• 공업화학
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• 제9권3호
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• pp.342-347
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• 1998

경량성의 전도성복합수지는 전도성고분자인 폴리피롤과 폴리티오펜이 다공성의 가교폴리스티렌의 내부에 분산되어 전도성네트워크를 형성시킴으로 제조된다. 높은 다공성과 친유성의 특성을 갖는 호스트고분자는 고농축에멀션중합방법을 이용하여 합성하고 전도성복합수지는 이 호스트고분자를 이용하여 이단계 함침방법으로 제조한다. $FeCl_3$을 개시제와 혼입체로 사용하여 제조한 폴리피롤복합수지의 전기전도도는 0.82 S/cm이며, $FeCl_3$-아세토니트릴을 개시제로 사용하여 제조한 폴리티오펜복합수지는 전기전도도가 6.05 S/cm에 이른다. 전도성복합수지의 전기전도도는 사용된 산화제 용매와 초기산화제와 단량체 몰비율에 크게 영향을 받는다. 전자현미경조사에 의하면 전도성고분자가 다공성 호스트고분자 내부벽에 필림을 형성한다. 폴리피롤소재복합수지와 폴리티오펜소재복합수지의 전기차단효율은 2.0 GHz에서 각각 15.2dB와 22.5dB였다. 20K-300K의온도범위에서 저항의 온도의존성에 대한 실험결과에 의하면 전도성복합수지는 반도체특성을 보이고 전기전도기구는 전형적인 VRH모델을 따른다.

• Imaging Science in Dentistry
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• 제43권3호
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• pp.145-151
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• 2013

Purpose: This study was performed to evaluate and compare the radiopacity of dentin, enamel, and 8 restorative composites on conventional radiograph and digital images with different resolutions. Materials and Methods: Specimens were fabricated from 8 materials and human molars were longitudinally sectioned 1.0 mm thick to include both enamel and dentin. The specimens and tooth sections were imaged by conventional radiograph using #4 sized intraoral film and digital images were taken in high speed and high resolution modes using a phosphor storage plate. Densitometric evaluation of the enamel, dentin, restorative materials, a lead sheet, and an aluminum step wedge was performed on the radiographic images. For the evaluation, the Al equivalent (mm) for each material was calculated. The data were analyzed using one-way ANOVA and Tukey's test (p<0.05), considering the material factor and then the radiographic method factor, individually. Results: The high speed mode allowed the highest radiopacity, while the high resolution mode generated the lowest values. Furthermore, the high resolution mode was the most efficient method for radiographic differentiation between restorative composites and dentin. The conventional radiograph was the most effective in enabling differentiation between enamel and composites. The high speed mode was the least effective in enabling radiographic differentiation between the dental tissues and restorative composites. Conclusion: The high speed mode of digital imaging was not effective for differentiation between enamel and composites. This made it less effective than the high resolution mode and conventional radiographs. All of the composites evaluated showed radiopacity values that fit the ISO 4049 recommendations.

• Composites Research
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• 제31권1호
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• pp.23-29
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• 2018

RFI 공정은 수지 점도에 제한이 없어 매우 두꺼운 구조물에도 적용이 가능하다. 수지필름 두께를 설정할 때 수지필름의 두께가 얇은 경우 미함침 구간이 발생하여 기계적 물성이 저하되고, 수지필름 두께가 두꺼운 경우 필요이상의 여분 수지가 발생하게 된다. 따라서 본 연구에서는 RFI 공정에서 수지필름 두께 설정을 위한 방법을 제시하였다. 적정 수지필름 두께를 설정하는 방법으로 섬유압착거동 시험을 제시하였고, 제시된 방법의 검증을 위해 숏빔전단강도시험, 압축시험, 기공률 측정을 통해 복합재 물성을 평가하였다. 복합재 물성 평가 결과, 섬유압착거동시험 결과를 바탕으로 적정 수준의 수지필름 두께를 찾을 수 있었다.

• Restorative Dentistry and Endodontics
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• 제40권2호
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• pp.128-135
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• 2015

Objectives: This study evaluated the effects of the resin thickness on the microhardness and optical properties of bulk-fill resin composites. Materials and Methods: Four bulk-fill (Venus Bulk Fill, Heraeus Kulzer; SDR, Dentsply Caulk; Tetric N-Ceram Bulk Fill, Ivoclar vivadent; SonicFill, Kerr) and two regular resin composites (Charisma flow, Heraeus Kulzer; Tetric N-Ceram, Ivoclar vivadent) were used. Sixty acrylic cylindrical molds were prepared for each thickness (2, 3 and 4 mm). The molds were divided into six groups for resin composites. The microhardness was measured on the top and bottom surfaces, and the colors were measured using Commission Internationale d'Eclairage (CIE) $L^*a^*b^*$ system. Color differences according to the thickness and translucency parameters and the correlations between the microhardness and translucency parameter were analyzed. The microhardness and color differences were analyzed by ANOVA and Scheffe's post hoc test, and a student t-test, respectively. The level of significance was set to ${\alpha}=0.05$. Results: The microhardness decreased with increasing resin thickness. The bulk-fill resin composites showed a bottom/top hardness ratio of almost 80% or more in 4 mm thick specimens. The highest translucency parameter was observed in Venus Bulk Fill. All resin composites used in this study except for Venus Bulk Fill showed linear correlations between the microhardness and translucency parameter according to the thickness. Conclusions: Within the limitations of this study, the bulk-fill resin composites used in this study can be placed and cured properly in the 4 mm bulk.

• 마이크로전자및패키징학회지
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• 제22권4호
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• pp.65-70
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• 2015

히트 싱크용 소재에 응용할 목적으로 단층금속과 2층 단면구조 복합재료에 대해 열전도 특성을 연구하였다. 단층금속으로는 알루미늄합금(Al6061)을 사용했으며, 2층 단면구조 복합재료로는 Al6061기판에 질화알루미늄(AlN)을 스크린 인쇄한 층상구조 복합재료를 선택하였다. 섬광법으로 측정한 열확산계수와 비열 및 밀도를 사용해서 열전도도를 측정하였다. 실험을 통해 얻은 열전도 특성 값을 참고문헌에 보고된 자료를 사용해 계산한 값과 비교하였다. Al6061 기판에 스크린인쇄법으로 AlN 후막을 형성시킨 2층 단면구조 복합재료 시편의 열전도도는 AlN 후막의 두께가 증가할수록 선형적으로 감소하였다. 측정한 복합재료의 열전도도는 두께가 $53{\mu}m$과 $163{\mu}m$일 때, 각각 $114.1W/m{\cdot}K$와 $72.3W/m{\cdot}K$로 나타났다. 또한, 스크린 인쇄한 AlN 후막의 열전도도를 열전도비저항에 대한 혼합법칙을 적용해서 평가하였다. AlN 후막의 두께가 $53{\mu}m$와 $163{\mu}m$인 경우, 스크린 인쇄한 AlN 후막의 열전도도는 각각 $9.35W/m{\cdot}K$와 $12.40W/m{\cdot}K$로 나타났다.

• 한국세라믹학회지
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• 제34권8호
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• pp.908-913
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• 1997

Multilayer NbCxC1-x/Y2O3/Ti were sputter-coated on the alumina substrate, starting with a 0.7 ㎛ thick NbCxC1-x layer grown on substrate, followed by 0.7 ㎛ thick Y2O3 layer and 1 ㎛ thick Ti layer. To find out the optimum conditions for thickness uniformity and adhesion, sputtering works have been done with the variation of sputtering power and Ar pressure. After vacuum annealing at 950℃ and 1000℃, the thermal stability of the NbCxC1-x/Y2O3/Ti coated alumina substrates has been investigated by peel off test. The coating scheme didn't cause any debonded layer after an annealing at 950℃ for 3hrs. However, it was peeled off after annealing at 1000℃ for 3hr. It was found that the thermal stability of Al2O3/NbCxC1-x/Y2O3/Ti coating scheme changed with the NbCxC1-x composition.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2004년도 학술대회지
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• pp.225-227
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• 2004

The compressive characteristics of thick carbon/epoxy composite in a submarine environment was investigated in this study. The specimens made of thick carbon fiber/epoxy composite that were immersed into seawater Jar thirteen months. the seawater content at saturation was about $1.2\%$ of the specimen weight. Compressive tests have been performed in different hydrostatic pressures of 0.1 MPa, 100 MPa, 200 MPa, and 270 MPa. The results showed that the compressive elastic modulus increased about $12.3\%$ as the hydrostatic pressure increased from 0.1 MPa to 200 MPa. The results also showed that compressive fracture strength increased $28\%$ and compressive fracture strain increased $8.5\%$ as the hydrostatic pressure increased from 0.1 MPa to 270 MPa.

• Restorative Dentistry and Endodontics
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• 제41권3호
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• pp.159-166
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• 2016

The purpose of this review was to suggest practical criteria for the clinical translucency evaluation of direct esthetic restorative materials, and to review the translucency with these criteria. For the evaluation of reported translucency values, measuring instrument and method, specimen thickness, background color, and illumination should be scrutinized. Translucency parameter (TP) of 15 to 19 could be regarded as the translucency of 1 mm thick human enamel. Visual perceptibility threshold for translucency difference in contrast ratio (${\Delta}CR$) of 0.07 could be transformed into ${\Delta}TP$ value of 2. Translucency differences between direct and indirect resin composites were perceivable (${\Delta}TP>2$). Universal and corresponding flowable resin composites did not show perceivable translucency differences in most products. Translucency differed significantly by the product within each shade group, and by the shade group within each product. Translucency of human enamel and perceptibility threshold for translucency difference may be used as criteria for the clinical evaluation of translucency of esthetic restorative materials.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2002년도 추계학술발표대회 논문집
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• pp.280-283
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• 2002

In the manufacturing of large scale composite structures, the cost-effective processing and the enhancement of structural performance are critical. One of the most effective ways for this purpose is to use stitched multiaxial warp knitted (MWK) perform in the resin transfer molding process. This study reports the effect of stitching on the mechanical properties of MWK composites, and the feasibility processing of the thick U-beam structure utilizing the stitched preforms. Permeability of the preform, viscosity and cure property of the epoxy resin have been measured. The results of resin flow analysis has been used in determining the gate/vent locations of the RTM mold. Cross-sectional observation of the channel beam prototype demonstrated that the resin impregnation was almost complete, except for some surrounding area of stitched yarns.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2003년도 춘계학술대회 논문집
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• pp.1390-1393
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• 2003

Work factor approach is conveniently used in metal fracture mechanics to determine fracture toughness from a single fracture test. In this work, we investigated the applicability of the work factor approach in order to determine fracture toughness of thick graphite/epoxy composites in the hydrostatic pressure environment from a single fracture test. The effect of hydrostatic pressure on the elastic work factor was studied, The stacking sequence used was multi-directional, [0$^{\circ}$/${\pm}$45$^{\circ}$/90$^{\circ}$]. The hydrostatic pressures applied were 0.1 MPa, 100 MPa, 200 MPa, and 300 MPa. The results showed that the elastic work factor was not affected by the hydrostatic pressure, The elastic work factor decreased in a linear fashion with crack length.