Metallurgy at Extreme Conditions: Molten Iron-Alloy Constraints on the Light Elements in Earth's Core

极端条件下的冶金：熔融铁合金对地核轻元素的限制

• 批准号: NE/F019084/1
• 负责人: Michael Walter
• 金额: $ 33.35万
• 依托单位: University of Bristol
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2009
• 资助国家: 英国
• 起止时间: 2009 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FF019084%2F1
• 关键词: Metallurgy; Extreme; Conditions; Molten; Iron

One of the outstanding mysteries in the Earth sciences is the composition of the core. We know from seismic and cosmochemical constraints that the core is made of a nearly pure iron (~95% Fe + 5% Ni), and that the inner core is solid and the outer core is molten. However, based on our knowledge of the behavior of molten iron at the extreme pressure and temperature conditions of the core, it is apparent that there must be some other light element or elements dissolved in the molten outer core as well. It is thought that the light element is related to convection in the outer core and is therefore important for spawning the Earth's magnetic field. The nature and abundance of the light element will also determine the kinds of reactions that might occur at the boundary between mantle silicate and the molten metal core. For the last half-century the primary candidates for the light elements in the core have included H, O, S, C, and Si. We will never be able to sample the core directly, hollywood movies notwithstanding, so other approaches are required to deduce the identity of the light elements. Basically, the approach has been to try and determine which elements can dissolve into molten iron at core conditions using experiment and theory. A perusal of the vast literature on this subject reveals that individual elements and cocktails of elements have come into, out of, and back into favor with time. Different experimental and theoretical approaches often lead to very different interpretations as to the identity of the light elements. Here we propose a method for deducing the light element in the core that relies on a combination of experiment, thermodynamic modeling, and seismic observations. Seismic data constrain the velocity at which compressional waves can move through molten iron as well as the density. They can also detect whether the core liquid has separated into more than one liquid (immiscibility). In principle, if one knows the same properties for various iron alloy - light element mixtures, one can deduce the composition of the core. The seismic observations are available. An internally consistent model for the properties of molten alloys at core conditions is not. However, thermodynamic relationships allow the physical properties to be determined through the equation of state of molten alloys. The parameters required to develop the thermodynamic model can be deduced through the melting curves of iron - light element alloy compositions. Here, we are proposing to make measurements of the melting curves of two-component (binary) alloys such as FeO, Fe3C, FeS, FeH and FeSi in order to derive the quantities required for the thermodynamic model. We have developed robust techniques in our lab for measuring melting points to very high pressures and temperatures using the laser-heated diamond anvil cell. Further, we have developed an exciting and novel new X-ray imaging technique with which we can measure directly the minimum melting compositions (eutectics) in iron - light element systems. These data further help constrain the thermodynamic models. In summary, we will use an experimental approach to measure how iron - light element alloys melt and from this data we will develop a multi-component thermodynamic model that will allow us to predict the seismic wave velocities and density of a wide range of possible core liquids. We will then compare the model with actual observations to deduce the identity of the elusive light elements in the molten outer core.

地核的组成是地球科学中最突出的谜团之一。我们从地震和宇宙化学的约束中知道，地核是由几乎纯铁（~95% Fe + 5% Ni）组成的，内核是固体的，外核是熔融的。然而，根据我们对铁水在核心极端压力和温度条件下的行为的了解，很明显，在熔融的外核中也必须有一些其他的轻元素或元素溶解。人们认为，轻元素与外核的对流有关，因此对产生地球磁场很重要。轻元素的性质和丰度也将决定在地幔硅酸盐和熔融金属核之间的边界可能发生的反应种类。在过去的半个世纪里，核心中主要的轻元素候选者包括氢、氧、硫、碳和硅。尽管有好莱坞电影，但我们永远无法直接对核心进行采样，因此需要其他方法来推断轻元素的身份。基本上，方法是通过实验和理论来尝试确定哪些元素可以在核心条件下溶解到铁水中。仔细阅读有关这一主题的大量文献就会发现，单个元素和元素的混合物已经随着时间的推移而进入、退出并重新受到青睐。不同的实验和理论方法往往导致非常不同的解释，对轻元素的身份。本文提出了一种基于实验、热力学建模和地震观测相结合的方法来推断岩心中的轻元素。地震数据限制了纵波穿过铁水的速度和密度。他们还可以检测核心液体是否已经分离成多个液体（不混溶）。原则上，如果知道各种铁合金-轻元素混合物的相同性质，就可以推断出核心的组成。地震观测资料是可用的。对于熔融合金在核心条件下的性质，内部一致的模型是不存在的。然而，热力学关系允许通过熔融合金的状态方程来确定物理性质。通过铁轻元素合金成分的熔炼曲线，可以推导出建立热力学模型所需的参数。在这里，我们建议测量双组分（二元）合金（如FeO， Fe3C, FeS， FeH和FeSi）的熔化曲线，以得出热力学模型所需的量。我们在实验室开发了强大的技术，用于使用激光加热的金刚石砧细胞测量高压和高温下的熔点。此外，我们还开发了一种新的x射线成像技术，可以直接测量铁-轻元素体系中的最小熔融成分（共晶）。这些数据进一步有助于约束热力学模型。总之，我们将使用一种实验方法来测量铁-轻元素合金是如何熔化的，并从这些数据中我们将开发一个多组分热力学模型，这将使我们能够预测地震波速度和各种可能的岩心液体的密度。然后，我们将把模型与实际观测结果进行比较，以推断出熔融外核中难以捉摸的轻元素的身份。

项目成果

Calibration of Raman spectroscopy in the stress measurement of air-plasma-sprayed yttria-stabilized zirconia.

空气等离子体喷涂氧化钇稳定氧化锆应力测量中拉曼光谱的校准。

• DOI: 10.1366/12-06676
• 发表时间: 2012
• 期刊: Applied spectroscopy
• 影响因子: 3.5
• 作者: Liu D

The role of beam dispersion in Raman and photo-stimulated luminescence piezo-spectroscopy of yttria-stabilized zirconia in multi-layered coatings

光束色散在多层涂层中氧化钇稳定氧化锆的拉曼和光激发光压电光谱中的作用

• DOI: 10.1016/j.actamat.2012.08.052
• 发表时间: 2013
• 期刊: Acta Materialia
• 影响因子: 9.4
• 作者: Liu D

The NiSi melting curve to 70GPa

NiSi熔化曲线至70GPa

• DOI: 10.1016/j.pepi.2014.05.005
• 发表时间: 2014
• 期刊: Physics of the Earth and Planetary Interiors
• 影响因子: 2.3
• 作者: Lord O