• 연구논문집
• /
• 통권25호
• /
• pp.163-168
• /
• 1995

The intermetallic compound $Ni_3Al$ causes a peritectic reaction at the composition and temperature very close to the eutectic reaction in Ni-Al system. Although the phase diagram accepted for this system by ASM Handbook has the eutectic forming between the $\gamma$ and $\gamma$ phases, directional solidification study has shown that the eutectic occurs between $\beta$ and $\gamma$. This work examines the liquidus region using quenched, directional solidification experiments that preserve the microstructrues formed at the solidification front. It is also shown that under certain composition and growth conditions a metastable eutectic between the $\beta$ and $\gamma$ phases forms in this system. Finding of the metastable eutectic provided an important information to understand the phase equilibria near the $Ni_3Al$ composition.

• 한국재료학회:학술대회논문집
• /
• 한국재료학회 2012년도 춘계학술발표대회
• /
• pp.104.2-104.2
• /
• 2012

이종 재료의 접합에 대한 연구는 단일 재료에서 얻을 수 없는 물리적/기계적 특성과 이종 재료의 우수한 특성을 얻을 수 있다는 장점이 있어 국내외 적으로 연구가 활발히 진행되고 있다. 이러한 이종 접합 기술은 구조재료와 에너지 변환분야에 가장 많이 사용되고 있으며, 그 외 광촉매와 Thin film, 경량구조재료 등에도 사용되고 있다. 그 중 FGM(Functional Graded Materials)는 조성의 점진적인 변화를 통하여 접합하는 방법으로 이종 재료 접합 시 발생하는 내부 응력을 해소해줌으로써 적합한 방법이라고 할 수 있다. FGM 제작에 사용되는 방법으로 널리 알려진 것들로는 plasma spraying, 원심주조, 분말 야금법, PVD, CVD 그리고 EPD(electrophoretic deposition) 등이 있다. 이중에서 EPD는 수용액이나 유기용매와 같은 분산매체 중에 콜로이드 입자의 표면에 대전되는 전하를 이용하여, 외부에서 전장을 걸어서 입자의 움직임을 제어하는 기술이다 EPD는 코팅 속도가 상대적으로 빠르고 두꺼운 코팅 층 제작이 가능하다. 또한 바인더, 윤활제 또는 가소제를 사용하지 않고 다양한 종류와 모양의 기판 위에 균일한 코팅이 가능하다는 장점이 있다. 본 연구에서는 Ni substrate를 이용하여 그 위에 Ni과 $Al_2O_3$의 조성을 점진적으로 변화시켜 FGM을 EPD 방법으로 코팅하였다. 여기서 사용된 Ni은 높은 녹는점과 좋은 연성으로 인해 성형이 용이하여 구조재료로 적합하며, $Al_2O_3$는 고내열성과 내부식성을 가지며 경도가 높다는 장점이 있다. 본 연구에서는 EPD 방식을 이용하여 Ni/$Al_2O_3$ FGM을 코팅하였으며, 코팅 후 발생하는 substrate와의 접착력 문제를 해결하기 위해서 건조 방식과 substrate의 표면 상태를 최적화하여 다층의 Ni/$Al_2O_3$ FGM을 코팅 및 소결하였다. Zeta-potential 측정을 통해 electrophoretic mobility와 suspension의 분산 안정도를 평가 할 수 있었으며, X-ray 회절 분석(XRD)을 통하여 Ni 의 환원 여부를 확인하였다. 또한 Scanning electron microscopy(SEM) 분석을 통하여 미세구조 분석을 하였고, 최종적으로 Electron Probe Micro Analyzer (EPMA) 를 이용하여 다층 구조의 조성변화를 확인함으로 Ni/$Al_2O_3$의 FGM 코팅이 이루어졌음을 확인하였다.

• 한국수소및신에너지학회논문집
• /
• 제21권5호
• /
• pp.412-418
• /
• 2010

Steam reforming of n-hexadecane, a major component of diesel over Ni-based hydrotalcite-like catalyst was carried out at $900^{\circ}C$ at atmospheric pressure with space velocity of $10,000h^{-1}$ and feed molar ratio of steam/carbon=3.0. Ni-based hydrotalcite catalyst was prepared by a solid phase crystallization (spc) method and characterized by $N_2$-physisorption, CO chemisorption, TPR., XRD, and TEM techniques. It was found that spc Ni/MgAl catalyst showed higher catalytic stability and inhibition of carbon formation than Ni/$\gamma-Al_2O_3$ catalyst under the tested conditions. The results suggest that the modified spc-Ni/MgAl catalyst after optimization may be applied for the SR reaction of diesel.

• 한국에너지공학회:학술대회논문집
• /
• 한국태양에너지학회, 한국에너지공학회 1993년도 춘계 공동학술발표회 초록집
• /
• pp.87-89
• /
• 1993

용융탄산염 연료전지 양극 재료인 tape casting된 다공성 Ni-Cr 합금과 Ni-Al 합금의 전기화학적 특성과 소결 및 creep특성이 양극조건의 분위기 $650^{\circ}C$에서 조사되었다. 이들 전극재료의 전류밀도는 100 mV의 과전압에서 약 100~150㎃/$\textrm{cm}^2$의 크기이었다. Ni-Al 합금에서는 Ni 표면에 형성된 $Al_2$O$_3$의 영향으로 소결저항성이 큰 것으로 나타났으며, Creep 특성도 Al 첨가량의 증가에 의해 향상되었다.

• 한국전기전자재료학회:학술대회논문집
• /
• 한국전기전자재료학회 2008년도 하계학술대회 논문집 Vol.9
• /
• pp.208-209
• /
• 2008

Ni/Ti/Al multilayer system was tested for low-resistance ohmic contact formation to Al-implanted p-type 4H-SiC. Compared with conventional process using Ni, Ni/Ti/Al contact shows perfect ohmic behavior, and possesses much lower contact resistance of about $2.5\times10^{-4}\Omega{\cdot}cm^2$ after $930^{\circ}C$ RTA, which is about 2 orders of magnitude smaller than that of Ni contact. Contact resistance gradually increased as the RTA temperature was lowered in the range of 840 ~ $930^{\circ}C$, and about $3.4\times10^{-4}\Omega{\cdot}cm^2$ was obtained at the lowest RTA temperature of $840^{\circ}C$. Therefore, it was shown that RTA temperature for ohmic contact formation can be lowered to at least $840^{\circ}C$ without significant compromise of contact resistance.

• 한국자기학회지
• /
• 제9권6호
• /
• pp.291-295
• /
• 1999

IrMn을 반강자성체로 사용하고 순수한 Al을 자연산화시켜서 제작한 Al203를 절연층으로 사용한 spin-valve 형태의 NiFe/Co/Al2O3/Co/IrMn 터널링 접합의 자기저항효과를 조사하였다. IrMn의 두께가 약 100$\AA$이상일 경우 강자성체와의 교환상호작용이 발생하기 때문에 NiFe(183$\AA$)/Co(17$\AA$)/Al-oxide(16$\AA$)IrMn(100$\AA$) 터널링 접합에서 자기저항효과가 관찰되며 TMR비(%)는 $\pm$20 Oe의 인가자장에서 10% 이상의 값을 갖는다. 하부 자성층인 NiFe/Co의 길이방향으로 수행한 자장 중 열처리에 의해 저항은 다소 감소하고 TMR비(%)는 열처리온도에 따라 증가하여 20$0^{\circ}C$에서 23%의 최대값을 갖는다. 자성층의 폭을 변호시켜 접합면적을 달리한 시료의 TMR비(%)는 접합면적이 증가할수록 증가하고 저항은 감소한다.

• 한국세라믹학회지
• /
• 제50권3호
• /
• pp.195-200
• /
• 2013

Here, we report preparation of cyan ceramic nano-pigment for inkjet printing and the Ni substitutional effects on the cyan color. $MgAl_2O_4$ was selected as the crystalline host network for the synthesis of nickel-based cyan ceramic nano-pigments. Various compositions of $Ni_xMg_{1-x}Al_2O_4$ ($0{\leq}x{\leq}1$) powders were prepared using the polymerized complex method. The powder was then preheated at $400^{\circ}C$ for 5 h and finally calcined at $1000^{\circ}C$ for 5 h. XRD patterns of $Ni_xMg_{1-x}Al_2O_4$ showed a single phase of the spinel structure in all the compositions. The particle sizes ranged from 20 to 50 nm in TEM observations. The characteristics of the color tones of $Ni_xMg_{1-x}Al_2O_4$ were analyzed by UV-Visible spectroscopy and CIE $L^*a^*b^*$ measurement. CIE $L^*a^*b^*$ measurement results indicate that the pigment color changes from light cyan to deep cyan due to the decrease of the $a^*$ and $b^*$ values with an increase of an Ni substitutional amount. In addition, the thermal stability and the binding nature of $Ni_xMg_{1-x}Al_2O_4$ are also discussed using TG-DSC and FT-IR results respectively.

• 한국재료학회지
• /
• 제17권8호
• /
• pp.420-424
• /
• 2007

Precipitation behavior has been studied in NiTi-based ordered alloy using transmission electron microscopy. The hardness after solution treatment is high in NiTi alloy suggesting the large contribution of solid solution strengthening in this alloy system. However, the amount of age hardening is not large as compared to the large microstructural variations during aging. At the beginning of aging, the $L2_1-type$ $Ni_2AlTi$ precipitates keep a lattice coherency with the NiTi matrix. By longer periods of aging $Ni_2AlTi$ precipitates lose their coherency and change their morphology to the globular ones surrounded by misfit dislocations. Misfit dislocations, which are observed on {100} planes of H-precipitates have the Burgers vector of a <100> with a pure edge type. The lattice misfits of $NiTi-Ni_2AlTi$ system is estimated from the spacings of misfit dislocations to be 1.3% at 1273 K. The lattice misfits decrease with increasing aging temperature in this system.

• 한국수소및신에너지학회논문집
• /
• 제21권6호
• /
• pp.500-506
• /
• 2010

The metal monolith catalyst coated with 15wt% Ni/$MgAl_2O_4$ is applied to the natural gas steam reforming for hydrogen production. To address the improvement of adherence between metal monolith and catalyst coating layer, the pre-calcination temperature as well as the coating conditions of $Al_2O_3$ sol are optimized. When the Fe-Cr alloy monolith is pre-calcined at $900^{\circ}C$ for 6 h, $Al_2O_3$ layer was formed uniformly on the entire surface of the metal substrate. It is seen that the formation of $Al_2O_3$ layer on the monolith surface is essential for the uniform coating of $Al_2O_3$ sol onto the monolith substrate. The monolith catalyst coated with 10wt% $Al_2O_3$ sol shows high $CH_4$ conversion and good thermal stability as compared with the monolith catalyst without $Al_2O_3$ sol coating under severe reaction conditions with high GHSV of 30,000 $h^{-1}$ at $700^{\circ}C$. In addition, the metal monolith catalyst shows higher catalytic activity and better thermal conductivity than 15wt% Ni/$MgAl_2O_4$ pellet catalyst.

• 한국분말재료학회지
• /
• 제9권5호
• /
• pp.352-358
• /
• 2002

The effects of boron or manganese added as $B_4C$, Mn, $TiB_2$, B on TiC-30vo1.%$Ni_3Al$ cermet sintered at 1380 and $1400^{\circ}C$ for 1 hour, were examined in relation with shrinkage, relative density, microstructure, lattice parameter, hardness and fracture toughness ($K_{IC}$). The results are summarized as follows: 1) The highest shrink-age showed about 30.5% in the specimen added B$_4$C and the maximum relative density was about 99% in the specimen added $TiB_2$; 2) The grains of TiC were grown during sintering and made the surrounding structure by adding boron and manganese. The largest grain size showed about $2.8\mutextrm{m}$ in the specimen with boron sintered at $1400^{\circ}C$;3) The lattice parameter of TiC was about $4.325\AA$ and $Ni_3Al$ about $3.592\AA$ by adding other elements; 4) The highest hardness was about $1100kgf/\textrm{mm}^2$ in the specimen with B4C; 5) The fracture toughness ($K_{IC}$) showed about $15MNm^{-3/2}$ in the specimen added $TiB_2$.