• Journal of the Korean Ceramic Society
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• v.32 no.5
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• pp.575-581
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• 1995

Zr0.94Y0.06O1.97 powder was synthesized by the ultrasonic spray pyrolysis with various concentrations of starting solution and the influence of powder characteristics on sintering behavior was investigated. Powders prepared at 75$0^{\circ}C$ were characterized as narrowly distributed submicron spherical particles, which were crystalline, nonagglomerated, and compositionally homogeneous. The changes in concentration from 0.01 to 01. mol/ι increased mean particle size from 0.24 to 0.38${\mu}{\textrm}{m}$ and decreased the specific surface area from 14.2 to 2.9$m^2$/g. The relative density of the specimen from the powders, prepared with the solution concentration of 0.01 mol/ι, was 98% after sintering for 2 hr at 1,45$0^{\circ}C$ and the monoclinic phase was observed after sintering at 1,55$0^{\circ}C$. As the concentration of starting solution was increased, the formation temperature of monoclinic phase was lowered.

• Journal of the Korean Ceramic Society
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• v.30 no.8
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• pp.651-656
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• 1993

Granulated Y-TZP powders were coated by using Sol-Gel method and the coating effect of Al2O3 on the isothermal phase transformation in Al2O3 coated Y-TZP powders was investigated. During aging, tetragonal phase in Y-TZP powder were isothermally transformed to monoclinic, but the tetragonal phase in Al2O3 coated Y-TZP powders was continuously retained in spite of long aging. It can be considered that the improvement of thermal stability of tetragonal phase in Al2O3 coated Y-TZP powders may be due to the increase of constraint effect near tetragonal phase, and the suppression of surface transformation by obstructing the reaction between the surface of Y-TZP and H2O.

• Journal of Powder Materials
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• v.17 no.3
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• pp.197-202
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• 2010

Low temperature degradation behavior in yttria stabilized tetragonal zirconia polycrystal (Y-TZP) ceramics was microscopically observed from the phase contrast between monoclinic surface and tetragonal matrix. The degradation behavior was dependent on the surface treatment of sintered Y-TZP, even if the sintering history is same. In the mirror polished specimen, the monoclinic layer appeared in a uniform thickness from the surface. On the contrary, for the specimen with coarse scratch, the thickness of degraded surface was more than double especially from the coarse scratch. Since the scratch results in local deformation, the residual stress should be induced around the scratch. With the transformation from tetragonal to monoclinic, the volume expansion exerts a stress on a neighboring grains and promotes a successive phase transformation. Such a autocatalytic effect can be triggered from the part of coarse scratch.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.2 no.2
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• pp.63-70
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• 1992

$AI_2O_3/Ca-TZP$ composites was prepared by using the starting powder of alumina and Ca-TZP synthesized by hydrothermal reaction and investigated to its characteristics. The ratio of tetragonal zirconia to monoclinic within $AI_2O_3$ matrix was decreased with an addition of Ca-TZP content, but the absolute amount of tetragonal phase in composites was increased with an addition of Ca-TZP content. The value of fracture toughness in $AI_2O_3/Ca-TZP$composites was proportional to the amounts of transformed tetragonal phase which formed by crack propagation in fracture, and therefore, it was gradually increased with an addition of Ca- TZP content.

• Journal of Powder Materials
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• v.29 no.5
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• pp.424-431
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• 2022

3Y-TZP ceramics obtained by doping 3 mol.% of Y₂O₃ to ZrO₂ to stabilize the phase transition are widely used in the engineering ceramic industry due to their excellent mechanical properties such as high strength, fracture toughness, and wear resistance. An additional increase in mechanical properties is possible by manufacturing a composite in which a high-hardness material such as oxide or carbide is added to the 3Y-TZP matrix. In this study, composite powder was prepared by dispersing a designated percentage of WC in the 3Y-TZP matrix, and the results were compared after manufacturing the composite using the different processes of spark plasma sintering and HP. The difference between the densification behavior and porosity with the process mechanism was investigated. The correlation between the process conditions and phase formation was examined based on the crystalline phase formation behavior. Changes to the microstructure according to the process conditions were compared using field-emission scanning electron microscopy. The toughness-strengthening mechanism of the composite with densification and phase formation was also investigated.

• Journal of the Korean Ceramic Society
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• v.29 no.11
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• pp.877-887
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• 1992

Tetragonal zirconia powder with 3 mol% Y2O3 mas mixed with up to 30 vol% of ${\beta}$-SiC powders, and the mixtures were hot-pressed at 1500$^{\circ}C$ for 60 min under a pressure of 30 MPa in Ar atmosphere. Flexural strength and fracture toughness were measured at room-and high-temperature (1000$^{\circ}C$). Evolution of microstructure was also conducted to investigate the effects of SiC addition on the properties of 3Y-TZP ceramics. Average grain size of the composites was about 0.5 $\mu\textrm{m}$, and decreased with SiC addition. Both room- and high-temperature mechanical properties of the composites were improved with SiC content. Particularly, high-temperature strength and fracture toughness of 3Y-TZP/30v/o SiC composite were twice as high as those of 3Y-TZP. The hardness of the composites also increased with SiC content and reached maximum value at 3Y-TZP/30v/o SiC composite.

• Korean Journal of Materials Research
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• v.23 no.4
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• pp.250-254
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• 2013

In order to increase the toughness of ZTA(zirconia toughened alumina) ceramics, the present study focused on rearrangement and densification of particles according to the particle size of the parent material. When rough alumina was used for production of ZTA, densification behavior was observed in the specimen sintered at a temperature over $1550^{\circ}C$. However, it was found that the densification behavior was occurred in the specimen sintered at $1450^{\circ}C$ when fine alumina powder was used. High relative density exceeding 98% was obtained when fine alumina powder was mixed with 15 wt% of 3Y-TZP and sintered at $1600^{\circ}C$. Also, a hardness of 1820.2 Hv was obtained when a specimen containing 10 wt% of 3Y-TZP was sintered at $1600^{\circ}C$. In the case of 3Y-TZP containing rough alumina powder that had been sintered the hardness value was around 1720.3 Hv. It was predicted that an improved toughening effect in ZTA could be achieved by using finer alumina powder as the parent material.

• Journal of the Korean Ceramic Society
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• v.26 no.5
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• pp.719-727
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• 1989

By using commercial zirconia powder CeO2-ZrO2 ceramics containing 8~16mol% CeO2 was made by heat treatment at 1350~155$0^{\circ}C$ for 1~10hr. The minimum amount of CeO2 for obtaining complete tetragonal phase was 12mol%, and in the tetragonal phase region fracture toughness of Ce-TZP was decreased with increasing CeO2 content and the maximum value was obtained when 12mol% CeO2 was added. The bending strength goes through maximum at 14mol% CeO2. Fracture mode of Ce-TZP transformed from intergranular to transgranular fracture with increasing CeO2 content, so the morphology of fracture surface of 16mol% Ce-TZP was wholly transgranular and this tendency was independent on grain size. The crystal structure of the 12mol% Ce-TZP was monoclinic with fringes along the grain boundaries which are lying in the particular plane from the TEM observation. The chemical composition of the sintered body was homogeneous as a whole and some amorphism or air pocket was observed at the triple junction.

• Journal of Powder Materials
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• v.13 no.5 s.58
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• pp.360-365
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• 2006

The phase stability of tetragonal phase in Y-TZP was investigated in terms of the distribution of grain sizes and heat-treating atmosphere. Y-TZP with various grain sizes were prepared using duration time at $1600^{\circ}C$ as experimental parameter. Accumulated grain size distributions were built from the SEM micrographs and the amount of tetragonal phase were measured using XRD. Both results were compared to determine the critical grain size before and after heat-treatment in vacuum. The critical grain size drastically decreased compared with the small increase of average grain size due to the autocatalytic effect which critically affects the tetragonal to monoclinic phase transformation. After heat-treatment in reductive atmosphere critical grain size relatively increased due to the stabilization of tetragonal phase. The formation of oxygen vacancies during heat-treatment was ascribed to the increase of stability.

• Journal of Technologic Dentistry
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• v.33 no.1
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• pp.15-23
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• 2011

Purpose: Thy yttria tetragonal zirconia polycrystalline(Y-TZP) is a good structural ceramic for dental restoration. But it have a problem that delamination of veneering ceramic from the Y-TZP core materials. The problem generally occur at the interface, thus this study was conducted to evaluate the interface of Y-TZP using scanning electron microscopy(SEM). Methods: To investigate this aspect, high-resolution SEM observations were made of polished and etched (HF content gel) cross-sections of the interface area. Dry and moist veneering porcelain powders were built up on the zirconia base. Results: The extent of this surface faceting is dependent upon the moisture content of the porcelain powder and the firing temperature. More moisture and higher final heating temperature accelerates the observed faceting of the Y-TZP grains at the interface to the veneering ceramic. Conclusion: These changes of the Y-TZP grains indicate that destabilization of the tetragonal phase of zirconia occurs at the interface during veneering with ceramic. It may result in a reduction of the stability of the zirconia and interface.