• Journal of the Korean Magnetic Resonance Society
• /
• v.4 no.1
• /
• pp.50-63
• /
• 2000

Titanium dioxide particles with three different average sizes, prepared by three different methods, were incorporated into silica gel pores by impregnation. The titanium dioxide incorporated into the silica gel pores was photoionized by 240-400 nm irradiation at 77 K by a one-photon process to from trapped hole centers on OH group and trapped electron centers on titanium which were detected by electron paramagnetic resonance at 77 K. During the impregnation the smallest size range of TiO2 particles can be incorporated into silica gels with 2.5-1.5 nm pores. However, the largest size range of TiO2 particles can only be incorporated into silica gels with 6-15 nm pores and not into silica gels with 2.5-4 nm pores. The photoyield and stability of photoinduced hole and electron centers depends on the silica pore sizes of silica gels and surface area as well as on the TiO2 loading. In large pore silica gels and large particle size of TiO2, photoinduced charge separation reaches to a plateau at shorter irradiation times and the trapped hole and electron centers are more stable to decay.

• The Korean Journal of Ceramics
• /
• v.6 no.1
• /
• pp.37-42
• /
• 2000

To reduce shrinkage and the possibility of fracture during ambient pressure drying, it is of great importance to increase the strength and stiffness of the wet gels. In this paper is presented the strengthening and stiffening of wet silica gels prepared from sodium silicate (water glass) as well as properties of the corresponding xerogels. By washing gels containing different initial silica contents in water solutions at elevated pH, a maximum in shear modulus of ~4 MPa was obtained. The maximum stiffness enabled xerogels with bulk density of 0.28g/$\textrm{cm}^3$ to be made regardless of silica content and washing conditions. However, by aging the wet gels in a solution providing fresh monomers to the gel network, a shear modulus of 20 MPa was obtained after 27h. By this method monolithic xerogels with a density down to ~0.2g/$\textrm{cm}^3$ was prepared. The results are compared to alkoxide based gels.

• Journal of the Korean Ceramic Society
• /
• v.28 no.6
• /
• pp.488-494
• /
• 1991

In this study, the effects of catalyst and DCCA content were investigated in order to determine the optimum conditions of monolithic silica gel formation through sol-gel process. Formamide, oxalic acid, glycerol and dimethylformamide are used as DCCA. To observe the phenomena in drying and heat-treating of gels, we examined structural exchange of gels using FT-IR, TG-DTA and XRD. Monolithic gels were obtained by adding formamide and dimethylformamide as DCCA. According to the heat treatment schedule, silica glass is prepared by heat-treatment up to 1050$^{\circ}C$.

• Advances in concrete construction
• /
• v.4 no.3
• /
• pp.195-206
• /
• 2016

Today, application of additives to replace cement in order to improve concrete mixes is widely promoted. Micro-silica is among the best pozzolanic additives which can desirably contribute to the concrete characteristics provided it is used properly. In this paper, the effects of AP2RC and P1RB micro-silica gels on strength characteristics of normal concrete are investigated. Obtained results indicated that the application of these additives not only provided proper workability during construction, but also led to increased tensile, compressive and flexural strength values for the concrete during early ages as well as ultimate ones with the resulting reduction in the porosity lowering permeability of the micro-silica concrete. Furthermore, evaluation of microbial contamination of the mentioned gels showed the resultant contamination level to be within the permitted range.

• Journal of the Korean Society of Tobacco Science
• /
• v.27 no.2
• /
• pp.171-177
• /
• 2005

Coconut based activated carbon and silica-gels were impregnated with 3-aminopropyltri ethoxysilan(APS) and N-(2-aminoethyl)-3-aminopropyl triethoxysilane (AEAPS) in order to investigate the effect of the amine group and the pore size of the supports on the removal of hydrogen cyanide(HCN) and aldehydes in mainstream smoke(MS). The physicochemical properties of the supports were analyzed by using thermal gravity analyzer(TGA), $N_2$ adsorption and desorption isotherms$(BET,\;N_2)$, and SEM-EDS. According to our experimental data, there was no significant difference in the delivery amount of HCN and aldehydes of non-functionalized silica-gels having meso-pores bigger than $20\AA$. In the case of silica-gels functionalized with APS(APS silica-gel), the delivery amounts of hydrogen cyanide(HCN) and aldehydes decreased with the increase of APS concentration. Silica-gel functionalized with AEAPS(AEAPS silica-gel) showed higher removal efficiency than that of APS silica-gels. The delivery amounts of HCN and aldehydes of activated carbon impregnated with APS and AEAPS increased with the increase of the APS and AEAPS concentrations. In accordance with the specific surface area analysis results, APS and AEAPS molecules decreased the specific surface area by blocking the micro-pores of the activated carbon. The volatile organic components removal efficiency by the micro-pores was higher than that of the amine group impregnated into the activated carbon.

• Journal of the Korean Ceramic Society
• /
• v.36 no.11
• /
• pp.1189-1197
• /
• 1999

Low-density silica gel monolith was synthesized at ambient pressure by surface modification with TMCS and sub-sequent heat treatment. The mechanical thermal and optical properties of gel were studied. Compressive strength and modulus of compression of 350$^{\circ}C$-heated gel with the density of 0.24g/cm3 were 250kPa and 0.2MPa respectively. The thermal conductivity of silica gels synthesized at ambient pressure exhibited 0.02 W/m$.$K for the density of 0.24g/cm3 which is similar to that of the gel via supercritical drying and their main thermal transfer mechanism is considered to be solid and radiation conduction at room temperature. Ambient-dried silica gels were transparent blue showing about 60% of transmittance in the wavelength of 1500-2100nm and typical absorption bands of existing bonds under heat treatment at 350$^{\circ}C$. Medium scale monolity(${\Phi}$=50mm) at ambient pressure could be successfully prepared through total 5-month process period.

• Journal of the Korean Ceramic Society
• /
• v.30 no.3
• /
• pp.169-174
• /
• 1993

The porous silica glass prepared by the sol-gel method from the mixed solution of Si(OCH3)4, H2O, HCl and CH3OH with HCONH2 as a DCCA (Drying Control Chemical Additives). For investigation the characteristics of gels and glasses, we examined gels and glasses using TG-DTA, XRD, IR, SEM and porosimeter. The more content of formamide in the mixed solution increased, the more pore size and porosity of gel increased. In the excess formamide added gel, the properties of pore of gel were not so changed. The porous silica glass was prepared from the dry gel after heat treatment at 75$0^{\circ}C$. Porosity and mean pore size of the porous silica glass was 17~25% and 40~60$\AA$ relatively.

• 한국신재생에너지학회:학술대회논문집
• /
• 2007.06a
• /
• pp.477-480
• /
• 2007

Hydrate phase equilibrium for the binary CO2+water and CH4+water mixtures in silica gel pore of nominal 6, 30, and 100 nm were measured and compared with the cacluated results based on van der Waals and Platteeuw model. At a specific temperature three-phase hydrate-water-vapor (HLV) equilibrium curves for pore hydrates were shifted to the higher-pressure condition depending on pore sizes when compared with those of bulk hydrates. Notably, hydrate phase equilibria for the case of 100 nominal urn pore size were nealy identical with those of bulk hydrates. The activities of water in porous silica gels were modified to account for capillary effect, and the calculation results were generally in good agreement with the experimental data.

• New & Renewable Energy
• /
• v.3 no.2 s.10
• /
• pp.47-52
• /
• 2007

Hydrate phase equilibrium for the binary $CO_{2}$+water and $CH_{4}$+water mixtures in silica gel pore of nominal 6, 30, and 100 nm were measured and compared with the cacluated results based on van der Waals and Platteeuw model. At a specific temperature three-phase hydrate-water-vapor (HLV) equilibrium curves for pore hydrates were shifted to the higher-pressure condition depending on pore sizes when compared with those of bulk hydrates. Notably, hydrate phase equilibria for the case of 100 nominal nm pore size were nearly identical with those of bulk hydrates. The activities of water in porous silica gels were modified to account for capillary effect, and the calculation results were generally in good agreement with the experimental data.

• International Journal of Railway
• /
• v.8 no.2
• /
• pp.42-45
• /
• 2015

Alkali-silica reaction (ASR) is a chemical reaction in concrete that alkalis in cement react with reactive silica in aggregate in the presence of water. When ASR takes place, it produces gels that absorb water and expand. Swelling of ASR gels can damage concrete and cause cracking and volume expansion in concrete structure. In this paper, mechanical consequences of ASR on concrete are simulated by a finite element (FE) analysis. An FE model of concrete is built. The evolution of concrete mechanical properties subjected to ASR is achieved by FE analyses. The constitutive model of concrete is attained via the FE analysis. A case study is used to demonstrate the proposed method. The simulated results using the proposed model are in good agreement with the observations of concrete with ASR reported in the literature. The results can be used for a basic research to enhance durability of concrete slab tracks and concrete railway sleepers.