Supercooling nucleation

Keywords metastable state, water, heavy water, superheating, supercooling, nucleation rate, explosive boiling up, density, sound velocity... 

Sirota EB. 1998. Supercooling, nucleation, rotator phases, and surface crystallization of n-Alkane melts. Langmuir 14 3133-3136. 

An interesting point is that AH itself varies with r [10].] As is the case when P is varied, the rate of nucleation increases so strongly with the degree of supercooling that a fairly sharp critical value exists for T. Analogous equations can be written for the supercooling of a melt, where the heat of fusion AH/ replaces AH . 

Classic nucleation theory must be modified for nucleation near a critical point. Observed supercooling and superheating far exceeds that predicted by conventional theory and McGraw and Reiss [36] pointed out that if a usually neglected excluded volume term is retained the free energy of the critical nucleus increases considerably. As noted by Derjaguin [37], a similar problem occurs in the theory of cavitation. In binary systems the composition of the nuclei will differ from that of the bulk... 

Bartell and co-workers have made significant progress by combining electron diffraction studies from beams of molecular clusters with molecular dynamics simulations [14, 51, 52]. Due to their small volumes, deep supercoolings can be attained in cluster beams however, the temperature is not easily controlled. The rapid nucleation that ensues can produce new phases not observed in the bulk [14]. Despite the concern about the appropriateness of the classic model for small clusters, its application appears to be valid in several cases [51]. 

The greater the undercooling, the more rapidly the polymer crystallizes. This is due to the increased probability of nucleation the more supercooled the liquid becomes. Although the data in Fig. 4.8 are not extensive enough to show it, this trend does not continue without limit. As the crystallization temperature is lowered still further, the rate passes through a maximum and then drops off as Tg is approached. This eventual decrease in rate is due to decreasing chain mobility which offsets the nucleation effect. 

Crystallization. Acidified aluminum sulfate solutions can be supercooled 10 °C or more below the saturation point. However, once nucleation begins, the crystallization rate is rapid and the supersaturated solution sets up. The onset of nucleation in a gentiy stirred supersaturated solution is marked by the appearance of silky, curling streamers of microscopic nuclei resulting from orientation effects of hydraulic currents on the thin, platelike crystals. Without agitation, nucleation in an acidified solution, in glass tubes, can yield extended crystalline membranes of such thinness to exhibit colors resulting from optical interference. 

Barium bromide is very soluble in methanol, yet almost insoluble in ethanol. Repotted uses of barium bromide include fabrication of phosphors, for example from Bap2, BaBi2 2H O and EuBy (6) as a crystallization nucleating agent to control supercooling of CaBi2 solutions (7) and in the production... 

A natural mechanism for the local reduction of cell spacings (or creation of a new cell) is either a nucleation in one of the grooves (the liquid is supercooled) or, even more likely, the formation of a new cell out of a side branch in such a groove. Alternatively, tip-splitting of a cell may give the same result [121]. 

In the primary nucleation stage of crystallization at small supercoolings and high pressures, the growth rate G and net transition rate J can be correlated by the following relation ... 

In contrast, there is no nucleation barrier for rough surface growth at any supercooling. The growth rate is then simply proportional to v as given by Eq. (3.4), and hence is expected to be linear in AT for small undercoolings. 

Fig. 3.3. Growth rate versus supercooling for two different face orientations. T is above its roughening temperature and is approximately linear. 2 is below its roughening temperature and is nucleation controlled at low supercooling but the growth rapidly increases after kinetic roughening...

---