The amorphous content of different Desferal samples was quantified by recording its recrystallization using isothermal microcalorimetry in a static as well as in a flowing humid atmosphere. Furthermore water vapor sorption gravimetry was performed for the same purpose. These analytical methods result in a quantitative signal directly dependent on the content of the amorphous phase (recrystallization, water sorption equilibrium). Their sensitivity allows the detection of amorphous content below 1%. Methods are compared and advantages and disadvantages are discussed.
Summary A pseudo-isothermal method for the kinetic analysis was applied to the recrystallisation of a to ß nickel sulphide based on the Ozawa model for non-isothermal crystallisation in the presence of pre-existing nuclei. The aim of the analysis was to determine the number of steps involved in the recrystallisation and, hence, determine the applicability of the kinetic equation based on a single step mechanism, as is commonly applied in the kinetic analysis of solid-state processes using thermal methods. The kinetic analysis yielded evidence of at least two processes indicating that physical and mechanistic significance should not be drawn from the use of a single step approximation of the rate equation.
A general model is discussed for assessing the energy release due to the pinning of solute atoms to partial dislocations. The present approach discloses the influence of dislocation character distributions on the magnitude of this energy. In order to test its validity in αCu-Al alloys, differential scanning calorimetry (DSC) evaluations associated with the different peaks involved during linear heating were performed employing both cold worked and quenched materials. Dislocation densities were calculated from recrystallization traces. On the basis of this model it was concluded that the observed energy difference between the deformed and the quenched materials during the exothermic peak designated as Stage 2 corresponds to the pinning process. It was also concluded that nearly equal number of edge and screw dislocations are present in the dislocation configuration of deformed alloys. Nevertheless, it is proposed that dislocation-induced order might also occur as a consequence of enhanced solute concentration around the partials.
Authors:C. C. Seow, C. H. Teo, and C. K. Vasanti Nair
Thermal characterization of gelatinized binary rice starch-water and ternary starch-sugar-water gels before and after aging was carried out using differential scanning calorimetry. The glass transition temperature of the maximally freeze-concentrated solution (T′g) in both fresh and aged gels was observed to decrease progressively with increasing sugar concentration. Aging of the gels generally shiftedT′g to higher temperatures, but had little or no effect on the ice melting peak temperature (Tm). The presence of various sugars could either accelerate or retard starch (amylopectin) recrystallization, depending on the type and concentration of sugar, as well as on starch/water ratio. A hypothesis based on the dual antiplasticizing-plasticizing effects of sugars was postulated to explain the observed effects. Of the sugars studied, xylose and fructose appeared to display exceptional retardative and accelerative effects, respectively, on retrogradation.
Ca salts of suberic (Ca-Sub) and pimelic acid (Ca-Pim) were synthesized and used as β-nucleating agents in different grades
of isotactic polypropylene (IPP). Propylene homo-, random- and block-copolymers containing these additives crystallize principally
in pure β-modification as demonstrated in isothermal and non-isothermal crystallization experiments. Ca-Sub proved the most
effective β-nucleating agent known, so far. It broadens the upper crystallization temperature range of pure β-IPP formation
up to 140C. The effect of the additives on the crystallization and melting characteristics of the polymers was studied. The
degree of crystallinity of the β-modification was found to be markedly higher than that of α-IPP. High temperature melting
peak broadening was first observed and discussed in literary results regarding the same phenomenon for α-IPP.
reversing heat capacity can be interpreted by considering annealing, recrystallisation and secondary crystallisation. Reversing and non-reversing processes have been separated by mT-DSC techniques for a considerable number of semicrystalline polymers, such
Authors:Robert A. Shanks and L. M. Wasantha K. Gunaratne
( Table 1 ) of TPS sheet was low compared with the component starches since native crystals were destroyed during extrusion and a slow recrystallization process (retrogradation) occurred afterwards. The slow retrogradation compared with unmodified high
the melting point), reorganization (crystal improvement at crystallization temperature), and recrystallization (melting and recrystallization) [ 10 ]. Softening and swelling of the amorphous regions of starch is a necessary thermophysical change