Electron Microscope Investigations of Frozen and Unfrozen Bentonite

摘要

Transmission and scanning electron micrographs of Umiat bentonite revealed thin, mica-like grains with irregular shapes. Most of the bentonite showed electron diffraction ring patterns, but some showed hexagonal net patterns as well as ring patterns. The lengths of the unit cells were calculated to be 5.18 A along the a-axis and 8.97 A along the b-axis. Semiquantitative analyses were made using an energy dispersive spectrometer. Common elements such as Si, Ti, Al, Fe, Mg, Na and K were determined. The molecular ratio of SiO2:Al2O3 was calculated to be 492:100 for the bulk sample, indicating that Umiat bentonite is similar in most respects to Wyoming bentonite, and is classified as a mont-morillonite. The microstructure of frozen Umiat bentonite was observed at a specimen temperature of -100 C using a scanning electron microscope equipped with a cold stage. Frozen bentonite and segregated ice patterns formed from wet bentonite were examined using an X-ray map and Si X-ray line scan. Sublimation processes of ice in the frozen bentonite were observed at specimen temperatures of -60 and -80 C. After sublimation of the ice the bentonite displayed a honeycomb structure. It was concluded that the freezing-sublimation cycle in frozen soil increases the permeability of water vapor due to the three-dimensional structure of the coagulated clay formed by freezing. (Author)