• Journal of the Korean Ceramic Society
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• v.48 no.5
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• pp.396-403
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• 2011

In this study, we investigated the mechanical behaviors of layered thermal barrier coatings by indentations. Various single and double-layered thermal barrier coatings were deposited by air plasma spray process using different type of commercialized YSZ (Yttria stabilized zirconia) starting powders. Indentation stress-strain curve, load-displacement curve and hardness of the single and the double-layered thermal barrier coatings were obtained experimentally and analyzed. The indentation damages at the same loads were compared, and thus, the results depend on the structure of each coating. The result indicates improvement in damage resistances from tailoring of layered structures in the component of gas turbine system is expected.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.670-671
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• 2006

We report on the mechanical and structural properties of nanocrystalline 8% and 10% mol yttria stabilized zirconia (YSZ) obtained using mechanical alloying (MA). The as-milled powders show a body-centered cubic structure with grain sizes in the nanometer scale. After uniaxial pressing and sintering the compacts exhibit good mechanical properties. We discuss the correlation of these enhanced properties with the microstructural changes induced by heat treatment.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.24 no.4
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• pp.140-144
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• 2014

Co-(0.7 wt%) and Pr-(2.0, 3.5 or 5.0 wt%) doped cubic zirconia ($ZrO_2:Y_2O_3=50:50wt%$) single crystals grown by a skull melting method were heat-treated in $N_2$ at $1150^{\circ}C$ for 5 hrs. The brown colored as-grown single crystals were changed into either dark brownish green, greenish blue and light green color after the heat treatment. Before and after the heat treatment, the YSZ (yttria-stabilized zirconia) single crystals were cut for wafer form (${\phi}7.5mm{\times}t3mm$). The optical and structural properties were examined by UV-VIS spectrophotometer and X-ray diffraction. Absorption by $Co^{2+}$(${\fallingdotseq}589nm$: ${\Gamma}_8[^4A_2(^4F)]{\rightarrow}{\Gamma}_8+{\Gamma}_7[^4T_1(^4F)]$, ${\fallingdotseq}610nm$: ${\Gamma}_8[^4A_2(^4F)]{\rightarrow}{\Gamma}_8[^4T_1(^4F)]$], ${\fallingdotseq}661nm$: ${\Gamma}_8[^4A_2(^4F)]{\rightarrow}{\Gamma}_6[^4T_1(^4F)]$]) and $Pr^{3+}$(${\fallingdotseq}450nm$: ${^3}H{_4}-{^3}P{_2}$, ${\fallingdotseq}473nm$: ${^3}H{_4}{\rightarrow}{^3}P{_1}$, ${\fallingdotseq}484nm$: ${^3}H{_4}{\rightarrow}{^3}P{_0}$), change of ionization energy and lattice parameter were confirmed.

• 한국신재생에너지학회:학술대회논문집
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• 2011.11a
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• pp.84.1-84.1
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• 2011

Typical solid oxide fuel cells (SOFCs) have limited applications because they operate at high temperature due to low ionic conductivity of electrolyte. Thin film solid oxide fuel cell with yttria stabilized zirconia (YSZ) electrolyte is developed to decrease operating temperature. Pt/YSZ/Pt thin film SOFC was fabricated on anodic aluminum oxide (AAO). The crystalline structure of YSZ electrolyte by sputter is heavily depends on the roughness of porous Pt layer, which results in pinholes. To deposit YSZ electrolyte without pinholes and electrical shortage, it is necessary to deposit smoother and denser layer between Pt anode layer and YSZ layer by sputter. Atomic Layer Deposition (ALD) technique is used to deposit pre-YSZ layer, and it improved electrolyte quality. 300nm thick Bi-layered YSZ electrolyte was successfully deposited without electrical shortage.

• Journal of the Korean Ceramic Society
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• v.36 no.2
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• pp.145-150
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• 1999

Gd1-xSrxMnO3(0$\leq$X$\leq$0.6) as the cathode for solid oxide fuel cell was synthesized by citrate process and studied for its crystal structure, electrical conductivity, thermal expansion coefficient (TEC), and investigated reactivity with 8 mol% yttria stabilized zirconia(8YSZ) or Ce0.8Gd0.2O1.9 (CGO). The crystal structure of Gd1-xSrxMnO3 changed from orthorhombic (0$\leq$X$\leq$0.3) through cubic (0.4$\leq$X$\leq$0.5) to tetragonal structure (X=0.6). When Sr contents was increased, the electrical conductivity of Gd1-xSrxMnO3 was inthose of La1-xSrxMnO3, 8YSZ and CGO if Sr content was above 30mol%. TEC of Gd1-xSrxMnO3 was increased with Sr content. After heat treatment at 1300$^{\circ}C$ for 48 hours, reaction product of Gd1-xSrxMnO3 and 8YSZ was SrZrO3. However CGO had no reaction product with Gd1-xSrxMnO3.

• Journal of the Korean Ceramic Society
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• v.51 no.6
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• pp.598-604
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• 2014

Considerable research efforts have been explored attempting to enhance the thermal durability of thermal barrier coatings (TBCs) at the high operating temperatures of gas turbines. In this study, the suspension plasma spray (SPS) process was applied to produce TBCs with a segmented structure by using an yttria-stabilized zirconia (YSZ) suspension. Four different experiment sets were carried out by controlling the ratio between surface roughness of the bond coat and feed stock size ($R_a/D_{50}$) in order to examine the effect of $R_a/D_{50}$ ratio on the microstructure of SPS-prepared coatings. When the $R_a/D_{50}$ had a high value of 11.8, a deposited thick coating turned out to have a cone-type columnar microstructure. In contrast, at the low $R_a/D_{50}$ values of 2.9 and 0.18, a deposited thick coating appeared to have a dense, vertically-cracked microstructure. However, with the very low $R_a/D_{50}$ value of 0.05 the coating was delaminated.

• Bulletin of the Korean Chemical Society
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• v.19 no.6
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• pp.661-666
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• 1998

Active reaction sites and electrochemical O2 reduction kinetics on La_{1-x}Sr_xMnO_{3+{\delta}} (x=0.1-0.4)/YSZ (yttria-stabilized zirconia) electrodes are investigated in the temperature range of 700-900 ℃ at $Po_2=10^{-3}$-0.21 atm. Results of the steady-state polarization measurements, which are formulated into the Butler-Volmer formalism to extract transfer coefficient values, lead us to conclude that the two-electron charge transfer step to atomically adsorbed oxygen is rate-limiting. The same conclusion is drawn from the $Po_2$-dependent ac impedance measurements, where the exponent m in the relationship of $I_o$ (exchange current density) ∝ $P_{o_{2}}^m$ is analyzed. Chemical analysis is performed on the quenched Mn perovskites to estimate their oxygen stoichiometry factors (δ) at the operating temperature (700-900 ℃). Here, the observed δ turns out to become smaller as both the Sr-doping contents (x) and the measured temperature increase. A comparison between the 8 values and cathodic activity of Mn perovskites reveals that the cathodic transfer coefficients $({\alpha}_c)$ for oxygen reduction reaction are inversely proportional to δ whereas the anodic ones $({\alpha}_a)$ show the opposite trend, reflecting that the surface oxygen vacancies on Mn perovskites actively participate in the $O_2$ reduction reaction. Among the samples of x= 0.1-0.4, the manganite with x=0.4 exhibits the smallest 8 value (even negative), and consistently this electrode shows the highest ${\alpha}_c$ and the best cathodic activity for the oxygen reduction reaction.

• Korean Journal of Metals and Materials
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• v.46 no.10
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• pp.646-651
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• 2008

The electrolytic reduction of spent oxide fuel involves the liberation of oxygen in a molten LiCl electrolyte, which results in a chemically aggressive environment that is too corrosive for typical structural materials. It is essential to choose the optimum material for the process equipment handling molten salt. IN713LC is one of the candidate materials proposed for application in electrolytic reduction process. In this study, yttria-stabilized zirconia (YSZ) top coat was applied to a surface of IN713LC with an aluminized metallic bond coat by an optimized plasma spray process, and were investigated the corrosion behavior at $675^{\circ}C$ for 216 hours in the molten salt $LiCl-Li_2O$ under an oxidizing atmosphere. The as-coated and tested specimens were examined by OM, SEM/EDS and XRD, respectively. The bare superalloy reveals obvious weight loss, and the corrosion layer formed on the surface of the bare superalloy was spalled due to the rapid scale growth and thermal stress. The top coatings showed a much better hot-corrosion resistance in the presence of $LiCl-Li_2O$ molten salt when compared to those of the uncoated superalloy and the aluminized bond coatings. These coatings have been found to be beneficial for increasing to the hot-corrosion resistance of the structural materials for handling high temperature lithium molten salts.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2003.02a
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• pp.129-132
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• 2003

Yttria stabilized zirconia (YSZ) buffer layers were deposited by a metal organic chemical vapor deposition (MOCVD) technique using single liquid source for the application of YBa$_2$Cu$_3$$O_{7-x}$ (YBCO) coated conductor. Y:Zr mole ratio was 0.2:0.8, and tetrahydrofuran (THF) was used as a solvent. The (100) single crystal MgO substrate was used for searching deposition condition. Bi-axially oriented CeO$_2$ and NiO films were fabricated on {100}〈001〉 Ni substrate by the same method and used as templates. At a constant working pressure of 10 Torr, the deposition temperatures (660~80$0^{\circ}C$) and oxygen flow rates (100~500 sccm) were changed to find the optimum deposition condition. The best (100) oriented YSZ film on MgO was obtained at 74$0^{\circ}C$ and $O_2$ flow rate of 300 sccm. For YSZ buffer layer with this deposition condition on CeO$_2$/Ni template, full width half maximum (FWHM) values of the in-plane and out-of-plane alignments were 10.6$^{\circ}$ and 9.8$^{\circ}$, respectively. The SEM image of YSZ film on CeO$_2$/Ni showed surface morphologies without microcrack.k.

• Journal of Powder Materials
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• v.29 no.6
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• pp.468-476
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• 2022

Yttria-stabilized zirconia (YSZ) has a low thermal conductivity, high thermal expansion coefficient, and excellent mechanical properties; thus, it is used as a thermal barrier coating material for gas turbines. However, during long-time exposure of YSZ to temperatures of 1200℃ or higher, a phase transformation accompanied by a volume change occurs, causing the YSZ coating layer to peel off. To solve this problem, YSZ has been doped with trivalent and tetravalent oxides to obtain coating materials with low thermal conductivity and suppressed phase transformation of zirconia. In this study, YSZ is doped with trivalent oxides, Nd₂O₃, Yb₂O₃, Al₂O₃, and tetravalent oxide, TiO₂, and the thermal conductivity of the obtained materials is analyzed according to the composition; furthermore, the relative density change, microstructure change, and m-phase formation behavior are analyzed during long-time heat treatment at high temperatures.