• 한국분말재료학회지
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• 제31권1호
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• pp.30-36
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• 2024

The aerospace and power generation industries have an increasing demand for high-temperature, high-strength materials. However, conventional materials typically lack sufficient fracture toughness and oxidation resistance at high temperatures. This study aims to enhance the high-temperature properties of Nb-Si-Ti alloys through ball milling. To analyze the effects of milling time, the progression of alloying is evaluated on the basis of XRD patterns and the microstructure of alloy powders. Spark plasma sintering (SPS) is employed to produce compacts, with thermodynamic modeling assisting in predicting phase fractions and sintering temperature ranges. The changes in the microstructure and variation in the mechanical properties due to the adjustment of the sintering temperature provide insights into the influence of Nb solid solution, Nb5Si3, and crystallite size within the compacts. By investigating the changes in the mechanical properties through strengthening mechanisms, such as precipitation strengthening, solid solution strengthening, and crystallite refinement, this study aims to verify the applicability of Nb-Si-Ti alloys in advanced material systems.

• 한국광물학회지
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• 제15권2호
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• pp.95-103
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• 2002

본 연구는 일라이트-스멕타이트 혼합층광물(I-S)의 구조를 MacEwan 결정자 모델과 기본입자 모델을 통하여 살펴봄으로써, 팽창성(% $S_{XRD}$), MacEwan 결정자두께( $N_{CSD}$), 평균기본입자두께( $N_{F}$ ) 간의 관계를 정량적으로 해석하고자 하였다. 두 모델에 대한 비교를 통하여, % $S_{XRD}$, $N_{CSD}$, $N_{F}$ 는 서로 독립된 변수들이 아니고 I-S 구조 내에서 특정한 기하학적 관계를 가지고 있음을 알 수 있었다. % $S_{XRD}$는 단범위적층효과에 의해 $N_{CSD}$에 영향을 받고, $N_{F}$ 및 스멕타이트 층간개수( $N_{S}$ )와 $N_{s}$ =( $N_{F-}$1)/(100%/% $S_{XRD-}$ $N_{F}$ ) 관계가 성립함을 알 수 있었다. 특히, 이 관계로부터 % $S_{XRD}$와 $N_{F}$ 는 물리적으로 제한된 조건인 1< $N_{F}$ <100%/ % $S_{XRD}$를 만족해야 한다는 결과를 도출할 수 있었다. 본 연구는 이러한 물리적 제한조건을 이용하여, % $S_{XRD}$, $N_{F}$ , $N_{s}$ , 질서도 등을 종합적으로 해석하는데 유용할 것으로 사료되는 다이어그램을 제시하였으며, 금성산화 산암복합체에서 산출되는 I-S에 대한 XRD 자료를 이용하여, 이를 검증하였다. 또한, 자연상 I-S는 % $S_{XRD}$가 감소할수록, $N_{F}$ 는 물리적 상한조건인 $N_{F}$ =100%/% $S_{XRD}$에서 점차 멀어지게 됨을 알 수 있었으며, 이러한 결과는 기본입자가 두꺼워질수록 적층능력이 감소하는 것에서 기인한 것으로 사료된다.다.하는 것에서 기인한 것으로 사료된다.다.

• Advances in nano research
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• 제1권4호
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• pp.193-202
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• 2013

In this article, we present the effects of Ag doping and after-growth thermal annealing on the photoluminescence (PL) and thermoluminescence (TL) behaviors of $SnO_2$ nanoparticles. $SnO_2$ nanoparticles of 4-7 nm size range containing different Ag contents were synthesized by hydrothermal process. It has been observed that the after-growth thermal annealing process enhances the crystallite size and stabilizes the TL emissions of $SnO_2$ nanostructures. Incorporated Ag probably occupies the interstitial sites of the $SnO_2$ lattice, affecting drastically their emission behaviors on thermal annealing. Both the TL response and dose-linearity of the $SnO_2$ nanoparticles improve on 1.0% Ag doping, and subsequent thermal annealing. However, a higher Ag content causes the formation of Ag clusters, reducing both the TL and PL responses of the nanoparticles.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2010년도 춘계학술대회 초록집
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• pp.101.3-101.3
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• 2010

Glass frit은 실리콘 태양전지의 Ag/Si contact을 위해 필수적이다. 태양전지의 고효율 특성 구현 때문에, Contact resistance(Rc)가 우수한 Pb-frit의 사용이 불가피한 상황이다. 본 연구는 기존의 Pb계를 무연화함과 동시에 동등수준의 효율을 목표로 하였다. Ag 분말 size 및 glass frit의 열적 거동 특성이 SiNx 코팅층 침투와 Ag re-crystallites에 미치는 영향에 대해 평가하였다. 6 inch 다결정 실리콘 웨이퍼를 사용하였으며, softening temperture(Sp)별로 4종의 Bi계 glass frit을 제조 하였고, 분말 size가 다른 3종의 Ag powder를 선정하였다. Glass frit Sp가 $460^{\circ}C$ 이상의 경우에는 효율이 10% 미만이였으나 Sp $460^{\circ}C$ 이하에서는 16% 수준의 효율을 확인할 수 있었다.

• 전자공학회논문지T
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• 제36T권3호
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• pp.13-18
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• 1999

다이아몬드 박막은 RF PACVD법에 의해 수소와 메탄으로부터 실리콘 웨이퍼 상에 성장되어졌다. 박막 성장 전에 표면의 핵생성 밀도를 증가시키기 위하여 1㎛의 다이아몬드 페이스트로 기계적 흡집을 내어 사용하였다. 메탄 농도를 변화시켜 제작한 박막에 대한 평가는 XRD, SEM 및 Raman Spectroscopy에 의해 이루어졌다. 성장된 박막의 결정성은 메탄 농도가 낮을수록 증가되었다.

• 한국표면공학회지
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• 제17권2호
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• pp.41-58
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• 1984

Zinc was electrodeposited from cyanide solutions at temperature from 20$^{\circ}C\;to\;40^{\circ}C$ in the range of current density from 0.5 to 8A/$dm^2$. The preferred orientation changed from (10.3)+(11.0) to (11.0) texture with increasing cathode overpotential in the additive free solution, while the (11.0) preferred orientation developed at lower overpotentials (800-1270 mV) and the (11.0)+(10.0) preferred orientation was formed at higher overpotential (1300-1400mV) in the solution with brightner. Mossy type of morphology developed mostly in the additive free deposits and the microstructure of the cross section of the above deposits changed from columar structure to granular structure with increasing overpotential. The surface appearance of the deposits with additive having (11.0) texture was the smooth deposit of very small crystallite, while that of the deposits having (11.0)+(10.0) texture was fine crystalline deposit. The microstructure of the cross section of them was the fine field oriented type of structure.

• 한국표면공학회지
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• 제37권2호
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• pp.92-98
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• 2004

The current efficiency and the microstructure of the trivalent Cr deposits plated in flow cell system were investigated according to additives in sulfate bath and current density. The current efficiency of the deposits plated in the formic acid complexed bath was noticeably higher than that of the deposits from glycine complexed bath. The current efficiency of the deposits from the complexed baths with boric acid buffer increased linearly with current density in the range of 60-100 A/dm$^2$, while that of the deposits from the baths with both Al sulfate and mixed buffers increased parabolically with current density. The nodular crystallite size of the deposits increased with current density, and the deposits plated in low current density region had relatively smooth surface appearance with fine grains. The structure of the deposits from the complexed baths with boric acid buffer changed from amorphous structure to crystalline one with strong (110)peak with increasing current density. The deposits from the baths with both Al sulfate and mixed buffers had generally amorphous structure.

• Carbon letters
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• 제14권2호
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• pp.117-120
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• 2013

In this study, an electro-catalyst of Pt nanoparticles supported by polypyrrole-functionalized graphene (Pt/PPy-reduced graphene oxide [RGO]) is reported. The Pt nanoparticles are deposited on the PPy-RGO composite by chemical reduction of H2PtCl6 using NaBH4. The presence of graphene (RGO) caused higher activity. This might have been due to increased electro-chemically accessible surface areas, increased electronic conductivity, and easier charge-transfer at polymer-electrolyte interfaces, allowing higher dispersion and utilization of the deposited Pt nano-particles. Microstructure, morphology and crystallinity of the synthesized materials were investigated using X-ray diffraction and transmission electron microscopy. The results showed successful deposition of Pt nano-particles, with crystallite size of about 2.7 nm, on the PPy-RGO support film. Catalytic activity for methanol electro-oxidation in fuel cells was investigated using cyclic voltammetry. The fundamental electrochemical test results indicated that the electro-catalytic activity, for methanol oxidation, of the Pt/PPy-RGO combination was much better than for commercial catalyst.

• 한국재료학회지
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• 제9권1호
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• pp.30-34
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• 1999

A polyacrylonitrile(PAN)-based carbon fiber tow was heat-treated by directly passing electric current through the tow. The effects of the stretching stress applied during high temperature heat-treatment of PAN-based carbon fibers were investigated by measuring the electric resistance changes taking place during the internal resistance heating. The structure parameters characterizing the stacks of carbon layer, such as interlayer spacing, sizes and orientation of the carbon fibers heat-treated with hot-stretching were evaluated as a function of surface temperature of tow during heat treatment in the range of $1000~2400^{\circ}C$. Though the layer extent in the fiber axis direction depends strongly on the electric resistance, the changes in a crystallite parameter is independent of the longitudinal strain.

• 한국재료학회지
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• 제17권1호
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• pp.1-5
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• 2007

GaN thin fan were grown by spin coated colloidal GaOOH precursor. Polycrystalline GaNs with crystalline size of $10{\sim}100nm$ were grown on $SiO_2$ substrate. The shape of crystallite above $900^{\circ}C$ had the hexagonal plate and column type. X-ray diffraction patterns for them correspond to those of the hexagonal wurtzite GaN. With increasing droplets. i.e, thickness of deposited layers, XRD intensity increased. PL (photoluminescence) spectrum consisted with an weak near band-edge emission at 3.45 eV and a broad donor-acceptor emission band at 3.32 eV. From the low temperature PL measurement on GaN grown at $800^{\circ}C$ that the shallow donor-acceptor recombination induced emission was more intense than the near band-edge excitonic emission.