• Journal of the Korean Ceramic Society
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• v.35 no.10
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• pp.1085-1093
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• 1998

Amorphous alumina powder prepared by the fast calcination of aluminum trihydroxide(Al(OH)3 gibbsite) for 0.5 second at 580$^{\circ}C$ was investigated rehydration propeties. Phase composition crystal size and mor-phology surface area pore volume and pore size distribution of pesudo-boehmite and bayerite crystals changed with temperature time water/alumina ratio and particle size when amorphous alumina rehydrated with water. Phase compositions were examined with XRD and DTA and crystal sized morphologies were investigaed with SEM and TEM. Also rehydration properties of amorphous alumina were in-vestigated by measuring the surface area pore volume and pore size distribution.

• Transactions on Electrical and Electronic Materials
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• v.14 no.2
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• pp.105-109
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• 2013

In order to develop high voltage (HV) insulation materials, epoxy/spherical alumina composites with two different particle sizes (in ${\mu}m$) were prepared and a dynamic mechanical analysis (DMA) and electrical insulation breakdown strength test were carried out in sphere-sphere electrodes and the data were estimated using Weibull statistical analysis. Alumina content varied from 50 to 70 wt%. The electrical insulation breakdown strength for epoxy/alumina (50 wt%) was 44.0 kV/1 mm and this value decreased with increasing alumina content. The effects of insulation thickness and alumina particle size on the insulation breakdown strength were also studied. The insulation thickness varied from 1 mm to 3 mm, and the particle sizes were 7.3 or $40.3{\mu}m$.

• Analytical Science and Technology
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• v.32 no.4
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• pp.121-130
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• 2019

Alumina is one of the most important ceramic materials because of its useful physical and chemical properties. Recently, high-purity alumina has been used in various industrial fields. This leads to increasing demand for reliable elemental analysis of impurities in alumina samples. However, the chemical inertness of alumina makes the sample preparation for conventional elemental analysis a tremendously difficult task. Herein, we demonstrated the feasibility of laser ablation for effective sampling of alumina powder. Laser ablation performs sampling rapidly without any chemical reagents and also allows simultaneous optical emission spectroscopy and mass spectrometry analyses. For six alumina samples including certified reference materials and commercial products, laser-induced breakdown spectroscopy (LIBS) and laser-ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS) analyses were performed simultaneously based on a common laser ablation sampling. LIBS was found to be useful to quantify alkali and alkaline earth metals with limits-of-detection (LODs) around 1 ppm. LA-ICP-MS could quantify transition metals such as Ti, Cu, Zn, and Zr with LODs in the range from a few tens to hundreds ppb.

• Proceedings of the Materials Research Society of Korea Conference
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• 1994.11a
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• pp.128-128
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• 1994

• Journal of the Korean Ceramic Society
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• v.33 no.3
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• pp.348-354
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• 1996

• Korean Journal of Materials Research
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• v.11 no.11
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• pp.978-985
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• 2001

The amorphous alumina was obtained by flash calcination of Bayer gibbsite[$Al(OH)_3$aluminum trihydroxide]. Rehydration and pore characteristics of $r-A1_2O_3$ prepared from rehydrated amorphous alumina were investigated. Crystal phases of pseudo-boehmite and bayerite were changed when amorphous alumina was hydrated at various conditions such as time, the ratio of water/alumina and pH. Specific surface areas and pore volumes of $r- A1_{2O}_3$ were influenced by the reaction time, water/alumina and PH of rehydration. The total pore volume of $r-A1_{2O}_3$increases with increasing the reaction time and ratio of water/alumina. Especially, the pure pseudo-boehmite of single phase could be prepared, when amorphous alumina was hydrated in the range of pH 6.5-8.0 in water/alumina= 10 at $90^{\circ}C$ for 7hr. The $r-Al_{2O}_3$, obtained by calcination of the prepared pseudo-boehmite at $500^{\circ}C$ for 2hrs, is characterized by the specific surface area of $265m^2$/g, total pore volume of $0.75cm^3$/g.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.11
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• pp.7-12
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• 2019

Generally, end effectors for automatic robots can use ceramics such as alumina(Al₂O₃) and silicon carbide(SiC). In this study, black alumina was developed and used in the semiconductor field through powder molding press forming. The black alumina can be mass produced.Alumina and black alumina were ground using a plane grinder to apply to the end effector of an automatic robot. The optimal cutting conditionswere found by analyzing the surface roughness(Ra) of black alumina through grinding. The alumina surface roughness is the feed rate was about 0.72 mm/sec, and the number of revolutions was best at 0.4879 ㎛ at 1700 rpm. In addition, the black alumina surface roughness shows a precision of less than 0.2 ㎛ in most cutting conditions. The feed rate was about 0.72 mm/sec, and the number of revolutions was best at 0.1361 ㎛ at 1900 rpm. The surface roughness of black alumina was better than that of alumina by about 0.35 to 0.47 ㎛.

• Transactions on Electrical and Electronic Materials
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• v.16 no.6
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• pp.351-354
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• 2015

In this study, alumina plates 9~25 μm in size were used as thermal fillers, and epoxy resin was used as a polymer matrix. Oriented alumina plate/epoxy composites were prepared using a rolling method. The effect of ordering alumina plates increased with alumina plate size. The thermal conductivity and flexural strength of the composites were investigated. The horizontal thermal conductivity of the oriented composite was significantly higher than the vertical thermal conductivity. The horizontal thermal conductivity of the 75 wt% alumina content was 8.78 W/mk, although the vertical thermal conductivity was 1.04 W/mk. Ordering of the alumina plate using a rolling method significantly improved the thermal conductivity in the horizontal direction. The flexural strengths of the ordered alumina/epoxy composites prepared at different curing temperatures were measured.

• Journal of the Korean Ceramic Society
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• v.33 no.8
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• pp.849-854
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• 1996

boehmite which is the by-product in alcohol process contains anions such as $Cl^-,{NO_3}^-.or\; CH_3COO^-$ Influe-nce of these anions was studied on properties of $\alpha$-alumina powders prepared by treating the transformed ${\gamma}$-alumina with the alumina sol and $\alpha$-alumina seeds (d_{50}=0.36\mu\textrm{m}$) Disperal 20/1 and 10/1 containing $Cl^-$ produced spherical powder Disperal 20/2 with ${NO_3}^-$ produced equiaxed powder and Disperal 10/3 with $CH_3$ $COO^-$ irregular shaped and sized powder. All of these $\alpha$-alumina powders were submicron. Although the green density of the alumina powder derived from Disperal 10/1 by calcination at $1200^{\circ}C$/1h. was 53% it did not sinter even at $1550^{\circ}C$ for 2h. which implies that its d50 is greater than $3\mu\textrm{m}$. The others gave green densities in the range of 44~47% but they sintered as well as the AKP-30 at $1500^{\circ}C$/2 h or $1550^{\circ}C$/2 h.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2004.10a
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• pp.27-30
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• 2004

Carbon nanotube reinforced alumina matrix nanocomposite was fabricated by sol-gel process and followed by spark plasma sintering process. Homogeneous distribution of carbon nanotubes within alumina matrix can be obtained by mixing the carbon nanotubes with alumina sol and followed by condensation into gel. The mixed gel, consisting of alumina and carbon nanotubes, was dried and calcinated into carbon nanotube/alumina composite powders. The composite powders were spark plasma sintered into carbon nanotube reinforced alumina matrix nanocomposite. The hardness of carbon nanotube reinforced alumina matrix nanocomposite was enhanced due to an enhanced load sharing of homogeneously distributed carbon nanotubes. At the same time, the fracture toughness of carbon nanotube reinforced alumina matrix nanocomposite was enhanced due to a bridging effect of carbon nanotubes during crack propagation.