Equations of State and Anisotropy of Fe‐Ni‐Si Alloys
Equations of State and Anisotropy of Fe‐Ni‐Si Alloys
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Fe-Ni-Si合金的状态方程和各向异性
DOI：
10.1029/2017jb015343
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发表时间：
2018
期刊：
影响因子：
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通讯作者：
Greenberg, Eran
中科院分区：
文献类型：
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作者：
Morrison, Rachel A.;Jackson, Jennifer M.;Sturhahn, Wolfgang;Zhang, Dongzhou;Greenberg, Eran
我们提供了体心立方（bcc）和六方密排（hcp）结构的Fe0.91Ni0.09和Fe0.8Ni0.1Si0.1在300 K下分别高达167和175 GPa的粉末X射线衍射数据。用钨粉作为压力校准剂，氦气作为传压介质，将合金装入金刚石压砧中，测量了它们的状态方程和轴比，具有较高的统计质量。这些状态方程与之前报告中的热参数相结合，以改进密度、绝热体积模量和体积声速对地球内核压力和温度的外推。我们通过将这些结果与铁的轻元素合金和地震观测的可用数据相结合，传播了不确定性并对地球内核的组成进行了限制。例如，在Fe0.95Ni0.05中单独添加4.3 - 5.3wt%的硅就可以解释内核边界的地球物理观测结果，高达7.5wt%的硫与可忽略的硅和氧也可以解释内核边界的地球物理观测结果。我们的研究结果有利于一个内核小于102重量%的氧和小于1重量%的碳，虽然不确定性的电子和非谐贡献的状态方程可能会改变这些值。考虑到内核地震梯度，成分空间向地球中心扩展。我们证明了hcp‐ Fe 0.91Ni 0.09和hcp‐ Fe 0.8Ni 0.1Si 0.1在测量的压力范围内具有比hcp‐Fe更大的轴向/轴向比。我们进一步研究了hcp结构材料的轴比、压力导数和弹性各向异性之间的关系。
We present powder X‐ray diffraction data on body centered cubic (bcc)‐ and hexagonal close packed (hcp)‐structured Fe0.91Ni0.09and Fe0.8Ni0.1Si0.1at 300 K up to 167 and 175 GPa, respectively. The alloys were loaded with tungsten powder as a pressure calibrant and helium as a pressure transmitting medium into diamond anvil cells, and their equations of state and axial ratios were measured with high statistical quality. These equations of state are combined with thermal parameters from previous reports to improve the extrapolation of the density, adiabatic bulk modulus, and bulk sound speed to the pressures and temperatures of Earth's inner core. We propagate uncertainties and place constraints on the composition of Earth's inner core by combining these results with available data on light‐element alloys of iron and seismic observations. For example, the addition of 4.3 to 5.3 wt% silicon to Fe0.95Ni0.05alone can explain geophysical observations of the inner core boundary, as can up to 7.5 wt% sulfur with negligible amounts of silicon and oxygen. Our findings favor an inner core with less than ∼2 wt% oxygen and less than 1 wt% carbon, although uncertainties in electronic and anharmonic contributions to the equations of state may shift these values. The compositional space widens toward the center of the Earth, considering inner core seismic gradients. We demonstrate that hcp‐Fe0.91Ni0.09and hcp‐Fe0.8Ni0.1Si0.1have measurably greaterc/aaxial ratios than those of hcp‐Fe over the measured pressure range. We further investigate the relationship between the axial ratios, their pressure derivatives, and elastic anisotropy of hcp‐structured materials.