• 한국세라믹학회지
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• 제28권12호
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• pp.1012-1018
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• 1991

SiC whisker-reinforced LAS matrix composites were developed by a mixed colloidal processing route. An optimization of processing conditions was made using the zeta potential data of silica, boehmite, and SiC whisker dispersions. Similarly, the SiC whisker-reinforced composites were also fabricated by the conventional sol-gel process using the hydrolysis-condensation reaction of relevant metal alkoxides. The composites fabricated by the mixed colloidal processing route were characterized by a uniform spatial distribution of SiC whisker throughout the matrix. The fracture toughness increased from 1.3 MPa.m1/2 for the LAS specimen to 5.0 Mpa.m1/2 for the hot-pressed composite (95$0^{\circ}C$ and 20 MPa for 20 min) containing 20 wt% SiC whisker. The increase in fracture toughness appears to result mainly from the crack deflection and the crack bridging by whiskers with some additional toughenings from the whisker pullout and the matrix prestressing mechanisms.

• 한국세라믹학회지
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• 제32권1호
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• pp.63-70
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• 1995

A crack-free ceramic composite membrane with micropores has been synthesized by the pressurized sol-gel coating technique using the mixed Al2O3-SiO2 sols. The mixed sols were prepared by mixing nanoparticulate SiO2 and boehmite sols. These sols were more stable at lower pH, but very unstable when their copositions were in the range of 50~75mol% of SiO2 at the same pH. The mixed Al2O3-SiO2 membrane prepared from the mixed sol (0.2mol/$\ell$ of solid content and pH=2) containing 40mol% of SiO2 had the mean pore radius of 0.80nm and the specific surface area of 280$m^2$/g. The nitrogen permeability through the coated Al2O3-SiO2 layer was 42$\times$107mol/$m^2$.s.Pa. It was found that the thermal stability of aluminosilicate membranes, even through similar to that of SiO2 membranes, was much improved in comparison with ${\gamma}$-alumina membranes.

• 한국산학기술학회논문지
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• 제20권11호
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• pp.537-543
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• 2019

세라믹 재료 중 알루미나(Al₂O₃)는 산업에서 널리 사용되는 세라믹 재료로서 최근의 기술발전에 따라 재료 크기가 작아지고 이에 따른 특성이 다양하여 그 중요성이 더해 가고 있다. 본 연구에서는 다양한 알루미늄 알콕사이드 중 Aluminum isopropoxide(AIP)를 출발 원료물질로 하여 졸-겔(Sol-Gel)법에 의해 가수분해 및 해교과정을 거쳐 boehmite 졸을 제조하고 이후 건조 및 하소시켜 γ-Al₂O₃를 제조하였다. 이러한 제조 과정 중 입자의 응집현상을 방지하기 위해 9,000 ~ 10,000, 31,000 ~ 50,000, 89,000 ~ 98,000, 130,000의 분자량을 갖는 4종류의 PVA(Polyvinyl alcohol)를 첨가하고 3종류 질산(0.1, 0.3, 0.5 몰비)을 첨가하여 입자에 미치는 영향을 확인하고자 하였다. 제조된 γ-Al₂O₃는 X선 회절분석기(XRD), X선 형광분석기(XRF), 입도분석기(PSA), 전계방사 주사전자현미경(FE-SEM) 등의 기기분석을 통하여 결정구조 및 조성, 입자크기, 그리고 입자형상을 확인하였다. 그 결과, 약 98.2 %의 순도를 갖는 γ-Al₂O₃가 합성되었으며 첨가되는 질산의 첨가비가 높을수록, 그리고 PVA 분자량이 클수록 입자크기가 감소하고 균일성이 높아지는 것을 확인할 수 있었다. 이러한 결과로부터, PVA와 질산의 첨가비 조절에 따라 γ-Al₂O₃의 제조공정 중 입자크기 제어가 가능할 것으로 사료된다.

• 한국수소및신에너지학회논문집
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• 제19권6호
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• pp.545-551
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• 2008

Fe/$Al_2O_3$ composite granules were prepared by combining sol-gel/oil drop method. The shape of granules were mainly determined by composition and concentration of aluminum precursor. The composite granule with the lowest aluminum concentration was synthesized with 0.75M boehmite solution. The prepared granules were tested as a catalyst in the plug-flow reactor for Fischer-Tropsch synthesis. Before the reaction, catalysts were activated by hydrogen reduction and synthesis gas treatment. The activation conditions and aluminum concentration have affected catalytic performance significantly.

• 한국세라믹학회지
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• 제36권7호
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• pp.773-781
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• 1999

A new technique to fabricate complex-shaped mullite has been developed through gelcasting without organic binder. The suspension of a commercial mullite powder and boehmite-SiO2 sol as binder was elecrtrosterically stabilized. Ammonium polymetharylyate was employed as a dispersant for the electrosteric stabilization. Complex-shaped bodies were made through casting and gelation at room temperature. The green bodies were dried at a temperature of 30$^{\circ}C$ and relative humidity of 98% without crack development. The dried bodies were then pressureless-sintered at 1650$^{\circ}C$ for 2 h to get a relative density of 98% The Vickers hardness and 4-point flexural strength of sintered parts were 11.0 GPa and 150MPa respectively which are similar to those of commercially available sintered mullite.

• 한국세라믹학회지
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• 제33권8호
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• pp.849-854
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• 1996

boehmite which is the by-product in alcohol process contains anions such as $Cl^-,{NO_3}^-.or\; CH_3COO^-$ Influe-nce of these anions was studied on properties of $\alpha$-alumina powders prepared by treating the transformed ${\gamma}$-alumina with the alumina sol and $\alpha$-alumina seeds (d_{50}=0.36\mu\textrm{m}$) Disperal 20/1 and 10/1 containing $Cl^-$ produced spherical powder Disperal 20/2 with ${NO_3}^-$ produced equiaxed powder and Disperal 10/3 with $CH_3$ $COO^-$ irregular shaped and sized powder. All of these $\alpha$-alumina powders were submicron. Although the green density of the alumina powder derived from Disperal 10/1 by calcination at $1200^{\circ}C$/1h. was 53% it did not sinter even at $1550^{\circ}C$ for 2h. which implies that its d50 is greater than $3\mu\textrm{m}$. The others gave green densities in the range of 44~47% but they sintered as well as the AKP-30 at $1500^{\circ}C$/2 h or $1550^{\circ}C$/2 h.

• 한국세라믹학회지
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• 제29권12호
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• pp.970-980
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• 1992

${\gamma}-alumina$ membranes were prepared by sol-gel dip coating or pressurized coating of boehmite sols on slipcasted ${\gamma}-alumina$ support tubes. The particle size of sols synthesized via the modified Yoldas-method could be controlled below 5 mn according to the mole ratio of nitric acid/aluminumtri-sec-butoxide (0.07~1.0). The reproducible crack-free composite membranes were produced by the 2nd dip coating or the pressurized coating technique using very stable sols with the particle size of 45 nm. Nitrogen gas permeability through the top-layer in the composite membrane was about $70~55{\times}10^{-7}\;mol/m^2{\cdot}s{\cdot}Pa$. The thermal stability of the top layer was proved to be good enough upto the heat-treatment temperature of $500^{\circ}C$.

• 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.

• 한국세라믹학회지
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• 제26권5호
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• pp.631-636
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• 1989

Submicron high-purity mullite powder was prepared by a colloidal sol-gel route. Boehmite and silica were the starting materials. 2wt% $\alpha$-Al2O3 or ZrO2 was used as a seeding material. The gelled powder was calcined at 130$0^{\circ}C$ for 100min and attrition milled for 3hrs. The mullite powder obtained was composed of submicrometer and uniform particles with a narrow size distribution. It was hot-pressed at 1$600^{\circ}C$ for 1hr under 10MPa or was sintered at 1$650^{\circ}C$ for 4hrs. The bulk densities of the products made by both processes were 3.14 and 3.12g/㎤. the mechanical, thermal and electrical properties of the sintered mullite were characterized by bending strength, thermal expansion coefficient, thermal conductivity, dielectric constant and dielectric loss, etc.

• 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.