirconolite-2M polytype all compositions, accompanied various secondary phases contingent on doping level,...
Abstract A series of zirconolite ceramics with composition CaZr 1‐x Th x Ti 2 O 7 (Δx = 0.10) were reactively sintered at 1350°C for 20 h, in air (0 ≤ 0.60) and 5% H /N 0.40). sample corresponding to 0.20 was also produced by hot isostatic pressing (HIP) 1300°C 100 MPa 4 hours. 4+ immobilization most readily achieved under oxidizing conditions, preferentially incorporated within a pyrochlore‐structured phase the range 0.10 0.50, yet formation zirconolite‐4M polytype not observed. We report...
Abstract A fraction of the UK Pu inventory may be immobilised in a zirconolite ceramic matrix prior to disposal. Two compositions, targeting CaZr 0.80 Ce 0.20 Ti 2 O 7 and U , were fabricated by hot isostatic pressing, alongside reformulated composition, nominally Ca Zr 0.90 0.30 1.60 Al 0.40 with an excess added preclude formation accessory perovskite phase. Materials subjected accelerated leaching variety acidic alkaline media at 90 °C, over cumulative period 14 d. The greatest release was...
Abstract In order to demonstrate the deployment of Hot Isostatic Pressing (HIP) for immobilisation Pu stocks and residues, a series active inactive zirconolite formulations have been processed characterised. this instance, Ce, U, Th applied as chemical surrogates 4+ . A range targeting isovalent Zr site substitution ( i.e. simulate CaZr 1-x x Ti 2 O 7 ) by HIP characterised powder X-ray diffraction, scanning electron microscopy, in determine surrogate partitioning between host phase,...
Abstract Reactive spark plasma sintering has been utilised as a high-throughput processing route for the synthesis of two simulant zirconolite wasteform materials, targeting Ca 0.80 Ce 0.20 ZrTi 1.60 M 0.40 O 7 (M = Fe 3+ and Al ). Materials were processed under 15 MPa uniaxial pressure, with heating/cooling rates 100 °C/min to 1320 °C, maintained vacuum. Despite moderate yield (> 80 wt%) zirconolite-2M, considerable Ce-rich perovskite phase was formed in both formulations, attributed...
Magnesium aluminosilicate and magnesium borosilicate glass formulations were developed evaluated for the immobilisation of radioactive waste known as Magnox sludge. Glass compositions synthesised using two simplified bounding simulants, including corroded metallic uranium at loadings up to 50 wt.%. The glasses immobilising simulant formed generally homogenous fully amorphous glasses, while those wastes contained crystallites UO2 U3O8. Uranium speciation within was investigated by micro-focus...
Altering the CaO to ZnO ratio of alkali borosilicate glass, in favour ZnO, causes phase separation with hardystonite-like (Ca 2 ZnSi O 7 ) and willemite-like (ZnSi 4 structures identified. This is concurrent increased glass durability.
Indium (In) is a neutron absorbing additive that could feasibly be used to mitigate criticality in ceramic wasteforms containing Pu the immobilised form, for which zirconolite (nominally CaZrTi2O7) candidate host phase. Herein, solid solutions Ca1-xZr1-xIn2xTi2O7 (0.10 ≤ x 1.00; air synthesis) and Ca1-xUxZrTi2-2xIn2xO7 (x = 0.05, 0.10; argon were investigated by conventional state sintering at temperature of 1350 °C maintained 20 h, with view characterise In3+ substitution behaviour phase...
The influence of A-site vacancies on zirconate perovskite structured ceramics formula A<sub>1−x</sub>La<sub>2x/3</sub>ZrO<sub>3</sub> (A = Ca, Sr, Ba) has been investigated using 400 keV Kr<sup>+</sup><italic>in situ</italic> ion irradiation in a TEM with varied temperature from 100 K to 673 K.
Abstract A sample of zirconolite with nominal composition Ca 0.80 Ce 0.20 ZrTi 1.60 Cr 0.40 O 7 was processed via Hot Isostatic Pressing (HIP), a dwell temperature and pressure 1320 °C/100 MPa maintained for 4 h. The produced wasteform characterised by powder XRD, SEM–EDS, L 3 K-edge XANES. significant portion the inventory did not fully partition within phase, instead remaining as CeO 2 microstructure. Inspection stainless steel–ceramic interface detailed presence an interaction region...
Uranium speciation and redox behaviour is of critical importance in the nuclear fuel cycle. X-ray absorption near-edge spectroscopy (XANES) commonly used to probe oxidation state uranium, other elements, at macroscopic microscopic scale, within materials. Two-dimensional (2D) maps, derived from microfocus fluorescence XANES data, provide essential information on spatial variation gradients active elements such as uranium. In present work, we elaborate evaluate approaches construction 2D an...