Supercooled liquid solidification

The main purpose of this section is to give an account of general peculiarities of the microscopic scenarios of the supercooled liquid solidification and to show that formation of the polycluster glasses is a commonplace case. A more detailed consideration of the supercooled liquid structure, its thermodynamics and solidification kinetics is given in Sect. 6.10. 

We see that to ascertain the scenario of supercooled liquid solidification and glass formation, it is necessary to calculate Af/ (/V) and AC/ fiV) with comparatively small number of atoms in nuclei N when the relative fraction of boundary atoms and their contribution to the free energy arc essential.2... 

Stein and Palmer [6.92] have discussed the scenario of supercooled liquid solidification, which is based on the assumption that the line of metastable... 

Consider now the solidification of a pure liquid that has been supercooled below its melting point without nucleation of the solid, as in Fig. 20.11. If the solid is nucleated by a seed at the center of the container, the solid will grow as the latent heat is conducted to the supercooled liquid and eventually out to the container walls. 

Figure 20.11 (a) Solidification of body in a supercooled liquid by removing the latent... 

SUPERCOOLING. The cooling of a liquid below its freezing point without the separation of the solid phase. This is a condition of metastable equilibrium, as is shown by solidification of the supercooled liquid upon the addition of the solid phase, or the application of certain stresses, or simply upon prolonged standing. 

Supercooled liquid One which has cooled below its freezing point without solidification. 

A supercooled liquid solidifies when inoculated with a small crystal of the solid, while the latent heat is evolved in the process. The solidification can be performed reversibly and made to yield work by evaporating the liquid at its vapour pressure allowing the vapour to expand isothermally until the pressure is equal to the vapour pressure of the solid, and then condensing to the solid state. 

Justify the statement that the solidification of a supercooled liquid is accompanied by a decrease in the entropy of the liquid but a greater increase in the entropy of the surroundings. Suggest how the change from supercooled water at... 

From the beginning of the 1930s, studies on a melt treatment by elastic oscillations were carried out in three main directions (1) the study of an effect of elastic oscillations of various frequencies with the aim to establish a mechanism of nucleation and growth of solidification nuclei in supercooled liquids, i.e. melts and solutions (2) the study of structure and properties of metals and alloys subjected to low-frequency vibration and (3) the study of an ultrasonic oscillation effect on molten metals. Significant research in this area was performed in the 1950s by Danilov, Kapustin, Polotskii, Sirota, and their associates on solidification of organic substances and a number of metals in ultrasonic field. 

This section presents the theory of liquid solidification, in which both crystalline and noncrystalline heterophase fluctuations in supercooled liquids are taken into account [6.76]. A general discussion of this problem is presented in Sect. 6.2... 

Our main aim was to clarify the role of clusters in the process of liquid solidification and to show that formation of the polycluster glass structure is a typical result of this process. On the basis of the developed approach, such important problems as entropy crisis and relaxation phenomena in supercooled liquids can be considered in detail, but this is far from the topic of this paper and will be considered elsewhere. 

Suspended Transformation.— Just as suspended transformation is rarely met with in the passage from the solid to the liquid state, so also it is found that in the case of the melting of substances under the solvent suspended fusion does not occur, but that when the temperature of the invariant point is reached at which, therefore, the formation of two liquid layers is possible, these two liquid layers, as a matter of fact, make their appearance. Suspended transformation can, however, take place from the side of the liquid phase, just as water or other liquid can be cooled below the normal freezing-point without solidification occurring. The question, therefore, arises as to the position of the equilibrium curve for the metastable, supercooled liquid phase. 

In the above equations Ap(7) = p(7) -p (7) < 0 represents the difference between the chemical potentials of the solid, p, and liquid, p, phases, i.e., the change in chemical potential that occurs due to solidification of a metastable (supercooled) liquid, and which characterizes supersaturation in the system is the specific (per mole of substance) heat of melting, which is assumed to be constant. The integration of eq. (IV. 17) over the range... 

Freezing or congealing point is the highest temperature observed during the solidification of a supercooled liquid. 

D. Turnbull, Kinetics of solidification of Supercooled Liquid-Mercury Droplets, /. Ghem. Phys. 20 411-24 (1952). 

Figure 9.2. Constitutional supercooling in alloy solidification (a) phase diagram (b) solute-enriched layer ahead of the solid/liquid interface (c) condition for a stable interface (d) condition...

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