• Korean Journal of Materials Research
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• v.8 no.12
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• pp.1165-1169
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• 1998

A single crystal cast blade was manufactured by CMSX 6, one of the first generarion nickel based single crystal superalloys by the selector method in a vacuum furnace. The single crystal has been grown with cooling rate of 2.5 mm/min, after pouring the molten alloy of 163$0^{\circ}C$ to the mold heated to 150$0^{\circ}C$. The cast structure could be classified into matrix (dendrite) and eutectic regions in ${\gamma}$'shape and size. The eutectic region showed higher Ti content. As the additional results of ${\gamma}$'precipitates by EPMA and CBED analysis the ${\gamma}$'size was less than 0.5~0.7$\mu\textrm{m}$, showing the chemical composition close to Ni$_3$Al of Ll$_2$ lattice structure. But ${\gamma}$'size has increased to bigger than 1.0$\mu\textrm{m}$, being near to eutectic region, changing its shape to bar or huge block types. These showed the chemical structure near to Ni$_3$Ti of D $O_{24}$ lattice structure. Therefore, ${\gamma}$'morphology of dendrite and eutectic regions depends absolutely on its chemical composition and lattice structure.

• Applied Chemistry for Engineering
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• v.8 no.3
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• pp.425-429
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• 1997

Polyisobutenylsuccinic anhydride(PIBSA), an intermediate for the lubricating oil additive, was prepared by the reaction of polyisobutylene(PIB) with maleic anhydride (MA). The functionality, which indicates the extent of reaction of PIB-a and MA, was determined in the various reaction conditions : fuctionality was 0.98 under the reaction conditions of no solvent for 12 hours at $190^{\circ}C$, 0.21 in benzyl alcohol solvent for 12 hours at $190^{\circ}C$, and 0.03~0.20 with various Lewis acids such as $AlCl_3$, $SnCl_4$, $Et_2AlCl$, and $TiCl_4$. The fuctionality also depended on the structure of PIBs. As ${\alpha}$-olefin content (exo-form) in PIB increased, the fuctionality had a higher value. The structure of PIBSA prepared from PIB and MA was determined with FT IR and $^1H$ NMR spectroscopy. Two strong anhydride IR bands at 1782 and $1855cm^{-1}$ were obserbed and two IR bands at 1639 and $897cm^{-1}$ for unsaturated groups of PIB disappeared. The presence of the anhydride was difficult to find by $^1H$ NMR spectroscopy because the anhydride protons gave relatively small peaks over a 2.0~3.0 range. Polyisobutenylsccinimide (PIBSI), a lublicating oil additive, was prepared by the reaction of PIBSA with diaminoethane.

• Korean Journal of Soil Science and Fertilizer
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• v.34 no.6
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• pp.373-379
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• 2001

The weathering rates and change of chemical composition of 6 residual Entisols derived from granite, granite-gneiss, limestone, sandstone, shale, amd basalt in Korea were studied. The chemical composition of each profile with parent rocks were determined using XRF with the physico-chemical properties and the morphology of soils. In the A horizons of all the soils except Euiseong series, the content of clay, organic matter and cation exchange capacity(CEC) showed higher than those of C horizon, but bulk density and pH showed lower than C horizon. Clay content in the soil from sandstone was decrease with soil depth, which may caused by the elluriation. In total element analysis. $SiO_2$ was high in the soil from granite. granite-gneiss, sandstone and compare with basalt and limestone. $Fe_2O_3$ and MgO was high in the soil from basalt, limestone and shale compare with granite. granite-gneiss and sandstone. And ignition loss was particularly high in the soil from basalt and limestone. The rate of element loss was higher in base cations(Ca, K, Mg, Na) than Si, Al, Fe in the soils. The concentrations of $TiO_2$ in the A horizon compare with that of the C horizon was due to resulting from losses of other less stable elements existed. Considering with relative rate of each elements in soils, $SiO_2$ and $Al_2O_3$ which originated from sandstone and granite, granite-gneiss, sandstone, shale, and basalt were lost higher than those from lime tone, but loss of basic cations were more in the soil from limestone which may be rapid weathering of calcite. The magnitude of losses of the overall elements were increased in the order of the soils from sandstone and granite ${\gg}$ limestone and shale) granite-gneiss and basalt.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.57 no.11
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• pp.2015-2022
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• 2008

The effect of content of $Al_2O_3+Y_2O_3$ sintering additives on the densification behavior, mechanical and electrical properties of the pressureless-sintered $SiC-ZrB_2$ electroconductive ceramic composites was investigated. The $SiC-ZrB_2$ electroconductive ceramic composites were pressurless-sintered for 2 hours at 1,700[$^{\circ}C$] temperatures with an addition of $Al_2O_3+Y_2O_3$(6 : 4 mixture of $Al_2O_3$ and $Y_2O_3$) as a sintering aid in the range of $8\;{\sim}\;20$[wt%]. Phase analysis of $SiC-ZrB_2$ composites by XRD revealed mostly of $\alpha$-SiC(6H), $ZrB_2$ and In Situ YAG($Al_5Y_3O_{12}$). The relative density, flexural strength, Young's modulus and vicker's hardness showed the highest value of 89.02[%], 81.58[MPa], 31.44[GPa] and 1.34[GPa] for $SiC-ZrB_2$ composites added with 16[wt%] $Al_2O_3+Y_2O_3$ additives at room temperature respectively. Abnormal grain growth takes place during phase transformation from $\beta$-SiC into $\alpha$-SiC was correlated with In Situ YAG phase by reaction between $Al_2O_3$ and $Y_2O_3$ additive during sintering. The electrical resistivity showed the lowest value of $3.l4{\times}10^{-2}{\Omega}{\cdot}cm$ for $SiC-ZrB_2$ composite added with 16[wt%] $Al_2O_3+Y_2O_3$ additives at 700[$^{\circ}C$]. The electrical resistivity of the $SiC-TiB_2$ and $SiC-ZrB_2$ composite was all negative temperature coefficient resistance (NTCR) in the temperature ranges from room temperature to 700[$^{\circ}C$]. Compositional design and optimization of processing parameters are key factors for controlling and improving the properties of SiC-based electroconductive ceramic composites.

• 한국정보디스플레이학회:학술대회논문집
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• 2004.08a
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• pp.1091-1094
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• 2004

High-luminous efficiency full-color emissions in photoluminescence (PL) were obtained in $GdVO_4$ phosphor thin films co-doped with various amounts of Eu, Er and/or Tm and postannealed at approximately 1000$^{\circ}C$. The $GdVO_4$:Eu,Er,Tm phosphor thin films were deposited on thick $BaTiO_3$ ceramic sheets by r.f. magnetron sputtering using powder targets and postannealed in an air atmosphere. The rare earth (RE) content (RE/(Gd+V+RE) atomic ratio) in the oxide phosphor thin films was varied in the range from 0.1 to 2 at.%. It was found that the excitation of $GdVO_4$:Eu.Er,Tm thin films is attributed to band-to-band transition. A white PL emission was obtained in a $GdVO_4$:Eu,Er,Tm thin film with Eu, Er and Tm contents of 0.2, 0.7 and 1 at.%, respectively: CIE chromaticity color coordinates. (X=0.352 and Y=0.351). In addition, a white emission was obtained in a thin-film electroluminescent (TFEL) device made with this thin film.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2002.05a
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• pp.215-225
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• 2002

In order to enhance the thermal stability of binder materials of bonded type solid lubricants, several combinations of metal-alkoxide based sol-gel materials such as methyltrimethoxysilane(MTMOS), $titaniumisopropoxide(Ti(Opr^{j})_{4})$, $zirconiumisopropoxide(Zr(Opr^{j})_{4})$ and $aluminumbutoxide(Al(Obu^{t})_{4})$ were chemically modified by epoxy-, acrylic- and fluoro-silane compounds, respectively, in this work. Friction and wear characteristics of these hybrid ceramic materials were tested with a micro tribe-tester where a reciprocating steel ball slid on a test material, and the tribological property was also evaluated with respect to both heat-curing temperature and tile time. Test results generally showed that hybrid ceramic materials modified by epoxy-silane compounds had a low friction compared to others. And the higher heat-curing temperature and the longer heat treatment time resulted in the higher friction and the lower wear. IR spectroscopic analyses revealed that it was caused mainly by the increased metal oxide content in hybrid ceramics when the heat-curing temperature was over $320^{\circ}C$.

• Ocean and Polar Research
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• v.24 no.2
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• pp.167-175
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• 2002

Sediment from six piston cores from the East Sea (Sea of Japan) was analyzed for evidence of paleoceanographic changes and paleoclimatic variation. A distinct geochemical boundary is evident in major element concentrations and organic carbon content of most cores near the 10-ka horizon. This distinctive basal Holocene change is interpreted to be largely the result of changing sediment sources, an interpretation supported by TiO_2/Al_2O_3$ ratios. Organic carbon and carbonate contents also differ significantly between the Holocene and glacial intervals. The C/N ratio of organic matter is greater than 10 during the glacial period, but is less than 10 for the Holocene, suggesting that the influx of terrigenous organic matter was more volumetrically important than marine organic matter during glacial times. The chemical index of weathering (CIW) is higher for the Holocene than the glacial interval, and changes markedly at the basal Holocene geochemical boundary. Silt fractions are higher in the glacial interval, suggesting a strong effect of climate on silt particle transportation: terrigenous aluminosilicates and continental organic carbon transport were higher during glacial times than during the Holocene. Differences in sediment composition between the Holocene and glacial period are interpreted to have been climatically induced.

• Tribology and Lubricants
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• v.18 no.5
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• pp.324-332
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• 2002

In order to enhance the thermal stability of binder materials of bonded type solid lubricants, several metal-alkoxide based sol-gel materials such as methyltrimethoxysilane(MTMOS), titaniumisopropoxide$(Ti(Opr^i)_4),$ zirconiumisopropoxide $(Zr(Opr^i)_4)$ and aluminumbutoxide$(Al(Obu^t)_4)$ were chemically modified by epoxy-, acrylic- and fluoro-silane compounds, respectively. Friction and wear characteristics of these hybrid ceramic materials were tested with a micro tribo-tester, and evaluated with respect to both heat-curing temperature and the time. Test results generally showed that hybrid ceramic materials modified by epoxy-silane compounds had a low friction compared to others. And the higher het-curing temperature and the longer heat treatment time resulted in the higher friction and the lower wear. IR spectroscopic analyses revealed that these results were caused mainly by the increased metal oxide content in hybrid ceramics when the heat-curing temperature was over $320^{\circ}C.$

• Korean Journal of Materials Research
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• v.16 no.1
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• pp.30-36
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• 2006

A novel method was proposed to grow an epitaxial $CoSi_2$ on (100)Si substrate. A $CoN_x$ interlayer was deposited by reactive sputtering of Co in an Ar+$N_2$ flow. From the Ti/Co/$CoN_x$/Si structure, a uniform and thin $CoSi_2$ layer was epitaxially grown on (100)Si by annealing above $700^{\circ}C$. Two amorphous layers were found at the $CoN_x$/Si interface, where the top layer has a silicon nitride (Si-N) bonding state with some Co content and the bottom layer has a Co-Si intermixing state. The SiNx amorphous layer seems to play a critical role of suppressing the diffusion of Co into Si substrate for the direct formation of epitaxial $CoSi_2$.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.08a
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• pp.31-34
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• 2003

($Ba_{0.6-x}Sr_{0.4}Ca_x)TiO_3$ (BSCT) (x=0.10, 0.15, 0.20) powder, prepared by the sol-gel method, were mixed with organic vehicle and the BSCT thick films were fabricated by the screen-printing techniques on alumina substrates using the BSCT paste. The structural and the electrical properties were investigated for various composition ratio and sintering temperature. BSCT thick film thickness, obtained by four printings, was approximately 110 ~ 120 ${\mu}m$. The Curie temperature and dielectric constant at room temperature were decreased with increasing Ca content. The relative dielectric constant, dielectric loss and tunability of the BSCT(50/40/10) specimen, which was sintered at $1420^{\circ}C$ and measured at 1MHz, were about 910, 0.46% and 9.28% at 5kV/cm, respectively.