• Title, Summary, Keyword: crystallization

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FLUCTUATION INDUCED CRYSTALLIZATION: IN A SIMULTANEOUSLY PHASE SEPARATION AND CRYSTALLIZATION POLYOLEFIN BLEND SYSTEM

  • Zhang Xiaohua;Han, Charles C.
    • Proceedings of the Polymer Society of Korea Conference
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    • pp.158-158
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    • 2006
  • The correlation between liquid-liquid phase separation (LLPS) and crystallization at several compositions in statistical copolymer blends of poly (ethylene-co-hexene) (PEH) and poly (ethylene-co-butene) (PEB) has been examined. In this case, the LLPS is coupled with the other ordering process, i.e. crystallization. The overwhelming change in the crystallization kinetics due to the composition fluctuation caused by the spontaneous spinodal LLPS is observed. This coupling mechanism suggests a new mechanism in the nucleation-crystallization process.

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Crystallization of amorphous Si by pulse annealing with Ni ferritins

  • Tojo, Yosuke;Miura, Atsushi;Fuyuki, Takashi;Yamashita, Ichiro;Uraoka, Yukiharu
    • 한국정보디스플레이학회:학술대회논문집
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    • pp.553-556
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    • 2009
  • We investigated an application of supramolecular protein, and demonstrated the metal induced lateral crystallization utilizing ferritins with Ni nanoparticles, named the "bio-nano-crystallization". So far, this method has required long time, because of this method condition based on the conventional solid phase crystallization. In this study, we applied the pulsed rapid thermal annealing to bio-nanocrystallization. As a result, we succeeded in the crystallization for a short time. We found that the TFTs characteristics were improved with decrease metal impieties in poly-Si thin films by this method.

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Effect of Activation Energy and Crystallization Kinetics of Polyethylenes on the Stability of Film Casting Processes

  • Lee, Joo-Sung;Cho, Joon-Hee
    • Korea-Australia Rheology Journal
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    • v.21 no.2
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    • pp.135-141
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    • 2009
  • Effect of activation energy and crystallization kinetics of polyethylenes (PEs) on the dynamics and stability has been investigated by changing rheological properties and crystallization rate in film casting process. The effect of changes of these properties has been shown using a typical example of short-chain branching (SCB) in linear polyethylenes. SCBs in linear polymers generally lead to the increase of the flow activation energy, and to the decrease of the crystallization rate, making polymer viscosity lower in the case of equivalent molecular weight. In general, the increment of the crystallinity of polymers under partially crystallized state helps to enhance the process stability by increasing tension, and lower fluid viscoelasticity possesses the stabilizing effect for linear polymers. It has been found that the fluid viscoelasticity plays a key role in the control of process stability than crystallization kinetics which critically depends on the cooling to stabilize the film casting process of short-chain branched polymers operated under the low aspect ratio condition.

Enhanced Crystallization of Bisphenol-A Polycarbonate by Organoclay in the Presence of Sulfonated Polystyrene Ionomers

  • Govindaiah, Patakamuri;Lee, Jung-Min;Lee, Seung-Mo;Kim, Jung-Hyun;Subramani, Sankaraiah
    • Macromolecular Research
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    • v.17 no.11
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    • pp.842-849
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    • 2009
  • Polycarbonate (PC)/sulfonated polystyrene (SPS) ionomer/organoclay nanocomposites were prepared by a solution intercalation process using the SPS ionomer as a compatibilizer. The effect of an organoclay on the melt crystallization behavior of the ionomer compatibilized PC were examined by differential scanning calorimetry (DSC). The melt crystallization behavior of PC was dependent on the extent of organoclay dispersion. The effect of the ionomer loading and cation size on intercalation/exfoliation efficiency of the organoclay in PC/SPS ionomer matrix was also studied using wide angle X-ray diffraction (WAXD) and transmission electron microscopy (TEM). Dispersion of the organically modified clay in the polymer matrix improved with increasing ionomer compatibilizer loadings and cation size. The SPS ionomer compatibilized PC/organoclay nanocomposite showed enhanced melt crystallization compared to the SPS ionomer/PC blend. Well dispersed organoclay nanocomposites showed better crystallization than the poorly dispersed clay nanocomposites. These nanocomposites also showed better thermal stability than the SPS ionomer/PC blend.

CRYSTALLIZATION KINETICS OF Fe-Si-B-Cu-Nb AMORPHOUS RIBBONS

  • Zhou, S.X.;Ulvensoen, J.H.;Hoier, R.
    • Journal of the Korean Magnetics Society
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    • v.5 no.5
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    • pp.511-514
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    • 1995
  • The crystallization kinetics of $Fe_{73.5}Si_{13.5}B_{9}Cu_{1}Nb_{3}$ amorphous alloy has been investigated using differential scanning calorimetry (DSC). The crystallization process had two stages, i.e. precipitation of the $\alpha$-Fe(Si) solid solution and the tetragonal borides. The isothermal transformation data of the amorphous alloy has been fitted successfully to the generalized Johnson-Mehl-Avrami equation. The mean time exponent, n, obtained is close to 2.5. The value of n=2.5 may be interpreted as being due to a diffusion-controlled transformation process with a constant nucleation rate, one likely transformation mode for the crystallization of metallic amorphous alloys. The activation energy of the overall crystallization process deduced from the time to 50% crystallization are about 81 kcal/mole. The value is of the same order as those estimated from viscous flow.

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Selective Crystallization of SAPO-5 and SAPO-34 Molecular Sieves in Alkaline Condition: Effect of Heating Method

  • Yoon, Ji-Woong;Jhung, Sung-Hwa;Kim, Young-Ho;Park, Sang-Eon;Chang, Jong-San
    • Bulletin of the Korean Chemical Society
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    • v.26 no.4
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    • pp.558-562
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    • 2005
  • Crystallization of SAPO-5 and SAPO-34 molecular sieves with microwave and conventional electric heating of the same gel has been investigated in an alkaline condition using N,N,N’N’tetraethylethylenediamine as a template molecule. SAPO-5 structure can be selectively prepared with microwave heating because of the fast crystallization of the technique. On the other hand, SAPO-34 is the sole product with usual conventional electric heating because SAPO-5 can be gradually transformed into SAPO-34 structure with an increase in crystallization time. This phase selectivity is probably because of the relative stability of the two phases at the reaction conditions (kinetic effect). Crystallization with microwave heating can be suggested as a phase selective synthesis method for relatively unstable materials because of fast crystallization.

Effects of Crystallization Behavior on Microwave Dielectric Properties of CaMgSi2O6 Glass-Ceramics

  • Choi, Bo Kyeong;Kim, Eung Soo
    • Journal of the Korean Ceramic Society
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    • v.50 no.1
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    • pp.70-74
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    • 2013
  • Dependence of microwave dielectric properties on the crystallization behaviors of $CaMgSi_2O_6$ (diopside) glass-ceramics was investigated with different heat treatment methods (one and/or two-step). The crystallization behaviors of the specimens, crystallite size and degree of crystallization, were evaluated by differential thermal analysis (DTA), scanning electron microscope (SEM) and X-ray diffraction (XRD) analysis by combined Rietveld and reference intensity ratio (RIR) methods. With an increase in heattreatment temperature, the dielectric constant (K) and the quality factor (Qf) increased due to the increase of the crystallite size and degree of crystallization. The specimens heat-treated by the two-step method had a higher degree of crystallization than the specimens heat-treated by the one-step method, which induced improvement in the quality factor (Qf) of the specimens.

Effects of salt crystallization on stone durability (염분의 결정화 현상이 석재 내구성에 끼치는 영향)

  • 김성수
    • Economic and Environmental Geology
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    • v.32 no.2
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    • pp.203-208
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    • 1999
  • The main objective of this study is to suggest a new assessment method of the influence of weathering due to salt crystallization on the engineering property of rock. For this purpose, various sources of salt and salt crystallization were investigated, and artificially accelerated weathering tests were carried out. In natural envionment, weathering rate is very slow and weathering process involves complex mechanisms. Therefore artificial weathering test is essential for systematic analysis. Arificial weathering test is defined as test which controls weathering rate and agents by controlling arificial environmental condition. In this study, salt crystallization test was selected among various artificial weathering test methods, for its important role in weathering. Change of various stone properties were detexted. The change of physical properties by salt crystallization were observed as follows : 72% in Brazilian tensile strength and 72% in Slake durability. These results explain the importance of salt crystallization in the mechanical behaviour and properties of stone.

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Joule-heating Induced Crystallization (JIC) of Amorphous Silicon Films

  • Ko, Da-Yeong;Ro, Jae-Sang
    • Journal of the Microelectronics and Packaging Society
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    • v.25 no.4
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    • pp.101-104
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    • 2018
  • An electric field was applied to a Mo conductive layer in the sandwiched structure of $glass/SiO_2/Mo/SiO_2/a-Si$ to induce Joule heating in order to generate the intense heat needed to carry out the crystallization of amorphous silicon. Polycrystalline silicon was produced via Joule heating through a solid state transformation. Blanket crystallization was accomplished within the range of millisecond, thus demonstrating the possibility of a new crystallization route for amorphous silicon films. The grain size of JIC poly-Si can be varied from few tens of nanometers to the one having the larger grain size exceeding that of excimer laser crystallized (ELC) poly-Si according to transmission electron microscopy. We report here the blanket crystallization of amorphous silicon films using the $2^{nd}$ generation glass substrate.

The Effect of Crystallization Condition on the Crystallization Rate of Zeolite A (제올라이트 A의 결정화 속도에 대한 결정화 조건의 영향)

  • Chung, Kyeong-Hwan;Seo, Gon
    • Applied Chemistry for Engineering
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    • v.4 no.1
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    • pp.94-102
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    • 1993
  • The effects of temperature and of $Na_2O$ and $SiO_2$ contents on the crystallization of zeolite A were studied, by examining crystallization curves and particle size distributions of final products at various crystallization conditions. Crystallization process could be simulated adopting the assumptions of constant linear growth rate and equilibrium between amorphous solid phase and soluble species. Rate constants were determined by comparing the simulated crystallization curves with experimental data. Rate constant for linear growth increased with temperature and crystallization rate at different mole ratio of $Na_2O/H_2O$ correlated reasonably well with increase of soluble species. The rate constant of crystallization did not increase with increase in mole ratio of $Na_2O/H_2O$, but the rate of nuclei formation and the fraction of soluble species were enhanced. The rate constants for linear growth of zeolite A were determined as $0.07{\sim}0.24{\mu}m{\cdot}min^{-1}$ at these experimental conditions Apparent activation energy was estimated as $49kJ{\cdot}mol^{-1}$.

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