• International Journal of Highway Engineering
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• v.7 no.3 s.25
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• pp.31-42
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• 2005

This study evaluates the physical mechanical properties, durability and sound absorbtion of porous concrete for pavement according to content of silica fume and steel fiber to elicit the presentation of data and the way to enhance its function for the practical field application of porous concrete as a material of pavement. The results of the test indicate that in every condition, the void ratio and the coefficient of water permeability of porous concrete for pavement satisfy both the domestic standards and proposition values. Among the properties of strength, the compressive strength satisfies the standards in the specification of Korea National Housing Corporation as for every factor of mixture but in the case of the flexural strength, more than 0.6vol.% of steel fiber satisfied the Japan Concrete Institute proposition values. The mixture of silica fume and steel fiber presents the excellent intensity, though. The case when silica fume and steel fiber are used simultaneously presents the strongest durability because the durability shows the similar tendency to the dynamic characteristics. The case when 10wt.% of silica fume and 0.6vol.% of steel fiber are used at the same time shows that the loss rate of mass by Cantabro test became 27% better and freeze-thaw resistance became 60% better. As for the characteristics of sound absorption of porous concrete for pavement, Noise Reduction Coefficient is 0.48 to prove that it possesses almost 50% sound absorption.

• Proceedings of the Korea Concrete Institute Conference
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• 2002.05a
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• pp.655-660
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• 2002

The purpose of this study is to analyze void ratio, coefficient of water permeability, and strength characteristics when silica fume and carbon fibers were added in order to improve the strength of porous concrete, and when recycled aggregates were used. Comparing with the case that recycled aggregate was not used, as the replacement ratio of recycled aggregate increased, the differences in void ratios and strength characteristics were decreased. In the case that silica fume was used, the content of 10% silica fume was most effective in improving strength. In the case that carbon fibers were used, the content of 3% carbon fiber were good to achieve the highest flexural strength, and Pan-derived CF was much better than pitch-derived CF in improving these effects.

• Journal of the Korean Ceramic Society
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• v.30 no.3
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• pp.189-198
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• 1993

A new pressurized sol-gel coating technique forming membrane layers inside pores of the porous support by the simple operation has been developed. Crack-free and reproducible nanoparticulate silica membranes supported on the porous $\alpha$-alumina tube are synthesized by pressurized coating at 600kPa for 2hr. The pore radius and N2 gas permiability at the room temperature of silica membrane layers are 8$\AA$ and 7.0$\times$10-7mol/$m^2$.s.Pa, respectively. The mechanism of N2 gas transfer through synthesized membrane layers is the perfect Knudeen flow, and the thermal stability of the silica composite membranes is excellent upto 40$0^{\circ}C$.

• Bulletin of the Korean Chemical Society
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• v.22 no.7
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• pp.678-684
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• 2001

Porous silica-pillared montmorillonites were prepared by simultaneous intercalation of dodecylamine-TEOS [tetraethylorthosilicate, Si(OC2H5)4] into the H-montmorillonite and intragallery amine-catalyzed hydrolysis of TEOS. Mixtures of the H-montmorillonite, dodecylamine and TEOS at molar ratios of 1 : 2 : 15-30 and 1 : 2-6 : 20 resulted to swollen and viscous gel once at room temperature, allowing intercalation compounds which dodecylamine and TEOS were simultaneously intercalated into interlayer of H-montmorillonite. The hydrolysis of the gallery TEOS was conducted in water solution for 40 min at room temperature, affording siloxane-pillared H-montmorillonite. Calcination of samples at 500 $^{\circ}C$ in air resulted in silica-pillared montmorillonite with large specific surface areas between 403 and 577 m2 /g, depending on the reaction stoichiometry. The reaction at H-montmorillonite : dodecylamine : TEOS reaction stoichiometries of 1 : 2 : 15 and 1 : 4 : 20 resulted in high specific surface areas and mesopores with a narrow pore size distribution. Result indicates that the intragallery-amine catalyze the hydrolysis of gallery-TEOS and simultaneously have a role of gallery-templated micellar assemblies.

• Resources Recycling
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• v.30 no.2
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• pp.68-74
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• 2021

This study investigated formaldehyde (HCHO) removal by preparing porous supports using domestic low-grade silica coated with Co-ZSM5 and Cu-ZSM5 as the catalysts. First, the sample of the raw material for the support contained 90% silica with quartz crystal phase, which was confirmed as low-grade silica. According to Energy-dispersive X-ray spectroscopy (EDS) and Fourier-transform infrared spectroscopy (FT-IR) analyses, the catalysts, Co-ZSM5 and Cu-ZSM5, were successfully coated on the surface of the porous silica supports. During the removal test of HCHO using the prepared Co-ZSM5 and Cu-ZSM5 coated beads, depending on the reaction temperature, the Co-ZSM5 coated beads exhibited higher removal efficiencies (>97%) than the Cu-ZSM5 beads at 200 ℃. The higher efficiency of the Co-ZSM5 coating may be attributed to its superior surface activity properties (BET surface area and pore volume) that lead to the favorable HCHO decomposition. Therefore, Co-ZSM5 was determined to be the suitable catalyst for removing HCHO as a coating on a porous support fabricated using domestic low-grade silica.

• Journal of the Korean Ceramic Society
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• v.55 no.3
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• pp.285-289
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• 2018

We synthesized silicon carbide (${\beta}-SiC$) nanowires with nano-scale diameter (30 - 400 nm) and micro-scale length ($50-200{\mu}m$) on a porous body using low-grade silica and carbon black powder by carbothermal reduction at $1300-1600^{\circ}C$. The SiC nanowires were formed by vapor-liquid-solid deposition with self-evaporated Fe catalysts in low-grade silica. We investigated the characteristics of the SiC nanowires, which were grown on a porous body with Ar flowing in a vacuum furnace. Their structural, optical, and electrical properties were analyzed with X-ray diffraction (XRD), transmission electron microscopy (TEM), and selective area electron diffraction (SAED). We obtained high-quality SiC single crystalline nanowire without stacking faults that may have uses in industrial applications.

• 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.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.148.2-148.2
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• 2013

We prepared hydrophobic PDMS-coated porous silica as pre-concentration adsorbent for chemical warfare agents (CWAs). Since CWAs can be harmful to human even with a small amount, detecting low-concentration CWAs has been attracting attention in defense development. Porous silica is one of the promising candidates for CWAs pre-concentration adsorbent since it is thermally stable and its surface area is sufficiently high. A drawback of silica is that adsorption of CWAs can be significantly reduced due to competitive adsorption with water molecule in air since silica is quite hydrophilic. In order to solve this problem, hydrophobic polydimethylsiloxane (PDMS) thin film was deposited on silica. Adsorption and desorption of chemical warfare agent (CWA) simulants (Dimethylmethylphosphonate, DMMP and Dipropylene Glycol Methyl Ether, DPGEM) on bare and PDMS-coated silica were studied using temperature programed desorption (TPD) with and without co-exposing of water vapor. Without exposure of water vapor, desorbed amount of DMMP from PDMS-coated silica was twice larger than that from bare silica. When the samples were exposed to DMMP and water vapor at the same time, no DMMP was desorbed from bare silica due to competitive adsorption with water. On the other hand, desorbed DMMP was detected from PDMS-coated silica with reduced amount compared to that from the sample without water vapor exposure. Adsorption and desorption of DPGME with and without water vapor exposing was also investigated. In case of bare silica, all the adsorbed DPGME was decomposed during the heating process whereas molecular DPGME was observed on PDMS-coated silica. In summary, we showed that hydrophobic PDMS-coating can enhance the adsorption selectivity toward DMMP under humid condition and PDMS-coating also can have positive effect on molecular desorption of DPGME. Therefore we propose PDMS-coated silica could be an adequate adsorbent for CWAs pre-concentration under practical condition.

• Bulletin of the Korean Chemical Society
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• v.30 no.3
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• pp.722-725
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• 2009

• Journal of Environmental Science International
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• v.9 no.4
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• pp.311-318
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• 2000

To improve $CO_2$pemselectivity, a modified silica membrane was prepared by chemical vapor deposition with tetraethoxysilane(TEOS)-ethanol-water, and TEOS-ethanol-water-HCI solution at 300-$600^{\circ}C$. The silica was effectively deposited in the mesopores of a ${\gamma}$-alumina film coated on a porous $\alpha$-alumina tube by evacuating the reactants through the porous wall. In this membrane, $CO_2$interacts, to some extent, with the pore wall, and $CO_2$/$N_2$selectivity then exceeds the value of the Knudsen diffusion mechanism, while the membrane derived from TEOS alone has no $CO_2$selectivity. The silica membrane prepared from TEOS-ethanol-water-HCI solution showed that $CO_2$permeance was $2.5$\times$10^{-7}mol/s^{-1}.m^{-2}.Pa^{-1} at 30{\circ}C$ and $CO_2$/$N_2$selectivity was approximately 3. The $CO_2$permeance and selectivity was improved by enlarging the surface diffusion with modification of chemical affinity of the silica pores.