• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.35-36
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• 2008

PTC thermistor are characterized by an increase in the electrical resistance with temperature. The PTC materials of middle Curie point were produced or that of high Curie point (above $200^{\circ}C$), it was determined that compositional modifications of $Pb^{2+}$ for $Ba^{2+}$ produce change sin the Curie point to higher temperature. PTC ceramic materials with the Curie point above $120^{\circ}C$ were prepared by adding $PbTiO_3$, PbO or $Pb_3O_4$ into $BaTiO_3$. Thereby, adding $Pb^{2+}$ into $BaTiO_3$-based PTC material to improve Tc was studied broadly, however, weal know that PbO was poisonous and prone to volatilize, then to pollute the circumstance and hurt to people, so we should dope other innocuous additives instead of lead to increase Tc of composite PTC material. In order to prepare lead-free $BaTiO_3$-based PTC with middle Curie point, the incorporation on $Bi_{1/2}K_{1/2}TiO_3$ into $BaTiO_3$-based ceramics was investigated on samples containing 0, 1, 2, 3, 4, and 50mol% of $Bi_{1/2}K_{1/2}TiO_3$. $Bi_{1/2}K_{1/2}TiO_3$ was compounded as standby material by conventional solid-state reaction technique. The starting materials were $Bi_2O_3$, $K_2CO_3$, $BaCO_3$ and $TiO_2$ powder, and using solid-state reaction method, too. The microstructures of samples were investigated by SEM, DSC, XRD and dielectric properties. Phase composition and lattice parameters were investigated by X-ray diffraction.

• Journal of the Korean Ceramic Society
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• v.42 no.2 s.273
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• pp.132-139
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• 2005

Sintering behavior of $BaO-Nd_{2}O_3-TiO_2$ with a Pb-based glassceramics frit were investigated in order to understand an effect of glassceramics as a low temperature sintering agent on dielectric ceramics. A green sheet form was fabricated through tape casting method with the glassceramic fut added $BaO-Nd_{2}O_3-TiO_2$. The dispersion properties, rheological properties and final density of dielectric composit slurry as a function of amount and composition of organic additives was examined. The dispersants' addition was effective in controlling dispersion of the ceramics in solution. The addition of excessive dispersant showed adverse effect on dispersion. The prepared slurries, containing ceramic : powders, glass-ceramics and various kinds of organic viechles, exhibited typical shear thinning behavior. The best properties of tape casting appeared powder to solvent ratio 65 : 35 and amount of the binder 6 wt$\%$ and plasticizer 3 wt$\%$. The viscosity of the slurry was 677 cps and green/sintered density in the tape was $3.3 g/cm^3,\;5.56 g/cm^3$ respectively.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.11a
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• pp.20-21
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• 2005

[ $BaZrO_3$ ], nanopowder was added to YBCO powder to make ($BazrO_3)_x(YBCO)_{(100-x)mol.-%}$ ($BZO_x$-YBCO) ($0{\leq}x{\leq}10$) composite targets fur pulsed laser deposition of superconducting layer in order to investigate the effect of the addition of BZO nanopowder in the YBCO target on the flux pinning properties of $BZO_x$-YBCO thin films. All the $BZO_x$-YBCO thin films were grown on single crystal STO substrate under similar conditions in the PLD chamber. The effect of YBCO targets doped with BZO on the flux pinning properties of $BZO_x$-YBCO thin films has been investigated comparatively. The isothermal magnetizations M(H) of the films were measured at temperatures between 5 and 80 K in fields up to 5 T, employing a PPMS. The optimal amount of BZO nanopowders in $BZO_x$-YBCO thin films to obtain the strongest flux pinning effects at high magnetic fields is about 6 mol.-%.

• Proceedings of the KACD Conference
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• 2001.05a
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• pp.235-237
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• 2001

;Dentistry has benefited from tremendous advances in technology with the introduction of new techniques and materials, and patients are aware that esthetic approaches in dentistry can change one's appearance. Increasingly. tooth-colored restorative materials have been used for restoration of posterior teeth. Tooth-colored restoration for posterior teeth can be divided into three categories: 1) the direct techniques that can be made in a single appointment and are an intraoral procedure utilizing composites: 2) the semidirect techniques that require both an intraoral and an extraoral procedure and are luted chairside utilizing composites: and 3) the indirect techniques that require several appointments and the expertise of a dental technician working with either composites or ceramics. But, resin restoration has inherent drawbacks of microleakage. polymerization shrinkage, thermal cycling problems. and wear in stress-bearing areas. On the other hand, Ceramic restorations have many advantages over resin restorations. Ceramic inlays are reported to have less leakage than resin restoration and to fit better. although marginal fidelity depends on technique and is laboratory dependent. Adhesion of luting resin is more reliable and durable to etched ceramic material than to treated resin composite. In view of color matching, periodontal health. resistance to abrasion, ceramic restoration is superior to resin restorationl. Materials which have been used for the fabrication of ceramic restorations are various. Conventional powder slurry ceramics are also available. Castable ceramics are produced by centrifugal casting of heat-treated glass ceramics. and machinable ceramics are feldspathic porcelains or cast glass ceramics which are milled using a CAD/CAM apparatus to produce inlays (for example, Cered. They may also be copy milled using the Celay apparatus. Pressable ceramics are produced from feldspathic porcelain which is supplied in ingot form and heated and moulded under pressure to produce a restoration. Infiltrated ceramics are another class of material which are available for use as ceramic inlays. An example is $In-Ceram^{\circledR}$(Vident. California, USA) which consists of a porous aluminum oxide or spinell core infiltrated with glass and subsequently veneered with feldspathic porcelain. In the 1980s. the development of compatible refractory materials made fabrication easier. and the development of adhesive resin cements greatly improved clinical success rates. This case report presents esthetic ceramic inlays for posterior teeth.teeth.

• Journal of the Korean Ceramic Society
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• v.38 no.9
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• pp.834-838
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• 2001

Attempts were made to improve mechanical properties of zirconia-based electrolyte by preparing yttria-stabilized cubic zirconia/alumina composite. It was performed by precipitating Yag precursor in aqueous m-zirconia slurry. The powder was separated and then followed by heat treatment with expecting yttria to react with m-$ZrO_2$ to give yttria stabilized zirconia and alumina to be dispersed homogeneously. When 17.8wt% Yag(6.3mol% $Y_2O_3$) was used, fracture toughness and strength were substantially improved from 1.44MPa${\cdot}m^{1/2}$ and 270Mpa for YZ8Y to 3.62MPa${\cdot}m^{1/2}$ and 447MPa respectively, but electrical conductivity at $^{\circ}$C in air was decreased from 0.126 to 0.057${\Omega}^{-1}cm^{-1}$. It seemed due to the presence of small amount of tetragonal zirconia. But when 21.58wt% Yag(8.0mol% $Y_2O_3$) was added, fracture toughness of 2.93MPa${\cdot}m^{1/2}$ and flexural strength of 388MPa were obtained with electrical conductivity of ${\Omega}^{-1}cm^{-1}$.

• Journal of the Korean Ceramic Society
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• v.51 no.4
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• pp.271-277
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• 2014

To overcome the limitations of the solid oxide fuel cells (SOFCs) due to the high temperature operation, there has been increasing interest in proton conducting fuel cells (PCFCs) for reduction of the operating temperature to the intermediate temperature range. In present work, the perovskite $BaCe_{0.85-x}Zr_xY_{0.15}O_{3-\delta}$ (BCZY, x = 0.1, 0.3, 0.5, and 0.7) were synthesized via solid state reaction (SSR) and adopted as an electrolyte materials for PCFCs. Powder characteristics were examined using X-ray diffraction (XRD), thermogravimetric analysis (TGA) and Brunauer, Emmett and Teller (BET) surface area analysis. Single phase BCZY were obtained in all compositions, and chemical stability was improved with increasing Zr content. Anode-supported cell with $Ni-BaCe_{0.55}Z_{0.3}Y_{0.15}O_{3-\delta}$ (BCZY3) anode, BCZY3 electrolyte and BCZY3-$Ba_{0.5}Sr_{0.5}Co_{0.8}Fe_{0.2}O_{3-\delta}$ (BSCF) composite cathode was fabricated and electrochemically characterized. Open-circuit voltage (OCV) was 1.05 V, and peak power density of 370 ($mW/cm^2$) was achieved at $650^{\circ}C$.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.06a
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• pp.57-58
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• 2008

PTC thermistor are characterized by an increase in the electrical resistance with temperature. The PTC materials of middle Curie point were produced or that of high Curie point (above $200^{\circ}C$), it was determined that compositional modifications of $Pb^{2+}$ for $Ba^{2+}$ produce change sin the Curie point to higher temperature. PTC ceramic materials with the Curie point above $120^{\circ}C$ were prepared by adding $PbTiO_3$, PbO or $Pb_3O_4$ into $BaTiO_3$. Thereby, adding $Pb^{2+}$ into $BaTiO_3$-based PTC material to improve Tc was studied broadly, however, weal know that PbO was poisonous and prone to volatilize, then to pollute the circumstance and hurt to people, so we should dope other innocuous additives instead of lead to increase Tc of composite PTC material. In order to prepare lead-free $BaTiO_3$-based PTC with middle Curie point, the incorporation on $Bi_{1/2}Na_{1/2}TiO_3$ into $BaTiO_3$-based ceramics was investigated on samples containing 0, 1, 2, 3, 4, and 50mol% of $Bi_{1/2}Na_{1/2}TiO_3$. $Bi_{1/2}Na_{1/2}TiO_3$ was compounded as standby material by conventional solid-state reaction technique. The starting materials were $Bi_{1/2}Na_{1/2}TiO_3$, $BaCO_3$, $TiO_2$ and $Y_2O_3$ powder, and using solid-state reaction method, too. The microstructures of samples were investigated by SEM, DSC, XRD and dielectric properties. Phase composition and lattice parameters were investigated by X-ray diffraction.

• Korean Chemical Engineering Research
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• v.44 no.2
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• pp.160-165
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• 2006

A Pd-Cu-Ni alloyed hydrogen membrane has fabricated on porous nickel support formed by nickel powder. Porous nickel support made by sintering shows a strong resistance to hydrogen embrittlement and thermal fatigue. Plasma surface modification treatment is introduced as pre-treatment process instead of conventional HCl wet activation. Nickel was electroplated to a thickness of $2{\mu}m$ in order in to fill micropores at the nickel support surface. Palladium and copper were deposited at thicknesses of $4{\mu}m$ and $0.5{\mu}m$, respectively, on the nickel coated support by DC sputtering process. Subsequently, copper reflow at $700^{\circ}C$ was performed for an hour in $H_2$ ambient. And, as a result PdCu-Ni composite membrane has a pinhole-free and extremely dense microstructure, having a good adhesion to the porous nickel support and infinite hydrogen selectivity in $H_2/N_2$ mixtures.

• Korean Journal of Materials Research
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• v.8 no.8
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• pp.757-765
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• 1998

This study was performed to investigate the influence of fuel/oxygen ratio (F/O= 3.2, 3.0, 2.8) on the oxidation behavior of two kinds of (20wt%NiCr claded $\textrm{Cr}_{3}\textrm{C}_{2}$, and 7wt%NiCr mixed $\textrm{Cr}_{3}\textrm{C}_{2}$) composite powder with different manufacturing method. The results show that the oxidation behavior between the 20wt% NiCr claded $\textrm{Cr}_{3}\textrm{C}_{2}$ and 7wt% NiCr mixed $\textrm{Cr}_{3}\textrm{C}_{2}$ coating was widely different. The surface morphology of the coating composed of 7wt% NiCr mixed $\textrm{Cr}_{3}\textrm{C}_{2}$ was changed to porous with F/O ratio by the aggressive evolution of gas phases($\textrm{CO}_2$, CO and $\textrm{CrO}_3$) and the oxide cluster composed of Ni and Cr were grown after oxidation at $1000^{\circ}C$ for 50 hours. But the surface morphology of the coating composed of 20wt% NiCr claded $\textrm{Cr}_{3}\textrm{C}_{2}$ was not changed to porous after oxidation at $1000^{\circ}C$ for 50 hours. Therefore, the reason for high oxidation rate is due to activation of $\textrm{Cr}_{3}\textrm{C}_{2}$ to oxidation by entrapped oxygen gases within coating layer, and to closely relate with the decomposition of $\textrm{Cr}_{3}\textrm{C}_{2}$ to $\textrm{Cr}_{7}\textrm{C}_{3}$ phase. Accordingly, On the evidence of these results, the study about the oxidation behavoir of the HVOF sprayed $\textrm{Cr}_{3}\textrm{C}_{2}$ coating depending on hydrogen flow rate must be done.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.15 no.5
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• pp.3286-3291
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• 2014

A study on the crack protection and thermal insulation properties of the expanded perlite inorganic composites was performed. Mixed expanded perlite with a water glass was stabilized for 24 hrs at room temperature in the mold and, thereafter, converted into a massive foamed body through complete drying process at $150^{\circ}C$. Aluminum phosphate and micron size mica powder were used as a reaction accelerator and a stabilizer for thermal crack, respectively. Especially, use of mica exhibited a remarkable effect on the protection of thermal crack at higher temperature over $500^{\circ}C$, and thermal conductivity of the composites was enhanced with higher perlite contents, showing ca. 0.09 W/mK for the sample of 100/200/10/1.5 water glass/perlite/mica/Al phosphate by weight. A severe dimensional deformation of the composite materials was observed over $600^{\circ}C$, however, showing a temperature limitation for a practical application. The facts were considered as the results from the glass transition temperature of the water glass, of which main component is sodium silicate.