Degree of crystallization

The normal boiling point of 2-methylthiazole is 17 0= 128.488 0.005°C. The purity of various thiazoles was determined cryometrically by Handley et al. (292), who measured the precise melting point of thiazole and its monomethyl derivatives. Meyer et al. (293, 294) extended this study and, from the experimental diagrams of crystallization (temperature/degree of crystallization), obtained the true temperatures of crystallization and molar enthalpies of fusion of ideally pure thiazoles (Table 1-43). 

The high degree of crystallization and the thermal stability of the bond between the benzene ring and sulfur are the two properties responsible for the polymer s high melting point, thermal stability, inherent flame retardance, and good chemical resistance. There are no known solvents of poIy(phenyIene sulfide) that can function below 205°C. 

Clay particles are so finely divided that clay properties are often controlled by the surface properties of the minerals rather than by bulk chemical composition. Particle size, size distribution, and shape the nature and amount of both mineral and organic impurities soluble materials, nature, and amount of exchangeable ions and degree of crystal perfection are all known to affect the properties of clays profoundly. 

Increase in the 1,2- and m-1,4-additions in the polychloroprene, reducing the degree of crystallization, and faster curing is necessary. 

A final point needs to be made. Theory has indicated that AB cements should be amorphous. However, a degree of crystallization does sometimes occur, its extent varying from cement to cement, and this often misled early workers in the field who used X-ray diffraction as a principal method of study. Although this technique readily identifies crystalline phases, it cannot by its nature detect amorphous material, which may form the bulk of the matrix. Thus, in early work too much emphasis was given to crystalline structures and too little to amorphous ones. As we shall see, the formation of crystalUtes, far from being evidence of cement formation, is often the reverse, complete crystallinity being associated with a non-cementitious product of an acid-base reaction. 

Tre Temp. (°c0 atment Time (min) Degree of Crystal. (56) Dimension of Crystallites (X) Amorphous Volume.Assoc. (a )... 

The equilibrium degree of crystallization, (0, can be determined from the condition 3AFc/3u) 0, or... 

One approach is to roughly estimate how the degree of crystallization would vary with time by making main simplifications in treating solidification, leading to the Avrami equation. 

The above discussion is for the crystallization of one single mineral (i.e., many crystals of the same mineral). If several minerals are crystallizing and they have different crystallization temperature (and hence different crystallization time), then the relation between the degree of crystallization and time would be much more complicated. 

Figure 4-13 Degree of crystallization based on the Avrami equation.

The majority of PEC studies have been carried out on either CdS or CdSe films, although many other CD semiconductors have been demonstrated to exhibit PEC activity. In most, though not all, cases, these films were annealed for optimum PEC response. Eilrns annealed at temperatures above ca. 300°C usually exhibit a large degree of crystal growth, and therefore such films will be discussed separately from as-deposited films, which, in most cases, are composed of crystals <20 nm in size. 

Semicrystalline polymer A material consisting of a combination of crystalline and amorphous regions. Essentially, all common plastics and elastomers with the tendency to crystallize are semicrystalline. The degree of crystallization depends on the structure of the polymer and the conditions of fabrication. 

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