Nikolaev Institute of Inorganic Chemistry SB RAS, Akad. Lavrentiev ave., 3, Novosibirsk, 630090, Russian Federation.
Chemphyschem. 2011 Sep 12;12(13):2476-84. doi: 10.1002/cphc.201100126. Epub 2011 Jun 29.
Experimental data on the pressure dependence of unit cell parameters for the gas hydrates of ethane (cubic structure I, pressure range 0-2 GPa), xenon (cubic structure I, pressure range 0-1.5 GPa) and the double hydrate of tetrahydrofuran+xenon (cubic structure II, pressure range 0-3 GPa) are presented. Approximation of the data using the cubic Birch-Murnaghan equation, P=1.5B(0)[(V(0)/V)(7/3)-(V(0)/V)(5/3)], gave the following results: for ethane hydrate V(0)=1781 Å(3) , B(0)=11.2 GPa; for xenon hydrate V(0)=1726 Å(3) , B(0)=9.3 GPa; for the double hydrate of tetrahydrofuran+xenon V(0)=5323 Å(3) , B(0)=8.8 GPa. In the last case, the approximation was performed within the pressure range 0-1.5 GPa; it is impossible to describe the results within a broader pressure range using the cubic Birch-Murnaghan equation. At the maximum pressure of the existence of the double hydrate of tetrahydrofuran+xenon (3.1 GPa), the unit cell volume was 86% of the unit cell volume at zero pressure. Analysis of the experimental data obtained by us and data available from the literature showed that 1) the bulk modulus of gas hydrates with classical polyhedral structures, in most cases, are close to each other and 2) the bulk modulus is mainly determined by the elasticity of the hydrogen-bonded water framework. Variable filling of the cavities with guest molecules also has a substantial effect on the bulk modulus. On the basis of the obtained results, we concluded that the bulk modulus of gas hydrates with classical polyhedral structures and existing at pressures up to 1.5 GPa was equal to (9±2) GPa. In cases when data on the equations of state for the hydrates were unavailable, the indicated values may be recommended as the most probable ones.
实验数据表明，乙烷（立方结构 I，压力范围 0-2 GPa）、氙（立方结构 I，压力范围 0-1.5 GPa）和四氢呋喃+氙的双水合物（立方结构 II，压力范围 0-3 GPa）的晶胞参数对压力的依赖性。使用立方 Birch-Murnaghan 方程 P=1.5B(0)[(V(0)/V)(7/3)-(V(0)/V)(5/3)] 对数据进行拟合，得到以下结果：对于乙烷水合物，V(0)=1781 Å(3)，B(0)=11.2 GPa；对于氙水合物，V(0)=1726 Å(3)，B(0)=9.3 GPa；对于四氢呋喃+氙的双水合物，V(0)=5323 Å(3)，B(0)=8.8 GPa。在后一种情况下，逼近是在 0-1.5 GPa 的压力范围内进行的；使用立方 Birch-Murnaghan 方程不可能在更宽的压力范围内描述结果。在四氢呋喃+氙双水合物存在的最大压力（3.1 GPa）下，晶胞体积为零压下晶胞体积的 86%。对我们获得的实验数据和文献中可用数据的分析表明，1）具有经典多面体结构的气体水合物的体积弹性模量在大多数情况下彼此接近，2）体积弹性模量主要由氢键水框架的弹性决定。客体分子对空穴的可变填充对体积弹性模量也有很大影响。基于获得的结果，我们得出结论，具有经典多面体结构且在 1.5 GPa 以下压力下存在的气体水合物的体积弹性模量等于（9±2）GPa。在无法获得水合物状态方程数据的情况下，建议使用这些值作为最可能的值。
