Assistant professor, Lehigh University, Bethlehem, PA
Graduate research assistant, Lehigh University, Bethlehem, PA
Pages: 14 Published: Jan 1999
Scanning electron microscopy (SEM) has been extensively used to examine individual and groups of clay platelets at high magnification. SEM and other optical and electron microscopy require that the pore fluid be removed, replaced, or frozen. To remove the pore water without disturbance of the original fabric is difficult. The environmental scanning electron microscope (ESEM) is a relatively new instrument that examines materials including liquids and oils in their natural state with no prior sample preparation. The environmental chamber can contain gas or vapor at a pressure as high as 50 Torr (0.066 atm). The gas in the environmental chamber operates as a cascade electron multiplier to enhance the secondary electron signal and to provide a source of positive ions, which neutralizes any negative charge, which in turn accumulate on the sample. The ability to manipulate temperature and pressure, and to add or remove fluids or gas in the ESEM greatly increases the range and diversity of experimental conditions. Accessory equipment for cooling, heating, and applying tension and compression makes it possible to image the effects of dynamic processes such as freezing, melting, desiccation, and consolidation on soil microstructure.
This paper describes the procedures for utilizing the ESEM and provides an example of its use to analyze soil fabric. In the first portion of the study, the ESEM was used to study the effects of freeze-thaw on the microstructure of fine-grained soils. Micrographs were obtained before and after laboratory freezing and thawing. The second phase showed the effect of hydration on a sand-bentonite mixture, and how the voids are affected
scanning electron microscope, environmental scanning electron microscope, fine grained soils, sand-bentonite
Paper ID: STP13307S