Internally consistent thermodynamic database for iron to the Earth's core conditions
Internally consistent thermodynamic database for iron to the Earth's core conditions
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DOI：
10.1029/2009jb006442
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发表时间：
2010-03
影响因子：
--
通讯作者：
T. Komabayashi;Y. Fei
中科院分区：
文献类型：
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作者：
T. Komabayashi;Y. Fei
[1]根据已有的静态实验数据和热化学测量数据，建立了压力（P）至360 GPa，温度（T）至7000 K的纯铁热力学数据库。该数据库包括体心立方（BCC）相（α或δ相）、面心立方（FCC）相（γ相）、六方密堆积（HCP）相（α相）和液相。我们描述的基本热力学关系吉布斯自由能分为热化学和热物理条款。从现有的冶金数据库中的热化学数据进行评估，实验确定的相关系。热物理项由各相的压力-体积-温度状态方程（EoS）得到。我们从我们最近的内部加热金刚石对顶砧单元（DAC）的实验数据构建了FCC相的EoS，并从现有的激光加热DAC实验中评估了液相的EoS，以及P = 1 bar，0.2 GPa和沿着Hugoniot的密度数据。HCP-FCC-液体三相点位于P = 90 GPa和T = 2800 K。HCP铁在内核边界（P = 330 GPa）的熔化温度为4900 K，熔化时的密度变化为− 1.2%。在内核边界处的内核密度赤字为8.1重量%和5.3重量%分别用于液体外核和固体内核。计算的熔化温度远低于动态冲击波实验，表明HCP结构可能是不稳定的内核。我们包括了一个假设的高压BCC相，它可以通过高P BCC-HCP相的固-固转变稳定在220 GPa以上。这个假设的体心立方相应该有一个大的熵，给出一个高的熔化温度，以调和现有的静态和冲击波实验研究之间的差异。
[1] An internally consistent thermodynamic database for pure iron has been established to pressures (P) up to 360 GPa and temperatures (T) up to 7000 K from existing static experimental data and thermochemical measurements. The database includes body-centered cubic (BCC) phases (α or δ phase), the face-centered cubic (FCC) phase (γ phase), the hexagonal close-packed (HCP) phase (ɛ phase), and the liquid phase. We describe fundamental thermodynamic relations as the Gibbs free energy divided into thermochemical and thermophysical terms. The thermochemical data were evaluated from existing metallurgy databases together with experimentally determined phase relations. The thermophysical term is obtained from the pressure-volume-temperature equations of state (EoS) for the phases. We constructed an EoS of the FCC phase from our recent internally-heated diamond anvil cell (DAC) experimental data and assessed the EoS of the liquid phase from existing laser-heated DAC experiments together with density data at P = 1 bar, 0.2 GPa, and along the Hugoniot. The HCP-FCC-liquid triple point is located at P = 90 GPa and T = 2800 K. The calculated melting temperature of HCP iron at the inner core boundary (P = 330 GPa) is 4900 K and the density change at melting is −1.2%. The core density deficits at the inner core boundary are 8.1 wt.% and 5.3 wt.% for the liquid outer core and solid inner core, respectively. The calculated melting temperature is much lower than that from dynamic shock wave experiments, suggesting that the HCP structure may not be stable in the inner core. We included a hypothetical high-pressure BCC phase which could be stabilized above 220 GPa by a solid-solid transition of high-P BCC-HCP phases. This hypothetical BCC phase should have a large entropy to give a high melting temperature in order to reconcile the existing discrepancies between the static and shock wave experimental studies.