• Journal of the Korean Ceramic Society
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• v.34 no.1
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• pp.88-94
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• 1997

The oxidation behavior of the NiCrAlY bond coat and thermal fatigue failure in the plasma-sprayed thermal barrier coating system, ZrO2.8wt%Y2O3 top coat/Ni-26Cr-5Al-0.5Y bond coat/Hastelloy X superalloy substrate, in commercial use for finned segment of gas turbine burner were investigated. The main oxides formed in the bond coat were NiO, Cr2O3, and Al2O3. It divided the oxide distribution at this interface into two types whether an Al2O3 thin layer existed beneath ZrO2/bond coat interface before operation at high temperature or not. While a continuous layer of NiO was formed mainly in the region where the Al2O3 thin layer was present, the absence of it resulted in the formation of mixture of Cr2O3 and Al2O3 beneath NiO layer. Analyses on the fracture surface of specimen spalled by thermal cycling showed that spalling occurred mainly along the ceram-ic coat near ZrO2/bond coat oxide layer interface, but slightly in the oxide layer region.

• Journal of the Korean Ceramic Society
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• v.44 no.6 s.301
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• pp.291-296
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• 2007

Porous $Al_2O_3-(m-ZrO_2)$ composites were fabricated by pressureless sintering, using different volume percentages (40% - 60%) of poly methyl methacrylate (PMMA) powders as a pore-forming agent. The pore-forming agent was successfully removed, and the pore size and shape were well-controlled during the burn-out and sintering processes. The average pore size in the porous $Al_2O_3-(m-ZrO_2)$ bodies was about $200\;{\mu}m$ in diameter. The values of relative density, bending strength, hardness, and elastic modulus decreased as the PMMA content increased; i.e., in the porous body (sintered at $1500^{\circ}C$) using 55 vol % PMMA, their values were about 50.8%, 29.8 MPa, 266.4 Hv, and 6.4 GPa, respectively. To make the $Al_2O_3-(m-ZrO_2)$/polymer hybrid composites, a bioactive polymer, such as PMMA, was infiltrated into the porous $Al_2O_3-(m-ZrO_2)$ composites. After infiltration, most of the pores in the porous $Al_2O_3-(m-ZrO_2)$ composites, which were made using 60 vol % PMMA additions, were infiltrated with PMMA, and their values of relative density, bending strength, hardness, and elastic modulus remarkably increased.

• Journal of the Korean Ceramic Society
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• v.38 no.11
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• pp.1042-1045
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• 2001

Microwave dielectric properties of Ba(Zn$_{1}$3/Nb$_{2}$3/) $O_3$-Sr(Zn$_{1}$3/Nb$_{2}$3/) $O_3$(BZN-SZN) system were investigated as a function of sintering temperature and Zr $O_2$content. Density was increased and the temperature coefficient of resonant frequency (TCF, $\tau$$_{f}$) decreased with increasing sintering temperature. However dielectric constant (K) and Q$\times$f value did not change markedly with the sintering temperature. For the samples sintered at the same temperature, density, dielectric constant, and Q$\times$f value were increased and TCF was decreased with increasing Zr $O_2$concentration. Especially, the dielectric constant of the sample increased with x and exhibited the maximum value ($\varepsilon$$_{r}$=41) when x=0.6 at 1575$^{\circ}C$ sintered. TCF decreased with x and exhibited the minimum value ($\tau$$_{f}$=+0.8ppm/$^{\circ}C$) when x=1.0..0.

• Journal of the Korean Ceramic Society
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• v.30 no.8
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• pp.635-642
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• 1993

To obtain a higher dielectric constant material, we investigated Ca substitution for Pb in PbZrO3. In this study, the four mixtures of (Pb0.68Ca0.32)ZrO3, (Pb0.65Ca0.37)ZrO3, (Pb0.63Ca0.37)ZrO3, and (Pb0.60Ca0.40)ZrO3 were prepared by coprecipitation reaction of Pb(NO3)2, ZrOCl2, and CaCl2 with (NH4)2CO3 and NH4OH in aqueous solution. The (Pb1-xCax)ZrO3 with different x mole fractions (x=0.35, 0.37) showed not only high dielectric constant, but also high Q values and low temperature coefficient of the capacitance.

• Korean Journal of Materials Research
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• v.9 no.10
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• pp.1041-1046
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• 1999

(Zr(sub)0.8Sn(sub)0.2)$TiO_4$세라믹스와 소결조제로서 ($B_2$$O_3$.Li$_2$O)의 첨가에 따른 마이크로파 유전특성 및 미세구조에 미치는 영향에 대하여 연구하였다. 1.0 mol.% $Sb_2$O(sub)5를 첨가하고 130$0^{\circ}C$에서 5시간 소결한 (Zr(sub)0.8Sn(sub)0.2)$TiO_4$세라믹스의 경우 ($B_2$$O_3$.Li$_2$O)첨가량 증가에 따라 치밀화 및 결정립 성장에 의해 유전상수와 Q.f값은 증가하여 첨가량이 0.35wt.%에서 최대값인 38과 59,000을 각각 나타내었으며, 0.50wt.% 이상 첨가한 경우에서는 제 2상의 생성으로 인하여 감소하였다. 1.0 mol% Sb$_2$O(sub)5와 0.35wt.% ($B_2$$O_3$.$Li_2$O)를 첨가한 (Zr(sub)0.8Sn(sub)0.2)TiO$_4$세라믹스를 125$0^{\circ}C$와 135$0^{\circ}C$에서 5시간 소결한 경우에는 각각 미반응 TiO$_2$의 존재와 과대입자성장에 의한 결정립내기공의 생성으로 인하여 마이크로파 유전특성은 저하되었다.

• Journal of the Korean Ceramic Society
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• v.33 no.1
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• pp.65-73
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• 1996

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.11a
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• pp.172-173
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• 2006

Metal-ferroelectric-insulator-semiconductor (MFIS) structures with $Bi_{3.35}La_{0.75}Ti_3O_{12}$ (BLT) ferroelectric film and Zirconium oxide ($ZrO_2$) layer were fabricated on p-type Si(100). $ZrO_2$ and BLT films were prepared by sol-gel technique. Surface morphologies of $ZrO_2$ and BLT film were measured by atomic force microscope (AFM). The electrical characteristics of Au/$ZrO_2$/Si and Au/BLT/$ZrO_2$/Si film were investigated by C-V and I-V measurements. No hysteretic characteristics was observed in the C-V curve of the Au/$ZrO_2$/Si structure. The memory window width m C-V curve of the Au/BLT/$ZrO_2$/Si diode was about 1.3 V for a voltage sweep of ${\pm}5$ V. The leakage current of Au/$ZrO_2$/Si and Au/BLT/$ZrO_2$/Si structures were about $3{\times}10^{-8}$ A at 30 MV/cm and $3{\times}10^{-8}$ A at 3 MV/cm, respectively.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.8 no.3
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• pp.518-523
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• 1998

The fracture toughness and hardness of 62 %$SiO_2-19%ZrO_2-9%Na_2O-10%B_2O_3$(wt%) glass ceramics system were investigated. As a result of DTA study to find crystallization temperature, an exothermic peak near $820^{\circ}C$ was observed. The optimum nucleation temperature and the optimum crystal growth temperature were determined by XRD and SEM analysis, and were approximately $650^{\circ}C$, $840^{\circ}C$ respectively. The fracture toughness of this zirconia glass ceramics was determined by Vickers Indentation Method. The hardness value was not changed with increasing of the heat treatment temperature, but fracture toughness value was increased up to $1.8 MPa{\cdot}m^{1/2}$ at $840^{\circ}C$, with increasing of heat treatment temperature.

• Journal of the Mineralogical Society of Korea
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• v.19 no.2 s.48
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• pp.81-88
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• 2006

The Yttria Partially Stabilized Zirconia powder was prepared by spontaneous precipitation method using $ZrOCl_2{\cdot}8H_O-YCl_33{\cdot}6H_2O$ solution as a starting materials. The optimal experimental conditions such as concentration and pH of starting solutions, the amounts of stabilizer $Y_2O_3$ used, and sintered temperature were carefully studied. The best condition for synthesizing $ZrO_2$ was experimentally selected and applied throughout this study for the preparation of the 3 mole% $Y_2O_3$ partially stabilized zirconia, 3YSZ. The physical properties of 3YSZ was examined by XRD, Raman, DT A, and SEM. The structural transition from pure monoclinic high temperature $ZrO_2$ to tetragonal room temperature 3YSZ was made possible by the added amount of $Y_2O_3$ in the $ZrO_2+Y_2O_3$ system. All Raman Spectrum band appeared in the lower wave numbers rather than in higher wave numbers as structure changes from monoclinic to tetragonal.

• Transactions on Electrical and Electronic Materials
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• v.16 no.2
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• pp.86-89
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• 2015

Uniform ZrO₂ nanoballs were synthesized at 700℃ using the inverse replication method through a colloid-imprinted carbon (CIC) template. The structural, dielectric, and conducting properties of the ZrO₂ nanoballs were investigated and compared with those of ZrO₂ film prepared by sol-gel method and powdered ZrO₂ chemical. Both the monoclinic and cubic phases were found in the ZrO₂ balls and film but the ZrO₂ chemical showed a monoclinic phase, where the cubic structure is known to be formed at above 2,300℃. ZrO₂ nanoballs showed the lower dielectric property of k = 21.2 at 1 MHz because the 8-coordinated cubic phase in the ZrO₂ nanoball produced lower polarization than the polarization of the 7-coordinated monoclinic ZrO₂ chemical (k = 23.6). The dielectric stability was maintained in each ZrO₂ ball, film, and chemical under the applied forward and reverse voltage range (−5 to +5 V) at 1 MHz. The ionic conductivities were 7.86 × 10⁻⁸/Ω·cm for ZrO₂ nanoballs, 3.29 × 10⁻⁸/Ω·cm for ZrO₂ chemical, and 6.70 × 10⁻⁵/Ω·cm for the thickness of 1,053 nm ZrO₂ film at room temperature with the electronic contribution being less than 0.006%.