• Journal of the Institute of Electronics Engineers of Korea TE
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• v.39 no.1
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• pp.1-8
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• 2002

The effects of the addition of either monoclinic $ZrO_2$($ZrO_2$(m)) or tetragonal $ZrO_2$($ZrO_2$(t)) containing 5.35wt% $Y_2O_3$ on the physical properties and electrical conductivity of TEX>$Al_2O_3$ were investigated. The addition of $ZrO_2$(m) and $ZrO_2$(t) increased sintered density of $Al_2O_3$. The Vickers hardness also increased as addition of >($ZrO_2$(t) increased going through a maximum at 20wt% and the hardness of the specimens was found to be dependent on the sintered density. The addition of $ZrO_2$(t) improved the hardness of $Al_2O_3$-$ZrO_2$ systems and the $ZrO_2$(m) addition showed the better effect on the thermal shock property of $Al_2O_3$-$ZrO_2$ systems than that of the $ZrO_2$(t) addition. Above 15wt% addition of $ZrO_2$(t), the electrical conductivity is gradually increased with increasing applied voltage but not effects by addition of $ZrO_2$(m).

• Journal of the Korean Ceramic Society
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• v.42 no.6 s.277
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• pp.384-390
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• 2005

[ ${\alpha}-Al_2O_3$ ] precursor was synthesised by sol-gel method using aluminum sulfate, sodium sulfate and sodium carbonate as law materials. The flaky ${\alpha}-Al_2O_3$ crystals were prepared by heating using precursor about $1,050^{\circ}C$. In this study, the effect of some transition-metal sulfate ($FeSO_4,\;SnSO_4,\;ZnSO_4$) addition have been investigated. When iron sulfate was added, it could see that act on impurities in crystal growth process. In case of tin sulfate, distribution of Platelets was very broad. When flaky ${\alpha}-Al_2O_3$ crystals were prepared zinc sulfate addition, thickness, size, and distribution of platelets was suited to industrial application. The average diameter of flaky ${\alpha}-Al_2O_3$ crystals was about 20 $\mu$m, and its thickness was about 0.3 $\mu$m. Increasing addition of zinc sulfate, thickness of ${\alpha}-Al_2O_3$ platelet was decreased.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.29 no.12
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• pp.791-795
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• 2016

The effects of $TiO_2$ addition on the electrical insulation of AlN ceramics with 1 wt% $Y_2O_3$ as a sintering aid have been investigated. Some of $TiO_2$ has reacted with AlN powders and transformed to fine TiN particles during sintering, which was uniformly dispersed along grain boundaries of AlN. At a high electrical field (500 V/mm), the resistivity of AlN ceramics with $TiO_2$ addition of 0.2 wt% increased about 1000 times from $3{\times}10^{10}{\Omega}cm$ to $3.1{\times}10^{13}{\Omega}cm$. Based on the impedance spectroscopy measurement, it was found that $TiO_2$ addition increased dramatically electrical resistivity of AlN grains much more than that of grain boundaries. Thus, $TiO_2$ was believed to dissolve inside AlN grains to suppress ionic conduction of Al vacancies. This suppressed ionic conduction by Ti incorporation into AlN grains seems to contribute to more electrically insulating AlN ceramics.

• Journal of the Korean Ceramic Society
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• v.34 no.6
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• pp.668-676
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• 1997

Al2O3/SiC nanocomposites are fabricated through intensive ball milling to mix fine SiC particles uniformly with the Al2O3 powder. Another role of milling is to reduce particle sizes by crushing particles as well as agglomerates. However, balls are worn during ball milling and the sample powder mixtures pick up to weight loss of the balls. In this study, pressureless sintering was performed to obtain Al2O3/SiC nanocomposites. It was found that the wear rate of zirconia balls during milling was considerable, and the zirconia addition after even a few hours of ball milling could increase the sintering rates of the nanocomposites significantly. Thus, addition of ZrO2 changed the sintering behaviors as well as mechanical properties of Al2O3/SiC nanocomposites.

• Journal of the Korea Concrete Institute
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• v.28 no.2
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• pp.205-212
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• 2016

This research investigates the influence of ground granulated blast furnace slag (GGBFS) composition on the alkali-activated slag cement (AASC). Aluminum oxide ($Al_2O_3$) was added to GGBFS binder between 2% and 16% by weight. The alkaline activators KOH (potassium hydroxide) was used and the water to binder ratio of 0.50. The strength development results indicate that increasing the amount of $Al_2O_3$ enhanced hydration. The 2M KOH + 16% $Al_2O_3$ and 4M KOH + 16% $Al_2O_3$ specimens had the highest strength, with an average of 30.8 MPa and 45.2 MPa, after curing for 28days. The strength at 28days of 2M KOH + 16% $Al_2O_3$ was 46% higher than that of 2M KOH (without $Al_2O_3$). Also, the strength at 28days of 4M KOH + 16% $Al_2O_3$ was 44% higher than that of 4M KOH (without $Al_2O_3$). Increase the $Al_2O_3$ contents of the binder results in the strength development at all curing ages. The incorporation of AASC tended to increases the ultrasonic pulse velocity (UPV) due to the similar effects of strength, but increasing the amount of $Al_2O_3$ adversely decreases the water absorption and porosity. Higher addition of $Al_2O_3$ in the specimens increases the Al/Ca and Al/Si in the hydrated products. SEM and EDX analyses show that the formation of much denser microstructures with $Al_2O_3$ addition.

• Korean Journal of Materials Research
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• v.12 no.1
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• pp.48-53
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• 2002

$Al_2O_3-SiC$ and $Al_2O_3-SiC$-TiC composite powders were prepared by SHS process using $SiO_2,\;TiO_2$, Al and C as raw materials. Aluminum powder was used as reducing agent of $SiO_2,\;TiO_2$ and activated charcoal was used as carbon source. In the preparations of $Al_2O_3-SiC$, the effect of the molar ratio in raw materials, compaction pressure, preheating temperature and atmosphere were investigated. The most important variable affecting the synthesis of $Al_2O_3-SiC$ was the molar ratio of carbon. Unreactants remained in the product among all conditions without compaction. The optimum condition in this reaction was $SiO_2$: Al: C=3: 5: 5.5, 80MPa compaction pressure under Preheating of $400^{\circ}C$ with Ar atmosphere. However there remains cabon in the optimum condition. The effect of $TiO_2$ as additive was investigated in the preparations of $Al_2O_3-SiC$. As a result of $TiO_2$ addition, $Al_2O_3-SiC$-TiC composite powder was prepared. The $Al_2O_3$ powder showed an angular type with 8 to $15{\mu}m$, and the particle size of SiC powder were 5~$10{\mu}m$ and TiC powder were 2 to $5{\mu}m$.

• Journal of the Korean Ceramic Society
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• v.51 no.5
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• pp.498-504
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• 2014

Particulate nitride composites have been fabricated by sintering the compacted powder of AlN and 5 - 64.3 mol% $Al_2O_3$, with a small addition of $Y_2O_3$ ($Y_2O_3$/AlN, 1 wt%), in 1-atm nitrogen gas at $1650-1900^{\circ}C$. The composites were characterized in terms of sintering behavior, phase relations, microstructure and thermal shock resistance. AlN, 27R AlN pseudopolytype, and alminium oxynitride (AlON, $5AlN{\cdot}9Al_2O_3$) were found to existin the sintered material. Regardless of batch composition, the AlN-$Al_2O_3$ powder compacts exhibited similar sintering behavior; however, the degree of shrinkage commonly increased with increasing $Al_2O_3$ content, consequently giving high sintered bulk density. By increasing the $Al_2O_3$ addition up to ${\geq}50 mol%$, the matrix phase in the sintered material was converted from AlN or 27R to AlON. Above $1850^{\circ}C$, a liquid phase was formed by the reaction of $Al_2O_3$ with AlN, aided by $Y_2O_3$ and mainly existed at the grain boundaries of AlON. Thermal shock resistance was superior in the sintered composite consisting of AlON with dispersed AlN or AlN matrix phase.

• Journal of the Korean Ceramic Society
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• v.23 no.2
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• pp.7-12
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• 1986

As the other silicate minerals such as kaolinite and pyrophyllite kyanite ($Al_2O_3$.$SiO_2$) is transformed to mullite and free silica or glassy phase at high temperature. Therefore $Al_2O_3$ is commonly added to kyanite in order to increase the mullite-yield. In case of $Al_2O_3$-addition mullite-yield depends on the reactivity of added $Al_2O_3$ with free silica which occurs from transformation of kyanite or exists as accessory minerals. It is well known that addition of activated $Al_2O_3$Al powder is added to kyanite to utilize the aluminothermal reac-tion of Al powder in reaction of mullite-formation.

• New & Renewable Energy
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• v.3 no.1 s.9
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• pp.54-59
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• 2007

A sintering aid, $B_{2}O_{3}$ have been included into a $LiAlO_{2}$ electrolyte support by a tape casting method in order to reinforce mechanical strength of the support for molten carbonate fuel cells [MCFCs). Starting idea originates from the low melting point of $B_{2}O_{3}$ ($450^{\circ}C$), which can provide the low temperature consolidation of ceramic materials. The mechanical properties and the microstructure changes of the $B_{2}O_{3}$-included electrolyte support were examined by scanning electron microscope, mercury porosimetry, X-ray powder diffraction [XRD], high temperature differential scanning calorimeter and three-point bending strength measurement. The mechanical strength was clearly improved by addition of $B_{2}O_{3}$. The increase of mechanical strength results from the neck growth of a new $LiAlO_{2}$ phase between $LiAlO_{2}$ particles by the liquid phase sintering. Average pore size and porosity of the electrolyte support reinforced by addition of the sintering aid, $B_{2}O_{3}$, was $0.24{\mu}m$ and 59%, respectively which were suitable microstructure of a matrix for an application of MCFCs.

• Journal of the Korean Ceramic Society
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• v.25 no.3
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• pp.201-206
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• 1988

To investigate the effects of Mo addition on the microstructures and mechanical properties of Al_2O_3$ ceramics, two kinds of Mo particles with average sizes of 2-${\mu}{\textrm}{m}$ and 6-${\mu}{\textrm}{m}$ were used as additives. It was shown that Mo particles inhibited the grain growth of Al_2O_3$, and the smaller Mo particles were more effective. In case of 2-${\mu}{\textrm}{m}$ Mo dispersion, the bending strength and the fracture toughness were increased. Dispersion of 6-${\mu}{\textrm}{m}$ MO did not increase the strength but improved the fracture toughness a little. The toughening mechanisms of Al_2O_3$-Mo composites are thought to be the crack deflection and microcracking mechanisms.