Amorphous materials: Properties, structure, and durability
Amorphous materials: Properties, structure, and durability
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非晶材料：特性、结构和耐久性
DOI：
10.2138/am.2012.3888
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发表时间：
2012
影响因子：
3.1
通讯作者：
B. Scaillet
中科院分区：
文献类型：
--
作者：
G. Giuli;R. Alonso;M. Cicconi;E. Paris;P. Glatzel;S. Eeckhout;B. Scaillet
摘要采用Fe - k边x射线吸收近边光谱（XANES）测定了三组不同过碱性流纹岩成分硅酸盐玻璃的铁氧化态和配位几何形状。选择这些成分来研究碱含量（和氧逸度）对铁氧化态的影响。样品采用热液容器制备，温度为800℃，氧逸度范围为NNO-1.61 ~ NNO+2.96 log单位。通过与已知氧化态和配位数的铁模型化合物的边前峰数据进行比较，可以确定所分析的所有玻璃中铁的氧化态和配位数。在每组样品中，铁趋于氧化，正如预期的那样，氧逸度增加。然而，在恒定氧逸度下，碱含量对Fe3+/(Fe3++Fe2+)比有很强的影响：过碱性最低的系列的比值在0.25 ~ 0.55（±0.05）之间，过碱性最高的系列的比值在0.45 ~ 0.80（±0.05）之间。此外，边前峰数据清楚地表明Fe3+在大多数过碱性玻璃中呈四重配位。边前峰数据的外推表明，在另外两个系列中，三价铁存在四倍和五倍配位。三种玻璃系中二价铁主要呈五重配位。单凭XANES数据不能排除微量六重和四重配位铁的存在。XANES数据表明，碱的用量也会影响Fe3+配位环境，导致平均配位数下降。最氧化和过碱性样品的扩展x射线吸收精细结构（EXAFS）数据表明，Fe3+呈四面体配位，= 1.85 Å（±0.02）。这一数值与文献中关于[4]Fe3+在结晶相（如四铁云母或铁云母）或硅酸盐玻璃（如phonolite玻璃）中的数据相比较，支持xanes测定的最过碱性玻璃配位数。计算得到的NBO/T比随着Fe的氧化而略有下降，因为形成网络的Fe的比例更高，从而增加了四面体网络的聚合。
Abstract Iron oxidation state and coordination geometry have been determined by Fe K-edge X-ray absorption near edge spectroscopy (XANES) for three sets of silicate glasses of peralkaline rhyolitic composition with different peralkalinity values. These compositions were chosen to investigate the effect of alkali content (and oxygen fugacity) on the Fe oxidation state. The samples were produced by means of hydrothermal vessels at 800 °C with oxygen fugacity conditions ranging from NNO-1.61 to NNO+2.96 log units. Comparison of the pre-edge peak data with those of Fe model compounds of known oxidation state and coordination number allowed determination of the Fe oxidation state and coordination number in all glasses analyzed. Within each group of samples, Fe tends to oxidize with increasing oxygen fugacity as expected. However, alkali content is shown to have a strong effect on the Fe3+/(Fe3++Fe2+) ratio at constant oxygen fugacity: this ratio varies from 0.25 to 0.55 (± 0.05) for the least peralkaline series, and from 0.45 to 0.80 (± 0.05) for the most peralkaline series. Moreover, pre-edge peak data clearly indicate that Fe3+ is in fourfold coordination in the most peralkaline glasses. Extrapolation of pre-edge peak data suggests the presence of both fourfold and fivefold coordination for trivalent Fe in the other two series. Divalent Fe is suggested to be mainly in fivefold coordination in all the three glass series. The presence of minor amounts of sixfold- and fourfold-coordinated Fe cannot be ruled out by XANES data alone. XANES data suggest that the amount of alkalis also affects the Fe3+ coordination environment resulting in a decrease in the average coordination numbers. Extended X-ray absorption fine structure (EXAFS) data of the most oxidized and peralkaline sample indicate that Fe3+ is in tetrahedral coordination with = 1.85 Å (± 0.02). This value compares well with literature data for [4]Fe3+ in crystalline phases (e.g., in tetra-ferriphlogopite or rodolicoite) or in silicate glasses (e.g., phonolite glasses) supporting the XANES-determined coordination number obtained for the most peralkaline glasses. Calculated NBO/T ratios decrease slightly with Fe oxidation because of the higher fraction of network forming Fe, thus increasing the polymerization of the tetrahedral network.