• 한국표면공학회지
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• 제44권4호
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• pp.125-130
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• 2011

$Cr_2AlC$ compounds were synthesized by hot pressing, and oxidized between 900 and $1200^{\circ}C$ in air for up to 50 hours. They oxidized to a thin $Al_2O_3$ layer containing a small amount of $Cr_2O_3$with the liberation of carbon as CO or $CO_2$ gases. The consumption of Al to form the $Al_2O_3$ layer led to the depletion of Al and enrichment of Cr just below the $Al_2O_3$ layer, resulting in the formation of an underlying $Cr_7C_3$ layer. As the oxidation temperature and time increased, the $Cr_7C_3$ oxide layer and the underlying $Cr_7C_3$ layer thickened. The oxidation resistance of $Cr_2AlC$ was generally good due to the formation of the $Al_2O_3$ barrier layer.

• 한국결정성장학회지
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• 제7권2호
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• pp.216-223
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• 1997

출발물질로 aluminum iso-propoxide ($Al(OC_3H_7)_3$, AIP)를 사용하여 화학증착법으로 Si-wafer(100)위에 알루미나 박막을 증착하였다. 증착된 박막의 조성을 알아보기 위해 ESCA를 이용하였으며, SEM을 이용하여 박막의 형상 및 두께를 평가하였다. 그리고 굴절율 및 C-V 특성은 각각 ellipsometry와 HP4192A를 사용하였다. ESCA와 SEM의 분석결과에서 상압보다는 저압에서 막이 균일하고 조성이 잘 맞는 것을 알 수 있었으며 열처리를 통해 굴절율의 변화를 볼 수 있었다. 그리고 NMOS소자에서의 C-V특성을 개선하기 위해, $Al_2O_3$와 Si사이에 $SiO_2$층을 형성하는 것이 좋음을 알 수 있었다.

• 한국분말재료학회지
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• 제11권3호
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• pp.247-252
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• 2004

Recently, it has been found that mechanical alloying (MA) facilitates the nanocomposites formation of metal-metal oxide systems through solid-state reduction during ball milling. In this work, we studied the MA effect of Fe$_{3}$O$_{4}$-M (M = Al, Ti) systems, where pure metals are used as reducing agents. It is found that composite powders in which $Al_{2}$O$_{3}$ and TiO$_{2}$ are dispersed in $\alpha$-Fe matrix with nano-sized grains are obtained by mechanical alloying of Fe$_{3}$O$_{4}$ with Al and Ti for 25 and 75 hours, respectively. It is suggested that the large negative heat associated with the chemical reduction of magnetite by aluminum is responsible for the shorter MA time for composite powder formation in Fe$_{3}$O$_{4}$-Al system. X-ray diffraction results show that the reduction of magnetite by Al and Ti if a relatively simple reaction, involving one intermediate phase of FeAl$_{2}$O$_{4}$ or Fe$_{3}$Ti$_{3}$O$_{10}$. The average grain size of $\alpha$-Fe in Fe-TiO$_{2}$ composite powders is in the range of 30 nm. From magnetic measurement, we can also obtain indirect information about the details of the solid-state reduction process during MA.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2016년도 추계학술대회 논문집
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• pp.153-153
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• 2016

Aluminum alloys have poor corrosion resistance compared to the pure aluminum due to the additive elements. Thus, anodizing technology artificially generating thick oxide films are widely applied nowadays in order to improve corrosion resistance. Anodizing is one of the surface modification techniques, which is commercially applicable to a large surface at a low price. However, most studies up to now have focused on its commercialization with hardly any research on the assessment and improvement of the physical characteristics of the anodized films. Therefore, this study aims to select the optimum temperature of sulfuric electrolyte to perform excellent corrosion resistance in the harsh marine environment through electrochemical experiment in the sea water upon generating porous films by variating the temperatures of sulfuric electrolyte. To fabricate uniform porous film of 5083 aluminum alloy, we conducted electro-polishing under the 25 V at $5^{\circ}C$ condition for three minutes using mixed solution of ethanol (95 %) and perchloric (70 %) acid with volume ratio of 4:1. Afterward, the first step surface modification was performed using sulfuric acid as an electrolyte where the electrolyte concentration was maintained at 10 vol.% by using a jacketed beaker. For anode, 5083 aluminum alloy with thickness of 5 mm and size of $2cm{\times}2cm$ was used, while platinum electrode was used for cathode. The distance between the two was maintained at 3 cm. Afterward, the irregular oxide film that was created in the first step surface modification was removed. For the second step surface modification process (identical to the step 1), etching was performed using mixture of chromic acid (1.8 wt.%) and phosphoric acid (6 wt.%) at $60^{\circ}C$ temperature for 30 minutes. Anodic polarization test was performed at scan rate of 2 mV/s up to +3.0 V vs open circuit potential in natural seawater. Surface morphology was compared using 3D analysis microscope to observe the damage behavior. As a result, the case of surface modification presented a significantly lower corrosion current density than that without modification, indicating excellent corrosion resistance.

• Transactions on Electrical and Electronic Materials
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• 제4권4호
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• pp.1-6
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• 2003

Aluminum oxide ($Al_2O_3$) nanotubes and nanorods were fabricated by coating and filling of multiwalled carbon nanotubes (MWNTs) with atomic-layer deposition (ALD). $Al_2O_3$ material was deposited on the MWNTs at a substrate temperature of $300^{\circ}C$ using trimethylaluminum and distilled water. Transmission electron microscopy, high resolution transmission electron microscopy, energy-dispersive X-ray spectroscopy, and selected area electron diffraction of the deposited MWNTs revealed that amorphous $Al_2O_3$ material coats the MWNTs conformally and that this material fills the inside of the MWNTs. These illustrate that ALD has an excellent capability to coat and fill any three-dimensional shapes of MWNTs conformally without producing any crystallites.

• 한국재료학회지
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• 제22권11호
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• pp.631-635
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• 2012

Nickel oxide was doped with a wide range of concentrations (mol%) of Aluminum (Al) by solvothermal synthesis; single-phased nano powder of nickel oxide was generated after calcination at$900^{\circ}C$. When the concentration of Al dopant was increased, the reduced intensity was confirmed through XRD analysis. Lattice parameters of the synthesized NiO powder were decreased after treatment of the dopant; parameters were increased when the concentration of Al was over the doping limit (5 mol% Al). The binding energy of $Ni^{2+}$ was chemically shifted to $Ni^{3+}$ by doping $Al^{3+}$ ion, as confirmed by the XPS analysis. The tilted structure of the synthesized NiO with 5 mol% Al dopant and the polycrystalline structure of the $Ni_{0.75}Al_{0.25}O$ were observed by HR-TEM analysis. The electrical conductivity of the newly synthesized NiO was highly improved by Al doping in the conductivity test. The electrical conductivity values of the commercial NiO and the synthesized NiO with 5 mol% Al dopant ($Ni_{0.95}Al_{0.05}O$) were 1,400 s/cm and 2,230 s/cm at $750^{\circ}C$, respectively. However, the electrical conductivity of the synthesized NiO with 10 mol% Al dopant ($Ni_{0.9}Al_{0.1}O$) decreased due to the scattering of free-electrons caused by the large number of impurity atoms; the electrical conductivity of $Ni_{0.9}Al_{0.1}O$ was 545 s/cm at $750^{\circ}C$.

• 한국재료학회지
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• 제2권1호
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• pp.3-11
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• 1992

점토 광물로부터 황산 처리법을 이용하여 수화 황산 알루미늄을 제조하였다. 하동 카올린 을 황산 처리하였을 때 수화 황산 알루미늄 형성에 미치는 카올린의 하소 온도와 하소 시간, 산처리 반응 온도와 반응 시간 및 황산의 농도의 영향을 조사하였다. 또한, 황산 처리된 용액으로부터 수화 황산 알루미늄이 석출되는 최적 조건을 구하였으며, 생성된 수화 황산 알루미늄을 상온에서 $1200^{\circ}C$ 까지 각각의 온도 구간에서 열처리한 분말에 대해서 XRD, TG-DTA, FT-IR, SEM, 입도 분석 및 불순물 분석을 하였다. 최적 조건 하에서, 카올린 중의 알루미나가 수화 황산 알루미늄으로 생성되는 전화율은 약 60%였고, XRD, TG-DTA, FT-IR 등의 분석 결과로 부터 생성된 수화 황산 알루미늄의 열분해 반응은 $Al_2(SO_4)_3{\cdot}18H_2O{\rightarrow}Al_2(SO_4)_3{\cdot}6H_2O{\rightarrow}Al_2(SO_4){\rightarrow}\;amorphous\;alumina{\rightarrow}{\gamma}-alumina{\rightarrow}{\delta}-alumina{\rightarrow}{\theta}-alumina{\rightarrow}{\alpha}-alumina$이었다. 또한 생성된 수화 황산 알루미늄을 $1200^{\circ}C$에서 하소 하여 얻은 알루미나 분말의 순도는 99.99%였다.

• 한국표면공학회지
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• 제40권3호
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• pp.107-112
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• 2007

Aluminum doped zinc oxide (AZO) films were deposited on non-alkali glass substrate by DC magnetron sputtering with 3 types of AZO targets (doped with 1.0 wt%, 2.0 wt%, 3.0 wt% $Al_2O_3$). Electrical, optical properties and microstructure of AZO films have been investigated by Hall effect measurements, UV/VIS/NIR spectrophotometer, and XRD, respectively. Crystallinity of AZO films increased with increasing substrate temperature ($T_s$) and doping ratio of Al. Resistivity and optical transmittance in visible light were $8.8{\times}10^{-4}{\Omega}cm$ and above 85%, respectively, for the AZO film deposited using AZO target (doped with 3.0 wt% $Al_2O_3$) at $T_s$ of $300^{\circ}C$. On the other hand, transmittance of AZO films in near-infrared region decreased with increasing $T_s$ and doping ratio of Al, which could be attributed to the increase of carrier density.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2010년도 춘계학술대회 초록집
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• pp.75.2-75.2
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• 2010

We studied the fabrication of polycrystalline silicon (pc-Si) films as seed layers for application of pc-Si thin film solar cells, in which amorphous silicon (a-Si) films in a structure of glass/Al/$Al_2O_3$/a-Si are crystallized by the aluminum-induced layer exchange (ALILE) process. The properties of pc-Si films formed by the ALILE process are strongly determined by the oxide layer as well as the various process parameters like annealing temperature, time, etc. In this study, the effects of the oxide film thickness on the crystallization of a-Si in the ALILE process, where the thickness of $Al_2O_3$ layer was varied from 4 to 50 nm. For preparation of the experimental film structure, aluminum (~300 nm thickness) and a-Si (~300 nm thickness) layers were deposited using DC sputtering and PECVD method, respectively, and $Al_2O_3$ layer with the various thicknesses by RF sputtering. The crystallization of a-Si was then carried out by the thermal annealing process using a furnace with the in-situ microscope. The characteristics of the produced pc-Si films were analyzed by optical microscope (OM), scanning electron microscope (SEM), Raman spectrometer, and X-ray diffractometer (XRD). As results, the crystallinity was exponentially decayed with the increase of $Al_2O_3$ thickness and the grain size showed the similar tendency. The maximum pc-Si grain size fabricated by ALILE process was about $45{\mu}m$ at the $Al_2O_3$ layer thickness of 4 nm. The preferential crystal orientation was <111> and more dominant with the thinner $Al_2O_3$ layer. In summary, we obtained a pc-Si film not only with ${\sim}45{\mu}m$ grain size but also with the crystallinity of about 75% at 4 nm $Al_2O_3$ layer thickness by ALILE process with the structure of a glass/Al/$Al_2O_3$/a-Si.

• 한국항공우주학회지
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• 제34권8호
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• pp.95-103
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• 2006

알루미늄 분말이 약 20% 포함된 2종류의 고체 추진제에 대해 원료성분, 연소실에서의 연소가스 물성치 및 산화알루미늄의 입자 크기를 비교 분석하였다. 산화제(AP/HNIW) 분말이 200과 5 ${\mu}m$로 이분양상이고 47% 부피분율을 지닌 알루미늄을 함유한 PCP계 추진제는 산화제(AP) 분말이 400, 200 및 6 ${\mu}m$로 삼분양상이고 64% 부피분율을 지닌 알루미늄을 함유한 HTPB계 추진제 보다 알루미늄들이 응집될 가능성이 크다는 것을 축소부 내열재에서 채취한 산화알루미늄 입자의 SEM 사진을 통해 확인할 수 있었다. PCP계 추진제를 적용한 고체 추진기관의 노즐 축소부 내열재에서는 큰 산화알루미늄 입자의 충돌로 인해 그레인 슬랏과 일치하는 4개 원주방향 부위에서 삭마가 크게 되었지만 HTPB계 추진제를 적용한 경우에는 원주방향으로 균일하게 삭마되었다.