Melting diagrams of Fe-rich alloys determined from synchrotron in situ measurements in the 15-23 GPa pressure range
Melting diagrams of Fe-rich alloys determined from synchrotron in situ measurements in the 15-23 GPa pressure range
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DOI：
10.1016/j.pepi.2008.09.020
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发表时间：
2009-05-01
影响因子：
2.3
通讯作者：
Funakoshi, K.
中科院分区：
文献类型：
--
作者：
Andrault, D.;Bolfan-Casanova, N.;Funakoshi, K.
本文报道了用X射线衍射仪(SPring8)，在15~24 Gpa的压力下，用10-20at.%C、O、S或Si合金化的铁的熔化行为的原位观察。铁合金的部分熔化程度是通过分析铁水的X射线散射强度随温度降低50度阶跃而变化的。结合对回收样品的微观分析，原位观察直接限制了熔化图中液、固两相曲线的形状和位置。对于Fe-S体系，我们的结果与前人的工作很好地吻合。我们观察到，随着压力的增加，共晶温度从15 GPa时的1023K上升到20.6 GPa时的1123K，而共晶成分则降低。对于Fe-C系，在20.7 GPa时的共晶温度为1460K，略低于前人工作的线性外推。在Fe-Ni-Si系和Fe-O系的情况下，我们发现共晶温度明显低于以前报道的温度。对于这两个体系，在15-20 Gpa范围内，共晶温度和成分都随着压力的增加而增加。与以前的工作相比，我们观察到：(A)Fe-O系中轻元素含量较高，在16.5和20.5 GPa时分别为9.0和10.5wt%O，而在16.9 Gpa时，含11.5wt%Si的Fe-Ni-Si系中的共晶成分较差。我们证实了Si和C在固体铁中具有很高的溶解度，并报告了16.9 GPa时Si的分配系数为1.3(2)。S和O在固体铁中的溶解度似乎很小。因此，S和/或O都可以解释密度，即在行星核的液体外层和固态内部之间的跳跃，至少高达25 Gpa。(C)2008爱思唯尔B.V.保留所有权利。
We report in situ observations of the melting behaviour of iron alloyed with 10-20 at.% C, O, S, or Si at pressures between 15 and 24 GPa, using X-ray diffraction in a multi-anvil press (SPring8). The degree of partial melting of the iron alloys has been quantified from analysis of the intensity of diffuse X-ray scattering of molten iron as a function for decreasing temperature with a 50 degrees step. Coupled with microanalysis of recovered samples, the in situ observations bring direct constraints on shape and positions of liquidus and solidus curves in the melting diagrams.For the Fe-S system, our results are in good agreement with previous works. We observe that the eutectic temperature increases from 1023 K at 15 GPa to 1123 K at 20.6 GPa and that the eutectic composition decreases with increases pressure. Concerning the Fe-C system the eutectic temperature of 1460 K at 20.7 GPa falls slightly below a linear extrapolation of the previous work. In the case of the Fe-Ni-Si system and the Fe-O system, we find eutectic temperatures significantly lower than previously reported. For the two systems, both eutectic temperature and composition increase with increasing pressure in the 15-20 GPa range. Compare to previous work, we observe eutectic compositions (a) richer in light elements in the Fe-O system, with 9.0 and 10.5 wt% O at 16.5 and 20.5 GPa, respectively, and (b) poorer in the Fe-Ni-Si system with 11.5 wt% Si at 16.9 GPa.We confirm very high solubility of Si and C with solid iron, and report a Si partitioning coefficient of 1.3(2) at 16.9 GPa. The S and O solubility in solid iron appears very small. Therefore, both S and/or O could explain density,jumps between liquid outer and solid inner parts of planetary cores, at least up to similar to 25 GPa. (C) 2008 Elsevier B.V. All rights reserved.