• 한국결정성장학회지
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• 제20권1호
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• pp.58-63
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• 2010

화력 발전소에서 발생하는 석탄 바닥재에 $Na_2O$와 $Li_2O$가 첨가된 결정화 유리를 제조하고, 비등온 열분석법을 이용하여 결정성장 거동을 분석하였다. 온도에 따른 결정화 분율 및 결정화 속도 변화를 계산한 결과, 결정화가 50% 진행된 온도는 DTA 상의 결정 발열피크 $T_p$ 보다 약간 높게 나타났으며, 결정화가 가장 빠르게 진행되는 온도는 $T_p$와 거의 일치함을 알 수 있었다. Kissinger 식을 이용하여 결정화 활성화 에너지(262 kJ/mol), Avrami 상수 (1.7) 그리고 진동수 ($5.7{\times}10^{16}/s$)를 계산하였으며, 이로부터 nepheline 결정 성장은 주로 1~2 차원적 표면 결정화 경향을 보이지만, 동시에 내부 결정화도 어느 정도 나타날 것으로 예측되었다. 실제 미세구조 관찰에서 수지(dendrite)상의 표면 결정화가 상당히 일어났고 동시에 낮은 분율의 내부 결정도 생성된 것이 확인되어, Kissinger식에 의해 예측된 결과가 본 연구에서 제조된 결정화 유리의 거동과 일치함을 알 수 있었다.

• 한국표면공학회지
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• 제41권6호
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• pp.301-307
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• 2008

In this paper, nanocrystallization of CuNiTiZr bulk metallic glass (BMG) subjecting to a kinetic spraying, dependent on impact velocity, was investigated by numerical and experimental approaches. The crystallization fraction and nucleation activation energy of initial feedstock and as-deposited coating were estimated by DSC and Kissinger method, respectively. The results of numerical modeling and experiment showed that the crystalline fraction and nucleation activation energy in BMG coatings were depended on kinetic energy of incident particle. Upon impact, the conversion of particle kinetic energy leads to not only decreasing free energy barrier but also increasing the driving force for an amorphous to crystalline phase transformation. The nanocrystallization of BMGs is associated with the strain energy delivered by a plastic deformation with a high strain rate.

• 한국전기전자재료학회논문지
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• 제15권12호
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• pp.1060-1064
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• 2002

We have studied the effect of crystallization temperature, composition and film thickness, which are the fundamental processing parameters of lead zirconate titanate(PZT) thin film fabrication, in the respect of the piezoelectric properties by our pneumatic loading method(PLM). A great deal of research has been done in the field of characterization for piezoelectric thin films after the first report on the measurement for the piezoelectric coefficient of thin films in 1990. Even though the piezoelectric properties of thin films are very critical factors in the micro-electro mechanical system(MEMS) and thin film sensor devices, a few reports for the piezoelectric characterization are provided for the last decade unlikely the bulk piezoelectric devices. We have found that the piezoelectric properties of thin films are improved as the increase of crystallization temperature up to 750$\^{C}$ and this behavior can be also explained by the analysis of dielectric polarization hysteresis loop, X-ray diffraction and scanning electron microscopy. The effect of Zr/Ti composition has been also studied. This gives us the fact that the maximum piezoelectricity is found near Morphotropic Phase Boundary(MPB) as bulk PZT system does.

• Macromolecular Research
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• 제9권4호
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• pp.228-237
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• 2001

The evolution of conformational constraints in bisphenol-A polycarbonate (BAPC) upon quiescent bulk crystallization was quantitatively analyzed from calorimetric study employing a rigid amorphous fraction (RAF) as an indicator of the level of conformational constraints. From the correlation between corrected crystallinity (X$\sub$c/) and total rigid fraction (f$\sub$r/), it was found that, regardless of molar mass distribution and thermal treatment conditions, semicrystalline BAPC always exhibits greater f$\sub$r/ than X$\sub$c/ maintaining a quantitative relationship of f$\sub$r/〓2X$\sub$c/ in the range of 0.0 $\sub$c/< 0.4. This directly indicates the evolution of approximately the same amount of RAF as X$\sub$c/, (i.e., RAF〓X$\sub$c/) upon bulk crystallization of BAPC. It was also found that T$\sub$g/ per se and T$\sub$g/ broadening enhance as RAF increases, and there appears to be a critical level of RAF (>0.2) needed to initiate significant changes in both quantities.

• Applied Microscopy
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• 제45권2호
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• pp.58-62
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• 2015

Formation of an icosahedral phase in the bulk glass forming $Ti_{40}Zr_{29}Be_{14}Cu_9Ni_8$ alloy during crystallization from amorphous phase and solidification from melt is investigated. The icosahedral phase with a size of 10 to 15 nm forms as a thermodynamically stable phase at intermediate temperature during the transformation from amorphous to crystalline phases such as Laves and ${\beta}$-(Ti-Zr) phases, indicating that the existence of the icosahedral cluster in the undercooled liquid. On the other hand, the icosahedral phase forms as a primary solidification phase even though the Laves phase is stable at high temperature, which is can be explained based on the high nucleation rate of icosahedral phase relative to that of competing crystalline Laves phase due to lower interfacial energy between icosahedral and liquid phases.

• 한국주조공학회지
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• 제28권6호
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• pp.261-267
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• 2008

In-situ quasicrystalline icosahedral (I) phase reinforced Ti-based bulk metallic glass (BMG) matrix composites have been successfully fabricated by using two distinct thermal histories for BMG forming alloy. The BMG composite containing micron-scale Iphase has been introduced by controlling cooling rate during solidification, whereas nano-scale I-phase reinforced BMG composite has been produced by partial crystallization of BMG. For mechanical properties, micron-scale I-phase distributed BMG composite exhibited lower strength and plasticity compared to the monolithic BMG. On the other hand, nano-scale icosahedral phase embedded BMG composite showed enhanced strength and plasticity. These improved mechanical properties were attributed to the multiplication of shear bands and blocking of the shear band propagation in terms of isolation and homogeneous distribution of nanosize icosahdral phases in the glassy matrix, followed by stabilizing the mechanical and deformation instabilities.

• 한국세라믹학회지
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• 제31권12호
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• pp.1545-1551
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• 1994

Various kinetic parameters of the nucleation and crystallization in anorthite glass (CaO.Al2O3.2SiO2) were calculated by nonisothermal differential thermal analysis. Base glass and glass with TiO2 were prepared by melting. In base glass, the temperature where nucleation can occur ranges from 85$0^{\circ}C$ to 9$25^{\circ}C$ and the temperature for maximum nucleation was 900$\pm$5$^{\circ}C$. In glass with TiO2, the nucleation temperature range was 800~875$^{\circ}C$ and the maximum nucleation temperature was 850$\pm$5$^{\circ}C$. Kissinger equation, Bansal equation, and modified Ozawa equation were used for calculating activation energy for crystallization, Ec. The results showed the same activation energies for both glasses with and without TiO2 in the different equations. The shape of maximum exotherm peak and Ozawa equation were used for Avrami exponent, n. The n value for each glass was 2, indicating that each glass crystallized primarily by bulk crystallization.

• 한국세라믹학회지
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• 제26권6호
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• pp.829-835
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• 1989

Devitrifing solder glasses in a specific group of glass ceramic materials are extensively used in hermetically sealing alumina electronics packages. Preferred frit glass compositions of this study consist of 37~40wt% PbO, 35~40wt% ZnO, 18~20wt% B2O3, 1~3wt% SiO2, 0~6wt% TiO2. The coated frit glasses crystallize during firing and form a strong hermetic seal. DTA and X-ray diffraction were used to characterize crystallization of the glass frit. Frit seal containing 2wt% TiO2 has crystallization temperature of 550~57$0^{\circ}C$ with surface nucleation. Frit seal containing 6wt% TiO2 has crystallization temperature of 515~5$25^{\circ}C$ with bulk nucleation, and the main crystalline phase was perovskite lead titanate having minus expansion coefficient. The average activation energy for the crystallization calculated from Ozawa equation was 65$\pm$10kcal/mol.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 1992년도 추계학술대회 논문집
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• pp.77-81
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• 1992

The purpose of this research was th evaluate conductivity of electricity of Ge-Se-Bi system Chalcogenide glass as a amorphous semiconductor by observing its dissolution and crystallization. In this experiment. Ge-Se-Bi metal powder in the rage of $Ge_{12-25}$, $Se_{65-85}$, $Bi_{2.5-15}$ was used as the sample ore. The ore was. put into a vaccous quartz tube and then melted. The condition of heat treatment was to dispose it to $1000^{\circ}C$ heat for 10 hours and then rapidly quenched it at $3834^{\circ}C$/see. The crystallization of the fused sample ripened as the change of temperature and time, after the crystal core was formell. At that time it was possible to observe the state that $Bi_2Se_3$ and $GeSe_2$ were crystallized. In the experiment of making memberance, the memberance was produced by using the previously experimented bulk sample. And decrystalization was well progressed when Ge was over 15 at %, Se was over 70 at %, and Bi was under 10 at%. As for bulk. when Ge was fixed to 20 at %, the conducting of electricity was increased as Bi gained at %. In the case of memberance, the conductivity was much more increased than that of bulk sample as the increase of at the increase of at % of Bi. In the experiment on $Ge_{20}$, $Se_{77.5}$ and $Bi_{2.5}$, the crystallization sswas most vigorous when they were kept at $330^{\circ}C$ for 4 hours.

• Macromolecular Research
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• 제11권1호
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• pp.25-35
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• 2003

A series of random poly(ethylene-co-1,4-butylene terephthalate)s (PEBTs), as well as poly(ethylene terephthalate) (PET) and poly(1,4-butylene terephthalate) (PBT), were synthesized by the bulk polycondensation. Their composition, molecular weight, and thermal properties were determined. All the copolymers are crystallizable, regardless of the compositions, which may originate from both even-atomic-numbered ethylene terephthalate and butylenes terephthalate units that undergo inherently crystallization. Non-isothermal crystallization exotherms were measured over the cooling rate of 2.5-20.0 K/min by calorimetry and then analyzed reasonably by the modified Avrami method rather than the Ozawa method. The results suggest that the primary crystallizations in the copolymers and the homopolymers follow a heterogeneous nucleation and spherulitic growth mechanism. However, when the cooling rate increases and the content of comonomer unit (ethylene glycol or 1,4-butylene glycol) increases, the crystallization behavior still becomes deviated slightly from the prediction of the modified Avrami analysis, which is due to the involvement of secondary crystallization and the formation of relatively low crystallinity. Overall, the crystallization rate is accelerated by increasing cooling rate but still depended on the composition. In addition, the activation energy in the non-isothermal crystallization was estimated.