Abstract
Transmission electron microscopy (TEM) images of clathrate hydrates were obtained with their electron diffraction patterns. A tetrahydrofran (THF) hydrate sample was used as the specimen, which was prepared by quenching or slow crystal growth methods from THF aqueous solution. The sample temperature was maintained at approximately K under a high vacuum condition (10^-5Pa) because clathrate hydrates are unstable at low pressure and are too brittle to undergo electron irradiation. Crystallographic structure characterization procedures from one diffraction pattern were proposed because we were able to obtain only one diffraction pattern of clathrate hydrate for each real image, owing to its instability under TEM observation conditions and to limitations of the apparatus. The validity of the proposed procedures was confirmed by ice crystal observations. The real image indicated that THF hydrate samples were either thin film-like specimens or small granular ones (less than nm in diameter). Even if THF hydrate had the morphology of a thin film, the diffraction pattern had spots similar to those of a single crystal. Type-II cubic structures of THF hydrates were identified by the electron diffraction patterns. Although most of the sample was found to be hexagonal ice Ih crystals, THF hydrates existed approximately of the specimen.
