• Journal of the Korea Concrete Institute
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• v.19 no.5
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• pp.539-547
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• 2007

The effects of binder and alumina content on the setting time, drying shrinkage, strength, freezing and thawing resistance and water absorption of polymer-modified pastes with alumina powder were examined. As a result the setting time of the polymer-modified pastes with alumina powder tended to delay with increasing binder content. Irrespective of the type of polymer, the drying shrinkage of the polymer-modified pastes with alumina powder tended to decrease with increasing binder content and alumina powder content. Regardless of the type of polymer, the tensile and adhesion strengths of the polymer-modified pastes with alumina powder tended to increase with increasing binder content and alumina powder content. Irrespective of the type of polymer, the durability factors of the polymer-modified pastes with alumina powder tended to increase with increasing alumina content. Irrespective of the type of polymer, the water absorptions of the polymer-modified pastes with alumina powder tended to decrease with increasing binder content and alumina content.

• Transactions on Electrical and Electronic Materials
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• v.16 no.6
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• pp.338-341
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• 2015

Epoxy/micro-sized alumina composite was prepared, and the effects of alumina content on the dielectric properties were investigated in order to develop an insulation material for gas-insulated switchgears (GIS). Nano-sized alumina (average particle size: 30 nm) was also incorporated into the epoxy/micro-sized alumina composite. Dielectric tests were carried out in ASTM D 150, and capacitance (Cp) and dielectric loss (tanδ) were measured. The dielectric constant increased with increasing alumina content in the epoxy/micro-alumina system and the epoxy/micro-alumina/nano-alumina system. As 1,3-diglycidyl glyceryl ether (DGE) content increased, the dielectric constant decreased and dielectric loss increased. This ocurred as a result of the weak electric field enhancement due to homogeneous dispersion of micro- and nano-sized alumina particles in an epoxy composite.

• Transactions on Electrical and Electronic Materials
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• v.16 no.5
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• pp.260-263
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• 2015

Epoxy/micro-sized alumina composite was prepared and the effects of alumina content on the electrical and mechanical properties were investigated in order to develop an insulation material for gas insulated switchgear (GIS). Nano-sized alumina (average particle size: 30 μm) was also incorporated into the epoxy/micro-sized alumina composite. An electrical insulation breakdown strength test was carried out in sphere-sphere electrodes and the data were estimated by Weibull statistical analysis. Tensile strength was measured at a crosshead speed of 10 mm/min using a universal testing machine. Alumina content was varied from 0 wt% to 70 wt%.). As micro-sized alumina content increased, insulation breakdown strength increased until 40 wt% alumina content and decreased after that content. The tensile strength of a neat epoxy system was 82.2 MPa and that value for 60 wt% alumina content was 91.8 MPa, which was 111.7% higher than inthe neat epoxy system. The insulation breakdown strength of micro-sized alumina (60 wt%)/nano-sized alumina (1 phr) glycerol diglycidyl ether (GDE) (1 phr) composite was 54.2 MPa, which was 116% higher than the strength of the system without nano-sized alumina.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.31 no.7
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• pp.496-501
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• 2018

In this study, we prepared 40, 45, 50, 55, 60, 65, and 70 wt% content composites filled in epoxy matrix for two micro silica and three micro alumina types for use as a GIS heavy electric machine. As a filler type of epoxy composite, micro silica composites showed excellent AC breakdown strength properties compared to micro alumina composites in the case of electrical properties of micro silica and alumina. The electrical breakdown properties of micro silica composites increased with increasing filler content, whereas those of micro alumina decreased with increasing filler content. In the case of mechanical properties, the micro silica composite showed improved tensile strength and flexural strength compared with the micro alumina composite. In addition, mechanical properties such as tensile strength and flexural strength of micro silica and alumina composites decreased with increasing filler content. This is probably because O-H groups are present on the surface of silica in the case of micro silica but are not present on the surface of alumina in the case of micro alumina.

• The Korean Journal of Ceramics
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• v.5 no.1
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• pp.25-29
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• 1999

Complex viscosities of dense alumina slurries over 45% volume density measured with the oscillating method were correlated well with Casson model. Among several monosaccharides and disaccharides studied here, fructose and sucrose showed good rheological properties in making dense alumina slurry plastic compared to other monosaccharides and disaccharides like glucose, galactose, arabinose, xylose and maltose. Sucrose content or additional water content in dense alumina slurry with sucrose contributed to the plasticity of the slurries.

• Polymer(Korea)
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• v.37 no.1
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• pp.47-51
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• 2013

In this work, the effect of alumina nanofibers on thermal conductivity and fracture toughness of alumina nanofibers and powder filled epoxy (EP) composites were investigated with varying alumina nanofiber content from 20 to 100 phr. Thermal conductivity was tested using a laser flash analysis (LFA). The fracture toughness of the composites were studied through the critical stress intensity factor ($K_{IC}$) measurement. The mophologies were observed by scanning electron microscopy (SEM). From the results, it was found that the thermal conductivity was enhanced with increasing alumina nanofiber content, which played a key factor to determine the thermal conductivity. The $K_{IC}$ value was increased with increasing alumina nanofiber content, whereas the value decreased above 40 phr alumina nanofiber content. This was probably considered that the alumina nanofiber entangled each other in EP due to an excess of alumina nanofibers.

• 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 $40.3{\mu}m$.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.10 no.1
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• pp.48-54
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• 2000

Influence of seed addition on the mullite synthesis was investigated from mixture powders of kaolin and aluminium trihydroxide which contain various $Al_2O_3$/SiO_2$ ratio (silica rich, stoichiometric, alumina rich). The flexural strength increases with the increase of the mullite-seed content in case of silica rich and stoichiometric mullite, but flexural strength decreases with the increase of the mullite-seed content in case of alumina rich mullite. Microstructural investigation revealed that aspect ratio of mullite grains increased with higher alumina content, along with lower sintered density. Mullite contents of specimens are increased with seed content regardless of $Al_2O_3$/SiO_2$ ratio of the mixture composition.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.8 no.1
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• pp.145-150
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• 1998

The electrical and mechanical properties of the 8 mol% yittria-stabilized zirconia and alumina composites have been examined as a function of the alumina content. The 3-point bending strength and fracture toughness of the composites increased with increasing alumina content up to 20 wt%. The average grain size of the composites decreased with increasing alumina content up to 20 wt%. The composite with 5 wt% $Al_2O_3$ showed a 3-point bending strength of 310 MPa and fracture toughness about $7.8MPa\cdot\textrm m^{1/2}$. The electrical conductivity of the composites at $1000^{\circ}C$ increased slightly with increasing alumina content up to 10 wt% and decreased monotonically with alumina content. The conductivity of the TZ-8YS with 5 wt% alumina was 0.4 S/cm at $1000^{\circ}C$.

• Journal of the Microelectronics and Packaging Society
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• v.6 no.1
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• pp.11-21
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• 1999

For microelectronic packaging application, the crystallizable glass powder in CaO-$A1_2O_3-SiO_2-B_2O_3$system was mixed with various amounts of alumina inclusions (\approx 4 $\mu \textrm{m}$), and its sintering behavior, crystallization behavior, and dielectric constant were examined in terms of vol% of alumina and the reaction between the alumina and the glass. Sintering of the CASB glass powder alone at $900^{\circ}C$ resulted in full densification (99.5%). Sintering of alumina-filled composite at $900^{\circ}C$ also resulted in a substantial denslfication higher than 97% of theoretical density, In this case, the maximum volume percent of alumina should be less than 40%. XRD analysis revealed that there was a partial dissolution of alumina into the glass. This alumina dissolution, however, did not show the particle growth and shape accommodation. Therefore, the sintering of both the pure glans and the alumina-filled composite was mainly achieved by the viscous flow and the redistribution of the glass. Alumina dissolution accelerated the crystallization initiation time at $1000^{\circ}C$ and hindered the densification of the glass. Dielectric constants of both the alumina-filled glass and the glass-ceramic composites were increased with increasing alumina content and followed rule of mixture. In case of the glass-ceramic matrix composites showed relatively lower dielectric constant than the glass matrix composite. Furthermore, as alumina content increased, crystallization behavior of the glass was changed due to the reaction between the glass and the alumina. As alumina reacted with the glass matrix, the major crystallized phase was shifted from wollastonite to gehlenite. In this system, alumina dissolution strongly depended on the particle size: When the particle size of alumina was increased to 15 $\mu\textrm{m}$, no sign of dissolution was observed and the major crystallized phase was wollastonite.