利用同步辐射X射线吸收精细结构谱技术研究古代壁画中铅丹的变色机制

铅丹是我国古代壁画中常见的一种红色天然矿石颜料，受壁画附存环境因素的影响，壁画中的铅丹常常存在变色褪色现象，严重影响了古代壁画的观赏与研究价值。研究表明，壁画中的铅丹变色后生成二氧化铅，但是对于变色反应的具体过程仍不清楚，而且之前的研究只考虑光照与湿度对铅丹的影响，忽略了壁画中微生物与其他物质的作用。同步辐射X射线吸收精细结构谱（XAFS），能够提供物质中心原子的元素价态与原子配位的信息，非常适于铅丹变色过程的研究。因此，本项目拟将SR-XAFS用于分析古代壁画颜料中铅的元素价态和配位结构，解析单一或混合颜料中铅的赋存状态；通过条件实验，研究光照、湿度、微生物、颜料掺杂等不同因素对铅丹稳定性的影响，明确铅丹变色中的关键影响因素；结合模拟壁画实验，利用X射线衍射、红外/拉曼光谱等传统方法与同步辐射XAFS技术相结合，探讨铅丹变色反应的具体机制，为我国的文物保护与修复工作提供理论参考。

Pb3O4 is a common red natural pigment in ancient Chinese murals. Influenced by the environmental factors attached to the murals, Pb3O4 is always discolored and faded, which seriously affects the value of appreciation and research of ancient murals. It is reported that Pb3O4 degradated to PbO2 when it is discolored in the murals, but the mechanism of Pb3O4 discoloration is still unclear. Moreover, the previous work mainly studied the influence of light and humidity on the stability of Pb3O4, the role of microorganisms and other pigments in the murals is neglected. Synchrotron radiation X-ray absorption fine structure spectroscopy (XAFS) can provide the information about the valence states and coordination of center atom, which is very suitable for the study of Pb3O4 discoloration process. Therefore, this project is to analyze the valence state and coordination structure of lead in ancient mural pigments by SR-XAFS, thus to make clear the existing state of lead in single or mixed pigments. With the conditional experiments, the influence of different factors such as light, humidity, microorganism and other pigments will be studied on the stability of Pb3O4 to identify the key factors in Pb3O4 discoloration; Combined with simulated mural experiments, XRD, Infrared/Raman spectroscopy and SR-XAFS will be used to explore the mechanism of Pb3O4 discoloration to provide theoretical reference for the conservation and restoration of cultural relics in China.