• Journal of the Korean Ceramic Society
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• v.27 no.6
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• pp.799-807
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• 1990

In this study, effects of oxide additives on mechanical properties and microstructure of A1N and A1N polytype ceramics were investigated. Fine A1N powder was synthesized by nitriding alumiuim hydroxide prepared from Al-isopropoxide, at 1350$^{\circ}C$ for 10h in N2 atmosphere. By adding 3w/o Y2O3, 0.56w/o CaO, and 10w/o SiO2 to AlN powder, AlN and AlN polytype ceramics were prepared by hot-pressing under the pressure of 30 MPa at 1800$^{\circ}C$ for 1h. AlN ceramics with no additives formed considerable amount of AlON phase, while AlN ceramics doped with Y2O3 or CaO decreased AlON phase and formed Y-Al or Ca-Al oxide compound. AlN＋10w/o SiO2(＋3w/o Y2O3) composition produced AlON and AlN polytype compound having 21R as a major phase. Room temperature flexural strength of AlN ceramics with no additive was 246MPa, and room temperature flexural strength and critical temperature difference by thermal shock(ΔTc) of AlN ceramics dooped with Y2O3 or CaO were 532MPa/340$^{\circ}C$ and 423MPa/300$^{\circ}C$, respectively. Y2O3 and CaO used as sintering agent played roles of densification and oxygen removal of AlN ceramics, and affected grain growth/grain morphologies of AlN ceramics.

• Journal of the Korea Furniture Society
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• v.17 no.1
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• pp.23-32
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• 2006

This study was carried out to explore a new application of traditional Hanji and obtain fundamental properties for producing Hanji wallpaper by incorporating ceramics from wood and rice-husk as an interior building material. The results of properties determined were summarized as follows: The addition of ceramics in Hanji paper reduced its apparent density, but increased bulk density due to the ceramic particles distributed on the surface and inside the fiber of Hanji wallpapers. In particular, woodceramic particles were specifically distributed on the fiber surface, while particles of rice-husk ceramics were permeated into the inside surface of fibers. The density of rice-husk ceramics were greater than that of woodceramics. The physical properties of Hanji wallpapers, such as breaking strength, wet breaking strength, burst strength, tear index and folding endurance were deteriorated with the addition of ceramics. However, the addition of woodceramics in the Hanji wallpaper resulted in better strength in most cases than that of rice-husk ceramics, except tear strength. Therefore, an optimum addition level of woodceramics into the wallpaper was found to be 5% on the basis of intensity. The addition of ceramics also prolonged the combustion time because it lowered air permeability and brightness of the wallpaper.

• Transactions on Electrical and Electronic Materials
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• v.14 no.4
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• pp.193-198
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• 2013

The effects of additives (Cr, Nb, Dy, and Bi) on microstructure, electrical properties, dielectric characteristics, and aging behavior of $ZnO-V_2O_5-MnO_2-Co_3O_4-La_2O_3$ (ZVMCL) ceramics were systematically investigated. The phase formed in common for all ZVMCL ceramics modified with various additives consisted of ZnO grain as a main phase, and $Zn_3(VO_4)_2$ and $ZnV_2O_4$ as the secondary phases. The sintered density and average grain size were in the range of $5.4-5.54g/cm^3$ and $3.7-5.1{\mu}m$, respectively. The ZVMCL ceramics modified with Cr exhibited the highest breakdown field (6,386 V/cm) and the ZVMCL ceramics modified with Nb exhibited the lowest breakdown field (3,517 V/cm). All additives enhanced the nonlinear coefficient (${\alpha}$), by a small or large margin, in particular, additives such as Bi and Nb noticeably increased the nonlinear coefficient, with ${\alpha}=25.5$ and ${\alpha}=23$, respectively. However, on the whole, all additives did not improve the stability against a DC stress, compared with ZVMCL ceramics.

• Journal of the Korean Ceramic Society
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• v.49 no.4
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• pp.308-317
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• 2012

Reactive processing, such as reactive hot pressing (RHP) and reactive spark plasma sintering (R-SPS), is effective densification method to prepare $ZrB_2$-based ultra high temperature ceramics (UHTCs). The present paper reviewed some typical reactive processing of $ZrB_2$-based UHTCs. All the reactions from the starting materials in the reactive processing are thermodynamically favorable, which generate enough energy and driving force for the densification of the final products under a relatively low temperature. Besides, compared with non-reactive processing, anisotropic $ZrB_2$ grains, such as $ZrB_2$ platelets, can only be obtained in the reactive processing, resulting in an improvement of the mechanical properties.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.04b
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• pp.76-79
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• 2000

The $Ba(Zn_{1/3}Ta_{2/3})O_3$ ceramics were prepared by conventional mixed oxide method. The structural properties of the BZT ceramics with the sintering temperature were investigated by XRD, SEM. The BZT ceramics have a complex-perovskite structure. The BZT ceramics sintered at $1550^{\circ}C$ had a superstructure plane of BZT(100). Increasing the sintering temperature, the bulk density and ordering were increased. The bulk density of the BZT ceramics sintered at $1550^{\circ}C$ was $7.50[g/cm^3]$. Increasing the sintering temperature, the average grain size were increased and pore were decreased.

• Journal of the korean Society of Automotive Engineers
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• v.12 no.5
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• pp.60-75
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• 1990

Advanced Ceramics have some excellent prosperities as the material for the mechanical component. It is, however, very difficult to grind ceramics with high efficiency because of their high strength, hardness and brittleness. In this study, various machining experiments are carried out to obtain the basic knowledge of grinding High Strength Ceramics with high efficiency and precision for the purpose of application to Automobile parts. Advanced Engineering Ceramics such as Si$_{3}$N$_{4}$, SiC, ZrO$_{2}$, $Al_{2}$O$_{3}$ are ground with diamond wheels using conventional grinding machine. Results obtained in this study provide some useful informations to attain the high efficiency grinding of Advanced Ceramics.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.07b
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• pp.629-633
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• 2002

The degradation behaviour of ZPCCL-based varistor ceramics composed of 97.5 mol%ZnO-0.5 mol% $Pr_6O_{11}-1.0$ mol% $Cr_2O_3-0.5$ mol% $La_2O_3$ was investigated under various DC accelerated aging streses. The varistor ceramics sintered for 1 h exhibited excellent nonlinearity, in which the nonlinear exponent is 81.6 and the leakage current is $0.2{\mu}A$. It was found that this varistor ceramics possess high stability, in which the variation rates of varistor voltage, nonlinear exponent, and leakage current are -1.14%, -3.7%, and 85.0%, respectively, against DC accelerated aging stress. On the contrary, the varistor ceramics sintered for 2 h also exhibited high nonlinearity and stability, but they were bad characteristics, compared with the varistor ceramics sintered for 1 h.

• Proceedings of the Korean Vacuum Society Conference
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• 1997.07a
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• pp.68-68
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• 1997

• Journal of the Korean Ceramic Society
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• v.42 no.8 s.279
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• pp.542-547
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• 2005

Keys to the attainment of tailored properties in SiC ceramics are microstructure control and judicious selection of the sintering additives. In this study, three different strategies for controlling microstructure of liquid-phase-sintered SiC ceramics (LPS-SiC) have been suggested: control of the initial $\alpha-SiC$ content in the starting powder, a seeding technique, and a post-sintering heat treatment. The strategies suggested offer substantial flexibility for producing toughened SiC ceramics whereby grain size, grain size distribution, and aspect ratio can be effectively controlled. The present results suggest that the proposed strategies are suitable for the manufacture of toughened SiC ceramics with improved toughness.

• Journal of the Korean Ceramic Society
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• v.52 no.1
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• pp.61-65
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• 2015

The effect of Sr addition on the flexural strength of bulk SiOC ceramics was investigated in polymer-derived SiOC ceramics prepared by conventional hot pressing. Crack-free, dense SiOC discs with a 30 mm diameter were successfully fabricated from commercially available polysiloxane with 1 mol% strontium isopropoxide derived Sr as an additive. Agglomerates formed after the pyrolysis of polysiloxane led to the formation of domain-like structures. The flexural strength of bulk SiOC was strongly dependent on the domain size formed and Sr addition. Both the minimization of the agglomerate size in the starting powders by milling after pyrolysis and the addition of Sr, which reinforces the SiOC structure, are efficient ways to improve the flexural strength of bulk SiOC ceramics. The typical flexural strength of bulk Sr-doped SiOC ceramics fabricated from submicron-sized SiOC powders was ~209 MPa.