• Journal of the Korean Ceramic Society
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• v.25 no.5
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• pp.488-494
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• 1988

Effects of MnO2 addition on themicrostructure, dielectric and piezoelectric properties of Rhombohedral, Tetragonal and Morphotropic phase boundary(MPB) in Pb(Ni1/3Nb2/3)O3-PbTiO3-PbZrO3 system were investigated and respectively the amount of MnO2 addition was 0, 0.2, 0.5, 1.0, 3.0wt%. In the tetragonal region, compared with the Rhombohedral and Morpotropic phase boundary, Mechanical quality factor(Qm), Curie temperature(Tc) and Dissipation factor were promoted by addition of MnO2. According to the results of the microstructure, dielectric and piezoelectric properties, the solid solution range of MnO2 addition in this system was 0.2-0.5wt%.

• Journal of the Korean Ceramic Society
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• v.25 no.5
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• pp.532-540
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• 1988

Even the finest cement as having a specific surface area of 6.000~8.500$\textrm{cm}^2$/g (Blaine) is to convert into low-porosity hardened cement paste by the use of appropriate plasticizer. In this study, tests were carried out on such a special cement mix(fineness of 6.000$\textrm{cm}^2$/g, Ca-lignosulfonate plus k2CO3 as plasticizer and W/C=0.25) in comparison with ordinary Portland cement. Owing mainly to the high fineness of the cement powder and the low water-to-cement ratio, the hardened low-porosity cement paste showed a very tight microstructure, the pore texture of which consisted of micropores and wide pores only of small radii. The consequence of such mix was hence that the low-porosity special cement had excellent properties of early-high and very high strengths as compared to ordinary Portland cement. Its volume change when dried in the air or re-wetted, exhibited superor behaviour as well.

• Journal of the Korean Ceramic Society
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• v.39 no.1
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• pp.21-25
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• 2002

Effect of abnormal grain growth and heat treatment time on the electrical properties of donor-doped semiconductive BaTiO$_3$ceramics was examined. La-doped BaTiO$_3$ceramics was sintered at 134$0^{\circ}C$ for different times from 10 to 600 min in order to change the volume fraction of the abnormal grains in samples. As a result, samples with different volume fraction of abnormal grain growth from 22 to 100% were prepared. The samples were annealed at 120$0^{\circ}C$ for various times. The resistivity of the sam-ples at room and above Curie temperature was examined. The complex impedance measurement as functions of the volume fraction of abnormal grains and annealing time was conducted. Separation of complex impedance semicircle was observed in a sample in which abnormal and fine grains coexist. The results are discussed from a viewpoint of microstructure-property relationship.

• Journal of the Korean Ceramic Society
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• v.29 no.7
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• pp.533-538
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• 1992

Effect of Li2O.4B2O frit on the microstructural and thermal expansion behaviour of $\beta$-spodumene ceramics was investigated. With 4.0~8.0 wt.% frit addition, sintering temperature range was enlarged and densification was enhanced through liquid phase sintering. As the amount of frit addition was increased, thermal expansion coefficient was increased to 1.72$\times$10-6$^{\circ}C$-1 of its highest value, which indicated that the increment of thermal expansion coefficient due to the second phase was constrained.

• Journal of the Korean Ceramic Society
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• v.29 no.11
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• pp.855-862
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• 1992

Thermoelectric power, electrical conductivity and Hall effect were measured, as functions of temperature in the range of 100 to 600 K, on polycrystalline Bi4/3Sb2/3Te3 which had been prepared via uniaxial hot-pressing at different temperatures in the range of 373 K to 773 K, aiming at searching a profitable processing route to a polycrystalline thermoelectric material, a promising, viable alternative to a single crystalline one. It was found that, with increasing temperature of pressing under a fixed pressure, the material, normally a p-type prior to being hot-pressed, underwent a transition to n-type. This transition was confirmed to be due to plastic deformation during hot-pressing and interpreted as being attributed to the change of the major ionic defect BiTe' into TeBi˙at temperature high enough for structure elements mobility. Thermoelectric figure-of-merit of the hot-pressed material was discussed in connection with the p-n transition in addition to microstructure.

• Journal of the Korean Ceramic Society
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• v.29 no.11
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• pp.877-887
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• 1992

Tetragonal zirconia powder with 3 mol% Y2O3 mas mixed with up to 30 vol% of ${\beta}$-SiC powders, and the mixtures were hot-pressed at 1500$^{\circ}C$ for 60 min under a pressure of 30 MPa in Ar atmosphere. Flexural strength and fracture toughness were measured at room-and high-temperature (1000$^{\circ}C$). Evolution of microstructure was also conducted to investigate the effects of SiC addition on the properties of 3Y-TZP ceramics. Average grain size of the composites was about 0.5 $\mu\textrm{m}$, and decreased with SiC addition. Both room- and high-temperature mechanical properties of the composites were improved with SiC content. Particularly, high-temperature strength and fracture toughness of 3Y-TZP/30v/o SiC composite were twice as high as those of 3Y-TZP. The hardness of the composites also increased with SiC content and reached maximum value at 3Y-TZP/30v/o SiC composite.

• Journal of the Korean Ceramic Society
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• v.39 no.11
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• pp.1011-1016
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• 2002

Colloidal particles of silica (100 nm in size) were electrostatically dispersed and adsorbed on a glass substrate coated with silica sol or alumina sol. Stability of the suspensions and microstructure of the adsorbed particle layers were discussed in terms of total potential energies between the particles and the substrate. Well-dispersed suspension resulted in a layer with densely packed and regularly arranged particles, whereas less stable suspension resulted in a porous layer with loosely packed and irregularly arranged particles. Despite repulsive interactions between the particles and the substrate coated with silica sol, the observed adsorption can be attributed to chemical bonds formed at the interface between the particle and silica sol. In contrast, the adsorption of the particles on the substrate coated with alumina sol formed a layer with strongly adhered and densely packed particles, due to large attractive interactions between the particles and alumina sol.

• Journal of the Korean Ceramic Society
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• v.29 no.4
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• pp.298-304
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• 1992

Flexural strength, microstructure, hydration reaction and moisture sensitivity in macro defect-free (MDF) cement, which basically prepared of high alumina cement (HAC) and hydroxypropyl methylcellulose (HPMC) and polyvinylalcohol (PVA) as water soluble polymer were investigated. Cement composites based on HAC-PVA system were improved in flexural strength than that of HAC-HPMC system especially, the strength of specimens added to 10 wt% of polyvinylalcohol was 160 MPa. These improvements of flexural strength were attributed to not only the effect of water soluble polymer in elimination of macropores (above 100 $\mu\textrm{m}$) and cement grain bridging, but the effect of unhydrate cement as an aggregate. Moisture sensitivity and flexural strength in wet condition of MDF cement composites immersed in water at 80$^{\circ}C$ for 3 days were decreased.

• Journal of the Korean Ceramic Society
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• v.30 no.10
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• pp.811-818
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• 1993

Al2O3/ZrO2-Spinel composites were prepared by infiltrating magnesium sulfate solution into the porous preform made from Al2O3-20wt% ZrO2 composite powders derived through an emulsion route. The microstructure and composition of the modified composites could be controlled by manipulating the presingtering temperature of the preform, infiltration time, and so on. It was found that spinel phases were concentrated near the surface than in the interior of the Al2O3/ZrO2-Spinel composites infiltrated for 6hrs, while spinel phases were uniformly distributed in the comosites infiltrated for 2 days. The relative density and fracture toughness of the composite infiltrated for 6 hrs were 98.6% and 7.2MN/m3/2, respectively.

• Journal of the Korean Ceramic Society
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• v.32 no.3
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• pp.289-294
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• 1995

As the results of the study on the effects of mixing time for raw materials to the electric and magnetic properties of Mg-ferrite, the fraction of spinel phase after calcination and the geometry density of sintered Mg-ferrite increased from 30% to 100% and from 2.5g/cc to 4.25g/cc respectively due to mixing-homobenity of raw materials. The AC resistivity of grains decreased and lattice parameter, saturation magnetization increased due to the increase in Fe+2 of sintered body. conclusively the characteristic of powder after calcination had strong influence on the microstructure, electric, and magnetic properties in Mg-ferrite sintered body.