• 한국표면공학회지
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• 제49권2호
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• pp.218-224
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• 2016

Thermal radiation pastes were prepared by dispersing carbon materials as fillers with a content of 1 weight percent in an acrylic resin. The kind of fillers was as follows; $25{\mu}m$ graphite, $45{\mu}m$ graphite, $15{\mu}m$ carbon nanotube(CNT), a 1:1 mixture of $25{\mu}m$ graphite and $15{\mu}m$ CNT, and a 1:1 mixture of $45{\mu}m$ graphite and $15{\mu}m$ CNT. Thermal emissivity was measured as 0.890 for the samples with graphite only, 0.893 for that with CNT only, and 0.892 for those containing both. After coating prepared pastes on a side of 0.4 mm thick aluminium plate and placing the plate over an opening of a box maintained at $92^{\circ}C$ with the coated side out, the temperatures on the uncoated side of the plates were measured. The samples containing graphite and CNT showed the lowest temperatures. The paste with mixed fillers was coated on the back side of the PCB of an LED module and thermal analysis was carried out using Thermal Transient Tester (T3ster) in a still air box. The thermal resistance of the module with coated PCB was measured as 14.34 K/W whereas that with uncoated PCB was 15.02 K/W. The structure function analysis of T3ster data revealed that the difference between junction and ambient temperatures was $13.8^{\circ}C$ for the coated case and $18.0^{\circ}C$ for the uncoated. From the infrared images of heated LED modules, the hottest-spot temperature of the module with coated PCB was lower than that of the uncoated one for a given period of LED operation.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2007년도 추계학술대회 논문집
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• pp.126-127
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• 2007

Sn-filled and Fe-doped $CoSb_3$ skutterudites were synthesized by encapsulated induction melting. Single ${\delta}$-phase was successfully obtained by subsequent annealing and confirmed by X-ray diffraction analysis. Temperature dependences of Seebeck coefficient, electrical resistivity and thermal conductivity were examined from 300 K to 700 K. The positive Seebeck coefficient confirmed the p-type conduction. Electrical resistivity increased with increasing temperature, which shows that the $Sn_zCo_3FeSb_{12}$ skutterudite is highly degenerate. Thermal conductivity was reduced by Sn-filling because the filler atoms acted as phonon scattering centers in the skutterudite lattice. Thermoelectric figure of merit was enhanced by Sn filling and its optimum filling content was considered to be z=0.3 in the $Sn_zCo_3FeSb_{12}$ system.

• 폴리머
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• 제26권5호
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• pp.623-633
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• 2002

적인을 이용한 ortho-cresol novolac (OCN)과 biphenyl계 혼합 에폭시 수지 조성물의 열적 특성과 난연 특성을 검토하였다. OCN과 biphenyl 에폭시의 부피비에 따라 5가지 조성물을 디자인하였으며, TGA 및 DTG, 그리고 UL-94V 테스트를 통해 난연 효과를 평가하였다. 충전제와 적인의 함량이 증가할수록 열적 성질 및 우수한 난연 효과를 보였으나, 과량의 적인을 적용하였을 경우에는 열안정성의 저하를 유발하였다. 복합재료의 기저 수지호서 OCN/biphenyl 혼합 에폭시를 사용하였을 경우 OCN의 내열특성과 biphenyl 에폭시의 높은 발포 특성에 기인하여 보다 향상된 난연 특성을 확보할 수 있었다. 적인을 적용한 에폭시 수지 조성물의 난연 기구는 표면에서 형성된 발포성 탄화층 (char-layer)의 열적 방어 효과로 판단할 수 있었다.

• 펄프종이기술
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• 제46권5호
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• pp.79-87
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• 2014

The enrichment with nutrients in rivers and lakes becomes serious problems in Korea. As the environmental friendly solution, the phytoremediation are getting more attention and the water hyacinth could be a strong candidate plant for this. Water hyacinth is a free floating freshwater plant proven to be a effective plant used for a purification of a polluted lakes, sewage wastewater, and livestock wastewater. The biggest obstacles for application of water hyacinth in Korea could be the disposal of the water hyacinth before winter, because there is no feasible use for the water hyacinth until now. In this study, the characteristics of water hyacinth were deeply investigated for providing background data to develop appropriate application of the water hyacinth. The water hyacinth was fractioned three parts, leaf, air blader, root of which morphological properties were evaluated with microscope and field emission scanning electron microscope (FE-SEM). The water contents of each parts of the water hyacinth were 87% for leaf, 96.5% for air bladder, 94.6% for root. The chemical compositions of each parts were also measured and showed around 29% of hot water extract in leaf and air bladder, 42% holocellulose for leaf, 47% holocellulose for air bladder. The application of water hyacinth biomass without root parts to papermaking provided bulkier structure, but the tensile strength was decreased.

• Restorative Dentistry and Endodontics
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• 제39권4호
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• pp.310-318
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• 2014

Objectives: This study examined the influence of the resin thickness on the polymerization of silorane- and methacrylate-based composites. Materials and Methods: One silorane-based (Filtek P90, 3M ESPE) and two methacrylate-based (Filtek Z250 and Z350, 3M ESPE) composite resins were used. The number of photons were detected using a photodiode detector at the different thicknesses (thickness, 1, 2 and 3 mm) specimens. The microhardness of the top and bottom surfaces was measured (n = 15) using a Vickers hardness with 200 gf load and 15 sec dwell time conditions. The degree of conversion (DC) of the specimens was determined using Fourier transform infrared spectroscopy (FTIR). Scratched powder of each top and bottom surface of the specimen dissolved in ethanol for transmission FTIR spectroscopy. The refractive index was measured using a Abbe-type refractometer. To measure the polymerization shrinkage, a linometer was used. The results were analyzed using two-way ANOVA and Tukey's test at p < 0.05 level. Results: The silorane-based resin composite showed the lowest filler content and light attenuation among the specimens. P90 showed the highest values in the DC and the lowest microhardness at all depth. In the polymerization shrinkage, P90 showed a significantly lower shrinkage than the rest two resin products (p < 0.05). P90 showed a significantly lower refractive index than the remaining two resin products (p < 0.05). Conclusions: DC, microhardness, polymerization rate and refractive index linearly decreased as specimen thickness linearly increased. P90 showed much less polymerization shrinkage compared to other specimens. P90, even though achieved the highest DC, showed the lowest microhardness and refractive index.

• 공업화학
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• 제32권2호
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• pp.157-162
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• 2021

본 연구에서는 1축 extruder를 원사 압출 장비로 사용하여 재활용 폴리프로필렌(rPP)으로 3D 프린터용 원사를 제조하였고, 전기화학적 박리 그래핀을 rPP 대비 10, 20 wt%로 첨가하여 그래핀 복합체 원사를 제조하였다. 전기화학적 박리그래핀은 그 분산도가 우수하여 균일한 rPP/그래핀 복합체 원사 제조를 가능하게 하였다. 그래핀의 함량이 증가할수록 열분해 속도 등 열적 성능이 향상되었다. 기계적 물성 또한 rPP 대비 그래핀 함량이 10 wt%일 때 증가하였는데, 20 wt%에서는 오히려 기계적 물성이 감소하는 것을 볼 수 있었다. 제조한 원사들을 사용하여 상용 3D 프린터를 통해 3D 성형체를 성공적으로 제조할 수 있었으며, 폐플라스틱을 재활용하여 제조하였기 때문에 환경적, 경제적으로 이점을 가질 것으로 기대된다.

• 마이크로전자및패키징학회지
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• 제28권2호
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• pp.51-57
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• 2021

이 연구에서는 에폭시 수지에 포함된 나노 실리카 입자의 농도가 재료의 열/기계적 물성에 미치는 영향에 대해 알아보았다. 약 12 nm 크기의 나노 입자를 에폭시 수지에 다섯가지 무게비로 섞은 나노복합소재를 제작하였다. DMA와 TMA 방법을 이용하여 유리전이온도, 응력이완, 열팽창 거동을 측정하였다. 이를 통해 나노입자가 재료의 점탄성 거동에 어떠한 영향을 미치는지 보였다. 실리카 입자의 함량이 증가할수록 순수 에폭시 재료 대비 탄성 물성은 증가하였고, 유리전이온도는 감소하였다. FTIR 결과는 분자구조의 관점에서 충진제 함량에 따른 물성변화의 원인을 찾고 나노입자가 에폭시 분자 구조에 어떠한 영향을 미치는지를 규명하는데 중요한 역할을 하였다.

• Steel and Composite Structures
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• 제37권6호
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• pp.711-731
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• 2020

This paper deals with free vibration of FG sandwich annular sector plates on Pasternak elastic foundation with different boundary conditions, based on the three-dimensional theory of elasticity. The plates with simply supported radial edges and arbitrary boundary conditions on their circular edges are considered. The influence of carbon nanotubes (CNTs) waviness, aspect ratio, internal pores and graphene platelets (GPLs) on the vibrational behavior of functionally graded nanocomposite sandwich plates is investigated in this research work. The distributions of CNTs are considered functionally graded (FG) or uniform along the thickness of upper and bottom layers of the sandwich sectorial plates and their mechanical properties are estimated by an extended rule of mixture. In this study, the classical theory concerning the mechanical efficiency of a matrix embedding finite length fibers has been modified by introducing the tube-to-tube random contact, which explicitly accounts for the progressive reduction of the tubes' effective aspect ratio as the filler content increases. The core of structure is porous and the internal pores and graphene platelets (GPLs) are distributed in the matrix of core either uniformly or non-uniformly according to three different patterns. The elastic properties of the nanocomposite are obtained by employing Halpin-Tsai micromechanics model. A semi-analytic approach composed of 2D-Generalized Differential Quadrature Method (2D-GDQM) and series solution is adopted to solve the equations of motion. The fast rate of convergence and accuracy of the method are investigated through the different solved examples. Some new results for the natural frequencies of the plate are prepared, which include the effects of elastic coefficients of foundation, boundary conditions, material and geometrical parameters. The new results can be used as benchmark solutions for future researches.

• Imaging Science in Dentistry
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• 제52권3호
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• pp.303-308
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• 2022

Purpose: This technical report aims to describe and detail the use of micro-computed tomography for a reliable evaluation of the bulk-fill composite/tooth interface. Materials and Methods: Bulk-fill composite restorations in tooth cavities were scanned using micro-computed tomography to obtain qualitatively and quantitatively valuable information. Two-dimensional information was processed using specific algorithms, and ultimately a 3-dimensional (3D) specimen reconstruction was generated. The 3D rendering allowed the visualization of voids inside bulk-fill composite materials and provided quantitative measurements. The 3D analysis software VG Studio MAX was used to perform image analysis and assess gap formation within the tooth-restoration interface. In particular, to evaluate internal adaptation, the Defect Analysis addon module of VG Studio Max was used. Results: The data, obtained with the processing software, highlighted the presence and the shape of gaps in different colours, representing the volume of porosity within a chromatic scale in which each colour quantitatively represents a well-defined volume. Conclusion: Micro-computed tomography makes it possible to obtain several quantitative parameters, providing fundamental information on defect shape and complexity. However, this technique has the limit of not discriminating materials without radiopacity and with low or no filler content, such as dental adhesives, and hence, they are difficult to visualise through software reconstruction.

• 공업화학
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• 제33권4호
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• pp.381-385
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• 2022

유해화학물질의 감지 센서 개발을 위해 기재 필름과 전도성 페이스트의 접착 내구성 확보가 매우 중요하다. 본 연구에서는 폴리에틸렌테레프탈레이트(polyethylene terephthalate, PET) 필름에 폴리아닐린/그래핀나노플레이트(graphene nano plate, GNP) 페이스트를 코팅하여 접착 특성을 평가한 결과 cross cut 0B 또는 1B 등급으로 센서 적용에 문제가 있어 에스테르계 바인더를 이용하여 접착 특성 개선 연구를 수행하였다. 에스테르계 바인더가 10 wt% 이상 첨가되면 센서 적용이 가능한 cross cut 등급이 3B 이상을 나타내었다. 바인더의 과량 첨가는 전도성 페이스트의 전기적 특성에 영향을 줄 수 있으며 실제로 황산에 대한 반응성이 감소함을 확인하였다. 전기적 특성 개선을 위해 카본블랙(carbon black, CB) 함량 변화 시험을 수행하였고 CB 2 wt%에서 최적의 전기적 특성을 보임을 확인하였다.