• Polymer(Korea)
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• v.28 no.1
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• pp.35-40
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• 2004

The formation mechanism of void defect which deteriorate composite's property is various according to each composite process. In this paper, void formation and growth mechanism is analyzed by thermal analysis and GC/MS. We made a vacuum chamber for observing pressure effect. Thermal analysis has been done in various condition. Elements of volatiles during resin curing were turned out by GC/MS. The most of volatiles of polyester were composed of styrene (over 80%) and a small quantity of toluene. In case epoxy resin, butyl glycidyl ether was the main element of volatiles (over 90%). We concluded that the original sites of void growth existed in resin and they were eliminated by vacuum and heating process. And the growth of void was influenced by water, diluents, solvent, and reactants in resin.

• Polymer(Korea)
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• v.24 no.2
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• pp.237-244
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• 2000

Phenolic resin used as a precursor of carbonized matrix for carbon-carbon composites was modified by addition of molybdenum disilicide (MoSi$_2$) in various concentrations of 0, 4, 12 and 20% by weight to improve the anti-oxidation properties of the composites. The green body was manufactured by a prepreg method and was submitted to carbonization up to 110$0^{\circ}C$. In this work, the oxidation behavior of carbon-carbon composites with MoSi$_2$ as an oxidation inhibitor was investigated at the temperature range of 600-100$0^{\circ}C$ in an air environment. The carbon-carbon composites with MoSi$_2$ showed a significantly improved oxidation resistance due to both the reduction of the porosity formation and the formation of mobile diffusion barrier for oxygen when compared to those without MoSi$_2$. Carbon active sites should be blocked, decreasing the oxidation rate of carbon. This is probably due to the effect of the inherent MoSi$_2$ properties, resulted from a formation of the protective layer against oxygen attack in the composites studied.

• Composites Research
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• v.20 no.2
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• pp.10-16
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• 2007

The 2-step manufacturing method consisting of preforming and stamping processes was developed to manufacture composite bipolar plates for PEMFCS. The preform was composed of expanded graphite, graphite flake and phenol resin. Procuring conditions were optimized by checking the electrical conductivity, flexural strength and microstructure. Procuring temperature $(100^{\circ}C)$ slightly above the melting point of phenol powders $(90^{\circ}C)$ induced moderate curing, but also prevented excessive curing. Preforms utilizing the tangled structure of expanded graphite were easily fabricated at low pressure of 0.07-0.28MPa. The proper procuring time, 5min, was determined to fabricate the preform stably because insufficient and excessive procuring deteriorated the flexural strength of composite bipolar plates.

• Proceedings of the KAIS Fall Conference
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• 2011.05a
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• pp.332-335
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• 2011

원적외선, 음이온 방출과 항균, 탈취, 난연등의 효과를 가지는 황토를 합성수지와 혼합하여 복합소재를 연구하여 환경 친화적인 특징과 원적외선, 음이온의 방출을 이룰 수 있는 복합소재 조성을 연구하였다. PP는 MI가 2~60이고, TPE로 Ethylene계을 사용하였으며, 황토와 PP의 혼련을 도와주기 위하여 MA-g-PP를 첨가하였고, 활제, 분산제 및 산화방지제를 첨가하여 compounding 하였다. 또한 황토의 종류에따라 적황토, 호황토, 홍토, 백토, 흑토등으로 구분되고, 각각의 황토 마다 다양한 종류의 입도를 가지고 있으며, 또한 환경 친화적이며 난연성을 부여하기 위하여 다양한 조성으로 compounding 하였다, 황토의 종류에 따른 복합재료의 물성으로부터 기계적 특성치, 원적외선 방사율, 난연성등을 확인하고, 친환경 난연 복합소재 기술을 연구하였다. 적황토의 경우 황토의 함량이 많을수록 인장강도는 작아지는 경향을 나타냈으며, 입도가 작을수록 인장강도가 커지는 경향을 나타냈다. 파단신율의 경우 적황토(#2000)에서 가장 양호하게 나타났으며, 굴곡강도, 충격강도의 경우 적황토(#5000)에서 MI 의 경우 적황토(#325)에서 양호하게 나타났다.

• New & Renewable Energy
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• v.3 no.4
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• pp.3-7
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• 2007

Graphite/polymer composite bipolar plates for PEMFC are successfully developed, and their typical properties are superior to commercially available ones. Thermal property of the developed bipolar plate was evaluated by dynamic mechanical analyzer, and the results were compared to commercial ones. The specimens were immersed into the deionized water bath at $80^{\circ}$... for 1500hrs to evaluate dimensional stability and durability. Dimension, weight of the specimens as well as extraction conductivity was measured as each 500hrs. Fully molded bipolar plates without any machining or milling were also prepared using a specially developed mold, and they were applied to the fuel cell performance test. Results were compared to the machined commercial bipolar plate.

• 한국신재생에너지학회:학술대회논문집
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• 2007.11a
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• pp.5-7
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• 2007

Graphite/polymer composite bipolar plates for PEMFC are successfully developed, and their typical properties are superior to commercially available ones. Thermal property of the developed bipolar plate was evaluated by dynamic mechanical analyzer, and the results were compared to commercial ones. The specimens were immersed into the deionized water bath at $80^{\circ}C$ for 1500hrs to evaluate dimensional stability and durability. Dimension, weight of the specimens as well as extraction conductivity was measured as each 500hrs. Fully molded bipolar plates without any machining or milling were also prepared using a specially developed mold, and they were applied to the fuel cell performance test. Results were compared to the machined commercial bipolar plate.

• Composites Research
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• v.20 no.5
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• pp.49-55
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• 2007

Nanocomposite blade for dicing semiconductor wafer is investigated for micro/nano-device and micro/nano-fabrication. While metal blade has been used for dicing of silicon wafer, polymer composite blades are used for machining of quartz wafer in semiconductor and cellular phone industry in these days. Organic-inorganic material selection is important to provide the blade with machinability, electrical conductivity, strength, ductility and wear resistance. Maintaining constant thickness with micro-dimension during shaping is one of the important technologies fer machining micro/nano fabrication. In this study the fabrication of blade by wet processing of mixing conducting nano ceramic powder, abrasive powder phenol resin and polyimide has been investigated using an experimental approach in which the thickness differential as the primary design criterion. The effect of drying conduction and post pressure are investigated. As a result wet processing techniques reveal that reliable results are achievable with improved dimension tolerance.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.2
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• pp.245-253
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• 2010

The reliability problems of flip chip packages subjected to temperature change during the packaging process mainly occur due to mismatches in the coefficients of thermal expansion as well as features with time-dependent material properties. Resin molding compounds like glass fiber reinforced epoxy composites used as the dielectric layer in printed circuit boards (PCB) strongly exhibit viscoelastic behavior, which causes their Young's moduli to not only be temperature-dependent but also time-dependent. In this study, the stress relaxation and creep tests were used to characterize the viscoelastic properties of the glass fiber reinforced epoxy composite. Using the viscoelastic properties, finite element analysis (FEA) was employed to simulate thermal loading in the pre-baking process and predict thermal warpage. Furthermore, the effect of viscoelastic features for the major polymeric material on the dielectric layer in the PCB (the glass fiber reinforced epoxy composite) was investigated using FEA.

• Transactions of the Korean hydrogen and new energy society
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• v.32 no.1
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• pp.86-91
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• 2021

In order to save the energy in vehicles using renewable energy, it is necessary to reduce the weight of parts with polymer matrix composites. Carbon nanotube (CNT) is the nano-scale reinforcement used to increase the interlaminar strength of fiber reinforced composites or enhance the fracture toughness of polymer. However, since the degree of improvement in mechanical properties varies according to the various experimental conditions such as shape of reinforcement, types of matrix and dispersion of reinforcement, research to find the optimal conditions is essentially needed. In this study, CNT/epoxy composites with different CNT concentration were fabricated under the same conditions, and the optimal CNT content (2 wt%) was found through Mode 1 fracture toughness test. Furthermore, through optical microscopy, it was confirmed that the fracture toughness was rather decreased due to the CNT aggregation when the CNT content exceeded 2 wt%.

• Composites Research
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• v.33 no.1
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• pp.7-12
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• 2020

Over the past decade, liquid crystalline epoxy (LCER) has attracted much attention as a promising matrix for the development of efficient heat dissipation materials. This study presents a comprehensive study including synthesis, preparation and chacterization of polymer/inorganic composites using typical 4,4-diglycidyloxybiphenyl (DP) epoxy among LECR. To confirm the thermal conductivity of composite materials, we have prepared composite samples composed of epoxy resin and single-wall carbon nanotube (SWCNT) as a filler. In particular, DP composites exhibit higher thermal conductivity than commercial epoxy composites that use the same type of filler due to the highly ordered microstructure of the LCER. In addition, the thermal conductivity of the DP composite can be controlled by controlling the amount of filler. In particular, the DP composite containing a SWCNT content of 50 wt% has the highest thermal conductivity of 2.008 W/mK.