Effect of Hydrogen on the Properties of Fe alloys in the Earth's Core

半个多世纪以来，科学家们已经知道，地核--位于地球中心的3500公里大球体，主要是铁--的密度比纯铁的密度低5%-10%。这是因为内核含有轻元素，如Si、O、S、C和H。当内核冷却形成固体内核时，轻元素优先在液体外核中偏析。这一过程在一定程度上为磁场提供动力，使我们免受太阳风的影响。此外，了解核心的组成对于限制其形成和演化至关重要。因此，金属铁中的轻元素在地球深处的极端压力和温度条件下得到了广泛的研究。然而，由于实验的限制，氢对堆芯材料的影响在很大程度上仍然是未知的。在这里，研究人员调查了氢是如何影响地核的性质的。利用最近的技术发展，他们研究了地球内部高压和高温下的铁-氢系统。这些实验在国家同步加速器设施中进行，量化了富铁合金的熔化温度和密度。原子水平的理论计算指导了实验方法和数据分析。这些结果改进了目前对地核的模型，对理解其形成、演化和现代磁场具有重要意义，在地球科学中产生了许多分支。这个为期两年的项目为职业生涯早期的女科学家和研究生提供支持，并为本科暑期实习生提供最先进的矿物物理培训机会。它还通过在亚利桑那州立大学开放参观活动中的演讲，提高了公众对氢在地球上的重要作用的认识。在这里，该团队在激光加热的钻石顶压室(DAC)中研究了Fe-H、Fe-Ni-H和Fe-Si-H合金，在DAC中，样品在两个相对的钻石的尖端被压缩，并由聚焦的激光束加热。目标压力和温度高达150 GPA(约150万大气压)，超过2000K。在DAC中，在这些条件下对氢-铁合金进行量化一直是一项挑战，因为氢在加热时往往会破坏砧板。该团队最近证明，这个问题可以通过脉冲激光加热来克服。这项技术与同步加速器设备中改进的X射线探测系统相结合，使研究人员能够在现场量化氢对富铁合金的结构、状态方程、体积弹性系数和熔化温度的影响。对RUN产物进行了电子显微镜观察，研究了RUN产物的织构和Si、Ni在相中的分配。从头计算指导实验方法和数据分析。引领这项研究的关键问题是：(1)氢是否会改变地核中铁、金属和合金的晶体结构？氢对(2)铁、金属和合金的状态方程和(3)它们在核心条件下的熔化温度有什么影响？该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

For more than half a century, scientists have known that the Earth's core - the 3500-km large ball of mostly iron at the center of the planet - has a density 5-10% lower than that of pure iron. This is because the core contains light elements, such as Si, O, S, C, and H. While the core cools down forming the solid inner core, light elements segregate preferentially in the liquid outer core. This process powers in part the magnetic field which shields us from the solar wind. Furthermore, knowing the composition of the core is critical to constrain its formation and evolution. Light elements in metallic iron have, thus, been extensively studied at the extreme pressure and temperature conditions of the deep Earth. However, because of experimental limitations, the effect of hydrogen on core materials is still largely unknown. Here, the researchers investigate how hydrogen affect the properties of the core. Taking advantage of recent technical developments, they study the iron-hydrogen system at the high pressure and temperature of Earth's interior. The experiments, carried out at national synchrotron facilities, quantify the melting temperature and density of iron-rich alloys. Theoretical calculations at the atomic level guide the experimental approach and the data analysis. The results improve current models of the core with implications for the understanding of its formation, evolution and present-day magnetic field, with numerous ramifications in Earth Sciences. This two-year project provides support for an early-career female scientist and a graduate student, and training opportunities for undergraduate summer interns in state-of-the art Mineral Physics. It also increases the public awareness of the important role of hydrogen in the Earth through presentations during open-house events at Arizona State University.Here, the team investigates Fe-H, Fe-Ni-H and Fe-Si-H alloys in the laser-heated diamond anvil cell (DAC), where specimens are compressed at the tips of two opposing diamonds and heated by focused laser beams. Target pressures and temperatures are up to 150 GPa (~1.5 million atm) and in excess of 2000 K. Quantifying hydrogen-iron alloys at these conditions in the DAC has been challenging because H2 tends to break the anvils on heating. The team has recently demonstrated that this issue can be overcome by pulsed laser heating. This technique, coupled with an improved X-ray detection system at synchrotron facilities, allows the researchers to quantify in situ the effect of hydrogen on the structure, equation of state, bulk modulus and melting temperatures of iron-rich alloys. Run products are investigated by electron microscopy to study their texture and the partitioning of Si and Ni among the phases in presence. Ab initio calculations guide the experimental approach and the data analysis. The key questions leading the research are: (1) Does hydrogen change the crystal structures of iron metal and alloys in the Earth's core? What is the effect of hydrogen on (2) the equations of state of iron metal and alloys and (3) their melting temperatures at core conditions?This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.