Studies on single crystal growth of methane-ethane hydrate and its elastic properties

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The purposes of this research are to make single crystals of methane-ethane and methane-ethylene hydrates, and to determine the elastic properties and structural stabilities of these synthesized hydrates.We succeeded in growing single crystals of ethylene and methane-ethylene hydrates using a high-pressure diamond anvil cell. By applying the high-pressure Raman spectroscopy to the above single crystals, we have found that the structure I of ethylene and methane-ethylene hydrates exist up to 1.6 GPa and 1.7 GPa, respectively, which are higher than methane hydrate. Furthermore, the high-pressure Brillouin experiments for the single crystalline ethylene and methane-ethylene hydrates and their computational analysis yielded the elastic properties of the structure I of ethylene and methane-ethylene hydrates which are stiffer than those of methane hydrate. These results suggest that the occupation of host water cages by larger ethylene molecule increases the structural stability of methane-ethylene hydrates. The results of this research are also contributed to the estimation of elastic properties of various gas hydrates such as natural methane hydrate in the deep sea deposit.