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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 $302\;m^2/g$.
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.
Al 분말의 수화 반응과 스파크 플라즈마 열처리법으로 제조된 알루미나 성형체 연구
엄영랑,이민구,이창규,Uhm Y. R.,Lee M. K.,Rhee C. K. 한국분말야금학회 2005 한국분말재료학회지 (KPMI) Vol.12 No.6
The $Al_2O_3$ with various phases were prepared by simple ex-situ hydrolysis and spark plasma sintering (SPS) process of Al powder. The nano bayerite $(\beta-Al(OH)_3)$ phase was derived by hydrolysis of commercial powder of Al with micrometer size, whereas the bohemite (AlO(OH)) phase was obtained by hydrolysis of nano Al powder synthesized by pulsed wire evaporation (PWE) method. Compaction as well as dehydration of both nano bayerite and bohemite was carried out simultaneously by SPS method, which is used to fabricate dense powder compacts with a rapid heating rate of $100^{\circ}C$ per min. under the pressure of 50MPa. After compaction treatment in the temperature ranges from $100^{\circ}C\;to\; 1100^{\circ}C$, the bayerite and bohemite phases change into various alumina phases depending on the compaction temperatures. The bayerite shows phase transition of $Al(OH)_3{\to}{\eta}-Al_2O_3{\to}{\theta}-Al_2O_3{\to}\alpha-Al_2O_3$ sequences. On the other hand, the bohemite experiences the phase transition from AlO(OH) to ${\gamma}-Al_2O_3\;at\;350^{\circ}C.$ It shows AlO(OH) ${\gamma}-Al_2O_3{\to}{\delta}-Al_2O_3{\to}{\alpha}-Al_2O_3$ sequences. The ${\gamma}-Al_2O_3$ compacted at $550^{\circ}C$ shows a high surface area $(138m^2/g)$.
자기펄스 압축성형법에 의한 다이아몬드 공구용 세그먼트 분말 성형
윤종수,이정구,이민구,이창규,박문석,홍순직,Yun, J.S.,Lee, J.G.,Lee, M.K.,Rhee, C.K.,Park, M.S.,Hong, S.J. 한국분말야금학회 2008 한국분말재료학회지 (KPMI) Vol.15 No.5
This article presents the successful consolidation of the mixed Co and Diamond powders for a drilling segment by the combined application of magnetic pulsed compaction (MPC) and subsequent sintering, and their properties were analyzed. Homogeneous hardness (Hv 220) and density (97%) of sintered bulks fabricated by MPC were obtained by the new technique, where higher pressure has been employed for short period of time than that of general process. A fine microstructure and homogeneous hardness in the consolidated bulk were observed without cracks. Relatively higher drilling speed of 9.61 cm/min and life time of 6.55 m were found to the MPCed specimens, whereas the value of the specimens fabricated by general process was 11.71 cm/min and 7.96 m, respectively. A substantial improvement of mechanical properties of segment was achieved through this study.
신촉매 나노 구리산화물을 이용한 심혈관 의약품용 Dihydropyrimidine 제조 연구
엄영랑,이민구,이창규,Uhm Y. R.,Lee M. K.,Rhee C. K. 한국분말야금학회 2005 한국분말재료학회지 (KPMI) Vol.12 No.6
The copper oxide nano powders were synthesized by levitational gas condensation (LGC) method, and were applied to catalyst to fabricate 3,4-dihydropyrimidin-2-(1H)-one. Processes of adsorption of Biginelli reaction reagents on the copper nanooxide surface $Cu_2O{\circ}CuO$ were studied by IR-spectroscopy. It was shown that benzaldehyde coordination, acetoacetic ether on the oxide surface is carried out with participation of carbonyl fragments, urea by N-H bonds which affects positively on the reagents reactivity.
자기펄스 가압성형법에 의한 알루미나 나노분말의 치밀화 및 특성 평가
강래철,이민구,김홍회,이창규,홍순직,Kang, R.C.,Lee, M.K.,Kim, W.W.,Rhee, C.K.,Hong, S.J. 한국분말야금학회 2008 한국분말재료학회지 (KPMI) Vol.15 No.1
This article presents the challenges toward the successful consolidation of $Al_2O_3$ nanopowder using magnetic pulsed compaction (MPC). In this research the ultrafine-structured $Al_2O_3$ bulks have been fabricated by the combined application of magnetic pulsed compaction (MPC) and subsequent sintering, and their properties were investigated. The obtained density of $Al_2O_3$ bulk prepared by the combined processes was increased with increasing MPC pressure from 0.5 to 1.25 GPa. Relatively higher hardness and fracture toughness in the MPCed specimen at 1.25 GPa were attributed to the retention of the nanostructure in the consolidated bulk without cracks. The higher fracture toughness could be attributed to the crack deflection by homogeneous distribution and the retention of nanostructure, regardless of the presence of porosities. In addition, the as consolidated $Al_2O_3$ bulk using magnetic pulsed compaction showed enhanced breakdown voltage.