加压含水体系中液体稳定性的平衡极限
On the equilibrium limit of liquid stability in pressurized aqueous systems
AI总结：
本研究利用等容冻结首次测定二元卤水液体稳定性的绝对极限，提出“cenotectic”概念，发现其约比1 bar共晶点低22 K、压力约213 MPa，并揭示高压水合物及行星海洋意义。
摘要：
相稳定性及其极限是材料热力学的核心问题。然而，化学体系中平衡液体稳定性的温度极限迄今仅在恒定（通常为大气压）压力条件下得到广泛表征，在此条件下该极限由共晶点表示。在更高压力下，这一极限会在温度和化学组成两方面发生移动，从而打开一个宽广的热力学参数空间，绝对极限——即在起作用的热力学力（此处为压力和浓度）取任意值时的极限——可能存在于其中。本工作中，我们利用等容冻结首次在若干二元卤水中测量了这一绝对极限，并呼应“eutectic（共晶）”一词的词源，将该极限命名为“cenotectic（泛共晶）”（源自希腊语“κοινός τήκτος”，意为“普遍熔体”）。我们观察到，当不存在含溶质的高压相时，cenotectic 一致地出现在比 1 bar 共晶点低 22 ± 2 K 的温度以及约 213 ± 3 MPa 的压力下，表明其由所存在冰相的液相线行为主导。在绘制各共晶构型的 T-P 演化时，我们还发现了若干此前未报道的 NaHCO2、MgCl2 和 NaCl 高压水合物，并发现这些高压相可产生涉及液体的复杂多相构型，这些构型可在显著更低的温度下保持亚稳态。我们讨论了这些发现对太阳系海洋世界及寒冷海洋系外行星的意义；利用 cenotectic 压力估算了冰壳厚度和最终海洋深度（“终局”）的热力学极限；最后给出了关于这一基本热力学不变点的广义热力学视角（及定义）。
英文摘要：
Phase stability, and the limits thereof, are a central concern of materials thermodynamics. However, the temperature limits of equilibrium liquid stability in chemical systems have only been widely characterized under constant (typically atmospheric) pressure conditions, whereunder the limit is represented by the eutectic. At higher pressures, this limit will shift in both temperature and chemical composition, opening a wide thermodynamic parameter space over which the absolute limit, i.e., the limit under arbitrary values of the thermodynamic forces at play (here pressure and concentration), might exist. In this work, we use isochoric freezing to measure this absolute limit for the first time in several binary aqueous brines, and, nodding to the etymology of "eutectic", we name this limit the "cenotectic" (from Greek " ", "universal-melt"). We observe that when no solute-bearing high-pressure phases exist, the cenotectic occurs consistently 22 +/- 2K below the 1 bar eutectic and at approximately 213 +/- 3 MPa, suggesting domination by the liquidus behaviors of the icy phases present. In charting the T-P evolution of each eutectic configuration, we also encounter several unreported high-pressure hydrates of NaHCO2, MgCl2, and NaCl, and we find that these high-pressure phases can produce complex multi-phase configurations involving the liquid that may remain metastable to significantly lower temperatures. We discuss the implications of these findings for ocean worlds of our solar system and cold ocean exoplanets; estimate thermodynamic limits on ice crust thickness and final ocean depth ("endgame") using the cenotectic pressure; and finally provide a generalized thermodynamic perspective on (and definition for) this fundamental thermodynamic invariant point.
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