• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.28 no.5
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• pp.208-215
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• 2016

This study was conducted to improve the performance of low-temperature vacuum dryer by applying desiccant to cold trap. Performance evaluation was carried out using several desiccants. The amounts of absorption and diffusivity were measured based on analytic model. Results of desiccant performance evaluation revealed that silica-gel had the most excellent performance for conditions of low-temperature vacuum drying process. Silica-gel was applied to cold trap for evaluating the drying performance. The experiment results showed that the drying time was extended as the thickness of sample was increased due to increased heat and mass transfer resistance of drying sample. In addition, as heating plate temperature was increased, drying time was decreased due to increased evaporation pressure of drying sample. Furthermore, drying time with desiccant was decreased approximately 20% than that without desiccant.

• Korean Chemical Engineering Research
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• v.53 no.1
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• pp.78-82
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• 2015

Hollow silica particles were prepared using sodium silicate and organic templates. Polystyrene latex (PSL) particles produced by dispersion polymerization were used as organic templates. PSL particles ranged from $1{\mu}m$ to $3{\mu}m$ in diameter were synthesized by adjusting the amount of 2,2'-azobisisobutyronitrile (AIBN). The PSL/$SiO_2$ core-shell particles were prepared by coating of silica nanoparticles originated from sodium silicate using sol-gel method. The organic templates were removed by the organic solvent, tetrahydrofuran (THF). Morphology of hollow silica particles was investigated with respect to types of the reaction medium and pH during the process. By changing the solvent from ethanol to water, hollow silica particles were successfully formed. Hollow silica particles with the uniform shell thickness were produced at low pH as well. The reflectivity of the as-prepared silica particles was measured in the range of the wavelength of UV and visible light. Hollow silica particles showed much better reflective properties than the commercial light reflector, Insuladd.

• Journal of the Korean Ceramic Society
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• v.36 no.2
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• pp.159-166
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• 1999

The physical properties and microstructural changes with heat-treatment of opacified silica aerogels doped by TiO2 were investigated. Monolithic SiO2-TiO2 aerogels were prepared by supercritical drying (25$0^{\circ}C$, 1250 psig) of wet gel obtained by adding titanium isopropoxide to prehydrolyzed TEOS-isopropanol solutions. The density and the porosity of SiO2-10 mol% TiO2 aerogels were 0.23 g/㎤ and 90%, respectively. During supercritical drying, the linear shrinkage of aerogels increased with increase in the titanium content an TiO2 was transformed to the anatase phase as well as particls agglomerates led to TiO2 clusters of 100~800 nm dispersed homogeneoulsy in the silica matrix. The IR transmittance of opacified silica aerogels was very low in the region of wavelengths below 8 ${\mu}{\textrm}{m}$ compared with pure silica aerogels and SiO2-TiO2 aerogels showed the high thermal stability of microstructures up to $600^{\circ}C$.

• Korean Chemical Engineering Research
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• v.55 no.6
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• pp.830-836
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• 2017

Hydrophilic coating solutions were prepared by reacting a silane coupling agent, GPTMS (3-glycidoxypropyl trimethoxysilane) with colloidal silica. Hydrophilic coating films were also obtained by depositing the hydrophilic coating solutions on polycarbonate substrates by spin-coating and subsequently by thermal curing at $120^{\circ}C$. During this process, the effect of average particle sizes of colloidal silica was studied on the properties of coating films. As a result, coating film, prepared from colloidal silica with average particle size of 25 nm, showed a low contact angle of $20^{\circ}$ and a good pencil hardness of H. On the other hand, coating films, prepared from colloidal silica with average particle sizes of 15 nm and 45 nm, exhibited high contact angles of $27^{\circ}$ and $36^{\circ}$ and pencil hardness of H and B, respectively.

• Elastomers and Composites
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• v.50 no.2
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• pp.103-109
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• 2015

In this study, epoxy/anhydride mixing ratio for the highly silica filled compounds with chromium (III) octoate catalyst was investigated at a low curing temperature ($71^{\circ}C$ for 40 hr) by evaluating the compressive strength with the weight ratio ranges from 0.3/1.0 to 1.0/1.0 of epoxy part (Part A)/anhydride part (Part B). In case of epoxy/anhydride compounds used surface unmodified silica by coupling agent, these compounds need excess anhydride unlike the weight ratio in the conventional epoxy/anhydride compounds. In curing behavior, the epoxy/anhydride compounds containing chromium (III) octoate showed high conversions at $71^{\circ}C$ for 40 hr, even if a dipropylene glycol (DPG) was not used as a polymerization initiator. Also, DPG leads to a poor epoxy network structure. In conclusion, the appropriate weight ratio of Part A/Part B of highly silica filled epoxy/anhydride compounds with chromium (III) octoate catalyst is 0.5/1.0 and the maximum amounts of silica is 1470 phr of epoxy resin.

• Elastomers and Composites
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• v.51 no.2
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• pp.81-92
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• 2016

1,3-Diphenylguanidine (DPG) is commonly used as a secondary accelerator which not only acts as booster of cure but also activating silanization reaction. The aim of this study is to increase the interaction between silica and rubber by using DPG. In this study, mixing was proceeded in two steps. The T-1 compound is mixed DPG with silica and silane coupling agent in the kneader at high temperature which is named as $1^{st}$ mixing step. T-3 compound is mixed DPG with curatives in the two-roll mill at low temperature which is named as $2^{nd}$ mixing step. The T-2 compound is mixed a half of DPG in $1^{st}$ mixing step and the remainder is mixed in $2^{nd}$ mixing step. Total DPG content was equal for all compounds. When DPG is mixed with silica, silane coupling agent during the $1^{st}$ mixing step, a decrease in cure rate and an increase in scorch time can be seen. This indicates that DPG is adsorbed on the surface of silica. during rubber processing. However, bound rubber content is increased and dynamic properties are improved. These results are due to the highly accelerated silanization reaction. However, there are no significant difference in 100%, 300% modulus.

• The Korean Journal of Physiology
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• v.30 no.1
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• pp.77-83
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• 1996

Platelet-activating factor(PAF) is a phospholipid mediator of pulmonary inflammation, and immunologic reaction. In this study, the role of PAF on tumor necrosis factor$(TNF_{-{\alpha}})$ production by rat alveolar macrophages(AM) was examined. When PAF $(10^{-12}{\sim}10{-16}\;M)$ alone was added to AM culture, $(TNF_{-{\alpha}})$ production was not significantly increased above the resting level. In contrast, the combined addition of PAF $(10^{-6}\;M)$ and muramyl dipeptide(MDP) $(1.0\;{\mu}g\ml)$ to AM cultures markedly enhanced $(TNF_{-{\alpha}})$ production with 8.2 fold increase compared with AM culture in resting state. This potentiative effect was 313% above the sum of the separate effects of PAF and MDP. To characterize MDP effects on $(TNF_{-{\alpha}})$ production, the dose-response of AM cultured with various concentrations of MDP was tested. High level of MDP $(10\;{\mu}g\ml)$ could not significantly enhance the potentiation effect on $(TNF_{-{\alpha}})$ production compared with AM cultures with low level of MDP $(0.1\;{\mu}g\ml)$, i.e. 112.5% vs 107.8%, respectively when $10^{-10}$ M of PAF was simultaneously added to the cell culture. These data support that the potentiation of TNF. g production in AM culture is mediated by PAF rather than MDf It was also evaluated whether the similar result was obtained in silica, respirable toxic particle-treated AM culture. $(TNF_{-{\alpha}})$ production was also significantly enhanced in the PAF $(10^{-6}\;M)$ and silica $(50\;{\mu}g\ml)$-added cell cultures with 4.7 fold above the value of silica alone-stimulated cells. These results indicate that PAF can potentiate $(TNF_{-{\alpha}})$ production by MDP-or silica- stimulated AM and suggest that PAF may play a potent role in lung inflammation and disease associated with microbe and occupational dust exposures.

• Journal of the Korean Ceramic Society
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• v.36 no.8
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• pp.829-834
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• 1999

The silica aerogels opacified via adding oxides were prepared by the sol-gel supercritical drying technique and their characteristics of mechanical strength and thermal conduction were investigated. The compressive strength of SiO2-10 mol% TiO2 and SiO2-10mol% Fe2O3 aerogels were 0.11 and 0.047 MP a respectively much higher than 0.025 MPa of pure silica aerogels. The thermal conductivity of silica aerogels opacified by TiO2 was as low as 0.02505 W/m${\cdot}$K at $400^{\circ}C$ It was found that the TiO2 -opacifier for improving mechanical strength and suppressing high temperature conduction of pure silica aerogels was more effective than the Fe2O3 -opacifier

• Applied Chemistry for Engineering
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• v.19 no.3
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• pp.310-315
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• 2008

Herein, we synthesized silica-coated chrome yellow particles having improved chemical resistance. The intermediate with a good dispersion stability was prepared and the chemical resistance of the final product was investigated. The effects of pH and temperature, as the main parameters influencing the formation of particles, the reduced particle size by homogenizer on the silica coating were investigated. The change in the particle morphology by temperature and pH was also studied. As the results, small and monodisperse particles were achieved at low pH and high temperature. Good silica coating was obtained when used reduced size of the particles by homogenizer. Furthermore, the sufficient silica coating by microencapsulation was obtained at 9~10 pH and the temperature above $90^{\circ}C$.

• Journal of the Korean Ceramic Society
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• v.56 no.1
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• pp.98-103
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• 2019

Optical filters to control light wavelength of displays or cameras are fabricated by multi-layer stacking process of low and high index thin films. The process of multi-layer stacking of thin films has received much attention as an optimal process for effective manufacturing in the optical filter industry. However, multi-layer processing has disadvantages of complicated thin film process, and difficulty of precise control of film morphology and material selection, all of which are critical for transmittance and coloring effect on filters. In this study, the composite $TiO_2$, which can be used to control of UV absorption, coated on nano hollow silica sol, was synthesized as a coating material for optical filters. Furthermore, systematic analysis of the process parameters during the chemical reaction, and of the structural properties of the coating solutions was performed using SEM, TEM, XRD and photo spectrometry. From the structural analysis, we found that the 85 nm nano hollow silica with 2.5 nm $TiO_2$ shell formation was successfully synthesized at proper pH control and titanium butoxide content. Photo luminescence characteristics, excited by UV irradiation, show that stable absorption of 350 nm-light, correlated with a 3.54 eV band gap, existed for the $TiO_2$ shell-nano hollow silica reacted with 8.8 mole titanium butoxide solution. Transmittance observed on substrate of the $TiO_2$ shell-nano hollow silica showed effective absorption of 200-300 nm UV light without deterioration of visible light transparency.