Abstract Metakaolin-based Na-Pollucite ceramics (high-temperature sintered Na-pollucite ceramics: HTNP), with a target composition close to Pollucite (CsAlSi2O6), were fabricated at sintering temperatures above 1000 °C to immobilize Cs as waste form material. The sintering behaviors of Metakaolin-based Na-Pollucite ceramics were investigated, in particular with respect to sintering temperature, grain size, and microstructure. The results indicate that major phases of the pollucite ceramics consist of pollucite phase and a small fraction of other mineral phases like Albite, SiO2, and Al2O3, and the microstructures greatly depends on the molar Cs/Na ratio. Furthermore, with increasing Cs content in the pollucite ceramics, the sintering temperature increases gradually, and the pollucite grain size decreases accordingly. On the other hand, to avoid the high-temperature volatilization of Cs-ions during sintering, low-temperature sintered Na-pollucite (LTNP) ceramics were prepared below 950 °C by introducing H3BO3 into the metakaolin-based Na-Pollucite ceramics. After the LTNP ceramics were sintered using a low-temperature liquid-phase process, even when the sintering temperature was decreased to 650 °C, they remained structurally as pollucite phase. In addition, the sintering-temperature and grain-size dependency on the molar Cs/Na ratio in LTNP ceramics is consistent with that in HTNP ceramics. Leaching in the PCT (Product Consistency Test) indicates that the leaching concentrations of HTNP ceramics are, in total, lower than in LTNP ceramics. However, the LTNP and HTNP ceramics samples, with the molar Cs/Na ratios 1:1.5, 1:0.67, and 1:0.25 show better immobilization abilities for the Cs ion. This indicates that, besides the pollucite phase formation, the immobilization of the Cs ion correlates also with dense microstructures, grain size, and good crystallization. More importantly, low sintering temperatures and the fabrication of Cs crystalline ceramics are the important factors to improve the Cs ion immobilization.

中文翻译：

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偏高岭土基 Na-Pollucite 陶瓷的烧结及其对 Cs 的固定

摘要 偏高岭土基 Na-Pollucite 陶瓷（高温烧结 Na-pollucite 陶瓷：HTNP）的目标成分接近于 Pollicite (CsAlSi2O6)，在 1000 °C 以上的烧结温度下制造，以固定 Cs 作为废物形式材料。研究了基于偏高岭土的 Na-Pollucite 陶瓷的烧结行为，特别是在烧结温度、晶粒尺寸和微观结构方面。结果表明，磷灰石陶瓷的主要相由磷灰石相和少量其他矿物相如钠长石、SiO2和Al2O3组成，微观结构很大程度上取决于Cs/Na的摩尔比。此外，随着磷灰石陶瓷中Cs含量的增加，烧结温度逐渐升高，磷灰石晶粒尺寸相应减小。另一方面，为了避免烧结过程中Cs离子的高温挥发，通过将H3BO3引入偏高岭土基Na-Pollucite陶瓷中，在950°C以下制备了低温烧结Na-pollucite（LTNP）陶瓷。LTNP 陶瓷采用低温液相工艺烧结后，即使烧结温度降至 650 °C，它们在结构上仍保持为磷灰石相。此外，LTNP陶瓷中烧结温度和晶粒尺寸对Cs/Na摩尔比的依赖性与HTNP陶瓷中的一致。PCT（产品一致性测试）中的浸出表明 HTNP 陶瓷的浸出浓度总体上低于 LTNP 陶瓷。然而，LTNP 和 HTNP 陶瓷样品的 Cs/Na 摩尔比为 1:1.5、1:0.67 和 1:0。图25显示了对Cs离子更好的固定能力。这表明，除了磷灰石相的形成之外，Cs 离子的固定还与致密的微观结构、晶粒尺寸和良好的结晶有关。更重要的是，低烧结温度和Cs晶体陶瓷的制备是提高Cs离子固定化的重要因素。