• 공학논문집
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• 제4권1호
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• pp.87-91
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• 2002

본 연구에서는 초임계 건조 및 유체법을 사용하여 얻어진 분말을 열처리하여 나노 크기의 알루미나 분말을 제조하였다. Al-isopropoxide를 출발 물질로 사용하였고, 용매로서는 2가 알코올류인 Ethylene glycol을 사용하였다. 또한 온도 및 압력의 영향을 조사하기 위하여 임계점 이하의 조건에서도 실험도 병행하였다. Autoclave에서 초임계 건조 및 유체법으로 제조된 알루미나는 XRD, SEM 및 TG-DTA 의해 특성을 조사하였고, 열처리 결과 새로운 route로 $\alpha-A12O3$로 전이 되었다.

• 한국세라믹학회지
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• 제29권6호
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• pp.480-488
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• 1992

The sintering behaviors of seeded alumina from alkoxide were studied. Room temp. desiccated powder exhibited better sintering behavior due to its packing ability and powder activity. $\alpha$-Al2O3 2wt% seeded compacts sintered with 97.5%TD, 1~3${\mu}{\textrm}{m}$ diameters at 140$0^{\circ}C$, 2hrs. Fe-nitrate doped compacts resulted in enhanced initial sintering behavior due to ionic effects of Fe3+ but failed to refined microstructure.

• 한국세라믹학회지
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• 제30권7호
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• pp.589-597
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• 1993

The optimum sol solution for making alumina membrane was synthesized by using sol-gel method with aluminium isopropoxide. Two types of supports were made from the $\alpha$-Al2O3 powder. The porosities of supports could be controlled by the forming methods and the heat treatment conditions. After the support was coated with optimum sol solution and heat-treated at 50$0^{\circ}C$ for 1hour, the thickness of crack-free membrane could be controlled reproductively with dipping time.

• 한국세라믹학회지
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• 제31권4호
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• pp.359-366
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• 1994

Tow types of supports were made using $\alpha$-Al2O3 powder and optimum conditions to prepare for supports were provided. Sol solution for coating was synthesized by sol-gel method with aluminum isopropoxide. Supports were coated and heat-treatemented, where the thickness of coating layer was controlled by dipping time. Flux and permeability of alumina membrane were measured by liquid and gas filtration apparatus and these were compared with the provided model. It was confirmed that the coating was done very well without micro~crack and defect.

• 한국재료학회지
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• 제24권12호
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• pp.652-657
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• 2014

The purpose of this study was to investigate the microstructures and mechanical properties of zirconia toughened alumina (ZTA) ceramics prepared from two kinds of 3Y-TZP powders. ZTA composites were prepared by adding two kinds of 3Y-TZP powders, 3YEH (BET = $7m^2/g$) and 3YEM (BET = $16m^2/g$), to ${\alpha}$-alumina in the range of 5-25 wt%. It was found that the microstructure photographs of the ZTA composites showed that the average grain size of alumina decreased as the content of zirconia increased. In our present study, specimens containing 3YEM zirconia exhibited smaller grain sizes compared to those of 3YEH zirconia. The Vickers hardness of the ZTA composites that were sintered at $1600^{\circ}C$ for 2 hrs was found to smoothly decrease with increasing zirconia content because of the low Young modulus in zirconia. The Vickers hardness of the ZTA containing 3YEH zirconia was greater than that of the 3YEM zirconia. In substance, the fracture toughness ($K_{1c}$) of the ZTA composites increased as the content of zirconia increased. The fracture toughness ($K_{1c}$) of ZTA containing 3YEM zirconia was greater than that of 3YEH zirconia.

• 대한기계학회논문집A
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• 제31권6호
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• pp.665-670
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• 2007

Alpha-phase alumina TGO(Thermally Grown Oxide) forms on the interface between zirconia top coat and bond coat of thermal barrier coating system for superalloys during exposure to high temperature over $1000^{\circ}C$. It is known to provide a good protection against hot corrosion and to cause surface failure such as rumpling and cracking due to difference in thermal expansion coefficient from the substrate metal and the lateral growth. Consequently, mechanical properties of the alumina TGO at the high temperature are the key parameters determining the integrity of TBC system. In this work, by using Fecralloy foils as the alumina forming substrate, creep tests and tensile tests have been performed with various TGO thicknesses$(h=0{\sim}4{\mu}m)$ and yttrium contents(0, 200ppm) at $1200^{\circ}C$. Displacement-time curves and load-displacement curves for each TGO thickness(h=1,2,..) were measured from the creep and tensile tests, respectively, and compared with the curves without TGO thickness(h=0). As the result, the intrinsic tensile and creep properties of TGO itself were determined.

• 한국세라믹학회지
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• 제28권7호
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• pp.568-576
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• 1991

The powder characterization and sintering behavior of alkoxide-derived alumina powders prepared by esterification were investigated. The dried powders were calcined at 700$^{\circ}C$, 900$^{\circ}C$, 1080$^{\circ}C$, 1170$^{\circ}C$ for 1 h. and the resulting crystalline forms were amorphous, {{{{ gamma }} phase, {{{{ theta }}+{{{{ alpha }} phase, and {{{{ alpha }} phase, respectively. The sinterability was best in the case of being calcined at 1170$^{\circ}C$. It was most effective to disperse sintering additive in the initial stage from which acetate was formed. At 1600$^{\circ}C$ for 4 h, 98.5% of relative density was obtained when MgO and Fe2O3 were simultaneously doped, and dense sintered body whose density was near theoretical value was obtained when heating schedule was controlled.

• 공학논문집
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• 제3권1호
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• pp.215-222
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• 1998

촉매 연소용 촉매 담체인 $\gamma-Al_2O_3$ 분말의 열안정화에 미치는 La과 Si의 첨가 효과에 대하여 연구하였다. 첨가제의 첨가는 습식 impregnation방법으로 행하였고, 출발 물질은 $La(NO_3)_3{\cdot}6H_2O$와 $Si(OC_2H_5)_4$를 사용하였다. 열안정화 효과는 혼합분말을 고온에서 열처리 한 후 비표면적을 측정하여 고찰하였다. 첨가제로 첨가한 La과Si는 모두 순수한 $\gamma-Al_2O_3$분말에 비하여 소결을 억제함으로써 열 안정화 효과가 있음이 확인되었으며, 특히 Si 첨가한 경우에는 $\alpha-Al_2O_3$의 생성을 현저히 억제한다는 것을 확인하였다. 이들 첨가제에 의한 열안정화 효과는 첨가제에 의한 새로운 상의 생성과 표면 확산의 억제등이 주된 요인으로 판단되었다.

• 한국재료학회지
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• 제10권9호
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• pp.619-623
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• 2000

알루미나 여과막은 boehmite 분말 (${\Upsilon}-AlOOH$)을 이용하여 졸-겔법으로 준비되어졌다. 제조된 여과막은 상전이 온도와 미세구조 변화를 관찰하기 위해 지지체 없이 형성된 여과막을 제조하였다. 여과 공정의 응용에서 균일한 기공크기와 분포를 제어하는 것이 중용하다. 다공성 담체 위에 형성된 여과막과 다공성 담체 없이 형성된 여과막의 ${\theta}-to\;{\alpha}-AL_2O_3$로의 상전이는 박막 XRD를 이용하여 분석하였고, 미세구조의 변화의 관찰은 주사전자현미경(SEM)을 사용하여 관찰하였다. XRD에서 분석된 결과는 다공성 담체 위에 형성된 여과막이 다공성 담체 없이 형성된 여과막과 비교하여 $100^{\circ}C$ 더 높은 상전이 온도를 가지는 것을 보여주었다. 이런 유사한 효과는 여과막의 미세구조 변화에서도 관찰되었다.

• 대한화학회지
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• 제55권1호
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• pp.81-85
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• 2011

이소부탄의 산화탈수소반응(ODH)에 대한 $V_{0.9}Sb_{0.1}O_x$ 촉매계의 5가지 담지체의 촉진효과를 조사하였다. 사용된 5가지 담지체는 감마-알루미나, 알파-알루미나, 실리카-알루미나, 실리카겔, 마그네슘 산화물이다. 촉매는 사용된 담지체에 따라 그 효과가 다르게 나타났다: ${\gamma}-Al_2O_3$ > $\alpha$-$Al_2O_3$ > Si-Al-O> $SiO_2$ $\approx$MgO$\gg$unsupported. V-Sb-O 비율은 별로 촉매 활성과 선택성에 영향을 미치지 않았다. 촉매 성분들이 담지체에 골고루 잘 분포된 이유로 인해 감마-알루미나에 담지된 $V_{0.9}Sb_{0.1}O_x$ 촉매계가 성능이 제일 뛰어났다.