• Bulletin of the Korean Chemical Society
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• v.27 no.6
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• pp.821-829
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• 2006

A series of catalysts, $NiO/La_2O_3-ZrO_2/WO_3$, for acid catalysis was prepared by the precipitation and impregnation methods. For the $NiO/La_2O_3-ZrO_2/WO_3$ samples, no diffraction lines of nickel oxide were observed, indicating good dispersion of nickel oxide on the catalyst surface. The catalyst was amorphous to X-ray diffraction up to 300 ${^{\circ}C}$ of calcination temperature, but the tetragonal phase of $ZrO_2$ and monoclinic phase of $WO_3$ by the calcination temperatures from 400 ${^{\circ}C}$ to 700 ${^{\circ}C}$ were observed. The role of $La_2O_3$ in the catalyst was to form a thermally stable solid solution with zirconia and consequently to give high surface area and acidity. The high acid strength and high acidity were responsible for the W=O bond nature of complex formed by the modification of $ZrO_2$ with $WO_3$. For 2-propanol dehydration the catalyst calcined at 400 ${^{\circ}C}$ exhibited the highest catalytic activity, while for cumene dealkylation the catalyst calcined at 600 ${^{\circ}C}$ showed the highest catalytic activity. 25-$NiO/5-La_2O_3-ZrO_2/15-WO_3$ exhibited maximum catalytic activities for two reactions due to the effects of $WO_3$ modifying and $La_2O_3$ doping.

• Journal of the Korean Ceramic Society
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• v.36 no.11
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• pp.1198-1204
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• 1999

The effect of sintering atmosphere on the grain sizes and phase distributions in 3Y-ZrO2 and 8Y-ZrO2 was investigated O2 and N2 were used as sintering atmospheres. In the case of 3Y-ZrO2 the sintered density was higher in N2 than in O2 while in the case of 8Y-ZrO2 contrary results were obtained. The observation can be explained by the nitrogen solubility into the zirconia lattice. That is nitrogen gas can behave as a diffusive gas contrary to the behavior in other oxides depending on the amount of Y2O3. In 3Y-ZrO2 tetragonal phase was retained at room temperature irrespective of sintering atmospheres. Grain sizes of two specimens were below 2㎛ and larger in O2 thin in N2 Under a given stress the transformability of tetragonal phase into monoclinic phase was higher in O2 than N2. The results are discussed on the basis of an effect of the grain size and non-transformable ttragonal(t') phase.

• Korean Journal of Materials Research
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• v.15 no.9
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• pp.608-612
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• 2005

Microstructure and mechanical properties of fibrous $A1_2O_3-(m-ZrO_2)/t-ZrO_2$ composite were investigated depending on the dimensional array. By the change of stacking arrangement of fibrous filaments, 2 and 3-dimensional fibrous composites were successfully obtained without bulk defects such as shrinkage cavity and cracks. The maximum mechanical properties were achieved In the 3-dimensional array composite, due to the fine fibrous and dense microstructure control, in which the values of vickers hardness, fracture toughness and bending strength were about 1507 Hv, $7.2MPa{\cdot}m^{1/2}$ and 650 MPa, respectively.

• Applied Science and Convergence Technology
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• v.24 no.2
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• pp.33-40
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• 2015

$ZrO_2$ and Al-Zr composite oxide film was prepared by vacuum assisted sol-gel dip coating method and anodizing. $ZrO_2$ films annealed above $400^{\circ}C$ have tetragonal structure. $ZrO_2$ layers inside etch pits were successfully coated from the $ZrO_2$ sol. The double layer structures of samples were obtained after being anodized at 100 V to 600 V. From the TEM images, it was found that the outer layer was $Al_2O_3$, the inner layer was multi-layer of $ZrO_2$, Al-Zr composite oxide and Al hydrate. The capacitance of $ZrO_2$ coated foil exhibited about 28.3% higher than that of non-coating foil after being anodized at 100 V. The high capacitance of $ZrO_2$ coated foils anodized at 100 V can be attributed to the relatively high percentage of inner layer in total thickness. The electrical properties, such as withstanding voltage and leakage current of coated and non-coated Al foils showed similar values. From the results, $ZrO_2$ and Al-Zr composite oxide is promising to be used as the partial dielectric of high voltage capacitor to increase the capacitance.

• Proceedings of the Materials Research Society of Korea Conference
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• 2004.05a
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• pp.47-47
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• 2004

• Journal of the Korean Ceramic Society
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• v.34 no.6
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• pp.569-576
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• 1997

Electrically-induced strain and polarization studies of the (1-x)Pb(Mg1/3Nb2/3)O3-PbZrO3 crystalline solutions have been done. Dielectric constants with temperature were investigated for 0$\leq$x$\leq$0.95. With increasing PbZrO3 content the transition maxima were found to move to higher temperature region and DPT (Diffused Phase Transition) properties were decreased for x$\leq$0.60. Phase transition between ferroelectric states and antiferroelectric states was confirmed for 0.93$\times$10-3 for 0.4

• Journal of the Korean Ceramic Society
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• v.27 no.4
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• pp.487-494
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• 1990

$Al_2O_3$-20w/o $ZrO_2$ composite powders were prepared by the emulsion-coprecipitation method and the effects of preparative conditions on powder characteristics were investigated. In the preparation of $Al_2O_3$-$ZrO_2$ composite powders, toluene was used instead of kerosene as the oil phase in emulsions. After coprecipitation, the emulsion was easily broken into a single liquid phase by adding methanol, and then precipitates could be effectively collected by filteration. The fact that all $ZrO_2$ phases present at room temperature in composite powders calcined at $1100^{\circ}C$ after washed by methanol had a tetragonal structure confirmed that methanol-washing enhanced the dispersibility of fine $ZrO_2$ particles in $Al_2O_3$ matrix. $Al_2O_3$-$ZrO_2$ composite powders were spherical particles of 0.2${\mu}{\textrm}{m}$ diameter. Pellets sintered at $1650^{\circ}C$ for 2hrs showed the relative theoretical density of 97.3% and the fracture toughness of 5.01MN/$m^{3/2}$.

• Proceedings of the Materials Research Society of Korea Conference
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• 1992.05b
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• pp.150-150
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• 1992

• Electrical & Electronic Materials
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• v.6 no.3
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• pp.241-247
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• 1993

본 연구에서는 투광성 0.085Ba(L $a_{1}$2/N $b_{1}$2/) $O_{3}$- 0.915Pb(Z $r_{y}$ $Ti_{1-y}$) $O_{3}$(0.45.leq.y.leq.0.70)세라믹을 2단 소성법으로 제작한 후, PbZr $O_{3}$조성 및 온도에 따른 구조적, 강유전적특성을 측정하였다. XRD측정 결과, PbZr $O_{3}$조성이 감소할수록 결자상수 및 단위격자 체적은 감소하였으며 시편의 결정구조는 입방정계에서 능면체정계, 정방정계로 변화되었다. 8.5/60/40시편의 경우 포화분극, 잔류분극 및 항전계가 각각 33.28[.mu.C/$cm^{2}$], 4.15[kV/cm]로 전형적인 메모리 특성을 나타내었으며 PbZr $O_{3}$조성이 증가함에 따라 강유전 이력곡선은 slim loop특성을 나타내었다. 잔류분극은 온도가 증가함에 따라 감소하였으며 특히 PE-FE상경계 부근에 위치한 조성의 경우, 상전이 온도 이하의 온도에서 급격히 감소하는 경향을 나타내었다.다.

• Korean Journal of Materials Research
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• v.13 no.4
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• pp.213-218
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• 2003

Fibrous monolithic control of$ Al_2$$O_3$ -$ZrO_2$composite was investigated by multi-pass extrusion process. To obtain sound $Al_2$$O_3$-X $O_2$sintered bodies, burning out and sintering process were carefully carried out. The sintered bodies showed continuous, fibrous monolithic microstructure without any swelling. Many microcracks were observed at the $Al_2$$O_3$-$ZrO_2$interfaces due to the mismatching of thermal expansion coefficient between $Al_2$$O_3$ and $ZrO_2$phase. Most of m- $ZrO_2$grains included twin defects such as (001), (010) and (011) type to accommodate the phase transformation induced stress.