Effect of sintering temperature on crystal growth and evolution of CaZrTi2O7–CaNdTiNbO7 ceramics: Minor actinides immobilization host materials

[Display omitted] •The higher sintering temperature was better to crystal growth and densification.•The structure transform from low to high-symmetry earlier in higher temperature.•The optimal sintering temperature for crystal phase evolution should be 1500 °C.•The high crystallinity of zirconolite-...

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Bibliographic Details
Published in:Nuclear engineering and design 2024-12, Vol.429, p.113643, Article 113643
Main Authors: Ji, Shiyin, Ji, Xiuhua, Song, Yanhao, Wei, Yanxia, Duan, Tao
Format: Article
Language:English
Subjects:
Crystal Evolution
High-level radioactive waste
Pyrochlore
Sintering Temperature
Zirconolite
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Summary:[Display omitted] •The higher sintering temperature was better to crystal growth and densification.•The structure transform from low to high-symmetry earlier in higher temperature.•The optimal sintering temperature for crystal phase evolution should be 1500 °C.•The high crystallinity of zirconolite-pyrochlore were synthesized above 1300 °C.•A novel perspective would be provided for the design of HLW immobilization. Regulation of microstructure and processing cost of waste form are important for the design and application of high-level radioactive waste immobilization. In this study, CaZrTi2O7 (zirconolite) – CaNdTiNbO7 (pyrochlore) ceramics were synthesized via conventional sintering method at 1000–1500 °C to investigate the effect of sintering temperature on the microstructure, solidification, and crystal evolution. The powder x-ray diffraction (XRD) and backscattered scanning electron microscopy–energy dispersive spectroscopy (BSEM–EDS) results indicated gradual formation of zirconolite and pyrochlore ceramics, following with their densification when increasing sintering temperature. It was found that sintering temperature should be higher than 1300 °C to form zirconolite-pyrochlore solid solutions. Densified pyrochlore was obtained at 1500 °C. In addition, transformation from relatively low-symmetry lattice to higher-symmetry lattice was found with an increase in sintering temperature. Furthermore, higher temperature can enhance the crystal growth and densification in the ceramic composite. The finding in this study could provide important suggestions to design and process zirconolite-pyrochlore waste forms for industrial application.
ISSN:0029-5493
DOI:10.1016/j.nucengdes.2024.113643