• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.07a
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• pp.955-958
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• 2001

The structure characteristics of varistor of Zn oxide to depend on the breakdown voltage has been investigated to annealing condition by additive material of Sb$_2$O$_3$ system. The breakdown voltage that has not doping Sb$_2$O$_3$ was 235[V]. ZnO varistors was shown ohmic properties when it's applied voltage was below critical voltage. It was shown non-ohmic properties over critical voltage, because current was increased with decreasing resistance. High voltage ZnO varistors had high breakdown voltage, but it had bad electrical stability with various surge. Sb$_2$O$_3$was increased non-linear coefficient in ZnO varistors grain boundary.

• Journal of the Korean Society of Industry Convergence
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• v.4 no.1
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• pp.61-69
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• 2001

Polycarbonate(PC) membranes for oxygen enrichment from air were prepared by the wet phase inversion method. In order to improve oxygen separation performances of the PC membrane, the effect of the added ethanol(nonsolvent) and $CuCl_2$(metal salt) concentration in the casting solution on morphology, oxygen permeability ami $O_2/N_2$ separation factor of the membrane was studied. In addition, tensile strength and elongation at break of the membrane were investigated. An asymmetric membrane with a dense top layer and a porous sublayer was obtained. The thickness of the dense top layer decreased with increasing amount of nonsolvent additive. Compared with pure PC membrane without additive(metal salt), the oxygen permeability and $O_2/N_2$ separation factor of the $PC/CuCl_2$ membrane are significantly improved. The oxygen permeability and $O_2/N_2$ separation factor is $5.25{\times}10^{-9}cm^3(STP){\cdot}cm/cm^2{\cdot}sec{\cdot}cmHg$ and 4.5, respectively. This improvement might be due to good interaction between metal salt and oxygen.

• Journal of the Korean Ceramic Society
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• v.23 no.6
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• pp.37-44
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• 1986

Yttria-antimonia-stabilized zirconia was investigated with respect to the amount of $Sb_2O_3$ addition in the range of 0.5~5mole% to the base composition of $(ZrO)_{0.92}(Y_2O_3)_{0.08}$ The sinterbility modulus of rupture Vickers hardness evaporation of components phase form-tion and mcicrostructure were evaluated with antimonia content. Also two probe A. C conductivity measurement was subjected to all specimens and the best results are achieved with 1mol% $Sb_2O_3$ as a sinter agent and relative density of~98% obtained at 140$0^{\circ}C$ and this composition has a maximum electrical conductivity due to the possible substition of $Sb^{3+}$ for $Zr^{4+}$ site. The effect of $Sb_2O_3$ on the electrical conductivity of th bulk and the grain boundaries has on investigated using frequency dispersion analysis (5~106 Hz) Antimonia addition has a negative in-fluence on both the bulk and the grain boundary conductivity except for a 1 mon% addition. The additive antimonia has improve a modulus of rupture to 60~MPa due to metastable-tetragonal phase apparence and decrease the hardness with increasing the $Sb_2O_3$ content.

• Journal of the Korean Ceramic Society
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• v.22 no.5
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• pp.35-42
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• 1985

$eta$-Sialon powders were prepared by reduction-nitridation from mixture of Wando pyrophyllite and graphite as a reducing agent at 135$0^{\circ}C$ in 80% $N_2$-20% $H_2$ atmosphere. As the reaction products $Si_2ON_2$, $\beta$-$Si_3N_4$ a--$Si_3N_4$ and $\beta$-SiC were observed. Additive agents of MgO, CaO, $Y_2O_3$ were used for promoting the reduction and nitridiation aeaction. The present study was conducted to investigate the effects of silica-carbon ratio ($SiO_2$/C=weight ratio), raction time gas flow rate pellet size and powder packing on synthesis of $\beta$-Sialon from Wando pyropyllite.

• Journal of the Korean Ceramic Society
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• v.28 no.7
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• pp.561-567
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• 1991

Submicron ${\alpha}-SiC$ powder with $Al_2O_3$ addition was hot-pressed under the controlled heating and pressurizing schedule. $SiO_2$ layer on ${\alpha}-SiC$ powder was effective for the sintering of ${\alpha}-SiC$ powder when $Al_2O_3$ was used as an additive. Applying of pressure under the controlled schedule accelerated the rearrangment of SiC grains, yielding 98% of theoretical density of SiC even at $1900^{\circ}C$. Flexural strength of the specimen containing 2 wt% $Al_2O_3$ was increased as increasing the hot-pressing temperature up to $2050^{\circ}C$ and maximum value was 800 MPa, while the flexural strength of the specimen containing 10 wt% $Al_2O_3$ was decreased as increasing the hot-pressing temperature above $2000^{\circ}C$ due to the formation of continuous grain boundary phase. Fracture toughness of the specimens was in the range of $3.5~4.5\;MNm^{-3/2}$ regardless of the amount of $Al_2O_3$ addition.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.31 no.11
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• pp.1108-1114
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• 2007

The low kinds of $Al_2O_3$ composite ceramics were prepared using a mixture of 85 wt.% $Al_2O_3$ (mean size $0.5\;{\mu}m$), 15 wt.% SiC Powder with $Y_2O_3$, as an additive powder (0, 1, 3 and 5 wt.%). The crack-healing strengths were studied as functions of crack-healing temperature and amount of $Y_2O_3$. The in-situ crack-healing behavior was observed at 1,573 K for 1 h in the air. The heat treated specimen with 3 wt.% of $Y_2O_3$ showed better crack-healing ability than specimen with 1 or 5 wt.% of $Y_2O_3$. In case of specimen with 3 wt.% of $Y_2O_3$, the bending strength of the crack-healed specimen at 1,473 K was recovered to the bending strength of smooth specimen treated at 1573 K. The heat-resistance limit temperature of $Al_2O_3$ composite ceramics was 1,073 K, 1,373 K, 873 K for the specimen with 1, 3, 5 wt.% of $Y_2O_3$.

• Journal of the Korean Ceramic Society
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• v.35 no.10
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• pp.1014-1019
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• 1998

As results of the study on the sinterbility of YIG at the low temperature using CuO as additive CuO com-pound which contain {{{{ { {Fe }_{2 }O }_{3 } }} was shown liquid in sintering process. YIG crystal dissolved into CuO compound liquid phase and then Y element which is considered no solubility in solid CuO compound moved to the grain during cooling. The abnormal grain growth up to 150${\mu}{\textrm}{m}$ at CuO 8.6mole% was shown due to shape accomdation reaction and local liquid distribution. The apparent density of YIG shows minimum at CuO 8.6 mole% due to abnormal grain growth and the saturation magnetization decrease dramatically at 32.5mole% due to orthoferrite formation.

• Journal of the Korea institute for structural maintenance and inspection
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• v.17 no.2
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• pp.135-141
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• 2013

In this study, to improve the early-age compressive strength of mortar, the compressive strength tests of mortar mixed smart BFS powder added powder of rapid setting additives milled by processing, using functional grinding aid, the power-typed rapid setting cement clinker developed by sintering industrial waste and by-products with much CaO-$SiO_2-Al_2O_3$ to cement were performed. From the tests, the followings are found that (1) for BFS early-age strength improvement test (Series I): early-age strength improvement of BFS mixed rapid setting additive milled after adding functional grinding aid, when the clinker is milled, is superior and (2) for OPC early-age strength improvement test (Series II): case of additive mixed rapid setting powder typed activator milled after adding functional grinding aid to Clinker-C showed the higher compressive strength.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.07a
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• pp.972-975
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• 2001

The effect of Cr$_2$O$_3$(0 to 0.5 wt%) doping on the microstructure and electrical properties of ternary Pb(Zr,Ti)O$_3$-Pb(Ni,Nb)O$_3$piezoelectric ceramic has been investigated. Abnormal grain growth (grain size 3.3 to 11.2 $\mu$m) and densification are found. Minor additives of $\leq$0.1 wt% improve the mechanical coupling factor, but with more additives of $\geq$0.2 wt% electrical properties deteriorate. Thus, these phenomna can be ascribed mainly to anomalous developed microstructure. The large grains were composed of a core region that is free of Cr and a surrounding shell region rich in Cr. The interfaces between the core and the shell were composed of misfit dislocations. The mechanical properties of the specimens were strongly influenced by this microstructural change. The microstrutural and compositonal evolution of the specimens containing different amounts of Cr$_2$O$_3$were monitored. Electrical properties were measured and related to the variations in the microstructure.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.11a
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• pp.279-282
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• 2003

For the millimeter-wave dielectrics, Forsterite-based ceramics were produced. Pure forsterite ceramics($Mg_2SiO_4$) shows porous micro-structure and very low Q*f values, which is not suitable for the dielectrics for the millimeter-wave band. Several sintering aids including $Al_2O_3$, $Li_2CO_3$, $Li_2SiO_4$, were added to the forsterite ceramics in order to produce dense low-loss dielectrics. Among these additives, $Li_2CO_3$ is the most effective sintering aids. Several sub-components including NiO, ZnO, $SnO_2$, $TiO_2$, were added to enhance the microwave dielectric properties. $TiO_2$ is the most effective additive to enhance the dielectric properties at microwave bands. The simultaneous addition of $TiO_2$ and $Li_2CO_3$ increases Q*f value over 170,000, which can be used as dielectrics in millimeter-wave bands.