Phase Separation and Crystallisation in UK HLW Vitrified Products

Short, Rick

doi:10.1016/j.mspro.2014.10.013

Cited by 25 publications

(21 citation statements)

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“…Journal of Non-Crystalline Solids 473 (2017) [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] an increase to T PS would cause the lower viscosity separated phase B to coalesce for a longer period of time during cooling forming larger regions. Furthermore, the higher viscosity Si-rich phase would cause the cation-rich phase B deposits to combine into the lowest possible surface area, hence why more spherical deposits are observed with increasing These observations indicate that an analogous theory can be proposed for calcium borosilicate systems, in which increasing [MoO 3 ] also causes an increase in T PS and T C .…”

Section: Kb Patel Et Almentioning

confidence: 99%

“…Journal of Non-Crystalline Solids 473 (2017) [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] phase, the lattice parameters determined by refinement are initially higher than that of CaMoO 4 monocrystals (a = 5.222 Å and c = 11.425 Å [62]). This observation has been previously recorded for soda-lime borosilicates employing a similar fabrication technique [12,63] and emphasizes how the properties of a glassy phase can increase the lattice energy of embedded crystal phases [64].…”

Section: Kb Patel Et Almentioning

confidence: 99%

“…Above this solubility limit, it is possible for metastable phases to form leading to crystallization of molybdenum-rich phases [11,12]. The production of alkali molybdates (Na 2 MoO 4 , Cs 2 MoO 4 ), known as yellow phase, are particularly problematic owing to their high water solubility and ability to act as carriers for radioactive cesium and strontium [1,13]. This ability thus creates a contamination risk during final geological deposition by increasing corrosion probabilities [14,15].…”

Section: Introductionmentioning

confidence: 99%

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Impacts of composition and beta irradiation on phase separation in multiphase amorphous calcium borosilicates

Patel

Boizot

Facq

et al. 2017

Journal of Non-Crystalline Solids

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A B S T R A C TBorosilicate glasses for nuclear waste applications are limited in waste loading by the precipitation of watersoluble molybdates. In order to increase storage efficiency, new compositions are sought out that trap molybdenum in a water-durable CaMoO 4 crystalline phase. Factors affecting CaMoO 4 combination and glass-inglass phase separation in calcium borosilicate systems as a function of changing [MoO 3 ] and [B 2 O 3 ] are examined in this study in order to understand how competition for charge balancers affects phase separation. It further examines the influence of radiation damage on structural modifications using 0.77 to 1.34 GGy of 2.5 MeV electron radiation that replicates inelastic collisions predicted to occur over long-term storage. The resulting microstructure of separated phases and the defect structure were analyzed using electron microscopy, XRD, Raman and EPR spectroscopy prior to and post irradiation. Synthesized calcium borosilicates are observed to form an unusual heterogeneous microstructure composed of three embedded amorphous phases with a solubility limit~2.5 mol% MoO 3. Increasing [B 2 O 3 ] increased the areas of immiscibility and order of (MoO 4 ) 2 − anions, while increasing [MoO 3 ] increased both the phase separation and crystallization temperature resulting in phases closer to metastable equilibrium, and initiated clustered crystallization for [MoO 3 ] > 2.5 mol%. β-irradiation was found to have favorable properties in amorphous systems by creating structural disorder and defect assisted ion migration that thus prevented crystallization. It also increased reticulation in the borosilicate network through 6-membered boroxyl ring and Si ring cleavage to form smaller rings and isolated units. This occurred alongside an increased reduction of Mo 6 + with dose that can be correlated to molybdenum solubility.In compositions with existing CaMoO 4 crystallites, radiation caused a scattering effect, though the crystal content remained unchanged. Therefore β-irradiation can preferentially prevent crystallization in calcium borosilicates for [MoO 3 ] < 2.5 mol%, but has a smaller impact on systems with existing CaMoO 4 crystallites.

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Section: Kb Patel Et Almentioning

confidence: 99%

Section: Kb Patel Et Almentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Impacts of composition and beta irradiation on phase separation in multiphase amorphous calcium borosilicates

Patel

Boizot

Facq

et al. 2017

Journal of Non-Crystalline Solids

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“…Other phases commonly reported include molybdates and the so-called yellow phase. 5,[9][10][11] The presence of these secondary phases may have significant and deleterious effects on material performance as a wasteform. For example, yellow phase is more soluble in water than the glass matrix, providing an efficient route for radionuclides to escape the wasteform.…”

Section: Introductionmentioning

confidence: 99%

Atomic-scale description of interfaces in rutile/sodium silicate glass–crystal composites

Fossati

Rushton

Lee

2018

Phys. Chem. Chem. Phys.

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In this work interfaces between (Na2O)x(SiO2)1-x glasses (for x = 0.0, 0.1 and 0.2) and TiO2 crystals are simulated using molecular dynamics and empirical potentials. Interfaces are presented for the distinct terminating surfaces of TiO2 with Miller indices ≤2, the properties of which have been investigated using atomistic models. Simulations showed that partially ordered layers had been induced in the glass close to the interfaces, with successive oxygen-rich and cation-rich planes being noted. The first silicate layer in contact with the crystal tended to be highly-structured, with Si ions occupying well-defined positions that depend on the orientation of the crystal at the interface, and showing 2-dimensional ordering depending on glass composition. Finally, interface energies were calculated. These indicated that the interface formation may stabilise a crystal surface in comparison to maintaining a free surface. Results are presented suggesting that the structural flexibility of the glass network allows it to conform to the crystal, thereby providing charge compensation and avoiding large relaxation of the crystal structure close to the interfaces. Such interfacial properties could be crucial to improving phenomenological models of glass-crystal composite properties.

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“…In the UK, and internationally, alkali borosilicate glasses are the material of choice for vitrification of the fission products and minor actinides arising from nuclear fuel reprocessing, classified as High Level Waste (HLW) [2][3][4][5][6][7]. Modification of the UK HLW glass composition, by addition of CaO and ZnO, has been studied with the aim of improving processing characteristics and long term durability, as discussed elsewhere [2][3][4][5][6].…”

Section: Introductionmentioning

confidence: 99%

Comment on “Preliminary assessment of modified borosilicate glasses for chromium and ruthenium immobilization”, by Farid and Rahman

Hyatt

Corkhill

Bailey

et al. 2017

Materials Chemistry and Physics

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Farid and Rahman recently reported an investigation of the microstructure and alteration of borosilicate glasses designed for the immobilisation of UK radioactive wastes [Preliminary assessment of modified borosilicate glasses for chromium and ruthenium immobilization, Materials Chemistry and Physics, 186 (2017) 462-469]. The authors draw conclusions concerning the partitioning of elements within two devitrified spinel phases, at variance with previous studies of these materials. The authors also present solution chemistry and surface analysis data for alteration of these glasses, and postulate micro-cracks apparent in the gel layer of the altered glass to govern the extent of alteration. From analysis of data presented by Farid and Rahman, and comparison with previous studies, we show that their data are consistent with the presence of a single spinel phase of complex chemical composition, (Mg,Zn,Ni)(Cr,Fe,Al) 2 O 4. We show the chemistry and surface analysis data presented by Farid and Rahman to be contradictory, in terms of the relative alteration behaviour of these glasses, as verified by previous studies, and deduce that an alternative explanation is required to rationalise their observations. We also comment on other aspects of the report which require clarification.

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Phase Separation and Crystallisation in UK HLW Vitrified Products

Cited by 25 publications

References 1 publication

Impacts of composition and beta irradiation on phase separation in multiphase amorphous calcium borosilicates

Impacts of composition and beta irradiation on phase separation in multiphase amorphous calcium borosilicates

Atomic-scale description of interfaces in rutile/sodium silicate glass–crystal composites

Comment on “Preliminary assessment of modified borosilicate glasses for chromium and ruthenium immobilization”, by Farid and Rahman

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