In general pure liquid water is not thermodynamically stable on Mars due to the extremely cold and dry environment. The presence in the soil of perchlorates, which could lower the freezing point of water and form aqueous solutions by taking up water vapor even under subsaturated conditions, has been proposed to explain the possible existence of liquid water on Mars and in some hyperarid environments on Earth. In this work, the phase transitions and hygroscopic growth of Mg(ClO₄)₂, NaClO₄, and NaClO₄·H₂O were investigated between 278 and 303 K. In this temperature range, we found that anhydrous Mg(ClO₄)₂ was completely converted to Mg(ClO₄)₂·6H₂O at a relative humidity (RH) as low as <1%. In contrast, anhydrous NaClO₄ was stable at RH below 20%, and NaClO₄·H₂O was completely transformed to anhydrous NaClO₄ at <1% RH; when RH was increased to 30%, anhydrous NaClO₄ was transformed to NaClO₄·H₂O. We also found that the deliquescence relative humidity (DRH) of NaClO₄·H₂O decreased from ∼51.5% at 278 K to ∼43.5% at 303 K, exhibiting a negative dependence on temperature. In addition, the amounts of water in the NaClO₄ solution were quantitatively determined as a function of RH at 278, 288, and 298 K. This work considerably furthers our understanding of the hygroscopic properties of perchlorates under different conditions, as well as the hydrological cycles on Mars and in other hyperarid environments, such as the Atacama Desert on Earth.

中文翻译：

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Mg（ClO ₄）₂，NaClO ₄和NaClO ₄ ·H ₂ O的相变和吸湿生长：对火星和地球上高干旱环境中水的稳定性的影响

通常，由于极端寒冷和干燥的环境，纯液态水在火星上不是热力学稳定的。有人提出在土壤中存在高氯酸盐，即使在不饱和的条件下，它也可以降低水的凝固点并通过吸收水蒸气而形成水溶液，从而解释了火星上以及地球上某些高干旱环境中可能存在液态水的原因。 。在这项工作中，研究了Mg（ClO ₄）₂，NaClO ₄和NaClO ₄ ·H ₂ O的相变和吸湿性生长，在278和303 K之间。在此温度范围内，我们发现无水Mg（ClO ₄）₂完全转化为Mg（ClO ₄）₂ ·6H ₂ O，相对湿度（RH）低至<1％。相反，无水NaClO ₄在相对湿度低于20％时是稳定的，而NaClO ₄ ·H ₂ O在<1％相对湿度下完全转化为无水NaClO ₄。当RH升至30％，无水的NaClO ₄，转化的NaClO ₄ ·H ₂ O.我们还发现，次氯酸钠的潮解相对湿度（DRH）₄ ·H ₂ ö从~51.5％下降在278 K至~43.5 ％在303K，表现出对温度的负相关性。此外，NaClO _4中的水量 溶液是在278、288和298 K下作为RH的函数定量确定的。这项工作极大地增进了我们对高氯酸盐在不同条件下的吸湿性能以及在火星和其他高干旱环境中的水文循环的了解，例如地球上的阿塔卡马沙漠。