• Ceramist
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• v.9 no.6
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• pp.7-11
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• 2006

The status of structural ceramics in Japan is presented. Use of ceramics for structural components had been limited due to their brittleness, and the successful application was wear resistant parts such as thread guides and ceramic cutting tools up to around 1980. Since then, considerable work has been done for applying ceramics to mechanical parts, and automotive components made of silicon nitride were developed and commercialized in 1980s. Unfortunately, the application of silicon nitride to automotive engines is not so popular in these days. Instead, a variety of structural ceramics such as alumina, silicon carbide and zirconia have recently extended the market, and the expanded application includes vacuum process parts for manufacturing semiconductor and liquid crystal devices, refractory tubes for casting aluminum alloy, and dies for optical lens forming. In addition, cordierite honeycombs and diesel particulate filters are widely used in automobiles. In the present review, the recent application of structural ceramics to automobiles and industries in Japan is summarized.

• Journal of the Korean Ceramic Society
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• v.13 no.4
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• pp.25-35
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• 1976

Mullite was synthesized by using kaolin and $\alpha$-alumina, and halloysite and aluminum hydroxide as raw materials at the various temperature in the range of 1200$^{\circ}$-1750$^{\circ}$C. The degree of mullitization was measured respectively by a quantitative X-ray diffraction method and a chemical analysis method. The rate and the maximum degree of mullitization were found to increase with temperature . The reaction completed at 1600$^{\circ}$Cfor less than 30 minutes, and yielded 98% mulllite inpurity in the case of kaolin-Al(OH)3. TiO$_2$ up to 3% was added to the batches of kaolin-Al(OH)$_3$. the effect of addition on the mullitization was investigated and found to decrease the sintering temperature for the mullitization. The mechanism of TiO$_2$ addition on the formation of mullite was also discussed.

• Journal of the Korean Ceramic Society
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• v.29 no.8
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• pp.617-622
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• 1992

In order to study on the effect of SiC whisker in flexural strength characterization of macro defect-free (MDF) cement composites, which composed of high alumina cement and polyvinyl alcohol, microstructural characterization of the composite specimens fabricated by the addition of SiC whiskers was investigated. Microproes are created around the SiC whisker, MDF cement didn't react with the SiC whisker. However, flexural strength of the composites have been improved. Fracture morphology of the composites, presents mainly intergranular type fracture passing around the unhydrated particles and siC whiskers, and partially transgranular type fracture. The main strengthening mechanisms of the MDF cement composites reinforced with SiC whiskers are characterized by crack deflection, microcracking, and bridging of cracks.

• Journal of the Korean Ceramic Society
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• v.29 no.2
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• pp.136-142
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• 1992

The effects of cyclic stress, frequency and bias-pressure on densification of Al2O3 powder cyclic compaction are investigated. The effect of frequency was not significant on densification of Al2O3 powder under cyclic compaction. The higher the cyclic stress and the lower the bias pressure, the higher densification was achieved. To obtain a higher densification, cyclic compaction was more efficient than 1 stroke compaction. A densification equation was proposed to describe an cyclic time dependent pressure-volume relation for Al2O3 powder under cyclic compaction. This equation was obtained empirically, based on the pressure-volume equation proposed by Cooper and Eaton, the time dependent densification equation by Kim and Suh and experimental data for Al2O3 powder under cyclic compaction. The agreement between the proposed equation and experimental data for Al2O3 powder under cyclic compaction was very good.

• Journal of the Korean Ceramic Society
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• v.27 no.6
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• pp.729-734
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• 1990

The microstructural dependence of thermal conductivity of a high-alumina (ca. 70%) heat-insulating frebricks(ca. 75%porosity) was investigated under special consideration of the tailored-pore shape effects. Pores different shape could be incorporated into the insulators through pore formers : Styrofoam produces spherical pores while saw dust results in parallel plate pores. Concerning the pore-shape effectiveness of thermal insulation, the specimen with irregular plate pores showed much lower values of heat conductivity than those with spherical pores, the values being 0.31 to 0.38 at $600^{\circ}C$ and 0.35 to 0.47 at 100$0^{\circ}C$, respectively. On the contrary, however, other material properties such as strength and softening temeprature under load were turned out to be better in the case of the spherical pores.

• Journal of the Korean Ceramic Society
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• v.12 no.1
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• pp.5-11
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• 1975

Thick film resistor paste was made utilizing oxide materials such as SnO, SnO＋Sb2O3, and SnO＋Zn. The oxide materials were mixed respectively with Q-12 glass powder and finally suspended in ethyl cellulose dissolved in ethyl cellosolve. Thick film resistor was made by screen printing the paste on the alumina substrate and firing it at a suitable temperature. Among thick films made from the resistor paste, the thick film containing 85% SnO and fired at $600^{\circ}C$ demonstrated the finest electrical properties showing 10 K ohm in sheet resistance, 110 ppm/$^{\circ}C$ in TCR. In general, TCR of the thick films made from the oxide-mixture paste is good in linearity, therefore it is suggested the oxide-mixture paste is utilized as the negative thermistor.

• Journal of the Korean Ceramic Society
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• v.20 no.2
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• pp.123-128
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• 1983

This research is aimed to synthesize the mullite by adding Al powder of $Al_2O_3$ to kaolin. Specimens fired at 1400, 1450 and 150$0^{\circ}C$ were compared in their X-ray diffraction patterns quantitative analysis of mullite formed and fine microstructures with those containing reactive $Al_2O_3$ activated $Al_2O_3$ as alumina source The experiment of Al oxdiation was also performed by measuring the weight increase of specimens. Two different shapes of mullites acicular and chunky were observed by SEM and the yield of mullites were in-creased by the order of adding activated $Al_2O_3$ reactive $Al_2O_3$ and Al powder to kaolin.

• Journal of the Korean Ceramic Society
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• v.27 no.6
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• pp.747-754
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• 1990

Aluminum hydrate gels were prepared from the mixtures of bauxite and ammonium sulfate by wet acid process. Optimum conditions for obtaining the maximum yield( 99%) of aluminum hydrates from the same amount of bauxite were confirmed as follows ; 1. Mixing ratio ; addition of 25mole% of ammonium sulfate to 1mole of bauxite. 2. Calcination ; heated at 350℃ for 1hr. 3. Extraction ; leached at 95℃ in 1% H2SO4 for 90min. 4. pH of precipitating solution; slight below 7.0. Amorphous aluminum hydrates were precipitated at the pH lower than 8.5, but the precipitates crystallized to bayerite at the pH was 10. Mean diameter of α-Al2O3 powders which were obtained by calcining the aluminum hydrates was below 0.2㎛, and EDS analysis revealed than SiO2 was it's primary impurity.

• Journal of the Korean Ceramic Society
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• v.26 no.3
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• pp.445-451
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• 1989

Hydrolysis of aluminum isopropoxide with excess water in the presence of excess isopropyl alcohol resulted in the formation of boehmite in independence of temperature of hydrolysis and aging. Stoichiometric and substoichiometric amount of water hydrolyzed aluminum isopropoxide to pseudo-boehmite and amorphous one, respectively. $\alpha$-Al2O3 with 0.3${\mu}{\textrm}{m}$ in median size was produced by calcination of boehmite, bseudo-boehmite and amorphous boehmite at 125$0^{\circ}C$, 120$0^{\circ}C$, and 115$0^{\circ}C$ for one hour, respectively. Singnificant reduction in particle size was found during transition from $\theta$-Al2O3 to $\alpha$-Al2O3. $\alpha$-Al2O3 produced in this study was relatively uniform spherical and its purity was found to be over 99.9%.

• Journal of the Korean Ceramic Society
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• v.44 no.5 s.300
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• pp.141-143
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• 2007

Nanotubes and microtubes of ferroelectric lead zirconate titanate (PZT) were synthesized by means of a simple and convenient process called a template-wetting process. Nanoporous alumina and macroporous Si were used as template materials to fabricate the corresponding tubes. For the improvement of the wetting properties of the wetting solution, the PZT solution was mixed with a polymer. The polymer was removed completely during annealing. The grain growth processes of the PZT nanotubes during baking and furnace annealing were examined by means of field emission electron microscope (FE-SEM) and X-ray diffractometry (XRD).