• Journal of Hydrogen and New Energy
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• 제23권6호
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• pp.654-659
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• 2012

The interest in water gas shift (WGS) reaction has grown significantly, as a result of the recent advances in fuel cell technology and the need to develop small-scale fuel processors. Recently, researchers have tried to overcome the disadvantages of the commercial WGS catalysts. As a consequence, supported Pt catalysts have attracted a lot of researchers due to high activity and stability for WGS at low temperatures. In this study, $Pt-Na/Ce_{(1-x)}Zr_{(x)}O_2$ catalysts with various Ce/Zr ratio have been applied to WGS at a gas hourly space velocity (GHSV) of $45,515h^{-1}$. According to TPR patterns of $Pt-Na/Ce_{(1-x)}Zr_{(x)}O_2$ catalysts, the reducibility increases with decreasing the $ZrO_2$ content. As a result, Cubic structure $Pt-Na/Ce_{(1-x)}Zr_{(x)}O_2$ catalysts exhibited higher CO conversion than tetragonal structure $Pt-Na/Ce_{(1-x)}Zr_{(x)}O_2$ catalysts. Expecially, Pt-Na/$CeO_2$ exhibited the highest CO conversion as well as 100% selectivity to $CO_2$. Moreover, Pt-Na/$CeO_2$ catalyst showed relatively stable activity with time on stream. The high activity of cubic structure Pt-Na/$CeO_2$ catalyst was correlated to its higher oxygen storage capacity (OSC) of $CeO_2$ and easier reducibility of Pt/$CeO_2$.

• Korean Journal of Materials Research
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• 제13권8호
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• pp.497-502
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• 2003

Crystallographic characteristics and interfacial structures of $Al_2$$O_3$and $ZrO_2$dielectric films prepared by atomic layer chemical vapor deposition (ALCVD) were investigated at atomic scale by high-resolution transmission electron microscopy (HRTEM) and energy dispersive X-ray spectroscopy (EDS)/electron energy-loss spectroscopy (EELS) coupled with a field-emission transmission electron microscope. The results obtained from cross-sectional and plan-view specimens showed that the $Al_2$$O_3$film was crystallized by annealing at a high temperature and its crystal system might be evaluated as either cubic or tetragonal phase. Whereas the $ZrO_2$film crystallized during deposition at a low temperature of ∼$300^{\circ}C$ was composed of both tetragonal and monoclinic phase. The interfacial thickness in both films was increased with the increased annealing temperature. Further, the interfacial structures of X$ZrO_2$$O_3$and $ZrO_2$films were discussed through analyses of EDS elemental maps and EELS spectra obtained from the annealed films, respectively.

• The Korean Journal of Ceramics
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• 제3권4호
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• pp.253-256
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• 1997

Epitaxially grown Pb(Zr, Ti)O$_3$thin films were prepared on LaAlO$_3$substrates by the dipping pyrolysis process using metal naphthenates as starting materials Homogeneous Pb-Zr-Ti solutions with toluene were spin-coated onto the substrates and pyrolyzed at 50$0^{\circ}C$ Highly oriented Pb(Zr, Ti)O$_3$films confirmed by X-ray diffraction $\theta$-2$\theta$ scans were obtained by heat-treated at 75$0^{\circ}C$ in air The X-ray pole-figure analysis and reciprocal-space mapping of the resulting 0.6$\mu\textrm{m}$ films showed that the thin films comprising the c-axis oriented tetragonal phase have an epitaxial relationship with the LaAlO$_3$substrates.

• Applied Microscopy
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• 제42권3호
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• pp.174-178
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• 2012

In the present study, the oxidation behavior of $Cu_{50}Zr_{50}$ and $Cu_{46}Zr_{46}Al_8$ metallic glasses has been investigated using transmission electron microscopy with a particular attention on the oxidation behavior in the supercooled liquid state. Identification of the oxidation product after continuous heating treatment shows that in $Cu_{50}Zr_{50}$ metallic glass, $ZrO_2$ with the monoclinic structure forms on the supercooled liquid as well as on the crystallized matrix. On the contrary, in $Cu_{46}Zr_{46}Al_8$ metallic glass, $ZrO_2$ with the tetragonal structure forms on the supercooled liquid, but that with the monoclinic structure forms on the crystallized matrix. The result indicates that the $Cu_{50}Zr_{50}$ metallic glass exhibits far better oxidation resistance in the supercooled liquid state than the $Cu_{46}Zr_{46}Al_8$ metallic glass.

• Journal of the Korean Ceramic Society
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• 제31권6호
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• pp.581-586
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• 1994

Effect of excess and deficiency of PbO on the sintering and electrical properties of tetragonal Pb(Zr0.5Ti0.5)O3 were investigated. Fired density revealed maximum value with 4 wt% of excess PbO, and decreased with increasing amount of both excess and deficient PbO. Grain size increased with excess PbO, and decreased with deficiency of PbO. It appeared that excess PbO forms a liquid phase to enhance grain growth and completely volatilizes after sintering, whereas ZrO2 particles formed in PbO-deficient PZT inhibit grain growth. The change in the values of the equivalent circuit elements of PZT corresponded well with thar of porosity formed by excess and deficiency of PbO; kp, Co and Cm decreased while Qm, Rm and Lm increased conosiderably with porosity. This change was more pronounced in PbO-deficient type probably due to change in Zr/Ti ratio of PZT.

• Proceedings of the Korean Vacuum Society Conference
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• 한국진공학회 2011년도 제40회 동계학술대회 초록집
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• pp.177-177
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• 2011

Complementary metal-insulator-metal capacitor에서 $SiO_2$는 절연체로 널리 사용되고 있었으나, 반도체 소자의 고직접화로 인한 선폭의 감소로 터널링 효과에 의해 누설전류가 증가하여, 대체 물질에 대한 연구가 활발히 진행되고 있다. 그 중 $ZrO_2$는 고유전율, wide bandgap, 열안정성의 특징을 가지고 있어 대체 물질로 주목 받고 있다. $ZrO_2$ 박막 제작에는 sputter, atomic layer deposition 등의 진공증착을 이용한 방법과 용액을 이용한 sol-gel 법이 있다. 화학용액을 이용한 sol-gel 법은 소자의 패턴을 프린트 할 수 있는 장점과 상대적으로 값싼 공정으로 인해 최근 주목 받고 있지만, 진공증착법에 비해서 연구가 전무한 실정이다. 본 연구에서는 sol-gel 법에 의해 프린트된 $ZrO_2$ 박막의 광특성을 분광타원편광분석법으로 연구하였다. Si 기판위에 0.1 M의 $ZrO_2$ sol을 입힌 뒤에 $300{\sim}700^{\circ}C$의 온도에서 열처리 하였다. 분광타원 편광분석기로 1.12~6.52 eV 에너지 영역에서 측정하였고, $ZrO_2$ 박막의 광특성 분석을 위해서 Tauc-Lorentz 모델을 이용하였다. 그 결과 고온에서의 열처리로 인해 효율이 높아서 소자로 이용할 수 있는 tetragonal 구조를 가진 $ZrO_2$ 박막이 형성됨을 분석할 수 있었다. 본 연구는 sol-gel법으로 제작된 $ZrO_2$ 박막의 고직접, 고속 소자응용성과 비파괴적인 광특성 분석법을 제시하고 있다.

• 전자공학회논문지 IE
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• 제49권2호
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• pp.1-8
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• 2012

The effects of the addition of either monoclinic $ZrO_2(pure)$ or tetragonal $ZrO_2$ containing 5.35wt% $Y_2O_3(Y-TZP)$ on the mechanical properties and thermal shock resistance of $Al_2O_3$ ceramics were investigated. The addition of $ZrO_2$(m) and Y-TZP increased sintered density of $Al_2O_3$. The Vickers hardness also increased as the volume fraction of Y-TZP increased going through a maximum at 20wt%. The hardness of the specimens was found to be dependent on the sintered density. The higher volume fraction of either $ZrO_2(m)$ or Y-TZP resulted in the higher fracture toughness of the composite was. This result may be taken as evidence that toughening of $Al_2O_3$ can be achieved by not only the transformation toughening but microcrack toughening of $ZrO_2$. The thermal shock property for $Al_2O_3-ZrO_2$ composites was improved by increasing the volume fraction of monoclinic $ZrO_2(pure)$. The grain size increased as the volume fraction of $ZrO_2$ did.

• Bulletin of the Korean Chemical Society
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• 제30권1호
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• pp.92-96
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• 2009

A new precursor [$Zr(acac)_{3}(H_{2}O)_{2}$] was synthesized by Sonochemical technique and used to deposit thin $ZrO_{2}$ film on quartz and ceramic substrate via ultrasonic aerosol assisted chemical vapour deposition (UAACVD) at 300 ${^{\circ}C}$ in oxygen environment followed by annealing of the sample for 2-3 minutes at 500 ${^{\circ}C}$ in nitrogen ambient. The molecular structure of the precursor determined by single crystal X-ray analysis revealed that the molecules are linked through intermolecular hydrogen bonds forming pseudo six and eight membered rings. DSC and TGA/FTIR techniques were used to determine thermal behavior and decomposition temperature of the precursor and nature of evolved gas products. The optical measurement of annealed $ZrO_{2}$ film with tetragonal phase shows optical energy band gap of 5.01 eV. The particle size, morphology, surface structure and composition of deposited films were investigated by XRD, SEM and EDX.

• Journal of the Korean Ceramic Society
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• 제22권1호
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• pp.11-18
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• 1985

The effect of stress induced phase transformation on $Al_2 O_3$ matrix dispersed with $ZrO_2-Y_2O_3$ has been studied. In order to determinate the mechanical properties three $Al_2O_3-ZrO_2$ composite series containing 1, 3 and 5 mole% $Y_2O_3$ were prepared. The starting materials were $Al_2O_3$ and $ZrO_2-Y_2O_3$ which was prepared from the aqueous solution of high purity $YCl_3$.$6H_2O$ and $ZrOCl_2$.$8H_2O$. Powder mixtures of $Al_2O_3-ZrO_2$ containing $Y_2O_3$ have been prepared by ball-milling with methanol and the samples were formed by isostatic press and sintered at 150$0^{\circ}C$ for 2hrs. After sintering. the specimens were polished for mechanical determination. The relative density of sintered specimens were also measured. It was found that the addition of 1, 3mole% to {{{{ { ZrO}_{2 } }} allowed full retention of the tetragonal phase in $Al_2O_3-ZrO_2$ but partially stabilized zirconia (PSZ) was produced by additions of 5 mole% $Y_2O_3$.The critical stress-intensity factor KIc of $A_2O_3-ZrO_2$ (containing 1 mole% $Y_2O_3$) composite materials increased with increasing $ZrO_2$ content, The maximum value of KIC=7Mn/$m^3$/2 at 20 mole% $ZrO_2$ exhibited about twice that of the $Al_2 O_3$ The modulus of rupture exhibited a trend similiar to KIC The maximum value of MOR was 580MN/m2. As the amount of Y2O3 increase it was observed that the maximum of KIC and MOR decreased : Additions of 3 mole% $Al_2O_3$ $Y_2O_3$ allowed the maximum of KIC 6MN/$m^3$/2 MOR 540MN/$m^2$ at 15 mole% $ZrO_2$ additions of 5 mole% $Y_2O_3$ allowed the maximum of KIC 5MN/$m^3$/2 MOR 410MN/$m^2$ at 10 mole% $ZrO_2$.

• Journal of the Korean Ceramic Society
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• 제31권6호
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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.