• Polymer(Korea)
• /
• v.27 no.6
• /
• pp.521-527
• /
• 2003

It was found that polypropylene shows rearrangement of crystal structure during the melting process. For the analysis of recrystallization behavior, the change of dynamic mechanical property, crystallinity, and crystal structure were studied by DSC, FT-IR, SAXS, and DMA. Melt-recrystallization-remelting behavior of iPP was clearly observed when iPP was cooled down kom the melt more rapidly. Elastic modulus of iPP increased during the recrystallization process but crystallinity of iPP shows constant value. Furthermore, the full width of half mean of SAXS pattern decreased about 30%, and intra-lamella ordering of iPP increased during the melt process but is was not found for sPP.

• Journal of the Korean Ceramic Society
• /
• v.44 no.11
• /
• pp.613-617
• /
• 2007

The variations of physical and dielectric properties of low temperature dielectrics based on typical aluminoborosilicate glasses modified with several divalent oxides were investigated. The divalent oxides studied here included CaO, MgO, BaO, SrO and ZnO. All samples containing either 35 wt% or 45 wt% alumina filler were prepared at the same processing condition and then fired at $850^{\circ}C$ for 30 min. The resultant characteristics of fired samples depended on the choice of the divalent ion and the content of the alumina filler. Except for the ZnO modification, all other samples containing 35 wt% filler demonstrated promising densification as they exhibited reasonably high densities of 3.07-3.31 $g/cm^3$ and high shrinkages of 14.0-16.4%. Particularly, the sample containing ZnO was distinguished with large variations compared to the base sample, which can be highlighted with earlier densification and crystallization at unexpectedly low temperatures. The negative effects of the ZnO modification on densification and dielectric properties were thought to be associated with earlier crystallization potentially by influencing effective densification via viscous flow. As an optimum composition, the sample containing only CaO showed the most promising characteristics such as $k{\sim}8.05$ and $tan{\delta}{\sim}0.0018$ when 35 wt% alumina filler was used.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
• /
• v.12 no.2
• /
• pp.15-20
• /
• 1998

The furfural, generated by decomposition of insulating paper, the amount of metal in insulating oil, and tano(electrical properties of insulating oil)have been studied for the insulating oil in pole transformer with accelarated thermal aging test. It has been found that tan $\delta$ is affected by adding components of the transformer. The examination of amount of metal, which exhibits catalytic behavior to oxidation of insulating oil, suggested that the amounts of copper increase with degradation time. A comparison between tano and copper amount suggested that the amounts of copper for attention are above 0.2[pp]). Finally, the examination of amount of furfural revealed that the amounts of furfural increase with degradation time. As a consequence, these results could be used for diagnosis of pole transformer.former.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2008.06a
• /
• pp.347-347
• /
• 2008

본 연구에서는 별도의 소결과정 없이 상온에서 치밀한 복합체 후막의 제조가 가능한 Aerosol Deposition Method (ADM)를 이용하여 SOP를 실현시키기 위한 기판 재료로서 알루미나 기반의 알루미나-폴리이미드 복합체를 제조하고 그 특성에 대한 평가를 진행하였다. SEM 관찰결과 기공이 거의 없고 치밀한 구조의 복합체가 상온에서 성공적으로 형성되었음이 확인되었다. XRD 와 FT-IR 분석 결과 알루미나와 폴리이미드 모두가 복합체에 존재함을 확인할 수 있었다. 또한 XRD 분석결과 출발 원료에 폴리이미드 함량이 증가할수록 ADM으로 제조된 복합체 내부의 알루미나의 결정자 크기가 증가하는 결과를 보였다. 복합체의 알루미나 충진율을 확인하기 위한 간접적인 방법으로 복합체 후막을 연마하여 복합체 내부를 노출시킨 후 폴리이미드의 용매인 Methyl Ethyl Ketone으로 폴리이미드를 식각시켜 남아있는 알루미나 영역을 관찰한 SEM 분석결과 알루미나가 60% 이상 복합체의 대부분을 이루고 있다는 사실을 관찰할 수 있었다. 복합체의 미세구조를 확인하기 위하여 TEM 분석결과 기존에 보고된 ADM으로 제조된 알루미나 후막의 결정자 크기인 10~20 nm 보다 큰 100 nm 범위의 결정자 크기를 관찰 할 수 있었다. 유전특성평가 결과 유전율과 tan$\delta$는 1 MHz에서 각각 9.0, 0.0072로서 알루미나만을 원료로 성막시킨 후막의 유전 특성을 크게 떨어뜨리지 않으며 알루미나 후막과 유사한 결과를 보였다. 추후 복합체의 균일성 향상 및 고주파 영역의 유전 특성 향상을 통하여 세라믹의 취성 및 가공성이 개선된 3 차원 적층 기판재료로의 응용이 기대될 것으로 전망된다.

• Transactions on Electrical and Electronic Materials
• /
• v.10 no.6
• /
• pp.217-221
• /
• 2009

The use of the carbon nanotube (CNT) is superior to the general powder state materials in their thermal and chemical properties. Because its ratio of diameter to length (aspect ratio) is very large, it is known to be a type of ideal nano-reinforcement material. Based on this advantage, the existing carbon black of the semiconductive shield materials used in power cables can acquire excellent properties by the use of a small amount of CNTs. Therefore, we fabricated specimens using a solution mixing method. We investigated the thermal properties of the CNT, such as its storage modulus, loss modulus, and its tan delta using a dynamic mechanical analysis 2980. We found that a high thermal resistance level is demonstrated by using a small amount of CNTs. We also investigated the chemical properties of the CNT, such as the oxidation reaction by using Fourier transform infrared spectroscopy (FT-IR) made by Travel IR. In the case of the FT-IR tests, we searched for some degree of oxidation by detecting the carboxyl group (C=O). The results confirm a tendency for a high cross-linking density in a new network in which the CNTs situated between the carbon black constituent molecules show a bond using similar constructive properties.

• Journal of the Korean Chemical Society
• /
• v.55 no.6
• /
• pp.932-935
• /
• 2011

Using tetrabutyl titanate as precursor, $Eu^{3+}$ doped $TiO_2$ nano-powder was prepared by sol-gel method, the nature of luminescence of nano-powder was studied. The interaction of chlorpyrifos with $Eu^{3+}$ doped $TiO_2$ was studied by absorption and fluorescence spectroscopy. The results indicated the fluorescence intensity of $Eu^{3+}$ doped $TiO_2$ was quenched by chlorpyrifos and the quenching rate constant ($k_q$) was $1.24{\times}10^{11}\;L/mol{\cdot}s$ according to the Stern-Volmer equation. The dynamics of photoinduced electron transfer from chlorpyrifos to conduction band of $TiO_2$ nanoparticle was observed and the mechanism of electron transfer had been confirmed by the calculation of free energy change (${\Delta}G_{et}$) by applying Rehm-Weller equation as well as energy level diagram. A new rapid method for detection of chlorpyrifos was established according to the fluorescence intensity of $Eu^{3+}$ doped $TiO_2$ was proportional to chlorpyrifos concentration. The range of detection was $5.0{\times}10^{-10}-2.5{\times}10^{-7}mol/L$ and the election limit ($3{\sigma}$) was $3.2{\times}10^{-11}$ mol/L.

• Journal of the Korean Magnetics Society
• /
• v.24 no.2
• /
• pp.56-59
• /
• 2014

The samples of $Ba_2CoZnFe_{12}O_{22}$ was synthesized by the solid-state reaction method. The toroids of $Ba_2CoZnFe_{12}O_{22}$ were sintered with various sintering temperature at 1050, 1100, 1150, and $1200^{\circ}C$, and studied by x-ray diffractometer, vibrating sample magnetometer, network analyzer, and Mssbauer spectrometer. From the XRD patterns, the density of samples increased with increasing sintering temperature. From the magnetic hysteresis curves up to 10 kOe at 295 K, the saturation magnetization ($M_s$) of $Ba_2CoZnFe_{12}O_{22}$ samples in various sintered at 1050, 1100, 1150 ,and $1200^{\circ}C$ were showed around $M_s$= 33.0 emu/g. However, With increasing sintering temperature, the coercivity ($H_c$) of samples decrease. Complex permeability and permittivity of samples in various sintering temperatures were measured between 100MHz to 4 GHz. With increasing sintering temperature, the permeability of samples increase.

• Elastomers and Composites
• /
• v.37 no.2
• /
• pp.86-98
• /
• 2002

The application of silica/carbon black dual phase fillers to natural rubber(NR) compound was investigated. When the amounts of filler content were restricted to 60phr, the optimum ratio of dual phase fillers were 25phr/35phr of silica/carbon black. It was found that these new fillers give better overall performance in comparison with carbon black in tear strength, crack resistance, and cutting resistance. Also the thermal degradation resistance of NR vulcanizates which were filled with dual phase fillers was better than that of the carbon black. Dual phase fillers filled NR vulcanizates showed better viscoelastic properties, like tan${\delta}$, for the wet skid resistance and rolling resistance of motor vehicle tires.

• Elastomers and Composites
• /
• v.34 no.1
• /
• pp.53-64
• /
• 1999

The mechanical, electrical, and thermal properties of polyamide-modified poly (vinyl chloride) (PVC)-sol was investigated. PVC-sol was plasticized with dioctyl phthalate (DOP). In this work, the effects of the addition of polyamide on the properties of PVC-sol seal-ants were investigated. Two kinds of polyamide resins having different amine value were used. It was found that the properties of the PVC-sol sealants were significantly affected by the contents and types of the added polyamide rosins. The PVC-sol sealants modified with polyamide A (low amino value) showed higher tensile properties than those modified with polyamide B(high amino value) did, and thermal stability of the sealants showed nearly the same trends. The tensile strength of sealants were decreased with increasing the $CaCO_3$ contents. The dielectric constant were not strongly dependent on the polyamide types and contents.

• Elastomers and Composites
• /
• v.39 no.2
• /
• pp.95-104
• /
• 2004

New compounds were made using various NR/BR blend ratio and oil content to improve mechanical properties of rubber isolator at low temperature. Mechanical properties were investigated as a function of NR/BR blend ratio and oil content. Hardness and tensile modulus generally increased, but tensile strength and elongation at break decreased with increasing BR content. Hardness, tensile modulus and tensile strength decreased, but elongation at break were nearly the same with increasing oil content. The glass transition temperature of NR and BR were found to be $-50^{\circ}C$ and $-90^{\circ}C$ respectively based on the abrupt drops in storage elastic modulus and peak of loss factor. Two distinct transition temperature were observed in NR/BR blend compounds and each transition point was not affected by blend level indicating incompatible nature of NR/BR blend.