• Computers and Concrete
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• v.6 no.1
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• pp.1-18
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• 2009

Chloride diffusivity of concrete is a crucial material parameter for service life determination and durability designing of marine concrete. Many research works on this issue have been conducted, varying from empirical solutions obtained experimentally to image analysis, based on multi-scale modeling. One of the simple approaches is to express the chloride diffusivity of concrete by a multi-factor function, however, the influences of various factors on the chloride diffusivity are ambiguous. Furthermore, the majority of these research works have not dealt with the carbonation process of concrete, although this process affects the chloride diffusivity of concrete significantly. The purpose of this study is to establish a simple approach to calculate the chloride diffusivity of (non)carbonated concrete. The chloride diffusivity of concrete should be defined, based on engineering and scientific knowledge of cement and concrete materials. In this paper, a lot of parameters affecting the chloride diffusivity, such as the diffusivity in pore solution, tortuosity, micro-structural properties of hardened cement paste, volumetric portion of aggregate, are taken into consideration in the calculation of the chloride diffusivity of noncarbonated concrete. For carbonated concrete, reduced porosity due to carbonation is calculated and used for calculating the chloride diffusivity. The results are compared with experimental data and previous research works.

• Bulletin of the Korean Chemical Society
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• v.30 no.1
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• pp.193-196
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• 2009

Mesoporous $TiO_2$ material was synthesized from diblock copolymers with ethylene oxide chains via a sol-gel process in aqueous solution. The properties of these materials were characterized with several analytical techniques including field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), wide angle X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) analysis, and Barrett-Joyner-Halenda (BJH) analysis. The mesoporous $TiO_2$ materials calcined at 400${^{\circ}C}$ were found to have specific surface areas 212 $m^2g^-1$, average pore sizes 6.2 nm, and their average crystal sizes were found to be 8.2 nm. The photocatalytic activity of mesoporous $TiO_2$ was characterized with UV-Vis spectroscopy, and it was found to be 5.8 times higher than that of Degussa P25 $TiO_2$ (P25). For deactivation of Escherichia coli, mesoporous $TiO_2$ also has high photocatalytic inactivity than that of P25. Such a high photocatalytic activity is explained with large surface area and small crystal size with wormhole-like mesoporous structure.

• Proceedings of the Membrane Society of Korea Conference
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• 1997.04b
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• pp.27-28
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• 1997

최근 들어 분리공정의 발달과 산업의 고도화에 따라 기체 및 액체분리의 중요성이 강조되면서 열적, 화학적 그리고 기계적 안정성이 좋으며, 수명이 길고, 세척과 재생이 용이하며, 미생물에 의한 손상이 없는 무기막에 대한 연구가 진행중이다. 무기막은 기공의 크기에 따라 크게 다공성 막과 비다공성 막의 두 종류로 구분된다. 비다공성 금속막은 특정 기체에만 투과성을 가지며, 이때 기체는 용해-확산(solution-diffusion)기구에 의해 금속막을 투과하므로 특정기체에 대한 선택도는 매우 크나 투과도가 매우 작고 가격이 비싼 단점을 가지고 있다. 다공성 막은 기체 투과율이 큰 반면 기체 선택도가 작은 단점을 가지고 있다. 현재 기체분리에 사용되고 있는 무기막은 기공크기가 40${\AA}$ 이상으로 기체 분리가 Kundsen diffusion에 의해 이루어지므로, 기체 투과도는 큰 반면에 기체에 대한 선택도는 그리 크지 않다. 따라서 최근 들어서는 다공성 담체에 기공이 작은 ($d_{pore}<20{\AA}$)박막을 담지시켜 기체의 분리 선택도를 향상시키기 위한 연구가 활발히 이루어지고 있다. 본 연구에서는 유기금속 화학증착법(metal-organic chemical vapor deposition:MOCVD)을 이용하여 수소 선택성을 가지는 $SiO_2/Al_2O_3$ 복합막을 비율별로 제조하여 증착속도를 알아보고, 열과 수분에 노출시켜 박막의 기체투과도 변화를 살펴보았다.

• Carbon letters
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• v.9 no.3
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• pp.188-194
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• 2008

Porous carbon materials synthesized from various plant derived precursors i.e. seeds of [Castor (Ricinus communis), Soap nut (Sapindus sp.), Cashew-nut (Semecarpus anacardium), Jack fruit (Artocarpus heterophyllus), Safflower (Carthamus tinctorius), Ambadi (Crotolaria juncea), Neem (Azadirachta indica), Bitter Almond (Prunus amygdalus), Sesamum (Sisamum indicum), Date-palm (Phoenix dactylifera),Canola (Brassica napus), Sunflower (Helianthus annulus)] and fibrous materials from [Corn stem- (Zea mays), Rice straw (Oryza sativa), Bamboo (Bombax bambusa) and Coconut fibers (Cocos nucifera)] were screened to make supercapacitor in 5M KOH solution. Carbon material obtained from Jack fruit seeds (92.0 F/g), Rice straw (83.0 F/g), Soap nut seeds (54.0 F/g), Castor seeds (44.34 F/g) and Bamboo (40.0 F/g) gave high capacitance value as compared to others. The magnitude of capacitance value was found to be inversely proportional to the scan rate of measurement. It is suggested that carbon material should possess large surface area and small pore size to get better value of capacitor. Moreover, the structure of carbon materials should be such that majority of pores are in the plane parallel to the plane of electrode and surface is fluffy like cotton ball.

• Journal of Applied Biological Chemistry
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• v.43 no.1
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• pp.18-24
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• 2000

A one-dimensional transport of displacing monovalent ion, $A^+$, and a trivalent ion being displaced, $B^{3+}^ in a porous exchange system such as soil was approximated using the Crank-Nicolson implicit finite difference technique and the Thomas algorithm in tandem. The variations in the concentration profile were investigated by varying the ion-exchange equilibrium constant (k) of ion-exchange reactions, the influent concentrations, and the cation exchange capacity (CEC) of the exchanger, under constant flux condition of pore water and dispersion coefficient. A higher value of k resulted in a greater removal of the native ion, behind the sharper advancing front of displacing ion, while the magnitude of the penetration distance of $A^+$ was not great. As the CEC increased, the equivalent fraction of $B^{3+}^ initially in the soil was greater, thus indicating that a higher CEC adsorbed trivalent cations preferentially over monovalent ions. Mass balance error from simulation results was less than 1%, indicating this model accounted for instantaneous charge balance fairly well.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2012.05a
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• pp.333-333
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• 2012

In this study, we investigated morphology of nanotube and micropore on the Ti-25Nb-xHf alloys with Hf contents after anodization. Ti-25Nb-xHf ternary alloys contained from (0~15) wt.% Hf contents were manufactured by vacuum arc-melting furnace. The obtained ingots were homogenized in an argon atmosphere at $1000^{\circ}C$ for 12h and then water quenching. The specimens were cut from ingots to 3mm thickness and first ground and polished using SiC paper (grades from 100 to 2000). 2steps anodization treatments on Ti-25Nb-xHf alloys were carried out at room temperature for experiments. Micro-pore formation was performed in Ca+P mixed solution at 265V for 3min. After that, nanotube formation was in 1M $H_3PO_4$ electrolytes containing 0.8wt.% NaF solutionat 10V for 120min. Morphologies of micropore and nanotube depended on the Hf content in Ti-25Nb-xZr ternary system.

• Bulletin of the Korean Chemical Society
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• v.19 no.11
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• pp.1185-1188
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• 1998

Layered nanocomposite, SiO2/TiO2 sol pillared clay, has been prepared by the ion exchange reaction of Na' ion in montmorillonite with positively charged mixed SiO2/TiO2 sol. The nanosized sol particles were synthesized by mixing SiO2 sol solution with TiO2 one, which is obtained by acidic hydrolysis of TEOS and TiCl4, respectively. From powder XRD, the basal spacing (d001) of the sample calcined at 400 ℃ was found to be ca. 60 Å, due to the multistacking of nanosized SiO2 and TiO2 sol particles, which was confirmed by the pore size analysis from 129Xe NMR and micropore analysis calculated from nitrogen adsorption. The BET specific surface area shows the value of 684 m2g-1 (Langmuir 1115 m2g-1), which is the highest among various pillared clays ever reported previously, and the total porosity is found to be 0.51 mlg-1, and the pores are mainly composed of micropore with a size of ca. 11.8 Å. This result agrees with the adsorption capacity obtained from water adsorption. According to diffuse reflectance ultraviolet-visible spectroscopy, it is found that the TiO2 particles stabilized in the interlayer space of montmorillonite are quantum-sized of ca. 20 Å.

• Journal of Powder Materials
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• v.27 no.6
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• pp.477-483
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• 2020

Metal-organic frameworks (MOFs) are of significant interest because of their high porosity, which facilitates their utilization in gas storage and catalysis. To enhance their current properties in these applications, it is necessary to elucidate the interactions between molecules in a confined environment that differ from those in bulk conditions. Herein, we study the confined molecular interaction by investigating the solvent-dependent photophysical properties of two different-sized molecules inside MOF-5. Ruthenium tris-bipyridine (Rubpy) and coumarin 153 (C153) are encapsulated in MOF-5. Rubpy with MOF-5 (Rubpy@MOF) is prepared by building MOF-5 around it, resulting in limited space for solvent molecules in the pores. The smaller C153 is encapsulated in the preformed MOF-5 (C153@MOF) by simply soaking the MOF in a concentrated C153 solution. C153@MOF permits more space for solvent molecules in the pore. Their characteristic absorption and emission spectra are examined to elucidate the confined molecular interactions. Rubpy@MOF and C153@MOF exhibit different spectral shifts compared to the guest molecules under bulk conditions. This discrepancy is attributed to the different micro-environments inside the pores, derived from confined host-guest interactions in the interplay of solvent molecules.

• Journal of Ceramic Processing Research
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• v.19 no.6
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• pp.492-498
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• 2018

In this study, a sea shell was converted into bioceramic phases at three different sintering temperatures ($450^{\circ}C$, $850^{\circ}C$, $1000^{\circ}C$). Among the obtained bioceramic phases, a valuable ${\beta}-TCP$ was produced via mechanochemical conversion method from sea snail Turritella terebra at $1000^{\circ}C$ sintering temperature. For this reason, only the bioceramic sintered at $1000^{\circ}C$ was concentrated on and FT-IR, SEM/EDX, BET, XRD, ICP-OES analyses were carried out for the complete characterization of ${\beta}-TCP$ phase. Biodegradation test in Tris-buffer solution, bioactivity tests in simulated body fluid (SBF) and cell studies were conducted. Bioactivity test results were promising and high rate of cell viability was observed in MTT assay after 24 hours and 7 days incubation. Results demonstrated that the produced ${\beta}-TCP$ bioceramic is qualified for further consideration and experimentation with its features of pore size and ability to support bone tissue growth and cell proliferation. This study suggests an easy, economic method of nanobioceramic production.

• Journal of Korean Society of Water Science and Technology
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• v.26 no.6
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• pp.125-132
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• 2018

We studied a simple approach for synthesis of mesoporous Y(M-Y) from commercial zeolite Y precursors by treating of NaOH with $CH_3(CH_2)_{15}N(Br)(CH_3)_3$ as template. The physicochemical properties of the mesoporous zeolites Y were then analyzed using XRD, nitrogen full-isotherms at 77 K, SEM and TEM. The nitrogen adsorption-desorption analysis showed that surface area and pore diameter of synthesized mesoporous zeolite Y(M-Y) were $1072m^2/g$ and ~3.3 nm, respectively. And M-Y was applied for the removal of $Mn^{2+}$ and $Fe^{2+}$ from aqueous solution. This material, which introduces mesoporosity with zeolite Y character, displayed a superior adsorption capacity than commercial zeolite Y when used as an adsorbent for the removal of $Mn^{2+}$ and $Fe^{2+}$.