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TiO<sub>2</sub> 나노 분말의 분산 안정성 및 침강 특성
우승희,이민구,이창규,Woo S.H.,Lee M.K.,Rhee C.K. 한국분말야금학회 2006 한국분말재료학회지 (KPMI) Vol.13 No.4
In this study, the colloidal stability and sedimentation behavior of crystalline $TiO_2$ particles (300nm) in various organic solvents have been investigated by means of a backscattered light flux profile (Turbiscan). The backscattered light flux profiles revealed that the $TiO_2$ nanoparticles were readily sedimented in water, methyl alcohol, and ethyl alcohol due to a flocculation-induced particle growth, while a particle coalescence and a sedimentation of the $TiO_2$ nanoparticles were hardly observed in isopropyl alcohol. The migration velocities of the $TiO_2$ particle were measured as around 6.15/min, 12.53 m/min, 6.51m/min, and 0.18m/min for water, methyl alcohol, ethyl alcohol, and isopropyl alcohol, respectively, showing a remarkably slow migration of the $TiO_2$ particles in isopropyl alcohol.
우승희,이민구,이창규,Woo S.H.,Lee M.K.,Rhee C.K. 한국분말야금학회 2006 한국분말재료학회지 (KPMI) Vol.13 No.2
Aluminum hydroxides were synthesized by a simple electrolytic reaction of aluminum plates. The aluminum hydroxide, boehmite (AlO(OH)), was predominantly formed in the application of electrical potential at and above 30V, while the mixture of bayerite ($Al(OH)_3$) and boehmite (AlO(OH)) phases were formed below 20V. The boehmite has a clear fibrous structure controlled on nanometer scale. On the contrary, the bayerite consists of the typical hourglass or semi-hourglass shaped coarse crystals as a result of aggregation of various crystals stacked together. The specific surface area of the boehmite nanofiber was markedly high, approaching at about $302\;m^2/g$.
화염경화 표면처리 공정에 의한 12Cr 강의 잔류응력 거동
이민구(M. K. Lee),김광호(G. H. Kim),김경호(K. H. Kim),김흥회(W. W. Kim) 한국표면공학회 2004 한국표면공학회지 Vol.37 No.4
The residual stresses on the surfaces of low carbon 12Cr steels used as a nuclear steam turbine blade material have been studied by controlling the flame hardening surface treatments. The temperature cycles on the surfaces of 12Cr steel were controlled precisely as a function of both the surface temperature and cooling rate. The final residual stress state generated by flame hardening was dominated by two opposite competitive contributions; one is tensile stress due to phase transformation and the other is compressive stress due to thermal contraction on cooling. The optimum processing temperatures required for the desirable residual stress and hardness were in the range of 850℃ to 960℃ on the basis of the specification of GE power engineering. It was also observed that the high residual tensile stress generated by flame hardening induced the cracks on the surfaces, especially across the prior austenite grain boundaries, and the material failure virtually, which might limit practical use of the surface engineered parts by flame hardening.
화염급냉 표면처리된 Cu-8.8Al-4.5Ni-4.5Fe 합금의 미세구조 분석 및 내마모성에 관한 연구
이민구 ( M. K. Lee ),홍성모 ( S. M. Hong ),김광호 ( G. H. Kim ),김경호 ( K. H. Kim ),김홍회,( W. W. Kim ) 한국열처리공학회 2004 熱處理工學會誌 Vol.17 No.6
N/A The flame quenching process has been employed to modify the surfaces of commercial marine propeller material, aluminum bronze alloy (Cu-8.8AI-5Ni-5Fe), and the microstructure, hardness and wear properties of the flame-quenched layers have been studied. The thermal history was accurately monitored during the process with respect to both the designed maximum surface temperature and holding time. The XRD and EDX analysis have shown that at temperatures above T_(β), the microstructure consisting of α+κ phases changed into the α+ß` martensite due to an eutectoid reaction of α+κ→ß, and a martensitic transformation of ß→ß`. The ß` martensite phase formed showed a face-centered cubic (FCC) crystal structure with the typical twinned structure. The hardness of the flame-quenched layer having the α+ß` structure was similar to that of the α+ß structure and depended sensitively on the size and distribution of hard κ and ß` phases with depth from the surface. As a result of the sliding wear test, the wear resistance of the flame-quenched layer was markedly enhanced with the formation of the ß` martensite.