Hydrogen Limits Carbon in Liquid Iron
Hydrogen Limits Carbon in Liquid Iron
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DOI：
10.1029/2019gl082591
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发表时间：
2019-05-28
影响因子：
5.2
通讯作者：
Genda, Hidenori
中科院分区：
文献类型：
--
作者：
Hirose, Kei;Tagawa, Shoh;Genda, Hidenori
Fe-C-H系在激光加热的金刚石顶压室中进行了127 Gpa的熔炼实验。在原位和非原位样品表征的基础上，我们发现碳在液态铁中的溶解度与氢浓度成反比，这表明在富C和H的条件下，液态铁优先结合氢而不是碳。虽然大量的C和H都可能被输送到成长的地球，但在核形成的后期，可能会有贫C/H的金属加入到原核中。我们还得到了Fall(X)(x>；1)的熔化曲线，远远超出了先前测定的压力范围。在135 GPa时，其液相线温度为2380K，低于与其他可能的核心轻元素合金化的Fe。因此，氢的存在支持了相对较低的核心温度。简单地说，碳和氢都可能是核心中的主要轻元素，但由于它们的高度挥发性，很难估计它们在核心和整体地球中的丰度。此外，对含氢铁合金的性能研究最少。在这里，我们进行了Fe-C-H到127 Gpa的熔化实验，接近地核顶部的压力。我们的主要发现是氢限制了碳在液态铁中的溶解度；碳含量与熔融铁中的氢浓度成反比，在大约60 Gpa和类似3500 K的温度下与钻石共存。最近的行星形成理论表明，大量的C和H被输送到不断增长的地球。在核形成的后期，液态金属优先结合氢而不是碳，可能已经添加到原核中。我们还发现，氢显著降低了Fe的熔化温度。FeHx(x&Gt；1)的熔化温度仅为2380K左右，低于Fe-Fe3S共晶和Fe与其他可能的核心轻元素合金化的温度。
Melting experiments were performed on the Fe-C-H system to 127 GPa in a laser-heated diamond anvil cell. On the basis of in situ and ex situ sample characterizations, we found that the solubility of carbon in liquid Fe correlates inversely with hydrogen concentration at similar to 60 GPa and similar to 3500 K, indicating that liquid Fe preferentially incorporates hydrogen rather than carbon under conditions with abundant C and H. While large amounts of both C and H may have been delivered to the growing Earth, C-poor/H-rich metals were likely added to the protocore in the late stages of core formation. We also obtained a melting curve of Fell(x )(x > 1) far beyond the pressure range in earlier determinations. Its liquidus temperature was found to be 2380 K at 135 GPa, lower than those of Fe alloyed with the other possible core light elements. Relatively low core temperature is thus supported by the presence of hydrogen.Plain Language Summary Both carbon and hydrogen are possible major light elements in the core but estimation of their abundance in the core as well as in the bulk Earth is difficult because of their high volatility. In addition, the property of hydrogen-bearing iron alloys has been the least studied. Here we performed melting experiments on Fe-C-H to 127 GPa, close to the pressure at the top of the Earth's core. Our main finding is that hydrogen limits the solubility of carbon in liquid Fe; the carbon content correlates inversely with hydrogen concentration in molten Fe coexisting with diamonds at similar to 60 GPa and similar to 3500 K. Recent planet formation theories suggest that large amounts of C and H were delivered to the growing Earth. In the late stages of core formation, liquid metals preferentially incorporating hydrogen rather than carbon may have added to the protocore. We also found that hydrogen decreases the melting temperature of Fe remarkably. The melting temperature of FeHx (x > 1) is only about 2380 K at the core-mantle boundary; lower than those of Fe-Fe3S eutectic and Fe alloyed with the other possible core light elements.