Highly compressed water structure observed in a perchlorate aqueous solution.
Highly compressed water structure observed in a perchlorate aqueous solution.
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DOI：
10.1038/s41467-017-01039-9
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发表时间：
2017-10-13
影响因子：
16.6
通讯作者：
Dougan L
中科院分区：
文献类型：
--
作者：
Lenton S;Rhys NH;Towey JJ;Soper AK;Dougan L
凤凰号着陆器在火星土壤样本中发现了高氯酸钙和高氯酸镁，这引发了许多人的猜测，即高氯酸盐卤水的流动可能是观测到的地表沟槽和风化的原因。在这里，我们用中子衍射结合氢同位素标记和经验势能结构修正，研究了一种模拟火星水的高氯酸镁水溶液在其共晶组成时的结构。我们发现水的四面体结构被严重扰动，这种效应相当于将纯水加压到2 Gpa或更高的压力。镁离子和ClO_4−离子看起来是电荷有序的，将水限制在9 ä量级的长度尺度上，防止在低温下结冰。这可能解释了这些盐溶液的低蒸发速率和高潮解度，这对于火星大气低相对湿度环境中的稳定性是必不可少的。在火星表面发现了大量不同的高氯酸盐。在这里，作者表明高氯酸镁对溶液中的水结构有重大影响，这为火星上存在的低温条件下的水流体可能存在提供了洞察力。
The discovery by the Phoenix Lander of calcium and magnesium perchlorates in Martian soil samples has fueled much speculation that flows of perchlorate brines might be the cause of the observed channeling and weathering in the surface. Here, we study the structure of a mimetic of Martian water, magnesium perchlorate aqueous solution at its eutectic composition, using neutron diffraction in combination with hydrogen isotope labeling and empirical potential structure refinement. We find that the tetrahedral structure of water is heavily perturbed, the effect being equivalent to pressurizing pure water to pressures of order 2 GPa or more. The Mg2+ and ClO4 − ions appear charge-ordered, confining the water on length scales of order 9 Å, preventing ice formation at low temperature. This may explain the low evaporation rates and high deliquescence of these salt solutions, which are essential for stability within the low relative humidity environment of the Martian atmosphere. Significant amounts of different perchlorate salts have been discovered on the surface of Mars. Here, the authors show that magnesium perchlorate has a major impact on water structure in solution, providing insight into how an aqueous fluid might exist under the sub-freezing conditions present on Mars.
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