应用与透射电子显微术相结合的电子能量损失谱(EELS)测定矿物中Ce和Fe的氧化态(英文)

Using Electron Energy-Loss Spectroscopy (EELS) Associated with Transmission Electron Microscopy to Determine Oxidation States of Ce and Fe in Minerals

在透射电子显微镜 (TEM )中 ,与样品发生弹性散射的高能电子可被用于成像和产生选区电子衍射 (SAED) ,它们能提供关于样品结构的重要信息。高分辨透射电子显微镜 (HRTEM )由于它具有高的空间分辨率 ,因而可以在原子的尺度上来研究样品的结构和微结构 (或织构 )。此外 ,TEM中入射的高能电子还经历了与样品的非弹性相互作用 ,它可以提供关于样品的化学和电子结构的进一步信息。据此 ,以TEM中的X射线能量色散谱学 (EDS)和电子能量损失谱学 (EELS)为基础 ,产生了分析电子显微术 (AEM )。其中EELS能够提供有关样品的诸如定量化学分析 (包括除氢以外的所有元素 )、氧化态、配位、结晶度以及化学键合类型等有价值的信息。HRTEM与EELS结合的研究则能从纳米尺度上提供关于矿物反应的微结构和微化学信息。应用以M4 和M5边的电子能量损失近边结构 (ELNES)为基础的EELS ,研究了被建议作为放射性废料寄主相的烧绿石中Ce的氧化态。与Ce3+ 相比 ,Ce4 + 的M4 和M5边具有较高的能量损失。M4 与M5边之间以及它们之后的弱峰之间的强度比可用于Ce3+ 与Ce4 + 的定量分析。在内蒙所产烧绿石矿物的颗粒 ,其未蚀变区的EELS数据指示出有Ce3+ 及其他稀士元素。然而由相邻蚀变区得出的EELS光谱则显示为Ce4 + 、Ba及其他稀土元素。

EELS based on features of ELNES of M 4 and M 5 ed ges can provide information regarding oxidation states of Ce in proposed host ph ases of radioactive wastes (e.g., pyrochlore) and other REE- bearing minerals. M 4 and M 5 edges of Ce- 4+ have higher energy-loss than those of Ce- 3+. Intensity ratio between M 4 and M 5 edges and weak peaks after the M 4 and M 5 edges can be used for quantifica tion of Ce- 3+ and Ce- 4+. EELS data from an unaltered area of pyrochlo re from Inner Mongolia o f China indicate Ce- 3+ and other rare earth elements (REE). However, EELS spectrum from the neighboring altered area shows Ce- 4+, Ba and other REE. The oxidation of Ce results in loss of REE, U, and alpha decay product Pb during the alteration of the pyrochlore. Based on features of ELNES of L 3 edges, EELS spectra can also provide quantitative information regarding oxidati on states of Fe in Fe-bearing amphiboles, Fe-bearing pyroxenes, and other sili ca te minerals. There is a large difference in Fe oxidation states of the amphibol e between the directly measured and indirectly calculated methods.