Effect of synthesis conditions on electrochemical properties of LiNi1−yCoyO2 cathode for lithium rechargeable batteries
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PVF film prepared by means of extruding casting was cooled in water bath at different temperature,the crystallinity of the film sample was tested by XRD,the desolvation of the PVF film was made at different given temperature and got the curves of the desolvation rate.The results showed the higher the cooling temperature of water bath,the higher the initial crystallinity would be; the lower the initial crystallinity of film,the faster the desolvation rate would be; the crystallinity of film would increase during the desolvation,and the increase of the crystallinity would decrease the desolvation rate simultaneous.
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This work employs the relaxed Stefan model and Nakamura crystallization kinetics to describe the nonisothermal crystallization process of polymeric materials by finite element discretization method (FEM) simulation, giving the evolution of crystallinity distribution on 2 D space. Numerical results show that the final crystallinity and its distribution are mainly dependent on the cooling rate. Crystallinity decreases with increasing cooling rate, but the influence is negligible as long as the cooling rate is below a critical value (ca. 30°C·min–1 for poly(ethylene terephthalate) (PET)). If the cooling rate is higher than this critical one, crystallinity drops sharply. It is also concluded that the crystallization behavior of polymeric samples in a mild cooling medium is quite different from that in a strong cooling medium. In the first case (for example, in silicon oil), crystallinity of the article is relatively high and its distribution is fairly uniform. During the initial short period, the crystallinity on the surface is higher than that on the inside. Crystallinity increases slowly with time, and finally, the crystallinity of the internal part exceeds the crystallinity on the surface. In the second case (for instance, in water), crystallinity is relatively low, and there is a serious gradient of crystallinity. The crystallinity on the surface reaches a very low equilibrium value in a short time and changes little afterwards. Although the crystallinity of the inside part can be improved by changing the shape of the polymeric article, the crystallinity on the surface essentially remains constant, which leads to a significant gradient. Geometrical shape and dimension of the article are also important to the crystallinity and its distribution, and the ratio of surface area to volume can be used as a rough index to estimate the shape/dimension influence on crystallinity. Except the coefficient of thermal conductivity, physical parameters of the polymeric material and kinetic parameters of crystallization show only weak effects compared to cooling conditions.
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Biological hydroxyapatite (BHAp) derived from thermally-treated fish bones was successfully produced. However, the obtained biological HAp was amorphous and thus making it unfavorable for medical application. Consequently, this research exploits and engineers the crystallinity of BHAp powders by addition of CaCO3 and investigates its degree of crystallinity using XRD and IR spectroscopy. On XRD, the HAp powders with [Ca]/[P] ratios 1.42, 1.46, 1.61 and 1.93 have degree of crystallinity equal to 58.08, 72.13, 85.79, 75.85% and crystal size equal to 0.67, 0.74, 0.75, 0.72 nm, respectively. The degree of crystallinity and crystal size of the obtained calcium deficient biological HAp powders increase as their [Ca]/[P] ratio approaches the stoichiometric ratio by addition of CaCO3 as source of Ca2+ ions. These results show the possibility of engineering the crystallinity and crystal size of biological HAp by addition of CaCO3. Moreover, the splitting factor of PO4 vibration matches the result with % crystallinity on XRD. Also, the area of phosphate-substitution site of PO4 vibration shows linear relationship (R2 = 0.994) with crystal size calculated from XRD. It is worth noting that the crystallinity of the biological HAp with [Ca]/[P] ratios 1.42 and 1.48 fall near the range 60-70% for highly resorbable HAp used in the medical application.
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Stoichiometry
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Abstract Poly(ethylene terephthalate) (PET) sheets of different crystallinity were obtained by annealing. The annealed PET sheets were characterized by the density measurement, differential scanning calorimetry (DSC), ultraviolet (UV)‐visible spectrometry, X‐ray diffraction, and infrared (IR) spectrometry. The density data can be used as a basic measurement of the degree of crystallinity. The total transition heat data obtained from the first run DSC heating curves can correlate with the crystallinity, although it may underestimate the crystallinity for those samples with higher crystallinity. The visible light transmittance data can be related to the crystallinity, and are very sensitive to the change of the crystallinity for the PET sheets of low crystallinity. The X‐ray diffraction data and IR transmittance data do not show strong linear relationship to the crystallinity in a quantitative way. Copyright © 2008 Curtin University of Technology and John Wiley & Sons, Ltd.
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Crystallinity of polymeric dielectrics is known to be influenced by cross-linking. To study that influence, gel fraction measurements and evaluation of the degree of crystallinity were performed under different cross-linking temperatures using XLPE samples with different DCP concentrations. Furthermore, the influence of antioxidants on XLPE crystallinity was studied. Gel fraction and crystallinity measurements were made of XLPE samples containing different concentrations of DCP and phenolic or sulfur-type antioxidants. The experimental results are used to discuss the influence of antioxidant on cross-linking and crystallinity of XLPE.
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Molar ratio
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This work employs the relaxed Stefan model and Nakamura crystallization kinetics to describe the nonisothermal crystallization process of polymeric materials by finite element discretization method (FEM) simulation, giving the evolution of crystallinity distribution on 2 D space. Numerical results show that the final crystallinity and its distribution are mainly dependent on the cooling rate. Crystallinity decreases with increasing cooling rate, but the influence is negligible as long as the cooling rate is below a critical value (ca. 30°C·min–1 for poly(ethylene terephthalate) (PET)). If the cooling rate is higher than this critical one, crystallinity drops sharply. It is also concluded that the crystallization behavior of polymeric samples in a mild cooling medium is quite different from that in a strong cooling medium. In the first case (for example, in silicon oil), crystallinity of the article is relatively high and its distribution is fairly uniform. During the initial short period, the crystallinity on the surface is higher than that on the inside. Crystallinity increases slowly with time, and finally, the crystallinity of the internal part exceeds the crystallinity on the surface. In the second case (for instance, in water), crystallinity is relatively low, and there is a serious gradient of crystallinity. The crystallinity on the surface reaches a very low equilibrium value in a short time and changes little afterwards. Although the crystallinity of the inside part can be improved by changing the shape of the polymeric article, the crystallinity on the surface essentially remains constant, which leads to a significant gradient. Geometrical shape and dimension of the article are also important to the crystallinity and its distribution, and the ratio of surface area to volume can be used as a rough index to estimate the shape/dimension influence on crystallinity. Except the coefficient of thermal conductivity, physical parameters of the polymeric material and kinetic parameters of crystallization show only weak effects compared to cooling conditions.
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Polypropylene specimens were made by the injection molding experiments under different processing conditions. The crystallinity of each polypropylene specimen was obtained using the X-ray diffraction method. The effects of the injection molding processes on the crystallinity of polypropylene were revealed: (1) the crystallinity decreases as the melt temperature increases, and the higher the melt temperature, the slower the crystallinity decreases, (2) the crystallinity decreases as the mould temperature increases, and the higher the mould temperature, the faster the crystallinity decreases, (3) the crystallinity increases as the injection speed increases, and the larger the injection speed, the faster the crystallinity increases. By the tensile experiments of the injection molded specimens, it is also found that the crystallinity has a major impact on the mechanical properties of polypropylene. The yield strength and tensile strength of polypropylene specimens increase as the crystallinity increases.
Polypropylene
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Abstract Crystallinity is an important parameter of thermoplastic polymers. Furthermore, crystallinity is closely related to processing conditions such as temperature and applied shear stress. However, determining the degree of crystallinity is very complicated because of the different interpretations of crystallinity according to each technique. In this paper, we analyze the crystallinity of polyethylene glycol-based composites using two instruments, i.e., X-Ray Diffraction (XRD) and wide-angle X-Ray Scattering (WAXS). The results showed that with the addition of 60 wt.% silica, the degree of crystallinity revealed by XRD was 81.24%, while WAXS showed a degree of crystallinity of 80.93%. In general, the crystallinity results obtained with WAXS were almost identical, only 0.31% different from the XRD results. This difference in results was due to more presence as a consequence of the broad amorphous halo and background instrumentation exhibited by the higher background from XRD. Thus, the instrument effect must first be removed from the XRD data and it is possible that the amorphous region of the sample will also be reduced and result in a slightly higher crystallinity. At the same time WAXS with the transmission technique will minimize the possibility of background instrumentation. Therefore, WAXS was recommended to analyze the crystallinity of polymer-based and amorphous materials.
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Abstract The crystalline-amorphous ratio, and consequently the degree of crystallinity of polychlorotrifluoroethylene was measured by use of the ratio of observed absorbance of crystalline band at 440 cm.−1 to that of amorphous band at 760 cm.−1. The crystallinity as a function of temperature was measured by this method, and it was in good agreements with that obtained by specific heat methd. Furthermore, a linear relationship between the degree of crystallinity and the specific volume was found, and it leads to extrapolated values of film and 0.4901 and 0.4575 for the specific volumes of completely amorphous and crystalline meterials, respectively.
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