Papers by Keyword: Crystallization Kinetics

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Authors: Bi Jun Luo, Hai Hong Wu, Shao Yan Lu, Yan An Zhang, Qi Zhang
Abstract: Crystallization kinetics experiment of calcium sulfate dehydrates, which is prepared by bittern under 40oC and 200r/min conditions, is carried out. According to the results of the experimental data, the relationship of nucleus particle-number density n0 and crystal growth rate G with the residence time is summarized. Also, the average diameter of gypsum crystal is decreasing with the residence time increase. Meanwhile, the crystallization kinetics formula is derived to be: B0=3.20×105G0.47.
Authors: Xin Zhu Li, Ji Shi Zhang
Abstract: Cr-substituted mesoporous aluminophosphate molecular sieve (Cr-MAP) was synthesized and characterized. Crystallization kinetics curves measured as an index to the relative degree of crystallinity, according to the Arrhenius equation to calculate the apparent nucleation activation energy and crystal growth activation energy of Cr-MAP, which was 63.7 and 14.7 kJ• mol-1, respectively. Cr-MAP had highly catalytic activity for fabricating acetophenone by selectively oxizing ethylbenzene. Using tert-butylhydroperoxide as oxidant and chlorobenzene as solvent at 100 °C for 8 h, acetophenone selectivity, acetophenone yield and ethylbenzene conversion reaches 85.4, 62.2 and 72.8 %, respectively.
Authors: Jason S.C. Jang, L.J. Chang, Y.T. Jiang, P.W. Wong
Authors: Mat Taib Razaina, Cho Yin Tham
Abstract: Isothermal crystallization kinetics and morphology of Poly (lactic acid) (PLA) and PLA/ethylene acrylate copolymer (EAC) blends were studied by differential scanning calorimetry (DSC) and polarized optical microscopy (POM) at various temperatures (95–125°C). The DSC data obtained was analyzed using the Avrami equation. The crystallization rate was found to depend on the crystallization temperature (Tc) and EAC content. At a given Tc, the crystallization rate value was greater in the blends than in PLA suggesting that the presence of EAC enhanced crystallization of PLA. Based on the DSC analysis the crystallization rate was maximum when PLA blend with 1 wt.% EAC was isothermally crystallized at 103°C. The presence of EAC did not significantly change in the spherulitic growth rate (G) of PLA. Analysis of the growth rates using the Lauritzen-Hoffman theory showed that a regime II to regime III transition was present for all PLA/EAC blends and that this transition occurred at temperature of 100°C. The fold surface energy values of PLA/EAC blends were lower than that of PLA indicating that PLA chains can readily fold onto the crystal nucleus surface after the incorporation of EAC.
Authors: Young Seok Kim, Kyu Ho Lee, Tae Ho Kim, Young Joon Jung, S. H. Yim, Bong Ki Ryu
Abstract: The nucleation and crystallization kinetics of P2O5-B2O3-ZnO-BaO-Al2O3-TiO2 crystals in bulk glass in which this crystals were found to crystallize in the heating process of the glass, were studied by non-isothermal measurements using differential thermal analysis (DTA). A nucleation rate-temperature was determined by plotting either the reciprocal of the temperature corresponding to the crystallization peak maximum, 1/Tp, or the height of the crystallization peak, (*T)p, as a function of nucleation temperature, Tn. The temperature where nucleation can occur for this glass ranges from 700°C to 890°C and the temperature for maximum nucleation is 760±5°C. The correct activation energy for crystallization, Ec, for this glass is the same for surface and/or bulk crystallization, and is 533±15°CkJ/mol. The analysis of the crystallization data with the Kissinger equation and the Marotta equation yields the correct value for Ec only crystal growth occurs on a fixed number of nuclei. The crystallization process of a sample heat treated at the temperature of the maximum nucleation rate was fitted to kinetic equations with an Avrami constant, n ≈2 and a dimensionality of crystal growth, m ≈2.
Authors: Qian Gao, Zeng Yun Jian, Jun Feng Xu, Man Zhu
Abstract: The crystallization kinetics of melt-spun Cu64.5Zr35.5 amorphous alloy ribbons was investigated using differential scanning calorimetry (DSC) at different heating rates. Besides, the Kissinger and isoconversional approaches were used to obtain the crystallization kinetic parameters. As shown in the results, the activation energies for glass transition and crystallization process at the onset, peak and end crystallization temperatures were obtained by means of Kissinger equation to be 577.65 ± 34, 539.86 ± 54, 518.25 ± 20 and 224.84 ± 2 kJ/mol, respectively. The nucleation activation energy Enucleation is greater than grain growth activation energy Egrowth, indicating that the nucleation process is harder than grain growth. The local activation energy Eα decreases in the whole crystallization process, which suggests that crystallization process is increasingly easy.
Authors: Tarek Benameur, Akihisa Inoue
Authors: Lan Qing Deng, Jun Fa Xue, Li Kuan, Jian Ming Ouyang
Abstract: The crystallization kinetics of calcium oxalate (CaOx) was comparatively studied by detecting the change of free Ca2+ ions concentration with the reaction time in artificial urine and in saline system. The dynamics equations of CaOx crystallization was r=kcα, and the average reaction order (α) was 3.3 regardless of the relative suprasaturation degree (RS) of CaOx in the range of RS=10.58~17.53. The average reaction rate constant (κ) was (0.97±0.1)×109 in artificial urine and κ=(3.1±1.8)×109 in saline system, due to the presence of inhibitors to CaOx crystallization in artificial urine.
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