Experimental determination of oxygen diffusion in liquid iron at high pressure
Experimental determination of oxygen diffusion in liquid iron at high pressure
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高压铁液中氧扩散的实验测定
DOI：
10.1016/j.epsl.2017.02.020
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发表时间：
2017
影响因子：
5.3
通讯作者：
Steinle-Neumann
中科院分区：
文献类型：
--
作者：
Posner;Steinle-Neumann
在3 - 18gpa和1975-2643 K条件下，用多砧装置进行了氧在铁液中的扩散实验。扩散偶由纯铁棒和Fe 0.85 O 0.15烧结盘组成，端对端垂直放置。在垂直于扩散界面的线上沿淬火试样的全长获得图像和化学斑点分析。淬火过程中形成的脱溶特征主要由至少两个大小种群的球形氧化物斑点组成，以及靠近样品顶部的富氧区域的羽毛状树枝状纹理。在加热过程中的扩散（即在达到峰值退火温度之前，tf）进行数值处理，以通过同时最小二乘拟合来改进从恒压和可变tf实验中获得的几个浓度曲线的阿伦尼安参数。在研究的P-T范围内，扩散系数范围为~ 6× 10−9至~ 2× 10−8 m 2 s−1，活化焓小于100 kJ mol−1。我们发现压力对氧扩散的影响非常弱，激活体积为0.1±0.1 cm 3 mol−1，与100 GPa以上的计算研究一致。氧到地球外核P-T条件的扩散系数的Arrhenian外推得出的平均扩散速率（~ 3× 10−8 m 2 s−1）比以前报道的富硅液态铁合金或纯液态铁中的Si或Fe （~ 5× 10−9 m 2 s−1）更快。氧扩散数据用于限制岩浆海洋中液态金属液滴下降的最大尺寸，这是实现化学平衡所必需的。我们的研究结果表明，如果地球的核心成分代表了与硅酸盐岩浆海洋的平衡化学交换，那么它只能通过撞击器核心的大规模分裂成不超过几十厘米的液态铁液滴来完成。
Oxygen diffusion experiments in liquid iron have been performed at 3–18 GPa and 1975–2643 K using a multi-anvil apparatus. Diffusion couples consisted of a pure iron rod and a sintered disk of Fe 0.85 O 0.15 placed end-to-end in a vertical orientation. Images and chemical spot analyses were acquired along the full length of the quenched sample on lines perpendicular to the diffusion interface. Exsolution features that formed during quenching consist mostly of spherical oxide blobs of at least two size populations, as well as feathery dendritic textures in more oxygen-rich regions near the top of the samples. Diffusion during heating (ie prior to reaching the peak annealing temperature, T f) is treated numerically to refine Arrhenian parameters from simultaneous least-squares fits to several concentration profiles obtained from experiments at constant pressure and variable T f. Diffusion coefficients range from∼ 6× 10− 9 to∼ 2× 10− 8 m 2 s− 1 over the P–T range of the study, with activation enthalpies of less than 100 kJ mol− 1. We find a very weak effect of pressure on oxygen diffusion with an activation volume of 0.1±0.1 cm 3 mol− 1, in agreement with computational studies performed above 100 GPa. Arrhenian extrapolation of diffusion coefficients for oxygen to P–T conditions of the Earth's outer core yields faster average diffusion rates (∼ 3× 10− 8 m 2 s− 1) than for Si or Fe in silicon-rich liquid iron alloys or pure liquid iron (∼ 5× 10− 9 m 2 s− 1) reported previously. Oxygen diffusion data are used to constrain the maximum size of descending liquid metal droplets in a magma ocean that is required for chemical equilibration to be achieved. Our results indicate that if the Earth's core composition is representative of equilibrium chemical exchange with a silicate magma ocean, then it could only have been accomplished by large-scale break-up of impactor cores to liquid iron droplet sizes no larger than a few tens of centimeters.
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DOI：
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发表时间：
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期刊：
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