Phase relations in the system Fe–Ni–Si to 200 GPa and 3900 K and implications for Earth's core
Phase relations in the system Fe–Ni–Si to 200 GPa and 3900 K and implications for Earth's core
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DOI：
10.1016/j.epsl.2019.01.056
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发表时间：
2019-04
影响因子：
5.3
通讯作者：
T. Komabayashi;G. Pesce;R. Sinmyo;T. Kawazoe;H. Breton;Yuta Shimoyama;K. Glazyrin;Z. Konôpková;M. Mezouar
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文献类型：
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作者：
T. Komabayashi;G. Pesce;R. Sinmyo;T. Kawazoe;H. Breton;Yuta Shimoyama;K. Glazyrin;Z. Konôpková;M. Mezouar
利用同步辐射X射线原位衍射技术，在高温高压（P）条件下，对Fe-5wt%Ni-4wt%Si合金的相关系进行了研究。在最高的P-T条件下观察到六方密排（hcp）结构，支持地球内核中稳定的铁合金结构是hcp的想法。面心立方（fcc）结构和六方晶系（hcp）结构之间相变的P-T位置也被限制在106 GPa。转变发生在15 GPa和1000 K类似于纯Fe。然而，Clausius-Clapeyron斜率为0.0480 GPa/K，其大于Fe（0.0394 GPa/K）、Fe-9.7重量% Ni（0.0426 GPa/K）和Fe-4重量% Si（0.0394 GPa/K）的报道斜率，使fcc结构朝向高压稳定。因此，同时添加Ni和Si到Fe中增加了fcc-hcp转变的dP/dT斜率。这与在Fe-Ni-Si中转变时的小体积变化有关。在145 GPa和3750 K下，在Fe-5 wt% Ni-4 wt% Si中fcc、hcp和液相共存的三相点被放置。在内核-外核边界处的hcp相的熔化温度比纯铁低550 K。
Phase relations in Fe–5 wt% Ni–4 wt% Si alloy was examined in an internally resistive heated diamond anvil cell under high pressure (P) and temperature (T) conditions to about 200 GPa and 3900 K by in-situ synchrotron X-ray diffraction. The hexagonal close-packed (hcp) structure was observed to the highest P–T condition, supporting the idea that the stable iron alloy structure in Earth's inner core is hcp. The P–T locations of the phase transition between the face-centred cubic (fcc) and hcp structures were also constrained to 106 GPa. The transition occurs at 15 GPa and 1000 K similar to for pure Fe. The Clausius–Clapeyron slope is however, 0.0480 GPa/K which is larger than reported slopes for Fe (0.0394 GPa/K), Fe–9.7 wt% Ni (0.0426 GPa/K), and Fe–4 wt% Si (0.0394 GPa/K), stabilising the fcc structure towards high pressure. Thus the simultaneous addition of Ni and Si to Fe increases the d P/d T slope of the fcc–hcp transition. This is associated with a small volume change upon transition in Fe–Ni–Si. The triple point, where the fcc, hcp, and liquid phases coexist in Fe–5 wt% Ni–4 wt% Si is placed at 145 GPa and 3750 K. The resulting melting temperature of the hcp phase at the inner core-outer core boundary lies at 550 K lower than in pure Fe.