Crystallization isothermal, quantitative measure

A quantitative measure of isothermal crystallization is the crystallization half-time, Crystallization times expressed as the reciprocal of (crystallization rate) are shown in Figure 9.4 as a function of crystallization temperature. These results indicate that the fastest crystallization for the PDS homopolymer can be obtained at approximately 47°C. For the sake of comparison, Figure 9.4 also includes spherulitic growth rates from HSOM. 

Comparisons of estimated diffusivity values on zeolites from sorption uptake measurements and those obtained from direct measurements by nuclear magnetic resonance field gradient techniques have indicated large discrepancies between the two for many systems [10]. In addition, the former method has often resulted in an adsorbate diffusivity directly proportional to the adsorbent crystal size [11]. This led some researchers to believe that the resistance to mass transfer may be confined in a skin at the surface of the adsorbent crystal or pellet (surface barrier) [10,11]. The isothermal surface barrier model, however, failed to describe experimental uptake data quantitatively [10,12]. 

Analysis of ternary mixtures of certain drugs including salicylamide were studied by plotting the refractive index isotherms of the fused mass and the isotherms of the primary crystals on triangular concentration diagrams. The influence of each factor upon the quantitative determination could be found. In each case there was an area unsuitable for measurement where the isotherms were practically parallel when this was not the case, quantitative determination was possible. Precaution should be taken to prevent loss of highly volatile components (7l). 

A quantitative, isothermal measurement of the crystallization kinetics, usable for analysis by the Avrami method, is illustrated in Fig. 3.98 by the upper left curve. Similar curves can be generated by dilatometry or adiabatic calorimetry as described in Sects. 4.1 and 4.2. At time zero, one assumes that the isothermal condition has been reached. The dotted segments of the heat-flow response are then proportional to the heat of crystallization evolved in the given time intervals and can be converted directly into the changes of the mass fraction of crystallinity after calibration or normalization to the total heat evolved. An independent crystallinity determination... 

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