a. The original snow (density 0.35 gm/cm2).
b. The same snow compressed to a density of 0.64
gm/cm2.
c. Further compressed to a density of 0.78 gm/cm2.
d. Final compaction to density of ice. (From Yosida
1963.)
Figure 16. Microstructure of snow at various stages of compaction.
pattern is shown in Figure 2. The sample was then
sintering or both) and uniform (so that large grains are
frozen onto a glass slide by warming the slide slightly.
not present to grow at the expense of smaller ones).
Samples were also taken from the natural snow ice
Hot pressing, which is the process used here, is often
collected from a pond and from clear S2 ice from Lake
used because it reduces defect size and grain growth
Superior. When the sample was securely frozen to the
over the standard method of forming the material under
glass, it was trimmed on the bandsaw to a thickness of
pressure followed by heating to complete the sintering
about 1 mm. It was then planed using sanding screen
(Moya et al. 1987).
and finally smoothed using a razor blade.
Table 1 shows the grain size distribution of the
The slides were then examined using a compound
undisturbed snow we used as well as the same snow
microscope, fitted with polarizing filters, with 3.5 and
after it had been stirred with a wire whisk. The size
10 objectives. Photographs were made of both
distribution does not differ greatly between these two,
horizontal sections and vertical sections. A 1-mm stage
with about 75% of the material showing a particle size
micrometer was also photographed at both mag-
greater than 0.84 mm. We examined thin sections of
nifications for later use in measuring crystal size.
representative samples of the CFG ice we made to
Crystal size was measured by the linear intersect
confirm that the crystal size distribution was uniform
method. Twenty measurements were taken on both
and to determine whether there were any obvious
horizontal and vertical transects of the photograph.
defects.
Results
Equipment and procedures
Microscopic examination of thin sections of our
Using a bandsaw, we cut a small slab of CFG ice
compacted material showed almost no crystal as large
about 7 mm thick from the crescents left after taking
samples for uniaxial compressive testing. The cutting
as 0.84 mm, and those that were appeared to be a
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