• Journal of the Korean Crystal Growth and Crystal Technology
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• v.1 no.2
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• pp.94-103
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• 1991

ZnO-$P_2O_5$ system glasses containing 45 to 60 mol% ZnO have been melted at$1200^{\circ}C$and crystallized through controlled heat treatment. The properties of the base glass and crystallized glass were examined with XRD. FTIR. density. thermal expansion, electric conductivity, hardness. The principal crystalline phase was identified as zinc metaphosphate [$Zn(PO_3)_2$ in crystallized glasses containing 45-55mol% ZnO and zinc pyrophosphate ($Zn_2P_2O_7$) in the sample of 60mol% ZnO with X - ray diffraction analysis. Thermal expansion coefficient and DC electrical conductivity were varied with direction of oriented crystalline in the samples containing 50-60mol% ZnO. This suggests the existance of the oriented crystalline.

• Journal of Hydrogen and New Energy
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• v.19 no.4
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• pp.331-339
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• 2008

본 논문은 내경 7.73 mm와 5.80mm의 수평관내 프레온계 냉매 R-22와 탄화수소계 냉매 R-290과 600a의 응축 열전달 계수의 실험적 결과를 나타내었다. 실험장치는 압축기, 응축기, 팽창밸브, 증발기 등으로 구성된다. 응축 실험은 질량유속 $35.5{\sim}210.4\;kg/m^2s$이고, 응축온도 40$^{\circ}C$인 조건에서 수행하였다. 주요 결과를 요약하면 다음과 같다. 탄화수소계 냉매 R-290과 R-600a의 평균 열전달 계수는 프레온계 냉매 R-22보다 높게 나타났으며, R-600a의 평균 열전달 계수가 모든 관경에 대해 가장 높게 나타났다. 실험결과와 종래의 상관식을 비교한 결과, 모든 관경과 냉매에 대해 Haraguchi 등의 상관식이 가장 좋은 일치를 보였다. 그 중에서 Cavallini-Zecchin의 상관식은 7.73 mm 관경의 실험데이터와, Dobson 등의 상관식은 내경 5.80 mm 관경의 데이터와 좋은 일치를 보였다.

• Journal of the Korean Ceramic Society
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• v.40 no.11
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• pp.1127-1131
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• 2003

Phosphate glasses known for low melting temperature glasses in electrical parts has been recently used in wide area with modification of thermal properties using alkali oxides. It is our purpose to find a correlation between thermal expansion coefficient, glass transition temperature and melting temperature through investigating thermal properties in P$_2$O$\sub$5/-SnO-ZnO-SiO$_2$/B$_2$O$_3$. As a result, the product of thermal expansion coefficient and the glass transition temperature in the glasses is found to be a constant value would be a unique value for knowing one of thermal properties.

• Polymer(Korea)
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• v.28 no.4
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• pp.321-327
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• 2004

The applications of dental restorative composite resins containing 2,2-bis [4-(2-hydroxy-3-me-thacryloyloxy propoxy) phenyl] propane as a base resin, and triethylene glycol dimethacrylate, as a diluent, were often limited in dentistry due to the relatively large amount of volumetric shrinkage that occurs during the curing reaction. In this study, in order to reduce volumetric shrinkage of the current dental restorative composite resin, asymmetric spiro orthocarbonates were synthesized and then the characteristics of resin composites containing them were explored. The volumetric shrinkage of the dental composites containing spiro orthocarbonates was decreased approximately 45%. However, the curing characteristics and mechanical properties of the new dental composites were slightly poor than those of the commercially available dental composite.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.41 no.8
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• pp.597-604
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• 2013

A coupled thermomechanical analysis of composite structures in pyrolysis and ablation environments is performed. The pyrolysis and ablation models include the effects of mass loss, pore gas diffusion, endothermic reaction energy, surface recession, etc. The thermal and structural analysis interface is based upon a staggered coupling algorithm by using a commercial finite element code. The characteristics of the proposed method are investigated through numerical experiments with carbon/phenolic composites. The numerical studies are carried out to examine the surface recession rate by chemical and mechanical ablation. In addition, the effects of shrinkage or intumescence during the pyrolysis process are shown.

• Composites Research
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• v.17 no.6
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• pp.37-43
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• 2004

To determine the effect of chain length and chemical structure of linear amine curing agents on thermal and mechanical properties, a standard bifunctional linear DGEBF epoxy resin was cured with EDA and HMDA having amine group at the both ends of main chain in a stoichiometrically equivalent ratio in condition of preliminary and post cure. From this work, the effect of linear amine curing agents on the thermal and mechanical properties is significantly influenced by numbers of carbon atoms of main chain. In contrast, the results show that the DCEBF/EDA system having two carbons had higher values in the thermal stability, density, shrinkage (%), grass transition temperature, tensile modulus and strength, flexural modulus and strength than the DGEBF/HMDA system having six carbons, whereas the DGEBF/EDA cure system had relatively low values in maximum ekothermic temperature, maximum conversion of epoxide, thermal expansion coefficient than the DGEBF/HDMA cure system. These findings indicate that the packing capability (rigid property) in the EDA structure affects the thermal and mechanical properties predominantly. It shows that flexural fracture properties have a close relation to flexural modulus and strength.

• Journal of the Korean Recycled Construction Resources Institute
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• v.10 no.4
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• pp.577-583
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• 2022

In this study, the characteristics of self-healing mortars produced using an inorganic self-healing material consisting of ground granulated blast furnace slag, expansion agent, and anhydrite, were investigated. For three types of self-healing mortars with different amounts of the inorganic healing material, compressive strength was measured and the self-healing performance was evaluated through the constant water head permeability test. The healing rate and equivalent crack width according to crack-induced aging were used as indicies of healing performance evaluation. Considering the development of compressive strength of the self-healing mortars, the change in the healing rate with healing periods, and the economic feasibility, the optimal amount of inorganic self-healing materials was suggested as 20 % of the mass of cement.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2009.11a
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• pp.181-181
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• 2009

전자부품용 Pb-free sealing frit의 열팽창계수를 기판에 matching 시키기 위하여 음의 열팽창계수를 가지고 있는 $\beta$-Eucryptite, $\beta$-Spodumene를 합성하여 filler로 첨가하였다. 합성된 filler는 저온소성용 유리프리트의 높은 열팽창계수를 조절하기 용이하고, 유리프리트와 복합화 하여 소성하면 낮은 열팽창계수로 인한 우수한 열충격 저항성을 갖는다. Filler로써 $\beta$-Eucryptite, $\beta$-Spodumene의 결정성을 향상시키기 위해 $1250^{\circ}C$에서 5 시간 동안 유지하는 합성공정을 3회 반복 진행한 후 XRD를 사용하여 결정성을 분석하였고, TMA를 이용하여 filler 첨가량에 따른 유리프리트의 열팽장계수의 변화를 측정하였다. 또한, filler 입도와 함량에 따른 melting 특성을 분석하기 위해 Pill test를 진행하였으며, soda-lime glass 기판과의 접합면을 SEM을 사용하여 관찰하였다.

• Proceedings of the International Microelectronics And Packaging Society Conference
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• 2001.11a
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• pp.189-194
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• 2001

PDP(Plasma Display Panel)의 투명 유전체에 적용 가능한 저융점 유리 중에서 납성분이 포함 되어 있지 않는 Bi계 유리의 연구를 행하였다. 기판과의 일체화를 위한 유리의 응용으로, 소자와의 반응 억제와 열응력 완화를 위해 유리의 저융점화 및 열팽창 계수를 제어하였다. 본 연구에서 제조된 Bi계 유리는 DTA와 TMA의 열분석을 통해 50$0^{\circ}C$부근에서 연화점이 있고, 7.31~10.02$\times$$10^{-6}$$^{\circ}C$, 비유전을 11.1~13.3, 광투과도가 80%이상으로 PDP 투명유전체에 적용 가능한 Bi계 유리를 얻을 수 있었다.

• KDI Journal of Economic Policy
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• v.15 no.3
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• pp.95-130
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• 1993

청년층(靑年層) 고용문제(雇傭問題)가 80년대 중반(中盤) 이후(以後) 계속 악화된 것은, 80년대 초 고등교육(高等敎育)의 확대와 80년대 일반계(一般系) 고교(高校)의 팽창에 따른 고학력화(高學歷化)의 충격(衝擊)에 대응(對應)하여 그동안 정부(政府) 학교(學校) 기업(企業)에서 적절한 제도적(制度的) 정비(整備)가 없었기 때문이다. 따라서 우리나라 청년층은 학교로부터 직장으로 이행(移行)하는 데 있어서 교육체계(敎育體系)의 선별기능(選別機能), 직업기술교육(職業技術敎育)의 현장성(現場性), 고등교육(高等敎育)의 경쟁성(競爭性), 고용관행(雇傭慣行), 산학협동체계(産學協同體系), 직업능력개발체계(職業能力開發體系), 학교(學校)-기업(企業)간 제도적(制度的) 네트워크, 병역제도(兵役制度) 등 제반제도(諸般制度)의 문제(問題)로 인하여 많은 어려움을 겪고 있다.