• 한국세라믹학회지
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• 제33권1호
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• pp.110-118
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• 1996

• 한국세라믹학회지
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• 제32권1호
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• pp.45-50
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• 1995

In order to densify LAS(Lithuim Aluminosilicate)system compounds, we used metal alkoxides as precursors. Also Mg was added by sol-gel method using metal alkoxides to the LAS system for improving the sinterability, thermal and mechanical properties. The result was that the synthesizing temperature was lowered about 10$0^{\circ}C$, the sintering temperature was lowered by over 10$0^{\circ}C$ and MOR of samples from metal alkoxides was two times larger than that of sample form oxide.

• 한국재료학회지
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• 제9권12호
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• pp.1188-1195
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• 1999

알루미노실리케이트 계 졸이 지르콘 쉘 몰드의 뮬라이트 층 생성에 미치는 영향을 고찰하였다. 알루미노실리케이트 졸은 콜로이달 실리카와 수용성 질산알루미늄을 혼합하여 제조하였으며 50$^{\circ}C$에서 48시간 조건에서 겔화 하였다. 이러한 겔은 깁사이트 및 알루미노실리케이트 복합 겔로 구성되어 있었으며, Si 이온과 결합하는 모든 Al 이온의 배위수가 4임을 확인하였다. 뮬라이트 상은 1300$^{\circ}C$ 이상에서 소결하였을 때 관찰되었으며 뮬라이트의 XRD 피크는 소결 온도와 질산알루미늄의 농도가 증가할수록 노실리케이트 졸 슬러리를 2차 층에 코팅하였다. 그 결과 1차 및 3차 층의 분리가 일어났으며, 이는 소결시 졸의 1차 및 3차 층으로 침윤 발생과 잔류 실리카와 뮬라이트 간의 열팽창계수 차이에 기인한 것으로 판단된다.

• 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.

• 한국세라믹학회지
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• 제28권5호
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• pp.365-372
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• 1991

LAS (lithium aluminosilicate) sol was synthesized using the hydrolysis-condensation reaction of TEOS, chelated Al(OBus)3 and Li-salt with H2O in alcohol (EtOH+2-Propanol) medium. Effects of important reaction parameters on the properties of sol and gel-derived LAS were examined. The crystallization of the sol-gel derived LAS with ${\beta}$-spodumene composition began at ∼600$^{\circ}C$, and a series of polymorphic transformations occurred as temperature was increased to 1100$^{\circ}C$: amorphous LAS\longrightarrowhexagonal LiAl(SiO3)2\longrightarrow${\beta}$-spodumene. Lowering Li content in the gel enhanced densification and retarded the crystallization significantly. Optimum reaction conditions of LAS sol formation for thin coating applications were derived from rheological measurements, and these can be summarized as: H2O/total alkoxides molar ratio=4, pH=∼2.5, and aging time of ∼250h.

• 한국재료학회지
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• 제12권7호
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• pp.573-579
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• 2002

Stoichiometric mullite ($3Al_2$$O_3$. $2SiO_2$) precursor sol has been prepared by sol-gel method. The effects of the precursor pH and sintering temperature on the synthesizing behavior and morphology of mullite have been studied. Mullite precursor sol was prepared by dissolution of aluminum nitrate enneahydrate (Al($NO_3$)$_3$.9H$_2O) into the mixture of silica sol. Precursor pH of the sols was controlled to acidic condition ($PH\leq$ 1~1.5) and to basic condition ($pH\geq$8.5~9). The synthesized aluminosilicate sols were formed under 20 MPa pressure after drying at $150^{\circ}C$ for 24 hours, and then sintered for 3hours in the temperature range of $1100~1600^{\circ}C$. From TGA/DTA analysis, total weight loss in the aluminosilicate gel of the acidic sample was (equation omitted) 56% and that of the basic sample was (equation omitted) 85%, indicating that the synthesizing temperature of mullite phase for acidic and basic samples was above $1200^{\circ}C$ and $1300^{\circ}C$, respectively. The morphologies of the synthesized mullite were fine and needle-like (or rod-like) for acidic sample, and granular for basic sample that has been sintered above $1300^{\circ}C$. It was found that the morphology of mullite particle was predominantly governed by precursor pH and sintering temperature.

• 한국세라믹학회지
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• 제28권11호
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• pp.865-872
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• 1991

LAS (lithium aluminosilicate) sol was synthesized using the hydrolysis-condensation reaction of TEOS, chelated Al(OBus)3 and LiNO3 with H2O in alcohol (ethanol+2-propanol) medium. Lowering Li content by a factor of 1/2 significantly enhanced densification and retarded the crystallization of LAS gel by ~30$0^{\circ}C$. Dense LAS specimen with essentially pore-free microstructure was obtained by sintering the sol-gel derived gel at 80$0^{\circ}C$ for 4 h and annealing at 120$0^{\circ}C$ for 2 h. Similary, a mixed colloidal processing was attempted as a convenient, alternative route for the fabrication of dense LAS sintered body. The $\beta$-spodumene seeding (~0.8 ${\mu}{\textrm}{m}$) in the sol-gel derived LAS modified the sequence of phase transformations and lowered the temperature of crystallization by ~12$0^{\circ}C$. Combining the epitaxial seeding with the sol-gel process, we could lower the crystallization temperature to the sintering temperature range (~80$0^{\circ}C$) and, demonstrate a possibility of making the viscous sintering/crystallization as a continuous as a continuous unit process.

• 한국세라믹학회지
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• 제45권5호
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• pp.303-308
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• 2008

Mullite precursors were synthesized with aluminosilicate gels from mixture of aluminum nitrate and sodium orthosilicate by the geopolymer technique at ambient temperature. Then, the gel was heat-treated in air up to $1200^{\circ}C$ at intervals of $100^{\circ}C$. Raw and heat-treated gels were characterized by TG-DTA, XRD, FTIR, $^{29}Si$ MAS-NMR, TEM. The result to examine the crystallization of behavior though DTA, the synthesized precursors were crystallized in the temperature range from $950^{\circ}C$ to $1050^{\circ}C$. The XRD results showed that the gel compositions were begun to crystallize at various temperature. Also, it was found that the precursors of M-4 begun to crystallize at about $950^{\circ}C$. The M-4 XRD peaks were characterized better than $M-1{\sim}M-3$ at $1000^{\circ}C$. The formation temperature of mullite in this study is much lower than that of previous sol-gel methods, which crystallized at up of $1200^{\circ}C$. TEM investigations revealed that the sample with 10 nm particle size was obtained via heat-treated at $1000^{\circ}C$ for M-4.

• 멤브레인
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• 제29권1호
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• pp.51-60
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• 2019

분리막 소재의 투과도와 선택도 사이의 trade-off 관계로 인해 여전히 많은 연구가 필요하다. 특히 고분자 분리막에 무기물 나노입자가 들어가 있을 때, 기체투과 거동의 학문적 이해는 여전히 부족하다. 따라서 본 연구에서는 분리막 소재로 가장 많이 사용되는 PDMS에 2~5 nm의 기공을 가지고 있으며 직경이 약 5 nm 크기의 aluminosilicate hollow nanoparticles인 allophane을 이용하여 복합매질 분리막을 제조하여 기체투과특성을 연구하였다. 대표적인 분리막 소재인 PDMS에 친수성 allophane, 그리고 나노입자에 undecylenic acid로 표면을 개질한 allophane을 막 내부에 고르게 분산시켜 함량 별로 복합매질 분리막을 제조하였다. 나노입자가 분산된 혼합매질 분리막 내에서 기체의 투과 특성을 파악하고, 이에 따른 기체투과 거동과 나노입자가 가지고 있는 기공의 역할을 평가하고자 하였다. 표면개질된 allophane을 첨가함에 따라 기체 투과도와 산소/질소 그리고 이산화탄소/메탄의 선택도가 동시에 점진적으로 향상되는 결과를 얻었다.

• 자원환경지질
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• 제45권2호
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• pp.89-104
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• 2012

본 연구에서는 제주도 토양 중 화산쇄설암과 현무암을 모재로 발달하는 두 Andisol 토양의 Al 용해도 특성을 규명하고자 하였다. 토양 A층은 높은 유기물함량과 $Al_{pyrophosphate}/Al_{oxalate}$ 비를 나타내는 반면, 토양 Bo층은 낮은 유기물함량과 $Al_{pyrophosphate}/Al_{oxalate}$ 비를 나타낸다. 이는 반응성 Al이 A층에서는 대부분이 유기물과 결합한 형태로 존재하고 있는 반면, 토양 Bo층에서는 무기질의 광물과 결합하고 있음을 지시한다. Acid-oxalate 용해처리, 그리고 150 및 $350^{\circ}C$ 열처리 전후의 FT-IR 스펙트럼 비교, 투과전자현미경(TEM)을 이용한 관찰결과, 토양 Bo층에 상당량의 이모골라이트(Imogolite)가 존재함을 확인하였다. 이들 시료에 대한 Al-용해도 특성규명을 위한 Batch 평형실험결과, 토양 Bo층에서의 Al-용해도는 ITM(Imogolite-type material)과 Al hydroxy-interlayered aluminosilicate에 의한 Simultaneous equilibrium보다는 ITM의 Congruent dissolution model을 따르는 것으로 나타났다. 투석과 Aging과정 후의 용해도 특성 변화는 PI(Proto imogolite) sol의 생성이 되고, 이들의 이모골라이트로의 상전이가 Al-용해도에 영향을 주었음을 지시한다. 이러한 결과는, 실내실험 결과를 보완해주는 것으로, 제주도 Andisol토양에서의 Al-용해도 특성이 ITM에 의한 Congruent dissolution에 의해 조절되고 있음을 지시한다.