• Journal of the Korean Ceramic Society
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• v.28 no.1
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• pp.37-45
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• 1991

The critical current density, electrical conductivity, critical magnetic field, Meissner effect, apparent density, and microstructure of YBa2Cu3O7-x ceramic superconductor prepared by polymeric precursor, while varing calcining and sintering conditions, were investigated. The best superconducting properties could be obtained from the body sintered at 93$0^{\circ}C$ for 10h after calcining at 90$0^{\circ}C$ for 10h, which gave 383A/$\textrm{cm}^2$ of critical current density(Jc), 96K of onset temperature(Tonset), 94. 8K of zero temperature (Tzero) 225 Oe of critical magnetic field (Hc1), 72.8% of superconducting volume fraction measured by Meissner effect and 6.28g/㎤ of apparent density.

• Journal of the Korean Ceramic Society
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• v.40 no.11
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• pp.1027-1046
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• 2003

Nanostructured materials can be engineered by the controlled assembly of several suitable nano-objects as the building blocks. While, materials properties are determined by their atomic and molecular constituents and structure, their functionalities emerge when the microstructure of these early ensembles is in the nanometer regime. The properties and functionalities of these ensembles may be different as their size grows from the nano-regime to the micron regime and bulk structures. Nanotechnology, offers a unique possibility to manipulate the properties through the fabrication of materials using the nano-objects as building blocks. Nanotechnology is therefore considered an enabling technology by which existing materials, virtually all man-made materials, can acquire novel properties and functionalities making them suitable for numerous novel applications varying from structural and functional to advanced biomedical in-vivo and in-vitro applications.

• Journal of the Korean Ceramic Society
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• v.40 no.9
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• pp.837-841
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• 2003

Duplex microstructure of zirconia and alumina has been achieved via an organic-inorganic solution technique. Zirconium 2,4-pentanedionate, aluminum nitrate and polyethylene glycol were dissolved in ethyl alcohol without any precipitation. The organicinorganic precursor gels were turned to porous powders having volume expansion through explosive, exothermic reaction during drying process. The volume expansion was caused by abrupt decomposition of the organic groups in the gels during the vigorous exothermic reaction. The volume expanded, porous powders were crystallized and densified at 1500$^{\circ}C$ for 1 h. At the optimum amount of the PEG polymer, the metal cations were well dispersed in the solution and a homogeneous polymeric network was formed. The polymer content also affected on the specific surface area of the synthesized powder and the grain size of the sintered composite.

• Journal of the Korean Ceramic Society
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• v.17 no.1
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• pp.27-34
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• 1980

The synthesis of glass-ceramic materials from glasses based on industrial wastes or natural rocks their physical properties were studied. Glasses of composition, CaO14.7∼16.1, MgO7.4∼9.0, Al2O38.3∼19.3, SiO2 48.9∼51.0wt% were prepared from domestic blast furnace slag, serpentine, sea sand and etc. with additions of chromic oxide, and fluoride as nucleating agent. The glasses were subjected to controlled heat treatments and yielded fine microstructure of glass-ceramics which were composed of monocrystalline phase of aluminous diopside. X-ray diffraction techniques were adopted to identify the crystalline phases and to determine the degree of crystallization quantitatively. Density, coefficient of thermal expansion, young's modulus, microhardness and modulus of rupture were measured and the resulting properties were discussed in terms of the heat-treatment conditions, the degree of crystallization, species of crystaline phase, the microstructures formed in glass-cramics and the chemical compositions of mother glasses.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.29 no.10
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• pp.601-607
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• 2016

Piezoelectric thick films of soft $Pb(Zr,Ti)O_3$ (PZT) based commercial material (S55) were fabricated using a conventional tape casting method. Ag-Pd electrodes were printed on the piezoelectric film at room temperature and all 5 layered films with a dimension of $12mm{\times}16mm$ were successfully laminated for a multi-layered piezoelectric ceramic actuator. The laminated specimens were co-fired at $1,100^{\circ}C$ for 1 h. A flat layered and dense microstructure was obtained for the $112{\mu}m$ thick piezoelectric actuator after sintering process. Thereafter, a prototype piezoelectric speaker was fabricated using the multi-layered piezoelectric ceramic actuator which can operate as a bimorph. Its SPL (sound pressure level) characteristic was also evaluated for speaker application. Frequency response revealed that the output SPL with a root mean square voltage of 10 V increased gradually to the highest peak of 87.5 dB for 1.5 kHz and exhibited a relatively stable behavior over the measured frequency range (${\leq}20kHz$) at a distance of 10 cm, implying that the fabricated piezoelectric speaker is potential for speaker applications.

• Journal of Powder Materials
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• v.21 no.6
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• pp.467-472
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• 2014

RBSC (reaction-bonded silicon carbide) represents a family of composite ceramics processed by infiltrating with molten silicon into a skeleton of SiC particles and carbon in order to fabricate a fully dense body of silicon carbide. RBSC has been commercially used and widely studied for many years, because of its advantages, such as relatively low temperature for fabrication and easier to form components with near-net-shape and high relative density, compared with other sintering methods. In this study, RBSC was fabricated with different size of SiC in the raw material. Microstructure, thermal and mechanical properties were characterized with the reaction-sintered samples in order to examine the effect of SiC size on the thermal and mechanical properties of RBSC ceramics. Especially, phase volume fraction of each component phase, such as Si, SiC, and C, was evaluated by using an image analyzer. The relationship between microstructures and physical properties was also discussed.

• Journal of Powder Materials
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• v.20 no.6
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• pp.453-459
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• 2013

Lanthanum/gadolinium zirconate coatings are deposited via suspension plasma spray with suspensions fabricated by a planetary mill and compared with hot-pressed samples via solid-state reaction. With increase in processing time of the planetary mill, the mean size and BET surface area change rapidly in the case of lanthanum oxide powder. By using suspensions of planetary-milled mixture between lanthanum or gadolinium oxide and nano zirconia, dense thick coatings with fully-developed pyrochlore phases are obtained. The possibilities of these SPS-prepared coatings for TBC application are also discussed.

• Korean Journal of Materials Research
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• v.28 no.12
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• pp.719-724
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• 2018

Cordierite composed of an alumina-silica-magnesia compound has a low coefficient of thermal expansion(CTE) and excellent thermal shock resistance. It also has a low dielectric constant and high electrical insulation. However, due to low mechanical strength, it is limited for use in a ceramic heater. In this study, $ZrO_2$ is added to an 80 wt% cordierite-20 wt% mullite composition, and the effect of $ZrO_2$ addition on the mechanical strength and thermal shock resistance is investigated. With an increasing addition of $ZrO_2$, cordierite-mullite formed $ZrO_2$, $ZrSiO_4$ and spinel phases. With sintering conducted at $1400^{\circ}C$ with the addition of 5 wt% $ZrO_2$ to 80 wt% cordierite-20 wt% mullite, the most dense microstructure forms along with an excellent mechanical strength with a 3-point flexural strength of 238MPa. When this composition is quenched in water at ${\Delta}T=400^{\circ}C$, the 3-point flexural strength is maintained. Moreover, when this composition is cooled from $800^{\circ}C$ to air, the 3-point flexural strength is maintained even after 100 cycles. In addition, the CTE is measured as $3.00{\times}10^{-6}{\cdot}K^{-1}$ at $1000^{\circ}C$. Therefore, 80 wt% cordierite-20 wt% mullite with 5 wt% $ZrO_2$ is considered to be appropriate as material for a ceramic heater.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.30 no.6
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• pp.349-355
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• 2017

Zinc sulphide (ZnS) nanoparticles were fabricated by hydrothermal synthesis at $180^{\circ}C$ for 12 h. Two kinds of ZnS powder (hydrothermal synthesized ZnS and commercial ZnS) were investigated by X-ray diffraction (XRD) and scanning electron microscopy (SEM) for phase and microstructure, respectively. The XRD patterns showed that all ZnS nanoparticles have a sphalerite (cubic) structure. The nanoparticles of two different ZnS powders were sintered by spark plasma sintering. The sintered ZnS were analyzed by XRD, SEM, and FT-IR. We found that the transmittance of the infrared region is highly dependent on the density and crystal structure of sintered ZnS and the purity of the starting ZnS powder.

• Journal of the Korean Ceramic Society
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• v.35 no.9
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• pp.939-944
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• 1998

The formation microstructure and properties of novel ceramic composite materials by active filler con-trolled polymer pyrolysis were investigated. Polymethlsiloxane filled with W is of particular interested be-cause of the formation of ceramic bonded hard materials (WC-$W_{2}C$-$S_{1}OC$) for wear resistant applications. Highly metal-filled polymer suspensions were prepared and their conversion to ceramic composites by an-nealing in $N_{2}C$ atmosphere at 1000-$1600^{\circ}C$ were studied. Dimensional change porosity and phase distribution (filler network) were analyzed and correlated to the resulting material properties. Microcrystalline com-posites with the filler reaction products embedded to the resulting material properties. Microcrystalline com-posites with the filler reaction products embedded in a silicon oxycarbide glass matrix were produced. De-pending on the pyrolysis conditions ceramic composites with a density up to 95 TD% a hardness of 7-8.8GPa Yong's modulus of 220-230 GPa a fracture toughness of 6-6.8$MPam^{1/2}$ and a flexual strength of 380-470 MPa were obtained.