• Applied Microscopy
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• v.36 no.spc1
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• pp.19-24
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• 2006

The alumina-aluminum solid-liquid interfaces were directly observed at atomic scale by heating the alumina single crystal in high-voltage electron microscope (HVEM) owing to the electron beam damage processes, Atomic ordering in the first several layers of the liquid was clearly resolved adjacent to the alumina surface and its relevance to the single crystal growth was examined with the real-time observations.

• Journal of the Korean Ceramic Society
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• v.35 no.12
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• pp.1308-1315
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• 1998

Effects of particle size of alumina on densification behavior during liquid-phase sintering of alumina-talc system were investigated with emphasis on particle rearrangement process. In the case of using coarse alu-mina powder densiication of specimens was rapidly accelerated after formation of liquid phase due to easy particle rearrangement process with addition of talc and increase of sintering temperature. On the contrary when fine alumina powder was used premature densification of alumina matrix region formed before for-mation of liquid phase rigid skeleton structure and then it seemed to inhibit rearrangement process during crease of sintering temperature. As results the densification of specimens using coarse alumina powder was higher than that of the case of using fine one.

• Journal of the Korean Ceramic Society
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• v.34 no.12
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• pp.1213-1220
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• 1997

Effect of particle size of alumina and amount of talc on tape casting and densification behaviors of alumina-talc system were investigated. The pseudoplastic behaviors of slurries increased with increase in amount of talc addition and decrease in alumina particle size. In case of using coarse alumina powder, densification of specimens were accelerated with increase of sintering temperature and amount of talc addition. On the contrary, fine alumina powder retarded of rearrangement of alumina particle during liquid phase sintering due to premature densification of alumina matrix region before formation of liquid phase and then densification of specimens were suppressed with increase of sintering temperature and amount of talc addition.

• The Korean Journal of Ceramics
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• v.6 no.1
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• pp.78-82
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• 2000

Although alumina aggregates have been used as refractory aggregates due to the improved mechanical properties of refractories as a result of the low contraction of alumina aggregates, the aggregates have a difficulty in fabrication due to its low sinterability. Two types of alumina aggregates and a fused alumina aggregate containing transient liquid forming additives are prepared to investigate the sintering characteristics of aggregates. $Al_2O_3$rich composition in the $Al_2O_3$-MgO-$SiO_2$(-$TiO_2$) system is chosen for the transient liquid phase sintering and the final recrystallized bonding phase between grains inside the fused alumina aggregates is found to be a needle-like mullite phase. The flexural strength of alumina bars, reaction-bonded using the paste having a composition of $Al_2O_3$-MgO-$SiO_2$-$TiO_2$, is about 78 MPa, which is one half value of that of pure alumina.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2017.05a
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• pp.412-415
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• 2017

In this study, the decomposition performance of ammonia dinitramide (ADN) based liquid monopropellant was evaluated by using metal supported alumina bead catalyst. Alumina bead was calcined at $1200^{\circ}C$, and Pt and Cu were impregnated on alumina bead by excess water impregnation using a rotary evaporator. The decomposition temperature ($T_{dec}$) of ADN-based liquid monopropellant was measured in a home-made batch reactor. The decomposition temperature of Cu/$Al_2O_3$ catalyst was lower than that of Pt/$Al_2O_3$ catalyst, and $T_{dec}$ was about $130^{\circ}C$.

• Journal of the Korean Ceramic Society
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• v.36 no.11
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• pp.1243-1251
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• 1999

Densification behavior and microstructural evolution during the liquid-phase sintering of alumina-anorhite system were investigated as a function of MgO addition. When MgO component was added in either alumina or anorthite glass powder the aspect ratio of alumina grains decreased and concurrently the are of flat interface which was formed as a result of contact solid alumina gains rather increased. Consequently addition of MgO component in the Al2O3-amorthite system brought about suppression of the rearrangement of solid grains during the liquid phase sintering and then densification of specimens was also retarded.

• The International Journal of Costume Culture
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• v.8 no.2
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• pp.124-131
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• 2005

This study focused on the change of skin temperature by the emissivity and emission power of far-infrared for conformant far infrared effect to naked eyes. The study method is to manufacture the bra pad by each concentration on far-infrared materials of illite powder $(K,H_3O)AI_2(Si,Al)_4O_{10}(H_2O,OH)_2)$, liquid alumina ($Al_2O_3$), the extracted liquid from 29 kind of medical plants, then, measured change of skin temperature. Result are as follows. Far-infrared were emitted each $90.2\%,\;90.1\%,\;89.7\%$ from the illite powder, liquid alumina, extracted liquid from medical plants. When the testee weared the bra pad, the temperature of coated bra pad was $0.5^{\circ}C$ higher than the non finished bra pad. Washing fastness on far-infrared finishing was better dope addition method than coating method.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.30 no.4
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• pp.150-155
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• 2020

Alumina (Al₂O₃) is mainly used as a structural ceramic material and to have good mechanical properties requires a dense microstructure. In commercial fabrication, the liquid phase sintering process is adjusted to reduce the sintering temperature of alumina. In this study, the effect of added amounts of cobalt oxide as a coloring agent on the microstructure and mechanical properties was investigated in the CaO-SiO₂-MgO-system liquid phase sintering of 92 % alumina at various sintering temperatures. When 11 wt% Co₂O₃ was added, a rearrangement of alumina particles, which is the main densification step in liquid phase sintering, occurred from a sintering temperature of 1200℃. Solution re-precipitation and coalescence steps followed from 1300℃ with the grain growth of alumina particles. The addition of excess Co₂O₃ and sintering temperatures above 1400℃ resulted in a decrease in sintered density and Vickers hardness, because of the low viscosity of the liquid phase. In 92 % alumina with the addition of 11 wt% Co₂O₃, a sintered density and Vickers hardness of 3.86 g/㎤ and 12.32 GPa, respectively, were obtained at a sintering temperature of 1350℃.

• Proceedings of the Korean Society of Laser Processing Conference
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• 2006.06a
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• pp.60-65
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• 2006

Previous studies demonstrated that laser ablation under transparent liquid can result in ablation enhacement and particle removal from the surface. In this work, the liquid-assisted excimer laser ablation process is examined fer polyethylene terephthalate (PET), polymethyl methacrylate (PMMA), Si, and alumina with emphasis on ablation enhacement, surface topography, and debris formation. In the case of PET and PMMA, the effect of liquid is analyzed both fer thin water film and bulk water. As the ablation enhanement by liquid is already known for Si and alumina, the analysis focuses on surface topography and debris formation resulting from the liquid-assisted laser ablation process. The results show that application of liquid increases the ablation rate of PMMA while that of PET remains unchanged even in the liquid-assisted process. It is also revealed that the liquid can significantly improve the surface quality by reducing the debris deposition. However, the surface roughness is generally deteriorated in the liquid-assisted process. The surface toporaphy is found to be strongly dependent on the method of liquid application, i.e., thin film or bulk liquid.

• Journal of the Korean Ceramic Society
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• v.26 no.2
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• pp.228-234
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• 1989

Pressureless-sintering of SiC with additions of yttria and alumina was studied. SiC could be densified to about 97% of its theoretical density at 185$0^{\circ}C$ which is about 20$0^{\circ}C$ below the normal sintering temperature of SiC with boron and carbon. Yttria and alumina formed intergranular liquid phases at the sintering temperature and promoted densification by the liquid phase sintering mechanism. The microstructure of sintered specimens was equiaxed and the liquid phase appeared to wet and dissolve SiC grains. The fracture toughness was measured by indentation method and found to be 5.3MPa.m1/2. Processing flaws near the surface of specimens appeared to be the major fracture origin during 3-point bending tests.