• Title/Summary/Keyword: Silica-Alumina

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Synthesis of Silica/Alumina Composite Membrane Using Sol-Gel and CVD Method for Hydrogen Purification at High Temperature (Sol-gel 및 CVD법을 이용한 고온 수소 분리용 silica/alumina 복합막의 합성)

  • 서봉국;이동욱;이규호
    • Membrane Journal
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    • v.11 no.3
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    • pp.124-132
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    • 2001
  • Silica membranes were prepared on a porous ${\alpha}$-alumina tube with pore size of 150nm by sol-gel and chemical vapor deposition(CVD) method for hydrogen separation at high temperatures. Silica and ${\gamma}$-lumina membranes formed by the sol-gel method possessed a large amount of mesopores of a Knudsen diffusion regime. In order to improve the $H_2$ selectivity, silica was deposited in the sol-gel derived silica/${\gamma}$-alumina layer by thermal decomposition of tetraethyl orthosilicate(TEOS) at $600^{\circ}C$. The CVD with forced cross flow through the porous wall of the support was very effective in plugging mesopores that were left unplugged in the membranes. The CVD modified silica/alumina composite membrane completely rejected nitrogen permeation and thus showed a high $H_2$ selectivity by molecular sieve effect. the permeation of hydrogen was explained by activated diffusion and the activation energy was 9.52kJ/mol.

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Electrical and Mechanical Strength Properties of Epoxy/Micro Silica and Alumina Composites for Power Equipment (전력기기용, 에폭시/마이크로 실리카 및 알루미나 복합제의 전기적·기계적 파괴 강도 특성)

  • Park, Joo-Eon;Park, Jae-Jun
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.31 no.7
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    • pp.496-501
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    • 2018
  • In this study, we prepared 40, 45, 50, 55, 60, 65, and 70 wt% content composites filled in epoxy matrix for two micro silica and three micro alumina types for use as a GIS heavy electric machine. As a filler type of epoxy composite, micro silica composites showed excellent AC breakdown strength properties compared to micro alumina composites in the case of electrical properties of micro silica and alumina. The electrical breakdown properties of micro silica composites increased with increasing filler content, whereas those of micro alumina decreased with increasing filler content. In the case of mechanical properties, the micro silica composite showed improved tensile strength and flexural strength compared with the micro alumina composite. In addition, mechanical properties such as tensile strength and flexural strength of micro silica and alumina composites decreased with increasing filler content. This is probably because O-H groups are present on the surface of silica in the case of micro silica but are not present on the surface of alumina in the case of micro alumina.

Fourier Transform Raman Studies of Methyl Red Adsorbed on γ-Alumina and Silica-Alumina

  • Park, Sun-Kyung;Lee, Choong-Keun;Min, Kyung-Chul;Lee, Nam-Soo
    • Bulletin of the Korean Chemical Society
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    • v.25 no.12
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    • pp.1817-1821
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    • 2004
  • Fourier transform Raman spectra of methyl red adsorbed on untreated and pretreated ${\gamma}$-alumina and silicaalumina calcined at 900 $^{\circ}C$ under 1 atm steam flowing were recorded. Spectral analysis shows that the active species adsorbed on ${\gamma}$-alumina was to be deprotonated methyl red, and on silica-alumina to be di-protonated. This indicates that ${\gamma}$-alumina adapted in this work holds Bronsted basicity, and silica-alumina Bronsted acidity. Raman intensities of methyl red on pretreated ${\gamma}$-alumina are about three times stronger than on untreated ${\gamma}$-alumina, while spectral features are unchanged. For silica-alumina, spectral features show modified vibrational characteristics upon surface hydroxylations generated from pretreatment. Consequently, the acidity loss for silica-alumina and the basicity gain for ${\gamma}$-alumina were observed by increasing the surface hydroxyl groups on the catalysts through pretreatment of the steam calcination.

Effect of Alumina Addition tn the Silica Slurry on the Chemical Mechanical Polishing of Laugasite (실리카 슬러리에 첨가된 알루미나가 Langasite의 기계.화학적 연마에 미치는 영향)

  • 장영일;윤인호;임대순
    • Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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    • 1999.11a
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    • pp.263-268
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    • 1999
  • Langasite, a new piezoelectric material was polished by CMP(chemical mechanical polishing). To enhance the polishing rate, alumina abrasives were added to commercial ILD1300 slurry which contains silica abrasive. The effect of added alumina 0 the silica slurry on the polishing rate and damage of langasite was investigated, Experimental results show that the polishing rate and roughness increases with increasing added alumina particle size, Crystallinity of the langasite is also lowered by alumina addition.

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The Effects of Silica-Alumina Type Inorganic Compounds on the Pyrolysis Reaction of EVA to Produce Fuel-Oil (EVA 수지 이용 연료유 생성을 위한 열분해 반응에서 실리카-알루미나 계열 무기물의 영향)

  • Bak, Young-Cheol;Choi, Joo-Hong;Oh, Se-Hui
    • Transactions of the Korean hydrogen and new energy society
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    • v.22 no.5
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    • pp.706-713
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    • 2011
  • The effects of silica-alumina type catalysts addition on the thermal decomposition of ethylene vinyl acetate (EVA) resin have been studied in a thermal analyzer (TGA, DSC) and a small batch reactor. The silica-alumina type compounds tested were kaolinite, bentonite, perlite, activated clay and clay. As the results of TGA experiments, pyrolysis starting temperature for EVA resin had the 1st pyrolysis temperature range of 300~$400^{\circ}C$ and the 2nd pyrolysis temperature range of 425~$525^{\circ}C$. The silica-alumina type catalysts did not affect the pyrolysis rate in EVA pyrolysis reaction. In the DSC experiments, addition of kaolinite and bentonite catalysts reduced the heat of fusion and heat of 2nd pyrolysis reaction. In the batch system experiments, the mixing of silica-alumina type catalysts enhanced the yield of fuel oil, and affected to the distribution of carbon numbers. In the silica-alumina type inorganic material used in this experiments, bentonite was the most effective from the pyrolysis heat, yields, and the characteristics of fuel oil.

Hydrogen Permeance of Silica Membrane Prepared by Chemical Vapor Deposition Method on an $\alpha$-Alumina Support Tube (기상 화학증착법에 의해 $\alpha$-Alumina 지지관 상에 제조한 Silica막의 수소투과 특성)

  • 김성수;이재홍;서동수;박상욱;서봉국
    • Journal of Environmental Science International
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    • v.7 no.5
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    • pp.669-677
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    • 1998
  • A porous $\alpha$-alumina tube of 2.5 mm O.D. and 1.9 mm I.D. was used as the support of an inorganic membrane. Macropores of the tube, about 150 nm in size, were plugged with silica formed by thermal decomposition of tetraethylorthosilicate at $600^{\circ}C$. The forced cross-flow CVD method that reactant was evacuated through the porous wall of the support was very effective in plugging macropores. The H$_2$ permeance of the prepared membrane was of the order of $10^{-8}/ molㆍs^{-1}/ㆍm^{-2}/. Pa{-1}$/, while the $N_2$ permeance was below $10^{-11}/ molㆍs^{-1}/ㆍm^{-2}/ㆍPa^{-1}$/ at $600^{\circ}C$. This was comparable to that of silica-modified Vycor glass whose size was 4 nm.

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De-soda Process Using Silica for Fabrication of Low Soda Alumina Powder

  • Park, Sang-Chun;Kim, Dae-Woong;Heo, In-Woong;Lee, Sang-Jin
    • Journal of the Korean Ceramic Society
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    • v.52 no.3
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    • pp.192-196
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    • 2015
  • Low soda alumina powder was fabricated using silica (${\alpha}$-quartz) as an agent for removing soda components in the alumina. Quartz powder 2 mm in size was added to aluminum hydroxide obtained through the Bayer process, and then the mixture was heated at various temperatures. Finally, the heat-treated powders were sieved for classification. In this study, the effects of the quartz amount and heating temperature on the mechanism of removing soda were examined. A minimum soda content of 0.005 wt% was observed at the conditions of 15 wt% quartz (based on $Al(OH)_3$ amount) heat-treated at $1600^{\circ}C$ for 8 h. The soda components, such as $Na_2O$, NaOH, and $Na_2CO_3$, in alumina were ionized and activated at high temperature, and this facilitated the reaction with quartz silica and alumina producing nepheline. The advantages of using quartz include low iron content and low cost in comparison with the conventional de-soda process using chamotte, another silicate mineral.

Adsorption of Colloidal Silica Particles on a Glass Substrate

  • Sim, Soo-Man
    • Journal of the Korean Ceramic Society
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    • v.39 no.11
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    • pp.1011-1016
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    • 2002
  • Colloidal particles of silica (100 nm in size) were electrostatically dispersed and adsorbed on a glass substrate coated with silica sol or alumina sol. Stability of the suspensions and microstructure of the adsorbed particle layers were discussed in terms of total potential energies between the particles and the substrate. Well-dispersed suspension resulted in a layer with densely packed and regularly arranged particles, whereas less stable suspension resulted in a porous layer with loosely packed and irregularly arranged particles. Despite repulsive interactions between the particles and the substrate coated with silica sol, the observed adsorption can be attributed to chemical bonds formed at the interface between the particle and silica sol. In contrast, the adsorption of the particles on the substrate coated with alumina sol formed a layer with strongly adhered and densely packed particles, due to large attractive interactions between the particles and alumina sol.

Influence of mullite-seed on the mullite synthesis from various compositions (Mullite 합성에 있어서 조성에 따른 Mullite-seed 첨가효과)

  • 김인섭;강상원;박주석;이명웅;이병하;이경희
    • Journal of the Korean Crystal Growth and Crystal Technology
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    • v.10 no.1
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    • pp.48-54
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    • 2000
  • Influence of seed addition on the mullite synthesis was investigated from mixture powders of kaolin and aluminium trihydroxide which contain various $Al_2O_3$/SiO_2$ ratio (silica rich, stoichiometric, alumina rich). The flexural strength increases with the increase of the mullite-seed content in case of silica rich and stoichiometric mullite, but flexural strength decreases with the increase of the mullite-seed content in case of alumina rich mullite. Microstructural investigation revealed that aspect ratio of mullite grains increased with higher alumina content, along with lower sintered density. Mullite contents of specimens are increased with seed content regardless of $Al_2O_3$/SiO_2$ ratio of the mixture composition.

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Influence of Zeta Potential on Fractional Precipitation of (+)-Dihydromyricetin ((+)-Dihydromyricetin 분별침전에 미치는 제타전위의 영향)

  • Ha, Geon-Soo;Kim, Jin-Hyun
    • Korean Chemical Engineering Research
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    • v.53 no.6
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    • pp.831-835
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    • 2015
  • This study evaluated the influence of the zeta potential of silica-alumina on the behavior in terms of purity, yield, and precipitate shape and size of fractional precipitation in the fractional precipitation process for the purification of (+)-dihydromyricetin. The optimal silica-alumina amount (surface area per working volume of reacting solution) for zeta potential control was $100mm^{-1}$. As the zeta potential value of silica-alumina increased, (+)-dihydromyricetin yield and precipitate size were increased. The use of silica with the highest value of the zeta potential (+4.99 mV) as a zeta potential-controlling material increased the (+)-dihydromyricetin yield by 2-fold compared with that of the use of alumina with the lowest value of the zeta potential (-19.00 mV). In addition, the (+)-dihydromyricetin yield and precipitate size was inversely correlated with the absolute value of the zeta potential. On the other hand, the purity of (+)-dihydromyricetin had almost no effect on changes in the zeta potential of silica-alumina.