Structure of Ice, Solutions and Dispersions

10 shows log J J = nuclei per unit time and volume) as a function of the temperature of the water-ice phase transition at different pressures of 1 and 2100 bar according to Riehle. At 2100 bar, J is comparable to J at an approximately 35 °C higher temperature. Under pressure, water can be subcooled further, with a delayed formation of nuclei. 

The growth of crystals is determined by the diffusion of molecules to the surface of the nucleus, the finding of a proper place and the distribution of the freed energy to the surroundings. Under normal conditions (cooling speed vf 102 °C/s and subcooling Tsc 10 °C) Eq. (8) can be used  

Dowell and Rinfret [1.9] demonstrated that the phase at temperatures above -160 °C consists of small crystals 400 A in size and having cubic and pseudohexag-onal structures. 

To summarize, amorphous ice is stable below -160 °C, until -125 °C when cubic ice is formed irreversibly from the amorphous phase above this temperature, hexagonal ice develops. Between -160 and -130 °C, cubic ice can be embedded in an amor- 

The freezing process will be discussed with model substances, which will be used as cryo-protective agents (CPAs). If a solution of water and glycerol is cooled quickly, 

As can be seen from Fig. 1.11, the phase of Ih (hexagonal ice) has to be passed quickly to reach the zone of Ic (cubic ice). At or below -160 °C, Ic is glassy and unstructured. In pure water Ic can only be reach under high pressure. The addition of e. g. glycerol (10 %) and a freezing rate of 4 - 103 cm/s leads to vitrification of the solution. 

The freezing process will be discussed with model substances, which will be used as 

liquid water Fh, hexagonal ice Ft, cubic ice ill to IX, cry.stal configurations of ice fFig. 1. from 11-71) 

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