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Abstract

Methane and carbon dioxide hydrate crystals were formed on nearly spherical water droplets at 274.6 K and 2,150 kPa or 1,000 kPa above the corresponding three-phase hydrate equilibrium pressure. Each experiment was performed with two droplets 5 mm and 2.5 mm in diameter or three droplets with a diameter of 2.5 mm. At the higher pressure the water droplets quickly became jagged and exhibited many needlelike or hairlike crystals extruding from the droplet, whereas at the lower pressure the surface was smooth. In almost all experiments, a depression or collapse of the hydrate layer was observed to occur. This collapse was interpreted as evidence of a continuing hydrate formation after the droplet surface was covered by the hydrate layer. The type of hydrate-forming gas and the size of the droplet was observed not to influence the macroscopic hydrate crystal morphology. The decomposition of the methane and carbon dioxide hydrate layers was also observed. Reformation was also experimented, and the effect of memory on the morphology of hydrate crystal growth was determined.