Simon Hayley, Cibin Giannantonio, Freestone Ian, Schofield Eleanor
Institute of Archaeology, University College London, 31-34 Gordon Square, London, WC1H 0PY, United Kingdom.
Diamond Light Source, Harwell Campus, Didcot, Oxfordshire, OX11 0DE, United Kingdom.
J Phys Condens Matter. 2021 Jul 1;33(34). doi: 10.1088/1361-648X/ac08b6.
Data analysis methods for iron x-ray absorption spectroscopy can provide extensive information about the oxidation state and co-ordination of an Fe-species. However, the extent to which techniques developed using a single-phase iron sample may be applied to complex, mixed-phase samples formed under real-world conditions is not clear. This work uses a combination of pre-edge fitting and linear combination analysis to characterise the near edge region of the x-ray absorption spectrum (XANES) for a set of archaeological iron corrosion samples from a collection of cast iron cannon shot excavated from theshipwreck and compares the data with phase compositions determined by synchrotron x-ray powder diffraction (SXPD). Archaeological powder and cross-section samples were compared to a library of iron standards and diffraction data. The XANES are consistent with previous observations that generation of the chlorinated phase akaganeite, β-FeO(OH,Cl), occurs in those samples which have been removed form passive storage and subjected to active conservation. However, the results show that if any metallic species is present in the sample, the contribution from Fe(0) to the spectral region containing a pre-edge for oxidised iron-Fe(II) and Fe(III)-causes the analysis to be less effective and the conclusions unreliable. Consequently, while the pre-edge fitting methodology may be applied to a mixture of iron oxides or oxyhydroxides, the procedure is inappropriate for a mixed metal-oxide sample without the application of a complimentary technique, such as SXPD.
铁X射线吸收光谱的数据分析方法可以提供有关铁物种氧化态和配位的广泛信息。然而，使用单相铁样品开发的技术在多大程度上可应用于实际条件下形成的复杂多相样品尚不清楚。这项工作结合了前缘拟合和线性组合分析，对一组从沉船上挖掘出的铸铁炮弹集合中的考古铁腐蚀样品的X射线吸收光谱（XANES）近边缘区域进行了表征，并将数据与通过同步加速器X射线粉末衍射（SXPD）确定的相组成进行了比较。将考古粉末和横截面样品与铁标准库和衍射数据进行了比较。XANES与先前的观察结果一致，即在那些从被动储存中取出并进行主动保护的样品中会生成氯化相针铁矿β-FeO(OH,Cl)。然而，结果表明，如果样品中存在任何金属物种，Fe(0)对包含氧化态铁Fe(II)和Fe(III)前缘的光谱区域的贡献会使分析效果降低且结论不可靠。因此，虽然前缘拟合方法可应用于铁氧化物或羟基氧化物的混合物，但在不应用互补技术（如SXPD）的情况下，该方法不适用于混合金属氧化物样品。
