The formation of stoichiometric uranium brannerite (UTi2O6) glass-ceramic composites from the component oxides in a one-pot synthesis
The formation of stoichiometric uranium brannerite (UTi2O6) glass-ceramic composites from the component oxides in a one-pot synthesis
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一锅合成中由组分氧化物形成化学计量铀镁矿 (UTi2O6) 玻璃陶瓷复合材料
DOI：
10.1016/j.jnucmat.2020.152516
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发表时间：
2020
影响因子：
3.1
通讯作者：
Dixon Wilkins M
中科院分区：
文献类型：
--
作者：
Dixon Wilkins M
镁锰矿玻璃陶瓷复合材料已被建议作为高锕系元素含量废物的合适废料材料，但含有化学计量铀镁锰矿（UTi2O6）的玻璃陶瓷复合材料的形成尚未得到充分研究。采用一锅冷压和烧结工艺以氧化物组分为原料合成了铀镁锰矿玻璃陶瓷复合材料。作为比较，使用醇盐-硝酸盐路线生产了另外两个样品。通过一系列不同的热处理（1200°C 12-48 小时，1250°C 12 小时）合成了一系列具有不同摩尔比的铀和钛氧化物（从 1:2 到 1:3.20）的组合物。通过X射线衍射、扫描电子显微镜、能量色散X射线光谱和X射线近边光谱分析所有组合物，发现含有UTi2O6作为在标称化学计量Na2AlBSi6O16的玻璃基质内形成的主要结晶相。在 UO2:TiO2 比例为 1:2 和 1:2.28 的组合物中，在玻璃基质中观察到 UO2 颗粒，这可能是由于 TiO2 在玻璃相中的溶解所致；通过添加过量的 TiO2 可以防止这种情况发生。这项工作证明了该系统即使采用简单的一锅法，也适用于生产具有出色锕系废物负载的高度耐用的废物形式。一些镁锰矿晶粒由封装在 UTi2O6 壳中的 UO2 颗粒组成，这表明镁锰矿在 UO2 颗粒周围结晶，直到 UO2 完全耗尽，或者动势垒变得太大而无法发生进一步扩散。我们认为，玻璃陶瓷复合材料中的镁锰矿在比纯陶瓷镁锰矿温度更低的温度下形成，是由于玻璃内反应物扩散速率的增加造成的。
Brannerite glass-ceramic composites have been suggested as suitable wasteform materials for high-actinide content wastes, but the formation of glass-ceramic composites containing stoichiometric uranium brannerite (UTi2O6) has not been well-studied. Uranium brannerite glass-ceramic composites were synthesised at by a one-pot cold-press and sinter route from the component oxides. As a comparison, two further samples were produced using an alkoxide-nitrate route. A range of compositions with varying molar ratios of uranium and titanium oxides (from 1:2 to 1:3.20) were synthesised, with a range of different heat treatments (1200 °C for 12–48 h, and 1250 °C for 12 h). All compositions were analysed by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, and X-ray near-edge spectroscopy, and found to contain UTi2O6as the majority crystalline phase forming within a glass matrix of nominal stoichiometry Na2AlBSi6O16. In compositions with UO2:TiO2ratios of 1:2 and 1:2.28, particles of UO2were observed in the glass matrix, likely due to dissolution of TiO2in the glass phase; this was prevented by the addition of excess TiO2. This work demonstrates the suitability of this system to produce highly durable wasteforms with excellent actinide waste loading, even with a simple one-pot process. Some grains of brannerite consist of a UO2particle encapsulated in a shell of UTi2O6, suggesting that brannerite crystallises around particles of UO2until either the UO2is fully depleted, or the kinetic barrier becomes too large for further diffusion to occur. We propose that the formation of brannerite within glass-ceramic composites at lower temperatures than that for pure ceramic brannerite is caused by an increase in the rate of diffusion of the reactants within the glass.
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