• Journal of the Microelectronics and Packaging Society
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• v.25 no.4
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• pp.143-148
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• 2018

Sodium silicate based silica aerogels are lower in cost than silica alkoxide based silica aerogels, but the demand is decreasing as their physical properties are lowered. In this research, acetonitrile as a drying control chemical additive (DCCA) is added in the sol state to improve the pore-structural properties of sodium silicate based silica aerogel by preventing the agglomeration of particles and cross-linked bond. The sodium silicate based silica aerogel by ambient pressure drying were prepared by sol-gel process. Acetonitrile/$Na_2SiO_3$ molar ratio of 0, 0.05, 0.1, 0.15, and 0.2 was added to the sol state. The physical properties of the final product were analyzed using Fourier transform infrared, contact angle measurement, Brunauer-Emmett-Teller and Barrett-Joyner-Halenda measurements and field emission scanning electron microscopy. It was confirmed that the sample with adding 0.15 molar ratio of acetonitrile and sodium silicate showed a high specific surface area ($577m^2/g$), a high pore volume (3.29 cc/g), and a high porosity (93%) comparable to the pore-structural properties of silica alkoxide based silica aerogels.

• Transactions of the Korean hydrogen and new energy society
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• v.18 no.3
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• pp.230-237
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• 2007

Titania nanotube(TiNT) and CdS sol were synthesized by hydrothermal reaction under strongly basic condition and by precipitation reaction of $Cd(N0_3)_2$ and $Na_2S$ aqueous solutions, respectively. After preparing a series of CdS-TiNT composite films on $F:SnO_2$ conducting glass with variation of the mole ratio (r) of TiNT/(CdS+TiNT), their visible light absorption, photocatalytic activities for hydrogen production, and the photocurrent generation were examined. In general, this CdS-TiNT series showed lower photocatalytic activities and photocurrent generation under Xe light irradiation compared to their counterparts, i.e., CdS-$TiO_2$ particulate series. It appeared that TiNTs are not so effective photocatalyic material in spite of their larger specific surface areas compared to $TiO_2$ nanoparticles, because they indicate a poor crystallinity and less intimate interaction or contact with CdS particles owing to the tubular morphology and an easy agglomeration among themselves.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.4
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• pp.772-779
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• 2016

Silver nanoparticles were prepared by reacting silver nitrate and trisodium citrate in an aqueous solution. Their size and shape were investigated by scanning electron microscopy (SEM). The synthesis was carried with different silver nitrate concentration, addition of TSC, solvent, surfactant, ultrasonication, and dispersing agent. With higher concentration of silver nitrate or TSC, the particles became large or agglomerated. The SEM results showed that the nanoparticles have spherical and pseudospherical shape with a narrow size distribution. The hydrophobic solvent did not affect the dispersibility, but the hydrophilic solvent enhanced it. The addition of HPMC surfactant caused the size to increase (50-100 nm) with non-uniform shapes and partial agglomeration. The dispersibility was significantly improved by ultrasonication for over 3 hours after the addition of a dispersing agent. Complete dispersion was achieved by adding the dispersant, and the nanoparticle sizes were as follows: 30-40 nm (BYK-182) < 42-78 nm (BYK-192) < 51-113 nm (BYK-142). The nanoparticles were 38.45-46.28 nm after the addition of 2-4 wt% TSC in 0.002 M silver nitrate solution.

• Polymer(Korea)
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• v.30 no.6
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• pp.498-504
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• 2006

A suspension polymerization of styrene In aqueous phase was employed to study if polystyrene particles ranging from 1 to $20{\mu}m$ can be produced. Hydrophobic silica was selected as a stabilizer and azo-bisisobutyronitrile (AIBN) as an initiator. Polymerization reaction was carried out at a selected temperature in the range of $65{\sim}95^{\circ}C$. Stabilizer concentration was varied from 0.17 to 3.33 wt% compared to the water while the concentration of the initiator was raised from 0.13 to 6.0 wt% compared to the monomer. Dispersion of hydrophobic silica into the water phase was achieved by precise control of pH. Optimum dispersion of silica was obtained at pH 10. Average particle diameter decreased with increasing amounts of stabilizer concentration initially, exhibiting the minimum average diameter at 1.67 wt% of stabilizer concentration, after which it started to Increase. It is speculated that an excessive presence of stabilizer encouraged a secondary reaction in the reaction medium, which led to particle agglomeration, and as a result an increase in average particle diameter. Molecular weight was found to be independent of stabilizer concentration between 0.13 and 1.00 wt% whereas, it increased when stabilizer concentration exceeded 1.67 wt%. Variation of molecular weight was probably caused by the reduced activity and efficiency of initiator due to the high concentration of silica, and the secondary reaction in the reaction medium, as well. An increase in the Initiator concentration and/or reaction temperature resulted in an increase in both reaction rate and particle diameter. Consequently, we have confirmed that spherical polystyrene particles with $1{\sim}20{\mu}m$ in diameter can be prepared by careful selection of the concentration of stabilizer, initiator, pH and reaction temperature.

• Korean Journal of Heritage: History & Science
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• v.50 no.4
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• pp.148-165
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• 2017

Mural paintings drawn inside ancient tombs are very sensitive to changes in the environment such as temperature and humidity, especially the finish layer of the tomb murals differ in preservability depending on the material properties and humidity conditions. In this study, I examined the mural painting of Songsan-ri Tomb No.6, where the finish layer was made of earth, and identified the physical changes that can occur due to drying, depending on the material properties of the finish layer. I found out through particle size analysis that the finish layer of the mural painting in Songsan-ri Tomb No.6 is about 85.0wt% below silt, about 14.0wt% clay therein, mostly composed of silt and below clay. I also found out through physical property evaluation that surface change rate of samples showed the largest change at 15.5% in reproduced finish layer sample made up of bentonite, followed by 7.8% of reproduced finish layer sample made up of celadon soil, 6.3% of reproduced finish layer sample made up of loess, 6.2% of reproduced finish layer sample composed of white clay and the same order of change in appearance was confirmed in each sample consisted of soil. In addition, it showed the same trend of surface change rate, and the bentonite condition showed the largest change, in the measurement of shrinkage rate and expansion rate. The experiment shows that the finish layer composed of soil is affected by cohesion among particles according to the content of fine parts and the relationship between the agglomeration due to the content of the differentiated part and the stress due to the expansibility depending on the kind of the clay mineral etc. Therefore, it can be concluded that the physical damage occurred in the mural painting finish layer of the Songsan-ri Tomb No.6 is related to the factors such as the material characteristics of the soil and the highly humid environmental change inside the tomb.