Ctystallization temperature

The motion actually observed by i.r. absorption is a small part of the whole pattern, since for effective absorption one must match both frequency and wavelength in the electromagnetic and crystal osdllations. Absorption occurs essentially at the frequency of the longest waves present in the crystal These waves are damped by anharmonic interaction with the numerous short-wave modes, except at very low temperatures where interaction with ctystal ddects and surfaces takes over. In spite of the complexity of the process one has to expect a simple lineshape and a fairly simple temperature dependence for a wave propagating in one crystal direction. 

Comparative economics favor ctystallization. If distillation requires high temperatures and energy usage, ctystallization may offer economic incentives. 

Establishing the temperature and/or premure ranges of the ctystallizer operation and the composition of the residne liquor exiling the crystallizer. 

Phase diagrams for crystallizing polymer-plasticizer systems are complicated by the influence of the crystallization processes. Steiic restrictions of polymer chains limit the completeness of the crystallization process. The rates of ctystallization can significantly change depending on pressure, temperature, and the presence of impurities. 

Thb section discusses various features of commercial types of solution crystallizers used in industrial processes. In solution crystallization a diluem solvent b added to fee mixture or b already present as a carrier liquid. The solution b then cooled aixi/or solvent b evgqiorated to cause crystallization. Another feature of solution ctystallization b feat the solid phase b ftmtied and maintained below ib pure-component freezing temperature. 

The material balance information in Table 11.3-7 suggests that cooling crystallization, although effective in obtaining product yield, does not provide the desired suspension density. To meet this condition, external heat must be added to evaporate additional solvent. For practical reasons (such as avoidance of refrigerated coolant in the condenser) the ctystallizer operating temperature is selected as SO C. Thus, the operating absolute pressure will be 90 mm Hg (see Table 11.3-6). 

Phosphine borane reacts at low temperature with n-butyl lithium to produce lithium phosphinidobo-rane (9.64). This salt forms colourless CTystals which are thermally more stable than phosphine borane, but they are decomposed by water to give phosphine and hydrogen. Ammonium phosphini-doborane is obtained from ammonia and phosphine borane (9.65). 

Figure 21 Tg2 vs. T max for the PEEK samples isothermally cold-crystallized at low temperature (153 C, 3.0 h) and progressively reheated stepwise to increasingly higher temperature, rcmax- Filled sq uares correspond to the initially cold-ctystallized sample and to Tcmax of 170,176,186,194,205,227,257,271, and 305 °C. The lines are guides to the eye. With permission from Ivanov, D. A. Jonas, A. M. Legras, R. PolymerZm, 41,3719. ...

Fig. 11.3 (a) SAXS profiles of iPP samples of Table 11.1 isothermally CTystallized from the melt at the indicated values of temperature (a) and corresponding normalized autocorrelation functions. SAXS data are recorded at Tc- Values of long spacing (L), and thickness of crystalline (4) and amorphous (k = L- 4) layers (c). They are evaluated from the autocorrelation function in (b) (full symbols) and also using the Bragg law for the calculation of L and successive multiplication of L times the crystallinity index (see the text) for 4 (open symbols)... 

An alternative to optical techniques is the measurement of film mass during dissolution, accomplished through the use of piezoelectric quartz ctystals (8-12). These crystals, fabricated to possess a known oscillation frequency at room temperature, are used as substrates for resist films. Deposition of a mass on the ciystal causes it to oscillate at a lower frequency than the uncoated substrate. As the film mass changes during dissolution, the corresponding frequency shift of the crystal can be monitored predsely and correlated to the film thickness throu instrument parameters and film density. A rigorous theoretical analysis... 

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