Supercooling and nucleation

ice would begin to form. This would release the latent heat, so that the temperature would then remain constant, until all the water had turned into ice. In fact, the temperature continues to fall below 0 °C, without the formation of ice, in this case to about —2°C. This phenomenon is called supercooling. At about 20 min, the temperature rises sharply, reaching 0 °C, where it again forms a plateau, before cooling again. 

To understand why supercooling occurs, we need to look at what is taking place at a molecular level. When ice crystals melt, the 

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Orlowska et al. (2009) studied the effect of high-voltage electrostatic fields on ice nucleation, their aim being to control the supercooling and nucleation rates, and this in turn would result in the preservation of the microstructure of a frozen tissue. An electrostatic field with a strength of up to 60kVcm was used for this... 

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... 

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 ... 

There are aspects of cell membranes other than their permeability to water and solutes that also play a critical role in the responses of cells to freezing. The structure of the plasma membrane allows cells to supercool and probably determines their ice-nucleation temperature. The nucleation temperature along with the permeability of membranes to water are the chief determinants of whether cells cooled at... 

When the crucible is full, gradually lower the melt temperature to aehieve supercooling and incipient nucleation. 

Turnbull and Cech [58] analyzed the solidification of small metal droplets in sizes ranging from 10 to 300 xm and concluded that in a wide selection of metals the minimum isothermal crystallization temperature was only a function of supercooling and not of droplet size. Later, it was found that the frequency of droplet nucleation was indeed a function of not only crystallization temperature but also of droplet size, since the probability of nucleation increases with the dimension of the droplet [76]. However, for low molecular weight substances the size dependence of the homogeneous nucleation temperature is very weak [77-80]. 

In order to achieve some understanding of the nucleation of hydrate crystals from supercooled water + gas systems, it is useful to briefly review the key properties of supercooled water (Section 3.1.1.1), hydrocarbon solubility in water (Section 3.1.1.2), and basic nucleation theory of ice, which can be applied to hydrates (since hydrate nucleation kinetics may be considered analogous, to some extent, to that of ice Section 3.1.1.3). The three subsections of 3.1.1 (i.e., supercooled water, solubility of gas in water, and nucleation) are integral parts of conceptual pictures of nucleation detailed in Section 3.1.2. 

Figure 30. Freezing behavior of an emulsion characterized by differential scanning calorimetry. The free water will freeze at approximately 273 K. Emulsified water will supercool and freeze at lower temperatures, depending upon size distribution. The smallest droplets freeze last because of the smaller volume, and so fewer nucleation sites are available for ice crystal formation and water freezing. The different freezing behavior of free versus emulsified water gives this technique the potential to quantify the relative proportions of these two types of water. (Reproduced with permission from reference 114.

Then, viscosity, supercooling, and cooling rate evidently determine the process of nucleation (i.e., ti). However, their effect on the free energy for TAG nucleation has not been evaluated. In the same way, the interaction among such... 

Fig. 5 gives temperature dependences of the stationary nucleation rate for supercooled and heavy water under crystallization of amorphous layers (dots on the low-temperature branch of the dome of J T)). 

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