• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1999.05a
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• pp.308-311
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• 1999

The varistor characteristics of $ZnO-Pr_6O_11-CoO-Er_2O_3$-based ceramics were investigated. $ZnO-Pr_6O_11-CoO-Er_2O_3$-based ceramics were sintered at $1300^{\circ}C$ and $1350^{\circ}C$in the addition range 0.0~2.0mol% $Er_2O_3$, respectively. $ZnO-Pr_6O_11-CoO-Er_2O_3$-based ceramics, which are added with 0.5mol% $Er_2O_3$ at $1300^{\circ}C$ and l.Omol% $Er_2O_3$ at $1350^{\circ}C$ sintering temperature, exhibited the bestexcellent varistor characteristics, namely, the nonlinear exponent was better 52.78 at $1300^{\circ}C$ thanat 13$1350^{\circ}C$ and the leakage current was better 6.57$\mu\textrm$A at $1350^{\circ}C$ than at $1300^{\circ}C$. Consequently, it is estimated that $ZnO-Pr_6O_11-CoO-Er_2O_3$-based ceramics, which $Er_2O_3$ is added in the range 0.5~l.Omol% will begin to be used as a predominant basic composition of $PR_6O_11$-based ZnO varistors.

• Journal of Korean Ophthalmic Optics Society
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• v.8 no.1
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• pp.17-22
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• 2003

The experimental FT-IR spectra and DTA curves of the $PbO-Bi_2O_3-B_2O_3-SiO_2$ glasses have been investigated. The composition ratio dependence of glass transition temperature showed that the structure of this glass system changes at 60 mol% $Bi_2O_3$. We have observed that the FT-IR spectra of the investigated samples with high bismuth content are dominated by bands associated to the structural units of the heaviest cation, $Bi^{3+}$ and the boron atoms in the treated samples are three and four coordinated even for very high $Bi_2O_3$ content. The low intensity of these non-bridging oxygen bands, for high PbO content glasses, can be attributed to the strong network-forming roles of PbO. The glasses absorption bands exhibited a greater change in intensities on crystallization.

• Korean Journal of Materials Research
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• v.5 no.2
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• pp.246-250
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• 1995

Microwave properties of $CaTiO_{3}$, MgO and CaO added $MgTiO_{3}$ ceramics are investigated. In the composition of $(Mg_{0.915}Ca_{0.085})TiO_3$, dielectric constant($varepsilon _T$) was 22, Qxf value was 50000, and temperature coefficient of resonant frequency($gamma_T$) approached to near zero $ppm/^{\circ}C$.$MgTiO_{3}$ ceramics with 0.1 mol of MgO showed the highest Qxf calue of 131000, dielectric constant of 17, and r, of -$50ppm/^{\circ}C$. Dielectric constant of 8 mol% CaO added to $MgTiO_{3}$-MgO was 20. Qxf valus was 52000, and sf was zero $ppm/^{\circ}C$. $MgTiO_{3}$-Mg0-Ca0 system showed higher Qxf value than ($Mg_{1-x}, Ca_x$) Ti03 system.

• Journal of Korean Society for Atmospheric Environment
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• v.20 no.4
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• pp.451-463
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• 2004

The performance of disk-type catalytic filters impregnated by TiO$_2$ or TiO$_2$-3Al$_2$O$_3$ㆍ 2SiO$_2$ supports and V$_2$O$_{5}$ catalyst was evaluated for selective catalytic reduction (SCR) of NO with ammonia as a reductant. XRD, FT -IR, BET and SEM were used to characterize the catalytic filters prepared in this work. Optimal V$_2$O$_{5}$ loading and reaction temperature for V$_2$O$_{5}$/TiO$_2$ catalytic filters were 3-6 wt.% and 350-40$0^{\circ}C$ at GHSV 14,300 $hr^{-1}$ in the presence of oxygen, respectively. With increasing the V$_2$O$_{5}$ loading from 0.5 to 6 wt%, NO conversion increased from 24 to 96% at 40$0^{\circ}C$ and 14.300$hr^{-1}$, and maintained at 80% over in the V$_2$O$_{5}$ loading range of 3-6 wt.% and then dropped at V$_2$O$_{5}$ loading of 7wt.% over. In comparing V$_2$O$_{5}$/ TiO$_2$ and V$_2$O$_{5}$/ TiO$_2$-3Al$_2$O$_3$ㆍ2SiO$_2$ catalytic fillers, which have same 3wt.% V$_2$O$_{5}$ loading, the V$_2$O$_{5}$/ TiO$_2$-3A1$_2$O$_3$ㆍ2SiO$_2$ catalytic filter showed higher activity than V$_2$O$_{5}$/ TiO$_2$ catalytic filter, but higher differential pressure drops owing to its low air permeability. low air permeability.

• Journal of the Korean Ceramic Society
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• v.35 no.9
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• pp.905-910
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• 1998

• Journal of the Korean Ceramic Society
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• v.34 no.11
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• pp.1129-1138
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• 1997

Al2O3/20 vol%YAG composite containing equiaxed grains and Al2O3/20 vol%LaAl11O18 composite containing elongated grains were fabricated using Al2O3-Y2O3 composition and Al2O3-La2O3 composition, respectively, by hot-pressing. In order to investigate the influence of microstructural control of second phase on toughening effect of toughened ceramic composites, AE (acoustic emission) measurements have been coupled with fracture toughness experiments(SENB and SEPB method). A separation of the fracture toughness and analysis of toughening mechanism was possible using the AE technique. The fracture toughness of hot-pressed materials was estimated to be 3.2 MPam0.5 for monolithic alumina, 4.7 MPam0.5 for Al2O3/20 vol%YAG composite and 6.2 MPam0.5 for Al2O3/20 vol%LaAl11O18 composite. In monolithic Al2O3, toughening does not occur as a result of either microcracking or grain bridging, whereas, composites exhibit toughening effects by both microcracking in the frontal zone and gain bridging in the wake zone, resulting in an improvement of fracture toughness as compared with monolithic Al2O3. The fracture toughness of Al2O3/20 vol%LaAl11O18 composite is higher than that of Al2O3/20 vol%YAG composite. It may be attributed to the elongated microstructure of Al2O3/20 vol%LaAl11O18 composite, resulting relatively greater bridging effect.

• Journal of the Korean Ceramic Society
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• v.33 no.11
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• pp.1209-1216
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• 1996

MoSi2-Al2O3 composites were prepared by thermal explosion mode of self-propagating high temperature syn-thesis (SHS) using element powders of MoO3 Mo Si and Al. The combustion products of MoSi2 which have 10, 20, 30 and 40 wt% Al2O3 showed the molten state in the range of Mo to MoO3 6:1-9.5:1, 2:1-8:1, 1:1-5:1, and 1:1-3:1 (molar ratio) respectively. The combustion products which made least seperation the molten phase from the slag phase were in Mo/MoO3=9, 5:1, 8:1, 5:1 and 3:1 (molar ratio) respectively. Particles size of MoSi2 and Al2O3 in the combustion product were decreased as the molar ratio of Mo to MoO3 increase. By XRD analysis only MoSi2 and $\alpha$-Al2O3 peaks were identified in the combusion products, In case of MoSi2 containing 20wt% Al2O3 5.1wt% Al existed into MoSi2 grains and 30.7wt% Si and 7.7wt% Mo existed into Al2O3 grains. The relative density of MoSi2 containing 10, 20, 30 and 40 wt% Al2O3 were 82.7, 85.2, and 81.9% respectively. The fracture strength of MoSi2-Al2O3 composites increased with increasing Al2O3 and that of MoSi2-20wt% Al2O3 composite was 195 MPa.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2018.05a
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• pp.238-239
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• 2018

This paper presents the synthesis results of CaO-Al₂O₃ system clinker using the CaCO₃ and the Al₂O₃ according to the synthesis methods dependent on the temperature. The purpose of this study is the formation of the CaO-Al₂O₃ system clinker containing high ratio of CaO·2Al₂O₃ (CA₂). The maximum sintering temperature for the synthesis of CaO-Al₂O₃ compounds was 1250℃, 1300℃ and 1400℃. The CaO-Al₂O₃ compounds was sintered at the maximum sintering temperature for three hours. After sintering, the compounds was analyzed using X-ray diffraction method. The 12CaO·7Al₂O₃ (C1₂A₇) and CaO·Al₂O₃ (CA) increased as elevating the maximum sintering temperature whereas the CA₂ decreased. Especially, at the 1250℃ of maximum sintering temperature, the un-reacted CaO and Al₂O₃ was identified.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1998.11a
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• pp.45-48
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• 1998

A BaTiO$_3$ was annexed to SrTiO$_3$, (x)BaTiO$_3$-(1-x)SrTiO$_3$ (0.7$\leq$X$\leq$1) ceramics with stable dielectric and electrical properties in high voltage were manufactured. Structural, dielectric and electrical properties were surveyed with the contents of SrTiO$_3$. The open porosity and sintering density were excellent in 0.9BaTiO$_3$-0.1SrTiO$_3$, the grain size of 0.9BaTiO$_3$-0.1SrTiO$_3$ was maximum at 12.40[${\mu}{\textrm}{m}$]. Increasing SrTiO$_3$ mol ratio, the curie temperature was shifted low temperature and the supreme permittivity was increased. In line with increasing of supplied voltage, permitivity was decreased slightly.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.11a
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• pp.400-403
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• 2004

The dielectric properties of $BaTiO_3/SrTiO_3$ multilayered thick films with printing times were investigated. $BaTiO_3/SrTiO_3$ thick films were deposited by Screen-printing method on alumina substrates. The obtained films were sintered at $1400^{\circ}C$ with bottom electrode(Pt) for 2hours. The structural and the dielectric properties were investigated for various printing times. The BST phase appeared in all of the $BaTiO_3/SrTiO_3$ mutilayered thick films. The $BaTiO_3/SrTiO_3$ multilayered thick film thickness, obtained by one printings, was $50{\mu}m$. The dielectric constant and dielectric loss of the $BaTiO_3/SrTiO_3$ multilayered thick film, obtained by five printings, were about 266, 0.8% at 1Mhz, respectively.