Crystallization temperature effects

Valov P M and Leiman V I 1997 Size effects in the melting and crystallization temperatures of copper chloride nanocrystals in glass JETP Lett. 66 510... 

The greater the undercooling, the more rapidly the polymer crystallizes. This is due to the increased probability of nucleation the more supercooled the liquid becomes. Although the data in Fig. 4.8 are not extensive enough to show it, this trend does not continue without limit. As the crystallization temperature is lowered still further, the rate passes through a maximum and then drops off as Tg is approached. This eventual decrease in rate is due to decreasing chain mobility which offsets the nucleation effect. 

To erase information by the transition amorphous — crystalline, the amorphous phase of the selected area must be crystallized by annealing. This is effected by illumination with a low power laser beam (6—15 mW, compared to 15—50 mW for writing/melting), thus crystallizing the area. This crystallization temperature is above the glass-transition point, but below the melting point of the material concerned (Eig. 15, Erase). 

The following is taken from U.S. Patent 3,061,517. Sixteen grams of racemic 3-(2-pYridyl)-3-p-bromophenyl-N,N,-dimethylpropylamine and 9,7 grams of d-phenylsuccinic acid are dissolved in 150 ml of absolute alcohol and kept at room temperature until crystallization is effected. The crystals are filtered, washed with absolute ethyl alcohol, and recrystallized from the same solvent using 5 ml thereof per gram of solid. Three subsequent crystallizations from 80% alcohol give d-3-(2-pYridYl)-3-p-bromophenYl-N,N-dimethylpropYlamine-d-phenylsuccinate MP 152°-154°C 91 (concentration, 1% in dimethylformamide). 

Twenty grams of d-phenylsuccinic acid and 28 grams of 3-(2-pyridyl)-3-p-chlorophenyl-N,N-dimethylpropylamine are dissolved in 400 ml of absolute ethyl alcohol and allowed to stand at room temperature until crystallization is effected. The crystals are filtered, washed with absolute ethyl alcohol and recrystallized from 300 ml of this solvent in the same manner. The crystals are recrystallized twice from 80% ethyl alcohol using 3.5 ml per gram of compound in the manner described above and pure d-3-(2-pyridyl)-3-p-chlorophenyl-N,N-dimethylpropylamine-d-phenylsuccinate is obtained, melting point 145°-147°C. 

Balabanov et al. [499] found an endothermic effect in the thermographic pattern of the decomposition of niobium hydroxide at 435°C that corresponds to complete removal of water. At the above temperature, amorphous niobium hydroxide also converts into amorphous niobium oxide. Ciystallization of the amorphous oxide occurs at a higher temperature with the release of energy [28]. Researchers [499] reported on another exothermal effect at 549°C that was attributed to the crystallization temperature of amorphous niobium oxide. Decomposition of tantalum hydroxide and its conversion into crystalline tantalum oxide occurs at about 710°C [502] or at 670-700°C according to another source [132]. 

As seen in Fig. 8 the experimentally determined magnetic moments at room temperature are in general much lower than the free ion values. To extract the contribution of orbital reduction, the influence of intermediate coupling, crystal field effects and j-j mixing must be considered. 

Theoretical analyses (75-77) of the matrix-induced changes in the optical spectra of isolated, noble-metal atoms have also been made. The spectra were studied in Ar, Kr, and Xe, and showed a pronounced, reversible-energy shift of the peaks with temperature. The authors discussed the matrix influence in terms of level shift-differences, as well as spin-orbit coupling and crystal-field effects. They concluded that an increase in the matrix temperature enhances the electronic perturbation of the entrapped atom, in contrast to earlier prejudices that the temperature dilation of the surrounding cage moves the properties of the atomic guest towards those of the free atom. 

In the latter type, the direction of the unique axis (b-axis) of the polymer coincides with that of the monomer while the directions of the other two axes do not. In the case of 3 OMe none of the directions of the axes of the polymer coincide with those of the monomer. However, the temperature effect on the reaction behaviour (see Section 3) and the continuous change of the X-ray diffraction pattern indicate a typical diffusionless crystal-lattice controlled mechanism (Hasegawa et al., 1981). 

We can nucleate crystallization from the melt by incorporating finely ground inorganic crystalline compounds such as silica. Nucleation of injection molded nylons has three primary effects it raises the crystallization temperature, increases the crystallization rate, and reduces the average spherulite size. The net effect on morphology is increased crystallinity. This translates into improved abrasion resistance and hardness, at the expense of lower impact resistance and reduced elongation at break,... 

Birefringence measurements have been shown to be very sensitive to bimodality, and have therefore also been used to characterize non-Gaussian effects resulting from it in PDMS bimodal elastomers [5,123]. The freezing points of solvents absorbed into bimodal networks are also of interest since solvent molecules constrained to small volumes form only relatively small crystallites upon crystallization, and therefore exhibit lower crystallization temperatures [124—126]. Some differential scanning calorimetry (DSC) measurements on... 

The initial melt of Ciooo was cooled down to various crystallization temperatures. Typical developments of crystalline domains at 370 K are shown in Fig. 37 here again the lamellae with the marked tapered shape are observed. Quite surprising is that the crystallization of Ciooo is rather fast in spite of the much longer chains. Any growth of lamellae of Ciooo at the temperature of 370 K, where Cioo did not show any appreciable growth, will be an indication of the molecular weight effect. 

For covalent crystals temperature has little effect on hardness (except for the relatively small effect of decreasing the elastic shear stiffness) until the Debye temperature is reached (Gilman, 1995). Then the hardness begins to decrease exponentially (Figure 5.14). Since the Debye temperature is related to the shear stiffness (Ledbetter, 1982) this softening temperature is proportional to C44 (Feltham and Banerjee, 1992). 

Precursor Structure Effects. The precursor structure can impact a broad range of properties, including crystallization temperature, the formation of intermediate phases during thermal treatment and film density, among other properties. Table 2.4 reports some of the key precursor properties that may affect densification and crystallization behavior, as well as the final film microstructure. 

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