• 한국산학기술학회논문지
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• 제16권4호
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• pp.2945-2950
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• 2015

경질 폴리우레탄 폼(RPUF) 제조에서의 단열성 향상을 위하여 사용되는 PFA (Perfluoroalkane)는 액상의 발포 기핵제로서 성능은 뛰어나지만 매우 고가일 뿐만 아니라 불소화합물로서 환경 유해성 물질이다. 따라서 이를 대체할 수 있는 고성능의 대체 기핵제 개발에 대한 많은 연구가 진행되고 있다. 본 연구에서는 이에 대하여 다중벽 탄소나노튜브(MWCNT)를 고상 기핵제로 사용하여 제조한 샘플에서의 셀 크기 및 단열 성능과 기계적 물성에 미치는 영향을 비교 연구하여 보고자 하였다. 셀의 평균크기는 $165.6{\mu}m$에서 $162.9{\mu}m$로 상대적으로 더 작아졌으며, 표준 편차 역시 각각 45.6 및 35.2로서 상대적으로 더 균일한 셀 크기 분포를 가진 것으로 나타났다. k-factor 값 역시 0.01763 및 $0.01745kcal/m.hr.^{\circ}C$의 값으로서 1.02%가 감소된 더 작은 값을 나타내었다. 또한 압축 응력 시험에서의 초기 모듈러스는 상대적으로 더 큰 값을 나타내었으나 압축항복 응력은 약 $0.030{\times}105Pa$로서 거의 같은 값을 나타내었다. 이러한 결과들로 부터 MWCNT는 매우 우수한 기핵제로 작용함을 알 수 있었고, 따라서 소량의 MWCNT를 기핵제로 사용하여 경제적이면서도 우수한 단열효과와 기계적 물성을 지닌 친환경적인 경질 폴리우레탄 폼을 제조할 수 있음을 알 수 있었다.

• 한국세라믹학회지
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• 제28권5호
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• pp.406-414
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• 1991

The composition of base glass was selected as MgO 8, Al2O3 24, SiO2 68 in weight percent. TiO2 and ZrO2 were added to the base glass to investigate their effects as nucleating agents. In the case of ZrO2 addition, the optimum temperature for nucleation, which was related to the precipitation of tetragonal ZrO2, was 80$0^{\circ}C$. The optimum growth condition for the crystal was 87$0^{\circ}C$ for 8 hrs, and the major crystal phases precipitated in the samples were $\beta$-quartz ss. and mullite. The light transmissivity turned out to be around 80 per cent. On the other hand, when the TiO2 was added, it was difficult to determine the nucleating temperature, because the samples turned easily into translucency during the heat treatment. Therefore, it was almost impossible to retain transparency in the samples. The light transmissivity was below 30 per cent.

• Advances in materials Research
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• 제4권4호
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• pp.207-214
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• 2015

It has been reported in the technical literature that orotic acid can be used in order to induce improved crystallization of biodegradable and biocompatible polymers like poly(L-lactic acid), polyhydroxybutyrate and poly(hydroxybutyrate-co-hydroxyhexaonat). The expected advantage of the changed crystalline structure is a reinforcing effect of the polymers. A lot of papers reported about the application of inorganic and organic agents for acceleration of heterogeneous nucleation. This study reports on an attempt to use orotic acid as appropriate non-toxic nucleating agent for improving mechanical properties of isotactic polypropylene. Special attention is given to demonstrate the effect of nucleation in a typical melt spinning process in order to improve the mechanical properties. The effects were demonstrated using rheology, thermal analysis and tensile testing.

• 한국세라믹학회지
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• 제26권3호
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• pp.315-322
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• 1989

Li2O-Al2O3-SiO2 system glasses contained P2O5, TiO2 and ZrO2as the nucleating agents were melted and formed. The glass was subsequently heated first to nucleate and then to grow the crystals. At constant nucleating agent content the base glass compositions were varied and the influences of these variations on the crystallization behaviour were investigated. The study was made by measurement of thermal expansion coefficient, differential thermal analysis, X-ray diffraction analysis, scanning electron microscope observation and transmission measurement of crystallized glass specimen in visible region. It was shown that the content of crystalline phase decreased with increasing SiO2 content as well as decresing Li2O in the base glass compositions. As the result of X-ray diffrection analysis, the major crystal was $\beta$-quartz solid solution. The degree of crystallinity which was calculated using the noncrystalline scattering methods increased in S-shape with increasing heat treatment time. This change was similar to that in thermal expansion coefficient. The transmissions of 5mm thick samples were 80-90% in visible ray region.

• 한국산학기술학회논문지
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• 제13권6호
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• pp.2846-2851
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• 2012

미세하게 분쇄된 폐타이어 분말(GTR)과 미발포 $Expancel^{(R)}$ 분말이 경질 폴리우레탄 발포체(PUF)의 열전도 특성에 미치는 영향을 연구하였다. 마이크론 크기로 분쇄된 GTR과 $100^{\circ}C$ 이상의 온도 영역에서 약 40배 부피로 팽창 가능한 $Expancel^{(R)}$ 미세분말을 사용하였고 이들이 경질 PUF 생성 시의 발포 기핵제 역할에 의한 기포크기 감소효과 및 이로 인한 PUF의 열전도특성 개선 효과를 집중적으로 살펴보았다. 연구의 결과로서, GTR이 충전된 PUF 샘플들의 열전도도는 GTR 함량이 증가함에 따라 선형적으로 증가하는 현상을 나타내는 반면, $Expancel^{(R)}$이 도입된 샘플들은 농도에 따라 약간 감소하는 특성을 보여 주었다. 이러한 결과로부터 GTR은 PUF 생성에서 증량제의 역할이 상대적으로 우세하여 단열 특성에 기여하지 못하는 반면, $Expancel^{(R)}$은 분말의 표면극성으로 인한 발포 기핵 작용에 의하여 셀 크기를 감소시킴으로서 단열효과에 기여할 수 있는 것으로 생각되었다.

• 한국세라믹학회지
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• 제18권1호
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• pp.3-12
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• 1981

A glass-ceramics based on blast-furnace slag, with some additives to the theoretical composition in order to control properties of mother glass and the heat treatment conditions, has been investigated. The raw materials in this study were blast-furnace slag, serpentine, feldspar and quartz as mother glass ingredients. Titanium dioxide and chromite were used as the nucleating agents. Batch compositions of the prepared glasses and ceraming conditions were found by trial and error method. The optimum conditions were confirmed by analyzing several measured physical properties such as density change during heat treatment, microhardness of slag-ceramics prepared, viscosity change of glass at heat treatment temperatures, nucleation density change, dilatometric properties, differential thermal analysis, identification of the grown crystal and crystal sizes. The batch composition feasible to prepare slag-ceramics was 40% of blast-furnace slag, 25% of serpentine, 18% of feldspar and 17% of silica sand. Three percent titanium dioxide and 1% chromite of the mother glass were added as nucleating agents. The ceraming conditions under which the slag-ceramics having considerably good properties can be developed found as: "The glass was heated at 75$0^{\circ}C$ for 2 hours for nucleation, and the temperature was raised up to 1, 00$0^{\circ}C$ with a rate of 0.75$^{\circ}C$/min for crystal growth.owth.

• 폴리머
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• 제39권2호
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• pp.268-274
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• 2015

In this paper, the isothermal crystallization kinetics of a functional PP (FPP) with different grafting yields (GY)-methacryloxyethyltrimethyl ammonium chloride (DMC) grafted PP were investigated by differential scanning calorimetry (DSC). The results showed that the crystallization rate of FPP (GY=4.83%) was the highest for all of the studied samples. Furthermore, for the FPP with different GY, the value of $t_{1/2}$ became longer with increasing the grafting yield (GY). The possible explanation was that the quaternary ammonium groups introduced affected the crystallization process of the FPP in two opposite directions, i.e. promoting the nucleation and hindering the transport of the chain molecules towards the growing nuclei. Polarized optical micrographs showed that the DMC chains acted as nucleating agents, which accelerated the nucleation. In addition, the results showed the FPP had lower nucleation free energy than the PP. This study would be useful for designing the processing parameters of the grafted samples.

• 한국전기전자재료학회논문지
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• 제26권12호
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• pp.920-923
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• 2013

In this paper, the characteristics of a carbon nanotube composite heat sink proposed to replace the advanced Al heat sinks for LED lighting devices were studied. Proposed CMP-PLA heat sink was made by mixing 20~70 wt% carbon nanotube, 20~70 wt% bio-degradable polymer of melt-blended PLA (poly lactic acid) and PBS (poly butylene succinate) and PLA nucleating agents composed of the mixture of soybean oil and biotites, at $150{\sim}220^{\circ}C$ with 1,000~1,500 rpm. Optical and electric characteristics of 7.5 W LED lighting devices using heat sinks with such prepared CMP-PLA were investigated. And, the properties of the heat, which was not released from the CMP-PLA type heat sinks, was also investigated. The color temperature of LED lighting devices using the CMP-PLA heat sinks was 5,956 K, which is x= 0.32 and y= 0.34 in the XY chromaticity, and the color rendering index was 75. The luminous flux and the luminous efficiency of LED lighting devices using the CMP-PLA heat sinks was 540.6 lm and 72.68 lm/W respectively. Measured initial temperature of the heat sinks was $27^{\circ}C$, and their temperature increased as time to be saturated at $52^{\circ}C$ after an hour.

• Bulletin of the Korean Chemical Society
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• 제32권7호
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• pp.2369-2376
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• 2011

Effect of heat treatment of carbon nanofibers (CNF) on electrical properties and crystallization behavior of polypropylene was reported. Two types of CNFs (untreated and heat treated at 2300 $^{\circ}C$) were incorporated into polypropylene (PP) using intensive mixing. A significant drop in volume resistivity was observed with composites containing untreated 5 wt % and heat treated 3 wt % CNF. In non-isothermal crystallization studies, both untreated and heat treated CNFs acted as nucleating agents. Composites with heat treated CNFs showed a higher crystallization temperature than composites with untreated CNFs did. TEM results of CNF revealed that an irregular structure of CNFs can be converted into the continuous graphitic structure after heat treatment. Furthermore, STM showed that the higher carbonization temperature leads to the higher graphite degree which presents the larger carbon network size, suggesting that a more graphitic structure of CNFs led to a higher crystallization temperature of PP.

• 한국세라믹학회지
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• 제54권5호
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• pp.395-399
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• 2017

The thermal properties and crystallization behavior of calcium phosphate glass fabricated using eggshell were examined. Nature eggshell has several impurities in the main component of $CaCO_3$. To manufacture calcium phosphate glass, washed eggshell was dissolved in aqua-regia while adding a solution of isopropyl alcohol, D. I. water and phosphoric acid. The calcined precursor was melted at $1000^{\circ}C$, and the glass ($T_g$ : $540^{\circ}C$) was crystallized at $620{\sim}640^{\circ}C$, which temperature range is relatively low compared to the crystallization temperature of other general types of calcium phosphate glass. The calcium phosphate glass using eggshell was successfully crystallized without any additional nucleating agents due to the multiple effects of impurities such as $Fe_2O_3$, $Al_2O_3$, SrO and $SiO_2$ in the eggshell. The main crystalline phase was ${\beta}-Ca(PO_3)_2$ and a biocompatible material, hydroxyapatite, was also observed. The crystallization process was completed under the condition of a holding time of only 1 h at the low temperature.