The phase diagram of the Fe-P binary system at 3 GPa and implications for phosphorus in the lunar core
The phase diagram of the Fe-P binary system at 3 GPa and implications for phosphorus in the lunar core
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3 GPa 下 Fe-P 二元系统的相图及其对月核中磷的影响
DOI：
10.1016/j.gca.2019.03.037
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发表时间：
2019
影响因子：
5
通讯作者：
Zhai Shuangmeng
中科院分区：
文献类型：
--
作者：
Yin Yuan;Li Zeming;Zhai Shuangmeng
磷是月球金属核心的潜在候选者。在3GPa和1600° C的温度下研究了Fe-P二元系的相图。在1100° C和3GPa下，高达3.0wt%和10.4wt%的磷可以分别溶解在固体铁和液体Fe-P相中。富铁侧的共晶温度在3GPa下确定为1085° C。磷在铁中的溶解度从1100° C下的1.4wt%降低到1500° C和3GPa下的1.7wt%。淬火态铁的结构为体心立方结构，对应于α-Fe相。将磷在固体铁中的溶解度扩展到目前的月核条件，在完全结晶的铁核中产生的最大磷浓度为0.85±0.15重量%。如果在芯中存在Ni和C，则该值将被降低到0.4± 0.1wt%。此外，基于月球体块（BM）和月球体块硅酸盐（BSM）之间的简单亲铁物质质量平衡和模拟的磷分配系数，月球岩浆海洋的DP-月球核/地幔（40-200），大量硅酸盐类地球磷含量（82±8 ppm），月核中的磷含量< 0.3 wt%。其他一些潜在的轻元素如S和C也可能降低月核中的磷含量。在3GPa下，磷在铁和液态熔体中的分配系数（DPSM/LM）为0.10±0.03。考虑到硫的存在，在5GPa下，富硫液态金属（~ 8wt%）的DPSM/LM增加到0.18±0.02。在固体月球内核和含硫液体月球外核的情况下，当月球内核的P储存量<0.3wt%时，它们的P含量分别小于0.09± 0.01wt%和0.51± 0.01wt%。在固体铁中适度的磷溶解度，结合月球中大量磷的假设，表明月球核心中的磷浓度可能比以前认为的要高。
Phosphorus is a potential candidate in the metallic core of the Moon. The phase diagram of the Fe-P binary system was investigated at the pressure of 3 GPa and temperatures of up to 1600° C. Up to 3.0 wt% and 10.4 wt% phosphorus can dissolve in the solid iron and liquid Fe-P phases at 1100° C and 3 GPa, respectively. The eutectic temperature on the iron-rich side was determined as 1085° C at 3 GPa. The solubility of phosphorus in the iron decreases from∼ 1.4 wt% at 1100° C to∼ 0.7 wt% at 1500° C and 3 GPa. Structure of the solid iron in the quenched sample is the body-center cubic, corresponding to α-Fe phase. Extending the phosphorus solubility in the solid iron to the present lunar core conditions yields a maximum phosphorus concentration in a fully crystallized iron core of 0.85±0.15 wt%. If there are Ni and C in the core, the value would be depressed to 0.4±0.1 wt%. In addition, based on a simple siderophile mass balance between the bulk Moon (BM) and bulk silicate Moon (BSM) and a modeled phosphorus partition coefficient, D P-Moon core/mantle (40–200) for the lunar magma ocean, a bulk silicate Earth-like P content (82±8 ppm) in the initial Moon yields a lunar core with< 0.3 wt% P. Some other potential light elements such as S and C could reduce the P content in the lunar core. Furthermore, the partition coefficient of phosphorus in the iron and liquid melt (D P SM/LM) was found to be 0.10±0.03 at 3 GPa. Taking the sulfur into account, the D P SM/LM increase to 0.18±0.02 at 5 GPa in the S-rich liquid metal (∼ 8 wt%). In the case of a solid lunar inner core and S-bearing liquid outer core, their P contents were assessed to be less than 0.09±0.01 wt% and 0.51±0.01 wt%, respectively, when the lunar core’s storage of P is< 0.3 wt%. The moderate phosphorus solubility in the solid iron, combined with the assumption of abundant phosphorus in the bulk Moon, indicates that the phosphorus concentration in the lunar core could higher than previously thought.