Melting of compressed iron-alloys using a multi-technique approach

对地核温度范围的准确估计对于理解内核结晶、磁场产生和通过核幔边界的热流等主要过程以及地球最低地幔中复杂多尺度结构的成分、相关系和动力学至关重要。由于它位于地球表面以下数千公里处，确定其确切的成分和温度分布是一项挑战。利用室内实验、理论、地震观测等手段推断岩心特征。地震学和宇宙化学观测表明，地核由一个固体内部区域和一个液体外部核心组成，铁是主要的组成成分，但需要一个较轻的元素与铁结合来解释地核的密度。该项目探索了镍或硅作为核心元素的可能性。外展活动和对社会的好处包括PI的强烈参与和参与加州理工学院地震实验室地震研究员计划的研究生，与露西·琼斯博士科学与社会中心的伙伴关系。该项目是一个多管齐下的项目的一部分，其目标是将地球物理科学带到南加州更广泛的社区，同时为历史上被边缘化和在科学中代表性不足的社区创造机会，以发展STEM技能。许多研究表明，硅是地球核心的候选轻元素，可以解释密度赤字，如果一个核心假设是纯粹由铁组成的话。然而，硅对核心材料的熔化温度和核心的热分布的影响知之甚少，由于熔体检测技术之间的分歧，加热过程中样品压力演变的不确定性，以及调查镍和硅对铁相图的综合影响的研究稀少。该项目采用了该研究团队开发的多技术方法，用于检测高压下铁合金的熔化，该方法结合了两个独立的原位探针的结果：同步加速器穆斯堡尔光谱，对固体结合铁的动力学敏感，以及X射线衍射，对长程结晶顺序敏感。他们将在与地核压力相当的压力下，对Fe、Fe-Ni和Fe-Ni-Si进行熔融检测的新的多技术方法，对地核温度施加更严格的限制。该奖项反映了NSF的法定使命，通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Accurate estimates of the temperature range of Earth’s core are essential for understanding major processes like inner core crystallization, magnetic field generation, and heat flow through the core-mantle boundary, as well as the compositions, phase relations, and dynamics of complex multiscale structures in Earth's lowermost mantle. With its location several thousand kilometers below the Earth's surface, determining its exact composition and temperature profile is a challenge. Laboratory experiments, theory, seismic observations are used to infer core characteristics. Seismological and cosmochemical observations indicate that Earth's core consists of a solid inner region surrounded by a liquid outer core, with iron as the main compositional constituent, but a lighter element is needed in combination with iron to explain the density of the core. This project explores the possibility of nickel or silicon as elements of the the core. Outreach activities and benefits to society include the strong engagement of the PI and involved graduate student in Caltech’s Seismological Laboratory’s Earthquake Fellows Program, a partnership with the Dr. Lucy Jones Center for Science and Society. This program is part of a multi-pronged program with the goal of bringing geophysical science to the wider community in Southern California, while creating an opportunity for communities that are historically marginalized and underrepresented in the sciences to develop STEM skills.Many studies have suggested silicon as a candidate light element for the core of the Earth to explain the density deficit if one assumes a core that is purely made of iron. However, the effect of silicon on the melting temperatures of core materials and the thermal profile of the core is poorly understood due to disagreements among melt detection techniques, uncertainties in sample pressure evolution during heating, and sparsity of studies investigating the combined effects of nickel and silicon on the phase diagram of iron. This project takes the multi-technique approach developed by this team of researchers for detecting melting of iron-alloys at high pressures that combines results from two independent in-situ probes: synchrotron Mössbauer spectroscopy, sensitive to dynamics of solid-bound iron, and x-ray diffraction, sensitive to long-range crystalline order. They will apply the new multi-technique method of melt detection to Fe, Fe-Ni, and Fe-Ni-Si at pressures equivalent to those in Earth’s core, placing tighter constraints on the temperature of Earth’s core.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.