Recrystallization line

Fig. 23.13. (T/n )-phase diagram for polymer layers in a melt ( a ) dealing with three phases mesomorphic m , native crystalline cn and stabilized crystalline cs . Two pathways for an isothermal crystallization followed by heating, A (low crystallization temperatures) and B (high crystallization temperatures). The experimental crystallization line is identical with Tmc , the melting line is identical with Tacg, the recrystallization line is to be identified with Tmcs...

Fig. 23.15. sPP-Mitsui SAXS data from Fig. 23.9 represented on the basis of the multiphase scheme. In addition to the crystallization line (Tmc ) and the melting line (Tkco), the figure includes now the recrystallization line (Tmco), the a-<4-m transition line and the crossing points Xn and Xs [9]... 

It again includes (here 195 °C) as the limiting temperature, but has another slope than the crystallization line (Cr < Cc). The final melting, indicated by a star, occurs at that temperature where the recrystallization line intersects the melting line. 

Fig. 5.33. A general scheme treating crystallization, recrystalUzation and melting of s-polypropylene Common crystallization line, common recrystallization line, sample-dependent melting hne (here for the sample of Fig. 5.31)...

What is the physical background of the linear dependencies showing up in the T/djT -diagram of Fig. 5.33, i.e., the meaning of the crystallization and the recrystallization lines First of all, the difference between the crystallization and the melting lines demonstrates that different laws control crystallization and melting in bulk polymers. Here, crystallization and melting are not reverse... 

Tmcs with the recrystallization line, i.e., Eq. (5.19) with the theoretical... 

Application of the scheme to experimental results, as given by the crystallization, melting and recrystallization lines of a system, the zero growth temperature as well as measured heats of fusion, yields the thermodynamic parameters included in the equilibrium relationships. Figure 5.42 shows once... 

Fig. 5.42. PeCL Crystallization line, recrystallization line dots) and melting line dashes) determined by SAXS, zero growth temperature (from Fig. 5.38) and a rn transition line dash-dots)...

Analysis of CEELS line shapes often show chemical shifts that have been used to study FeB alloys after recrystallization, C-H bonding in diamondlike films and multiple oxidation states. 

Chloro-2-hydrazino-4-phenylquinoline A stirred mixture of 2,6-dichloro-4-phenylquino-line 12.7 g,0.01 mol) and hydrazine hydrate (6.8 g) was refluxed under nitrogen for 1 hour and concentrated in vacuo. The residue was suspended in warm water, and the solid was collected by filtration,dried and recrystallized from ethyl acetate-Skelly B hexanes to give 1.81 g (67% yield) of 6[Pg.46]

A mixture consisting of 22.7 g potassium o-bromobenzoate, 16.6 g 2,6-dichloro-3-methvlani-line, 12 ml N-ethylmorpholine, 60 ml diethylene glycol dimethyl ether, and 1.0 g anhydrous cupric bromide is heated in a nitrogen atmosphere at 145 C to 155°C for 2 hours. The reaction mixture is diluted with 60 ml diethylene glycol dimethyl ether and acidified with 25 ml concentrated hydrochloric acid. The acidic mixture is diluted with 100 ml of water and the liquid phase decanted from the insoluble oil. The insoluble oil is stirred with methanol and the crystalline N-(2,6-dichloro-3-methylphenyl)anthranilic acid which separates is collected and washed with methanol. The product, after recrystallization from acetone-water mixture melts at 248 C to 250°C. 

The dominant mechanism of purification for column crystallization of solid-solution systems is recrystallization. The rate of mass transfer resulting from recrystallization is related to the concentrations of the solid phase and free liquid which are in intimate contact. A model based on height-of-transfer-unit (HTU) concepts representing the composition profile in the purification section for the high-melting component of a binary solid-solution system has been reported by Powers et al. (in Zief and Wilcox, op. cit., p. 363) for total-reflux operation. Typical data for the purification of a solid-solution system, azobenzene-stilbene, are shown in Fig. 20-10. The column crystallizer was operated at total reflux. The solid line through the data was com-putecfby Powers et al. (op. cit., p. 364) by using an experimental HTU value of 3.3 cm. 

Because of the sensitivity of chromium(II) to air oxidation, synthetic work on these systems requires the use either of vacuum-line techniques12 or of a nitrogen-filled box,6 or both. This synthesis describes the preparation of chromium(II) complexes using a combination of a closed ground-glass filter stick 18 and a nitrogen-filled box.6 The filter stick enables preparations, filtrations, and recrystallizations to be carried out... 

Every silver lining has a cloud. More often than not, compounds recrystallized from a mixed-solvent system don t form crystals. Your compound may form an oil instead. 

Exothermic events, such as crystallization processes (or recrystallization processes) are characterized by their enthalpies of crystallization (AHc). This is depicted as the integrated area bounded by the interpolated baseline and the intersections with the curve. The onset is calculated as the intersection between the baseline and a tangent line drawn on the front slope of the curve. Endothermic events, such as the melting transition in Fig. 4.9, are characterized by their enthalpies of fusion (AHj), and are integrated in a similar manner as an exothermic event. The result is expressed as an enthalpy value (AH) with units of J/g and is the physical expression of the crystal lattice energy needed to break down the unit cell forming the crystal. 

Supercooling has been observed in an extreme form in molten ibuprofen if the molten solid is allowed to cool from the melting point to room temperature without vibration in a smooth-lined container [48]. For instance, undisturbed rac-ibuprofen can exist as an oil phase for several hours to a few days. If disturbed, however, an exothermic recrystallization proceeds and bulk crystalline material rapidly grows vertically out of the oil phase so energetically that the system emits an audible cracking sound. 

The simultaneous presence of the CaC03-reflections and of the CaO-reflections over a wide temperature range, and the persistence of certain calcite reflections point to topotaxy. This behaviour was generally observed during decomposition and recrystallization processes. The growth of the CaO crystallites with increasing temperature can be also seen in Fig. 61 (decrease of line broadening in the diffraction pattern). 

Figure 3.2. Differential calorimetric curves for the molecular glasses (a) Spiro-sexiphenyl (second heating curve) and (b) Spiro-PBD (first and second heating curve). The glass transition is indicated by a characteristic step, the melting point by an endothermic peak. In (a) recrystallization occurs above Tg, which can be seen by an exothermic peak. The material in (b) forms a stable amorphous glass without recrystallization. The melting point from the first heating curve of a crystalline sample (dotted line) disappears in the second heating cycle (solid line). Only the glass transition is visible.

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