• Journal of the Korean Ceramic Society
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• v.36 no.12
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• pp.1350-1355
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• 1999

Sintering characteristics and dielectric properties of low temperature sinterable Glass/Ceramic dielectric materials were investigated. The dielectric materials which were developed for microwave frequency applications consist of SiO2-TiO2-Bi2O3-RO system(RO:BaO-CaO-SrO) crystallizable glass and Al2O3 as a ceramic filler. Sintering experiments showed that no more densification occurred above 80$0^{\circ}C$ and bulk density and shrinkage depended on Al2O3 content only. Results of dielectric measurements showed that $\varepsilon$r Q$\times$f and $\tau$f of the material containing 30wt% Al2O3 were 17.3, 600 and +23 ppm respectively. Those values for 45 and 60wt% Al2O3 samples were 11.6, 1400, +0.7 ppm and 7.2, 2000, -8.5 ppm, repectively. The results clearly showed that the Glas/Ceramic materials of present experiment decreased in $\varepsilon$r and increased in $\times$f value and changed from positive to negative value in $\tau$f value with the increasement of Al2O3 content.

• Journal of the Korean Ceramic Society
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• v.33 no.7
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• pp.832-838
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• 1996

Thermite reaction products of MgO and Al were added to MgO-C refractory to improve the properties of corrosion against the attack of slag, oxidation and mechanical spalling. Corrosion rate of MgO-C-MgAl2O4 spinel refractory at the ratio of 3.3(CaO/SiO2) slag was smaller than that of MgO-C and MgO-C-Al refractory. The excellent corrosion resistance of the MgO-C-MgAl2O4 spinel refractory against the slag attack was appeared by Al and MgAl2O4 spinel with high melting point and corrosion resistance and the high thermal conductivity and low thermal expansion of AIN. Hot M.O.R at 140$0^{\circ}C$ and the resistance of oxidation weight loss at 90$0^{\circ}C$ were 210kg/cm2 and -12% respectively.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.18 no.4
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• pp.160-164
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• 2008

Insulating and conducting 12CaO ${\cdot}7Al_2O_3$ (Cl2A7)-doped indium tin oxide (ITO) (ITO:Cl2A7 insulator and electride) thin films were deposited on glass substrates by an RF magnetron co-sputtering method with increasing number of insulating and conducting Cl2A7 target chips. The structural, electrical and optical properties of these films were investigated. The carrier concentration decreased and resistivity increased in the films with increasing number of Cl2A7 target chips. The optical transmittance of all of the thin films was above 80 % in the visible wavelength range. The structural property and surface roughness of the films were examined and the decrease of crystallinity and surface roughness was strongly dependent on the change of grain size.

• Journal of the Korean Ceramic Society
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• v.40 no.12
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• pp.1154-1158
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• 2003

Hydrothermal deposition of hydroxyapatite coatings on $Al_2$O$_3$ substrates was studied using aqueous solutions of Ca(NO$_3$)$_2$ㆍ4$H_2O$ and (NH$_4$)$_2$HPO$_4$ containing EDTA disodium salt as a chelating agent for $Ca^{2+}$. For the precipitation of the coatings the EDTA-Ca$^{2+}$ chelates were dissociated thermally at 20$0^{\circ}C$ or decomposed by oxidation with $H_2O$$_2$ at 9$0^{\circ}C$. Scanning electron microscopy and X-ray diffraction were used to investigate the deposition behavior and the phase of the coatings. Hydroxyapatite coatings were not deposited with the thermal dissociation method, whereas uniform deposition of the coatings (about 0.7 $\mu\textrm{m}$ thickness) was obtained with the oxidative decomposition method. The coatings consisted of fine rod-like hydroxyapatite crystals (hexagonal structure) with 60-80 nm diameters, having some preferred orientation with their length (i.e., the c axis) perpendicular to the substrate.ate.

• 한국정보디스플레이학회:학술대회논문집
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• 2006.08a
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• pp.921-924
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• 2006

In an attempt to enhance secondary electron emission characteristics of PDP, $12CaO{\cdot}7Al_2O_3$ electride was used as electron emission layer of PDP discharge cells. The compound was synthesized by Ca-treatment and its electron emission behavior during the glow discharge was measured. The results indicated that the spayed electride reduces the discharge voltage by ${\sim}20$ volts and decrease the discharge delay by more than 70%.

• Journal of the Mineralogical Society of Korea
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• v.22 no.4
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• pp.307-312
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• 2009

Motukoreaite and quintinite-3T, Mg-Al layered double hydroxides, were found in the Sinyangri Formation of Jeju Island. They fill the pores of basaltic volcaniclastic sediments in globular and botryoidal aggregates of fine platy particles. Globular aggregates of quintinite-3T were crusted with the parallel overgrowth of motukoreaite plates. X-ray diffraction data and chemical composition are consistent with those reported in literature, while the Mg/Al ratio of motukoreaite is higher. Structural formula of motukoreaite and quintinite-3T derived from electron microprobe analysis are $Na_{1.6}Ca_{0.1}Mg_{40.7}Al_{20.7}Si_{0.9}(CO_3)_{13.6}(SO_4)_{7.4}(OH)_{108}56H_2O$, and $Mg_{3.7}Al_{1.9}Si_{0.2}(OH)_{12}(CO_3)_{0.8}(SO_4)_{0.2}3H_2O$, respectively. Motukoreaite and quintinite-3T were formed by reaction between seawater and basaltic glass, and contributed to the cementation and lithification of the volcaniclastic sediments.

• Journal of the Korean earth science society
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• v.27 no.1
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• pp.49-60
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• 2006

The purpose of this study is to investigate geochemical characteristics for stream sediments in the Naju area. We collected 139 stream sediments samples from primary channels. Samples were dried slowly in the laboratory and chemical analysis was carried out using XRF. ICP-AES and NAA. In order to investigate geochemical characteristics, the geological groups categorized into granitic gneiss area, schist area, granite area, arenaceous rock area, tuff area, andesite area, and rhyolite area. Average contents of major elements for geological groups are $SiO_2\;58.37{\sim}66.06wt.%,\;Al_2O_3\;13.98{\sim}18.41wt.%,\;Fe_2O_3\;4.09{\sim}6.10wt.%,\;CaO\;0.54{\sim}1.33wt.%,\;MgO\;0.86{\sim}1.34wt.%,\;K_2O\;2.38{\sim}4.01wt.%,\;Na_2O\;0.90{\sim}1.32wt.%,\;TiO_2\;0.82{\sim}1.03wt.%,\;MnO\;0.09{\sim}0.15wt.%,\;P_2O_5\;0.11{\sim}0.18wt.%$. According to the comparison of average contents of major elements, $Al_2O_3\;and\;K_2O$ are higher in granitic gneiss area, $Fe_2O_3,\;CaO,\;P_2O_5$ are higher in tuff area, MgO and $TiO_2$ are higher in andesite area, $Na_2O_$ is higher in rhyolite area, $SiO_2$, and MnO are higher in arenaceous rock area. Average contents of minor and rare earth elements for geological groups are $Ba\;1278{\sim}1469ppm,\;Be\;1.1{\sim}1.5ppm,\;Cu\;18{\sim}25ppm,\;Nb\;25{\sim}37ppm,\;Ni\;16{\sim}25ppm,\;Pb\;21{\sim}28ppm,\;Sr\;83{\sim}155ppm,\;V\;64{\sim}98ppm,\;Zr\;83{\sim}146ppm,\;Li\;32{\sim}45ppm,\;Co\;7.2{\sim}12.7ppm,\;Cr\;37{\sim}76ppm,\;Cs\;4.8{\sim}9.1ppm,\;Hf\;7.5{\sim}25ppm,\;Rb\;88{\sim}178ppm,\;Sc\;7.7{\sim}12.6ppm,\;Zn\;83{\sim}143ppm,\;Pa\;11.3{\sim}37ppm,\;Ce\;69{\sim}206ppm,\;Eu\;1.1{\sim}1.5ppm,\;Yb\;1.8{\sim}4.4ppm$. According to the comparison of average contents of minor and rare earth elements for geological groups, Pb, Li, Cs, Hf, Rb, Sb, Pa, Ce, Eu, and Yb are higher in granitic gneiss area; Ba, Co, and Cr in schist area; Nb, Ni, and Zr in arenaceous rock area; Sr in tuff area: and Be, Cu, V, Sc, and Zn are such in andesite area.

• Journal of the Korean Chemical Society
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• v.39 no.1
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• pp.7-13
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• 1995

The crystal sructures of $X(Ca_{46}Al_{92}Si_{100}O_{384})$ and $Ca_{32}K_{28}-X(Ca_{32}K_{28}Al_{92}Si_{100}O_{384})$ dehydrated at $360^{\circ}C$ and $2{\times}10^{-6}$ Torr have been determined by single-crystal X-ray diffraction techniques in the cubic space group Fd3 at $21(1)^{\circ}C.$ Their structures were refined to the final error indices, R_1=0.096,\;and\;R_2=0.068$ with 166 reflections, and R_1=0.078\;and\;R_2=0.056$ with 130 reflections, respectively, for which I > $3\sigma(I).$ In dehydrated $Ca_{48}-X,\;Ca^{2+}$ ions are located at two different sites opf high occupancies. Sixteen $Ca^{2+}$ ions are located at site I, the centers of the double six rings $(Ca(1)-O(3)=2.51(2)\AA$ and thirty $Ca^{2+}$ ions are located at site II, the six-membered ring faces of sodalite units in the supercage. Latter $Ca^{2+}$ ions are recessed $0.44\AA$ into the supercage from the three O(2) oxygen plane (Ca(2)-O(2)= $2.24(2)\AA$ and $O(2)-Ca(2)-O(2)=119(l)^{\circ}).$ In the structure of $Ca_{32}K_{28}-X$, all $Ca^{2+}$ ions and $K^+$ ions are located at the four different crystallographic sites: 16 $Ca^{2+}$ ions are located in the centers of the double six rings, another sixteen $Ca^{2+}$ ions and sixteen $K^+$ ions are located at the site II in the supercage. These $Ca^{2+}$ ions adn $K^+$ ions are recessed $0.56\AA$ and $1.54\AA$, respectively, into the supercage from their three O(2) oxygen planes $(Ca(2)-O(2)=2.29(2)\AA$, $O(2)-Ca(2)-O(2)=119(1)^{\circ}$, $K(1)-O(2)=2.59(2)\AA$, and $O(2)-K(1)-O(2)=99.2(8)^{\circ}).$ Twelve $K^+$ ions lie at the site III, twofold axis of edge of the four-membered ring ladders inside the supercage $(K(2)-O(4)=3.11(6)\AA$ and $O(1)-K(2)-O(1)=128(2)^{\circ}).$

• Journal of the Korean Ceramic Society
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• v.47 no.5
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• pp.401-406
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• 2010

For the lower-temperature preparation of calcium monoaluminate(CA, C:CaO, A:$Al_2O_3$) clinker which is hard to synthesize purely within its melting point, an equimolar hydrate was obtained and then used as a starting raw material of clinker burning. The hydrate was prepared from a mixture of waste oyster shell and industrial aluminium hydroxide by heating to $1200^{\circ}C$, grinding and mixing with water. The hydrate was composed of amorphous aluminium hydroxide and $C_3AH_6$(H:$H_2O$) formed by resolution-precipitation mechanism of the system C-A-H. By heating the hydrate, nearly pure and porous calcium monoaluminate clinker was formed at $1400^{\circ}C$ which is fairly lower temperature than that of its melting point. The formation of calcium monoaluminate was performed mainly by the reaction between amorphous alumina and $C_{12}A_7$ caused by the decomposition of $C_3AH_6$. The immediate and earlier formation of $C_{12}A_7$ seemed to be accelerated by not only high surface area and instability of the thermally decomposed hydrate but also the catalytic effect of water decomposed from the hydrate. The final calcium monoaluminate clinker was very porous because of the influence of highly porous shape of the thermally decomposed hydrate.

• Proceedings of the Korean Vacuum Society Conference
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• 2007.08a
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• pp.109-109
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• 2007