Synthesis and characterization of complex phosphates of alkaline elements, magnesium and zirconium as potential ceramics for nuclear waste immobilization

Synthesis and characterization of complex phosphates of alkaline elements, magnesium and zirconium as potential ceramics for nuclear waste immobilization

Phases of variable composition A2−хА'хMg0.5Zr1.5(PO4)3 (АA' – KNa, KRb, KCs, 0 ≤ x ≤ 2) with langbeinite and kosnarite structures can serve as matrices immobilizing radioactive waste. They were synthesized by sol-gel method followed by heat treatment and investigated by X-ray diffraction a...

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Bibliographic Details
Published in:Solid state sciences Vol. 149; p. 107481
Main Authors: Pet'kov, V.I., Alekseev, A.A., Asabina, Е.А., Zanozin, I.D., Kulikova, E.V., Borovikova, Е.Y.
Format: Journal Article
Language:English
Published: Elsevier Masson SAS 01-03-2024
Subjects:
Alkali metals
Chemical durability
Complex phosphates
Kosnarite
Langbeinite
Phase formation
Radwaste
Thermal expansion
Thermal expansion
Complex phosphates
Langbeinite
Alkali metals
Kosnarite
Radwaste
Chemical durability
Phase formation
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Summary:Phases of variable composition A2−хА'хMg0.5Zr1.5(PO4)3 (АA' – KNa, KRb, KCs, 0 ≤ x ≤ 2) with langbeinite and kosnarite structures can serve as matrices immobilizing radioactive waste. They were synthesized by sol-gel method followed by heat treatment and investigated by X-ray diffraction at different temperatures, IR spectroscopy, scanning electron microscopy and electron probe microanalysis. A Rietveld refinement of the KCsMg0.5Zr1.5(PO4)3 structure showed that the framework is formed by octahedra (Mg/Zr)O6 and tetrahedra PO4 connected by vertices; potassium and cesium cations are located in cavities. When the temperature changes, phosphates with the langbeinite structure expand uniformly in all directions: αа = αb = αc = (4.2−6.6) ∙ 10−6 °C−1, without undergoing polymorphic transitions. Phosphate Na2Mg0.5Zr1.5(PO4)3, which crystallizes in the kosnarite structure type, expands anisotropically: αа = −2.6·10−6, αс = 8.2·10−6, αav = 1.0·10−6 °C−1. The chemical durability test shows that the leaching rate of Cs ions from the solid solution with langbeinite structure is of the order of 10−5 g cm−2 d−1. [Display omitted] •A2−хА'хMg0.5Zr1.5(PO4)3 (АA' – KNa, KRb, KCs, 0 ≤ x ≤ 2) phosphates were synthesized.•KCsMg0.5Zr1.5(PO4)3 structure is based on framework from octahedra and tetrahedra.•K2−хRbхMg0.5Zr1.5(PO4)3 phosphates (langbeinite) have isotropic thermal expansion.•Na2Mg0.5Zr1.5(PO4)3 (NZP) is a low-expanding substance with a significant anisotropy.
ISSN:1293-2558
1873-3085
DOI:10.1016/j.solidstatesciences.2024.107481