Geoscience Reference
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of crystal count and the modal value of crystal dimension with seeding
temperaturehavehighdegreeofconsistency. As already stated, the seeding
temperature is varied from
22.0
◦
Cto0
◦
C. Both, the crystal count and
the modal value of dimension have a sharp peak at
−
21
◦
C, which is also
the eutectic temperature of DMSO and water bivariate system. As Gibb's
free energy becomes minimum at the eutectic point,
27
there is a common
tendency for freezing at that temperature. The count as well as the modal
dimension show a sharp rise as the temperature is raised from
−
22
◦
Cto
−
21
◦
C. On the other hand, as the seeding temperature is raised above
−
21
◦
C, both the crystal count and the modal dimension show a gradual fall.
However, after a sharp fall in crystal count up to
−
19
◦
C, the fall becomes
−
14
◦
C, there occurs a small peak in
the crystal count, and at 0.5
◦
C, both these quantities show insignificant
values. From the nature of the curve, one can conclude that DMSO nuclei
have no nucleation above 0
◦
C.
On the other hand, in the case of mode of crystal dimension, a sharp
fall in value occurs as the temperature rises from
more gradual. Except that, close to
−
21
◦
Cto
18
◦
C. There
−
−
17
◦
Candcloseto
14
◦
C.
are two small peaks in the modal value at
−
−
4.2
. Variation of crystal habit with seeding
temperature in case of DMSO
The overall variation of crystal habit with a change of seeding temperature
is presented in Table 1. The observation is consistent with the fact that
the principal factor governing the basic habit of ice crystal structure is
temperature.
28
Rogers and You
29
have also concluded that the basic habits
Table 1.
Crystal habits when DMSO is seeded.
Temperature
Crystal habit
−
22
◦
Cto
−
17
◦
C
Dominantly dendrite (Photo 1), some are hexagonal and cubic
[Dendrite (80.54%): 9.12-45.56
µ
m; Hexagonal (10.16%):
4.25-25.12
µ
m; Cubic (9.3%): 5.13-11.24
µ
m]
17
◦
Cto
15
◦
C
−
−
Mostly cubic (Photo 2), some are hexagonal [Cubic (85.35%):
4.55-40.14
m; Hexagonal (14.65%): 25.2-45.5
m]
µ
µ
15
◦
Cto
7
◦
C
−
−
Mostly hexagonal (Photo 3), some are cubic or prism like
[Hexagonal (88.12%): 25.32-50
m; Cubic or prism (11.88%):
µ
10.25-45.32
µ
m]
−
7
◦
Cto
−
0.5
◦
C
Almost all crystals are cubic or rod (Photo 4): (1.24-11.32
µ
m)
