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플라즈마 용사에 의한 Y-Ba-Cu-O 계 고온초전도체의 후막 제조에 관한 연구
주승기,이헌 대한금속재료학회(대한금속학회) 1990 대한금속·재료학회지 Vol.28 No.2
YBa₂Cu₃O_7 thick films whose thickness varies from 150㎛ to 500㎛ were fabricated by a plasma spraying technique. It turned out that fresh films didn't show the 123 superconducting phase by XRDP regardless of spraying conditions but annealed films showed high Tc under the particular spraying conditions. It was found that a particle size of the feeding powder and the annealing temperature after spraying play an important role on determining the superconductivity of the thick films. In this set of experiments, a particle size of over 100㎛ and the annealing temperature of 950℃ in O₂ ambient after the plasma spray turned out to be the best conditions to obtain a sharp Tc at around 85 K. Also it has been found that when H₂ gas instead of He was used as a secondary plasma gas superconduction phase formation was depressed and the reason has not been varified in this work.
W-Cu 의 액상소결시 코발트 첨가에 의한 치밀화 촉진
주승기,이석운,인태형 대한금속재료학회(대한금속학회) 1993 대한금속·재료학회지 Vol.31 No.10
In order to obtain uniformly distributed tungsten-copper powder, the submicron tungsten powder was coated with copper by a newly developed process : fluidized bed reduction. Tungsten powder was initially coated with copper dichlorides and then reduced in fluidized beds by hydrogen gas flow. By the same method, cobalt was added to this binary alloy for the purpose of altering the chemical relations between tungsten and copper. In case of 75W-25Cu, full densification could not be attained even after the prolonged sintering of 4 hours at 1200 C because of a large wetting angle of copper on tungsten. The addition of cobalt of 0.5 weight percent, however, considerably enhanced the densification of 75W-24. 5Cu-0.5Co and high density above 95% was attainable within ramping-up to 1200℃. The enhancement of sintering by cobalt addition was revealed to result from the decrease of the wetting angle of liquid copper, which was due to the formation of an intermetallic compound between tungsten and cobalt dissolved in liquid copper.
반응성 스퍼터링법에 의해 형성된 니켈 산화물 박막에서 리튬의 전기화학적 거동에 관한 연구
주승기,이세희,황규호 대한금속재료학회(대한금속학회) 1994 대한금속·재료학회지 Vol.32 No.10
Electrochemical insertion and removal of lithium into nickel oxide films prepared by reactive sputtering have been investigated. The chemical diffusion kinetics of lithium in NiO thin films have been evaluated by Cyclic Voltammetry and AC impedance spectroscopy. It has been found that charge transfer density improves as NiO becomes lithiated and enhancement of lithium diffusion coefficient with increase of x in Li_xNiO is mainly responsible for it.
Co-Cu 과립박막의 거대자기저항 현상에 대한 조성의존성과 열처리의 영향
주승기,박주욱,고이홍의,관원귀언,등삼계안 대한금속재료학회(대한금속학회) 1994 대한금속·재료학회지 Vol.32 No.11
The composition and the annealing effect on the giant magnetoresistance of Co-Cu granular films fabricated by RF sputtering were investigated by TEM and NMR analysis. The maximum MR of 17% at 4.2K could be obtained at cobalt composition of 20 at%. From the TEM and NMR analysis, it has been found that the size of cobalt particles and the composition profile near the interfaces of cobalt particles are almost invariable with increase of cobalt concentration, while the interparticle distance decreases. Therefore, it could be concluded that the interparticle distance was mainly responsible for the existence of the maximum MR with respect to the cobalt composition in this system. According to the analysis of NMR spectrum, annealing of the films sharpened the composition profile of the interface between the cobalt particles and the copper matrix, which resulted in enhancement of the GMR values.