• Journal of the Korean Ceramic Society
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• v.41 no.8
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• pp.605-609
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• 2004

The microstructure, electrical and dielectric characteristics of ZnO varistors were investigated at various metal oxide (NiO, MgO, and Cr$_2$O$_3$) additives. The average grain size was increased with addition of NiO while that was decreased with addition of Cr$_2$O$_3$-Thereby, the varistor voltage was higher in Cr$_2$O$_3$-added composition. Among varistors, the varistor added with Cr$_2$O$_3$ exhibited the highest nonlinearity, with 40.5 in the nonlinear exponent and 2.7 ${\mu}$A in the leakage current and its dielectric dissipation factor was relatively low value of 0.0589.

• Journal of the Korean Ceramic Society
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• v.48 no.4
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• pp.269-277
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• 2011

Glass-ceramics based on lithium disilicate($Li_2Si_2O_5$) are prepared by heat-treatment of glasses in a system of $SiO_2-Li_2O-K_2O-Al_2O_3$ with different compositions. The crystallization heat-treatment was conducted at the temperature range of $700{\sim}900^{\circ}C$ and samples were analyzed by XRD and SEM. Mechanical properties were determined by a Vicker's hardness and 4 point bending strength. When $SiO_2/Li_2O$ ratio increased, cristobalite and tridymite crystals showed more predominate than lithium disilicate crystals. Increase in $Al_2O_3$ contents in the glass suppressed crystallzation of lithium disilicate crystals. Increase in ZnO, $B_2O_3$ contents in the glass decreased crystallization temperature of lithium disilicate crystals, and increased mechanical properties because of the reduction of the lithium disilicate crystal size.

• Journal of the Korean Ceramic Society
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• v.40 no.8
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• pp.725-729
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• 2003

The fluorine doping along with heavy metal oxides remarkably raised the $^3$H$_4$ lifetime and the quantum efficiency in Tm$^{3+}$-doped silicate glasses. 29 mol% of fluorine substitution for oxygen in 70SiO$_2$-15Pbo-12ZnO-3KO$_{1}$2/ glass raised $^3$H$_4$ lifetime to 193 $mutextrm{s}$. Refractive indices were raised by heavy metal oxide substitution, but hardly changed by fluorine substitution. The fluorine doping changed the local structure around Tm$^{3+}$ions, then low energy vibrations related to fluorine are considered to largely reduce the multi-phonon relaxation rates in the oxyfluoride silicate glasses. The $^3$H$_4$ lifetimes and absorption and emission spectra of Tm$^{3+}$doped silicate and oxyfluoride silicate glasses are reported, and Judd-Ofelt calculation results are discussed in this paper.

• Journal of the Korean Ceramic Society
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• v.55 no.2
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• pp.160-165
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• 2018

This paper investigates the reaction rate of $CO_2$ storing carbonation hybrid reaction by comparing the behavior of carbonation between $Ca(OH)_2$ and fly ash with that of CFBC (Circulating Fluidized Bed Combustion) containing plenty of Free-CaO. Because fly ash with CFBC contains a lot of unreacted CaO, it cannot be used as a raw material for concrete admixtures and its usages are limited. To reuse such material, we stabilized unreacted CaO by carbonation and investigated the carbonation rate. We used a pH meter and a thermometer to check the rate of the carbonization. Also, we set the contents of fly ash with CFBC, $Ca(OH)_2$, flow and fluid of $CO_2$, respectively, to 100 g, 50 g, 100 ~ 1000 cc/min and 400 g based on the content of Free-CaO. We used carbonated water instead of water, and added an alkaline activator to promote the carbonation rate. As a result, the addition of the alkaline activator and carbonated water promoted the rate of carbonation via a hybrid reaction.

• Journal of the Korean Ceramic Society
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• v.39 no.2
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• pp.190-193
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• 2002

3mol% $Y_2O_3$ Partially-Stabilized Zirconia single Crystals (PSZCs) containing a small quantity (<0.5%) of rare-earth oxides ($CeO_2,\;Tb_2O_3$) were prepared by using a direct high-frequency skull melting technique to evaluate hydrothermal stability in an autoclave. Pole exhibited no $t{\rightarrow}m$ phase transformation during aging for 5h at temperatures from 150 to 250$^{\circ}C$ and 4MPa water vapor pressure in an autoclave, resulting in excellent hydrothermal stability.

• Journal of the Korean Ceramic Society
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• v.47 no.1
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• pp.61-65
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• 2010

Ultrathin atomic layer deposition (ALD) coatings were found to enhance the performance of lithium-ion batteries (LIBs). Previous studies have demonstrated that $LiCoO_2$ cathode powders coated with metal oxides with thicknesses of $\sim100-1000{\AA}$ grown using wet chemical techniques improved LIB performance. In this study, $LiCoO_2$ powders were coated with conformal $Al_2O_3$ ALD films with thicknesses of only $\sim3-4{\AA}$ established using 2 ALD cycles. The coated $LiCoO_2$ powders exhibited a capacity retention of 89% after 120 charge-discharge cycles in the 3.3~4.5 V (vs. $Li/Li^+$) range. In contrast, the bare $LiCoO_2$ powders displayed only a 45% capacity retention. This dramatic improvement may result from the ultrathin $Al_2O_3$ ALD film acting to minimize Co dissolution or to reduce surface electrolyte reactions.

• Journal of the Korean Ceramic Society
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• v.49 no.1
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• pp.56-65
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• 2012

Functional materials are often exposed to high temperatures and inherent temperature gradients. These temperature gradients act as thermodynamic driving forces for the diffusion of mobile components. The detailed consequences of thermodiffusion depend on the boundary conditions of the non-isothermal sample: Once the boundaries of the sample are inert and closed for exchange of the mobile components, thermodiffusion leads to their pile-up in the stationary state (the so called Soret effect). Once the system is open for an exchange of the mobile component, chemical diffusion adds to the Soret effect, and stationary non-zero component fluxes are additionally observed in the stationary state. In this review, the essential aspects of thermodiffusion and Soret effect in inorganic functional materials are briefly summarized and our current practical knowledge is reviewed. Major examples include nonstoichiometric binary compounds (oxides and other chalcogenides) and ternary solid solutions. The potential influence of the Soret effect on the long term stability of high temperature thermoelectrics is briefly discussed. Typical Soret coefficients for nonstoichiometric compounds are found to be of the order of (d${\delta}$/dT) ${\approx}$ 1%/K.

• Journal of Korea Foundry Society
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• v.36 no.6
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• pp.208-214
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• 2016

Casting defects, which are closely related to entrapped air bubbles and metallic oxides, occur very frequently in the casting process. Many researchers have shown that these defects can be reduced by adopting an appropriate gating system design. But, it is difficult for field engineers to identify a specific gating system that is more appropriate for their products. In this study, we tried to draw a comparison of gating system designs with and without ceramic foam filters. A ceramic foam filter was added to the horizontal runner just after the sprue to prevent air bubble generation and to reduce turbulence without change of the gating system design. To verify the effects of initial pouring velocity, the experiment was conducted with four different amounts of water volume in the reservoir. Results of the water modeling experiment applying the filter showed remarkably changed flow characteristics. Although the study confirmed that use of the filter may change the flow characteristics, it needs to be noted that only filter use alone cannot solve all the problems caused by a poorly designed gating system.

• Journal of the Korean Ceramic Society
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• v.30 no.12
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• pp.1071-1079
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• 1993

Interaction of alkali oxides and SO3 and C3S formation and microstructure was studied using K2CO3 and Na2CO3 as alkali sources and (NH4)2SO4 for SO3. When SO3/K2O=1.43 as mole ratio, K2O and SO3 react to form K2SO4, this phase is immiscible with other oxide melt and thus could not affect C3S formation as well as its microstructure. In a condition of SO3/K2O 1, C3S crystals were round and grown in a much larger size. With addition of Na2O and SO3 by only 1wt% each, C3S formation was strongly hindered. Since C2S was stabilized by Na+ and SO4-2, it could not react to give C3S formation. However in the condition of SO3/Na2O=1.43, a little amount of C3S was formed. It is considered that small amount of Na2SO4 was formed, this phase was immiscible with clinker liquid, and the C3S crystals were formed locally in the liquid part of relatively low Na2O and SO3 compositions. These crystals had irregular and rough surfaces and contained more inclusions than those grown from K2O.SO3 system.

• Journal of the Korean Ceramic Society
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• v.43 no.10 s.293
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• pp.660-665
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• 2006

The mechanical properties of $Al_2O_3$-SiC composites manufactured with adding various amount and size of SiC particles have been measured and analyzed. Generally, the elastic modulus of the composites shows about 50% less than that of PL-8 (45 wt% $Al_2O_3$-51 wt% $SiO_2$-4 wt% other oxides), but the flexural strength is similar with each other. The impact resistance property of $Al_2O_3$-SiC composite against high velocity copper jet was lower than that of PL-8 when SiC particles of approximately 3 $\mu$m diameter was added to. It is caused probably due to the micro-pores made by oxidation of SiC particles. However, in the case of the less-weighted $Al_2O_3$-SiC composite adding to 10 wt% SiC with average diameter of 10 $\mu$m and sintering at 1200$^{\circ}C$, the impact resistance property was improved up to 37 percent compared with that of PL-8.