• 한국재료학회지
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• 제24권9호
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• pp.502-507
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• 2014

Recently, improvement in the conversion efficiency of silicon-based solar cells has been achieved by decreasing emitter doping concentration, because the lightly doped emitter can effectively prevent the recombination of electrons and holes generated by solar light irradiation. This type of emitter is very thin due to the low doping concentration, thus conductive materials (i.e., silver) used for front electrodes can easily penetrate the emitter during a firing process because of their large diffusivity in silicon. This results in junction leakage currents which might reduce cell efficiencies. In this study, $Al_2O_3$-coated Ag powders were synthesized by an ultrasonic spray pyrolysis method and applied to the conductive materials of the front electrode to control the junction leakage current. The $Al_2O_3$ shell obstructs the Ag diffusion into the emitter during the firing process. The powder is spherical with a core-shell structure and the thickness of the $Al_2O_3$ shell is tens of nanometers. Solar cells were fabricated using pure Ag powders or the $Al_2O_3$-coated Ag powder as front electrode materials, and the conversion efficiency and junction leakage current were compared to investigate the role of the $Al_2O_3$ shell during the firing processes.

• 암석학회지
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• 제3권3호
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• pp.234-240
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• 1994

국내 담홍색 화강암 석재의 대표적 산출지인 문경 가은읍 완장리에서 암반 시추탐사가 실시되었다. 코아상에서 풍화암, 연암, 보통암 및 경암으로 분류하여 물리적 및 화학적 차이 등을 연구 하였다. 비중과 흡수율은 각각 2.37~2.64와 0.27~1.87%이며, 풍화암에서 경암으로 갈수록 비중은 미약하게 증가하나 흡수율은 다소 크게 증가한다. 풍화가 심화될수록 공극율과 함수능력이 증가하여 뚜렷한 정의 상관관계를 가진다. 압축강도는 풍화정도가 감소될수록 크게 증가하나, 흡수율과 공극율은 경암에서 강도 증가에 관계없이 거의 균일하다. 풍화암으로 갈수록 점토질 성분의 잔존에 의한 것으로 해석되는 $Al_2O_3$+FeO(t)는 증가하여 $SiO_2$, CaO와 $K_2O$는 미약하게 감소한다.

• 한국자기학회지
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• 제18권1호
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• pp.43-47
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• 2008

[ $ZnO-Bi_2O_3-Al_2O_3-B_2O_3-SiO_2$ ] nano-glass를 sol-gel 법으로 제조 하였다. 평균 입자 크기는 60.3 nm였으며 매우 균일한 입도 분포를 가졌다. Nano-glass를 NiZnCu ferrite의 저온소성용 소결조제로 사용하였으며 NiZnCu ferrite에 nano-glass를 첨가한 후 $840{\sim}900^{\circ}C$에서 2시간 소결을 진행하였다. 소결성 및 자기적 특성에 대해 연구하였으며 밀도, 수축율, 초투자율, 품질계수, 및 포 화자화값을 측정하였다. nano-glass를 0.5 wt% 첨가하여 $900^{\circ}C$에서 소결한 토로이달 core 시편의 초투자율은 1 MHz에서 측정 시 193.3의 값을 가졌다. 초투자율과 포화자화값은 소결온도가 증가함에 따라 증가하는 경향을 나타내었다. sol-gel 법에 의해 제조된 $ZnO-Bi_2O_3-Al_2O_3-B_2O_3-SiO_2$ nano-glass를 칩인덕터용 NiZnCu ferrite의 저온 소결조제로 사용 가능함을 알 수 있었다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2006년도 제37회 하계학술대회 논문집 C
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• pp.1341-1342
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• 2006

Electrical characteristics of field-effect thin film transistors (TFTs) with p-channels of CdTe/CdHgTe core-shell nanocrystals are investigated in this paper. For the fabrication of bottom- and top-gate TFTs, CdTe/CrHgTe nanocrystals synthesized by colloidal method are first dispersed on oxidized p+ Si substrates by spin-coating, the dispersed nanoparticles are sintered at $150^{\circ}C$ to form the channels for the TFTs, and $Al_{2}O_{3}$ layers are deposited on the channels. A representative bottom-gate field-effect TFT with a bottom-gate $SiO_2$ layer exhibits a mobility of $0.21cm^2$/ Vs and an Ion/Ioff ratio of $1.5{\times}10^2$ and a representative top-gate field-effect TFT with a top-gate $Al_{2}O_{3}$ layer provides a field-effect mobility of $0.026cm^2$/ Vs and an Ion/Ioff ratio of $2.5{\times}10^2$. $Al_{2}O_{3}$ was deposited for passivation of CdTe/CdHgTe core-shell nanocrystal layer, resulting in enhanced hole mobility, Ior/Ioff ratio by 0.25, $3{\times}10^3$, respectively. The CdTe/CdHgTe nanocrystal-based TFTs with bottom- and top gate geometries are compared in this paper.

• 한국분말재료학회지
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• 제4권2호
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• pp.106-112
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• 1997

$Cu-Al_20_3 $ composite powders were prepared by hydrogen reduction of $Cu^{2+}$ from ammoniacal copper sulfate solution on alumina core using autoclave. The copper reduction rate and the properties of copper layer were investigated using Scanning Electron Microscope(SEM), X-ray diffractometer, size and chemical analyzers. The reduction rate of $Cu^{2+}$ showed the maximum value when the molar ratio of [$NH_3$]/[$Cu^{2+}$] was 2. In order to prevent the agglomeration of Cu powder and ethane reduction rate, $Fe^{2+}$ and anthraquinone which act as catalysis were added in the solution. Catalysis was effectively chanced with the addition of two elemerts at a time. Optimum conditions obtained in this study were hydrogen reduction temperature of 205$^{\cire}C$, stirring speed of 500 rpm and hydrogen partial pressure of 300 psi. Obtained $Cu-Al_20_3 $ composite Powders were found to have the uniform and continuous copper coating layer of nodule shape with 3~5 $\mu$m thickness.

• 한국재료학회지
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• 제20권11호
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• pp.559-569
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• 2010

The liquid-phase sintering method was used to prepare a glass lens forming core composed of SiC-$Al_2O_3-Y_2O_3$. Spark plasma sintering was used to obtain dense sintered bodies. The sintering characteristics of different SiC sources and compositions of additives were studied. Results revealed that, owing to its initial larger surface area, $\alpha$-SiC offers sinterability that is superior to that of $\beta$-SiC. A maximum density of $3.32\;g/cm^3$ (theoretical density [TD] of 99.7%) was obtained in $\alpha$-SiC-10 wt% ($6Al_2O_3-4Y_2O_3$) sintered at $1850^{\circ}C$ without high-energy ball milling. The maximum hardness and compression stress of the sintered body reached 2870 Hv and 1110 MPa, respectively. The optimum ultra-precision machining parameters were a grinding speed of 1243 m/min, work spindle rotation rate of 100 rpm, feed rate of 0.5 mm/min, and depth of cut of $0.2\;{\mu}m$. The surface roughnesses of the thus prepared final products were Ra = 4.3 nm and Rt = 55.3 nm for the aspheric lens forming core and Ra = 4.4 nm and Rt = 41.9 for the spherical lens forming core. These values were found to be sufficiently low, and the cores showed good compatibility between SiC and the diamond-like carbon (DLC) coating material. Thus, these glass lens forming cores have great potential for application in the lens industry.

• 대한전자공학회논문지SD
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• 제37권6호
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• pp.34-42
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• 2000

우수한 성능을 가지며 소형${\cdot}$경량인 무선통신기기를 구현하기 위해서는 GHz 대의 고주파수에서 동작하는 소형 RF chip 인덕터의 개발은 중요한 연구분야가 되어왔다. 또한 최근 많이 사용되는 자성 ferrite core 재료는 300MHz 이상의 주파수영역에서 자화율이 급속하게 감소하여 고성능 RF chip 인덕터 개발에 큰 장애가 되고 있다. 따라서 본 논문에서는 비정질 $Al_2O_3$ 코아 재료를 응용한 단순 solenoid 형태의 소형${\cdot}$고성능 RF chip 인덕터를 연구하였다. Cu를 코일 (직경=40${\mu}m$)로 사용하였고 인덕터 크기는 $2.1mm{\times}1.5mm{\times}1.0mm$였다. 외부 전류원은 코일의 양단을 코아 가장자리에 적층된 Au 막에 본딩시킨 후 인가되었다. 코아의 성분은 EDX를 사용하여 분석하였다 개발된 인덕터의 인덕턴스 (L), quality factor (Q), 인피던스(Z)등의 주파수 특성은 RF impedance/Material Analyzer (HP16193A test fixture가 장착된 HP4291B)로 측정되었다. 인덕터들의 인덕턴스 값은 22 nH ~ 150 nH 범위를 가지며, 이들의 자기공진주파수 (SRF)는 1~3.5GHz 영역을 나타낸다. 또한 자기공진주파수가 증가함에 따라 인덕턴스 값이 감소하는 경향을 보이고 있다. 임피던스는 공진주파수에서 최대 값을 가지며 Q-factor의 값은 500 MHz ~ 1.5 GHz 주파수 범위에서 최대 70~97까지 얻어졌다.

• 한국주조공학회지
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• 제17권4호
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• pp.402-410
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• 1997

Developing a salt core for squeeze casting process, two different salt cores(pure salt core and mixed salt core) were fabricated and investigated. Pure salt core was composed of 100% NaCl and mixed salt core was made by mixtures of NaCl with MgO(1%), $Na_2B_4O_7$(2%), and talc(1%) as a binder or a strengthening agent. Salt cores were compacted to various theoretical density, heat treated, and then squeeze-cast with molten Al alloy(AC8A). The compression strength of salt cores were measured and the squeeze-cast products were examined for shape retention, infiltration of molten metal into the cores, and microstructures. The shape of salt core compacted at above 75% of the theoretical density was maintained stably. The higher theoretical density of salt cores gave higher compression strength, and the compression strength of mixed salt core was higher than that of pure salt core. Namely at 90% theoretical density, the compression strength of mixed salt core was $6.3 kg/mm^2$, compared to $4.6 kgmm^2$ for pure salt core. At a squeeze casting pressure of $1000 kg/cm^2$, molten Al alloy was infiltrated into pure salt core of under 85% of the theoretical density. At squeeze casting pressure of $1000 kg/cm^2$, only mixed salt core above 90% of the theoretical density were valid, but the shape of the core was altered in the case of pure salt core at 90% of theoretical density. A key factor for developing a salt core for squeeze casting process was estimated as the ultimate compressive strength of salt core.

• The Journal of Advanced Prosthodontics
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• 제6권3호
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• pp.224-232
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• 2014

PURPOSE. The purpose of the present study was to evaluate the effect of thermocycling and mechanical loading on the biaxial flexural strength and the phase transformation of one Ce-TZP/$Al_2O_3$ and two Y-TZP core materials. MATERIALS AND METHODS. Thirty disc-shaped specimens were obtained from each material. The specimens were randomly divided into three groups (control, thermocycled, and mechanically loaded). Thermocycling was subjected in distilled water for 10000 cycles. Mechanical loading was subjected with 200 N loads at a frequency of 2 Hz for 100000 times. The mean biaxial flexural strength and phase transformation of the specimens were tested. The Weibull modulus, characteristic strength, 10%, 5% and 1% probabilities of failure were calculated using the biaxial flexural strength data. RESULTS. The characteristic strengths of Ce-TZP/$Al_2O_3$ specimens were significantly higher in all groups compared with the other tested materials (P<.001). Statistical results of X-ray diffraction showed that thermocycling and mechanical loading did not affect the monoclinic phase content of the materials. According to Raman spectroscopy results, at the same point and the same material, mechanical loading significantly affected the phase fraction of all materials (P<.05). CONCLUSION. It was concluded that thermocycling and mechanical loading did not show negative effect on the mean biaxial strength of the tested materials.

• 한국전기전자재료학회논문지
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• 제25권8호
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• pp.593-601
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• 2012

Ordered mesoporous oxide films have been focused because of their low density, high interior specific surface area, and high thermal insulation. Specially, the ordered mesoporous oxide films prepared by self-assembly has many advantages due to easy process and high reproducibility. In this work, ordered mesoporous $SiO_2$, $Al_2O_3$, and $TiO_2$ films were synthesized by control of composition and processing parameter. Also, their structural, thermal, and mechanical properties were characterized variously. In conclusion, ordered mesoporous oxides will be one of core materials in new technology due to their excellent and unique properties.