• 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.

• Journal of Power System Engineering
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• v.21 no.2
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• pp.14-19
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• 2017

The corrosion characteristics of Al-Si-Mg alloy were investigated in $O_2$ and $H_2S/H_2$ environments at high temperature. The weight gain and the reaction rate constant of the Al-Si-Mg alloy were measured in the oxygen and hydrogen sulfide environments at 773K. The weight gain of Al-Si-Mg alloy was showed parabolic increase in the oxygen and hydrogen sulfide environments. The reaction rate constants were confirmed to be $1.45{\times}10^{-4}mg^2cm^{-4}sec^{-2}$ in the oxygen environment and $6.19{\times}10^{-4}mg^2cm^{-4}sec^{-2}$ in the hydrogen sulfide environment respectively. As a result of XPS analysis on the specimen surface, $Al_2O_3$ and MgO compounds were detected in oxygen environment and $Al_2(SO_4)_3$ sulfate was detected in the hydrogen sulfide environment. Corrosion rate of Al-Si-Mg alloy was about 4.3 times faster in hydrogen sulfide environment than oxygen environment.

• Journal of the Mineralogical Society of Korea
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• v.22 no.4
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• pp.343-352
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• 2009

High-resolution Solid-state NMR provides element specific and quantitative information and also resolves, otherwise overlapping atomic configurations in multi-component non-crystalline silicates. Here we report the preliminary results on the effect of composition on the structure of CMAS (CaO-MgO-$Al_2O_3-SiO_2$) silicate glasses, as a model system for basaltic magmas, using the high-resolution 1D and 2D solid-state NMR. The $^{27}Al$ MAS NMR spectra for the CMAS silicate glasses show that four-coordinated Al is predominant, demonstrating that $Al^{3+}$ is network forming cation. The peak position moves toward lower frequency about 4.7 ppm with increasing $X_{MgO}$ due to an increase in $Q^4$(4Si) fraction with increasing Si content, indicating that Al are surrounded only by bridging oxygen. $^{17}O$ MAS NMR spectra for $CaAl_2SiO_6$ and $CaMgSi_2O_6$ glasses qualitatively suggest that NBO fraction in the former is smaller than that in $CaMgSi_2O_6$ glasses. As $^{17}O$ 3QMAS NMR spectrum of model quaternary aluminosilicate glass resolved distinct bridging and non-bridging oxygen environments, atomic structure for natural magmas can also be potentially probed using high-resolution 3QMAS NMR.

• Journal of the Korean Ceramic Society
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• v.33 no.6
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• pp.653-659
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• 1996

• 한국정보디스플레이학회:학술대회논문집
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• 2004.08a
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• pp.575-578
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• 2004

The charging tendency of $Zn_2SiO_4:Mn^{2+}$ phosphor surface was modified in order to improve discharging characteristic of green cell in an ac-plasma display panel (ac-PDP). The Zinc-silicate ($Zn_2SiO_4:Mn^{2+}$) green-emitting phosphor was coated with magnesium oxide(MgO), which is viable to have positive charge on the surface. After fabricating the green cell with MgO-coated $Zn_2SiO_4:Mn^{2+}$, the electrical and optical properties in the cell were examined. It was found that the dynamic voltage margin could be increased while the address time was reduced. It may be ascribed to the change of charging tendency of $Zn_2SiO_4:Mn^{2+}$ phosphor by MgO coating, which makes it possible to stable wall-charge accumulation. When $Zn_2SiO_4:Mn^{2+}$ phosphor was coated with 1.3wt%-MgO, the address time was reduced 1.2 ${\mu}s$ and the address voltage lowered 25 V without any misfiring problem, compared to those of typical $Zn_2SiO_4:Mn^{2+}$ phosphor layer. The luminescence intensity of green cell using MgO-coated phosphor layer was also improved by 10%.

• Journal of the Korean Ceramic Society
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• v.31 no.5
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• pp.505-512
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• 1994

It has been reported that a biocement obtained by mixing CaO-SiO2-P2O5 glass powder and ammonium phosphate solution has biocompatibility as well as high strength. However, the compositional dependence on its hardening and hydroxyapatite formation phenomena has not been studied. Therefore, the main objective of this work is to study the effects of P2O5, MgO in CaO-SiO2 system glass on the hardening and hydroxyapatite formation. When more than 50 mole% of CaO containing CaO-SiO2 glasses was reacted with ammonium phosphate solution, CaNH4PO4.H2O crystal was formed, but the glass with less than 50 mol% of CaO formed (NH4)2HPO4 and NH4H2PO4 crystals which are derived from ammonium phosphate solution without reacting with the glasses. As the amount of P2O5 in CaO-SiO2-P2O5 glass system was increased, the formation of CaNH4PO4.H2O crystal was enhanced. When those hardened samples were reacted with tris-buffer solution, hydroxyapatite was obtained only for the sample with CaNH4PO4.H2O. While the substitution of MgO for CaO decreased the formation of CaNH4PO4.H2O crystal. MgNH4PO4.H2O crystla was formed in high MgO containing glass, which did not react with tris-buffer solution.

• Korean Journal of Materials Research
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• v.12 no.11
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• pp.870-874
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• 2002

$Mg_2$$SiO_4$: Dy, Tb pellets were made by using a sintering process, including pressing and heat treatment. In the present study, the optimum parameters of the sintering for the $Mg_2$$SiO_4$: Dy, Tb pellets obtained such as the pressing pressure, the sintering temperature and the sintering time were in terms of thermoluminescence. Experimental results showed that the main peak of the glow curve for $Mg_2$$SiO_4$: Dy, Tb thermoluminescence dosimeter was clearly correlated with the energy of the UV and with the grain size. The intensity of the TL glow curve increased and its main peak position shifted to lower temperature with increasing UV irradiation time.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.11a
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• pp.274-274
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• 2007

LTCC 소재로 응용을 위해 Mg-Si-O계 세라믹스에 glass frit을 첨가하여 소결 및 마이크로파 유전특성에 관한 연구를 진행하였다. $Mg_2SiO_4$를 기본조성으로 하고 $B_2O_3-ZnO-Na_2O-SiO_2-Al_2O_3$계 glass를 20~40wt%로 첨가하여 $900^{\circ}C$에서 1시간 소결하였을 때 glass 함량이 증가함에 따라 밀도$(g/cm^3)$ 및 유전율$(\varepsilon_r)$은 증가하였고 품질계수$(Q{\times}f_0)$ 값은 감소하는 경향을 보였다. $900^{\circ}C$에서 1시간 소결한 소결체의 유전특성은 유전율 $(\varepsilon_r)$ = 6.5, 품질계수 $(Q{\times}f_0)$ = 4,000(GHz), 온도계수 $({\tau}_f)={\pm}10ppm/^{\circ}C$로 우수한 특성을 확인하였다. 그리고 Glass Milling 효과에 따른 glass-ceramics 소결체의 미세구조, 마이크로파 유전특성을 비교 고찰하였다.

• Journal of the Korean Ceramic Society
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• v.33 no.9
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• pp.985-994
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• 1996

The initiation and growth of $\alpha$-Al2O3/metal composites by the directed oxidation of molten commercial AlZnMg-alloy at 1223-1423K were investigated. Spontaneous bulk growth did not occur on the alloy alone. but the uniform initiation and growth of the composite were obtained by putting a thin layer of SiO2 particles on the surface of the alloy. Without SiO2 the external surface of the oxide layer was convered by MgO and MgAl2O4. But with the SiO2 reaction initiate the porous ZnO layers were found on the growth surface. The higher process temperature yielded a lower metal content. The oxidation product of $\alpha$-Al2O3 was found to be oriented with c-axis parallel to th growth direction. The growth rates increased with temperature and the apparent activation energy was 111.8 kJ/mol.

• Bulletin of the Korean Chemical Society
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• v.18 no.2
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• pp.203-208
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• 1997

A series of MgO-SiO2 catalysts were prepared by coprecipitation from the mixed solution of magnesium chloride and sodium silicate. Some of the sample were modified with 1 N H2SO4 and used as modified catalysts. The addition of MgO to SiO2 caused the increase of acidity and the shift of O-H and Si-O stretching bands of the silanol group to a lower frequency in proportion to the MgO content. The acid structure of MgO-SiO2 agreed with that proposed by Tanabe et al.. Catalytic activity for 2-propanol dehydration increased in relation to the increase of acidity and band shift to a lower frequency.