• Journal of the Korean Ceramic Society
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• v.53 no.1
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• pp.50-55
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• 2016

In order to make a highly ordered three-dimensionally macro-porous structure of zirconia ceramics, porogen precursors PMMA beads were prepared by emulsion polymerization using acrylic monomer. The monodisperse PMMA latex beads were closely packed by centrifugation as a porogen template for the infiltration of zirconium acetate solution. The mixed compound of PMMA and zirconium acetate was dried. According to the firing schedule, dry compacts of PMMA and zirconium acetate were calcined at $475^{\circ}C$ to obtain micro-, macro-, and meso- structures of polycrystalline zirconia with monodispersed porosity. Inorganic frameworks composed of $ZrO_2$ were formed and showed a three Dimensionally Ordered Microstructure [3DOM] of $ZrO_2$ ceramics. The obtained $ZrO_2$ skeleton was calcined at $710^{\circ}C$. The 3DOM $ZrO_2$ skeleton showed color tuning in solutions such as deionized [DI] $H_2O$ and/or methanol. The monodispersed crystalline micro-structure with micro/meso porosity was observed by FE-SEM.

• Journal of the Korean Ceramic Society
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• v.46 no.1
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• pp.10-15
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• 2009

We have fabricated silicon-rich silica thin films via RF magnetron sputtering using a SiO target. Thickness evolution and microstructure change of such $SiO_x$ (1$SiO_x$ thin films turned out to be mainly responsible for the increase of refractive index.

• Journal of the Korean Ceramic Society
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• v.29 no.7
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• pp.517-524
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• 1992

For the present study two alumina bodies were prepared. The sinter-aid alumina body(SAA) was made by conventional sinter-process using sintering additives of TiO2 & MgO/CaO and the reaction-bonded alumina (RBA) made from Al-Al2O3 mixed powder. A comparison was made between those two bodies and this investigation seeks to evaluate their microstructure, physical properties and material's reliability as well as their fracture behaviour. In spite of its considerable microstructural densification accompanied by sintering shrinkage, SAA is largely inferior to RBA in fracture strength. However, SAA shows a somewhat higher m-value than RBA in respect to the material's reliability, the Weibull modulus(m). RBA, which has high fracture strength, shows much longer lifetime under static loading than SAA. Though, as with m of fracture strength, the reliability(mt) of lifetime prediction in RBA is less high than of SAA.

• Journal of the Korean Ceramic Society
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• v.29 no.11
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• pp.912-918
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• 1992

Microstructure evolution including morphological change in the vicinity of the electrodes, porosity change and grain boundary migration was observed in polycrystalline CoO subject to electric fields at 1100 and 121$0^{\circ}C$ in air. At the cathode, the transported cations react with oxygen in the surrounding to form new lattices, while, at the anode, the reverse reaction occurs leading to lattice annihilation. Lattice formation also takes place at the surface of pores near the cathode inducing pore-filling effect. Grain boundary migration was found bo be enhanced or retarded depending on the field direction. It is therefore implied that the driving force of grain boundary migration is the vectorial sum of the curvature-induced chemical potential gradient and the electric field applied.

• Journal of the Korean Ceramic Society
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• v.29 no.4
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• pp.253-258
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• 1992

ZnO varistors were prepared by the organochemical method which used citric acid and ethylene glycol as gelling agents. The microstructure of the sintered specimens exhibited small grains, uniform grain size distribution, and few intragranular pores. Thermal decomposition of the organic resin formed during the powder preparation process was completed around 450$^{\circ}C$. No significant changes were observed in microstructure and current voltage characteristic with respect to calcination temperatures. A major advantage of the organochemical method used in this experiment is a possible uniform mixing of trace amounts of dopants. Therefore, this powder preparation method seems promising in investigating the effect of Li or In ion, which is added in ppm level to ZnO varistors, on the pulse respose characteristic.

• Journal of the Korean Ceramic Society
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• v.30 no.10
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• pp.871-879
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• 1993

Effects of K2SO4 and Na2SO4 on C3S formation and its microstructure were investigated. C3S formation was not influenced by addition up to 6.0wt% of K2SO4 as SO3 base, however it was prevented by only 1.0wt% of Na2SO4 addition. C3S prevention by added Na2SO4 was the reason why C2S stabilized by Na+ and SO42- could not react to C3S. Added K2SO4 appeared as K2SO4, however added Na2SO4 appeared as the form of Na2xCa3-xAl2O6, (Na0.8Ca0.1)SO4 and Na2SO4 in interstitial phase.

• Journal of the Korean Ceramic Society
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• v.32 no.2
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• pp.257-269
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• 1995

The TiC-Co/Al reaction-sintered products were prepared by the infiltration of various Co/Al metal mixture into the preform, and their microstructure, phases, and mechanical properties were investigated. With increasing the atomic ratio of Co/Al, tiC grain shape was changed from spherical to platelet particles, and the grain size increased. The crystalline phases found in the liquid matrix formed by the infiltration of Co/Al metal mixture were determined to be Al5Co2 and AlCo by EDS and XRD, and the two crystalline phases were located dominantly between TiC grains, when the Co/Al atomic ratio was lower than an unity. There was a tendency that the density, bending strength and fracture toughness increase with Co/Al atomic ratio until the infiltrated metal was 100% Co. The maximum value was achieved by the composition containing 100% Co infiltrated metal. The Vickers hardness decreased as Co/Al atomic ratio increased.

• Journal of the Korean Ceramic Society
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• v.40 no.4
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• pp.380-384
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• 2003

The effects of the mole concentrations of precursor solution on the microstructure and dielectric properties of sol-gel deposited $Ba_{0.85}$S $r_{0.15}$Ti $O_3$(BST) thin films have been investigated. The films were of single perovskite phase with strong (100) preferred orientation when grown on LaNi0$_3$ buffered Pt/Ti/ $SiO_2$Si substrates using a diluted precursor solution. Variation of the precursor solution concentration resulted in a different microstructure and, in turn, affected the tunability of the sol-gel deposited films. It was observed that leakage currents increased asymmetrically for the negative and positive bias voltage with decreasing thickness. Overall results suggest that those BST films have acceptable properties f3r applications as room-temperature tunable elements.

• Journal of the Korean Ceramic Society
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• v.41 no.8
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• pp.582-587
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• 2004

Biphasic Calcium Phosphate (BCP) consisted of hydroxyapatite (HAp) and $\beta$-tricalcium phosphate (P-TCP) has been prepared by solid state reaction. The size reduction of the resultant BCP agglomerate was carried out by reaction with hot water under atmospheric condition uld also under high pressure using an autoclave. The influence of processing conditions on the change of crystalline phase and composition, relative amount of constituent, specific surface area, and microstructure was investigated by means of XRD, FT-IR, BET method using a nitrogen adsorption and SEM.

• Journal of the Korean Ceramic Society
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• v.24 no.3
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• pp.263-269
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• 1987

It is investigated that the determination of the correlation between the change of microstructure and electrical properties. Yttria is added to the compositiojn of rhombohedral region in Pb(Mg1/3Nb2./3)O3-PbTiO3-PbZrO3 ternary system. Average grian size, lattice parameters and distribution of yttrium are characterized by XRD, SEM and EDS. Electrical properties are determined by measurement of Curie temperature, piezoelectric properties and hysteresis loops. The results are as follows; 1. Both lattice parameters, a and ${\alpha}$, are changed by addition of yttria to the composition of rhomboheadral region in Pb(Mg1/3Nb2./3)O3-PbTiO3-PbZrO3 ternary system and Curie temperature is proportional to the values at (90-${\alpha}$).