• Journal of Welding and Joining
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• 제16권2호
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• pp.122-128
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• 1998

This investigation was performed to collect fundamental informations concerning the behavior of glass solders on ceramic joining process. The wettability of glasses on two types of alumina was evaluated by sessile drop method. SiO$_2$-CaO-Al$_2$O$_3$system glasses were selected as solder glasses, and alumina that have different purities were used for substrate materials. It is indicated that contact angles of glasses on 99% purity of alumina substrate do not change as increasing time at elevated temperature, however the contact angles on the 92% purity of alumina substrate exhibit the strong time dependency. The time-dependent property on 92% alumina was due to the interlayer reactions occurred between the glass solder and impurities on the substrate.

• 한국세라믹학회지
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• 제33권9호
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• pp.1045-1049
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• 1996

Pressureless-sintered polycrystalline alumina and carbon steel were joined with Ag-33.5Cu-1.5Ti (wt%) brazing alloy. SEM observation revealed that two reaction layers with different thicknesses were continuously formed between the alumina and the brazing alloy. A thick layer formed on the brazing alloy side was identified as Ti3(Cu0.93Al0.07)3O phase with diamond cubic structure. Another thin layer adjacent to the alumina was revealed as $\delta$-TiO phase of which the crystal structure was HCP with a lattice parameter of a0=0.419 nm and c0=0.284 nm. It was confirmed using XPS analysis that $\delta$-TiO was formed directly by a redox reaction of alumina with titanium ir, molten brazing alloy.

• 한국산학기술학회논문지
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• 제11권3호
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• pp.853-858
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• 2010

본 논문은 알루미늄의 양극산화를 통하여 알루미나(Alumina, $Al_2O_3$)를 형성함으로써 알루미나 및 알루미늄의 적층 구조 DRAM 패키지 기판을 구현하였다. 전송선 기반의 설계를 적용하기 위해 2차원 전자장 시뮬레이션을 수행하였다. 분석 결과를 바탕으로 새로운 기판에 적용할 신호선의 폭 및 간격과 알루미나 두께 등의 설계인자를 최적화하였다. 테스트 패턴 제작 및 측정을 통해 설계인자를 검증하였으며, 이를 바탕으로 설계 룰(Design rule)을 정하고 패키지의 개념 설계 및 상세 설계를 진행하여 DDR2 DRAM 패키지 기판을 성공적으로 제작하였다.

• 공업화학
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• 제28권1호
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• pp.87-94
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• 2017

본 연구에서는 다양한 알루미나 지지체의 $CH_4-SCR$ 반응특성을 확인하기 위하여 $Pt/Al_2O_3$를 기본으로 한 촉매에 Mg을 담지하여 습식함침법으로 제조하였다. $Pt/Al_2O_3$ 촉매에 지지체인 알루미나를 복합형태(composite-$Al_2O_3$)로 바꾸고, Mg을 담지시킬 경우 electrophobic 특성으로 인해 활성금속 Pt의 산소종을 제어하였다. 산소종이 제어된 Pt는 환원제로 사용되는 $CH_4$에서 $CO_2$로의 산화를 억제시킨다. 또한 Mg의 첨가는 촉매표면에서의 NOx storage 특성으로 인한 NO species 흡착 증진과 NO의 $NO_2$로의 전환을 증진시켰다.

• 한국재료학회지
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• 제22권4호
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• pp.195-201
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• 2012

$Ce^{3+}$-doped yttrium aluminum gallium garnet (YAGG:$Ce^{3+}$), which is a green-emitting phosphor, was synthesized by solid state reaction using ${\alpha}$-phase or ${\gamma}$-phase of nano-sized $Al_2O_3$ as the Al source. The processing conditions and the chemical composition of phosphor for the maximum emission intensity were optimized on the basis of emission intensity under vacuum UV excitation. The optimum heating temperature for phosphor preparation was $1550^{\circ}C$. Photoluminescence properties of the synthesized phosphor were investigated in detail. From the excitation and emission spectra, it was confirmed that the YAGG:$Ce^{3+}$ phosphors effectively absorb the vacuum UV of 120-200 nm and emit green light positioned around 530 nm. The crystalline phase of the alumina nanoparticles affected the particle size and the luminescence property of the synthesized phosphors. Nano-sized ${\gamma}-Al_2O_3$ was more effective for the achievement of higher emission intensity than was nano-sized ${\alpha}-Al_2O_3$. This discrepancy is considered to be because the diffusion of $Al^{3+}$ into $Y_2O_3$ lattice is dependent on the crystalline phase of $Al_2O_3$, which affects the phase transformation of YAGG:$Ce^{3+}$ phosphors. The optimum chemical composition, having the maximum emission intensity, was $(Y_{2.98}Ce_{0.02})(Al_{2.8}Ga_{1.8})O_{11.4}$ prepared with ${\gamma}-Al_2O_3$. On the other hand, the decay time of the YAGG:$Ce^{3+}$ phosphors, irrespective of the crystalline phase of the nano-sized alumina source, was below 1 ms due to the allowed $5d{\rightarrow}4f$ transition of the $Ce^{3+}$ activator.

• 한국세라믹학회지
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• 제38권7호
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• pp.621-627
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• 2001

알루미나 졸에 평균 25nm의 TiO$_2$(Degussa P25) 광 촉매 분말을 분산하여 광촉매 코팅제를 제조하였다. 점도 약 24 cps를 가지 4.4 wt%의 알루미나 졸로부터 약 300nm 두께의 코팅막이 제조되었으며, 졸 점도의 증가에 비례하여 코팅막의 두께도 증가하였다. TiO$_2$광 촉매의 코팅용 바인더로 이용한 알루미나 졸의 결정형은 25~30$0^{\circ}C$에서 pseudo boehmite (AlOOH)이었으며, 50$0^{\circ}C$ 이상에서는 ${\gamma}$-Al$_2$O$_3$으로 전환되었다. AlOOH/TiO$_2$코팅막은 oleic acid와 humic acid에 대한 기상 및 수상 조건에서의 광 촉매 실험에서 우수한 유기물의 광분해 효능을 나타내었다. 아울러 EGI(Electro-Galvanized Iron)에 코팅된 AlOOH/TiO$_2$코팅막은 내식성 및 내지문성의 효과도 부수적으로 나타내었다.

• 한국재료학회지
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• 제9권2호
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• pp.132-138
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• 1999

In order to investigate the toughening characteristic by microcrack formation in ceramic composites, $Al_2$O$_3$/(0~20)vol% YAG composites containing equiaxed second grains were fabricated using$ Al_2$$O_3$ during hot-pressing. AE(acoustic emission) measurements have been coupled with fracture toughness experiments of SENB method, to evaluate the microcrack formation and the improvement in fracture toughness of ceramic composites. Formation of microcrack was detected by Ae. The generation of AE events increased with increasing of load when load was applied at specimen. The AE events are generated mainly around at maximum load. Specially, the detected AE evetns of composites are many as compared with monolithic $Al_2$$O_3$. Fracture toughness of composites was improved than that of monolithic alumina. $Al_2$O$_3$/YAG composites exhibit main toughening effects by microcracking, results from mutual coalesence of microcracks being generated under applied load. However, there are few toughening mechanism like microcracking in monolithic alumina.

• 한국표면공학회지
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• 제43권4호
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• pp.165-169
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• 2010

$Ni-Al_2O_3$ nanocomposite coatings were fabricated by conventional electrodeposition technique using nickel sulfamate bath. Effect of plating parameters on electrodeposition of $Ni-Al_2O_3$ nanocomposite were studied. The properties of the nano composite were investigated by using SEM, XRD, and Vicker's microhardness test. The results demonstrated that $Al_2O_3$ incorporation in the composite coatings was found to be increased by increasing stir rate and $Al_2O_3$ content in plating bath. Microhardness of the composite coatings was also increased with increasing content of the nano particles in the plating bath. The surface morphologies of the nanocomposite coatings were found to be varied with varying pH, current densities as well as alumina content in the plating bath.

• 한국세라믹학회지
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• 제27권6호
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• pp.790-798
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• 1990

Al2O3 film was chemically deposited by pyrolytic decom,positio of the Al-tri-isopropoxide/N2 system at 350$^{\circ}C$, 30 and 1.86torr. FTIR analysis showed a deposited film was a hydrated alumina and transformed to an anhydrous one after heat treatment(1hr, >800$^{\circ}C$ or 4hr, >500$^{\circ}C$) in N2 atmosphere. This transformation influenced on the CV-hysteresis of Si-Al2O3 structure. Also, a pH sensitivity of EIS(Electrolyte-Insulator-Semiconductor)structure using Si-Al2O3/SiO2 film was 50mV/pH in the range of pH 3 to 7.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part 1
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• pp.327-328
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• 2006

We have demonstrated that textured $Al_2O_3-mullite-SiC$ nanocomposites can be fabricated by slip casting followed by partial oxidation - reaction sintering of mixed suspensions of $Al_2O_3$ and SiC powders in a high magnetic field. The sintered density was changed by the degree of oxidation at 1200C and 1300C. The degree of orientation of alumina in the nanocomposite was examined on the basis of the X-ray diffraction patterns and scanning electron micrographs. It is confirmed that alumina-oriented nanocomposites were fabricated. The three-point bending strength at room temperature was observed for the nanocomposites.