• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.06a
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• pp.340-341
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• 2008

본 논문에서는 미세 패턴을 구현하기 위해 폴리머 소재의 조성에 따른 공정의 영향에 대해서 연구를 하였다. 제작된 본딩 필름은 난연계 에폭시수지와 고내열 특성을 위해서 경화제 조화 성분 폴리머를 이용하였다. 또한, CTE 값을 향상하기 위해서 필러로서 SiO2 분말을 이용하였다. 조성물은 혼합하여 슬러리를 만들고, 테입 캐스터를 이용하여 필름을 제작하였다. 제작된 필름은 150 및 160도의 온도에서 가열 가압하여 경화하였다. 제작된 수지는 유전율 3.2의 유전율과 loss tan 6값이 0.015값을 나타내었다. 또한 제작된 본딩 필름의 조화특성 연구를 위해서 경화조건, 스웰링 조건, 디스미어 시간에 따른공정 변화의 영향에 대해 고찰하였으며 제작된 시편의 조도는 SEM으로 관찰하여 조화성분 함량에 따른 최적 조건을 선정하였다.

• Journal of Electrical Engineering and Technology
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• v.13 no.2
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• pp.892-901
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• 2018

Because of excellent electrical properties, epoxy resin is widely used in packaging and casting power equipment. Moisture and temperature in the environment are inclined to seriously affect the insulation tolerance of epoxy resin. This work focuses on the aging characteristics of epoxy resin in hygrothermal environment. Scanning electron microscopy images show that there are micro-crack, micro-slit and holes inside aged samples. The moisture absorption process undergoes three equilibrium stages and it does not follow the Fick's second law. Observing the change of hydrogen bonds in the infrared spectra of the dried samples, it is found that chemically moisture absorption immerges when the physical moisture absorption entered the third equilibrium stage. By Debye equation to fit the imaginary part of the dielectric constant, it is concluded that the uniformity of water molecule has a great influence on the electrical conductivity loss. Furthermore, the polarization loss can be more easily affected by water molecules than small free molecules. After the aged samples being dried, their real and imaginary part of the dielectric constant descend, but their original electrical properties cannot completely restored. After chemical moisture absorption appears inside the material, the residual space charges increase significantly and the charge dissipation rate slow down obviously.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.18 no.5
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• pp.445-449
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• 2005

Aging phenomena of 0.2PMN-0.8PZT multilayered ceramic actuators(MCA) have been investigated at the room temperature. The piezoelectric materials were synthesized as conventional ceramic process, and MCA were fabricatedby tape casting methods. The crystalline structures and lattice parameters were investigated by X-ray diffraction analysis, showing the structure was tetragonal and c/a was about 1.01. And, the effective electromechanical coupling coefficient keff and pseudo-piezoelectric constant $d_{33}$were measured. Variable unipolar electric fields, $2{\sim}4kV/mm$, were applied to MCh to investigate the aging characteristics. After 2 kV/mm unipolar electric field, keff and $d_{33}$ were 0.454 and 4.44 respectively. The measured and simulated values using for aging phenomena analysis, had a good fit to the linear logarithmic stretched exponential law.

• Macromolecular Research
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• v.14 no.3
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• pp.267-271
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• 2006

Polyelectrolyte complex films were prepared with two compounds, chitosan and poly(ethylene glycol)-monosuccinate, using a casting in order to synthesize a polyelectrolyte complex film with various mole ratios of chitosan and poly(ethylene glycol)-monosuccinate. The solution properties of isolated PEC were investigated for the effects of FTIR, pH value, Brookfield viscosity and cell viability assay using MTT staining. The PEC films were evaluated for mechanical properties by typical stress-strain curve, far thermal properties by DSC and TGA and for surface morphology Properties by SEM. Furthermore, the surface resistance, moisture regain and water content of the films were characterized. The solution properties were affected by several factors including the chitosan content in the PEC, the mixing ratio of PEG and chitosan, and pH. Several PEC in acidic conditions exhibited film formation under appropriate conditions of mixing ratio and chitosan concentration in the mixing process. These PEC films were found to have sufficiently flexible and stable properties due to their hydrophilic structure, which was farmed by the oppositely charged interaction between PEG-MS and chitosan matrix. The results showed the potential applicability of chitosan and poly(ethylene glycol)-monosuccinate films as a biocompatible polymer.

• Nuclear Engineering and Technology
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• v.40 no.3
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• pp.183-190
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• 2008

Pyroprocessing is the optimal means of treating spent metal fuels from metal fast fuel reactors and is proposed as a potential option for GNEP in order to meet the requirements of the next generation fuel cycle. Currently, efforts for research and development are being made not only in the U.S., but also in Asian countries. Electrorefining, cathode processing by distillation, injection casting for fuel fabrication, and waste treatment must be verified by the use of genuine materials, and the engineering scale model of each device must be developed for commercial deployment. Pyroprocessing can be effectively extended to treat oxide fuels by applying an electrochemical reduction, for which various kinds of oxides are examined. A typical morphology change was observed following the electrochemical reduction, while the product composition was estimated through the process flow diagram. The products include much stronger radiation emitter than pure typical LWR Pu or weapon-grade Pu. Nevertheless, institutional measures are unavoidable to ensure proliferation-proof plant operations. The safeguard concept of a pyroprocessing plant was compared with that of a PUREX plant. The pyroprocessing is better adapted for a collocation system positioned with some reactors and a single processing facility rather than for a centralized reprocessing unit with a large scale throughput.

• International Journal of Precision Engineering and Manufacturing
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• v.8 no.2
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• pp.20-25
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• 2007

This paper describes a second-generation dual sine-grid surface encoder for 2-D position measurements. The surface encoder consisted of a 2-D grid with a 2-D sinusoidal pattern on its surface, and a 2-D angle sensor that detected the 2-D profile of the surface grid The 2-D angle sensor design of previously developed first-generation surface encoders was based on geometric optics. To improve the resolution of the surface encoder, we fabricated a 2-D sine-grid with a pitch of $10{\mu}m$. We also established a new optical model for the second-generation surface encoder that utilizes diffraction and interference to generate its measured values. The 2-D sine-grid was fabricated on a workpiece by an ultra precision lathe with the assistance of a fast tool servo. We then performed a UV-casting process to imprint the sine-grid on a transparent plastic film and constructed an experimental setup to realize the second-generation surface encoder. We conducted tests that demonstrated the feasibility of the proposed surface encoder model.

• Proceedings of the Membrane Society of Korea Conference
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• 2003.07a
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• pp.61-64
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• 2003

Optical resolution of a-amino acid (tryptophan and tyrosine) optical isomers was achieved by a pressure driven membrane separation process, using self-supporting crosslinked membranes base on polysaccharide with different swelling indices that ranged from 100 to 70%. The membranes prepared by casting and drying the polymer solution containing 5wt% acetic acid on an acryl plate followed by crosslinking with glutaraldehyde were characterized using such analytical methods as FTIR and swelling index measurements. On the way of separating the optical isomers, several experimental factors such as the concentration of the feed solutions, operating pressure and temperature, and degree of crosslinking of the membranes have been studied. When the chitosan membranes with 70% of swelling index were used , almost complete optical resolution was obtained; 97.92% of enantiomeric excess (ee %) and 2.26 g/$m^2$ㆍh of flux. The operating pressure and the concentration of feed solutions were respectively 1.0 kgf/$\textrm{cm}^2$ and 0.49 mmol/L.

• Journal of Technologic Dentistry
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• v.16 no.1
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• pp.57-77
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• 1994

The purpose of this study is to investigate the extent to which dental laboratories use proper materials, procedures, devices, and equipments to fabricate crown & bridge, PFM(Porcelain Fused to Metal) crown & bridge, partial denture, complete denture, and other prosteses. 100 laboratories in Seoul were selected for this investigation. Questionnaires were constructed focusing on five topocs:crown & bridge, PFM crown & bridge, partial denture, complete denture, and other prostheses. The results from this survey were as follows : 1. Most dental laboratories used old, inexpensive, and familiar materials rather than newly developed ones. 2. Most of the dental technicians did not stick to the standard procedures of handling materials, but to their own experiences. 3. Newly developed equipments to fabricate dental prostheses were possessed by nearly 30% dental laboratories. 4. About 80% of dental laboratories were using the procedures they had learned in the school : die trimming for accurate crown margin and softening heat treatment after RPD gold casting. But less than 30% of laboratories were shown to follow the boxing procedure to produce master cast and laboratory remounting in the process of complete denture. The findings show that dental laboratory procedures to fabricate dental prostheses are incomplete and inaccurate in some instances. So, further studies are neededs to clarify the causes of some inaccurate procedures, the better and more equipments should be supplied to produce the more accurate dental posthesis, and more efforts at enancing the appropriate use of dental materials and procedures should be made.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.11 no.4
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• pp.281-287
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• 1998

$BiNbO_4$ ceramics doped with 0.07wt% $V_2O_5$ and 0.03wt% CuO (BNC3V7) were sucessfully sintered at $900^{\circ}C$ through the firing process with Ag electrode. The BNC3V7 shows typically Dielectric constant of 44.3, Thermal Coefficient of resonance Frequency(TCF) of 2 ppm/$^{\circ} and $Qxf_o$ value of 22,000 GHz. The laminated chip Low Pass Filter (LPF) is very sensitive to chip processing parameters, was confirmed by the computer simulation as a function of Q(Quality factors), filter size, capacitor layer thickness, inductor pattern widths. The multilayer type LPF was fabricated by screen-printing with Ag electrode after tape casting and then compared with the simulated characteristics. The results show that characterization of band pass width was similar to that of designed ones.

• Journal of Korea Foundry Society
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• v.28 no.3
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• pp.129-135
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• 2008

The reheating stage of electromagnetically stirred Al billet is a critical factor in the thixoforming process. When reheated to the solid-liquid state, the microstructure evolves to a more globular and more homogeneous structure by a coarsening mechanism, the kinetics depending on the initial microstructure. Microstructural evolution has been characterized by conventional parameters (mean size of particle and shape factor) as a function of holding time in the solid-liquid state. The aim of this study is to report experimental results concerning microstructural evolution in the solid-liquid state of electromagnetically stirred Al billet. The material was elaborated in the form of continuously cast bars solidified with electromagnetic stirring to degenerate the dendritic structure. The choice of the reheating conditions is determined by a dendritic ripening and coalescence mechanism, involving variations of both the shape and size of the particles. The reheating time has to be long enough to allow a minimum degree of spheroidizing, but has to be limited as much as possible in order to avoid excessive ripening. The optimum microstructure was obtained at the reheating temperature of near $584^{\circ}C$ and the holding time of 5 min. The only means of combining high productivity with good casting quality was to use feedstock billets whose microstructure showed rapid transformation characteristics.