• Journal of the Korean Ceramic Society
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• v.25 no.3
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• pp.231-236
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• 1988

In order to investigate the effect of second phase on $Al_2O_3$ matrix, SiC particles were dispersed in $Al_2O_3$ matrix as a second phase over the content range of 5 vol.% to 20 vol.%. To this mixture, $Y_2O_3$ or $TiO_2$ powders were added as a sintering additive before isostatically pressing and pressurelessly sintering at 180$0^{\circ}C$ for 90 min in $N_2$ atmosphere. With increasing SiC content, relative densities of composites were decreased but mechanical properties of composites were improvjed. In the case of adding $Y_2O_3$ as a sintering additive, maximum values of flexural strength, hardness and fracture toughness were 525 MPa, 17.1 GPa, 4.1 MPa.m1/2 respectively. In the case of adding X$TiO_2$ as a sintering additive, maximum values of flexural strength, hardness were 285 MPa, 12.1 GPa respectively. Improved mechanical properties were found to be the results of grain growth control of $Al_2O_3$ matrix and crack deflection by the second phase SiC particles.

• Journal of the Korean Ceramic Society
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• v.40 no.5
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• pp.494-500
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• 2003

The effects of $Al_2$O$_3$ addition upon the sintering range of clay-EAF dust (the specified wastes produced from steel making process) system body which would be used as a constructing bricks were investigated. The slope of apparent density to sintering temperature decreased for Clay-dust body containing 5~15 wt% A1203 sintered at 1200-125$0^{\circ}C$, and the absorption(%) of specimen sintered above 125$0^{\circ}C$ decreased due to the formation of open pores produced by pore bloating. For the specimen without any $Al_2$O$_3$ addition sintered at 1275$^{\circ}C$, the major phase was cristobalite, the small amount of mullite (3Al$_2$O$_3$ 2SiO$_2$) formed and the hematite (Fe$_2$O$_3$) remained. In the Clay-dust system body containing $Al_2$O$_3$ 15 wt%, however, the cristobalite disappeared and the major phase was mullite. Also the part of $Al_2$O$_3$ reacted with hematite to form hercynite (FeAl$_2$O$_4$). From the these results, addition of $Al_2$O$_3$ to Clay-dust system body enlarges a sintering range; decreasing an apparent density and absorption slop to sintering temperature owing to consumption of liquid phase SiO$_2$ at higher temperature and gas-forming component Fe$_2$O$_3$ at reduced atmosphere which would decrease an amount of liquid formed and increase the viscosity of the liquid produced during the sintering process.

• 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.38 no.5
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• pp.454-460
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• 2001

장석, 석영, 점토와 17 wt% $Al_2$O$_3$를 함유한 알루미나질 자기 애자를 제조하였다. 분말을 ball milling으로 6시간 분쇄하였으며 성형체를 압출법으로 제조한 후 터널가마에서 130$0^{\circ}C$, 50분 동안 소결하였다. 터널가마에서 소결한 시편의 소결밀도는 이론밀도의 97%에 도달하였고, 3점 꺾임강도는 1658kgf/$ extrm{cm}^2$ 이었으며 ICL(indentation crack length) 방법으로 측정한 파괴인성은 2.3 MPa.m$^{1}$2/이었다. 기계적 성질을 향상시키기 위하여 ZrO$_2$를 첨가하여 15 wt% $Al_2$O$_3$-2 wt% ZrO$_2$와 12 wt% $Al_2$O$_3$-5 wt% ZrO$_2$를 복합체를 제조하였다. ZrO$_2$를 첨가한 시편의 꺾임강도는 1740kgf/$\textrm{cm}^2$이고 파괴인성은 2.4 MPa.m$^{1}$2/로 약 10% 기계적 성질이 향상되었다.

• 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.

• Journal of the Microelectronics and Packaging Society
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• v.5 no.1
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• pp.19-30
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• 1998

Aluminium secondary butoxide(ASB)를 출발물질로 하여 졸-겔방법에 의해 소결거 동에 미치는 $\alpha$-Al2O3 seed의 첨가효과에 따른 알루미나의 저온소결 가능성과 알루미나의 상전이에 대하여 TEM, DTA, XRD, FT-IR등으로 고찰을 하였다. TEM 분석결과 초기 생 성물인 boehmite가 비정질에서 단결정질로 진행되어 가고 있음을 확인하였다. 그리고 DTA 분석결과 $\alpha$-Al2O3 seed의 첨가한 경우 seed의 함량이 증가함에 따라 상전이 온도는 점차 낮아졌으며 약 0.4wt%일 때 seed를 첨가하지 않은 시료의 전이온도(약 1126$^{\circ}C$)에 비하여 약 7$0^{\circ}C$ 저하된 약 1056$^{\circ}C$로나타났으며 그 이상의 seedcja가에 있어서는 전이온도에 크게 영향을 나타내지 않았다. 또한 XRD분석결과 $\alpha$-Al2O3 seed를 첨가하지 않은 경우 110$0^{\circ}C$이 상의 온도에서 $\alpha$상이 생성되었음을 알수 있었다. 또한 100$0^{\circ}C$이상의 온도에서 $\alpha$상이 생성 되었음을 나타내는 Al-O 흡수특성 피크가 400~1000cm-1 범위에서 나타내고 있는 것을 FT-IR 분석결과에서도 확인할수 있었다. 그리고 $\alpha$-Al2O3 seed를 약 0.4wt% 첨가시 900~ 95$0^{\circ}C$에서 $\alpha$상이 형성됨을 관찰할 수 있었다.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.18 no.6
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• pp.237-241
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• 2008

Hot-press sintering of AlN ceramics were carried out with $Y_2O_3$ as sintering additive at a sintering temperature $1,750{\sim}1,850^{\circ}C$. The effect of $Y_2O_3$ addition and sintering time on sintering behavior and thermal conductivity of AlN ceramics was investigated. $Y_2O_3$ added AlN showed noticeably higher denazification rate than pure AlN. The thermal conductivity of AlN specimens was promoted by the addition of $Y_2O_3$ in spite of the formation of YAG secondary phase in AlN grain boundaries and grain boundary triple junction because $Y_2O_3$ addition could reduced the oxygen contents in AlN lattice which is primary factor of thermal conductivity. Typically, the thermal conductivity of 5 wt% $Y_2O_3$ added specimen was dramatically improved by the increase of sintering time because the elimination of YAG secondary phases from the grain boundary due to the evaporation, as well as the grain-growth of AlN grains.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.07a
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• pp.138-141
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• 2004

[ $MnO_2$ ]가 첨가된 $0.9Pb(Zr_{0.5}Ti_{0.5})O_3-0.2Pb[(Zn_{0.8}Ni_{0.2})_{1/3}Nb_{2/3}]O_3$(0.8PZT-0.2PZNN) 세라믹스는 그 압전특성과 유전특성이 뛰어나지만 $1000^{\circ}C$ 이하의 낮은 소결 온도에서는 소결되지 않는다. $1000^{\circ}C$이하의 낮은 소결온도에서 소결하기 위해 CuO를 첨가한 결과, 소결온도 $920^{\circ}C$에서 소결성은 우수하였으나 그 압전 특성의 저하가 두드러졌다. 이는 XRD에서 확인한 결과에 따르면 CuO의 첨가가 우수한 MPB 조성으로 판명된 $MnO_2$ 가 첨가된 0.8PZT-0.2PZNN 세라믹스의 결정구조를 Rhombohedral 구조로 바꾸기 때문인 것으로 보였으며 이러한 문제는 PZNN의 비율을 조절하여 0.875PZT-0.125PZNN 세라믹스를 선택함으로 인해 해결할 수 있었다. 그러나 여전히 낮은 $Q_m$값을 높이기 위해서 $Al_2O_3$를 첨가하였고 그 결과 시편의 tetragonality 감소와 $Q_m$값의 증가를 확인할 수 있었으나 그 첨가량이 0.2wt% 이상일 경우에는 밀도의 감소로 인한 압전특성의 저하가 나타났다. 밀도의 향상을 위해 Zn and Ni excess 조성을 선택하였고 그 결과 0.5wt% $MnO_2$와 0.2wt% CuO 그리고 0.3wt% $Al_2O_3$를 첨가한 0.875PZT-0.125PZNN 세라믹스(Zn and Ni excess 조성)를 $920^{\circ}C$에서 소결한 경우 $k_p=0.581,\;Q_m=809,\;d_{33}=345\;pC/N\;and\;{\varepsilon}_{33}/{\varepsilon}_0=1345$의 빼어난 압전 및 유전특성과 $330^{\circ}C$의 높은 $T_c$를 보였고 그 조성의 vibration velocity는 약4.5 m/s로 나타났다.

• Journal of the Korean Ceramic Society
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• v.36 no.1
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• pp.1-6
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• 1999

Mullite was synthesized by adding industrial by-products, Al(OH)3 and boehmite, to a natural kaolin of pink A-grade. The attrition milling method, which has simultaneously milling and mixing effects, was carried out. The specimens were formed by uni-axial pressing of 1.5 ton/$\textrm{cm}^2$ and then fired. When the Al(OH)3 was added, the flexural strength of 71.8 wt% Al2O3 specimen fired at 1600$^{\circ}C$ for 4 hrs was 22.3 MPa and the amount of synthesized of 71.8 wt% Al2O3 specimen fired at 1600$^{\circ}C$ for 10 hrs was about 85%. When the boehmite was added, the flexural strength of 68 wt% Al2O3 speciment fired at 1600$^{\circ}C$ for 10 hrs was 147 MPa, and the high purity mullite of about 95% was synthesized for 71.8 wt% Al2O3 specimen fired at 1600$^{\circ}C$ for 10 hrs.

• Journal of the Korean Ceramic Society
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• v.28 no.8
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• pp.593-602
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• 1991

Al2O3 and NiO-doped Al2O3 powders were prepared from the ethanol solution of Al (NO3)3$.$9H2O and Ni(NO3)2$.$6H2O by spray pylolysis method using two-fluid nozzle. As a result of spraying test with 0.3 mol/{{{{ iota }} concentration starting solution, mean droplet sizes varied with 8.99∼9.69$\mu\textrm{m}$ and those standard deviation were 4.57∼5.12. As-prepared powders which were synthesized at 1000$^{\circ}C$ have spherical shape, sizes of 0.1∼3.0$\mu\textrm{m}$ and specific surface area of 22.34∼24.20㎡/g. Most powders consisted of {{{{ gamma }}-Al2O3 phase and transforned into ${\alpha}$-A;2O3 phase by calcination at 1100$^{\circ}C$ for 1 hr. NiO-doped Al2O3 sintered bodies had better sinterability than those of pure Al2O3 and 0.3 wt% NiO-doped Al2O3 had near theoretical density and dense microstructure.