The pressure dependence of the elastic properties of sII-type Ar hydrate has been determined up to 0.70 GPa at room temperature by using a high-pressure Brillouin scattering method. At about 0.10 GPa, ratios of the elastic constants to the density of C 11 /ρ = 10.16, C 12 /ρ = 6.30, C 44 /ρ = 2.32 × 10 6 m 2 s −2 are obtained. Comparing with sI-type CH 4 hydrate, the acoustic velocities for the longitudinal acoustic and transverse acoustic modes of Ar hydrate (sII) were found to be about 15 and 25% lower, respectively.
Acoustic velocities and adiabatic elastic constants of structure I of methane hydrate (MH) have been determined as a function of pressure up to 0.6 GPa at 23 • C by the high-pressure Brillouin spectroscopy developed for a single molecular crystal. The pressure dependence of the acoustic velocities of MH is very similar to that of ice-Ih except for the longitudinal acoustic (LA) velocity. The value of the LA velocity along the 100 direction of MH at 0.02 GPa is 3.63 km s −1 which is about 7% lower than the average of the LA velocities in the ice-Ih phase at −35.5 • C and atmospheric pressure.
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