高温高压下NaCl-CaCl2-H2O体系Raman光谱的定量研究

三元体系NaCl-CaCl₂-H₂O是一种重要的天然水-盐体系。然而，研究人员在过去只研究了低温下该体系的相变，但在高温高压条件下拉曼位移和物理参数之间的定量关系却并没有被报道。利用利用热液金刚石压腔(HDAC)和石英压标，对高温高压下三元体系NaCl-CaCl₂-H₂O的拉曼光谱特征进行了系统的研究，并获得了水的O—H伸缩振动谱带的拉曼位移、溶质质量分数和压力之间的定量关系。其中盐的质量分数相等(NaCl与CaCl₂)，分别为4.0 mass％，8.0 mass％和12.0 mass％。实验结果表明，当盐的质量分数和体系的压力保持不变时，O—H伸缩振动的标准拉曼位移差(Δν_(O—H))伴随着温度的升高而增大。当温度和压力恒定时，Δν_(O—H)随盐的质量分数的增加而增大。对于这个三元体系，其Δν_(O—H)与压力近似为线性关系，且不同盐度条件下的关系斜率相近。Δν_(O—H)与温度(T)、压力(P)、溶质质量分数(M)之间的定量关系为P＝-31.892Δν_(O—H)+10.131T+222.816M-3 183.567，其中该方程的有效PTM范围为200 MPa≤P≤1 700 MPa, 273 K≤T≤539 K 以及M≤12 mass%。该公式可以用来作为地质压力计，用于研究等盐度条件下在NaCl-CaCl₂-H₂O体系流体包裹体。该方法作为一种直观的地质探测技术，具有潜在的应用价值。

Raman Spectroscopic Quantitative Study of NaCl-CaCl2-H2O System at High Temperatures and Pressures

Raman spectra features of the ternary system NaCl-CaCl₂-H₂O under high temperatures and high pressures were systematically studied in the present work by using hydrothermal diamond anvil cell (HDAC) and Raman shifts of quartz to determine pressures, and it has been obtained for the quantitative relationship between Raman shifts of the O—H stretching band of water, mass fractions of solutes and pressures was obtained. The mass fractions of salts, where salinity of NaCl equal to that of CaCl₂, are 4.0 mass%, 8.0 mass%, and 12.0 mass%, respectively. Experimental results indicate that the standardized Raman frequency shift differences of the O—H stretching vibration (Δν_(O—H)) rise with the increasing temperatures when the mass fractions of salts and pressures of the NaCl-CaCl₂-H₂O system remain constant. Δν_(O—H) increases with the increase in mass fractions of salts in the system when the temperatures and pressures are constant. Linear relationship between Δν_(O—H) and pressure with similar slopes can be found for the NaCl-CaCl₂-H₂O system with different salinities. The quantitative relationship between Δν_(O—H), temperature (T), pressure (P), and mass fraction of solute (M) is P＝-31.892Δν_(O—H)+10.131T+222.816M-3 183.567, where the valid PTM range of the equation is 200 MPa≤P≤1 700 MPa, 273 K≤T≤539 K and M≤12 mass%. The equation can be used as a geobarometer in the studies of fluid inclusions of NaCl-CaCl₂-H₂O system with equal salinities. The method, as a direct geological detecting technique, has a potential application value.