Electron microprobe technique for the determination of iron oxidation state in silicate glasses
Electron microprobe technique for the determination of iron oxidation state in silicate glasses
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DOI：
10.2138/am-2018-6437
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发表时间：
2018-09
影响因子：
3.1
通讯作者：
Chaogang Zhang;R. Almeev;Ery C. Hughes;A. Borisov;Eric P. Wolff;H. Höfer;R. Botcharnikov;J. Koepke
中科院分区：
文献类型：
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作者：
Chaogang Zhang;R. Almeev;Ery C. Hughes;A. Borisov;Eric P. Wolff;H. Höfer;R. Botcharnikov;J. Koepke
本文提出了一种用电子探针（EPMA）测定硅酸盐玻璃中铁氧化态的新标定方法。该方法基于FeLα和FeLβ X射线发射线随铁氧化态的强度和波长的变化。侧翼法利用不同标准物质峰侧翼处观察到的FeLα和FeLβ光谱的最大差异，其与Fe 2+含量定量相关。如果在参考材料上校准了这种相关性，则可以确定具有已知总Fe含量的样品的Fe 2 +/Fe 2 O3 Fe比率。两种合成的富Fe铁和亚铁石榴石端元，即，用铁钠长石和铁铝榴石确定了FeLα和FeLβ侧边法的测量位置，并将其应用于已知Fe ~（2+）/Fe_2Fe ~（2+）比值（范围为0.2 ~ 1.0）的各种硅酸盐玻璃的测量。在这些侧面位置处测量的FeLβ与FeLα的强度比（Lβ/Lα）是Fe 2+含量（以wt%计）的线性函数。对于具有4-18重量% FeOT（总铁表示为FeO）的石榴石和硅酸盐玻璃两者，可以建立单一线性趋势。在玻璃与高达18重量%的FeOT和15重量%的TiO 2，没有系统的组成（矩阵）的影响进行了观察。一个可能的影响，钛的Fe 2+测定只观察到一个高钛玻璃与~25重量%的TiO 2，含量是不典型的天然陆地硅酸盐熔体。对于FeOT> 5 wt %的硅酸盐玻璃，Fe 2 +/Fe 2 O3 Fe测定的准确度估计在±0.1以内，对于FeOT ≤ 5 wt %的硅酸盐玻璃，其准确度估计在±0.3以内。在硅酸盐玻璃上应用侧面法需要最小化EPMA束损伤，这可以通过在分析期间在电子束下连续移动样品台成功地实现，例如，速度为2 μm/s。
Abstract We present a new calibration for the determination of the iron oxidation state in silicate glasses by electron probe microanalysis (EPMA) with the “flank method.” This method is based on the changes in both intensity and wavelength of the FeLα and FeLβ X-ray emission lines with iron oxidation state. The flank method utilizes the maximum difference for the FeLα and FeLβ spectra observed at the peak flanks between different standard materials, which quantitatively correlates with the Fe2+ content. Provided that this correlation is calibrated on reference materials, the Fe2+/ΣFe ratio can be determined for samples with known total Fe content. Two synthetic Fe-rich ferric and ferrous garnet end-members, i.e., andradite and almandine, were used to identify the FeLα and FeLβ flank method measuring positions that were then applied to the measurement of a variety of silicate glasses with known Fe2+/ΣFe ratio (ranging from 0.2 to 1.0). The measured intensity ratio of FeLβ over FeLα at these flank positions (Lβ/Lα) is a linear function of the Fe2+content (in wt%). A single linear trend can be established for both garnets and silicate glasses with 4–18 wt% FeOT (total iron expressed as FeO). In glasses with up to 18 wt% FeOT and 15 wt% TiO2, no systematic compositional (matrix) effects were observed. A possible influence of Ti on the Fe2+ determination has only been observed in one high-Ti glass with ~25 wt% TiO2, a content that is not typical for natural terrestrial silicate melts. The accuracy of the Fe2+/ΣFe determination, which depends on both the Fe2+ content determined with the flank method and on the total Fe content, is estimated to be within ±0.1 for silicate glasses with FeOT > 5 wt% and within ±0.3 for silicate glasses with low FeOT ≤ 5 wt%. The application of the flank method on silicate glasses requires minimization of the EPMA beam damage that can be successfully achieved by continuous movement of the sample stage under the electron beam during analysis, e.g., with a speed of 2 μm/s.