• Journal of the Korean Ceramic Society
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• v.34 no.11
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• pp.1113-1120
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• 1997

The 2, 4, 6 and 8mol% Y2O3 doped-ZrO2 powders (20 kinds) with the addedtion of Al2O3 upto 8wt% were prepared by coprecipitation method using the zirconium oxyacetate, yttrium chloride and aluminum nitrate as starting materials. The coprecipitated powders were characterized by XRD, TG-DTA, FT-IR and SEM. The sintering properties of zirconia-alumina composites prepared by 2YSZ and 8YSZ powders containing various Al2O3 contents were also investigated. With increasing the yttria stabilizer contents, the amount of exothermic heat for zirconia crystallization decreased. And it was confirmed that the crystallizing temperature of coprecipitated zirconia powders increased and the crystallization process occurred in a wide temperature range, as Al2O3 content increased in 8YSZ.

• Journal of the Mineralogical Society of Korea
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• v.14 no.2
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• pp.99-110
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• 2001

A gem-quality yttria-stabilized zirconium oxide crystals were synthesized by the skull-melting method, using the RF electrical apparatus. Principal raw materials used were $ZrO_2$and 25 wt.% $Y_2O_3$as stabilizer and 0.03~0.05 wt.% $Nd_2O_3$decolorizing agent were added to it. The single crystals were approximately 20$\times$63 mm in size with chemical composition $Zr_{0.73}$ $Y_{0.27}$ $O_{1.87}$ . The crystals are isotropic with no appreciable anisotropism under a polarizing microscope. Their refractive indices are in the range of 2.15~2.18, specific gravity 5.85, Mohs' hardness 8~8.5, and reflectivity 13.47%. The zirconia crystals were confirmed to have cubic structure with Face-centered lattice(Z=4), space group Fm3m ($CaF_2$-type structure) and unit cell parameters are a=5.157 $\AA$. The optimal growing conditions for yttria-stabilized zirconia are 50 kW, 2.94 MHz in power and to use a crucible with 105 mm $\times$ 135 mm in size. When the lowering speed of the crucible was set 16mm/hr gave the best yield, 42%. Since the refractive index(2.15~2.18) of cubic zirconia is smaller than that of diamond, the angle between crown and pavilion should be fashioned to make it smaller than $40.5^{\circ}$ to show the maximum brilliancy and fire.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.20 no.6
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• pp.289-294
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• 2010

Ni-YSZ (Yttria Stabilized Zirconia) composite powders for SOFC were fabricated by glycine nitrate process. $ZrO(NO_3)_2{\cdot}2H_2O$, $Y(NO_3)_3{\cdot}6H_2O$, $Ni(NO_3)_2{\cdot}6H_2O$ and glycine were chosen as the starting materials. The structural properties of the sintered Ni-YSZ cermets have been investigated with respect to the volume contents of Ni. A porous microstructure consisting of homogeneously distributed Ni and YSZ phases together with well-connected grains was observed. The sintered Ni-YSZ cermets showed a porous microstructure consists of homogeneously distributed Ni and YSZ phases and the grains were well-connected. It was found that the open porosity is sensitive to the volume content of Ni. The Ni-YSZ cermet containing 35 vol% Ni seems to be suitable for the electrode material of SOFC since it provides sufficient open porosity higher than 30%.

• Proceedings of the Korean Vacuum Society Conference
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• 1999.07a
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• pp.150-150
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• 1999

재료의 광학적 특성을 변화시키기 위한 표면 코팅의 사용을 잘 알려져 있다. 그리고 이러한 광학 코팅은 우리가 주위에서 볼 수 있는 렌즈에서부터 레이저반사경 다 나아가 다양한 광학 필터에 이르기까지 빛의 간섭을 이용한 광학 박막의 코팅은 폭넓게 이용되고 있다. 그러한 응용가운데 불필요한 표면 반사를 방지함으로써 전체 투과율을 강화시키기 위한 무반사(Anti-Reflection) 코팅은 오늘날 광대역 무반사 특성 등 다양한 광학적 요구에 따라 하나 또는 그 이상의 층을 형성함으로써 극적으로 성취할 수 있다. 본 실험은 기존 많이 활용되는 증발법 그리고 스퍼터링 방법과는 달리 고진공하에서 증착 변수를 효과적으로 제어, 박막을 형성할 수 있는 자체 제작된 단일 IBS(Ion Beam Sputtering) 시스템을 이용하여 우수한 광학적 특성을 갖는 광학 재료로써 무반사용 다층박막 형성하기 앞서 MgF2, ZrO2 (yttria stabilized zirconia) 단층 박막을 제조하였으며, 각 증착 변수에 따른 결정학적 및 광학적 특성을 관찰하였다. 본 실험에 사용된 제조 장비로 Kaufman type 2.5inch의 이온 건이 장착된 Ion Beam sputtering 시스템으로 초기 진공도는 5$\times$10-6orr이며, 이온 빔의 전류 밀도는 Fareday cup을 이용했다. 6inch 크기의 ZrO2(yttria stabilized zirconia), MgF2 타겟트를 이용하여 Si(100), glass 기판위에 박막을 성장시켰다. 각 타겟트에 대한 증착변수로 이온 에너지, 기판온도, Ar 가스량을 변화시키면서 박막을 제조하였다. 제조된 박막의 광학적 특성으로 가시 영역에서 투과율의 변화는 자외/가시광선 분광 분석기 (UV/VIS specrophotometer)를 이용하여 측정했다. 그리고 박막의 조성 및 결정학적 구조는 AES EDS와 XRD로 확인하였다. 이온 빔 전압 500V, 빔 저류 55mA일 때 온도는 상온에서 30$0^{\circ}C$까지 승온 후 MgF2 박막의 XRD분석결과 우세한 결정성을 관찰할 수 없었으며, 이 때의 광 투과도는 가시영역에서 80~90%의 값으로 측정되었다. 추후 증착된 막의 결정성을 위해 열처리를 실시하고, 각 증착조건에 대한 결과는 학회 발표시 보고한다.

• Journal of Ceramic Processing Research
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• v.20 no.6
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• pp.609-616
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• 2019

The optimum powder to ball ratio was examined, which is one of the important conditions in reactive mechanical grinding processing. Yttria (Y2O3)-stabilized zirconia (ZrO2) (YSZ), Ni, and graphene were chosen as additives to enhance the hydriding and dehydriding rates of Mg. Samples with a composition of 92.5 wt% Mg + 2.5 wt% YSZ + 2.5 wt% Ni + 2.5 wt% graphene (designated as Mg-2.5YSZ-2.5Ni-2.5graphene) were prepared by grinding in hydrogen atmosphere. Mg-2.5YSZ-2.5Ni-2.5graphene had a high effective hydrogen-storage capacity of almost 7 wt% (6.85 wt%) at 623 K in 12 bar H2 at the second cycle (n = 2). Mg-2.5YSZ-2.5Ni-2.5graphene contained Mg2Ni phase after hydriding-dehydriding cycling. Mg-2.5YSZ-2.5Ni-2.5graphene had a larger quantity of hydrogen absorbed for 60 min, Ha (60 min), than Mg-2.5Ni-2.5graphene and Mg-2.5graphene. The addition of YSZ also increased the initial dehydriding rate and the quantity of hydrogen released for 60 min, Hd (60 min), compared with those of Mg-2.5Ni-2.5graphene. Y2O3-stabilized ZrO2, Ni, and graphene-added Mg had a higher initial hydriding rate and a larger Ha (60 min) than Fe2O3, MnO, or Ni and Fe2O3-added Mg at n = 1.

• Journal of the Mineralogical Society of Korea
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• v.13 no.3
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• pp.164-170
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• 2000

Neutron single crystal and powder diffraction techniques have been applied to the structure analysis of yttria-stabilized zirconium, Z $r_{0.73}$ $Y_{0.27}$ $O_{1.87}$., prepared by the skull-melting method. The crystal structure has been determined to be cubic symmetry, space group Fm/equation omitted/ with a=5.155(2)$\AA$, V=136.99(5)$\AA$, Z=4, and R(F)=5.65%, $\omega$R(I)=10.57% for 70 integrated intensities of Bragg Peaks observed from single crystal of Z $r_{0.73}$ $Y_{0.27}$ $O_{1.87}$. The stabilizer atoms randomly occupy the zirconium sites and there are displacements of oxygen atoms with amplitudes of $\Delta$/a~0.033 and 0.11 along <110> and <100> directions from the ideal positions of the fluorite structure, respectively. There are no significant differences in crystallographic data between the single crystal and powder studies. Diffraction pattern after Rietveld refinement, using neutron powder data, has shown the evidence of a tetragonal impurity phase, or a slight tetragonal distortion.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.7 no.3
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• pp.377-383
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• 1997

Yttria-stabilized TZP alloyed with pentavalent oxides $(Ta_2O_5,\;Nb_2O_5)$ were fabricated by the conventional sintering method at $1500^{\circ}C$ in air to construct the simplified ternary phase diagram. The phase stability of tetragonal -$ZrO_2$ from the quasi-binary system $ZrO_2-YTa(Nb)O_4$, which do not transform to monoclinic-$ZrO_2$ even for a wide range of grain size and annealing temperature, was investigated to determine composition region of the non-transformable $t-ZrO_2$ solid solution$(NT_{ss})$. Phase stability of $NT_{ss}$ was probably due to the enhanced stability of $_YTa(Nb)O4$ having the tetragonal fergusonite structure. It was experimentally found that mixtures having $NT_{ss}$ alloyed with $T_{ss}$ by weight%% showed both excellent phase stability of $t-ZrO_2$ and fracture toughness even though the calculated composition of the mixture /was located outside $NT_{ss}$ composition region.

• Korean Journal of Materials Research
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• v.8 no.9
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• pp.783-790
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• 1998

New process development of nuclear fuel fabrication for nuclear power plant was attempted by induction plasma technology with yttria-stabilized-zirconia ($\textrm{ZrO}_{2}$-$\textrm{Y}_{2}\textrm{O}_{3}$)powder, similar to $\textrm{UO}_{2}$, in the respect of melting point and physicochemical characteristics. Extent of powder melting was affected greatly by plasma plate power and particle size. Being optimized such as, sheath gas composition, probe position, particle size and spraying distance, dense deposit of 97.91% T.D. with deposition rate 20mm/min was attained at the condition of 120/20$\ell$/min of Ar/$\textrm{H}_{2}$ flow rate, 80kw of plate power, 8cm of probe position, 200Torr of chamber pressure and 18cm of spraying distance. The pellet of 96.5% of theoretical density was formed with homogeneity and nice exterior view at the best condition of deposition experiments, and the possibility of new nuclear pellet fabrication process was confirmed. The main and interrelated effects on deposit density were assessed by ANOVA(Ana1ysis of Variance).

• 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.

• Journal of the Korean Ceramic Society
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• v.43 no.2 s.285
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• pp.69-73
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• 2006

A full retention of the tetragonal phase with coarse grains $(50\~60\;{\mu}m)$ was possible with the specimen $ZrO_2-1.9\;mol\%\;Y_2O_3$. In these coarse grains, $\{101\}_t$ annealing twins were frequently observed, although they do not exist in the usual fine grained specimens. The morphology and growth rate of the isothermally formed individual products are studied at an optical microscopic level. The habit planes of both products are also identified by performing two-surface trace analysis on the grains whose orientations are determined by the Electron Back Scattering Pattern (EBSP) method. The morphologies of isothermal martensite were well-defined thin plates and lenticular types. The growth rate in their longitudinal directions was quite slow and temperature-dependent. A two-surface trace analysis, incorporated with the EBSP method, identified the habit planes near $\{013\}_c$, in agreement with previous reports obtained from TEM works.