• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2010.06a
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• pp.99-99
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• 2010

Polymer nanocomposite has been attracting much attention as a new insulation material, since homogeneous dispersion of nm-sized inorganic fillers can improve various properties significantly. In this paper, various kinds of epoxy based nanocomposites were made and AC breakdown strength of Nano-TiO2 and micro-silica filler mixture of epoxy based composites were studied by sphere to sphere electrode. Moreover, nano- and micro-filler combinations were adopted as an approach toward practical application of nanocomposite insulation materials. Nano-TiO2 particle size is about 10nm and composites ratio was resin (100) : hardener (82) : accelerator (1.5). AC breakdown test was performed at room temperature (25 [$^{\circ}C$], 80 [$^{\circ}C$] and 100 [$^{\circ}C$] in the vicinity of Tg (90[$^{\circ}C$]). And thermal conductivity were measured by ASTM-D5470.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.31 no.9
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• pp.910-914
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• 2007

We present a simple and an inexpensive method for the fabrication of a nano-fluidic filter and a nano-pore micromixer using self-assembly of nano-spheres and surface tension. Colloid-plug was formed by surface tension of liquid in a microchannel to fabricate nanofluidic filter. When colloid is evaporated, nano-spheres in a colloid are orderly stacked by a capillary force. Orderly stacked nano-spheres form 3-D nano-mesh which can be used as a mesh structure of a fluidic filter. We used silica nano-sphere whose diameter is $567{\pm}85nm$, and silicon micro-channel of $50{\mu}m$-diameter. Fabricated nano-fluidic filter in a micro-channel has median pore diameter of 158nm which was in agreement with expected diameter of the nano-pore of $128{\pm}19nm$. A nano-pore micromixer consists of $200\;{\mu}m-wide,\;100\;{\mu}m-deep$ micro-channel and self-assembled nano-spheres. In the nano-pore micromixer, two different fluids had no sooner met together than two fluids begin to mix at wide region. From the experimental study, we completely apply self-assembly of nano-spheres to nano-fluidic devices.

• Advances in nano research
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• v.3 no.4
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• pp.243-255
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• 2015

In this investigation, ecotoxicity of nano and micro metal oxides, namely silica ($SiO_2$) and alumina ($Al_2O_3$), on the growth of green algae (Porphyridium aerugineum Geitler) is discussed. Effects of nano and micro particles on the growth, chlorophyll content and protein content of algae are analysed using standard protocols. Results indicate that $SiO_2$ nano and micro $SiO_2$ particles are non-toxic to P. aerugineum Geitler up to a concentration of 1000 mg/L. In addition, $Al_2O_3$ microparticles are less toxic to P. aerugineum Geitler, whereas $Al_2O_3$ nanoparticles are found to be highly toxic at 1000 mg/L. Moreover, $Al_2O_3$ nanoparticles decrease the growth, chlorophyll content, and protein content of tested algae. In addition, zeta potential and contact angle are also important in enhancing the toxicity of metal oxide nanoparticles in aquatic environment. This study highlights a new insight into toxicity evaluation of nanoparticles on beneficial aquatic organisms such as algae.

• Computers and Concrete
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• v.26 no.4
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• pp.309-316
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• 2020

The application of multi-variable adaptive regression spline (MARS) in predicting he long-term compressive strength of a concrete with various admixtures has been investigated in this study. The compressive strength of concrete specimens, which were made based on 24 different mix designs using various mineral and chemical admixtures in different curing ages have been obtained. First, The values of fly ash (FA), micro-silica (MS), water-reducing admixture (WRA), coarse and fine aggregates, cement, water, age of samples and compressive strength were defined as inputs to the model, and MARS analysis was used to model the compressive strength of concrete and to evaluate the most important parameters affecting the estimation of compressive strength of the concrete. Next, the proposed equation by the MARS method using particle swarm optimization (PSO) algorithm has been optimized to have more efficient equation from the economical point of view. The proposed model in this study predicted the compressive strength of the concrete with various admixtures with a correlation coefficient of R=0.958 rather than the measured compressive strengths within the laboratory. The final model reduced the production cost and provided compressive strength by reducing the WRA and increasing the FA and curing days, simultaneously. It was also found that due to the use of the liquid membrane-forming compounds (LMFC) for its lower cost than water spraying method (SWM) and also for the longer operating time of the LMFC having positive mechanical effects on the final concrete, the final product had lower cost and better mechanical properties.

• Journal of Korean Ophthalmic Optics Society
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• v.5 no.2
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• pp.187-192
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• 2000

We prepared $SiO_2-Na_2O-R_mO_n$ thin films based on economics of water glass and investigated optical, mechanical properties of product thin films. Coating sol stabilized with 1 N HCl and 1 N $NH_4OH$, was fabricated by using water glass and calcium nitrate, and aluminum nitrate as starting materials. As-coated films on stainless steel, Si wafer and soda-lime-silica glass by spinning were finally annealed at 500, 750 and $900^{\circ}C$. Micro hardness and nitrogen content in film surface of annealed films were measured by Knoop hardness tester and EDX, respectively. Field Emission Scanning Electron Microscope (FE-SEM) and UV-VIS spectroscopy were adopted to analyze surface morphology and thickness and reflectance of our films.

• Economic and Environmental Geology
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• v.39 no.6 s.181
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• pp.699-710
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• 2006

Batch scale experiments to investigate the efficiency of the solidification process for metal mine tailing treatment were performed. Portland and MSG (micro silica pouting) cements were used as solidifier and three kinds of mine tailings (located at Gishi, Daeryang, and Aujeon mine) were mixed with cements to paste solidified matrices. Single axis com-pressible strengths of solidified matrices were measured and their heavy metal extraction ratios were calculated to investigate the solidification efficiency of solidified matrices created in experiments. Solidified matrices ($5cm{\times}5cm{\times}5cm$) were molded from the paste of tailing and cements at various conditions such as different tailing/cement ratio, cement/water ratio, and different cement or tailing types. Compressible strengths of solidified matrices after 7, 14, and 28 day cementation were measured and their strengths ranged from 1 to $2kgf/mm^2$, which were higher than Korean limit of compressible strength for the inside wall of the isolated landfill facility ($0.21kgf/mm^2$). Heavy metal extractions from intact tailings and powdered matrices by using the weak acidic solution were performed. As concentration of extraction solution for the powdered solidified matrix (Portland cement + Gishi tailing at 1:1 w.t. ratio) decreased down to 9.7 mg/L, which was one fifth of As extraction concentration for intact Gishi tailings. Pb extraction concentration of the solidified matrix also decreased to lower than one fourth of intact tailing extraction concentration. Heavy metal extraction batch experiments by using various pH conditions of solution were also performed to investigate the solidification efficiency reducing heavy metal extraction rate from the solidified matrix. With pH 1 and 13 of solution, Zn and Pb concentration of solution were over the groundwater tolerance limit, but at pH $1{\sim}13$ of solution, heavy metal concentrations dramatically decreased and were lower than the groundwater tolerance limit. While the solidified matrix was immerged Into very acidic or basic solution (pH 1 and 13), pH of solution changed to $9{\sim}10$ because of the buffering effect of the matrix. It was suggested that the continuous extraction of heavy metals from the solidified matrix is limited even in the extremely high or low pH of contact water. Results of experiments suggested that the solidification process by using Portland and MSG cements has a great possibility to treat heavy metal contaminated mine tailing.

• International Journal of Concrete Structures and Materials
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• v.2 no.1
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• pp.41-48
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• 2008

This study investigates the spalling properties of high strength concrete designed with various types of mineral admixture and diverse content ratios of polypropylene (PP) fiber. Experimental factors considered in series I are four pozzolan types of mineral admixture and series II consists of three shrinkage reducing types of mineral admixture. PP fiber was added 0.05, 0.10 and 0.15vol. % in each mixture of series I and series II, so that totally 27 specimens including control concretes in each series were prepared. Test results showed that the increase of fiber content decreased the slump flow of fresh concrete and increased or decreased the air content depending on the declining ratio of slump flow. For the properties of compressive strength, all specimens were indicated at around 50 MPa, which is high strength range; especially all specimens in series II were 60 MPa. Fire test was conducted in standard heating curve of ISO 834 with ${\phi}100{\times}200\;mm$ size of cylinder moulds for 1 hour. The specimens incorporating silica fume exhibited severe spalling and most specimens without the silica fume could be protected from the spalling occurrence in only 0.05vol % of PP fiber content. This fire test results demonstrated that the spalling occurrence in high strength concrete was not only affected by concrete strength related to the porosity of microstructure but also, even more influenced by micro pore structure induced by the mineral admixtures.

• Journal of the Korean Ceramic Society
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• v.56 no.2
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• pp.205-210
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• 2019

Bioactive glass (BG) finds limited use as a bone replacement material owing to its low mechanical properties. In order to solve this problem, the micro-sized 13-93 BG was prepared as a fabric composite with SiC microfibers, and its mechanical properties and biocompatibility were investigated in this study. The tensile strengths of BG-SiC fiber-bundle composites increased in proportion to the number of SiC fibers. In particular, even when only one SiC fiber was substituted, the tensile strength increased by 81% to 1428 MPa. In the early stage of the in-vitro test, a silica-rich layer was formed on the surface of the 13-93 BG fibers. With time, calcium phosphate grew on the silica-rich layer and the BG fibers were delaminated. On the other hand, no products were observed on the SiC fibers for 7 days, therefore, SiC fibers are expected to maintain their strength even after transplantation in the body.

• International Journal of Precision Engineering and Manufacturing
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• v.9 no.1
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• pp.25-29
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• 2008

We introduce a new fabrication process for antireflective structured surfaces. A 4-inch silicon wafer was dipped in a suspension of 300-nm-diameter silica particles dispersed in a toluene solution. When the wafer was drawn out of the suspension, a hexagonally packed monolayer structure of particles self-assembled on almost the complete wafer surface. Due to the simple process, this could be applied to micro- and nano-patterning. The self-assembled silica particles worked as a mask for the subsequent reactive ion etching. An array of nanometer-sized pits could be fabricated since the regions that correspond to the small gaps between particles were selectively etched off. As etching progressed, the pits became deeper and combined with neighboring pits due to side-etching to produce an array of cone-like structures. We investigated the effect of etching conditions on antireflection properties, and the optimum shape was a nano-cone with height and spacing of 500 nm and 300 nm, respectively. This nano-structured surface was prepared on a $30\;{\times}\;10-mm$ area. The reflectivity of the surface was reduced 97% for wavelengths in the range 400-700 nm.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.1113-1116
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• 2008

The application of High Performance Concrete (HPC) for protecting bridge deck concrete with micro-silica, fly-ash and ground granulated blast-furnace slag was introduced to North America in the early 1980's. This report introduces the literature reviews of high performance concrete for protecting concrete bridge deck and explains 2-different types of construction methods using this materials. One is high performance concrete overlay method and the other is full depth bridge deck method. Both methods have been successfully applied and demonstrated in north america. Especially, modified high performance concrete overlay method including silica-fume and PVA fiber has been successfully applied in korea also. Therefore, both methods that high performance concrete overlay and full depth bridge deck are considered as reasonable bridge deck protecting methods compared with the conventional bridge deck system using asphalt modified materials.