In this study, a hydrothermal treatment (HT) at 200 °C was used to deal with the cracking of the external gelation-made thorium oxide (ThO2) microspheres and the effects of HT on the composition, microstructure, and cracking fraction of the microspheres were investigated. The results showed that HT removed the light weight impurities such as ammonium nitrate, degraded polyvinyl alcohol with light weight as well as absorbed and bonded water, thus resulting in a reduction of the weight loss of the gel microsphere by 26%. Owing to the removal of the impurities, HT led to the improvement of the crystallinity of the dried microspheres and the increase of specific surface area and pore size of the dried ones. Further, HT had distinct effect on the heat treatment of the microspheres: (1) For the drying process (240 °C) where an atmosphere of humidified air and wet microspheres were essential, the cracking fraction of the treated microspheres was only one-tenth of that of the original ones due to the removal of the bonded water by the HT. (2) In the case of elevated temperature treatment (650 and 1350 °C), the removal of residual polyvinyl alcohol by thermal oxidation was easy for the treated microspheres without obvious occurrence of cracking, however, it was not the case for the original counterparts. With the aid of HT, high-quality crack-free ThO2 microspheres were available after the heat treatment and would be potentially used as nuclear fuel for a solid-fueled thorium molten salt reactor.
Intact high-quality external gelation-made ThO2 ceramic microspheres were prepared.
PVA was eliminated by hydrothermal degradation and then an easy thermal oxidation process.
Hydrothermal-induced changes of the microstructure and composition of the thorium gel microspheres.
Hydrothermal treatment reduced the cracking fraction of the gel microspheres from 100 to 8.4%.
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This study was supported by the Thorium Molten Salt Reactor Nuclear Energy System under the Strategic Pioneer Sci. & Tech. Project of Chinese Academy of Sciences [Grant Number XDA02030000 and XDA02030200] and the Frontier Science Key Program of the Chinese Academy of Sciences [Grant Number QYZDY-SSW-JSC016].
Conceptualization: PW, JL; Methodology: PW, CY, HH; Formal analysis and investigation: JZ, SX, JC; Writing-original draft preparation: PW; Writing-review and editing: PW, CC; Funding acquisition: JL; Resources: PW, JL; Supervision: JL, CC, ZZ.
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Wang, P., Zou, J., Huang, H. et al. Efficient prevention of cracking of external gelation-made thorium oxide microspheres by hydrothermal treatment. J Sol-Gel Sci Technol 105, 709–720 (2023). https://doi.org/10.1007/s10971-023-06046-5