• 한국세라믹학회지
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• 제26권1호
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• pp.31-36
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• 1989

In order to synthesize AlN-polytypes from AlN-SiO2-Al2O3 system, composition A (AlN/SiO2/Al2O3=1/0.3/0.05, mole ratio) and composition B(AlN-SiO2-Al2O3=1/0.2/0.05, mole ratio) were used. AlN-polytypes were produced by nitriding the mixture at 175$0^{\circ}C$~190$0^{\circ}C$ under N2 atmosphere. For lower reaction temperature, 15R phase was produced and in the case of higher reaction temperature, AlN phase was only produced. As each composition was heated at 185$0^{\circ}C$ in N2 atmosphere, produced main phases were 15R phase for composition A and 21R phase for composition B respectively. The fracture surfaces of produced reactants showed porous skeleton structure.

• 한국세라믹학회지
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• 제29권6호
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• pp.419-430
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• 1992

Fabrication possibility of low-shrinkage alumina without oxidation and wetting agent was presented on the basis of observation about oxidation behavior, microstructure and physical characteristics of such reaction agents free Al2O3-Al system. The composition less than Al 10w/o where Al can act as a sintering agent for Al2O3 was excluded. Under the condition of present experiments oxidation of Al2O3-Al system was dependent not on holding time but mainly on oxidation temperature. In thes case of Al powder not comminuted effectively during powder mixing of Al2O3-Al, columnar structure which would act as a hindrance to the densification during sintering developed more during oxidation with higher Al contents, and which made the fabrication of low-shrinkage Al2O3 ceramics impossible. If Al powder was comminuted effectively due to co-mixed Al2O3 characteristics, densification was improved because of no columnar structure and made the fabrication of sintered body with -2.7% dimensional change and 81% relative density possible. As a result, it is possible to fabricate dense low-shrinkage Al2O3 ceramics without oxidation and wetting agent under conditions such as smaller particle size of Al, Al contents below 50v/o, higher green density of Al2O3-Al compact and the use of Al2O3 powder used for high-density ceramics.

• 한국세라믹학회지
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• 제28권1호
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• pp.11-18
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• 1991

A precipitation method, one of the most effective liquid phase reaction methods, was adopted in order to prepare high-tech Al2O3/ZrO2 composite ceramics, and the effects of stress-induced phase transformation of ZrO2 on thermal shock behavior of Al2O3-ZrO2 ceramics were investigated. Al2(SO4)3.18H2O, ZrOCl2.8H2O and YCl3.6H2O were used as starting materials and NH4OH as a precipitation agent. Metal hydroxides were obtained by single precipitation(process A) and co-precipitation(process B) method at the condition of pH=7, and the composition of Al2O3-ZrO2 composites was fixed as Al2O3-15v/o ZrO2(+3m/o Y2O3). Critical temperature difference showing rapid strength degradation by thermal shock showed higher value in Al2O3/ZrO2 composites(process A : 20$0^{\circ}C$, process B : 215$^{\circ}C$) than in Al2O3(175$^{\circ}C$). The improvement of thermal shock property for Al2O3/ZrO2 composites was mainly due to the increase of strength at room temperature by adding ZrO2. The strength degradation was more severe for the sample with higher strength at room temperature. Crack initiation energies by thermal shock showed higher values in Al2O3/ZrO2 composites than in Al2O3 ceramics due to increase of fracture toughness by ZrO2.

• 한국세라믹학회지
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• 제36권4호
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• pp.410-416
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• 1999

The reactivity of three kinds of spinels which CaO-Al2O3-SiO2 slag was investigated in terms of mineral phases and microstructures. New crystal products were not formed by reaction of 12CaO.7Al2O3 in the slag with spinels and free MgO components was preferenctially dissolved into slag for MgO-rich spinel and stoichiometric spinel. Meanwhile mineral phase was changed from 12CaO.7Al2O3 to CaO.Al2O3 to CaO.2Al2O3 finally to CaO.6Al2O3 having high melting point for Al2O3 -rich spinel. The Fe-oxide component of the slag was taken up by only stoichiometric spinel grains within the spinel clinker and the trapped amount of Fe-oxide was independent of MgO content of MgO in spinel clinker the more th resistance to slag corrosion but the less resistance to slag penetration.

• 마이크로전자및패키징학회지
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• 제12권3호
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• pp.259-265
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• 2005

도금전류밀도에 따른 Ni박막과 $Ni-Al_2O_3$복합박막의 항복강도, 파괴 연신율 및 $Ni-Al_2O_3$ 복합박막내 $Al_2O_3$ 함유량을 분석하였다. $5\~20\;mA/cm^2$로 형성한 $Ni-Al_2O_3$ 내 $Al_2O_3$ 함유량은 $11.48\~11.64\;vol\%$로 거의 일정하였으나, 도금전류밀도가 $30\;mA/cm^2$로 증가함에 따라 $Al_2O_3$함유량이 $8.41\;vol\%$로 감소하였다. $Ni-Al_2O_3$ 복합박막은 모두 Ni 박막보다 높은 항복강도를 나타내었으며, 특히 $5\;mA/cm^2$로 도금한 $Ni-Al_2O_3$의 항복강도는 Ni에 비해 $50\%$증가하였다. 도금전류밀도가 증가함에 따라 Ni박막과 $Ni-Al_2O_3$복합박막의 파괴 연신율이 감소하였다. $5\;mA/cm^2$에서 도금한 $Ni-Al_2O_3$복합박막이 다른 전류밀도에서 형성한 복합박막에 비해 $Al_2O_3$가 균일하게 분산되어 있으며 가장 높은 항복강도와 파괴 연신율을 나타내었다.

• 한국결정성장학회지
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• 제8권2호
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• pp.332-341
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• 1998

${\alpha}-Al_2O_3$와 비정질 SiO2부터 Mullite를 합성하기 위한 고체상태반응의 반응속도를 1450~$1480^{\circ}C$ 온도 범위에서 연구하였다. 반응속도는 $Al_2O_3$분말을 코팅한 28.16wt%의 $SiO_2$와 일정한 온도에서 여러 시간동안 가열하여 생성된 혼합물에 의하여 결정되었다. MgO안의 반응물과 미반응물의 양은 X-선 회절분석에 의하여 결정되었다. Mullite의 부피율과 peak intensity 비의 자료로부터 $Al_2O_3$와 $SiO_2$의 $3Al_2O_3\;{\cdot}\;2SiO_2$형태로의 반응은 $1450^{\circ}C$와 $1480^{\circ}C$ 사이에서 시작되었다. 고체상태반응 활성화 에너지는 Arrhenius 식에 의하여 결정되었다. 활성화 에너지는 31.9KJ/mol이다.

• 한국세라믹학회지
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• 제34권6호
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• pp.553-560
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• 1997

A fine $\alpha$-Al2O3 powder was prepared by sol-gel process for membrane application. And it was carried out by adding 1.5wt% $\alpha$-Al2O3 powders(mean size : 87 nm) as seeds to the prepared sols and by controlling the heating schedule (the heating rate and the soaking time) to prevent the microstructural change, which occured during $\theta$-to $\alpha$Al2O3 phase transformation. The seeded $\alpha$-Al2O3 particles acted as the heterogeneous nucleation sites for the $\alpha$-Al2O3 nucleation during the transformation of $\theta$- to $\alpha$-Al2O3 and resulted in increasing the driving force of phase transformation to activate the formation of $\alpha$-Al2O3 phase at 82$0^{\circ}C$. By $\alpha$-Al2O3 seeding and controlling of heating condition the phase transformation of $\theta$- to $\alpha$-Al2O3 was accomplished at low temperature and the grain growth process was depressed. Therefore, the unsupported membrane could be fabricated in $\alpha$-Al2O3 . The average diameter of pores in the fabricated membrane was 7 nm and the porosity was 47%.

• 대한전자공학회논문지
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• 제27권6호
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• pp.886-894
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• 1990

Sinterbility, microstructure, mechenical and electrical properties of yttriastabilized zirkconiz (92 mole % ZrO2 + 8 mole % Y2O3) doped with 0.5 mole % SiO2 and 0-2.O mole% Al2O3 were studied as a functin of Al2O3 addition. Sintered density increased with increasing Al2O3 addition up to o.5 mole%but decreased up to 1.0mole% Al2O3. Vickers hardness is proportional to sintered density. The specimen added 0.5mole% Al2O3 and 0.5mole% SiO2 exhibited a maximum conductivity. And the specimen added 0.5 mole % Al2O3 and 0.5 mole% SiO2 was measured a maximum electromotive force for a characteristics of oxyzen partial pressure.

• 한국결정성장학회지
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• 제8권1호
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• pp.97-105
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• 1998

$Al_2O_3-C$계 내화물에 Al 금속분말을 첨가하여 $800^{\circ}C$에서 $1400^{\circ}C$의 온도영역에서 탄소의 산화억제 메카니즘을 조사하였다. 탄소의 산화는 Al 금속분말을 5wt% 첨가한 $Al_2O_3-C-Al $ 시편에서 억제되었으며, 시편의 표면과 내부계면에 탄소가 비교적 균일하게 분포되어 있었다. Al-C 시편의 조성에서 중간생성물인 $Al_4C_3$ 및 AlN이 $800-1200^{\circ}C$의 온도범위에서 존재하였으며, $1400^{\circ}C$ 이상의 고온에서 모두 $Al_2O_3$로 전이하였다. $1000^{\circ}C$에서 1시간 가열한 Al-C 시편에서 $Al_4C_3$의 생성과 관계있는 cavity structure가 관찰되었다. 열역학적 고찰을 기초로 하여 산환억제 효과와 관계있는 $Al_4C_3$와 AlN의 생성, $Al_2O_3$로의 전이, C(s)의 형성등이 논하였다.

• 한국세라믹학회지
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• 제27권5호
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• pp.583-588
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• 1990

Glass films in the binary system B2O3-SiO2 and Al2O3-SiO2 were prepared on soda-lime-silica slide glass by the dip-coating technique from TEOS and boric acid or aluminum nitrate. Thickness of the films varying with viscosity and withdrawal speed were measured and effect of composition and firing temperature on the properties such as transmittance and refractive index were investigated. nM2O3.(100-n)SiO2(M=B or Al) films containing up to 20mol% B2O3 and 40mol% Al2O3 were transparent. Maximum transmittance at visible range were obtained for the sample containing 15mol% Ba2O3 and 32.5mol% Al2O3 and heat-treated at 50$0^{\circ}C$, respectively. Refractive index of the film containing 15mol% B2O3 was mininum in the B2O3-SiO2 binary system and minimal refractive index was appeared at the film containing 32.5mol% Al2O3. In IP spectra, addition of B2O3 were increased absorption peak intensity of B-O and Si-O-B bond and addition of Al2O3 were decreased absorption peak intensity of Si-O bond, respectively.