• The Journal of the Korean dental association
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• v.49 no.5
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• pp.260-264
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• 2011

Zirconia ($ZrO_2$) is a crystalline dioxide of zirconium. Dental zirconia blocks for CAD/CAM are usually fabricated with powders of tetragonal zirconia polycrystals (TZP) stabilized with 3mol% yttria. Because of its mechanical properties similar to those of metals and color similar to tooth, it is evaluated to attain the two purposes at a time, strength and aesthetic in prosthetic dentistry. The ability of transformation of Y-TZP from tetragonal to monoclinic helps to prevent crack propagation and contributes the increase of strength and fracture toughness. Two different types of blocks, soft and hard, are used to prepare the zirconia frameworks. The fuzzy-sintered block is difficult in machining, so pre-sintered soft 3Y-TZP block is usually used to mill by computer aided machining.

• Journal of the Korean Ceramic Society
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• v.34 no.2
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• pp.171-174
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• 1997

It was experimentally identified, for the first time, that oxygen phonons play an important role in the low temperature degradation(tetragonallongrightarrowmonoclinic phase transformation) of yttria stabilized tetragonal zir-conia polycrystals (Y-TZP). The degradation accompanied by immersing the samples in the boiling water were markedly reduced by substituting of 18O for 16O in Y-TZP. This was attributed to the heavier mass of 18O which leads to the smaller probability to find oxygen atoms beyond certain critical displacements.

• Korean Journal of Materials Research
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• v.29 no.4
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• pp.233-240
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• 2019

This study analyzes the mechanical properties, including the attrition rate, of $50{\mu}m$ size yttria-stabilized zirconia (YSZ) beads with different microstructures and high-energy milling conditions. The yttria distribution in the grain and grain-boundary of the fully sintered beads relates closely to Vickers hardness and the attrition rate of the YSZ beads. Grain size, fractured surfaces, and yttrium distribution are analyzed by electronic microscopes. For standardization and a reliable comparison of the attrition rate of zirconia beads with different conditions, Zr content in milled ceramic powder is analyzed and calculated by X-ray Fluorescence Spectrometer(XRF) instead of directly measuring the weight change of milled YSZ beads. The beads with small grain sizes sintered at lower temperature exhibit a higher Vickers hardness and lower attrition rate. The attrition rate of $50{\mu}m$ YSZ beads is measured and compared with the various materials properties of ceramic powders used for high-energy milling. The attrition rate of beads appears to be closely related to the Vickers hardness of ceramic materials used for milling, and demonstrates more than a 10 times higher attrition rate with Alumina(Hv ~1650) powder than $BaTiO_3$ powder (Hv ~315).

• Journal of Korean Dental Science
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• v.10 no.2
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• pp.74-81
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• 2017

This report describes two cases of complete arch implant-supported restorations. The first patient had seven dental implants in each arch with monolithic zirconia frameworks. At four weeks' follow-up, the one-piece maxillary framework was fractured, which was re-designed and re-fabricated using laser-sintered cobalt-chrome alloy. The second patient had four implants in the mandible only. A mandibular monolithic zirconia framework and a maxillary conventional complete denture were fabricated and delivered. At five years' follow-up, the patient reported no significant discomfort. Careful consideration and monitoring of the status of antagonistic arches and stress distribution on zirconia frameworks were suggested for complete arch implant-supported fixed restorations.

• Journal of the Korean earth science society
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• v.18 no.6
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• pp.553-558
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• 1997

Colorless and transparent cubic zirconia($Zr_{0.73}Y_{0.27}O_{1.87}$) crystal has been synthesized by the Bridgman-Stock-bager method(also called Skull melting method). $Y_2O_3$ is used as stabilizer. The crystal shows a vitreous luster with a slight oily appearance. Under a polarizing microscope, it shows isotropic nature with no appreciable anisotropism. Mohs hardness value is measured to be $8{\sim}8\frac{1}{2}$ and specific gravity 5.85. Under ultraviolet light it shows a faint white glow. The crystal structure of yttria stabilized zirconia was determined, using single crystal X-ray diffraction techniques to be a cubic symmetry, space group $Fm\overline{3}m({O^5}_h)$ with $a=5.1552(5){\AA}$, $V=136.99(5){\AA}^3$, Z=4, and R=0.0488 for 29 unique reflections. Each zirconium atom is at the center of eight oxygen atoms situated at the corners of a surrounding cube and each oxygen atom is at the center of a tetrahedron of zirconium atoms. So a coordination of 8:4 holds in the structure.

• The Journal of Advanced Prosthodontics
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• v.10 no.4
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• pp.259-264
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• 2018

PURPOSE. The purpose of this study was to evaluate the effect of the zirconia surface architecturing technique (ZSAT) on the bond strength between veneering porcelain and zirconia ceramic. MATERIALS AND METHODS. 20 sintered zirconia ceramic specimens were used to determine the optimal surface treatment time, and were randomly divided into 4 groups based on treatment times of 0, 1, 2, and 3 hours. After etching with a special solution, the surface was observed under scanning electron microscope, and then the porcelain was veneered for scratch testing. Sixty 3 mol% yttria-stabilized tetragonal zirconia polycrystal ceramic blocks were used for tensile strength testing; 30 of these blocks were surface treated and the rest were not. Statistical analysis was performed using ANOVA, the Tukey post-hoc test, and independent t-test, and the level of significance was set at ${\alpha}=.05$. RESULTS. The surface treatment of the zirconia using ZSAT increased the surface roughness, and tensile strength test results showed that the ZSAT group significantly increased the bond strength between zirconia and veneering porcelain compared to the untreated group (36 MPa vs. 30 MPa). Optimal etching time was determined to be 2 hours based on the scratch test results. CONCLUSION. ZSAT increases the surface roughness of zirconia, and this might contribute to the increased interfacial bond strength between zirconia and veneering porcelain.

• Journal of the Korean Institute of Telematics and Electronics
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• v.27 no.9
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• pp.1419-1426
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• 1990

The microstructure and electrical conductivity characteristics were examined for the Yttria Stablized Zirconia that were added Titania with the concentration of 0.02wt%, 0.05wt% and 0.1wt%. The stabilized cubic phase had not been changed. The obtained density of the sintered body was higher than 97% of the theoretical density as the grain growth and proe removal. And the highest density of 5.91g/cm**3 was obtained for 0.02wt% addition of TiO2. When 0.02 wt% TiO2 was added to YSZ, the electrical conductivity was 0.293.(\ulcorner.cm)**-1 and the limit of electrolyte regime Pn was 4x10**-28 atm. at 1, 100\ulcorner, respectively. Those were improved value compared with the electrical conductivity 0.107 (\ulcorner.cm)**-1 and Pn 1.5x10**-27atm. without adding TiO2.

• Journal of the Korean Ceramic Society
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• v.41 no.2
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• pp.111-117
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• 2004

3Y-TZP containing 0.3∼1.2 wt% of $Al_2$O$_3$ was prepared by slip-casting after attrition milling. The specimen was sintered at 1390∼151$0^{\circ}C$ and mechanical characterization and microstructure analysis were conducted. Monoclinic content of the specimen was calculated by XRD. The apparent density of specimen increased with increasing sintering temperature. While above 1470%, the formation of m-ZrO$_2$ degraded the density. The microhardness of specimen decreased with temperature because monoclinic phase increased wit the grain growth. The specimen containing $Al_2$O$_3$ below 0.9 wt% sintered at 143$0^{\circ}C$ showed the highest microhardness of 1360 Hv.

• Journal of Applied Reliability
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• v.15 no.3
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• pp.216-221
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• 2015

Sintering behavior of 3%yttria-stabilized zirconia was comparatively studied using a spray-dried powder produced by a domestic and global company. Quality of the sintered block was analysed in terms of relative density, shrinkage rate, grain growth, hardness, and fracture toughness. Relative density, shrinkage rate, and hardness value of the finally sintered block was similar between domestic and global zirconia powder, respectively. But, flexural strength of the domestic powder specimen was about 70% of the sintered block produced by using a global powder. The poor sintering quality of the domestic powder was discussed in relation with compressibility of the spray-dried granule-type powder and the amount of monoclinic phase in the as-received powder.

• Journal of the Korean Ceramic Society
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• v.25 no.2
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• pp.161-167
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• 1988

Yttria-Stabilized Cubic Zirconia Crystals with Various Y2O3 amounts (6-15mol%) were grown by the Skull melting technique. The modeling of the nucleation at the Skull bottom and the best growth condition were studied. The abrupt changes in generator heating Power and lowering rate of crucible caused the dendritic growth in the grown crystal. The optimum condition of cubic Zirconia single crystals was obtained when the lowering rate was gradually increased. The effect of Y2O3 amounts on the perfection adn the color of the grown crystal were determined. The darkish color generated in the crystals added Y2O3 amounts over 12mol% was eliminated by the annealing in air at 1200$^{\circ}C$ for 24hrs.