• Proceeding of EDISON Challenge
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• 2015.03a
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• pp.338-342
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• 2015

Ripples and charge impurity effect of graphene are considered as the origin of charge puddles in graphene sheet on SiO2. However, this topic is very controversial among researchers in graphene community. In this study, by using density functional theory, we calculate the band structure of the rippled graphene model and charged impurity model that is located close to the (0001) ${\alpha}$-quartz surface. We expect that this study will provide great insight on this matter.

• Journal of the Korean Ceramic Society
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• v.25 no.5
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• pp.431-436
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• 1988

The properties of scid-resistance to boiling HCl, thermal expansion coefficient and softening temperature of mother glass and glass-ceramic of LAS systems were investigated at the contents of SiO2 varing from 57 to 67wt%. The nucleation and growth of crystalline phase of LAS compositions were carried out at 50$0^{\circ}C$ and $700^{\circ}C$. The crystalline phase jconsists of lithium alumino silicate, lithum meta silicate, lithium disilicate, $\alpha$-crystobalite and $\alpha$-quartz. Lithium alumino silicate(virgilite) is the major crystalline phase in the glass ceramics. The degree of acid resistant property was increased in proportion with the silica content for both glass and ceramics. Glass-ceramic gives lower acid-resistance and thermal expansion coefficient while softening temperature shows higher for glass-ceramic than for mother glass.

• Journal of the Korean Ceramic Society
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• v.17 no.3
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• pp.141-144
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• 1980

Thermal expansion property of $SiO_2-Al_2O_3$ system consisted of Muan clay, Hadong Pink Kaolin and Dangjin Silica was studied. Specimens were heated at the constant rate of 18$0^{\circ}C$/hr to the max. temperatures of 115$0^{\circ}C$ to 130$0^{\circ}C$ with an interval of $25^{\circ}C$, and matured for 3hrs. The result of X-Ray diffraction analysis showed that main crystals formed were $\alpha$-quartz, $\alpha$-cristobalite and mullite. Linear thermal expansion was measured at 90$0^{\circ}C$. The results of the linear thermal expansion were decreased regularly with the increase of the sintering temperature in accordance with the following equation. $y=5$\chi$\perp1100^{\circ}$. Where $\chi$ is amounts of kaolin (wt%), and y is temperature of the changing point of linear thermal expansion.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.4 no.4
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• pp.336-346
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• 1994

We studied the reaction between silicon and carbon. Silicon granules and silicon with 0.2 wt% carbon powders were prepared for sample and then they were heated up to the $1450^{\circ}C, 1550^{\circ}C, 1650^{\circ}C, 1700^{\circ}C$ and were dwelled 1 hr and 4 hrs, respectively. we studied the change of morphologies of molten silicon and the formation of SiC following the reaction withcarbon using optical microscope, SEM, and XRD. Above the melting point of silicon, oxygens are precipitated during the decomposition of quartz used crucible. SiO formed from the reaction between molten silicon and precipitated oxygen evaporated and made the surface defects. SiC were formed with the reaction between the unreacted carbon and molten silicon. Polytype of the SiC formed at the solidification interface was ${\alpha}-SiC$.

• Resources Recycling
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• v.13 no.3
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• pp.19-26
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• 2004

In order to use the mine tailing which was generated in the flotation process of scheelite ore into the raw material of ordinary portland cement, the characteristics of the prepared cement clinker was investigated. Scheelite mine tailing is composed of 68.8% of $SiO_2$, 8.6% of $Al_2$$O_3$, 10.8% of $Fe_2$$O_3$, 5.0% of CaO, respectively. It exists as $\alpha$-quartz, muscovite, clinochlore and has 8.0% of 88 $\mu\textrm{m}$ residue. When LSF, SM, and IM of the raw materials (such as limestone, convertor slag, fly ash, and mine tailing) are 91.0, 2.60, and 1.60, respectively, the burnability index of the raw materials is 50.7, the crystal size of $C_3$S and $\beta$-C$_2$S in the prepared clinker is 15∼35$\mu\textrm{m}$, and about 3.8% of scheelite mine tailing can be used as raw material.

• 보존과학연구
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• s.21
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• pp.233-271
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• 2000

This study has proved if there are homogeneities in crystal structures, firing temperaures and element compositions of 69 specimens for potteries and soils from Changdo, Kangjin-gun, Jinjuk-Ri in Korea and Yaezhou inChina and obtained the following results.1. XRD analyses showed that soft potteries seemed to contain ($\alpha$)quartz, feldspar, while hard potteries seemed to contain ($\alpha$-)quartz, mullite, tridymite, feldspar. Jinjuk-Ri soils consisted of clays such as Kiolinite, Montmorillonite, Muscovite, Illite and, mica and feldspar etc.2. It was estimated that the firing temperatures which are determined by crystals using XRD, ranged from $550^{\circ}C$ to $870^{\circ}C$ for soft potteries and $870^{\circ}C$ to $975^{\circ}C$ for hard potteries.3. The firing temperatures for 4-pieces of Changdo pottery were measured by using TG-DTA, and it was found that specimen No. 10 was fired at temperatures below $600^{\circ}C$, while specimens No. 14, No. 23 and No. 29 were fired at temperatures above $1000^{\circ}C$.4. It was found that the specimems for potteries and porcelains from Changdo, Kangjin-gun, Jinjuk-Ri in Korea and Yaezhou in China were apparently classified into 4 clusters. This suggests that there are no correlations between the raw materials used in each 4 regions. Among the porcelains from Changdo, there were many typologically similar ones to those from Yaezhou in China in the 9th centry, but the analyses of porcelains only from Changdo, Kangjin in Korea and Yaezhouin China showed that they were classified into 3 clusters. This suggest that there are no correlations between the raw materials used for making porcelains in Changdo, Kangjin-gun, Jinjuk-Ri in Korea and Yaezhou in China.

• Proceedings of the Korea Association of Crystal Growth Conference
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• 1997.06a
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• pp.145-145
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• 1997

Recent progress of electric technology requires new piezoelectric crystals having superior properties such as zero temperature coefficients and large electromechanical coupling factors. We have developed a series of new leading chandidates, La$_3$Ga5SiO14(langasite, LGS), La3Nb0.5Ga5.5O14(LNG), La3Ta0.5O14(LTG), to satisfy those requirements. High quality LGS, LNG and LTG single crystals, with dimensions of 2 inches in diameter, were successfully grown by the Czochralski method at a pulling rate of 1mm/h. Since no variation of chemical composition was observed when whole melt in a crucible was crystallized, congruency of these compositions was confirmed. Physical constants such as elastic constants, dielectric constants and piezoelectric constants were measured. Filters and oscillators made of grown LGS, LNG and LTG single crystals showed superior properties such as three times wider passband than that of quartz, low insertion loss and easy processing, Langasite family crystals were shown to be superior materials to other known materials such as quartz, LiTaO$_3$, $\alpha$-AlPO$_4$ and Li$_2$B$_4$O7.

• Journal of the Korean Ceramic Society
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• v.11 no.1
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• pp.10-18
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• 1974

The hydration at $23^{\circ}C$ between $Ca(OH)_2$ and siliceous materials with various compositions of silica gel and quartz were studied in paste state, and also diatomite was empolyed as another form of silica. The effect of the structural state of silica on the pozzolanic reactivity was investigated by X-ray, DTA, electron microscopy, and chemical analysis. The results obtained were as follows. (1) The molar ratio of $Ca(OH)_2$ to silica gel(C/Sg) being changed in 0.49, 0.81 and 1.22, the free $Ca(OH)_2$ was disappeared within six hours, three days and two weeks respectively and ill-crystallized CSH(I) was formed. However, in the case fo molar ratio of C/Sg=2.45, almost lime was remained uncombinedly after twenty four weeks yet. (2) Though the molar ratio C/Sg of diatomite was 0.71, the hydration was stabilized at three weeks and the result exhibited very peculiar characteristics from silica gel. (3) Pozzolanic reactivity of quartz was negligible, but $\alpha$-cristobalite in diatomite showed appreciable reactivity. (4) The thermal curves showed the exothermic peaks in the range 830 to $930^{\circ}C$ and lower broad peaks at high temperature in the initial steps of hydration, transfered to lower temperature with sharp peaks by proceeding of hydration. (5) The samples containing more silica gel exhibited higher pozzolanic reactivity and martar strength, but the diatomite gave remarkable result for them and they were matched to the strength development rate.

• International Journal of Oral Biology
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• v.36 no.2
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• pp.103-108
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• 2011

Measurement of estrogen concentration in bio-samples are very important for differential diagnosis of various disease or evaluation of health status. However, it is difficult to collect immediate data of estrogen concentration because they are measured by radioimmunoassay or chromatography which need time- and cost-consuming sample pre-treatment. This study was performed for development of new estrogen biosensor employing taste principles, and for evaluation of cross reactivity between various steroid hormones. Gene sequence of ligand binding domain of ${\alpha}$-human estrogen receptor (amino acid 302-553; hER-LBD) was cloned from human breast cancer cell line. The proteins of hER-LBD were produced by T7-E.coli expression system, and isolated by chromatography. hER-LBD were coated on the gold plated quartz crystal (AT-cut 9MHz), and resonance frequencies were measured by universal frequency counter. Estradiol, progesterone, testosterone, and aldosterone were used for cross reactivity of the hER-LBD. We also monitored influences of pH change in resonance frequency. The resonance frequencies of hER-LBD coated quartz crystal were decreased during increase of estrogen concentration from $15 \;{\mu}g/mL$ to $50\;{\mu}g/mL$. However, similar steroid hormones, progesterone and aldosterone, did not elicit the change in resonance frequency. Testosterone evoke weak change in resonance frequency. The new estrogen biosensor was more sensitive in pH 7.2 than in pH 7.6. These results suggest that hER-LBD coated quartz crystal biosensor is a probable estrogen biosensor.

• Journal of the Mineralogical Society of Korea
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• v.30 no.2
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• pp.59-70
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• 2017

$SiO_2$ is one of the most abundant constituents of the Earth's crust and mantle. Probing its electronic structures at high pressures is essential to understand their elastic and thermodynamic properties in the Earth's interior. The in situ high-pressure x-ray Raman scattering (XRS) experiment has been effective in providing detailed bonding transitions of the low-z materials under extreme compression. However, the relationship between the local atomic structures and XRS features at high pressure has not been fully established. The ab initio calculations have been used to overcome such experimental difficulties. Here we report the partial density of states (PDOS) of O atoms and the O K-edge XRS spectra of ${\alpha}-quartz$, ${\alpha}-cristobalite$, and $CaCl_2$-type $SiO_2$ phases calculated using ab initio calculations based on the full-potential linearized augmented plane wave (FP-LAPW) method. The unoccupied O PDOSs of the $CaCl_2$-type $SiO_2$ calculated with and without applying the core-hole effects present significantly distinctive features. The unoccupied O p states of the ${\alpha}-quartz$, ${\alpha}-cristobalite$ and $CaCl_2$-type $SiO_2$ calculated with considering the core-hole effect present similar features to their calculated O K-edge XRS spectra. This confirms that characteristic features in the O K-edge XRS stem from the electronic transition from 1s to unoccupied 2p states. The current results indicate that the core-hole effects should be taken in to consideration to calculate the precise O K-edge XRS features of the $SiO_2$ polymorphs at high pressure. Furthermore, we also calculated O K-edge XRS spectrum for $CaCl_2$-type $SiO_2$ at ~63 GPa. As the experimental spectra for these high pressure phases are not currently available, the current results for the $CaCl_2$-type $SiO_2$ provide useful prospect to predict in situ high-pressure XRS spectra.