• Journal of the Mineralogical Society of Korea
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• v.15 no.2
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• pp.132-139
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• 2002

The physical properties of Uhangri sedimentary rocks were investigated to provide the conservation strategy of Dinosaur trace fossil in the Haenam. The porosity, void ratio, dry density, water content, and degree of saturation were calculated according to the proper laboratory experiments for 9 sedimentary specimens. The flexural strength (or modulus of rupture) and thermal expansion coefficient were measured using the universal testing machine and dilatometer, respectively. The Uhangri sedimentary rocks have very low porosity, void ratio, and water content. The flexural strength of shales are 24.16~42.84, and those of sandstones are 16.34~ $43.52N/mm^2$, which are much weaker than common sedimentary rocks. The very low flexural strength of sedimentary rocks despite very low porosity, is ascribed to fine fissures in the rocks. The thermal expansion coefficient of rocks were $14.7~21.3\Times10^{-6 }$, which are 2~2.5 times as high as alumina and about 10 times as high as talc. As the content of chert in the sandstone increases, the porosity, void ratio, and water content increase, while the dry density and degree of saturation decrease. The chert-bearing sandstone have higher porosity and thermal expansion coefficient, and lower flexural strength compared to those free of chert.

• Polymer(Korea)
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• v.34 no.4
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• pp.352-356
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• 2010

The effects of the filler shapes and contents on the coefficient of thermal expansion (CTE) for polypropylene (PP) composites which included three dimensional ellipsoids ($a_1>a_2>a_3$), as determined by two aspect ratios (${\rho}_\alpha=a_1/a_3$ and ${\rho}_\beta=a_1/a_2$) were analyzed by the theoretical approach proposed by Lee and Paul and compared with the experimental results. The shapes of fillers in the composites were various, such as spherical, fiber, disc, and ellipsoid, using barium sulfate, glass fiber, and mica. The longitudinal CTE of barium sulfate whose shape was sphere ($\rho_\alpha=\rho_\beta=1$) decreased. For the glass fiber, primary aspect ratio decreased with the filler content, and longitudinal CTE decreased as filler contents increased. Normal CTE initially increased in the lower filler content. For the mica, longitudinal and transverse CTE decreased but normal CTE increased in the lower filler content like predicted values.

• Composites Research
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• v.27 no.2
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• pp.52-58
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• 2014

Short fiber reinforced composites manufactured by injection molding have diverse fiber orientations variable with measuring positions even in the same specimen, which is caused by the flow induced fiber orientation. Fiber orientations considerably affect the mechanical and thermal properties of final composite products. In this study, fiber orientation of injection molded carbon fiber reinforced PA6/PPO composite was measured at several points of the specimen by optical microscopy analysis and the corresponding izod impact strength, coefficients of thermal expansion (CTE) were also measured to investigate the influence of local fiber orientation on the mechanical and thermal properties. Izod impact strength where fiber was perpendicular to the direction of crack propagation was higher than where fiber was parallel to the direction, which could be explained be the impact resistance reinforcing mechanism by fiber orientation. CTE was also lower where fiber was parallel to the measurement direction of CTE than where fiber was perpendicular to the direction, which could be also explained by the dimensional stability mechanism by fiber orientation.

• Proceedings of the KIEE Conference
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• 2011.07a
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• pp.1599-1600
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• 2011

현재 사용되는 전력기기와 전기에너지로 구동되는 기기등은 환경 조화와 에너지 절약을 목표로 고전압 대용량화, 축소 소형화 및 고효율화가 진행되는 과정에 있다. 이런 기기들은 전위를 유지하기 위해서 전기절연기술이 필수적이다. 특히 전기절연재료의 역할이 중요해서 재료의 특성이 기기전체의 종합성능을 지배하기도 한다. 본 연구에서는 몰드 변압기의 절연수지로 사용되는 에폭시 복합체와 마이크로 $SiO_2$와 Ag 각 시편의 열팽창률과 유전 특성 및 온도에 따른 절연파괴강도를 측정하여 열적 특성 및 전기적 특성을 검토하고 분석한다.

• Polymer(Korea)
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• v.36 no.3
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• pp.281-286
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• 2012

Experimental study was performed regarding the effects of disc-like filler orientation and contents on the coefficient of thermal expansion (CTE) of polypropylene composites using the three dimensional ellipsoids ($a_1$ > $a_2$ > $a_3$) analyzed by two aspect ratios(${\rho}_{\alpha}=a_1/a_3$and ${\rho}_{\beta}=a_1/a_2$). Measured data were compared with the theoretical approaches proposed by Lee et al. Mica and talc were useed as disk-like fillers in the composites. As experimental results, ${\alpha}_{11}/{\alpha}_m$ decreased down to ca. 0.56 with mica content of 20 wt% and the aspect ratios, ${\rho}_{\alpha}=13.5$, ${\rho}_{\beta}=1.8$. However, ${\alpha}_{33}/{\alpha}_m$ increased to more than 1. In the case of talc, ${\alpha}_{11}/{\alpha}_m$ decreased to ca. 0.63 with 20 wt% and ${\rho}_{\alpha}=3.7$, ${\rho}_{\beta}=1.4$. Finally, the longitudinal CTEs (${\alpha}_{11}$) of polypropylene composites decreased as filler contents increased, but normal CTE (${\alpha}_{33}$) increased in the low filler contents like the theory.

• Journal of the Korean Ceramic Society
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• v.36 no.2
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• pp.145-150
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• 1999

Gd1-xSrxMnO3(0$\leq$X$\leq$0.6) as the cathode for solid oxide fuel cell was synthesized by citrate process and studied for its crystal structure, electrical conductivity, thermal expansion coefficient (TEC), and investigated reactivity with 8 mol% yttria stabilized zirconia(8YSZ) or Ce0.8Gd0.2O1.9 (CGO). The crystal structure of Gd1-xSrxMnO3 changed from orthorhombic (0$\leq$X$\leq$0.3) through cubic (0.4$\leq$X$\leq$0.5) to tetragonal structure (X=0.6). When Sr contents was increased, the electrical conductivity of Gd1-xSrxMnO3 was inthose of La1-xSrxMnO3, 8YSZ and CGO if Sr content was above 30mol%. TEC of Gd1-xSrxMnO3 was increased with Sr content. After heat treatment at 1300$^{\circ}C$ for 48 hours, reaction product of Gd1-xSrxMnO3 and 8YSZ was SrZrO3. However CGO had no reaction product with Gd1-xSrxMnO3.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.02a
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• pp.199-199
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• 2012

최근 그래핀의 대면적 합성 및 롤투롤 전사 공정의 개발로 그래핀의 상용화가 가시화 되고 있다. 하지만, 그래핀의 독특한 특성인 선형적이고 밴드갭이 없는 에너지 띠 분포 때문에 반도체 소자로서의 직접적인 적용에는 한계가 있다. 이러한 문제를 해결하기 위한 돌파구로써, 그래핀 복합체의 연구와 개발이 활발히 진행되고 있으며 본 연구에서는 그래핀 복합 적층 구조를 다룬다. 이는 디스플레이, 초고속 반도체 소자, 고성능 광전자소자 및 초고감도 센서 등 다양한 분야에 대한 그래핀의 실용화 가능성이 높아진 것을 의미한다. 특히, 높은 가시광 투과도와 낮은 면저항으로 기존 투명 전극에 대표적으로 사용되고 있는 ITO (Indium Tin Oxide)를 그래핀으로 대체하는 것에 관한 연구가 활발히 진행되고 있다. 하지만 그래핀이 높은 전자이동도를 가지는 것에 비하여 비저항과 투과도 측면에 있어서는 ITO의 성능을 뛰어넘지 못하는 실정이다. 따라서 본 연구에서는 ITO가 가지는 취약점인 기판과의 약한 접착력, 높은 취성, 기판과의 열팽창률 차이 등의 공정상 문제점을 극복하고자 하였다. 그래핀 복합 적층 필름은 플라스틱 기판 (PET) 위에 열 화학기상증착법(Chemical Vapor Deposition, CVD)을 이용하여 합성한 그래핀을 전사하고, ITO 용액을 도포한 다음 다시 그래핀을 씌워 제작하여 샌드위치 구조(sandwich structure)를 형성하였다. 완성된 필름은 광학적, 전기적 특성 분석을 수행하였다. 광학적 분석으로는 라만 분광을 이용한 그래핀 품질평가와 파장대에 따른 광 투과도, 그리고 반사도 측정을 하였으며, 전기적 특성은 면저항을 측정함으로써 분석한다. 결함이 적고, 대면적에 걸쳐 한 층을 이루어야 하는 고품질 그래핀의 요구사항에 따라 라만 분광의 G, 2D, D 띠를 분석하였다. G와 2D 띠의 비율을 통해 그래핀의 층 수를, D 띠의 강도를 통해 결함의 유무를 판단하였다. 또한, 가시광 영역에서 90% 이상의 광 투과도를 보여야 하는 투명 소자의 요구사항 달성 정도를 UV-VIS를 이용하여 확인하였다. 마지막으로, 제작한 필름의 면저항 또한 4-프로브 멀티미터를 이용하여 측정하고, 일반적인 터치스크린의 면저항인 $500{\Omega}/sq$를 만족하는지 평가하였다.

• Journal of the Korean Ceramic Society
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• v.24 no.3
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• pp.243-250
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• 1987

The effects aging on some properties and thermal-shock behavior of zirconia partially stabilized with 9 mol% MgO (9MZ) were studied. 9MZ specimens were aged over $1200^{\circ}$-$1400^{\circ}C$ for 12hours subsequently, after sintering at $1650^{\circ}C$ for 4 hours. Fracture strength(both before and after thermal-shock test), linear thermal expansion, monoclinic fraction and phase transition by XRD, density, galvanic potential and microstructure were measured. Quantitative chemical analysis around the grain-boundary of the specimen aged at $1350^{\circ}C$ was also conducted by EDX. The aging of 9MZ specimen causes a thermal decomposition of cubic-$ZrO^{2}$ into the formation metastable tetragonal-$ZrO^{2}$ and MgO. The former increases the residual strength after thermal-shock test and the latter improves the thermal-shock resistance due to thermal conduction through the continuous magnesia phase and the formation of monoclinic phase content in matrix were increased with decreasing the aging temperature from $1400^{\circ}C$ to $1200^{\circ}C$. Galvanic potential of the aged specimen exhibited a proper emf characteristic.

• Proceedings of the Materials Research Society of Korea Conference
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• 2003.03a
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• pp.217-217
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• 2003

W-Cu 합금은 우수한 전기적, 열적 특성으로 인하여 열소산재료(Heat sink)로 많이 응용되고 있다. 첨단 전자부품 이외에도 핵융합로의 Diverter가 그 예로서, 내부는 고강도와 고융점의 특성을 요구하는 반면, 외부는 높은 열전도성을 필요로 한다. 그래서 동일한 조성의 일반적인 W-Cu 합금보다 W과 Cu의 조성이 점차적으로 변화하는 경사기능재료(Functionally Graded Materials)가 냉각효율이 클 것으로 기대된다. 현재, W-Cu FGM에 대한 많은 연구가 진행되고 있지만, 그 조성이 연속적으로 변화하는 W-Cu FGM에 대한 연구는 전무한 실정이다 본 연구에서는 방전플라즈마 소결장치(Spark Plasma Sintering System)와 용침고정을 이용하여 연속적인 조성변화를 갖는 W-Cu FGM을 제조하고 그 특성에 관해 분석하고자 하였다. 소결체가 밀도 변화를 갖게 되도록 제작한 특수 경사기능 몰드에 W분말을 장입한 후, 15㎬의 압력하에서 SPS를 이용하여 W소결체를 제조하였다. 제조된 W소결체는 수평관상로에서 수소분위기 하에 Cu 용침을 실시하여 W-Cu FGM을 제조하였다 SEM을 이용한 각 위치별 조직관찰과 Image Analyzer를 이용한 W과 Cu의 면적비, 그리고 비커스경도계에 의한 경도 측정을 실시하였다. 또 열기계적 분석기를 이용하여 측정된 선팽창률로부터 열팽창계수를 구하였다. 80$0^{\circ}C$에서 ？칭하는 반복적인 싸이클을 통해 열충격시험을 실시하였고, Laser flash method로 열확산계수를 측정하였다.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.9
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• pp.823-828
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• 2013

To reduce the cost per watt of photovoltaic power, it is important to reduce the cell thickness of crystalline silicon solar cells. As the thickness of the silicon layer is reduced, two distinctive thermal expansion rates between the silicon and the aluminum layer induce bowing in a solar cell. With a thinner silicon layer, the bowing distance grows exponentially. Excessive bowing could damage the silicon wafer. In this study, we tried to measure an irregularly curved silicon solar cell more accurately using a 3D image scanner. For the detailed analysis of the three-dimensional bowing shape, a least square fit was applied to the point data from the scanned image. It has been found that the bowing distance and shape distortion increase with a decrease in the thickness of the silicon layer. An Ag strip on top of the silicon layer can reduce the bowing distance.