• Journal of Powder Materials
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• v.8 no.3
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• pp.186-191
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• 2001

Several fabrication processes, corresponding nanostructural features and multifunctionality as well has been investigated for oxide ceramic based nanocomposites with metal nanodispersion (i.e., ceramic/metal nanocomposites). Transition metal (Ni, Co, etc) dispersed alumina and zirconia based nanocomposites have been synthesized by reducing and hot-press sintering of ceramic and metal oxide mixtures prepared by several method. Improved fracture strength (1.1 and 1.9 GPa for $Al_2O_3/Ni$ and $ZrO_2/Ni$ nanocomposites, respectively) of these composites have been achieved according to their nanostructures. In addition, ferromagnetic characteristic has been kept. The variation of magnetization with an applied stress has found to be more sensitive as smaller as the magnetic metal dispersion is. This result thus suggests the possibility of fracture and/or stress sensing of the composites by simple magnetic measurement.

• Journal of Powder Materials
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• v.13 no.1 s.54
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• pp.25-32
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• 2006

The alumina dispersion-strengthened (DS) C15715 Cu alloy fabricated by a powder metallurgy route was annealed at temperatures ranging from $800^{\circ}C\;to\;1000^{\circ}C$ in the air and in vacuum. The effect of the annealing on microstructural stability and room-temperature mechanical properties of the alloy was investigated. The microstructure of the cold rolled OS alloy remained stable until the annealing at $900^{\circ}C$ in the air and in vacuum. No recrystallization of original grains occurred, but the dislocation density decreased and newly formed subgrains were observed. The alloy annealed at $1000^{\circ}C$ in the air experienced recrystallization and grain growth took place, however annealing in vacuum at $1000^{\circ}C$ did not cause the microstructural change. The mechanical property of the alloy was changed slightly with the annealing if the microstructure remained stable. However, the strength of the specimen that was recrystallized decreased drastically.

• Proceedings of the International Microelectronics And Packaging Society Conference
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• 2002.05a
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• pp.252-254
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• 2002

Metal oxides with high dielectric constants have the potential to expend scaling of transistor gate capacitance beyond that of ultrathin silicon dioxide. However, during deposition of most metal oxides on silicon, an interfacial region of SiOx is formed and limits the specific capacitance of the gate structure. We deposisted aluminum oxide and examined the composition of the interfacial layer by employing high-resolution X-ray photoelectron spectroscopy and X-ray reflectivity. We find that the interfacial region is not pure SiO$_2$, but is composed of a complex depth-dependent ternary oxide of $AlSi_xO_y$ and the pure SiO$_2$.

• Korean Journal of Materials Research
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• v.8 no.8
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• pp.714-719
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• 1998

저용융점을 가진 새로운 무기접착제인 단사정 HBO2가 알루미나 분말의 선택적 레이저 소결을 하기 위한 접착제로서 개발되었다. 12$0^{\circ}C$로 유지된 진공오븐 안에서 Boron Oxide 분말을 탄수시키면 단사정 HBO2가 만들어진다. 이것을 이용하여 만들어진 green body는 현재까지 알루미나 분말의 선택적 레이저 소결을 위하여 개발된 다른 무기 접착제들인 알루미늄(AI)과 Ammonium Phosphate(NH4H2PO4)을 이용하여 제조된 것에 비교하여 훨씬 높은 굽힘 강도를 가지고 있고 또 정밀도가 우수하였다. Green body를 열처리하여서 얻은 세라믹 시편도 똑같은 결과를 보여주었다. 이 이유는 단사정 HBO2가 낮은 점도를 보여주고 알루미나 분말에 대하여 좋은 젖음성을 가지고 있기 때문에 가능한 것으로 사료되어진다. 접착제로서 Boron Oxide의 양, 레이저 에너지밀도 등이 SLS에 의하여 제조되어진 복합재료의 굽힘강도에 미치는 영향이 조사되었다.

• Journal of Surface Science and Engineering
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• v.50 no.6
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• pp.427-431
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• 2017

Anodic aluminum oxide (AAO) film has recently attracted much attention as a key material for the fabrication of various nanostructures. A control of anodizing voltage (U) was employed to render different anodic aluminum oxide (AAO) nanostructures with pore diameter ($D_p$) and interpore distance ($D_{int}$) in oxalic acid. In this work, we study the effect of stepwise modulation of anodizing voltages on the shape and dimension of porous structures along the vertical direction and demonstrate the fabrication of hierarchical layers of systematically controlled three-dimensional (3D) pore profile.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.06a
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• pp.77-78
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• 2006

We fabricated photonic crystals on GaAs and GaN substrates. After anodizing the aluminium thin film in electrochemical embient, the porous alumina was implemented to the mask for reactive ion beam etching process of GaAs wafer. And photonic crystals in GaN wafer were also fabricated using electron beam nano-lithography process. The coated PMMA thin film with 200 nm-thickness on GaN surface was patterned with triangular lattice and etched out the GaN surface by the inductively coupled plasma source. The fabricated GaAs and GaN photonic crystals provide the enhanced intensities of light emission for the wavelengths of 858 and 450 nm, respectively. We will present the detailed dimensions of photonic crystals from SEM and AFM measurements.

• Journal of Surface Science and Engineering
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• v.33 no.4
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• pp.281-288
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• 2000

To understand the effect of Fe on the oxidation behavior of TiAl alloys, TiAl-(2, 4, 6at% )Fe were oxidized at 800 and 90$0^{\circ}C$ in air. The oxidation resistance of TiAl-Fe alloys increased with increasing an iron content. The scales formed consisted of an outer $TiO_2$ layer, an intermediate $A1_2$$O_3$ layer, and an inner mixed ($TiO_2$+$A1_2$$O_3$) layer, being similar to other common TiAl alloys. But, the scales formed on TiAl-Fe alloys were generally thin compared to those formed on pure TiAl, and contained dissolved iron. Below the oxide scale, an oxygen affected zone was formed. This beneficial effects of Fe on increasing the oxidation resistance and scale adherence of TiAl alloys were attributed to the refinement of oxide grains, increased scale adherence and the enhanced alumina-forming tendency.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.11a
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• pp.217-220
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• 2008

Slag mass deposition was required to predict accurate performance of kick motor (KM) system. Slag mass accumulation was analyzed through the aluminum oxide particle paths to predict slag mass deposition. Numerical analysis to solve both flow field and droplet accumulation was performed with Fluent 6.3 program. The effects for the acceleration and diameters of the aluminum oxide particles was analyzed, finally total slag mass accumulation was acquired. It confirmed that the slag mass deposition was agreed well with previously slag mass prediction based on KM ground test.

• Korean Journal of Materials Research
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• v.22 no.6
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• pp.316-320
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• 2012

$Co_3O_4$, $Al_2O_3$ and $Co_3O_4$/$Al_2O_3$ mesoporous powders were prepared by a sol-gel method with starting matierals of aluminum isopropoxide and cobalt (II) nitrate. A P123 template is employed as an active organic additive for improving the specific surface area of the mixed oxide by forming surfactant micelles. A transition metal cobalt oxide supported on alumina with and without P123 was tested to find the most active and selective conditions as a heterogeneous catalyst in the reaction of styrene epoxidation. A bBlock copolymer-P123 template was added to the staring materials to control physical and chemical properties. The properties of $Co_3O_4$/$Al_2O_3$ powder with and without P123 were characterized using an X-ray diffractometer (XRD), a Field-Emission Scanning Electron Microscope (FE-SEM), a Bruner-Emmertt-Teller (BET) surface analyzer, and $^{27}Al$ MAS NMR spectroscopy. Powders with and without P123 were compared in catalytic tests. The catalytic activity and selectivity were monitored by GC/MS, $^1H$, and $^{13}C$-NMR spectroscopy. The performance for the reaction of epoxidation of styrene was observed to be in the following order: [$Co_3O_4$/$Al_2O_3$ with P123-1173 K > $Co_3O_4$/$Al_2O_3$ with P123-973 K > $Co_3O_4$-973 K>$Co_3O_4$/$Al_2O_3$-973 K > $Co_3O_4$/$Al_2O_3$ with P123-1473 K > $Al_2O_3$-973 K]. The existence of ${\gamma}$-alumina and the nature of the surface morphology are related to catalytic activity.

• Journal of the Korean Electrochemical Society
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• v.8 no.4
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• pp.181-185
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• 2005

Lithium cobalt oxide thin film cathode, having thickness of $2.9{\mu}m$ with area of $4cm^2$, was deposited on platinum patterned alumina substrate by radio frequency magnetron sputtering. Li/Co molar ratio, which is an important factor for battery performance, was measured as a function of argon working pressure and applied R.F. power. Constant current charge and discharge performances were characterized with high rate discharge and cycling behavior. Using AC impedance analysis, internal resistance of the thin film battery was measured and simulated by proposed equivalent circuit model.