| Budget Amount *help |
¥3,600,000 (Direct Cost: ¥3,600,000)
Fiscal Year 2003: ¥1,400,000 (Direct Cost: ¥1,400,000)
Fiscal Year 2002: ¥2,200,000 (Direct Cost: ¥2,200,000)
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| Research Abstract |
The purpose of this research is to determine the pressure dependences of elastic properties of single crystalline gas clathrate hydrates with structure II, and to clarify the mechanical stability and the host water-guest gas interaction. The results are as follows: We grew the single crystals of nitrogen hydrate, argon hydrate, krypton hydrate, and THF hydrate by using a new helium gas driven diamond anvil cell, and investigated their pressure-induced phase transformations by the visual observation through the microscope and the high-pressure Raman spectroscopy. From these results, it is found that the gas hydrates with cubic structure II are eventually transformed to the cage-less "filled ice" by way of structure H, and the pressure regions of cubic structure II for nitrogen hydrate, argon hydrate, and krypton hydrate are 0.1-0.85 GPa, 0.2-0.43 GPa, and 0.01-0.45 GPa., respectively. Moreover, we applied the high-pressure Brillouin analysis to the single crystals of argon hydrate and krypton hydrate in cubic structure II phase in order to determine their pressure dependences of elastic properties. From this analysis, we found that the elastic properties of the structure II gas hydrates are almost elastically isotropic and are similar to that of the cubic structure I methane hydrate. However, the elastic constants, the pressure dependences, and the pressure regions of structure II gas hydrates are dependent on the size of guest molecules (atoms). Therefore, the host water-guest gas interaction and the mechanical stability have relation to the size of guest molecule relative to that of host water cage.
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