• Journal of the Korean Vacuum Society
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• v.16 no.6
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• pp.474-478
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• 2007

Nanostructures of $SiN_x$ were made by bombardment of ionized $N_2$ on Si surface and subsequent annealing. Atomic force micrograph showed the density of $SiN_x$ nanostructures was $3\times10^{10}/cm^2$. Their lateral size and height were 40$\sim$60 nm and 15 nm, respectively. The chemical state of the nanostructure was measured using X-ray photoelectron spectroscopy, which changed from $SiN_x$ to $Si_3N_4\;+\;SiN_x$ as the bombarding ionized gas current increases. Upon annealing, transmission electron micrograph showed a clear evidence for crystalline Si phase formation inside the $SiN_x$ nanostructures. Photoluminescence peak observed at around 400nm was thought to be originated from the interface states between the nanocrystalline Si and surrounding $SiN_x$ nanostructures.

• Textile Coloration and Finishing
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• v.28 no.1
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• pp.48-56
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• 2016

Improvement of heat sink technology related to the continuous implementation performance and extension of device-life in circumstance of easy heating and more compact space has been becoming more important issue as multi-functional integration and miniaturization trend of electronic gadgets and products has been generalized. In this study, it purposed to minimize of decline of the heat diffusivity by gluing polymer through compounding of inorganic particles which have thermal conductive properties. We used NH-9300 as base resin and used inorganic fillers such as silicon carbide(SiC), aluminum nitride(AlN), and boron nitride(BN) to improve heat diffusivity. After making film which was made from 100 part of acrylic resin mixed hardener(1.0 part more or less) with inorganic particles. The film was matured at $80^{\circ}C$ for 24h. Diffusivity were tested according to sorts of particles and density of particles as well as size and structure of particle to improve the effect of heat sink in view of morphology assessing diffusivity by LFA(Netzsch/LFA 447 Nano Flash) and adhesion strength by UTM(Universal Testing Machine). The correlation between diffusivity of pure inorganic particles and composite as well as the relation between density and morphology of inorganic particles has been studied. The study related morphology showed that globular type had superior diffusivity at low density of 25% but on the contarary globular type was inferior to non-globular type at high density of 80%.

• Journal of Korean Society of Environmental Engineers
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• v.38 no.9
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• pp.521-527
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• 2016

Nanoscale zero valent iron (nZVI) has been intensively studied for the treatment of a plethora of pollutants through reductive reaction, however, the nano size should be of concern when nZVI is considered for water treatment, due to difficulties in recovery. The loss of nZVI causes not only economical loss, but also potential risk to human health and environment. Thus, the immobilization onto coarse or structured support is essential. In this study, two representative processes for nZVI immobilization on granular activated carbon (GAC) were evaluated, and optimized conditions for synthesizing Fe/GAC composite were suggested. Both total iron content and $Fe_0$ content can be significantly affected by preparation processes, therefore, it was important to avoid oxidation during preparation to achieve higher reduction capacity. Synthesis conditions such as reduction time and existence of intermediate drying step were investigated to improve $Fe_0$ content of Fe/GAC composites. The optimal condition was two hours of $NaBH_4$ reduction without intermediate drying process. The prepared Fe/GAC composite showed synergistic effect of the adsorption capability of the GAC and the degradation capability of the nZVI, which make this composite a very effective material for environmental remediation.

• Journal of the Korean Applied Science and Technology
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• v.24 no.2
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• pp.174-181
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• 2007

In this study, $SiO_2/poly(ethylene-co-vinyl$ alcohol)(EVOH) hybrid coating materials with gas barrier property could be produced using sol-gel method. The biaxially oriented polypropylene (BOPP) substrate with surface pretreatment was coated with the prepared hybrid sols containing various inorganic silicate component by a spin coating method. Crystallization behavior of the hybrids was investigated in terms of analysis of X-ray diffraction and cooling thermogram from DSC experiment. From the morphological observation of the $SiO_2/EVOH$ hybrid gel, it was confirmed that there existed an optimum content of inorganic silicate precursor, Tetraethylorthosilicate (TEOS), to produce hybrid materials with dense microstructure, exhibiting uniformly dispersed silica particles with average size below 100 nm. When TEOS was added at below or above the optimum content, particle clusters with large domain were observed, resulting in phase separation. This morphological result was found to be in good agreement with that of oxygen permeability of the hybrid coated films. In the case of film coated with hybrid prepared from addition of 0.01 - 0.02mol of TEOS, a remarkable improvement in barrier property could be obtained, however, with the addition of TEOS more than 0.04 mol, the barrier property was dramatically reduced because of phase separation and micro-crack formation on the film surface.

• Journal of Korean Society of Environmental Engineers
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• v.30 no.1
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• pp.85-89
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• 2008

The purpose of this study is to understand the removal possibility of microalgae using inorganic coagulants in coagulation and sedimentation process for water treatment. Removal of microalgae was studied according to coagulant type(Alum and PAC), coagulation factors(alkalinity, coagulant dosage, and setting time), and size fraction of microalgae. The contribution of applied coagulants for removal of microalgae was also examined. The removal rate of the microalgae by change of alkalinity was most high in 25 mg/L of alkalinity(Alum) as 87.2% and 30 mg/L of that(PAC) as 90.1%. Optimal coagulant dosage to remove the microalgae was 40 mg/L(removal effi.; 88.1%), and PAC was 50 mg/L(removal effi.; 90.1%). Alum was better than the PAC to remove the microlgae. In the water treatment processes such as rapid slow mixing and sedimentation the removal efficiency of microalgae with coagulants was 2 times higher than that of without. In optimal condition, the removal efficiencies of microalgae were nanoplankton > microplankton > picoplankton. Especially, the removal efficiency of the picoplankton was very low as below 30%.

• Korean Chemical Engineering Research
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• v.48 no.1
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• pp.75-79
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• 2010

The precursor powders with thin wall structure were prepared by spray pyrolysis from the spray solution with ethylenediaminetetraacetic acid, citric acid and $NH_4Cl$ flux. The $BaMgAl_{10}O_{17}:Eu$ phosphor powders formed from the spray solution without organic additives and flux material had sizes of $1{\sim}5{\mu}m$ and hollow structure with high thickness at post-treatment temperature of $1,200^{\circ}C$. However, $BaMgAl_{10}O_{17}:Eu$ phosphor powders formed from the spray solution with ethylenediaminetetraacetic acid, citric acid and $NH_4Cl$ flux had fine size and plate-like shape. The mean crystallite sizes of the phosphor powders with fine sizes were 23, 35, and 33 nm when the content of $NH_4Cl$ flux were 0, 6, 35 wt% of phosphor. The photoluminescence intensity of the phosphor powders formed from the spray solution with the optimum amount of $NH_4Cl$ flux as 35 wt% was 215% of that of the phosphor powders formed from the spray solution without flux material.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.19 no.4
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• pp.202-207
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• 2009

Nanocomposite formation of metal-metal oxide systems by mechanical alloying (MA) has been investigated at room temperature. The systems we chose are the $Fe_3O_4$-M (M = AI, Ti), where pure metals are used as reducing agent. It is found that $Fe/Al_2O_3$ and $Fe/TiO_2$ nanocomposite powders in which $Al_2O_3$ and $TiO_2$ are dispersed in ${\alpha}$-Fe matrix with nano-sized grains are obtained by MA of $Fe_3O_4$ with Al and Ti for 25 and 75 hours, respectively. It is suggested that the shorter MA time for the nanocomposite formation in $Fe/Al_2O_3$ is due to a large negative heat associated with the chemical reduction of magnetite by aluminum. X-ray diffraction results show that the average grain size of ${\alpha}$-Fe in $Fe/TiO_2$ nanocomposite powders is in the range of 30 nm. The change in magnetic properties also reflects the details of the solid-state reduction of magnetite by pure metals during MA.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.23 no.3
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• pp.135-141
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• 2013

Mechanical alloying was carried out to produce $CrSi_2$ thermoelectric compound using a mixture of elemental $Cr_{33}Si_{67}$ powders. An optimal milling and heat treatment conditions to obtain the single phase of $CrSi_2$ compound with fine microstructure were investigated by X-ray diffraction and differential scanning calorimetry measurement. $CrSi_2$ intermetallic compound with a grain size of 70 nm could be obtained by MA of $Cr_{33}Si_{67}$ powders for 70 hours and subsequently annealed at $650^{\circ}C$. Consolidation of the MA powders was performed in a spark plasma sintering (SPS) machine using graphite dies at $600{\sim}1000^{\circ}C$ under 60 MPa. The shrinkage of MA samples during SPS consolidation process increased gradually with increasing temperature up to $1000^{\circ}C$ and relatively significant at about $600^{\circ}C$. We tend to believe that these behaviors are deeply related to form a $CrSi_2$ compound during heating process, as can be realized from the DSC measurement. Electrical conductivity and Seebeck coefficient of sintered bodies were measured up to $900^{\circ}C$. Seebeck coefficient and power factor of $Cr_{33}Si_{67}$ compact prepared by MA and SPS at $1000^{\circ}C$ showed the maximum value of $125{\mu}V/K$ at $400^{\circ}C$ and $4.3{\times}10^{-4}W/mK^2$ at $350^{\circ}C$, respectively.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.23 no.5
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• pp.241-245
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• 2013

Granular bamboo-derived active carbons (AC) were impregnated (or coated) with $TiO_2$ nano crystalline powders. The photocatalytic activity of the $TiO_2$-impregnated active carbons ($TiO_2$/AC) were determined on the basis of the degradation rate of methylene-blue aqueous solution under UV irradiation. The active compounds of $TiO_2$ were impregnated onto the AC under moderate hydrothermal conditions (${\leq}200^{\circ}C$, pH 11). The mean size of $TiO_2$ particles calculated from BET surface area were found to be as 50 nm. The $TiO_2$ precipitates were coated on the cavities or pores on the surfaces of highly activated carbons. Since the hydrothermal process led to a lowering of the on-set temperature of the anatase-to-rutile transition of $TiO_2$ as low as $200^{\circ}C$, $TiO_2$ crystallites of a pure anatase or a mixed form with rutile were successfully coated on the AC depending on the synthesis temperatures.

• Journal of the Korean Magnetics Society
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• v.20 no.5
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• pp.196-200
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• 2010

$\gamma-Fe_2O_3$ nanoparticles have been prepared by a sol-gel method. The structural and magnetic properties have been investigated by XRD, VSM and Mossbauer spectroscopy. $\gamma-Fe_2O_3$ powder annealed at $150^{\circ}C$ has a spinel structure and superparamagnetical behavior. The estimated size of superparammagnetic $\gamma-Fe_2O_3$ nanoparticle is around 7 nm. The hyperfine fields at $-261^{\circ}C$ for the A and B patterns were found to be 503 and 485 kOe, respectively. The blocking temperature ($T_B$) of superparammagnetic $\gamma-Fe_2O_3$ nanoparticle is about $-183^{\circ}C$. The magnetic anisotropy constant of $\gamma-Fe_2O_3$ nanoparticle was calculated to be $1.6{\times}10^6ergs/cm^3$. $\gamma-Fe_2O_3$ nanoparticle annealed at $150^{\circ}C$ can be a candidate for biomedicine applications as magnetic carriers.