Nondestructive Imaging of Anomalously Preserved Methane Clathrate Hydrate by Phase Contrast X-ray Imaging

Nondestructive observation of anomalously preserved methane (CH 4 ) hydrate stored outside its thermodynamically stable zone below the melting point of ice was performed at 193 K. By use of two different types of phase contrast X-ray imaging techniques, X-ray interferometric imaging and diffraction enhanced imaging, it was shown that CH 4 hydrate stored under anomalous preservation conditions was completely enveloped and stabilized by a thin layer of ice. The thickness of the ice layer was inhomogeneous, with an average thickness of about 100 μm after storage for 24 h at 253 K. These results obtained were consistent with quantitative analysis by means of powder X-ray diffraction and Raman spectroscopy. It was revealed that the interior of CH 4 hydrate retained a high CH 4 gas storage capacity even after one month under thermodynamically unstable conditions.