Cerium LIII-edge XAS investigation of the structure of crystalline and amorphous cerium oxides
Cerium LIII-edge XAS investigation of the structure of crystalline and amorphous cerium oxides
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DOI：
10.1021/cm0492437
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发表时间：
2005-01-25
影响因子：
8.6
通讯作者：
Schuman, TP
中科院分区：
文献类型：
--
作者：
Shahin, AM;Grandjean, F;Schuman, TP
在不同比例的过氧化氢 (H2O2) 存在下，通过水合硝酸铈 (111) 水溶液的沉淀制备氧化铈固体样品，作为铝合金的模型腐蚀抑制涂层材料。 Ce L-III 边缘的 X 射线吸收光谱用于表征结晶无水 CeO2、纳米晶水合 CeO2、在 H2O2 存在下沉淀的纳米晶 CeO2 样品 I 以及在较高 H2O2 浓度下沉淀的非晶 CeO2 样品 II。对氧化铈的 X 射线吸收近边结构 (XANES) 分析并未表明与无水 CeO2 相比，沉淀样品中的铈价态存在较大变化。此外，XANES 分析表明，相对于无水 CeO2 中的白线峰，沉淀样品的白线峰强度有所降低。氧化物的 EXAFS 光谱表明，H2O2 降低了沉淀物的粒径和块体结晶度。在水合和沉淀 CeO2 样品中，随着键距 RCe-O 的增加，观察到第一层 Ce-O 壳的配位数增长。然而，与无水 CeO2 相比，第二壳（Ce-Ce）和第三壳（Ce-O）的配位数减少了。在氧化铈的碱性沉淀过程中，H2O2 浓度的增加导致水合作用增加，相应于外壳配位数减少和整体结晶度降低，但铈价态没有相应的变化。
Cerium oxide solid samples were prepared via precipitation from aqueous solution of hydrous cerium(111) nitrate in the presence of different percentages of hydrogen peroxide (H2O2) as model corrosion inhibiting coatings materials for aluminum alloys. X-ray absorption spectroscopy at the Ce L-III-edge was applied for the characterization of crystalline anhydrous CeO2, nanocrystalline hydrous CeO2, nanocrystalline CeO2 sample I precipitated in the presence of H2O2, and an amorphous CeO2 sample II precipitated at a higher H2O2 concentration. An analysis by X-ray absorption near-edge structure (XANES) for cerium oxides did not indicate a broad variation in cerium valence state in the precipitated samples as compared to anhydrous CeO2. Furthermore, XANES analysis revealed a decrease in the intensity of the white line peaks for the precipitated samples relative to those in anhydrous CeO2. The EXAFS spectra of the oxides showed that H2O2 reduced the precipitate's particle diameter and bulk crystallinity. Growth in the coordination number of the first, Ce-O, shell was observed with an increased bond distance RCe-O in hydrous and precipitated CeO2 samples. However, the coordination numbers of the second, Ce-Ce, and third, Ce-O, shells were reduced in comparison with anhydrous CeO2. Increasing concentration of H2O2 during alkaline precipitation of cerium oxides caused increased hydration, corresponding to a reduced outer-shell coordination number and reduced bulk crystallinity but no corresponding change in the cerium valence state.