• 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.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1999.11a
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• pp.335-338
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• 1999

The effect of monoclinic $ZrO_2$(pure) and tetragonal $ZrO_2$ containing 5.35wt% $Y_2$$O_3$(Y-TZP) addition on the mechanical properties and thermal shock resistance of $Al_2$$O_3$ ceramic were investigated. The addition of $ZrO_2$(m) and Y-TZP increased sintering density of $Al_2$$O_3$. The vickers hardness increased with increasing the volume fraction of Y-TZP going through a maximum at 20wt%. The hardness of the specimens was found to be depend on the sintering density. With increasing the volume fraction of $ZrO_2$(m) and Y-TZP, the fracture toughness of the composite is increased. This result may be taken as evidence that toughening of ${Al_2}{O_3}$ can also be achieved by the transformation toughening and microcrack toughening of $ZrO_2$. The property of the& shock for ${Al_2}{O_3}$-$ZrO_2$ composites was improved by increasing the volume fraction of monoclinic $ZrO_2$(pure).Grain size increased with increasing the volume fraction of $ZrO_2$.

• Journal of the Institute of Electronics Engineers of Korea TE
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• v.39 no.4
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• pp.341-349
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• 2002

Electrical, mechanical and sinterability properties of yttria-stabilized zirconia doped with 5.35wt% $Y_2$O$_3$(Y$_2$O$_3$- containing stabilized zirconia : YSZ) were studied as a function of $Al_2$O$_3$, CoO, Fe$_2$O$_3$ and MnO$_2$ addition. The ratio of monoclinic phase to tetragonal phase was changed by the addition of $Al_2$O$_3$, CoO, Fe$_2$O$_3$ and MnO$_2$ to 8.00 wt% and sintered density decreased with increasing $Al_2$O$_3$, CoO, Fe$_2$O$_3$ and MnO$_2$ addition. Fracture toughness increased with the increase of monoclinic to tetragonal phase ratio and was maximum at about 18%. When transition metals such as CoO, Fe$_2$O$_3$ or MnO$_2$ was added more than 1.5 wt%, the electrical conductivity of YSZ increased. But $Al_2$O$_3$ hardly affected the electrical conductivity of YSZ. The addition of $Al_2$O$_3$, CoO, Fe$_2$O$_3$ and MnO$_2$ into YSZ resulted in the more complex behavior of fracture toughness and hardness variation and the specimen with 1.5wt%-Fe$_2$O$_3$, 3.0wt%-Al$_2$O$_3$ and 1.5wt%-CoO showed the monoclinic to tetragonal phase ratio of 18% and the highest toughness of 10.8 MPa.m$^{1}$2/ and Vickers hardness of 1201 kgf/mm$^2$.

• Journal of the Korean Electrochemical Society
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• v.25 no.4
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• pp.191-200
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• 2022

Na-β"-Al₂O₃ has been widely employed as a solid electrolyte for high-temperature sodium (Na) beta-alumina batteries (NBBs) thanks to its superb thermal stability and high ionic conductivity. Recently, a vapor phase conversion (VPC) method has been newly introduced to fabricate thin Na-β"-Al₂O₃ electrolytes by converting α-Al₂O₃ into β"-Al₂O₃ in α-Al₂O₃/yttria-stabilized zirconia (YSZ) composites under Na⁺ and O^2- dual percolation environments. One of the main challenges that need to be figured out is lowered conductivity due to the large volume fraction of the non-Na⁺-conducting YSZ. In this study, the effect of lithia addition in the β"-Al₂O₃ phase on the grain size and ionic conductivity of Na-β"-Al₂O₃/YSZ solid electrolytes have been investigated in order to enhance the conductivity of the electrolyte. The amount of pre-added lithia (Li₂O) precursor as a phase stabilizer was varied at 0, 1, 2, 3, and 4 mol% against that of Al₂O₃. It turns out that ionic conductivity increases even with 1 mol% lithia addition and reaches 67 mS cm^-1 at 350 ℃ of its maximum with 3 mol%, which is two times higher than that of the undoped composite.

• Journal of the Korean Ceramic Society
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• v.30 no.8
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• pp.615-622
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• 1993

In order to increase chemical durability of thin films in binary system B2O3-SiO2 and Al2O3-SiO2 on the slide glass by the dip-coating technique from TEOS(Tetraethyl Orthosilicate) and boric acid or aluminum nitrate, phosphoric acid(5~20mol%) was added, respectively. Corrosion of acid and alkali of samples treated with 1N, HCl, NaOH and distilled water at 10$0^{\circ}C$ for 15 minute, were measured IR transmittance and variance of transmittance at visible range. Surface structure of thin film was investigated with SEM and formation of crystal phase according to additiion of phosphoric acid was measrued with XRD. In Al2O3-SiO2 system, change of remarkable characteristic was not obtained at the addition of P2O5 but transmittance of thin film was decreased with addition of P2O5 in B2O3-SiO2 system.

• Journal of the Korean Ceramic Society
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• v.46 no.3
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• pp.323-329
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• 2009

Influences of ceramic filler types and dose on the sintering, phase evolution, and dielectric properties of ceramic/CaO-$Al_2O_3-SiO_2$ glass composites were investigated. All of the specimens were sintered at $900^{\circ}C$ for 2 h, which conditions are required by the lowtemperature co-firing ceramic (LTCC) technology. Ceramic fillers of $Al_2O_3,\;SiO_2$, kaolin, and wollastonite were used. The addition of $Al_2O_3$ filler yielded the crystalline phases of alumina and wollastonite, and the densification over 95% of the relative density was achieved up to 50 wt% addition of the filler. For the cases of the fillers of $SiO_2$, kaolin, and wollastonite, crystalline phases of quartz, mullite, and wollastonite formed, while the densification decreased monotonically with the filler addition. In overall, all the investigated fillers with 10 wt% addition resulted in a reasonable sintering (over 95 %) and low dielectric constants (less than 6), demonstrating the feasibility of the investigated composites for application to a LTCC substrate material with a low dielectric constant.

• Journal of the Korean Ceramic Society
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• v.15 no.2
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• pp.66-71
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• 1978

The cobalt blue spinel stains (main composition; CoO:$Al_2O_3$=1 : 1) in CoO-NiO-$Al_2O_$3 and $CoO-Al_2O_3-Cr_2O_3$ system were prepared by the calcination of each component oxides to be adequate for the factory. The color development, the change of the lattice constnat of the spinel and its application to colored glazes were studied. The results were summarized as follows. 1) In CoO-Al_2O_3$ spinel, the excess addition of each component hardly made any variation in lattice constantand alumina-rich spinel specimens caused the brilliant blue color fade. 2) An increase of $Ni^{2+}$ in $CoO-NiO-Al_2O_3$ system, made the lattice constnat of the $CoO-Al_2O_3$ spinel smaller, and an increase of $Cr^{3+}$ in $CoO-Al_2O_3-Cr_2O_3$, larger. 3) Glazed stains under lead glaze were colored nearly same dark blue color fade.

• Korean Chemical Engineering Research
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• v.48 no.6
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• pp.776-783
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• 2010

Co and Ni catalysts supported on $Al_2O_3$ for partial oxidation of methane producing hydrogen were synthesized using impregnation to incipient wetness. The activities of these catalysts for the partial oxidation of methane was investigated at 1 atm and $CH_4/O_2=2.0$ in the temperature range of $450{\sim}650^{\circ}C$. The reaction activity of $Ni/Al_2O_3$ and $Co/Al_2O_3$ catalysts with different loading was investigated. And the beneficial effects of Ni addition to $Co/Al_2O_3$ and the promotional effects of Ce and La addition to $Ni/Al_2O_3$ and $Co/Al_2O_3$ were investigated. These catalysts were characterized by XRD and SEM/EDX. Comparing catalyst loadings, 10 wt% Co and 10 wt% Ni were found to be optimal at the experimental conditions. The 10 wt% $Ni/Al_2O_3$ and 10 wt% $Co/Al_2O_3$ catalysts in partial oxidation of methane showed $CH_4$ conversions and CO selectivity close to the thermodynamic equilibrium levels, but showed lower $H_2$ selectivity than equilibrium level. The addition of Ni to $Co/Al_2O_3$ exhibited higher $H_2$ selectivity but beneficial effect was not observed in the $CH_4$ conversion. Addition of Ce to $Co/Al_2O_3$ and addition of La to $Ni/Al_2O_3$ a improved the $CH_4$ conversion level and $H_2$ selectivity.

• Journal of the Korean Ceramic Society
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• v.25 no.3
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• pp.251-260
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• 1988

Ion-exchange porous glasses were prepared by heat treatment and subsequently hydro thermalor acid leaching treatment $10Li_2O$.$(90-x)B_2O_3$.$xSiO_2$ base glasses containing various amount of $Al_2O_3$ or $MoO_3$. It was investigated how the phase separation and the cation exchange capacity(CEC) were affected by the addition of $Al_2O_3$ or $MoO_3$. The optimum condition of phase separation in these glasses was about 48$0^{\circ}C$ for 10 hrs. The degree of phase separation was rapidly suppressed by the addition of $Al_2O_3$ up to 10 mol% and thereafter suppression effect was decreased. The maximum value of CEC, about 252meq/100g, was observed with the $1OLi_2O$.$45B_2O_3$.$45SiO_2＋7.5Al_2O_3$ porous glass prepared by hydrothermal treatment and its mean pore radius was about 16.3A. The addition of $MoO_3$ accelerated phase separation and leaching rate. Looking at the remakable increment of pore diameter and pore volume of these porous glasses by the addition of $MoO_3$, the effect of $MoO_3$ may be ascribed to the lowering of silica concentration in the borate phase and to the forming of water-soluble complex with silica during the leaching treatment.

• Journal of the Korean Ceramic Society
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• v.33 no.3
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• pp.285-292
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• 1996

The effect of AlN on the thermal conductivity of aluminum oxide pressurelessly sintered at nitrogen atmos-phere was investigated. Increasing aluminium nitride content up to 1~10 mol% the thermal conductivity of $Al_{2}O_{3}$-AlN system was singnificantly decreased and was constant with adding 20 and 25 mol% aluminium nitride. The thermal conuctivity of $Al_{2}O_{3}$ containing 1~10 mol% the thermal conductivity of $Al_{2}O_{3}$-AlN system was singificantly decreased and was constant with adding 20 and 25mol% aluminum nitride. The thermal conctivity of $Al_{2}O_{3}$ containing 1~10 mol% AlN showed a maximum at $1700^{\circ}C$ and decrea-sed with increasing sintering tempertures. This phenomenon was attributed to $\alpha$-$Al_{2}O_{3}$ and ALON formed by reacting $Al_{2}O_{3}$ with AlN up to $1700^{\circ}C$ and the secondary phases such as ${\gamma}$-ALON ($9Al_{2}O_{3}$.AlN)and $\Phi$($5Al_{2}O_{3}$.AlN) phase above $1750^{\circ}C$ The thermal conductivity of $Al_{2}O_{3}$ containing 20 and 25 mol% AlN showed maximum value at $1800^{\circ}C$ Both $\alpha$-$Al_{2}O_{3}$ and ALON existed up to $1600^{\circ}C$ value at $1800^{\circ}C$ Both $\alpha$-$Al_{2}O_{3}$ and ALON existed up to $1600^{\circ}C$ while only AlON phase existed above $1650^{\circ}C$.