• Korean Journal of Materials Research
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• v.19 no.10
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• pp.550-554
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• 2009

Unreported dielectrics based on the binary system of MgO-SiO$_2$ were investigated as potential candidates for microwave dielectric applications, particularly those demanding a high fired density and high quality factors. Extensive dielectric compositions having different molar ratios of MgO to SiO$_2$, such as 2:1, 3:1, 4:1, and 5:1, were prepared by conventional solid state reactions between MgO and SiO$_2$. 1 mol% of V$_2$O$_5$ was added to aid sintering for improved densification. The dielectric compositions were found to consist of two distinguishable phases of Mg$_2$SiO$_4$ and MgO beyond the 2:1 compositional ratio, which determined the final physical and dielectric properties of the corresponding composite samples. The increase of the ratio of MgO to SiO$_2$ tended to improve fired density and quality factor (Q) without increasing grain size. As a promising composition, the 5MgO.SiO$_2$ sample sintered at 1400 $^{\circ}C$ exhibited a low dielectric constant of 7.9 and a high Q $\times$ f (frequency) value of $\sim$99,600 at 13.7 GHz.

• Korean Journal of Metals and Materials
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• v.49 no.7
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• pp.565-569
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• 2011

Nanopowders of MgO, $Al_2O_3$ and $SiO_2$ were made by high-energy ball milling. The fast sintering of nanostructured $Al_2O_3-MgSiO_3-SiO_2$ composites was investigated from mechanically activated powders of MgO, $Al_2O_3$ and $SiO_2$ by a pulsed-current activated sintering process. Nanocrystalline materials have received much attention as advanced engineering materials with improved physical and mechanical properties; in particular greater strength, hardness, excellent ductility and toughness. Highly dense nanostructured $Al_2O_3- MgSiO_3-SiO_2$ composites were produced with simultaneous application of 80 MPa and pulsed output current of 2800A within 2 minutes. The sintering behavior, grain size and mechanical properties of $Al_2O_3-MgSiO_3-SiO_2$ composites were investigated.

• Proceedings of the Plant Resources Society of Korea Conference
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• 2018.10a
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• pp.132-132
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• 2018

The aim of this study was to enhance the Tartary buckwheat growth and phenolic profile by the application of $SiO_2$ on potsin the glasshouse. The liquid of $SiO_2$ were applied at three times after three weeks of sowing at ten days interval. The doses of the $SiO_2$ was low (2.5 ml/5 L water), high (10 ml in 5 L water) and control experiment was done without $SiO_2$. In this study, it is clearly shown that high dose of $SiO_2$ increased the buckwheat plant growth including, plant height, leaf length and width, stem diameter, fresh weight and number of seed per plant compared to control treatment. In the same way, the total phenolic compound (1421 mg/100 g), total flavonoid (35.1 mg/100g), rutin (3,130 mg/100g) and DPPH (82%) in plant were also increased high dose of $SiO_2$ compared to control (1,175 mg/100g, 31.9mg/100g, 860 mg/100g, 59%, respectively). Moreover, higher phenolic compound (1,421 mg/100g) and DPPH (82%) was observed in plant compared to seed (196 mg/100mg, 72 %, respectively). In the contrary, total flavonoid (36.2 mg/100g) and rutin (1,400 mg/100g) was higher in buckwheat seed compared to plant (35.1 mg/100g, 3,130 mg/100g, respectively). Finally, it is concluded that higher dose of $SiO_2$ enhance buckwheat growth and phenolic profile. Further investigation is needed to evaluate the optimum dose of $SiO_2$ according to soil conditions in the field.

• Journal of Korea Foundry Society
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• v.20 no.1
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• pp.13-20
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• 2000

In the present study,($10%Al_2O_3+5%Si$)/AZ91 Mg hybrid composite was fabricated using the squeeze casting method. During squeeze casting, Molten Mg was infiltrated into the preform of $10%Al_2O_3+5%Si$ and reaction product of $Mg_2Si$ intermetallic compound was formed by the reaction between molten Mg and Si Powder. Microstructure has been observed and mechanical properties were evaluated for the reaction squeeze cast(RSC) hybrid composite. It was found that Si powder totally reacted with molten Mg to form $Mg_2Si$. Reinforcement($Al_2O_3$) and the reaction product ($Mg_2Si$) are fairly uniformly distributed in Mg Matrix for the squeeze cast hybrid composite. Mechanical Properties were improved with hybridization of reinforcements, namely higher hardness and enhanced wear resistance comparing squeeze cast($15%Al_2O_3$)/AZ91 Mg composite.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.11a
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• pp.392-393
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• 2007

PDP용 녹색 $Zn_2SiO_4$:Mn 형광체의 발광특성과 결정성을 향상시키기 위해 co-dopant로 Mg를 첨가한 $(Zn_{1-x}Mg_x)_2SiO_4$:Mn 형광체를 합성하였다. 합성된 형광체의 발광특성을 PL로 조사한 결과, $Zn_2SiO_4$:Mn 형광체는 Mg의 농도에 관계없이 530nm에서 녹색 발광을 하였고, Mg의 농도가 0.5 mol%일 때 가장 높은 발광세기가 나타났다. 이것은 Zn과 이온반경이 비슷한 Mg가 치환되어 모체에서의 Mn으로의 에너지 전이가 증가하여 발광세기가 증가한 것으로 생각된다.

• Korean Journal of Materials Research
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• v.28 no.8
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• pp.474-477
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• 2018

$Ca_3MgSi_2O_8:Eu^{2+}$(x = 0.003, 0.005, 0.007, 0.01, 0.03 mol) white phosphors for Light Emitting Diodes(LED) are synthesized with different concentrations of $Eu^{2+}$ ions using a solid state reaction method. The crystal structures, surface and optical properties of the phosphors are investigated using X-Ray Diffraction(XRD), Scanning Electron Microscope(SEM) and photoluminescence(PL). The X-Ray Diffraction results reveals that the crystal structure of the $Ca_3MgSi_2O_8:Eu^{2+}$ is a monoclinic system. The particle size of $Ca_3MgSi_2O_8:Eu^{2+}$ white phosphors is about $1{\sim}5{\mu}m$, as confirmed by SEM images. The maximum emission spectra of the phosphors are observed at 0.01 mol $Eu^{2+}$ concentration. The decrease in PL intensity in the $Ca_3MgSi_2O_8:Eu^{2+}$ white phosphors with $Eu^{2+}$ concentration is interpreted by concentration quenching. The International Commission on Illumination(CIE) coordinate of 0.01 mol Eu doped $Ca_3MgSi_2O_8$ is X = 0.2136, Y = 0.3771.

• Korean Chemical Engineering Research
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• v.57 no.5
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• pp.714-722
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• 2019

Catalysts were prepared by using incipient wetness impregnation method with 17 wt% Ni on a support ($SiO_2-Y_2O_3$, $Al_2O_3$, $SiO_2-ZrO_2$, $SiO_2$, $TiO_2$, MgO) and the catalytic activity in the reductive amination of ethanol with ammonia in the presence of hydrogen was compared and evaluated. The catalysts used before and after the reaction were characterized using X-ray diffraction, nitrogen adsorption, ethanol-temperature programmed desorption (EtOH-TPD), isopropanol-temperature programmed desorption (IPA-TPD), and hydrogen chemisorption etc. In the case of preparing $ZrO_2$ and $Y_2O_3$ supports, the small amount of Si dissolution from the Pyrex reactor surface provoked the formation of mixed oxides $SiO_2-ZrO_2$ and $SiO_2-Y_2O_3$. Among the catalysts used, $Ni/SiO_2-Y_2O_3$ catalyst showed the best activity, and this good activity was closely related to the highest nickel dispersion, and low desorption temperature in EtOH-TPD and IPA-TPD. The low catalytic activity on Ni/MgO catalysts showed low activity due to the formation of NiO-MgO solid-solutions. In the case of $Ni/TiO_2$, the reactivity was low due to the low nickel metal phase due to strong metal-support interaction. In the case of using a support as $SiO_2-Y_2O_3$, $Al_2O_3$, $SiO_2-ZrO_2$, and $SiO_2$, the selectivities of ethylamines and acetonitrile were not significantly different at similar ethanol conversion.

• Journal of the Korean Vacuum Society
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• v.9 no.3
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• pp.227-232
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• 2000

$MgTiO_3$thin films have been grown on various substrates by pulsed laser deposition (PLD) to investigate the application for microwave dielectrics and optical devices. Epitaxial $MgTiO_3$thin films were obtained on sapphire (c-plane$A1_2O_3$$MgTiO_3$thin films deposited on $SiO_2/Si$ and platinized silicon ($Pt/Ti/SiO_2/Si$) substrates were highly oriented. $MgTiO_3$thin films grown on sapphire were transparent in the visible and had a sharp absorption edge about 290 nm. These $MgTiO_3$thin films had extremely fine feature of surface morphology, i.e., rms roughness of 0.87 nm, which was examined by AFM. We have investigated the dielectric properties of the $MgTiO_3$thin films in $MIM(Pt/MgTiO_3/Pt)$ capacitors. Dielectric constant and loss of $MgTiO_3$thin films deposited by PLD were about 24 and 1.5% at 1 MHz, respectively. These $MgTiO_3$thin films also exhibited little dielectric dispersion.

• Korean Journal of Metals and Materials
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• v.49 no.8
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• pp.614-618
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• 2011

Nanopowders of MgO, $Al_2O_3$ and $SiO_2$ were made by high energy ball milling. The rapid sintering of nanostructured $MgAl_2O_4-Mg_2SiO_4$ composites was investigated by a high-frequency induction heating sintering process. The advantage of this process is that it allows very quick densification to near theoretical density and inhibition of grain growth. Nanocrystalline materials have received much attention as advanced engineering materials with improved physical and mechanical properties. As nanomaterials possess high strength, high hardness, excellent ductility and toughness, undoubtedly, more attention has been paid for the application of nanomaterials. Highly dense nanostructured $MgAl_2O_4-Mg_2SiO_4$ composites were produced with simultaneous application of 80MPa pressure and induced output current of total power capacity (15 kW) within 2min. The sintering behavior, gain size and mechanical properties of $MgAl_2O_4-Mg_2SiO_4$ composites were investigated.

• Journal of the Mineralogical Society of Korea
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• v.27 no.1
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• pp.1-15
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• 2014

Probing the electronic structures of crystalline Mg-silicates at high pressure is essential for understanding the various macroscopic properties of mantle materials in Earth's interior. Quantum chemical calculations based on the density functional theory are used to explore the atomic configuration and electronic structures of Earth materials at high pressure. Here, we calculate the partial density of states (PDOS) and O K-edge energy-loss near-edge structure (ELNES) spectra for $MgSiO_3$ perovskite at 25 GPa and 120 GPa using the WIEN2k program based on the full-potential linearized projected augmented wave (FP-LPAW) method. The calculated PDOS and O K-edge ELNES spectra for $MgSiO_3$ Pv show significant pressure-induced changes in their characteristic spectral features and relative peak intensity. These changes in spectral features of $MgSiO_3$ Pv indicate that the pressure-induced changes in local atomic configuration around O atoms such as Si-O, O-O, and Mg-O length can induce the significant changes on the local electronic structures around O atoms. The result also indicates that the significant changes in O K-edge features can results from the topological densification at constant Si coordination number. This study can provide a unique opportunity to understand the atomistic origins of pressure-induced changes in local electronic structures of crystalline and amorphous $MgSiO_3$ at high pressure more systematically.