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Samples must be representative and specimen preparation must introduce as few changes as possible if microscopic information is to be significant in characterization and classification of soils and rocks and in interpretation of their engineering behavior. Soils and recent sediments are damaged most easily, and specimen preparation is most complex for these materials. Air drying may cause shrinkage and distortion; freeze drying and drying by the critical point method provide partial solutions. Even so, differences in the procedure followed in the removal or replacement of water can cause marked differences in appearance of specimens examined on the electron and optical microscopes. Sectioning and surface exposure may also introduce artifacts. Soil specimens for fabric study commonly are fractured when frozen, since cutting may not be used generally. The use of ion bombardment in metal coating and as an etch method is discussed, and the possibility of improving specimen preparation procedures by combining an etch technique with freeze drying is outlined.
soils, rocks, microscopy, water replacement, freeze drying, ion beams ion bombardment
Professor, University of Calgary, Calgary, Alta.