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

Nondestructive observation of anomalously preserved methane (CH4) 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 CH4 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 CH4 hydrate retained a high CH4 gas storage capacity even after one month under thermodynamically unstable conditions.