• Journal of the Korean Crystal Growth and Crystal Technology
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• v.31 no.4
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• pp.182-189
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• 2021

Porous ceramics were manufactured using the foaming method for the development of inorganic insulating materials. Silica fume and SiO₂ were used as main raw materials, and bentonite was used as a rapid setting agent for uniform structure formation of porous ceramics. The porous ceramics were sintered at 1200℃, and porosity, density, compressive strength, microstructure and thermal conductivity were analyzed. As the content of silica fume to SiO₂ of the porous ceramics increased 70 to 90 %, the specific gravity increased from 0.63 to 0.69, and the compressive strength increased from 9.41 Mpa to 12.86 Mpa. But, the porosity showed a tendency to decrease from 72.07 % to 70.82 %, contrary to the specific gravity. As a result of measuring the thermal conductivity, the porous ceramic with a silica fume content of 70 % showed a thermal conductivity of 0.75 to 0.72 W/m·K at 25 to 800℃, respectively, and, another that a silica fume content of 90 % showed a 0.66~0.86 W/m·K. So the lower the silica f ume content, the lower the thermal conductivity, which was conf irmed to be consistent with porosity result. As a result of microstructure analysis using SEM (Scanning Electron Microscope), pores in the range of tens to hundreds ㎛ were observed inside and outside the porous ceramic, and it was confirmed that the pore distribution was relatively uniform.

• Journal of the Korean Ceramic Society
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• v.42 no.8 s.279
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• pp.554-560
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• 2005

The engineering ceramic needs the properties of high strength, hardness, corrosion-resistance and heat-resistance in order to withstand thermal shock or applied nonuniform stresses without failure. The densely coated porous ceramics can be used for machine component, electromagnetic component, bio-system component and energy-system component by their high-performances from superior coating properties and light-weight characteristics due to the structure including pore by itself. In this study we controlled the porosity of silica and alumina, $8.2\~25.4\%$ and $23.4\~36.0\%$, respectively, by the control of sintering temperature and starting powder size. We made bilayer structures, consisting of a transparent glass coating layer bonded to a thick substrate of different porous ceramics by a thin layer of epoxy adhesive, facilitated observations of crack initiation and propagation. The elastic modulus mismatch could be controlled using different porous ceramics as the substrate layer. Then we applied 150 N force using WC sphere with a radius of 3.18 mm by Hertzian indentation. As a result, the crack initiation in the coating layer was delayed at lower porosity in the substrate layer, and the damage in the coating layer was relatively smaller at the bilayer structure coated on higher elastic substrate.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.28 no.6
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• pp.263-270
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• 2018

Recently, porous ceramic materials with anti-static performance are urgently needed for semiconductor and OLED/LCD display manufacturing industry. In this work, we fabricated porous titanium manganese oxide ceramics having the surface resistivity of $10^8-10^{10}$ ohm and enhanced mechanical strength by partial sintering method using nanosized titanium oxide. By addition of nano-sized titanium oxide in the matrix, neck formation between grains was strengthened, which remarkably increased flexural strength up to 170 MPa (@porosity: 15 %), 110 MPa (@porosity: 31 %), compared to 80 MPa (@porosity: 26 %) for pristine titanium manganese oxide ceramics. We evaluated the performances of our ceramics as air-floating module for OLED flexible display manufacturing devices.

• Journal of the Korean Ceramic Society
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• v.27 no.3
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• pp.412-422
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• 1990

Porous SiC ceramics were proposed to be promising materials for high-temperature thermoelectric energy conversion. Throughthe thermoelectric property measurements and microstructure observations on the porous alpha SiC and the mixture of $\alpha$-and $\beta$-SiC, it was experimentally clarified that elimination of stacking faults and twin boundaries by grain growth is effective to increase the seebeck coefficient and increasing content of $\alpha$-SiC gives rise to lower electrical conductivity. Furthermore, the effects of additives on the thermoelectric properties of 6H-SiC ceramics were also studied. The electrical conductivity and the seebeck coefficient were measured at 35$0^{\circ}C$ to 105$0^{\circ}C$ in argon atmospehre. The thermoelectric conversion efficiency of $\alpha$-SiC ceramics was lower than that of $\beta$-SiC ceramics. The phase homogeneity would be needed to improve the seebeck coefficient and electrical conductivity decreased with increasing the content of $\alpha$-phase. In the case of B addition, XRD analysis showed that the phase transformation did not occur during sintering. On the other hand, AlN addiiton enhanced the reverse phase transformation from 6H-SiC to 4H-SiC, and this phenomenon had a great effect upon the electrical conductivity.

• Journal of the Korean Ceramic Society
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• v.44 no.5 s.300
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• pp.184-189
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• 2007

In this study, a novel-processing route for producing microcellular cordierite ceramics has been developed. The proposed strategy for making the microcellular cordierite ceramics involves three steps: (i) fabricating ceramic-filled preceramic foams by heating a mixture of polysiloxane, expandable microspheres, talc, and alumina in a mold, (ii) cross-linking the foamed body, and (iii) transforming the body into microcellular cordierite ceramics by sintering. Cu jig was used for near net shaping in the foaming step. The experimental variables such as the shape of foaming jig and the content of expendable microsphere were investigated. By controlling the content of expendable microsphere, it was possible to make the porous cordierite ceramics with cell density of ${\sim}1.0{\times}10^9\;cells/cm^3$.

• Journal of the Korean Ceramic Society
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• v.55 no.1
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• pp.74-79
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• 2018

Active clay, bentonite and zeolite were used as porous materials for humidity controlling ceramic boards. The specific area and the pore volume of active clay were higher than those of bentonite and zeolite. It was effective to add white cement as well as a retarding agent to control the setting time of the ceramic paint. As the amount of added porous materials increases, the specific surface area and total pore volume of ceramic paint increase, but the average pore diameter decreases. The addition of porous materials having a high specific area and a large pore volume improves the moisture absorptive and desorptive performance of the ceramic paint. Therefore, in this experiment, the moisture absorptive and desorptive properties were best when active clay was added. Also, as the added amount of porous materials increases, the moisture absorptive and desorptive properties improve. In this experiment, when 70 mass% of active clay was added to ceramic paint, the hygroscopicity was highest at about $80g/m^2$.

• International Journal of Precision Engineering and Manufacturing
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• v.9 no.1
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• pp.47-50
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• 2008

This paper presents a new water-lubricated hybrid sliding bearing for a high speed and high accuracy main shaft system, along with the numerical method used for its design. The porous material for the restrictor and the restriction parameter were chosen based on the special requirements of the water-lubricated bearing. Subsequent numerical calculations give the load capacity, stiffness, and friction power of different forms of water-lubricated bearings. The pressure distribution of the water film in a 6-cavity bearing is shown, based on the results of the numerical calculations. A comparison of oil-lubricated and water-lubricated bearings shows that the latter benefits more from improved processing precision and efficiency. An analysis of the stiffness and friction power results shows that 6-cavity bearings are the preferred type, due their greater stiffness and lower friction power. The average elevated temperature was calculated and found to be satisfactory. The relevant parameters of the porous restrictor were determined by calculating the restriction rate. All these results indicate that this design for a water-lubricated bearing meets specifications for high speed and high accuracy.

• Journal of the Korean Ceramic Society
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• v.42 no.10 s.281
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• pp.691-697
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• 2005

Porous ceramics which have closes pore were fabricated by heat treatment at 100$\∼$ 600$^{\circ}C$ for 30 min using dried water glasses with 25, 35, and 45 wt$\%$ water contents. Size and distribution of the closed pore were varied depending on the water contents and heat treatment temperature. The expansion procedure could be distinguished by two stages. The frist stage occurred around loo$\%$ due to the evaporation of water and the second stage occurred at 200$\∼$400$^{\circ}C$ due to the decomposition of Si-OH compounds. The specimen was not expanded successfully because of the softening of the dried water glass at 500$\∼$600$^{\circ}C$.

• Korean Journal of Materials Research
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• v.23 no.3
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• pp.206-210
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• 2013

In the segmented-in-series solid-oxide fuel cells (SIS-SOFCs), fabrication techniques which use decalcomania paper have many advantages, i.e., an increased active area of the electrode; better interfacial adhesion property between the anode, electrolyte and cathode; and improved layer thickness uniformity. In this work, a cell-stack was fabricated on porous ceramic flattened tube supports using decalcomania paper, which consists of an anode, electrolyte, and a cathode. The anode layer was $40{\mu}m$ thick, and was porous. The electrolyte layers exhibited a uniform thickness of about $20{\mu}m$ with a dense structure. Interfacial adhesion was improved due to the dense structure. The cathode layers was $30{\mu}m$ thick with porous structure, good adhesion to the electrolyte. The ohmic resistance levels at 800, 750 and $700^{\circ}C$ were measured, showing values of 1.49, 1.58 and $1.65{\Omega}{\cdot}cm^2$, respectively. The polarization resistances at 800, 750 and $700^{\circ}C$ were measured to be 1.63, 2.61 and $4.17cm^2$, respectively. These lower resistance values originated from the excellent interfacial adhesion between the anode, electrolyte and cathode. In a two-cell-stack SOFC, open-circuit voltages(OCVs) of 1.915, 1.942 and 1.957 V and maximum power densities(MPD) of 289.9, 276.1 and $220.4mW/cm^2$ were measured at 800, 750 and $700^{\circ}C$, respectively. The proposed fabrication technique using decalcomania paper was shown to be feasible for the easy fabrication of segmented-in-series flattened tube SOFCs.

• The Korean Journal of Ceramics
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• v.5 no.1
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• pp.73-77
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• 1999

Capsule free hot isostatic pressing (HIPing) of 12 mol% $CeO_2-88 mo% ZrO_2 (12CeO_2-88ZrO_2)$ powder was conducted at 1100~$1200^{\circ}C$ using the powder crystallized in supercritical methanol followed by supercritical drying. Porous $12CeO_2-88ZrO_2$ ceramics with ~35% open porosity, micropore diameter of ~23 nm and a narrow pore size distribution were fabricated by capsule free hot isostatic pressing at $1100^{\circ}C$. The porosity increased with decrease in HIPing temperature and was accompanied by a steady decrease in fracture strength.