Density and Isothermal Compressibility of Supercritical H2O-NaCl Fluid: Molecular Dynamics Study from 673 to 2000 K, 0.2 to 2 GPa, and 0 to 22 wt% NaCl Concentrations
Density and Isothermal Compressibility of Supercritical H2O-NaCl Fluid: Molecular Dynamics Study from 673 to 2000 K, 0.2 to 2 GPa, and 0 to 22 wt% NaCl Concentrations
复制标题
密度%20和%20等温%20压缩率%20of%20超临界%20H2O-NaCl%20流体:%20分子%20动力学%20研究%20从%20673%20到%202000%20K、%200.2%20到%202%20GPa、%20和%200%20到
作者：
H. Sakuma;M. Ichiki
我们报道了用分子动力学(MD)模拟来预测H2O-NaCl流体的密度和等温压缩系数随温度(673-2000℃)、压力(0.2-2.0 Gpa)和盐浓度(0.0-21.9wt%)的变化。通过离子的水化数和离子对的数目来分析原子化行为。Na+和Cl-−的水化数随压力的升高和温度的降低而增大。相反，钠氯离子对的比例随着压力的降低和温度的升高而增加。这种水化和缔合行为与H2O在这些条件下的低介电常数一致。在高温、低压和高盐浓度下，证实了Na-Cl多核团簇的存在。我们提出了高温高压下H2O-NaCl流体的纯经验状态方程(EOS)，该方程可用于估计地壳和上地幔中与地震和火山喷发有关的流体分布。
We report on molecular dynamics (MD) simulations for predicting the density and isothermal compressibility of an H2O–NaCl fluid as a function of temperature (673–2000 K), pressure (0.2–2.0 GPa), and salt concentration (0.0–21.9 wt%). The atomistic behavior was analyzed via the hydration number of ions and number of ion pairs. Hydration numbers of Na+and Cl−increased with increasing pressure and decreasing temperature. Conversely, the fraction of Na–Cl ion pairs increased with decreasing pressure and increasing temperature. This hydration and association behavior is consistent with the low dielectric constant of H2O under these conditions. The presence of polynuclear clusters of Na–Cl was confirmed at high temperatures, low pressures, and high salt concentrations. We propose a purely empirical equation of state (EoS) for H2O–NaCl fluids under high temperatures and pressures that should be useful for estimating the fluid distribution in Earth's crust and upper mantle in relation to effects on earthquakes and volcanic eruptions.