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首页> 外文期刊>Earth and Planetary Science Letters: A Letter Journal Devoted to the Development in Time of the Earth and Planetary System >Transport properties of Fe-Ni-Si alloys at Earth's core conditions: Insight into the viability of thermal and compositional convection
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Transport properties of Fe-Ni-Si alloys at Earth's core conditions: Insight into the viability of thermal and compositional convection

机译：地球核心条件下Fe-Ni-Si合金的运输特性：深入了解热和组成对流的可行性

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摘要

Thermal and compositional convection in Earth's core are thought to be the main power sources driving geodynamo. The viability and strength of thermally and compositionally-driven convection over Earth's history depend on the adiabatic heat flow across the core-mantle boundary (CMB) which is governed by the thermal conductivity of a constituent Fe-Ni-light element alloy at the pressure-temperature (P-T) conditions relevant to the core. Silicon is often proposed to be an abundant light element alloyed with Fe along with similar to 5 wt% Ni, but the thermal transport properties of Fe-Ni-Si alloys at high P-T remain largely uncertain. Here we measured the electrical resistivities of Fe-10wt%Ni and Fe-1.8wt%Si alloys up to similar to 142 GPa and similar to 3400 K using four-probe van der Pauw method in laser-heated diamond anvil cell experiments. Our results show that the resistivities of hcp-Fe-1.8Si and Fe-10Ni display quasi-linear temperature dependence from similar to 1500 to 3400 K at each given high pressure. Addition of similar to 2 wt% Si in hcp-Fe significantly increases its resistivity by similar to 25% at similar to 138 GPa and 4000 K, but Fe-10wt%Ni has similar resistivity to pure hcp-Fe at near CMB P-T conditions. Using our measured values of electrical resistivities, we model thermal conductivities via the Wiedemann-Franz law, giving a nominal thermal conductivity of similar to 50 W m(-1) K-1 for liquid Fe-5Ni-8Si alloy at the topmost outer core, implying an adiabatic (conductive) core heat flow of similar to 8.0 TW. The outer core has a much lower thermal conductivity than the inner core due to light-element differentiation across the solidifying inner-core boundary. Our studies imply that the adiabatic core heat flow is low enough to enable thermal convection to drive the geodynamo over most and possibly all of Earth's history, while the strength of compositional convection increases with the inner-core growth and accounts for similar to 83% of the buoyancy flux to the present-day geodynamo. (C) 2020 Elsevier B.V. All rights reserved.
机译：地核内的热对流和成分对流被认为是驱动geodynamo的主要动力来源。在地球历史上，热驱动和成分驱动对流的可行性和强度取决于穿过核幔边界（CMB）的绝热热流，该绝热热流由组成Fe-Ni轻元素合金在与核相关的压力-温度（P-T）条件下的热导率决定。硅通常被认为是一种与Fe以及类似于5 wt%Ni的合金化的丰富的轻元素，但Fe-Ni-Si合金在高P-T下的热传输性能仍存在很大的不确定性。在这里，我们在激光加热的金刚石顶砧实验中，使用四探针范德堡法测量了Fe-10wt%Ni和Fe-1.8wt%Si合金的电阻率，最高可达142 GPa，最高可达3400 K。我们的结果表明，hcp-Fe-1.8Si和Fe-10Ni的电阻率在1500到3400 K的范围内，在每个给定的高压下表现出准线性的温度依赖性。在hcp Fe中添加类似于2 wt%的Si，在类似于138 GPa和4000 K的条件下，其电阻率显著增加25%，但在接近CMB P-T条件下，Fe-10wt%Ni的电阻率与纯hcp-Fe的电阻率相似。利用我们测得的电阻率值，我们通过魏德曼-弗兰兹定律对热导率进行了建模，给出了最顶部外芯液态Fe-5Ni-8Si合金的标称热导率为50 W m（-1）K-1，这意味着绝热（导电）芯热流为8.0 TW。由于轻元素在凝固的内芯边界上的差异，外芯的导热系数比内芯低得多。我们的研究表明，绝热核心热流足够低，足以使热对流在地球的大部分历史上，甚至可能在地球的所有历史上，驱动地球动力学，而成分对流的强度随着内核的增长而增加，并占当今地球动力学浮力通量的83%。（C） 2020爱思唯尔B.V.版权所有。

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