• 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.

• 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.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part 1
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• pp.242-243
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• 2006

NiTiZrSiSn bulk metallic glass powder was produced using inert gas atomization and then was sprayed onto a SS 41 mild steel substrate using the kinetic spraying process. Through this study, the effects of thermal energy of in-flight particle and crystallization degree by powder preheating temperature were evaluated. The deformation behavior of bulk metallic glass is very interesting and it is largely dependent on the temperature. The crystalline phase formation at impact interface was dependent on the in-flight particle temperature. In addition, variations in the impact behavior need to be considered at high strain rate and in-flight particle temperature.

• 한국섬유공학회:학술대회논문집
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• 한국섬유공학회 2003년도 The Korea-Japan Joint Symposium
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• pp.5-6
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• 2003

Kinetic study on the colloidal crystallization of single component and mixture of different sizes or densities of spheres was made in the exhaustively deionized suspensions and in microgravity, and compared with the results in normal gravity. Colloidal crystallization rates were retarded in microgravity for single component of spheres, whereas rates of alloy crystallization were enhanced substantially in microgravity. The rotational diffusion coefficients of colloids and the formation reaction rates of colloidal silica spheres were also studied in microgravity.

• 한국세라믹학회지
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• 제35권11호
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• pp.1162-1170
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• 1998

PbO-TiO2-B2O3-BaO 계 유리상에서 PbTiO3의 결정화 메커니즘에 대한 이론적 고찰 및 전자현미경 관찰 그리고 결정화 기구의 열시차 분석에 대한 응용성을 조사하였다. 열시차 분석에 대한 Kissinger 식의 응용은 DTA 분석시 시료내 핵밀도가 변하지 않을 때 적용할 수 있으며, 표면결정화를 유도하기 위해 분말시료를 사용하는 경우도 활성화 에너지를 시료의 결정화 메커니즘에 크게 영향을 받는다. Ozawa 식에 의한 Avrami parameter n은 전자현미경 관찰에 의해 파악된 결정화메커니즘과 잘 일치하고 있었으며, 수정 Kissinger 식은 시료의 결정화 메커니즘을 반영하고 있어 시료의 전처리와 관계없이 참값의 활성화에너지를 구할 수 있다.

• 한국세라믹학회지
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• 제30권5호
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• pp.389-396
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• 1993

We studied the crystallization behavior of amorphous PbTiO3 thin film grown at 30$0^{\circ}C$ by RF magnetron sputtering on Pt substrate. Crystallization to full perovskite phase was observed after annealing at 475$^{\circ}C$, for 9min, without PbO volatilization. The higher the annealing temperature, the shorter the time required for crystallization. The isothermal kinetic study at 475$^{\circ}C$ showed that the Avrami constant was approximately 4, which implies that the crystallization can be characterized by isotropic 3-dimensional growth with a constant nucleation rate. The TEM study revealed that the crystallized thin film was composed of very fine (20~100nm) grains oriented randomly without any evidence of 90$^{\circ}$domain boundaries.

• 한국포장학회지
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• 제21권3호
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• pp.107-113
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• 2015

This work focused on the study of thermal properties and kinetic behavior of LDPE-nanoclay composite films. The effect of nanoclay content (0.5, 1, 3, and 5 wt%) on thermal stability and crystallization characteristics of the nanocomposites were investigated by Thermogravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC). The results from endothermic curve showed that the nanoclay played an important role in the crystallization of nanocomposites by acting as nucleating agent. From exothermic curve, there was a crystallization temperature shift which was attributed to crystallization process induced by nanoclay. The TGA results showed that the addition of nanoclay significantly increased the thermal stability of LDPE matrix, which was likely due to the characteristic of layered silicates/clays dispersed in LDPE matrix as well as the formation of multilayered carbonaceous-silicate char. A well-known Coats-Redfern method was used to evaluate the decomposition activation energy of nanocomposite. It was demonstrated that introducing of nanoclay to LDPE matrix escalated the activation energy of nanocomposite decomposition resulting in thermal stability improvement.

• 유변학
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• 제9권4호
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• pp.174-182
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• 1997

결정성 고분자수지는 가공조건에 의해 결정되는 미세구조의 변화에 따라 최종물성 이 현저히 달라지므로 최종 성형품의 물성을 극대화하기 위해서는 성형가공 중에 필연적으 로 부가되는 열이력 뿐만 아니라 전단이력이 결정화 거동에 미치는 영향을 규명하고 가공조 건의 최적화를 통하여 미세구조를 적절히 제어하는 것이 요구된다. 따라서 본 연구에서 in-situ 상태로 전단유도 결정화거동을 조사할수 있는 rheo-kinetic 실험 방법을 개발하고 결정화 거동에 미치는 열이력과 전단이력의 영향을 규명하고자 하였다. 이를 위해 비교적 결정화 속도가 빠른 폴리 부틸렌 테레프탈레이트 수지를 대상으로 냉각조건, 전단부가시간, 전단속도등을 다양하게 변화시키면서 plate-plate 레오미터로 시간에 따른 전단응력의 변화 를 조사하는 rheo-kinetic 연구를 수행하였다. 아울러 실험 중에 액체 질소로 급냉하여 얻은 시료를 대상으로 등온 및 비등온의 열분석 실험을 수행하고 JMA식과 Hoffman-Lauritzentlr 을 사용하여 분석한 다음, 그 결과를 rheo-kinetic 해석결과와 비교함으로써 결정화 거동에 미치는 전단응력의 영향을 규명하였다. 일정전단속동하에서 수행한 rheo-kinetic 실험결과, 시간에 따른 저난응력의 증가와 용융열이 증가하는 경향이 매우 유사한 거동을 보이므로 전 단응력의 증가는 결정화가 일어남에 기인한 결과임을 확인할수 있었으며 고분자수지가 전단 이력을 받게 되면 분자배향의 결과로 결정화 유도시간이 짧아지고 결정화속도가 증가할 뿐 만 아니라 보다 더 높은 온도에서 결정화가 일어나게 됨을 알수 있었다. 또 결정화 반가기 시간과 Hoffman-Lauritzen 식의 매개변수들이 전단속도, 전단부가시간, 결정화 온도 등의 이력에 무관하게 전단응력에 따라 선형적으로 변하고 있으므로 전단유도 결정화거동은 수지 에 부가되는 전단응력에 직접적인 영향을 받음을 알수 있었다. 이상과같은 전단유도 결정화 거동에 관한 결과를 가공공정상의 열전달 현상과 결합하여 해서하면 성형품 내부의모폴로지 의 예측이 가능하므로 성형품 물성의 극대화 방안의 수립에 이용될수 있을것으로 사료된다.

• Bulletin of the Korean Chemical Society
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• 제26권4호
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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.

• 한국물환경학회지
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• 제26권4호
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• pp.664-672
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• 2010

This study was performed to evaluate the feasibility of industrial by-products such as converter slag, olivine, red mud and fly ash as a seed crystal of struvite crystallization for the removal of highly concentrated $NH_4-N$ and $PO_4-P$. In the kinetic experiments, more than 90% of $NH_4-N$ and $PO_4-P$ was eliminated by struvite crystallization within 30 minutes of reaction time. The pH range in meta-stable region of struvite crystallization was found to be pH 7.0~9.0 under the Mg:N:P=1:1:1 equi-molar condition with 100 mg/L of $NH_4-N$. Total removal efficiencies of $NH_4-N$ and $PO_4-P$ by both struvite precipitation and crystallization were increased with the increase of pH. Removal efficiencies of $NH_4-N$ and $PO_4-P$ were significantly enhanced by struvite crystallization using industrial by-products as a seed crystal compared with those by struvite precipitation without seed crystal. Red mud, converter slag, olivine and fly ash enhanced the removal efficiencies of $NH_4-N$ by 40.9%, 37.7%, 28.4% and 16.4%, respectively. Removal efficiencies of $PO_4-P$ for converter slag, red mud, fly ash, olivine were increased by 3.7 times, 2.6 times, 72.4% and 68.0%, respectively. Converter slag and red mud showed higher feasibility as a seed crystal than others for the removal of highly concentrated $NH_4-N$ and $PO_4-P$. In particular, converter slag might have a high capacity of phosphorus removal.