• Applied Chemistry for Engineering
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• v.4 no.3
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• pp.544-548
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• 1993

Glass transition temperatures($T_g$) of poly(phenylene sulfide sulfone)[PPSS], which were heat treated at various temperature and time, were studied by DSC. Up to $230^{\circ}C$, $T_g$ of heat treated PPSS were increased with increasing the heat treated time. When the sample was heated at $260^{\circ}C$ for 30 minute and $280^{\circ}C$ for 10 minute, however, $T_g$ of those samples were decreased. These phenomena can be explained by the factors of chain extension reaction, oxidative crosslinking, and thermal crosslinking.

• Proceedings of the Korean Reliability Society Conference
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• 2001.06a
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• pp.337-337
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• 2001

High voltage ceramic capacitors are widely applied in power electronic circuits, such as filters, snubbers, and resonant circuits, due to their excellent features of high voltage endurance and low aging. This paper presents a result of failure analysis and reliability evaluation for high voltage ceramic capacitors. The failure nodes and failure mechanisms were identified in order to understand the failure physics in a component. The causes of failure mechanisms for zero resistance phenomena under withstanding voltage test in high voltage ceramic capacitors molded by epoxy resin were studied by establishing an effective closed-loop failure analysis. Also, the condition for dielectric breakdown was investigated. Particular emphasis was placed on breakdown phenomena at the ceramic-epoxy interface. The validity of the results in this study was confirmed by the results of accelerated testing. Thermal shock test as well as pressure cooker test for high voltage ceramic capacitor mounted on a magnetron were implemented. Delamination between ceramic and epoxy, which, might cause electrical short in underlying circuitry, can occur during curing or thermal cycling. The results can be conveniently used to quickly identify defective lots, determine mean time to failure (MTTF) of each lot at the level of Inspection, and detect major changes in the vendors processes.

• Journal of Hydrogen and New Energy
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• v.28 no.1
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• pp.77-84
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• 2017

In this study, Poly-urethane acrylate (PUA) was synthesized by the reaction between Polycaprolactonetriol (PCLT) and Isophorone dissocyanate (IPDI) and hybridized with inorganic materials. Tetraethylortho silicate (TEOS) and nano clay (Closite 20A) were used as inorganic particles. For the hybridization of TEOS with PUA, sol-gel method is used, in which TEOS is made into spherical particle in the firsthand. In the case of Nano clay, hybridization is carried out through the dispersion as Nano clay has a layered structure. The solution of PUA hybrid was made into a film after UV curing and its thermo and electrical properties were measured. The experimental analysis and result demonstrate that the PUA hybrid shows an improved thermal properties and lower dielectric constant than that of the non-hybrid PUA. The trend of improved properties was different depending on structure of inorganic materials.

• Composites Research
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• v.15 no.2
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• pp.40-47
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• 2002

The di-functional epoxy resins, i.e., diglycidylether of bisphenol A(DGEBA) and diglycidylethere of bisphenol F(DGEBF) were initiated by cationic catalyst, i.e., benzylquinoxalinium hexafluoroantimonate(BQH) using electron-beam(EB) technique. And the effect of structure of DGEBA and DGEBF on thermal stabilities and cure behaviors was investigated. According to the experimental results, the decomposed activation energy based on Horowitz-Metzger method was higher in the case of DGEBA, but intergral procedural decomposition temperature(IPDT) of DGEBA was lower than DGEBF. This could be interpreted in terms of high crosslink density resulted from hydroxyl bond of DGEBF backbone. It was confirmed in increasing the hydroxyl band at $7000\;cm^{-1}$ and $5235\;cm^{-1}$ using near-infrared spectroscopy(NIRS).

• Macromolecular Research
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• v.15 no.6
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• pp.533-540
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• 2007

We designed and successfully synthesized UV curable, functional acrylate monomers having a polarizing group, i.e., an electron-withdrawing and/or electron-donating group for the optical materials of high refractive index. Optical polymer films made from the functional methacrylate monomers were achieved with photo crosslinking under UV illumination. A monomer having amino and cyano groups (Dimer-CN) exhibited the highest refractive index ($n_{TE}$=1.595 at 850nm) among the studied methacrylate derivatives, due to the large polarizability of the dipolar monomer structures with electron-donating and withdrawing groups. By controlling the compositions of the functional acrylate monomer of copolymers, the refractive indices of the polymers were readily adjusted within a wide range of 1.498-1.595. The copolymers showed a high glass transition temperature $(T_g)$ and good thermal stability, which are desirable for optical applications. $T_g$ and $T_{10%}$ (10%-weight loss occurred) of the copolymers ranged from $120-140^{\circ}C$ and from $329-387^{\circ}C$, respectively.

• Carbon letters
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• v.11 no.2
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• pp.107-111
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• 2010

We prepared the amine epoxy adducts (AEA)/thin multiwalled carbon nanotubes (TWCNTs) composite particles using nonsolvent based methods including dry mechano-chemical bonding(MCB) process and supercritical fluid (SCF) process. The resulting TWCNTs/AEA composite particles have been used as curing agents for urethane modified bispheol A type epoxy resin. The thermal, thermomechanical properties of the epoxy resins cured with TWCNTs/AEA composite particles were measured by DMA and the dispersion of CNT was characterized by SEM. Because of high degree of CNT dispersion, thermal and mechanical properties of the epoxy resin cured with TWCNTs/AEA composite particles prepared by SCF process are better than those cured with mechano-chemically prepared TWCNTs/AEA composite particles.

• Journal of Advanced Marine Engineering and Technology
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• v.32 no.5
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• pp.724-729
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• 2008

Umbilical cord blood has been recently considered an attractive potential alternative as a source of stem cell transplantation to curing diseases such as leukemia, cancers, immune disorders. Normally the stored system of the umbilical cord blood specimen is equipped with a computer-controlled robotic arm that enables the samples to locate the identification places in liquid nitrogen tank at regulated temperature as about $-196^{\circ}C$. As the half of robotic arm is in the air and the rest part is submerged in liquid nitrogen, the temperature of robotic arm varies from ambient to liquid nitrogen temperature. In this study the temperature variation of upper part of arm above tank lid was thermally analysed by using the commercial code of Ansys. The result of analysis was that the upper part of robotic arm was seriously frozen due to heat transfer from liquid nitrogen as low as -$120^{\circ}C$. In order to solve the frost problem of robotic arm, small PTFE tube block as resistance material was introduced into the lower part of tank lid instead of the whole stainless steel(SUS) robotic arm. The results showed that the temperature of robotic arm above the lid was higher enough, and this method would be one of the very effective measure to solve the problem.

• Composites Research
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• v.27 no.6
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• pp.231-235
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• 2014

Autoclave processing has a good quality of product, but manufacturing cost is expansive. After curing of composite, the unwanted deformation and distortion increase the manufacturing cost by redesign of tool parts. Therefore, manufacturing cost down is a big issue in processing level. For the reduction of tool costs, it is important to investigate the effects of tool materials and tool surface conditions. In this paper, we organized user subroutine in ABAQUS to consider the thermal effects of part and tool, and the results are compared with commercial code, COMPRO. And this paper suggests reference point for the selection of tool materials to reduce manufacturing costs.

• Polymer(Korea)
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• v.26 no.2
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• pp.193-199
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• 2002

The dichloro-polyester polyol (DCBAO) which was synthesized in our earlier work was cured at room temperature with two different type of curing agents including Desmodur N-3300 and Desmodur L-75 to get a polyurethane flame-retardant coatings (DCBAO/N-3300=DEBAN and DCBAO/L-75=DCBAL). We could not observe any deterioration of physical properties of the flame-retardant PU coatings (UCBAN and DCBAL) in comparison with the conventional PU coatings. Thermal resistance of DCBAL-type flame-retardant coatings, which was measured by yellowness index difference, was inferior to that of DCBAL-type PU coatings. We believe that this phenomena is attributed to the poor thermal resistance of Desmodur L-75 isocyanate. It was observed that the LOI values were 25∼26% for the PU coatings containing 20∼30 wt% of 2,4-dichlorobenzoic acid.

• Korean Journal of Materials Research
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• v.27 no.9
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• pp.471-476
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• 2017

In order to improve the high temperature oxidation resistance and lifespan of mat type porous carbon insulation, SiC was coated on carbon insulation by solution coating using polycarbosilane solution, curing in an oxidizing atmosphere at $200^{\circ}C$, and pyrolysis at temperatures up to $1200^{\circ}C$. The SiOC phase formed during the pyrolysis process was converted into SiC crystals as the heat treatment temperature increased, and a SiC coating with a thickness of 10-15 nm was formed at $1600^{\circ}C$. The SiC coated specimen showed a weight reduction of 8.6 % when it was kept in an atmospheric environment of $700^{\circ}C$ for 1 hour. On the other hand, the thermal conductivity was 0.17 W/mK, and no difference between states before and after coating was observed at all.