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Thermodynamic modelling of perchlorate/chloride and perchlorate/chlorate deliquescence at Mars-relevant temperatures
Geochimica et Cosmochimica Acta ( IF 5 ) Pub Date : 2022-06-20 , DOI: 10.1016/j.gca.2022.06.011
Vincent F. Chevrier , Alec Fitting , Amira Elsenousy , Edgard G. Rivera-Valentín

Perchlorate (ClO4) salts were discovered on Mars and are known to absorb water vapor from the atmosphere and deliquesce into the aqueous phase. Other species such as chlorides (Cl) and chlorates (ClO3) were also identified; these species can affect the deliquescence of perchlorates. Here we generate phase diagrams of perchlorate/chloride and perchlorate/chlorate binary mixtures for K, Na, Mg and Ca in the temperature range 223–273 K. Using a new approach based on thermodynamic modelling of evaporation, we determined the deliquescence relative humidity (the minimum relative humidity at which a salt converts into a liquid by absorbing atmospheric water vapor) and the eutonic relative humidity (the minimum relative humidity at which two salts are in equilibrium with liquid) for binary salt mixtures. Our modelling results show that the deliquescence relative humidity values of all salt mixtures is always lower than that of each individual end-member salt at a fixed temperature, typically a few percent lower. The closer the eutonic is to one of the end-member, the smaller the decrease in relative humidity compared to the pure pole. Thus, only eutonics which are far from both poles exhibit a significant drop in relative humidity. Moreover, the eutonic relative humidity always increases with decreasing temperature, which does not favor liquids in the dry and cold Martian environment. Finally, the increased stability of water ice at the lowest temperatures always reduces or even eliminates the stability of liquids. Therefore, the favorable temperature and relative humidity conditions under which binary salt liquid mixtures exist are generally not significantly improved compared to single salts.



中文翻译:

火星相关温度下高氯酸盐/氯化物和高氯酸盐/氯酸盐潮解的热力学模型

高氯酸盐 (ClO 4 - ) 盐是在火星上发现的,已知会吸收大气中的水蒸气并潮解到水相中。其他种类如氯化物 (Cl - ) 和氯酸盐 (ClO 3 -)亦被识别;这些物种会影响高氯酸盐的潮解。在这里,我们生成了 223-273 K 温度范围内 K、Na、Mg 和 Ca 的高氯酸盐/氯化物和高氯酸盐/氯酸盐二元混合物的相图。使用基于蒸发热力学模型的新方法,我们确定了潮解相对湿度(对于二元盐混合物,盐通过吸收大气水蒸气转化为液体的最小相对湿度)和超子相对湿度(两种盐与液体平衡时的最小相对湿度)。我们的建模结果表明,在固定温度下,所有盐混合物的潮解相对湿度值始终低于每个端元盐的潮解相对湿度值,通常低几个百分点。eutonic 越接近末端成员之一,与纯极相比,相对湿度的降低越小。因此,只有远离两极的超子会表现出相对湿度的显着下降。此外,优子相对湿度总是随着温度的降低而增加,这不利于干燥和寒冷的火星环境中的液体。最后,在最低温度下水冰稳定性的提高总是会降低甚至消除液体的稳定性。因此,与单盐相比,二元盐液体混合物存在的有利温度和相对湿度条件通常没有显着改善。只有远离两极的超子会表现出相对湿度的显着下降。此外,优子相对湿度总是随着温度的降低而增加,这不利于干燥和寒冷的火星环境中的液体。最后,在最低温度下水冰稳定性的提高总是会降低甚至消除液体的稳定性。因此,与单盐相比,二元盐液体混合物存在的有利温度和相对湿度条件通常没有显着改善。只有远离两极的超子会表现出相对湿度的显着下降。此外,优子相对湿度总是随着温度的降低而增加,这不利于干燥和寒冷的火星环境中的液体。最后,在最低温度下水冰稳定性的提高总是会降低甚至消除液体的稳定性。因此,与单盐相比,二元盐液体混合物存在的有利温度和相对湿度条件通常没有显着改善。在最低温度下水冰稳定性的提高总是会降低甚至消除液体的稳定性。因此,与单盐相比,二元盐液体混合物存在的有利温度和相对湿度条件通常没有显着改善。在最低温度下水冰稳定性的提高总是会降低甚至消除液体的稳定性。因此,与单盐相比,二元盐液体混合物存在的有利温度和相对湿度条件通常没有显着改善。

更新日期:2022-06-20
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