Investigation on the effect of growth temperature and contact interface on surface characteristics of THF clathrate hydrates by atomic force microscopy

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A sound knowledge of surface topography and property of natural gas hydrates is of great importance to understand the interaction between hydrate and hydrate particles, or hydrate particles with other media such as steels in petroleum pipelines and minerals in natural settings. However, a solid and effective approach to investigation on the surface topography and property of clathrate hydrates remains a longstanding challenge. Here, we firstly report the characterization of THF clathrate hydrates using atomic force microscopy (AFM). These hydrate samples grew from the THF solution liquid drop in air or confined at the liquid-solid interfaces at the temperature range from –5°C to –30°C. The results show that for THF clathrate hydrates grown at gas-liquid interface, the lower growth temperature, the smaller hydrate crystalline grains. At the same time, the shapes of these THF hydrate crystalline grains change from polygonal to amorphous. The cross section of grain boundary is “V” shape, and its width and depth decrease with the decrease of the growth temperature.The avulsed surface morphology and roughness of THF clathrate hydrate grown at the solid-liquid interface, are not only affected by the growth temperature, but also related to the solid medium. At a relatively high growth temperature, the crystalline grains are bigger, and the grain boundary can be observed. However, when the temperature is low, there are micropores on the hydrate surface and the roughness is larger. And no grain boundary can be observed. The findings have an important significance for explaining the mechanical behaviors of hydrate deposits.