• 한국분말재료학회지
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• 제16권4호
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• pp.280-284
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• 2009

The pressureless sintering behavior of $Al_2O_3$/Cu powder mixtures, prepared from $Al_2O_3$/CuO and $Al_2O_3$/Cu-nitrate, has been investigated. Microstructural observation revealed that $Al_2O_3$ powders with nano-sized Cu particles could be synthesized by hydrogen reduction method. The specimens, pressureless-sintered at $1400^{\circ}C$ for 4 min using infrared heating furnace with the heating rate of $200^{\circ}C$/min, showed the relative density of above 90%. Maximum hardness of 16.1 GPa was obtained in $Al_2O_3$/MgO/Cu nanocomposites. The nanocomposites exhibited the enhanced fracture toughness of 4.3-5.7 $MPa{\cdot}m^{1/2}$, compared with monolithic $Al_2O_3$. The mechanical properties were discussed in terms of microstructural characteristics.

• The Korean Journal of Ceramics
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• 제5권4호
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• pp.371-374
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• 1999

Y2O3 and Nb2O5 co-doped tetragonal zirconia polycrystals((Y, Nb)-TZP) containing 10 to 30 vol% $Al_2O_3$ were prepared and hydrothermal stability of the composites was evaluated after aging for 5 h at the temperature range of $150^{\circ}C$ $250^{\circ}C$ under 4 MPa $H_2O$ vapor pressure in an autoclave. The (Y, Nb)-TZP/Al2O3 composites showed excellent phase stability under the hydrothermal conditions, as compared with the 3Y-TZP/$Al_2O_3$ composites, due to the combined effects of the Y-Nb ordering in the $t-ZrO_2$ lattice, the reduction of oxygen vacancy concentration, and the $Al_2O_3$ addition. The strength and fracture toughness of the (Y, Nb)-TZP/$Al_2O_3$ composite, containing 20 vol% of 2.8 $Al_2O_3$ particles, were 700 MPa and 8.1 MP.$am^{1/2}$, respectively.

• 한국전기전자재료학회논문지
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• 제21권7호
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• pp.665-668
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• 2008

Multi-layered thin films of $Fe_2O_3/Na_3AlF_6/Fe_2O_3/Cu$, Cr, Al were deposited on glass substrate by evaporation process. As high and low refractive index material, $Fe_2O_3$ and $Na_3AlF_6$ were selected and additionally Cu, Al and Cr were chosen as mid reflective layer respectively. Optical properties including reflectance were systematically studied depending on optical thickness of $Na_3AlF_6$ especially $0.25{\lambda}$ and $0.5{\lambda}$. In order to expect the experimental result, the simulation program, the Essential Macleod Program(EMP) was adopted and compared with the experimental data. Based on the results taken by spectrophotometer at viewing angle $45^{\circ}C$, the $Fe_2O_3/Na_3AlF_6/Fe_2O_3/Cu$ show the colour rage between red and orange in $0.25{\lambda}$ and green and pupple in $0.5{\lambda}$ respectively. When the Al was used as mid reflective layers in $Fe_2O_3/Na_3AlF_6/Fe_2O_3$ system, typical yellow colour and mixed colour between green and pupple were appeared in $0.25{\lambda}$ and $0.5{\lambda}$ of $Na_3AlF_6$ respectively. As compared the experimental result to simulation data, it was found out that the experimental data is relatively well matched with the EMP simulation data.

• 한국세라믹학회지
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• 제31권12호
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• pp.1475-1482
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• 1994

Compositionally triphasic boehmite-silica-zirconia composite gels were prepared by a multiphasic sol-gel route. Phase-formation characteristics and densification behavior of the gel compacts were examined with and without $\alpha$-Al2O3 seeding. In the unseeded triphasic gels, both $\alpha$-Al2O3 and mullite crystallize simultaneously at 130$0^{\circ}C$. On the other hand, the $\alpha$-Al2O3 seeding selectively induces the formation of corundum phase ($\alpha$-Al2O3) at a significantly lower temperature (~110$0^{\circ}C$) and facilitates an epitaxial growth of $\alpha$-Al2O3 between 1100~130$0^{\circ}C$. The densification of alumina-mullite-zirconia composite (derived from the triphasic gels) was also enhanced by the $\alpha$-Al2O3 seeding, and this was attributed to the delayed crystallization of mullite in the $\alpha$-Al2O3 seeded gel.

• 한국세라믹학회지
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• 제25권4호
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• pp.364-372
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• 1988

The mechanical properties and microstructure of ceramics of the system Al2O3-ZrO2-Y2O3 sintered at 1$650^{\circ}C$ for 2h after powder preparation by the precipitation method from Al2(SO4)3.18H2O, ZrOCl2.8H2O and YCl3.6H2O were investigated. The Al2O3-ZrO2-Y2O3 ceramics sintered at 1$650^{\circ}C$ for 2h after mixing alpha-Al2O3 and ZrO2-Y2O3 powders, both were separately precipitated and calcined, were found to have the relative density higher than 97.5% so that the strengthening and toughening mechanisms could be explained mainly as the stress-induced phase transformation. On the other hand, the sintered bodies prepared by co-precipitating the three starting materials were measured to have the relative density lower than 85% so that the degradation of strength were observed above 15 vol% ZrO2 contents due to the high porosity by which the effect of stress-induced phase transformation was assumed to be depressed.

• 한국재료학회지
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• 제8권12호
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• pp.1158-1164
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• 1998

깁사이트를 황산수용액에 용해하여 제조된 황산알루미늄 용액에 에틸알코올을 사용하여 결정을 석출시킨 후 여과, 건조를 통하여 수황산알루미늄 결정 [$Al_2(SO_4)_3$ · $nH_2O$]을 제조하였다. XRD분석 결과 수황산알루미늄에 포함된 결정수는 n=18, 16, 12, 0이었으며, TG분석 결과 평균결정수($n_{av}$)는 14.7이었다. 수황산알루미늄을 열처리한 결과 $800^{\circ}C$에서는 무수황산알루미늄, $900^{\circ}C$와 $1000^{\circ}C$에서는 $\gamma-Al_2O_3$, $1200^{\circ}C$에서는 $\alpha-Al_2O_3$의 생성을 확인할 수 있었다. $\gamma-Al_2O_3$에 니켈피착을 위하여 0.025M농도의 황산알루미늄과 황산니켈을 사용하고 $Ni^{+2}$ 이온과 $Al^{+3}$ 이온의 농도비가 0.5인 혼합용액을 제조한 후 $\gamma-Al_2O_3$ 분말을 혼합하여 슬러리를 제조하였다 제조된 혼합슬러리에 우레아와 $NH_4OH$수용액을 첨가하여 pH를 9.0로 조절하고 $80^{\circ}C$에서 니켈피착을 하였으며, 니켈피착의 진행사항은 ORP(oxidation reduction potential), 전도도 그리고 pH값을 측정하여 관찰하였다. 니켈량에 따른 니켈피착 $\gamma-Al_2O_3$의 특성을 조사하기 위하여 피착된 $\gamma-Al_2O_3$를 $900^{\circ}C$에서 열처리하고 비표면적 변화와 열확산도를 측정하였다. 또한 $1250^{\circ}C$에서 니켈피착 $\gamma-Al_2O_3$의 열안정성은 비표면적과 XRD의 결정상변화로 확인하였다 니켈피착 $\gamma-Al_2O_3$의 표면은 XPS분석으로 Ni $2P_{3/2}$의 화학결합에너지의 변화를 확인한 결과 $NiAl_2O_4$, 상의 화학결합에너지가 증가되었다. 본 연구 결과로 니켈피착 $\gamma-Al_2O_3$가 순수 $\gamma-Al_2O_3$에 비하여 열적 안정성을 지닌 것으로 확인 되었다.

• 한국세라믹학회지
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• 제34권9호
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• pp.921-926
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• 1997

Two NbCx-C1-x/Y2O3/Ti sputter-coated Al2O3 substrates (L 5.5 cm$\times$W 0.5 cm) were diffusion bonded together using hot press method at 95$0^{\circ}C$ for 3 hours under 1 MPa of applied pressure. 4 points bending tests were used to evaluate the mechanical performance of these precracked laminate beams. Two types of mechanical responses were observed: crack penetration through the interface for x=0.75, 1 and crack deflection into an interface for x=0.25, 0.5. The Al2O3/NbCx-C1-x/Y2O3/Ti system suggested here has been proves to be effective for the thermokinetical stability and tailorability of the interfaces of Al2O3/Ti composites at 95$0^{\circ}C$.

• 광물과 암석
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• 제33권3호
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• pp.195-214
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• 2020

삼광 금-은 광상은 과거 한국에서 가장 큰 금-은 광상들 중의 하나였다. 이 광상은 선캠브리아기의 변성퇴적암류내에 발달된 열극대를 충진한 8개조의 석영맥으로 구성된 조산형 금-은 광상이다. 이 광상에서 함 티타늄 광물로는 설석, 티탄철석 및 금홍석이며 설석과 티탄철석은 모암에서만 산출되나 금홍석은 모암과 엽리상 석영맥에서 산출된다. 이들 광물들은 모암에선 흑운모, 백운모, 녹니석, 백색운모, 모나자이트, 저어콘 및 인회석과 엽리상 석영맥에선 백색운모, 녹니석 및 유비철석 등과 함께 산출된다. 설석은 최대 3.94 wt.% (Al₂O₃), 0.49 wt.% (FeO), 0.52 wt.% (Nb₂O₅), 0.46 wt.% (Y₂O₃) 및 0.43 wt.% (V₂O₅) 값을 갖는다. 이 설석은 0.06~0.14 (Fe/Al 비) 값으로 변성기원의 설석이고 X_Al (=Al/Al+Fe³⁺+Ti) 값이 0.06~0.15 값으로 저 함량 알루미늄 설석에 해당된다. 티탄철석은 최대 0.07 wt.% (ZrO₂), 0.12 wt.% (HfO₂), 0.26 wt.% (Nb₂O₅), 0.04 wt.% (Sb₂O₅), 0.13 wt.% (Ta₂O₅), 2.62 wt.% (As₂O₅), 0.29 wt.% (V₂O₅), 0.12 wt.% (Al₂O₃), 1.59 wt.% (ZnO)로써 As₂O₅ 함량이 높게 산출된다. 금홍석의 화학조성은 모암과 엽리상 석영맥에서 각각 최대 0.35 wt.%, 0.65 wt.% (HfO₂), 2.52 wt.%, 0.19 wt.% (WO₃), 1.28 wt.%, 1.71 wt.% (Nb₂O₃), 0.03 wt.%, 0.07 wt.% (Sb₂O₃), 0.28 wt.%, 0.21 wt.% (As₂O₅), 0.68 wt.%, 0.70 wt.% (V₂O₃), 0.48 wt.%, 0.59 wt.% (Cr₂O₃), 0.70 wt.%, 1.90 wt.% (Al₂O₃), 4.76 wt.%, 3.17 wt.% (FeO)로써 엽리상 석영맥의 금홍석에서 HfO₂, Nb₂O₃, As₂O₅, Cr₂O₃, Al₂O₃ 및 FeO 원소들의 함량이 모암의 금홍석보다 높지만 WO₃ 원소의 함량은 낮다. 이 미량원소들은 모암의 금홍석[(Fe³⁺, Al³⁺, Cr³⁺) + Hf⁴⁺+(W⁵⁺, As⁵⁺, Nb⁵⁺) ⟵⟶; 2Ti⁴⁺+ V⁴⁺, 2Fe²⁺+(Al³⁺, Cr³⁺) + Hf⁴⁺+(W⁵⁺, As⁵⁺, Nb⁵⁺) ⟵⟶ 2Ti⁴⁺+2V⁴⁺], 엽리상 석영맥의 금홍석 [(Fe³⁺, Al³⁺) + As⁵⁺ ⟵⟶ Ti⁴⁺+ V⁴⁺, (Fe³⁺, Al³⁺) + As⁵⁺ ⟵⟶ Ti⁴⁺+Hf⁴⁺, 4(Fe³⁺, Al³⁺) ⟵⟶ Ti⁴⁺+(W⁵⁺, Nb⁵⁺) + Cr³⁺]로써 치환관계가 있었다. 이들 자료를 근거로, 모암내 산출되는 설석, 티탄철석 및 금홍석은 광역변성작용 동안 모암광물들의 변질 시 광물내 존재했던 W⁵⁺, Nb⁵⁺, As⁵⁺, Hf⁴⁺, V⁴⁺, Cr³⁺, Al³⁺, Fe³⁺, Fe²⁺ 등과 같은 양이온들의 재 용해 및 농집에 의해 형성되었다. 그후 계속된 연성전단 시 엽리상 석영맥내 금홍석은 열수 용액의 유입에 따른 백색운모와 녹니석의 모암변질작용에 의한 양이온들의 재 용해 및 재 농집과 더불어 초기에 형성된 설석, 티탄철석 및 금홍석과의 반응에 의해 기존에 이들 광물내에 존재하였던 Nb⁵⁺, As⁵⁺, Hf⁴⁺, Cr³⁺, Al³⁺, Fe³⁺, Fe²⁺과 같은 양이온들의 재농집에 의해 형성된 것으로 생각된다.

• 한국세라믹학회지
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• 제19권3호
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• pp.179-186
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• 1982

This research is to aim at the study of sintering mechanism through the observation of microstructure by scanning electron microscopy, after the mixture of 30wt% $Al_2O_3$ (White Alundum) powder is fired in air at the temperature range of 1350~150$0^{\circ}C$ in order to sinter $Al_2O_3$-Al through the oxidation of Al powder. The results obtained in this experiment are as follows: 1. While the compressive strength of $Al_2O_3$(WA) body fired at $1450^{\circ}C$ for 5hrs in air is 150kg/$\textrm{cm}^2$, that of Al-$Al_2O_3$ body fired at 135$0^{\circ}C$, $1400^{\circ}C$ for 5hrs in air is 1100kg/$\textrm{cm}^2$, 1600kg/$\textrm{cm}^2$ respectively, and the higher the firing temperature, the more the compressive strength increases. These results from the sintering effect between $Al_2O_3$(WA) grains and surrounding Al-oxidation layer. 2. While the compressive strength of Al2O3(WA) body fired at 150$0^{\circ}C$ for 5hrs in air is 250kg/$\textrm{cm}^2$, the compressive strength of Al-$Al_2O_3$body fired under the same condition is 2050kg/$\textrm{cm}^2$ and water absorption 9.0%, porosity 23.3%, bulk density 2.60gr/$cm^3$. It is assumed that these results come from not only the grain growth of oxidized Al grains but also the increase of bonding strength between $Al_2O_3$(WA) grains.

• 분석과학
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• 제5권1호
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• pp.115-120
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• 1992

강유전체인 $LiTaO_3$ 소재는 SAW filters나 IR sensors의 기본재료로 사용되고 있다. Dopant로서 $Al_2O_3$를 $LiTaO_3$에 일부 치환함으로써 유전 특성을 변화시키고 특히 용융점을 낮춤으로써 단결정 제조를 용이하게 한다. X-선 회절분석에 의한 격자상수 변화와 Raman spectroscopy의 band broadening을 측정한 결과 $LiTaO_3$에 대한 $Al_2O_3$의 고용한계가 $Li_{1-X}Al_{2X}Ta{1-X}O_3$에서 X=0.25mol이었으며, 고용한계 이상에서는 2차상인 $Al_2O_3$상이 XRD로 관찰되었다. Grain size에 의한 Raman band의 broadening을 고려하기 위하여 단결정과 소결체 $LiTaO_3$를 측정 비교하였다.