In Situ Study of Fe-FeS Melt System at High Pressures and Temperatures

自从地核被发现以来，地核相对于纯铁成分的密度赤字一直是一个长期存在的问题。缺乏关于高压下铁与其他轻元素熔融合金的知识是造成这样一个长期谜团的原因。利用国家实验室的同步辐射光源，该项目开发了最先进的技术来解决高压下熔体的密度和局部结构问题。本项目目前的目标包括：a)测量Fe-FeS熔体体系的状态方程与硫含量的关系；b)研究高压下Fe-FeS熔体的结构。虽然S、O、Si、C和H等轻元素被认为是解释密度亏损的候选元素，但从地球化学和宇宙化学的角度来看，硫是最有利的候选元素之一。然而，目前关于铁硫合金系统的现有密度数据仍然存在巨大的不确定性。该项目应用了最新开发的高压原位同步辐射X射线测量技术，并继续提高高压熔体实验数据的准确性，以从矿物物理的角度解决多学科的挑战。在该项目中，多台顶压机和钻石顶压机技术的集成不仅在不同的压力范围内提供了互补的数据，而且还为这两种新开发的实验方法提供了交叉检查。这项研究的成功将为了解地核的组成和结构，以及由地球外核的成分浮力驱动的对流提供非常有用的信息。该项目积极整合了包括本科生和研究生在内的研究和教育培训，这将提高大学生，特别是佛罗里达国际大学的少数民族学生对现代技术的认识，并培养出工作在高级研究前沿的新一代科学家。该项目加强了国家同步加速器X射线源社区设施的实验能力，从而为地球科学界和一般材料科学的科学研究作出了更广泛的贡献。

The density deficit of Earth's core with respect to a pure iron composition has been a long-standing problem since the core was discovered. Lack of knowledge about molten alloys of iron with other light elements at high pressures is responsible for such a persistent puzzle. Taking advantage of synchrotron radiation sources at national laboratories, this project has developed state-of-the-art techniques to tackle the issue of density and local structure of melts at high pressures. The objectives for the current period of the project include a) measuring sulfur-content dependence of EOS (equation of state) of Fe-FeS melt system and b) investigating structure of Fe-FeS melts at high pressures. While many light elements, e.g. S, O, Si, C and H, have been considered as candidates to account for the density deficit, sulfur is one of the most favorable candidates from geochemical and cosmochemical points of view. However, current available density data on the iron-sulfur alloy system remain a huge uncertainty. This project applies the newly developed technique of in situ synchrotron x-ray measurement at high pressures, and continues improving accuracy of experimental data on high pressure melts to address the multidisciplinary challenge from the mineral physics point of view. Integration of multi anvil press and diamond anvil cell techniques in this project offers not only complementary data in different pressure ranges but also serves a cross check for both newly developed experimental approaches. Success of this research will provide very useful information for understanding the composition and structure of the Earth's core, and the convection driven by compositional buoyancy in the Earth's outer core. The project actively integrates research and educational training including both undergraduate and graduate levels, which will enhance the awareness of modern technology among college students, especially minority students at Florida International University, and produce a new generation of scientists who are working at the frontier of advanced research. The project enhances the experimental capability of a community facility at national synchrotron x-ray sources, and therefore generates broader contributions to the scientific research in Earth science community and general material science.