Decompression-induced melting of ice IV and the liquid-liquid transition in water
Decompression-induced melting of ice IV and the liquid-liquid transition in water
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DOI：
10.1038/32386
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发表时间：
1998-03-12
期刊：
影响因子：
64.8
通讯作者：
Stanley, HE
中科院分区：
文献类型：
--
作者：
Mishima, O;Stanley, HE
尽管液态水在100多年来一直是深入研究的焦点，但仍然缺乏一个能统一这种液体所有已知异常现象的连贯物理图景。其中一些异常现象出现在过冷区域，并且基于气 - 液亚稳极限线可能延伸到过冷液态区域，或者基于该区域存在一条一阶液 - 液相变线且在一个临界点终结这两种情况而得到了合理化解释（4 - 7，8 - 14）。但是这些观点在实验上仍未得到验证，部分原因是过冷水只能在均相成核温度\(T_H\)以上进行探测，在该温度下，水会自发结晶。在此我们报道一种不受\(T_H\)所设障碍限制的实验方法，它涉及对小乳化液滴中几种高压冰相的减压诱导熔化曲线的测量。我们发现，冰Ⅳ的熔化曲线似乎恰好在为液 - 液相变线所提出的位置发生不连续（8）。这与（过冷）液态水的两种不同相的共存是相符的，但并不能证明这一点。根据实验数据，我们计算出一个可能的吉布斯势面以及水的一个相应的状态方程，从其形式我们估计液 - 液临界点的坐标为压力\(P_c\approx0.1\)吉帕，温度\(T_c\approx220\)开尔文。
Although liquid water has been the focus of intensive research for over 100 years, a coherent physical picture that unifies all of the known anomalies of this liquid(1-3) is still lacking, Some of these anomalies occur in the supercooled region, and have been rationalized on the grounds of a possible retracing of the liquid-gas spinodal (metastability limit) line into the supercooled liquid region(4-7) or alternatively the presence of a line of first-order liquid-liquid phase transitions in this region which ends in a critical points(8-14). But these ideas remain untested experimentally, in part because supercooled water can be probed only above the homogeneous nucleation temperature T-H at which water spontaneously crystallizes. Here we report an experimental approach that is not restricted by the barrier imposed by T-H, involving measurement of the decompression-induced melting curves of several high-pressure phases of ice in small emulsified droplets. We find that the melting curve for ice IV seems to undergo a discontinuity at precisely the location proposed for the line of liquid-liquid phase transitions(8). This is consistent with, but does not prove, the coexistence of two different phases of (supercooled) liquid water. From the experimental data we calculate a possible Gibbs potential surface and a corresponding equation of state for water, from the forms of which we estimate the coordinates of the liquid-liquid critical point to be at pressure P-c approximate to 0.1 GPa and temperature T-c approximate to 220 K.