• Journal of Korea Foundry Society
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• v.22 no.2
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• pp.75-81
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• 2002

The main objectives were to investigate the suitability of CaO crucible for melting TiAl alloys and to develop investment mold for investment casting of TiAl alloys. TiAl alloy specimen were prepared by plasma arc furnace under argon atmosphere. After melting of TiAl alloy using CaO crucible, the results showed that there is little contamination of oxygen in the TiAl bulk. Conventional vacuum induction furnaces can be readily adaptable to produce cast parts of TiAl without high skilled techniques. The determination of optical metallography and microhardness profiles in investment cast TiAl alloy rods has allowed the gradation of the relative thermal stability of the oxides examined. The molds used for the present study were $ZrO_2$, $Al_2O_3$, CaO stabilized $ZrO_2$ and $ZrSiO_4$. Even although high temperature of mold preheating, $Al_2O_3$ mold is a promising mold material for investment casting of TiAl alloys in terms of thermal stability, cost and handling strength. It is important to take thermal stability and preheating temperature of mold into consideration for investment casting of TiAl alloys.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.55 no.1
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• pp.1-5
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• 2006

The effect of A/B moi ratios and sintering temperatures on dielectric properties and microstructure of $(Ba_{0.93}Ca_{0.07})_m(Ti_{0.82}Zr_{0.18})O_3$ ceramics were investigated. The dielectric constant decreased with increasing the A/B mol ratio. However, the dielectric loss is improved. As the dielectric properties of A/B mol ratio with m = 1.009 at sintered temperature $1260^{\circ}C$, we obtained dielectric constant 12,800, dielectric loss $3.5\%$ and Y5V temperature characteristics. Highly reliable Ni-MLCCs, 1.6mm$(length){\time}0.8mm(width){\time}0.8mm$(height) with capacitance of 1.23 ${\mu}F$ and 야ssipation loss of $5.2\%$ were obtained employing dielectric material composed of $(Ba_{0.93}Ca_{0.07})_{1.009}(Ti_{0.82}Zr_{0.18})O_3$ - $MnO_2\;0.2wt\%-Y_2O_3\;0.18wt\%,\;-\;SO_2\;0.15wt\%-(Ba_{0.4}Ca_{0.6})SiO_3\;1wt\%$.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.06a
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• pp.259-259
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• 2007

The low temperature sintering of dolomite type borates, $CaZr(BO_3)_2$[CZB] ceramics and their microwave dielectric properties were investigated The sintering temperature of CZB ceramics could be reduced from $1150^{\circ}C$ to $925^{\circ}C$ by the addition of sintering additive. $CaZrO_3$, $ZrO_2$ and $CaB_2O_4$ second phases were found in the CZB ceramics. The syntheses, sintering properties, microstructures, and dielectricnproperties of dolomite-type borates were examined by XRD, thermal analysis, electron microscopy, network analyzer, and the results are discussed intensively. The compatibility with silver electrode was also explored.

• Journal of the Korean Ceramic Society
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• v.39 no.4
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• pp.420-426
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• 2002

$ZrO_2$, $Y_2O_3$-doped $ZrO_2$ and CaO-doped $ZrO_2$ powders were prepared by hydrothermal crystallizing spherical $ZrO_2$ gel which had been synthesized by thermal hydrolysis reaction. After the hydrothermal crystallization process, the formed crystallized powders sustained its original spherical shape and had the mean particle size of $0.4{\mu}m$. The particles were composed of about 10nm sized primary particles. The agglomeration strength between the primary particles appears very weak considering that the spherical particles were broken into the primary particles during the pressing process. The particle shape, size, phase fraction and dopant content were analyzed and crystallization mechanism of spherical gel was discussed.

• Korean Journal of Materials Research
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• v.11 no.6
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• pp.460-464
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• 2001

The ceramic diffusion coupling with the green body of calcium-doped lanthanum chromite(La$_{0.8}$Ca$_{0.2}$CrO$_3$CLC- G) and sintered calcium-doped lanthanum chromite(La$_{0.8}$Ca$_{0.2}$CrO$_3$ CLC) by Pechini's method on yttria stabilized zirconia(YSZ) plate has been investigated. The X-ray diffraction pattern of CLC sides at the reacted CLC-G/ CLC and CLC/YSZ interface were identified as La$_{1-x}$ Ca$_{x}$CrO$_3$ and the unreacted YSZ side was cubic-ZrO$_2$ at the treated condition, 1300~1500 C for 10 hr in air, respectively. The order of migration components between CLC/YSZ interface was Zr>La>>Cr>>>Ca and these changes were not dependent upon the treated conditions. The grain shape and size at the interface of CLC-G/CLC was appeared to have a uniform distribution with increasing temperature. The bonding reaction of YSZ/CLC was occurred without a large amount change of the compositions in SEM photos.os.otos.os.

• 한국전기화학회:학술대회논문집
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• 1998.10a
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• pp.60-60
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• 1998

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.19 no.3
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• pp.130-134
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• 2009

A new long persistent phosphors of $CaZrO_3$ was synthesized at high temperature with weak reduction atmosphere by a traditional solid state reaction method. Photoluminescence spectra analysis showed that the $CaZrO_3$ doped with $Tb^{3+}$ emitted green-yellow emission caused by the energy level transition from the $^5D_3$ and $^5D_4$ to $^7F_1{\sim}^7F_6$. The main emission spectra of 542 nm peak by the $^5D_4{\rightarrow}^7F_5$ transition was revealed through synthesizing at high temperature in $N_2$ gas atmosphere. The afterglow emission spectra of $CaZrO_3:Tb^{3+}$ long persistent phosphores arise at 546 nm peak of narrow range. After the 254 nm ultraviolet light excitation source was switched off, the green-yellow long persistent phosphor can be observed which could last for 8 h in the limit of light perception of dark-adapted human eyes ($0.32\;mcd/m^2$).

• Journal of the Korean Ceramic Society
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• v.31 no.6
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• pp.651-659
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• 1994

BaTiO3 ceramics were sintered on Al2O3, MgAl2O4, MgO and Mg-, Ca-, Y-stabilized zirconia setters. Then the influence of setters on the microstructure of BaTiO3 ceramics and the stability of setters were investigated by SEM, EDAX and XRD analyses. The microstructure of BaTiO3 ceramics sintered on Al2O3, MgAl2O4, MgO and Mg-PSZ showed large grain growth, but little grain growth on Ce-TZP(Tetragonal Zirconia Policrystal). Mg-PSZ(Partially Stabilized Zirconia), Ca-PSZ, Ce-TZP setters showed extensive phase transformation. Y-TZP and fused Y-SZ (Stabilized Zirconia) setters were stable. The liquid sintering aids of BaTiO3 ceramics accelerate mass transport. The reaction of SrTiO3 in BaTiO3 with ZrO2 resulted in the formation of SrZrO3.

• Electrical & Electronic Materials
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• v.10 no.10
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• pp.1041-1047
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• 1997

In this paper the dielectric properties of (0.8-x)Pb(Mb$_{1}$3//Nb/2/3)O$_3$/BaTiO$_3$-CaZrO$_3$(x=0.1, 0.15, 0.2, 0.25) ceramics were investigated. Specimens were prepared by the conventional mixed oxide method and sintering temperature and time were 1000~115$0^{\circ}C$ 2hr, respectively. The structural and dielectric properties with variation of sintering temperature and composition were investigated. All the specimens sintered at 115$0^{\circ}C$ for 2hr showed the highest value of 1043. With increasing the contents of CZ and frequency dielectric constant was decreased and which was decreased with increasing temperature from 3$0^{\circ}C$ to 15$0^{\circ}C$.

• Journal of the Korean Ceramic Society
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• v.16 no.3
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• pp.135-141
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• 1979

This study seeks to find optimum conditions for the heating schedule of the Diopside-Devitrite system, to find the amounts and the kinds of nucleus which effect the crystal growth and forming nucleus. Generally, crystallization in the glass depends on the number of nucleus growing in the internal system and the rate of crystal growth. In order to obtain homogeneous polystalline phae, Diopside as MgO source and $ZrO_2$.$P_2O_5$, $TiO_2$, NaF, $CaF_2$ as nucleating agents were added to the $Na_2O$.CaO.$6SiO_2$ glass. The results obtained were Summarized as follows. 1) Optimum Batch Composition of base glass is 76.82 wt.% $SiO_2$, 5.84 wt.% CaO, 4.54 wt.% MgO and 9.80 wt.% $Na_2O$. 2) Best heating schedule.140$0^{\circ}C$(Melting)coolinglongrightarrow95$0^{\circ}C$reheatinglongrightarrow$1100^{\circ}C$coolinglongrightarrowRoom Temp. 3) The optimum amounts of $ZrO_2$.$P_2O_5$, $TiO_2$ and $CaF_2$ are 3wt.% and that of NaF is 4 wt.% as a nucleating agents.