Structure of Glass‐Forming Melts‐Lanthanide in Borosilicates

Li, Hong; Li, Liyu; Qian, Morris; Strachan, Denis M.; Wang, Zheming

doi:10.1002/9781118408063.ch6

Cited by 3 publications

(2 citation statements)

References 41 publications

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“…For instance, Gasnier et al 33 observed an amorphous phase separation with Nd + B enriched versus Nd + Si enriched phases only when the RE oxide concentration was high (8‐10 mol.% Nd 2 O 3 ). By contrast, studies by Li and co‐workers 86‐89 suggest that RE (La, Nd, and Gd were studied) ions partition first to a borate phase then with increasing concentration to a silicate phase. The compositions described in the current paper have considerably less Al 2 O 3 than the cited studies, but contain other metals requiring charge compensation to dissolve in the glass network (Mo, Zr).…”

Section: Discussionmentioning

confidence: 90%

Partitioning of rare earths in multiphase nuclear waste glass‐ceramics

Chen

Marcial

Ahmadzadeh

et al. 2020

Int J of Appl Glass Sci

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Alumino‐borosilicate glass‐ceramics (GCs) containing alkali (Na), alkaline earth (Ca), rare earth (RE) (one of La … Lu, Y), and transition metals (Zr and Mo) were formulated to test the effects of composition and RE cation size on the crystallization of simulated nuclear waste GCs. Eight‐oxide glasses were formulated in the peraluminous ([Na2Oexcess]=[Na2O]‐[Al2O3]‐[ZrO2]<0) region with 10 mol.% RE2O3 and 15 mol.% B2O3. Glasses were melted and quenched, reheated, and slow‐cooled to promote crystallization, and then characterized using quantitative X‐ray diffraction and electron probe microanalysis. Transition metal phases [powellite (Ca,Na,RE)MoO4 and zirconia (Zr,RE)O2 or zircon (Zr,RE)SiO4] always formed, while borosilicate (RE3BSi2O10) or silicate [oxyapatite (RE,Ca,Na)10Si6O26 or keiviite (RE2Si2O7)] plus borate (REBO3) phases also formed, depending on the size of the RE cation and hence its preferred coordination number. All crystalline phases were found to contain RE elements, and often phases incorporated other cations (Zr, Ca, B) which were not nominally part of their pure stoichiometry. These results suggested that the glass formulation and RE size strongly influenced the RE environment in the glass and hence the crystal phases formed. The formation of RE borosilicate, versus separate RE borate and RE silicate phases, also suggested original differences in the glass structure.

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Section: Discussionmentioning

confidence: 90%

Partitioning of rare earths in multiphase nuclear waste glass‐ceramics

Chen

Marcial

Ahmadzadeh

et al. 2020

Int J of Appl Glass Sci

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“…Before we discuss the impact of Nd 2 O 3 on the solubility of MoO 3 in the aluminoborosilicate glasses under investigation, it is important to understand the structural role of Nd 2 O 3 in these glasses, as it has direct implications on the solubility of MoO 3 . The structural coordination of rare-earth cations in alkali/alkaline-earth aluminoborosilicate glasses has been studied in detail primarily by researchers from two countries, United States − and France, ,− owing to their high relevance in the field of nuclear waste immobilization. On the basis of the investigated compositional chemistries, there exist two different opinions about the coordination of rare-earth cations in these glasses.…”

Section: Discussionmentioning

confidence: 99%

Compositional Dependence of Solubility/Retention of Molybdenum Oxides in Aluminoborosilicate-Based Model Nuclear Waste Glasses

et al. 2018

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Molybdenum oxides are an integral component of the high-level waste streams being generated from the nuclear reactors in several countries. Although borosilicate glass has been chosen as the baseline waste form by most of the countries to immobilize these waste streams, molybdate oxyanions (MoO) exhibit very low solubility (∼1 mol %) in these glass matrices. In the past three to four decades, several studies describing the compositional and structural dependence of molybdate anions in borosilicate and aluminoborosilicate glasses have been reported in the literature, providing a basis for our understanding of fundamental science that governs the solubility and retention of these species in the nuclear waste glasses. However, there are still several open questions that need to be answered to gain an in-depth understanding of the mechanisms that control the solubility and retention of these oxyanions in glassy waste forms. This article is focused on finding answers to two such questions: (1) What are the solubility and retention limits of MoO in aluminoborosilicate glasses as a function of chemical composition? (2) Why is there a considerable increase in the solubility of MoO with incorporation of rare-earth oxides (for example, NdO) in aluminoborosilicate glasses? Accordingly, three different series of aluminoborosilicate glasses (compositional complexity being added in a tiered approach) with varying MoO concentrations have been synthesized and characterized for their ability to accommodate molybdate ions in their structure (solubility) and as a glass-ceramic (retention). The contradictory viewpoints (between different research groups) pertaining to the impact of rare-earth cations on the structure of aluminoborosilicate glasses are discussed, and their implications on the solubility of MoO in these glasses are evaluated. A novel hypothesis explaining the mechanism governing the solubility of MoO in rare-earth containing aluminoborosilicate glasses has been proposed.

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