Research Center for Advanced Measurement and Characterization, National Institute for Materials Science (NIMS), Tsukuba, Ibaraki305-0044, Japan.
Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki305-8567, Japan.
J Phys Chem B. 2023 Feb 16;127(6):1414-1421. doi: 10.1021/acs.jpcb.2c08342. Epub 2023 Feb 6.
Experimental and theoretical evidence has been accumulating to support the liquid-liquid critical point (LLCP) hypothesis for water. However, no agreement has yet been reached on the pressure and temperature of LLCP. Here we made simple experimental equations that reproduced the volume of liquid water measured over a wide pressure-temperature range. They were polynomials that calculate pressure using volume and temperature as variables, and coefficients were determined by the method of least-squares. We analyzed the polynomials by changing the volume data and the number of terms in the polynomials and extrapolated them slightly to low temperatures. Consequently, the available experimental volume of liquid water indicated (but did not prove) the existence of LLCP at low temperature. Representative polynomials suggested that LLCP locates around 105 ± ∼ 9 MPa, 207 ± ∼ 5 K, and 0.993 ± ∼ 0.009 cm/g.
实验和理论证据不断积累，支持水的液-液相变临界点（LLCP）假说。然而，对于 LLCP 的压力和温度，尚未达成共识。在这里，我们提出了简单的实验方程，能够再现宽压力-温度范围内测量到的液态水体积。这些方程是使用体积和温度作为变量计算压力的多项式，系数是通过最小二乘法确定的。我们通过改变体积数据和多项式的项数来分析多项式，并对其进行略微低温外推。因此，可用的液态水实验体积表明（但并未证明）在低温下存在 LLCP。代表性的多项式表明，LLCP 位于约 105 ± ∼ 9 MPa、207 ± ∼ 5 K 和 0.993 ± ∼ 0.009 cm/g。
