Abstract
Gas hydrates are known to have a slowed decomposition rate at ambient pressure and temperatures below the melting point of ice termed “self-preservation” or “anomalous preservation.” As hydrate exothermically decomposes, gas is released and water of the clathrate cages transforms into ice. Two regions of slowed decomposition for methane hydrate, 180 – 200 K and 230 – 260 K, were observed, and the kinetics were studied by in situ low temperature x-ray powder diffraction. The kinetic constants for ice formation from methane hydrate were determined by the Avrami model within each region and activation energies, Ea, were determined by the Arrhenius plot. Ea determined from the data for 180 – 200 K was 42 kJ/mol and for 230 – 260 K was 22 kJ/mol. The higher Ea in the colder temperature range was attributed to a difference in the microstructure of ice between the two regions.
