• Journal of the Korean Ceramic Society
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• v.30 no.6
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• pp.433-440
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• 1993

The bioactivity of glasses in the CaO-SiO2 system and CaO-P2O5-SiO2 system with less than 10mol% of P2O5 was investigated by in vitro test in simulated body flood(SBF). The formation of Ca.P film and hydroxyapatite on the surface of glasses after in vitro test was analysed by X-ray photoelectron spectoscopy (XPS), fourier transform infrared reflection spectroscopy (FT-IRRS), energy dispersive X-ray spectroscopy (EDS), and scanning electron microscopy (SEM) observation. In the early stage of Ca.P film formation after in vitro test for CaO-SiO2 and CaO-P2O5-SiO2 glasses, the rate of Ca.P film formation on the surface of the glasses was dependent of structural parameter (Y) evaluated from the glass composition. First, in the case of the glasses having Y value below 2, Ca.P film and SiO2-rich layer were formed simultaneously, and there were no differences of the rate of Ca.P film formation in terms of the Y values. Second, in the case of the glasses having Y value above 2, the SiO2-rich layer was formed, and then Ca.P.Si mixed layer was formed in the silica gel structure of the SiO2-rich layer, and finally the Ca.P film on the surface of SiO2-rich layer. The rate of Ca.P film formation delayed as the Y values increased. The rate of hydroxyapatite formation of glasses (the rate of transformation from Ca.P film to hydroxyapatite) seems to be propotional to the rate of Ca.P film formation and Y value. The rate of hydroxyapatite formation of glasses belonging to the second group was delayed as structural parameter increased, and the hydroxyapatite crystal showed spherical growth in the early reaction stage, and then showed silkworm-like linear growth as the reaction time increased.

• Journal of the Korean Ceramic Society
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• v.39 no.6
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• pp.604-609
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• 2002

Nanosized $BaCeO_3$ powders with the stoichiometric composition of a molecular level were synthesized by the citrate process based on the Pechini method. Polymeric precursor was formed by use of citric acid and ethylen glycol, as chelating agent of metal ions and reaction medium, respectively. Single phase orthorhombic structured $BaCeO_3$powders, about 100 nm sized and uniform shaped were obtained through the calcination of the polymeric precursor at $900^{\circ}C$ for 4 h. Extremely small quantities of carbonate ions($CO_^{2-}$) were completely decomposed at over $1100^{\circ}C$. The mean size of the powders was increased twice, however, it has very uniform distribution in its size and shape.

• Journal of the Korean Ceramic Society
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• v.36 no.2
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• pp.122-129
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• 1999

Alumina tapes, having various weight ratios of alumina powder/(alumina+binder+plasticizer), X, and binder / (binder+plsticizer), Y, were prepared and their complex modulus was measured using Micro Fourier Rheometer. As the X and Y ratios increased, Transfer function(TF) magnitude and Transfer function (TF) phase increased and decreased, respectively, indicating that the elastic modulus of the tapes depends on the weight ratios. The temperature dependence of the viscosity of the tapes was visualized by the decreased TF magnitude and the increased TF phase. The Y ratio dependence of the complex modulus related to the glass transition temperature of the tapes and the moduls change by the Y ratio was higher than that by the X ratio within the comperature of the tapes and the modulus changes by the Y ratio was higher than that by the X ratio within the composition range, investigated in the present study. The measurement of the complex modulus of the alumina tapes suggested that the TF phase should be higher that 17$^{\circ}$for the tapes to be utilized for 3-dimensional shaping.

• Journal of the Korean Ceramic Society
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• v.45 no.10
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• pp.644-650
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• 2008

It has been proposed that the Cao-$SiO_2$ binary system can be good basic composition of bioactive glasses and glass-ceramics. In the present study, various kinds of Cao-$SiO_2$ gels were prepared by sol-gel method in order to control the microstructure which are related to their dissolution rate, induction period of apatite formation in body environment. Characterization of the gels were done by wet chemical analysis, SEM observation, FT-IR spectroscopy and XRD. The gelation time decreased with CaO content. However, the volume of all the dried gel decreased to 50% of the wet gels irrespective of increasement of CaO content. All the Cao-$SiO_2$ gels were amorphous and contained a large amount of silanol groups on their surfaces after heat treatment up to $800^{\circ}C$. The interconnected structure of the gel changed to agglomerated spherical powders when Ca content exceed to 20 mol%. Most of the Cao-$SiO_2$ gel showed amorphous when heat-treated up to $900^{\circ}C$. However, quartz and cristobalite was produced when heat-treated at $1000^{\circ}C$ and resultant microstructure of the gel contained microporous structure.

• Proceedings of the Korean Vacuum Society Conference
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• 1999.07a
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• pp.168-168
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• 1999

Recently, Fe/Si multilayered films (MLF) have been a focus of interest due to the strong antiferromagnetic (AF) coupling observed in such kind of MLF originates from the same nature as in the metal/metal MLF. In particular, a question of whether the spacer layer in the Fe/Si MLF is metallic or semiconducting is of interest. In spite of various experimental techniques envolved in the study, the chemical composition and the properties of the interfacial regions in the MLF exhibiting the AF coupling is still questionable. The nature of the AF coupling and the interfacial properties of Fe/Si MLF are investigated in this study. A series of Fe/Si MLF with a fixed nominal thickness of Fe(3nm) and a variable thickness of Sk(1.0-2.2nm) were deposited by RF-sputtering onto glass substrates at room temperature. The atomic structures and the actual sublayer thicknesses of the Fe/Si MLF are investigated by using x-ray diffraction. The magnetic-field dependence of the equatorial Kerr effect clearly shows an appearance of the AF coupling between Fe sublayers at tsi = 1.5 - 1.8 nm. the drastic discrepancies between the experimental magnetooptical (MO) and optical properties, and based on the assumption of sharp interfaces between Fe and Si sublayers leads to a conclusion that pure si is absent in the AF-coupled Fe/Si MLF. Introducing in the model nonmagnetic semiconducting FeSi alloy layers between Fe and Si sublayers or as spacer between pure Fe sublayers only slightly improves the agreement between model and experiment. A reasonable agreement between experimental and simulated MO spectra was reached with using the fitted optical properties for the spacer with a typical metallic type of behavior. The results of the magnetic properties measured by vibrating sample magnetometer and magnetic circular dichroism are also analyzed in connection with the MO and optical properties.

• Journal of the Korean Ceramic Society
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• v.32 no.10
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• pp.1169-1177
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• 1995

Barium nitrate and yittrium nitrate were dissolved into distilled water. Titaium hydroxide precipitated from titanium chloride with NH4OH was dissolved into nitric acid. Each aqueous solution was mixed for 12 hr in the composition of Ba1-xYxTiO3 (x=0.1∼0.6) and the concentration of mixed solution was 0.1 mol/ι. The mixed solution was sprayed with an ultrasonic atomizer and carried into an electric furnace which was kept at 900∼1000$^{\circ}C$ and pyrolyzed. Pyrolyzed powders were collected on the glass filter with vacuum pump. Aqueous Mn solutiion was added into the synthesized powders, mixed with ultrasonic vibration and sintered at 1300∼1400$^{\circ}C$. Synthesized powders were characterized with SEM, XRD, DT-TGA, and BET. Microsture and resistivity of sintered body were investigated with SEM and multimeter. The results of this experiment were as follows; 1) Yittrium dooped BaTiO3 powders were synthesized above 950$^{\circ}C$. 2) The average particle sizes of powders from BET specific surface area and SEM were 0.045$\mu\textrm{m}$, 0.046$\mu\textrm{m}$ respectively. The particle size distribution was narrow in the range of 0.1∼1.0$\mu\textrm{m}$ from SEM. 3) Room temperature resistivity and pmax/pmin of 0.4 mol% Y doped specimen which was sintered at 1375$^{\circ}C$ were 102∼3 (Ω$.$cm) and 102∼3 respectively. 4) Room temperature resistivity and pmax/pmin of 0.4 mol% Y and 0.04 at% Mn added specimen which was sintered at 1375$^{\circ}C$ were 102∼3 (Ω$.$cm) and 106∼7 respectively. 5) Grain growth was inhibited with addition of Y2O3 and enhanced in addition of Mn by 0.05 atm%.

• Journal of the Korean Ceramic Society
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• v.40 no.12
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• pp.1165-1169
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• 2003

The Ta$_2$O$_{5}$ thin film was deposited on Si-(III) and glass substrate with the change of Ar:O$_2$ gas flow rate in the assist ion gun by the Dual ion-Beam Sputtering (DIBS). As the $O_2$ gas flow of the assist ion gun was decreased, the deposition rate of the thin films decreased. The refractive index was fixed (2.11, at 1550 nm) without regarding to $O_2$ gas flow of the range 3∼12 sccm in assist ion gun. The condition of Ar:O$_2$=3:12 was formatted stoichiometry composition of Ta$_2$O$_{5}$ and the ms roughness was small (0.183 nm).

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.22 no.3
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• pp.262-268
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• 2009

We investigated the properties of inorganic diatomic films like silicon oxide ($SiO_2$) and zinc oxide (ZnO) and their composite films are packed as a passivation layer around Ca cells on glass substrates by using an electron-beam evaporation technique and rf-magnetron sputtering method. When these Ca cells are exposed to an ambient atmosphere, the water vapor penetrating through the passivation layers is adsorbed in the Ca cells, resulting in a gradual progress of transparency in the Ca cells, which can be represented by changes of the optical transmittance in the visible range. Compared with the saturation times for the Ca cells to become completely transparent in the atmosphere, the protection effects against permeation of water vapor are estimated for various passivation films. The thin composite films consist of$SiO_2$ and ZnO are found to show a superior protection effect from water vapor permeation compared with diatomic inorganic films like $SiO_2$ and ZnO. Also, this inorganic thin composite films are also found that their protection effect against permeation of water vapor can be significantly enhanced by choosing their suitable composition ratio and deposition method, in addition, the main factors affecting the permeation of water vapor through the oxide films are found to be the polarizability and the packing density.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.12
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• pp.1345-1350
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• 2014

This paper presented analysis methods for adapting E-glass fiber/epoxy composite (GFRP) materials to an automotive leaf spring. It focused on the static behaviors of the leaf spring due to the material composition and its fiber orientation. The material properties of the GFRP composite were directly measured based on the ASTM standard test. A reverse implementation was performed to obtain the complete set of in-situ fiber and matrix properties from the ply test results. Next, the spring rates of the composite leaf spring were examined according to the variation of material parameters such as the fiber angles and resin contents of the composite material. Finally, progressive failure analysis was conducted to identify the initial failure load by means of an elastic stress analysis and specific damage criteria. As a result, it was found that damage first occurred along the edge of the leaf spring owing to the shear stresses.

• Proceedings of the Materials Research Society of Korea Conference
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• 2010.05a
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• pp.18.2-18.2
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• 2010

For the past a few years, we have intensively researched the printable inorganic conductors and ZnO-based amorphous oxide semiconductors (AOSs) for thin-film transistors. For printable conductor materials, we have focused on the aqueous Ag and Cu ink which possess a variety of advantages, comparing with the conventional metal inks based on organic solvent system. The aqueous Ag ink was designed to achieve the long-term dispersion stability using a specific polymer which can act as a dispersant and capping agent, and the aqueous Cu ink was carefully formulated to endow the oxidation stability in air and even aqueous solvent system. The both inks were successfully printed onto either polymer or glass substrate, exhibiting the superior conductivity comparable to that of bulk one. For printable ZnO-based AOSs, we have researched the noble way to resolve the critical problem, a high processing-temperature above $400^{\circ}C$, and recently discovered that Ga doping in ZnO-based AOSs promotes the formation of oxide lattice structures with oxygen vacancies at low annealing-temperatures, which is essential for acceptable thin-film transistor performance. The mobility dependence on annealing temperature and AOS composition was analyzed, and the chemical role of Ga are clarified, as are requirements for solution-processed, low-temperature annealed AOSs.