• 한국세라믹학회지
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• 제25권3호
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• pp.193-200
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• 1988

침전법에 의해서 pH가 7, 9, 10, 11인 조건에서 생성된 알루미늄 수산화물을 출발물질로 하여 열처리에 따른 알루미나 분말의 특성을 연구하였다. $600^{\circ}C$에서 2시간 동안 열처리하였을 때 비정질 알루미늄 수산화물의 결정수가 탈수된 후에 생성된 최초의 상은 비정질 알루미나의 비표면적은 감소하였다. 비정질 알루미늄 수산화물을 제외한 나머지 알루미늄 수산화물로부터 결정수의 탈수는 비표면적을 증가시켰으며 AlOOH 형태의 수산화물의 존재비가 클수록 전이 알루미나 존재영역까지는 비표면적이 더 크게 나타났다. $\alpha-Al_2O_3$로의 전이속도는 동일온도에서 pH=7 > pH=10 > pH=9 > pH=11의 순서로 일어났으며, 생성된 $\alpha-Al_2O_3$ 분말의 morphology는 알루미늄 수산화물의 외형을 남긴 형골입자(skeleton particle였다. 또한, 열처리 온도의 증가와 $\alpha-Al_2O_3$로의 전이가 일어남에 따라 비표면적의 감소와 더불어 입자성장이 일어나다.

• 한국세라믹학회지
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• 제46권4호
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• pp.385-391
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• 2009

Need for plasma resistant ceramic materials has been continuously increased in semiconductor and display industry requiring plasma processing to realize ultra fine circuit process. Among promising candidates, alumina ceramics have still some advantages with respect to its economic aspect. In this study, fabrication of plasma resistant alumina ceramics was tried, and its processing optimization was also aimed. Careful processing control and thereby uniform microstructure of $Al_2O_3$ gave rise to enhanced plasma resistance, even comparable to market-governing commercial $Al_2O_3$. A further study is needed concerning ${\beta}-Al_2O_3$ materials system, presumably playing a decisive role in decreasing plasma resistance of $Al_2O_3$ ceramics.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2011년도 제40회 동계학술대회 초록집
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• pp.318-318
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• 2011

Etching of an ultrathin aluminum oxide film on NiAl(110) substrate by methanol is studied by home-built scanning tunneling microscopy at room-temperature. We deposited liquid methanol on thin alumina film by using a high speed solenoid valve suitable for deposition of thermally unstable molecules. It is found that only the reflection domain boundary between two domains was preferentially etched by methanol. Since the reflection domain boundary has many oxygen vacancies and irregular structures, judging from the fact, we assume that oxygen vacancies cause the chemically reactive phenomena of methanol in reflection domain boundary on an alumina film. The reactivity of the reflection domain boundary is attributed to the oxygen vacancies due to irregular structures. Similar reactivity is found on the oxygen deficient alumina produced on top of the intact alumina.

• 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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• 제25권2호
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• pp.89-94
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• 1988

Alumina gel was prepared by the hydrolysis of aluminum isopropoxide Al(OC3H7i)3 at low temperature. Sample were calcined at the various temperatures for 10 houres in the electric furnace, respectively. In order to investigate the various propertis-thermal properties, pore size and distribution, and the transition of crystals, infrared spectroscopy, thermal analysis, particle size analysis, scanning electron microscopy, and porosimetry were employed. Transparent alumina gel was opalized at 1200$^{\circ}C$. Porosity was about 87% with pores below 0.7$\mu\textrm{m}$ and 55% at 1200$^{\circ}C$. The gel was transformed along the rising of temperature as follows; Boehmite\longrightarrow$\delta$-Al2O3\longrightarrow$\theta$\longrightarrowAl2O3\longrightarrow${\alpha}$-Al2O3.

• 한국세라믹학회지
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• 제39권3호
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• pp.272-277
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• 2002

전구체로 ($NH_4)[Al(ethylenediaminetetraacetate)]{\cdot}2H_2O$ 착물을 이용한 수정된 열탄소환원질화법으로 질화알루미늄(AlN) 분말과 휘스커를 합성하였다. 이 분말은 질소분위기에서 별도의 환원용 탄소를 혼합하지 않고 1200$^{\circ}$C에서 1500$^{\circ}$C까지의 온도에서 하소시킨 다름 잔류탄소를 태워 버림으로써 얻어졌다. 이 질화과정을 Al-27 마법각 스핀 핵자기공명, 적외선 분광법 및 X-선 회절법으로 연구했다. 전구체 착물은 열분해되어 ${\rho}$-알루미나와 ${\gamma}$-알루미나로 되었다가 ${\gamma}-{\alpha}$알루미나 전이없이 AlN으로 바뀌었다. ${\gamma}$-알루미나가 AlN으로 바뀌면서 분말의 형상이 유지되는 것으로 보아 이 변환과정에서의 중간체는 알루미늄이나 aluminum suboxides와 같은 기체상이 아니고, 고체상의 $AlO_xN_y$임을 알 수 있다. (0001) 사파이어를 이용하면 AlN 휘스커를 합성할 수 있다.

• 대한화학회지
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• 제33권2호
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• pp.263-270
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• 1989

금속알루미늄 조각과 alcohols을 반응시켜 Al-alkoxides를 합성하였으며 이것을 가수분해하여 얻은 Al-hydroxides와 시약 AlCl3로부터 얻은 Al-hydroxides를 여러 온도에서 소성하여 여러 상의 고순도 $Al_2O_3$를 제조하였다. 제조한 ${\gamma}$와 ${\eta}$상 알루미나의 촉매적 특성을 알아보았고, $Al(OH)_3$로부터 ${\alpha}-Al_2O_3$의 생성과정을 속도론적으로 고찰하였다.

• 공업화학
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• 제9권3호
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• pp.377-382
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• 1998

본 연구는 낮은 활성으로 활용성이 제한된 ${\gamma$-알루미나의 이용을 높이기 위하여 표면을 처리한 알루미나의 계면전기적 특성과 표면활성간의 상관성을 규명하기 위하여 수행되었다. 질산알루미늄을 출발 물질로 하고 암모니아수를 침전제로 사용하여 제조한 알루미나와 황산, 질산, 염산으로 표면 처리한 알루미나를 질량이동법과 site-binding theory를 이용하여 영점전하점을 측정하였다. Amine Titration법과 Hammett 지시약법으로 표면활성점을 구하였다. 전해질에 분산된 알루미나의 계면특성은 전위차적정방법에 의하여 측정된 표면 전하밀도값을 이용하여 분석하였다. 표면전하밀도와 산량의 결과를 이용하여 얻은 ${\gamma$-알루미나의 표면특성과 계면전기적 특성의 상관성은 다음과 같다. 표면을 처리하지 않은 알루미나는 $H_o{\leq}+9.3$인 조건에서 소성온도가 증가함에 따라 산도는 감소한다. 표면처리한 알루미나는 표면을 처리하는 데 사용한 음이온의 농도가 증가하면 표면 이온화상수와 영점전하점은 감소한다. 표면을 처리한 알루미나의 표면전하밀도와 산량은 $H_o{\leq}+4.8$인 조건에서 다음과 같은 상관관계를 갖는다. $SO_4^2-/Al_2O_3:Q_A=-0.172ln(0.0418{\sigma}+1.448)$ $NO_3^-/Al_2O_3:Q_A=-0.024{\sigma}-0.0189$ $Cl^-/Al_2O_3:Q_A=-0.01{\sigma}-0.2006$.

• Bulletin of the Korean Chemical Society
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• 제34권12호
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• pp.3559-3564
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• 2013

Alumina particles were grafted onto the surface of manganese oxide particles via the coprecipitation process using surfactant and cosurfactant. The phase of Mn/Al salts (Phase I) and the phase of precipitation agent (Phase II) were prepared in aqueous surfactant solution, separately. Phase II was added into Phase I and the reaction was performed to form the precursors of composites through hydrogen bonding between $Mn(OH)_2$ and $Al(OH)_3$ prepared by the reaction of Mn/Al salts with the precipitation agent. The alumina-grafted manganese oxide particles were obtained as a final product after calcination. The concentrations of Al salt and surfactant were varied to investigate their effects on the formation and the crystallinity of composites. In addition, the crystal structure of products could be controlled by changing the calcination temperature. Through thermal analyses, it was found that the thermal stability of manganese oxide was improved by the introduction of alumina on its surface.

• 한국세라믹학회지
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• 제36권5호
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• pp.513-520
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• 1999

Alumina-coated SiC whiskers wee prepared by the calcination (1150$^{\circ}C$, 1h, Ar) of the alumina hydrate layer which was precipitated homogeneously on whisker surface from a solution of Al2(SO4)3 and urea as a precipitant. In addition carbon coated SiC whiskers were prepared by the pyrolysis (1000$^{\circ}C$, 4h Ar) of phenolic resin coated whisker. The effects of coating conditions on the thickness and morphology of the coated layers were examined by SEM and TEM. It was found that Al2O3-coating layers become thinner and more uniform with decreasing the Al2(SO4)3 concentration. Thin (0.075-0.1$\mu\textrm{m}$) and uniformly alumina-coating layers were obtained at the Al2(SO4)3 concentration 0.010mol/l. On the other han carbon-coating layers were uniform but very thin (5-16 nm) in thickness. For thicker carbon-coating layers ethanol as a disperse medium was found to be more efficient compared tousing acetone.