• Journal of the Korean Ceramic Society
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• v.27 no.5
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• pp.668-676
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• 1990

Glass in the ZrO2-SiO2 system containing up to 30mol% ZrO2 were prepared by heating the gel made from the mixed solutions of Zr(OC3H7)4 and partial hydrolysed Si(OC2H5)4. As a result, the monolith gel was made from the HCl and water content as 2.7$\times$10-3 and 8 molar ratio to alkoxide and drying temoperature as 4$0^{\circ}C$. Heating rate of dry gel maintained under 0.5$^{\circ}C$/min and heating at a temperature as 90$0^{\circ}C$ was found to be for making the transparent glass.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.21 no.11
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• pp.613-620
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• 2009

The thermal stresses of a ceramic heat exchanger were analyzed numerically since the ceramic material is good in heat resistance but weak in the thermal stress. The analysis of thermal stress was conducted in the ceramic core with two boundary conditions depending on bolt jointing. The thermal stresses were computed by applying temperature and pressure distributions obtained from the numerical results of conjugate heat transfer to ANSYS WORKRBENCH. When number of bolt joining halls was reduced from $8\times2$ to $4\times2$, the maximum principal stresses decrease by 47.6~50.5% and increase in safety factors by 2.18~2.5 for ultimate tensile strength. Thus, it can be said that bolt joining halls should be minimized in ceramic heat exchanger to be efficient in reducing thermal stress. In addition, the width of particular gas flow passages were revised from 52 mm to 42 mm to reduce maximum thermal stresses since certain passages experienced high thermal stresses. From the revision, safety factors were increased by 13.8~14.1% for the boundary condition of $4\times2$ bolt joining halls. Therefore, it is suggested that thermal stress can be reduced by changing local geometry of a ceramic heat exchanger.

• Clean Technology
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• v.7 no.1
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• pp.65-74
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• 2001

Modified dip-coating method 8.3 times shorten in solution volume-coated and 83.3 times in coating time than existing dip-coating method. Coating weight increased nearly 2~3 times. So modified dip-coating method is evaluated that it is economic and has a efficiency. When we make an experiment in coated $LaCoO_3$ on ceramic monolith in modified dip-coating method which use 2 coating applications with relative viscosity $0.006202kg{\cdot}m/sec$, it showed a superior reaction at 88.56mg per ceramic unit gram in NO-CO reaction(optimum coating amount). When we make an experiment in the same size of ceramic filter cell with different conditions 100, 200cell per square inch, the result in low temperature($200^{\circ}C{\sim}350^{\circ}C$), 200cell3 per square inch is 6~23% higher in NO reduction and 11% in CO oxidation than 100cell per square inch. It is because the more the number of cells in the ceramic filter increase, the more catalytic surface area is expanded.

• Journal of the Korean Ceramic Society
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• v.47 no.6
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• pp.485-490
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• 2010

In our previous studies, continuous SiC fiber-reinforced SiC-matrix composites ($SiC_f$/SiC) had been fabricated by two different slurry infiltration methods: vacuum infiltration and electrophoretic deposition (EPD). 12 wt% of $Al_2O_3-Y_2O_3$-MgO with respect to SiC powder was used as additives for liquid-phase assisted sintering. After hot pressing at $1750^{\circ}C$ under 20 MPa for 2 h in Ar atmosphere, a high composite density could be achieved for both cases, whereas the problems such as large grain size and non-uniform distribution of liquid phase were observed, which was resulted in the relatively poor mechanical properties of composites. Therefore, efforts have been made to reduce the grain growth during the sintering, including the optimization for hot pressing condition and utilization of spark plasma sintering using a SiC monolith. Based on the results, spark plasma sintering was found to be effective method in decreasing the amount of sintering additive, time and grain growth, which will be explained in comparison to the results of hot pressing in this paper.

• Journal of the Korean Ceramic Society
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• v.52 no.5
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• pp.374-379
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• 2015

Mullite-matrix and $Al_2O_3$-matrix composites were fabricated with 30 wt% hydroxyapatite (HA) and tricalcium phosphate (TCP), respectively, as additives to give bioactivity. A diphasic gel process was employed to lower the densification temperature of the mullite matrix to $1320^{\circ}C$. A polymer complexation process was used to synthesize a TCP powder that was fully densified at $1250^{\circ}C$, for application to the matrix. For the HA/mullite composite, HA decomposed during sintering by reactions with the matrix components of $Al_2O_3$ and $SiO_2$, resulting in a mixture of $Al_2O_3$, TCP, and other minor phases with a low densification of less than 88% of the theoretical density (TD). In contrast, the TCP/$Al_2O_3$ composite was highly densified by sintering at $1350^{\circ}C$ to 96%TD with no reaction between the components. Different from the TCP monolith, the TCP/$Al_2O_3$ composite also showed a fine microstructure and intergranular fracture, both of which characteristics are advantageous for strength and fracture toughness.

• Journal of the Korean Ceramic Society
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• v.42 no.8 s.279
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• pp.582-587
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• 2005

AlN-BN ceramic composites were fabricated and their mechanical properties were investigated. The relative density of hot-pressed composites decreased with increasing BN content, but over $99\%$ could be obtained with 30 $vol\%$ BN in AlN. YAG was formed in the composites and monolithic AlN as a second phase by the reaction between $Y_2O_3$, added as sintering aid, and $Al_2O_3$. As expected, Vickers hardness and Young's modulus decreased with increasing BN content. The three-point flexural strength also showed similar behavior decreasing from 500 MPa of monolith down to 250 MPa by the addition 30 $vol\%$ BN. However, interestingly, the standard deviation of the strength values decreased significantly as BN was added to AlN. As a result, the Weibull modulus of the AlN-30 $vol\% BN composite was 21.3, which was extremely high. Fractography and crack path studies revealed that BN platelets induced grain pull-out and crack bridging in a bigger scale during crack propagation. Consequently, fracture toughness increased as more BN was added, reaching 4.5 $MPa\sqrt{m}$ at 40 $vol\%$ BN.

• Proceedings of the KSME Conference
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• 2001.06d
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• pp.802-806
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• 2001

Diesel particulate trap is the most reliable system to reduce the particulate matters from diesel engine. Filter is the core component of DPF and ceramic monolith type is dominantly used, which is expensive and fragile relatively at thermal shock. Porous metal filter, which has superior thermal characteristics and low cost, was tested in order to analyze the regeneration performance by using with ferrocene additive. This filter showed the 72% filtration efficiency, additives itself diminished 48% of PM from engine out emission, and final PM reduction ratio of 89% was achieved by DPF system with D-13 test mode.

• The Korean Journal of Ceramics
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• v.6 no.1
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• pp.15-20
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• 2000

Thick inorganic-organic hybrid films were prepared on ITO-coated glass substrates by the electrophoretic sol-gel deposition of polyphenylsilsesquioxane particles. The morphology of the deposited films changed from the aggregate of the spherical particles to monolith by heat treatment at temperatures higher than $200^{\circ}C$. Transparency of the films was significantly improved accompanied by the morphological change of the particles. The degree of the morphological change was governed by two factors; maximum heat treatment temperature and heating rate. Transparent thick films of ca. 3$\mu\textrm{m}$ in thickness were obtained only by heat treatment at $400^{\circ}C$ for 2h with rapid heating from room temperature to $400^{\circ}C$. These films obtained were strongly adhered to the ITO-coated glass substrates and has a very smooth surface.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2006.10a
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• pp.615-616
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• 2006

A micro-fuel processor system integrating steam reformer and partial oxidation reactor was manufactured using low temperature cofired ceramic (LTCC). A CuO/ZnO/$Al_2O_3$ catalyst and Pt-based catalyst prepared by wet impregnation were used for steam reforming and partial oxidation, respectively. The performance of the LTCC micro-fuel processor was measured at various operating conditions such as the effect of the feed flow rate, the ratio of $H_2O/CH_3OH$, and the operating temperature on the LTCC reformer and CO clean-up system. The catalyst layer was loaded with "Fill and Dry" coating for small volume. The product gas was composed of $70\sim75%$ hydrogen, $20\sim25%$ carbon dioxide, and $1\sim2%$ carbon monoxide at $250\sim300^{\circ}C$, respectively.

• Journal of the Korean Ceramic Society
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• v.34 no.6
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• pp.645-651
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• 1997

Tetragonal zirconia polycrystals (TZPs) doped with $Y_{2}O_{3}$ and $Nb_{2}O_{5}$ were prepared by the conventional sintering to enhance fracture toughness and phase stability of TZPs without controlling the grain size. TZP composites were obtained by adding the transformable TZP to the non-transformable TZP in wt%. The monolithic tetragonal $ZrO_2$, same as the composite composition containing 15 wt% transformable TZP, sintered at $1550^{\circ}C$ for 10h in air, exhibited the fracture toughness of 9$MPam^{1/2}$ and no low-and high-temperature degradation at temperatures in the range of 220 to $1000^{\circ}C$ for 100h in air. The corresponding single composition was 90.24 mol% $ZrO_2$-5.31 mol% $Y_{2}O_{3}$-4.75 mol% $Nb_{2}O_{5}$. The microstructure observation revealed that the t-$ZrO_2$ grains grew grandually with sintering time and no microcraking and twinning were observed.