2002 Volume 118 Issue 3,4 Pages 223-228
It has been speculated that there are large oceanic methane hydrate deposits adjacent to Japan, and it is important to elucidate the mechanical and chemical properties of the hydrate to develop commercial technologies for identifications and extracting hydrate concentrations to utilize these resources. The occurrence of methane hydrate is controlled by severe conditions such as high pressure and low temperature and the decomposition processes of synthetic methane were observed microscopically hydrate under the conditions of a wide range of temperatures and atmospheric conditions. The results are summarized as follows:
(1) Microscopic observation of thin sections of synthetic methane hydrate is available using a sample sowed by microtome using a tungsten knife covered with a plastic plate. However, it is very difficult to reduce the hydrate to a thickness of about 0.02 mm, which is the common thickness for rock thin sections. Hydrate and ice are identified under crossed nicols based on the differences in crystal systems.
(2) Occurrence of the common decomposition in methane hydrate processes were observed at temperature increases of between 2 °C / min and 10 °C / min and in the temperature range of -100-0 °C. When methane hydrate was maintained at 5 °C or 10 °C on the surface of the thin section, it took about 10 or 100 minutes respectively for the hydrate to decompose into methane and ice. When the temperature of methane hydrate was increased at a high rates, a small amount of ice gradually formed until temperature reached 0 °C, and then a large amount of ice was shortly formed near 0 °C. When the rate of temperature increases was low, ice was formed slowly and at an even rate. We speculated that this phenomenon was related to self-preservation. Based on the results of this study, we found that for a long period of time is required to decompose methane hydrate into methane and ice or water.
