Hydrogen solubility in FeSi alloy phases at high pressures and temperatures
Hydrogen solubility in FeSi alloy phases at high pressures and temperatures
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DOI：
10.2138/am-2022-8295
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发表时间：
2022-12-16
影响因子：
3.1
通讯作者：
Shim, Sang-Heon
中科院分区：
文献类型：
--
作者：
Fu, Suyu;Chariton, Stella;Shim, Sang-Heon
轻元素与金属铁的合金化可以改变行星核的性质，因此在行星核的结构和动力学中起着关键作用。氢和硅可能是这些岩石行星核心中的轻元素。然而，由于实验上的困难，Fe-Si合金系统在高压和高温下的储氢仍然不清楚。利用脉冲激光加热与高能同步X射线衍射相结合的方法，研究了激光加热至61.9 Gpa和3500K的金刚石对顶盒(LHDAC)中FeSi与H的反应。结果表明，在H饱和条件下，FeSi与H合金化的量(B20和B2结构分别为0.3和0.1wt%)远小于纯Fe金属(>；1.8wt%)。我们的实验还表明，当恢复到1bar时，H仍然保留在FeSi合金的晶体结构中。进一步的密度泛函理论(DFT)计算表明，低H溶解度可能是由于B20和B2结构中高度扭曲的间隙位造成的，这不利于H的掺入。在环境条件下恢复B_(20)FeSi晶体结构中的H，可能为在未来的实验中理解H在岩心形成过程中的地球化学行为提供可能。FeSi合金中的低H含量表明，如果行星核是富硅的，硅可以限制H进入富Fe核。
Light elements alloying with metallic Fe can change the properties and therefore play a key role in the structure and dynamics of planetary cores. Hydrogen and silicon are possible light elements in the rocky planets' cores. However, hydrogen storage in Fe-Si alloy systems remains unclear at high pressures and high temperatures because of experimental difficulties. Taking advantage of pulsed laser heating combined with high-energy synchrotron X-ray diffraction, we studied reactions between FeSi and H in laser-heated diamond-anvil cells (LHDACs) up to 61.9 GPa and 3500 K. We found that under H-saturated conditions the amount of H alloying with FeSi (0.3 and < 0.1 wt% for the B20 and B2 structures, respectively) is much smaller than that in pure Fe metal (> 1.8 wt%). Our experiments also suggest that H remains in the crystal structure of FeSi alloy when recovered to 1 bar. Further density functional theory (DFT) calculations indicate that the low-H solubility likely results from the highly distorted interstitial sites in the B20 and B2 structures, which are not favorable for H incorporation. The recovery of H in the B20 FeSi crystal structure at ambient conditions could open up possibilities to understand geochemical behaviors of H during core formation in future experiments. The low-H content in FeSi alloys suggests that if a planetary core is Si-rich, Si can limit the ingassing of H into the Fe-rich core.