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Crystal Transformation (crystal + transformation)
Selected AbstractsStorage stability study of margarines produced from enzymatically interesterified fats compared to margarines produced by conventional methods.EUROPEAN JOURNAL OF LIPID SCIENCE AND TECHNOLOGY, Issue 7-8 2005Physical properties Abstract In this study, margarine hardstocks were produced from two enzymatically interesterified fats at conversion degrees of 80 and 100%, a chemically randomized fat and a physically mixed fat, respectively. These four hardstocks blended with 50% of sunflower oil were mainly used for the production of table margarines in a pilot plant. Storage stability studies were carried out at storage temperatures of 5 and 25,°C during 12,wk. Margarines from the enzymatically interesterified fats were compared to the margarines produced by conventional methods and to selected commercial products. The changes in the physical properties of margarines, including hardness, dropping point, crystal form, and sensory evaluation, were examined during storage. It was observed that margarine storage stability increased with increasing conversion degree. The color of margarines made from the enzymatically interesterified fats was more similar to that of the physically mixed fat than that of the margarine from the chemically randomized fat, which had less color. Crystal transformation was accelerated at high storage temperature. Crystal size was not only related to the types of crystals, but also to the driving force of temperature difference. A larger crystal size was observed at 5,°C than at 25,°C for the margarine made from the blend. Margarines produced from interesterified fats had better physical properties than the blend. Overall, the margarine produced from the enzymatically fully converted fat had physical properties similar to the margarine produced from the chemically interesterified fat. [source] Double Hysteresis Loop and Aging Effect in K0.5Na0.5NbO3,K5.4Cu1.3Ta10O9 Lead-Free CeramicsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 6 2009Dunmin Lin In this work, the double-loop-like characteristics of K0.5Na0.5NbO3+x mol% K5.4Cu1.3Ta10O9 ceramic and its relationships with the transition temperature, aging, and switching have been investigated. Our results reveal that the phase transition temperature is an important parameter determining the aging requirement for the ceramics to exhibit the double-loop-like characteristics. For a ceramic with a high transition temperature, e.g. the ceramic with x=0.75 (tetragonal,orthorhombic phase temperature ,206°C), the vacancies can migrate during the crystal transformation and settle in a distribution with the same symmetry as the crystal after the transformation. As a result, defect dipoles along the polarization direction are formed and provide restoring forces to reverse the switched polarizations, and thus producing a double polarization hysteresis (P,E) loop. On the other hand, aging is required for a ceramic with a low transition temperature, e.g. aging at 80°C for 30 days is required for the ceramic with x=1.5 (transition temperature ,175°C). Our results also reveal that the defect dipoles can be switched under a slow-switching electric field (<1 Hz) or at high temperatures (>100°C), thus leading to an opening of the double P,E loop. [source] Solid state 19F NMR study of crystal transformation in PVDF and its nanocompositesPOLYMER ENGINEERING & SCIENCE, Issue 12 2006Pramoda K. Pallathadka The polymorphism of poly(vinylidene fluoride) (PVDF) and its nanocomposites was studied by means of solid state nuclear magnetic resonance spectroscopy. 13C cross polarization magic angle spinning (13C CP MAS) NMR spectra were recorded using simultaneous high-power decoupling on both the proton and fluorine channels. Both 1H , 13C and 19F , 13C CP experiments were conducted, giving identical results apart from intensity variations due to the CP efficiency. Two main resonances for the CF2 and the CH2 groups were observed for both neat PVDF (PVDF-C0) and the nanocomposite containing 2 wt% clay (PVDF-C2) samples. 19F CP MAS spectra were obtained from long proton spin-lock experiments with a shorter contact time. The results showed two strong resonances at ,84 and ,98 ppm with equal intensities, representing the ,-form crystalline structure of PVDF. It was shown that the clay induces the crystallization of PVDF in ,-form. Our earlier investigations using thermal analysis and X-ray scattering methods also showed crystal transformation of PVDF in its clay nanocomposites. POLYM. ENG. SCI. 46:1684,1690, 2006. © 2006 Society of Plastics Engineers [source] Crystallization and melting behavior of multi-walled carbon nanotube-reinforced nylon-6 compositesPOLYMER INTERNATIONAL, Issue 1 2006In Yee Phang Abstract The crystallization and melting behavior of neat nylon-6 (PA6) and multi-walled carbon nanotubes (MWNTs)/PA6 composites prepared by simple melt-compounding was comparatively studied. Differential scanning calorimetry (DSC) results show two crystallization exotherms (TCC, 1 and TCC, 2) for PA6/MWNTs composites instead of a single exotherm (TCC, 1) for the neat matrix. The formation of the higher-temperature exotherm TCC, 2 is closely related to the addition of MWNTs. X-ray diffraction (XRD) results indicate that only the ,-phase crystalline structure is formed upon incorporating MWNTs into PA6 matrix, independently of the cooling rate and annealing conditions. These observations are significantly different from those for PA6 matrix, where the increase in cooling rate or decrease in annealing temperature results in the crystal transformation from ,-phase to ,-phase. The crystallization behavior of PA6/MWNTs composites is also significantly different from those reported in PA6/nanoclay systems, probably due to the difference in nanofiller geometry between one-dimensional MWNTs and two-dimensional nanoclay platelets. The nucleation sites provided by carbon nanotubes seem to be favorable to the formation of thermodynamically stable ,-phase crystals of PA6. The dominant ,-phase crystals in PA6/MWNTs composites may play an important role in the remarkable enhancement of mechanical properties. Copyright © 2005 Society of Chemical Industry [source] Phase transition of triclinic hen egg-white lysozyme crystal associated with sodium bindingACTA CRYSTALLOGRAPHICA SECTION D, Issue 4 2004Kazuaki Harata A triclinic crystal of hen egg-white lysozyme obtained from a D2O solution at 313,K was transformed into a new triclinic crystal by slow release of solvent under a temperature-regulated nitrogen-gas stream. The progress of the transition was monitored by X-ray diffraction. The transition started with the appearance of strong diffuse streaks. The diffraction spots gradually fused and faded with the emergence of diffraction from the new lattice; the scattering power of the crystal fell to a resolution of 1.5,Å from the initial 0.9,Å resolution. At the end of the transition, the diffuse streaks disappeared and the scattering power recovered to 1.1,Å resolution. The transformed crystal contained two independent molecules and the solvent content had decreased to 18% from the 32% solvent content of the native crystal. The structure was determined at 1.1,Å resolution and compared with the native structure refined at the same resolution. The backbone structures of the two molecules in the transformed crystal were superimposed on the native structure with root-mean-square deviations of 0.71 and 0.96,Å. A prominent structural difference was observed in the loop region of residues Ser60,Leu75. In the native crystal, a water molecule located at the centre of this helical loop forms hydrogen bonds to main-chain peptide groups. In the transformed crystal, this water molecule is replaced by a sodium ion with octahedral coordination that involves water molecules and a nitrate ion. The peptide group connecting Arg73 and Asn74 is rotated by 180° so that the CO group of Arg73 can coordinate to the sodium ion. The change in the X-ray diffraction pattern during the phase transition suggests that the transition proceeds at the microcrystal level. A mechanism is proposed for the crystal transformation. [source] | ||||||||||