Completion of crystallization

At higher crystallization temperatures, wait at least 15 min for the completion of crystallization. 

In molten state PETP consists of associates which may be the cores of formation of crystallization nuclei. Completion of crystallization process and crystal size depend very much on rates chains lay-up on the side of growing crystal and relaxation of large segments relation. 

Assume that upon the completion of crystallization at 40°C, we have a solution containing 100 g of water (MW =18) and the equilibrium solubility of sodium acetate (MW = 82), or 65.5 g of sodium acetate from the above table. Let the solid crystals at 40°C be a g of solid crystalline trihydrate of sodium acetate (MW = 136). For a thermod3mamic path, take crystallization at 20°C, but with the 40°C solubility, followed by heating the crystaUine solids and the solution to 40°C. Therefore, specific heats are needed for the solid and the solution. In the absence of data for the trihydrate of sodium acetate, Kopp s rule (Felder and Rousseau, 2000) is applied with atomic heat capacities in cal/mol-°C of 1.8 for C, 2.3 for H, 4.0 for 0, 9.8 for water of crystallization, and 6.2 for all other atoms in the four salts. Thus, for NaC2H302 3H2O,... 

Furthermore, the second (low-temperature) exothermal peak observed upon cooling of the as-spun CPE-1 samples from 380°C seems not to be related to CPE-1 crystallization from the nematic melt, but to the completion of crystallization, which coincides with the onset of glass transition in CPE-1. 

The small angle X-ray scattering (SAXS) curves of the metallocene-made iPP samples are shown in Fig. 11.3a. The samples have been isothermally crystallized at temperatures lower than the melting temperature of Table 11.1 by 40-50 °C. SAXS data were recorded at the crystallization temperature on samples first rapidly cooled to room temperature immediately after completion of crystallization process, and successive heating at The simultaneous recording of the X-ray... 

Only under one condition can something resembling a synthesis be accomplished (4). It has been mentioned that after tiie completion of crystallization of ferritin, there remains a brown mother liquor from which no further crystals can be obtained. When apoferritin is dissolved in this brown mother liquor and CdSO added, brown crystals of ferritin are formed. 

The most usual way is effectively the same as is used for completion of crystal structures during structure solution (Section 10.7.6 andEq. 10.12). When a reasonable part of the structure has been described and some atoms positions have been defined, along with correct scattering factors and thermal parameters, a difference map can be calculated between this (incomplete) model and the Fourier transform of the experimental structure amplitudes. This map is a representation of the difference between the electron density of the model and that determined by the experiment. The biggest accumulations of electron density are assigned as new atoms until the structural model is complete. But even then there is residual electron density, which describes the difference between the true electron density and the model of a sum of independent spherical atom contributions, taking some simplified model of displacement into account There is also some random noise. 

To minimize the damage that could occur to a furnace and danger to personnel in the event of a spill, the furnace floor was covered with a course sand to absorb as much of a spill as possible. A bed of sand was also maintained at the base of the furnace to trap any spillage, keeping it from flowing. Fortunately, this never became a problem. Several crucibles cracked during their use, but none catastrophically. Since crucibles were intentionally sacrificed upon the completion of crystallization, cracked crucibles presented no significant problems. 

Completion of crystallization Product solution concentrations are determined before and after crystallization. ... 

It should be noted that DSC measurement delivers the relative mass crystallinity, which can be recalculated to volume degree of crystallinity. Based on the assumption of one crystalline and one amorphous phase, and a constant volume crystallinity inside spherulites, the momentary value of the degree of conversion is calculated by dividing the momentary value of volume degree of crystallinity by the final volume crystallinity obtained after the completion of crystallization. 

Isothermal crystallization characterization was performed using a Perkin - Elmer Pyris 1 system, which was calibrated using the melting temperature and enthalpy of indium. The samples with a weight around 12 mg were put into an aluminum pan and hermetically sealed. An empty pan was used as a reference. For crystallization characterization, a sample was heated from 20 to 200°C at 20°C/min and maintained at 200°C for 2 min. Subsequently, it was rapidly quenched (-80°C/min) to the isothermal crystallization temperature and held there until completion of crystallization. Once crystallized, the samples were then reheated to 200°C at a rate of 20°C/min in order to investigate the melting behavior. 

Isothermal crystallization kinetics was evaluated by following the degree of crystallization Xt as a function of time. The degree of crystallization was expressed by the ratio of enthalpy Xt=AH,IAH where AH, corresponds to the partial area of the DSC curve between the onset of crystallization and time t and AH, is the melting enthalpy integrated between the onset until completion of crystallization. 

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