Thompson Samuel, Sugimura-Komabayashi Emiko, Komabayashi Tetsuya, McGuire Chris, Breton Helene, Suehiro Sho, Ohishi Yasuo
School of GeoSciences and Centre for Science at Extreme Conditions, University of Edinburgh, Edinburgh, EH9 3FE, United Kingdom.
Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Tokyo 152-8551, Japan.
J Phys Condens Matter. 2022 Jul 29;34(39). doi: 10.1088/1361-648X/ac8263.
Melting experiments on FeS were conducted to 75 GPa and 2800 K in laser-heated and internally resistive-heated diamond anvil cells withx-ray diffraction and/or post-mortem textural observation. From the constrained melting curve, we assessed the thermal equation of state for FeS liquid. Then we constructed a thermodynamic model of melting of the system Fe-FeS including the eutectic relation under high pressures based on our new experimental data. The mixing properties of Fe-S liquids under high pressures were evaluated in order to account for existing experimental data on eutectic temperature. The results demonstrate that the mixing of Fe and S liquids are nonideal at any core pressure. The calculated sulphur content in eutectic point decreases with increasing pressure to 120 GPa and is fairly constant of 8 wt% at greater pressures. From the Gibbs free energy, we derived the parameters to calculate the crystallising point of an Fe-S core and its isentrope, and then we calculated the density and the longitudinal seismic wave velocity () of these liquids along each isentrope. While FeS liquid can account for the seismologically constrained density andprofiles over the outer core, the density of the precipitating phase is too low for the inner core. On the other hand, a hypothetical Fe-S liquid core with a bulk composition on the Fe-rich side of the eutectic point cannot represent the density andprofiles of the Earth's outer core. Therefore, Earth's core cannot be approximated by the system Fe-S and it should include another light element.
在激光加热和内电阻加热的金刚石对顶砧中，对FeS进行了高达75吉帕和2800开尔文的熔化实验，并结合X射线衍射和/或事后组织观察。根据约束熔化曲线，我们评估了FeS液体的热状态方程。然后，基于我们的新实验数据，构建了包括高压下共晶关系的Fe-FeS系统熔化的热力学模型。为了解释现有的共晶温度实验数据，评估了高压下Fe-S液体的混合性质。结果表明，在任何核心压力下，Fe和S液体的混合都是非理想的。计算得出，共晶点处的硫含量随压力增加到120吉帕而降低，在更高压力下相当恒定，为8重量%。从吉布斯自由能出发，我们推导出计算Fe-S核心及其等熵线结晶点的参数，然后计算了这些液体沿每条等熵线的密度和纵向地震波速度（）。虽然FeS液体可以解释地震学约束的外核密度和剖面，但沉淀相的密度对于内核来说太低了。另一方面，一种假设的、整体成分位于共晶点富铁一侧的Fe-S液体核心不能代表地球外核的密度和剖面。因此，地球的核心不能用Fe-S系统近似，它应该包含另一种轻元素。
