Crystallization onset

The degree of change in and rj increases with antimony content (see the corresponding figures). Apart from this, the addition of Sb to a-Se shifts the crystallization onset to higher exposure values. 

Figure 20 shows the thermal traces of (a) nonirradiated and 500 kGy-irradiated PTFE powder and (b) the corresponding PTFE0kGy-EPDM and PTFE500kGy-EPDM composites. The crystallization peak of 500 kGy-irradiated PTFE powder shifts to a lower temperature of about 303.5°C. Also, the crystallization onset occurred at lower temperature and continued down to approximately 290°C. These distinct variations in 500 kGy-irradiated in comparison to nonirradiated PTFE powder is due to the E-beam treatment process, which caused degradation of 500 kGy-irradiated PTFE powder. The molecular weight decreases due to chain scission and leads to PTFE macromolecules of different chain lengths. As a result, the crystallization peak occurs at lower temperatures and the crystallization process continues until much lower temperatures in comparison to nonirradiated PTFE powder. 

Lee et al. (1996) applied step-wise crystallization fractionation to SME and reported similar results (Table 1.5). The liquid fraction had a total saturated FAME content = 5.5 wt% and crystallization onset temperature = -7.1 °C (determined by differential scanning calorimetry (DSC), compared to values of 15.6% and 3.7 °C before fractionation. Liquid product yield was also relatively low (25.5%). 

Lee et al. (1996) also investigated crystallization fractionation of SME from several solvents. Fractionation from hexane in three sequential steps with a final bath temperature of -28.4 °C resulted in a liquid product yield of 77% and total saturated FAME content of 6.0wt%. Crystallization onset temperature by DSC of the liquid fraction was -5.8 °C. Fractionation of SME from methanol solvent separated into two liquid layers as cooling temperatures approached -1.6°C. Acetone did not reduce crystallization onset temperature of the liquid fraction, and chloroform failed to form crystals at temperatures below -25 °C. Hanna et al. (1996) studied fractionation of TME... 

Form I obtained at a supersaturation x, temperature y, and time z at which crystals were harvested after crystallization onset Form II obtained at supersaturation x, etc. 

Critical cooling rate, Rc, can also be obtained on the basis of an empirical correlation between the crystallization onset temperature (7 ) obtained from the exothennic peaks in the DTA curves and the cooling rate, R, employed in the DTA experiment using the relation. 

The aim of this investigation is to examine the effect of nucleating agents on factors such as crystallization onset temperature and spherulite size. The nucleating potential of titanium dioxide based pigment and that of regranulated process waste is also examined since a knowledge of such effects is essential if process and product consistency is to be achieved. 

Relaxation profiles obtained as loss peak in imaginary dielectric curve and as step jump of real permittivity line Partial miscibility might exhibit multiple relaxation peaks overlaying or towards individual components, or display diverse relaxation rate even >T, Non-isothermal crystallization by isochronal temperature sweep DSC (cold crystallization and melting discernible as sudden drop and steep rise of static dielectric permittivity, respectively) Crystallization onset predicted using DRS relaxation time in coupUng model faster than the experimental time... 

Fig. 27a-b represents the SEM micrographs taken from the surface and the cross-section of the 0.90Te02-0.10W03 sample heat-treated at 410 °C, above the first crystallization onset temperature, respectively. Fig. 27a exhibits the presence of dendritic leaf-like crystallites differently oriented on the surface. However, in the cross-sectional micrograph (see Fig. 27b), a typical amorphous structure without any crystallization on bulk structure can be clearly observed following the crystallites on the surface. Based on the SEM investigations, it was determined that the crystallites formed on the surface and did not diffuse into the bulk structure proving the surface crystallization mechanism (Qelikbilek et al., 2011). 

By using the values of glass transition, Tg, crystallization onset, Tx, and crystallization p>eak, Tp, temperatures a Kissinger plot yields approximate straight fines as shown in Fig. 30. From... 

Figure 17 shows the onset of crystallization temperatures of NIE and CIE blends (60-100% butterfat in the blend). At the crystallization onset temperature, viscosity increased dramatically. All CIE samples had a higher crystallization onset temperature than their NIE counterparts. Both the proportion of butterfat and interesterification had significant effects on crystallization onset temperature... 

The higher crystallization onset temperatures of the CIE blends are not readily explainable. A plausible explanation is that the randomization of saturated fatty acids created a greater number of potential nucleation sites in the CIE blends than were present in the NIE blends. For example, dilution of butterfat with 10% canola oil led to a a drop in crystallization onset temperature. This was due to a lower proportion of TAGs containing saturated fatty acids, which reduced the number of nucleation sites. Interesterification of the 90 10 blend increased the onset temperature. Quite possibly, the UUU TAGs present in the canola oil were restructured and now contained a saturated fatty acid (SUU), thereby increasing the number of nucleation sites. Although not examined, the crystallization rate would have probably been slower for the CIE blends than for NIE blends. 

Hie analysis of each of the most abundant FAMEs by DSC at 5 C/min has permitted us to identify the peaks obtained on the cooling and heating scans of rapeseed and palm biodiesels. Table 13.2 lists the FAME composition of rapeseed (ME2) and palm (MEl) biodiesels as well as the melting and crystallization onset and enthalpy. Methyl oleate and elaidate are the predominant FAMEs in MEl and ME2 at 53.2% and 57.1 %, respectively. For palm biodiesel, methyl palmitate was the next most abundant FAME (27.4 %), followed by methyl stearate (9.4 %) and methyl linoleate (6.4 %). Concerning the rapeseed biodiesel, methyl linoleate was the next most abundant FAME (24.5 %) after methyl oleate, followed by methyl linolenate (8.6%) and methyl palmitate (4.6%). Rapeseed biodiesel (ME2) has a higher amount of unsaturated fatty acids (UFA, 92 %) than palm biodiesel (UFA, 61 %). The total saturated fatty acid (SEA) content for palm ester was 38 %, and 7 % for rapeseed ester. 

The addition of Pr to iron-boron melts, Pr (Feo.gBo.2)i- t5 was observed to stabilize the glassy structure. At x=0.1 and J = 899K a maximum appeared in the crystallization onset temperature, measured at a heating rate of 20 K/min (Kabacoff et al., 1982). 

Variable temperature study with a subsequent line shape analysis enables a clear insight of the temperature-dependent dynamics of the system, where the glass transition temperature (Tg) of the amorphous phase, melting point or a crystallization onset of a present crystalline phase, or any other changes caused by altered dynamics of the involved species can be assessed. This was recognized by early investigations of polymer electrolytes and will be discussed in greater detail later. 

The determination of the crystallization temperature of a sample is subject to many of the same considerations that apply to melting temperature determination. The crystallization temperature is normally reported as the temperature at which the exothermic peak maximum occurs but may also be reported as the temperature at which crystallization begins (the crystallization onset temperature). The observed crystallization peak temperature is always considerably lower (20°C or more) than the melting temperature observed subsequently for the same sample. The difference between the observed crystallization and melting peak temperatures increases as the rate of temperature ramp increases. 

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