Article

Effect of Al 2 O 3 concentration on zirconolite (Ca (Zr, Hf) Ti 2 O 7) crystallization in (TiO 2, ZrO 2, HfO 2)-rich SiO 2–Al 2 O 3–CaO–Na 2 O glasses

Journal of Materials Science (Impact Factor: 2.31). 01/2007; 42(20). DOI: 10.1007/s10853-007-1810-8

ABSTRACT Glass-ceramic matrices containing zirconolite (nominally Ca(Zr,Hf)Ti 2 O 7) crystals in their bulk that would incorporate high proportions of minor actinides (Np, Am, Cm) or plutonium could be envisaged for their immobilization. Zirconolite-based glass-ceramics can be prepared by controlled crystallization of zirconolite in glasses belonging to SiO 2 –Al 2 O 3 –CaO–Na 2 O–TiO 2 –ZrO 2 – HfO 2 system. In this study, neodymium was used as tri-valent actinides surrogate. Increasing Al 2 O 3 concentration in glass composition had a strong effect on the nucleation rate I z of zirconolite crystals in the bulk, on the amount of neodymium incorporated in zirconolite phase and on the crystal growth rate of silicate phases (titanite + anorthite) from glass surface. These results could be explained by the existence of competition—in favor of aluminum—between Al 3+ and (Ti 4+ , Zr 4+ , Hf 4+) ions for their association with charge compensators cations to facilitate their incorpora-tion in the glassy network. Differential thermal analysis (DTA) was used to study exothermal effects associated with bulk and surface crystallization. 27 Al magic angle spinning nuclear magnetic resonance (MAS NMR) spectra showed that aluminum enters glasses network predomi-nantly in 4-fold coordination. Neodymium optical absorp-tion and fluorescence spectroscopies showed that the Al 2 O 3 concentration changes performed in this study had not significant effect on Nd 3+ ions environment in glasses.

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