• Journal of the Korean Ceramic Society
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• v.33 no.5
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• pp.563-571
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• 1996

In order to fabricate solid electrolyte CaO-stabilized ZrO2 of high density sintered body economically 13 mol% CaO-stabilized ZrO2 powders were synthesized by the coprecipitation method. The characteristics and sintering behavior of fine powder were investigated. The precipitates has the specific surface area of 193 m2/g and apperaed to be fine and spherical primary particles with a size of approximately 5nm. The crystalliza-tion temperture of CaO-stabilized ZrO2 was 462$^{\circ}C$. The tetragonal phase was stable in the low calcining tempe-rature regions and the cubic zirconia solid solution was formed from above 120$0^{\circ}C$ through an intermediate stage of formation of CaZrO3 By introducing fine powders washed with alcohol and ball-milling process after calcination the sintered body was possible to attain the value of above 92% of the theoretical density at low temperature of 120$0^{\circ}C$.

• Journal of the Korean Ceramic Society
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• v.16 no.4
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• pp.213-224
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• 1979

The present work was undertaken: (1) to determine if CaO-partially stabilized $ZrO_2$ prepared by Hot Petroleum Drying Method would show better ionic conductor as an oxygen sensor in molten metals than that prepared by Oxide Wet Mixing Method and than CaO-fully stabilized $ZrO_2$, and (2) to understand the nature of conduction mechanism of CaO-partially stabilized $ZrO_2$ by a comparison of measured electrical conductivity data with theory on defect structure of pure monoclinic $ZrO_2$ and fully stabilized cubic $ZrO_2$. The DC electrical conductivity was measured by 3-probe technique and the AC electrical conductivity by 2-probe technique as a function of temperature in the range 973-1373 K and oxygen partial pressure in the range 10-1-10-25Mpa. The results of the experiments were as follows: 1. CaO-partially stabilized $ZrO_2$ prepared by Hot petroleum Drying Method showed at T=1094-1285 K and $Po_2$=10-7-10-25 MPa a nearly ionic conduction with 4 times higher conductivity than that prepared by Oxide Wet Mixing Method. 2. High-oxygen pressure conductivity tends toward a Po_2^{+1/5}-Po_2^{+1/6}$dependence. An analysis of possible defect structures suggests that CaO-partially stabilized $ZrO_2$ has an anti-Frenkel defect in which singly or doubly ionized oxygen interstitials and defect electrons predominate at T=1094-1285 K and $Po_2$=10-1-10-7MPa. 3. The activation energy for pure electron hole-conduction and ionic conduction of CaO-partially stabilized $ZrO_2$ was found to be 130 KJ/mol at T=973-1373 K, $Po_2$=2, 127 10-2 MPa(air) and 153KJ/mol at T=1094-1285 K respectively.

• Journal of the Korean Ceramic Society
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• v.28 no.7
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• pp.541-548
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• 1991

Sinterability and stability of TZP ceramics co-stabilized by 12 mol% CeO2 and divalent or trivalent oxides less than 1 mol% were investigated. Divalent and trivalent oxides increased stability of tetragonal ZrO2. 100% tetragonal ZrO2 phase was obtained by doping 12 mol% CeO2 and 0.2 mol% CaO and MgO respectively when sintering was carried out at 1500$^{\circ}C$ for 2 hours. Divalent and trivalent oxides improved sinterability and inhibit grain growth of ZrO2. And it was found that CaO was the most effective sintering aid and grain growth inhibitor for ZrO2 in this study. Incorporation of divalent and trivalent oxides into 12Ce-TZP increased the strength of 12Ce-TZP and particulary 12Ce, 0.4Ca-TZP exhibited a flexural strength of about twofold greater than 12Ce-TZP.

• Korean Journal of Materials Research
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• v.30 no.4
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• pp.176-183
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• 2020

The high-temperature stability of YSZ specimens fabricated by die pressure and cold isostatic press (CIP) is investigated in CaCl₂-CaF₂-CaO molten salt at 1,150 ℃. The experimental results are as follows: green density 46.7 % and 50.9 %; sintering density 93.3 % and 99.3 % for die press and CIP, respectively. YSZ foremd by CIP exhibits higher stability than YSZ formed by die press due to denseness dependency after high-temperature stability test. YSZ shows peaks mainly attributed to CaZrO₃, with a small t-ZrO₂ peak, unlike the high-intensity tetragonal-ZrO₂ (t-ZrO₂) peak observed for the asreceived specimen. The t-ZrO₂ phase of YSZ is likely stabilized by Y₂O₃, and the leaching of Y₂O₃ results in phase transformation from t-ZrO₂ to m-ZrO₂. CaZrO₃ likely forms from the reaction between CaO and m-ZrO₂. As the exposure time increases, more CaZrO₃ is observed in the internal region of YSZ, which could be attributed to the inward diffusion of molten salt and outward diffusion of the stabilizer (Y₂O₃) through the pores. This results in greater susceptibility to phase transformation and CaZrO₃ formation. To use SOM anodes for the electroreduction of various metals, YSZ stability must be improved by adjusting the high-density in the forming process.

• Korean Journal of Materials Research
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• v.22 no.5
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• pp.220-226
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• 2012

Pure zirconia and $x$ mol% calcia partially stabilized zirconia ($x$ = 1.5, 3, and 8) nanopowders were synthesized by hydrothermal method with various reaction temperatures for 24 hrs. The precipitated precursor of pure zirconia and $x$ mol% calcia doped zirconia was prepared by adding $NH_4OH$ to starting solutions; resulting sample was then put into an autoclave reactor. The optimal experimental conditions, such as reaction temperatures and times and amounts of stabilizer CaO, were carefully studied. The synthesized $ZrO_2$ and $x$ mol% CaO-$ZrO_2$ ($x$ = 1.5, 3, and 8) powders were characterized by XRD, SEM, TG-DTA, and Raman spectroscopy. When the hydrothermal temperature was as low as $160^{\circ}C$, pure $ZrO_2$ and $x$ mol% CaO-$ZrO_2$ ($x$ = 1.5 and 3) powders were identified as a mixture of monoclinic and tetragonal phases. However, a stable tetragonal phase of zirconia was observed in the 8 mol% calcia doped zirconia nanopowder at hydrothermal temperature above $160^{\circ}C$. To observe the phase transition, the 3 mol% CaO-$ZrO_2$ and 8 mol% CaO-$ZrO_2$ nanopowders were heat treated from 600 to $1000^{\circ}C$ for 2h. The 3 mol% CaO-$ZrO_2$ heat treated at above $1000^{\circ}C$ was found to undergo a complete phase transition from mixture phase to monoclinic phase. However, the 8 mol% calcia doped zirconia appeared in the stable tetragonal phase after heat treatment. The result of this study therefore should be considered as the preparation of 8 mol% CaO-$ZrO_2$ nanopowders via the hydrothermal method.

• Journal of the Korean Ceramic Society
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• v.31 no.6
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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.

• Journal of the Korean Ceramic Society
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• v.31 no.1
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• pp.104-114
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• 1994

ZrO2 fibers were fabricated by means of the Sol-Gel process using Zr(O-nC3H7)4-H2O-C2H5OH-HNO3 solution as a starting material. The optimum experimental parameters such as molar ratio of starting materials, concentration, temperature, viscosity, the amounts of stabilizer and the pH of solution were determined. The experimentally determined optimum variables which produce good ZrO2 fibers were used to manufacture the Y2O3-and CaO-ZrO2 fibers. The amounts of Y2O3 and CaO were varied within the range from 1.5~5 mol% and 3~15 mol% respectively. The phase transformation and microstructural evolution of the fabricated ZrO2 gel fibers were investigated after heat treatments up to 120$0^{\circ}C$ by X-ray diffraction, Raman microprobe spectroscopy, SEM, and specific surface area and pore volume measurements. From the analysis of X-ray diffraction and Raman spectra, the phase of heat treated Y2O3-and CaO partially stabilized ZrO2 gel fibers(Y2O3:2.5~3 mol%, CaO:6~9 mol%) were identified as a tetragonal phase up to 100$0^{\circ}C$. The maximum tensile strength of 2.5Y2O3-97.5ZrO2 and 6CaO-94ZrO2 (in mol%) fibers heat treated at 100$0^{\circ}C$ for 1 hr was found be 1.3~2 GPa with diameters of 10~20 ${\mu}{\textrm}{m}$.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2001.07a
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• pp.211-214
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• 2001

The undesirable phase transformation of zirconium dioxide at high temperatures can be eliminated by stabilization of the cubic phase with an addition of a selected alkaline earth or rare-earth oxide. In this paper the ionic conductivity of cubic solid solutions in the stabilized ZrO$_2$ by CaO-Y$_2$O$_3$ system was examined. The higher ionic conductivity appears to be related to lower activation energy rather than to the number of oxygen vacancies dictated by composition. Those compositions of highest conductivity lie close to the cubic-monoclinic solid-solution phase boundary. Conductivity temperature data are presented that indicate a reversible order-disorder transition for Zr$_2$2-Y$_2$O$_3$cubic solid solutions containing 20 and 25 mole % $Y_2$O$_3$.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.15 no.4
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• pp.349-355
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• 2002

The ionic conductivity of cubic solid solutions in the systems of CaO-$ZrO_2$, $Y_2O_3-ZrO_2$ prepared by SHS was examined. The higher conductivity appears to be related to a lower activation energy rather than to the number of oxygen vacancies dictated by composition. Conductivity-temperature data was obtained at 1000 $^{\circ}C$ in atmosphere of low oxygen partial pressure (~$10^{-40}$ atm) for $Y_2O_3-ZrO_2$ cubic solid solutions. The data indicated that these materials could be reduced, and the decree of reduction would be related with the measuring electric field.

• Journal of Korea Foundry Society
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• v.28 no.6
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• pp.282-287
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• 2008

The effect of CaO mold on the formation of reaction layer was investigated. CaO mold was prepared by mixing of Colloidal silica($NALCO^{(R)}$ 1130) and an $ZrO_2$, CaO at room temperature. The dried at $20{\pm}3^{\circ}C$, 75% humidity for 12hrs. Sample was prepared from the Cp-Ti(grade-2) and melted by high frequence induction melting system in the vacuum condition. The react ion layer of Ti was confirmed by optical microscopy, microhardness(Hv) and X-ray diffraction. Thickness of reaction layer using the CaO stabilized ZrO2 was thinner than the CaO added ZrO2. And thickness of reaction layer were decreased with decreasing pH of slurry. CaO addition in the slurry could not controlled reaction between molten Ti and investment mold. On the other hand, the CaO chemical bonded ZrO2 by stabilization treatment could controlled reaction between molten Ti and investment mold.