Melting mechanisms of crystals

Melting Mechanisms of Crystals (Ubbelohde). Metal-Ammonia Systems, Structure and Properties of... 

An analysis of the mechanism of crystallization can best be carried out at a constant temperature. A sample is rapidly cooled down from the melt to a temperature below Tm and kept constant at that level. The crystallization process can then be studied by measuring the volume as a function of time in a dilatometer. The result is a curve as shown in Figure 4.9. The volume approaches to an equilibrium value at which the maximum possible crystallization is reached, and the rate of crystallization can, for example, be expressed as l/to.5, in which fo.5 is the time in which half of the route is... 

Structural studies in fused salts by means of careful and thorough high-temperature measurements of electrical conductivity, density, viscosity, and laser- Raman spectroscopy have been reviewed. Four problem areas are discussed (1) melting mechanisms of ionic compounds with large polyatomic cations, (2) salts as ultra-concentrated electrolyte solutions, (3) structural aspects and Raman spectroscopy, and (4) electrolysis of molten carbonates. The results in these areas are summarized and significant contributions to new experimental techniques for molten-salt studies are discussed.275 The physical properties and structure of molten salts have also been reviewed in terms of operational (hole, free volume, partly disordered crystal) and a priori (intermolecular potential) models.276 Electrochemistry... 

The cluster mechanisms of crystal nucleation and growth as well as crystal melting/dissolution are viewed. The nature of nanoparticles and the processes of nanostructured materials formation are discussed from the point of view of the cluster concept. 

The mechanisms of crystal phase formation are a key problem in materials science that has not clear comprehension still now. At present, the study of this problem is especially important in connection with the development of nanostructured materials. There are two different approaches to consideration of crystal nucleation/growth as well as crystal melting/dissolution processes [1,2], In accordance with the first approach based on the atomic-molecular theory, the individual atoms or molecules take the leading part in these processes (the role of clusters is ignored). In accordance with the second approach based on the cluster theory, these processes are carried out mainly by means of clusters. Till recently the atomic-molecular theory was generally accepted. However, today many scientific data vote for the cluster theory. The aim of this paper is to analyze the main statements of the cluster conception of crystal phase formation and as a result to consider the nature of nanocrystal. 

Considerations about mechanisms of crystallization and melting in polymers require as some basic ingredients... 

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