• 한국세라믹학회지
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• 제19권1호
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• pp.13-18
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• 1982

The crystallization of metastable "orthorhombic" phase from the glass in the system of Na $AlSi_3O_8-CaAl_2Si_2O_8$ is studied. These crystals are crystallized in the range of composition from $Ab_80An_20$ to An100. The symmetry of these crystals show orthorhombic as a possible space group P22121. Two probable twin models are proposed. proposed.

• 한국세라믹학회지
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• 제33권9호
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• pp.985-994
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• 1996

The initiation and growth of $\alpha$-Al2O3/metal composites by the directed oxidation of molten commercial AlZnMg-alloy at 1223-1423K were investigated. Spontaneous bulk growth did not occur on the alloy alone. but the uniform initiation and growth of the composite were obtained by putting a thin layer of SiO2 particles on the surface of the alloy. Without SiO2 the external surface of the oxide layer was convered by MgO and MgAl2O4. But with the SiO2 reaction initiate the porous ZnO layers were found on the growth surface. The higher process temperature yielded a lower metal content. The oxidation product of $\alpha$-Al2O3 was found to be oriented with c-axis parallel to th growth direction. The growth rates increased with temperature and the apparent activation energy was 111.8 kJ/mol.

• 한국재료학회지
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• 제14권9호
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• pp.649-654
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• 2004

In this paper, the fracture toughness and mechanisms of failure in a random SiC-whisker/$Al_{2}O_3$ ceramic composite were investigated using in situ observations during mode I(opening) loading. $SiC_{w}/Al_{2}O_3$ composite was obtained by hot press sintering of $Al_{2}O_3$ powder and SiC whisker as the matrix and reinforcement, respectively. The whisker and powder were mixed using a turbo mill. The composite was produced at SiC whisker volume fraction of $0.3\%$. Compared with monolithic $Al_{2}O_3$, fracture toughness enhancement was observed in $SiC_{w}/Al_{2}O_3$ composite. This improved fracture toughness was attributed to SiC whisker bridging and crack deflection. $SiC_{w}/Al_{2}O_3$ composite exhibited typically brittle fracture behavior, but a fracture process zone was observed in this composite. This means that the load versus load-line displacement curve of $SiC_{w}/Al_{2}O_3$ composite from a fracture test may involve a small non-linear region near the peak load.

• 한국재료학회지
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• 제21권4호
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• pp.220-224
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• 2011

Zircon has excellent thermal, chemical, and mechanical properties, but it is hard to make a dense sintered product because of dissociation during the sintering process. This study analyzes how the addition of $SiO_2$ and $Al_2O_3$ affects the mechanical properties of sintered zircon, particularly in regards to reducing the thermal dissociation and improving the mechanical properties of $ZrSiO_4$. Zircon specimens containing different amounts of $SiO_2$ and $Al_2O_3$ were prepared and sintered to observe how the mechanical properties of $ZrSiO_4$ changed according to the differing amount of $SiO_2$ and $Al_2O_3$. The $ZrSiO_4$ that was used for the starting material was ground by ball mill to an average particle size of 3 ${\mu}m$. The $SiO_2$ and $Al_2O_3$ that was used for additives were ground to an average particle size of 3 ${\mu}m$ and 0.5 ${\mu}m$, respectively. Adding $SiO_2$ resulted in transformation in the liquid phase at high temperatures, which had little effect on suppressing the thermal dissociation but enhanced the mechanical properties of $ZrSiO_4$. When $Al_2O_3$ was added, the mechanical properties of $ZrSiO_4$ decreased due to the formation of pores and abnormal grains in the microstructure of the sintered zircon.

• 대한화학회지
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• 제32권3호
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• pp.267-275
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• 1988

$Al(OC_3H_7)_3$ 및 $Si(OC_2H_5)_4$, 알콕사이드를 합성하고 그 물질을 각각 또는 혼합가수분해하여 $Al_2O_3,\;SiO_2,\;Al_2O_3-SiO_2$계의 물질을 얻고 $Al_2O_3-SiO_2$계에 환원제로서 carbon black을 혼합하여 $N_2$분위기에서 환원질화반응시켜 고순도의 ${\beta}-sialon$ 초미분말을 합성하였다. 가수분해 과정에서는 반응조건이 가수분해반응에 미치는 영향을 알아보았고, 환원질화반응 과정에서는 중간생성물을 분석하여 반응경로를 추정하고 ${\beta}-sialon$의 생성반응에 대한 동력학적 고찰을 하였다.

• 한국세라믹학회지
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• 제20권1호
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• pp.3-12
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• 1983

In the present study an attempt was made to synthesize the $Al_2O_3$.$2SiO_2$ glass in which atomic ratio is Al:Si=1:1 by sol-gel process. And at such a low temperature as 55$0^{\circ}C$ clear amorphous gel derived glass with Si-O-Al bonding was obtained. $Si(OC_2H_5)_4$ and $Al(NO_3)_3$.$9H_2O$ were used as the precursor and among the mutual solvents only n-butanol gave good results for the synthesis of the gel derived glass. Partial hydrolysis of TEOS with one-fold mol of $H_2O$ prior to the reaction with aluminum nitrate gave the better results., Total oxide content to the total reactants by weight was affective to the results.

• 한국세라믹학회지
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• 제32권4호
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• pp.507-515
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• 1995

The monolithic dry gels of the Li2O-Al2O3-TiO2-SiO2 system were prepared by the sol-gel technique using metal alkoxides as starting materials to obtain monolithic glass-ceramics at low temperature without melting. Activation energy for the crystal growth of the gel with 6.05% TiO2, nucleating ageng, for the preparation of Li2O-Al2O3-TiO2-SiO2 system glass-ceramic was 101.14kcal/mol. As a result of the analysis of DTA & XRD, it was confirmed that the crytallization of Li2O-Al2O3-TiO2-SiO2 system glass-ceramic was the most efficient when 6.05% TiO2, nucleating agent, was added. $\beta$-eucryptite solid solution crystals and $\beta$-spodumene solid solution crystals were detected in the sample heat treated above 85$0^{\circ}C$. The sintered gel heat treated at 85$0^{\circ}C$ had the specific surface area of 185$m^2$/g, the pore volume of 0.19cc/g and the average pore radius of 20.8$\AA$. This shows that the sintered gel is also comparatively porous material. In temperature range of 25~85$0^{\circ}C$ thermal expansion coefficient of the specimen which was crystallized for 10hrs at 85$0^{\circ}C$ was 6.7$\times$10-7/$^{\circ}C$, which indicated that the crystallized specimen was turned out to be the glass-ceramic with low thermal expansion.

• Bulletin of the Korean Chemical Society
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• 제28권12호
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• pp.2288-2292
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• 2007

The catalytic activities of nickel-based catalysts were estimated for oxidizing acetaldehyde of VOCs exhausted from industrial facilities. The catalysts were prepared by sol-gel methods of SiO2 and SiO2-TiO2 as a xerogel followed by impregnating Al2O3 powder with the nickel nitrate precursor. The crystalline structure and catalytic properties for the catalysts were investigated by use of BET surface area, X-ray diffraction (XRD), Xray photoelectron spectroscopy (XPS) and temperature programmed reduction (TPR) techniques. These results show that nickel oxide is transformed to NiAl2O4 spinel structure at the calcination temperature of 400 °C in response to the steps with after- and co-impregnation of Al2O3 powder in sol-gel process. The NiAl2O4 could suppress the oxidation reaction of acetaldehyde by catalysts. The NiO is better dispersed on SiO2-TiO2/Al2O3 support than SiO2/Al2O3 and SiO2-TiO2-Al2O3 supports. From the testing results of catalytic activities for oxidation of acetaldehyde, Catalysts showed a big difference in conversion efficiencies with the way of the preparation of catalysts and the loading weight of nickel. The catalyst of 8 wt.% Ni/TiO2-SiO2/Al2O3 showed the best conversion efficiency on acetaldehyde oxidation with 100% conversion efficiency at 350 °C.

• 한국진공학회지
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• 제22권3호
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• pp.126-130
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• 2013

PSG/$SiO_2$ 보호막 처리된 Al-1%Si 박막배선 내 sodium (Na)과 수분($H_2O$) 게터링(gettering) 현상을 측정, 분석하였다. PSG/$SiO_2$ 보호막과 Al-1%Si 박막을 상압CVD (APCVD: atmosphere pressure chemical vapor deposition)법과 DC 마그네트론 스퍼터로 각각 증착하였고, 이차이온 질량분석기(SIMS: secondary ion mass spectrometry)를 이용한 깊이분포측정(depth profiling) 분석을 통해 PSG/$SiO_2$ 보호막으로부터 Al-1%Si 박막배선 층까지의 sodium과 수분 등 성분들의 분포를 확인하였다. Sodium과 수분 피크 모두 Al-1%Si 박막배선 내부보다는 막 간 계면에서 강하게 나타났다. PSG와 $SiO_2$ 보호막 계면에서는 sodium 피크는 관찰되었지만 수분 피크는 관찰되지 않았다.

• 한국결정성장학회지
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• 제13권6호
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• pp.309-314
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• 2003

방전 플라즈마 소결법을 적용하여 $Al_2O_3$-SiC 나노 복합체를 150$0^{\circ}C$ 이하의 온도에서 완전치밀화를 이루었다. 제조된 $Al_2O_3$-SiC 복합체는 이상 결정립 성장 없이 매우 균질한 미세구조를 형성하고 있는데, 첨가된 SiC 입자는 주로 결정립 내 및 결정립계에 존재하면서 $Al_2O_3$기지상에서 결정립 성장을 억제하는데 매우 유호하였음을 확인 할 수 있다. 한편, SiC 입자의 첨가는 크랙 회절 및 브릿징 등에 의해서 유도된 재료 강도 및 인성 강화 기구에 의해서 $Al_2O_3$-SiC 복합체의 기계적 물성을 크게 향상시켰다.