5:15 PM - 5:30 PM
[SMP42-12] Physical properties of methane hydrate under low temperature and high pressure
Keywords:Methane hydrate, Low temperature and high pressure, Guest orientational ordering, Volume change
High pressure and low temperature experiments were performed using clamp-type diamond anvil cells and a helium-refrigeration cryostat. The pressure and temperature conditions were 2.0 to 77.0 GPa and 30 to 300 K, respectively. As the initial materials light-water host sample and deuterated-water one were used.
In situ X-ray diffractometry and Raman spectroscopy revealed existence of three phases and the phase boundaries between them. The first phase is guest orientationaly disordered phase, i.e. well-known FIIhS, which exists below 20 GPa, the second one is guest orentaional ordering phase above 20 GPa, and the third one is another guest ordering phase with different ordering manner. The results demonstrate that phase changes of methane hydrate proceed via proceeding of guest orientational ordering. However, it seemed a quite peculiar that the slopes of phase boundary are negative. Another low temperature experiments performed revealed the volume expansion at low temperature below 150- 100 K. The expansion was confirmed not due to non-hydrostatic effect but to be intrinsic by annealing treatment. The peculiar phenomenon were examined considering to host proton ordering.