• Journal of the Korean Ceramic Society
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• v.50 no.5
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• pp.348-352
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• 2013

The evaluation of plasma resistance and the characteristics of yttria ceramics fabricated by calcination yttria as a starting material without dopants under an oxidation atmosphere was investigated. Regardless of the starting materials, as-received, and calcined yttria powder, XRD patterns showed that all samples have $Y_2O_3$ phase. The three cycling process inhibited a large grain, which occurs frequently during the yttria sintering, and a high density ceramic with a homogeneous grain size was obtained. The grain size of the sintered ceramic was affected by the starting powders. The smaller the grain size, the larger were the Young's modulus and KIC. Compared to $Al_2O_3$ and $ZrO_2$ ceramics, yttria ceramics showed a 3 times larger plasma resistance and a 1.4~2.2 times lower weight loss during the plasma etching test, respectively.

• Restorative Dentistry and Endodontics
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• v.45 no.4
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• pp.52.1-52.11
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• 2020

Objectives: Yttria-stabilized tetragonal phase zirconia has been used as a dental restorative material for over a decade. While it is still the strongest and toughest ceramic, its translucency remains as a significant drawback. To overcome this, stabilizing the translucency zirconia to a significant cubic crystalline phase by increasing the yttria content to more than 8 mol% (8YTZP). However, the biocompatibility of a high amount of yttria is still an important topic that needs to be investigated. Materials and Methods: Commercially available 8YTZP plates were used. To enhance cell adhesion, proliferation, and differentiation, the surface of the 8YTZP is sequentially polished with a SiC-coated abrasive paper and surface coating with type I collagen. Fibroblast-like cells L929 used for cell adherence and cell proliferation analysis, and mouse bone marrow-derived mesenchymal stem cells (BMSC) used for cell differentiation analysis. Results: The results revealed that all samples, regardless of the surface treatment, are hydrophilic and showed a strong affinity for water. Even the cell culture results indicate that simple surface polishing and coating can affect cellular behavior by enhancing cell adhesion and proliferation. Both L929 cells and BMSC were nicely adhered to and proliferated in all conditions. Conclusions: The results demonstrate the biocompatibility of the cubic phase zirconia with 8 mol% yttria and suggest that yttria with a higher zirconia content are not toxic to the cells, support a strong adhesion of cells on their surfaces, and promote cell proliferation and differentiation. All these confirm its potential use in tissue engineering.

• Journal of the Korean Ceramic Society
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• v.42 no.11 s.282
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• pp.718-721
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• 2005

The high temperature tetragonal phase of zirconia containing $1.40{\~}1.60\;mol\%$ of yttria can be fully retained at room temperature by rapid cooling. The metastable tetragonal phase transforms into the monoclinic phase athermally upon subzero cooling. The transformation exhibited an athermal burst transformation. The effects of yttria content and grain size on the athermal martensitic transformation were studied in detail. The burst temperature linearly decreased with increasing yttria content or decreasing grain size. To consider the distribution of martensite nuclei, the Weibull modulus of the athermal martensitic transformation was evaluated from the distribution of the burst transformation temperature. From the Weibull analysis, the distribution of embryos appears to be more homogeneous than that of the defects responsible for the fracture of similar material.

• Proceedings of the Materials Research Society of Korea Conference
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• 1997.10a
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• pp.116-116
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• 1997

• Journal of the Korean Ceramic Society
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• v.46 no.5
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• pp.441-446
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• 2009

Dense crack-free yttria film with 10 $\mu m$ thickness was prepared on aluminum by aerosol deposition. X-ray diffraction pattern on the film showed that it contained the same crystalline phase as the raw powder. Transmission electron microscopy revealed a nanostructured yttria film with grains smaller than 100 nm. Tensile adhesion strength between the film and aluminum substrate was 57.8 $\pm$ 6.3MPa. According to the etching test with $CF_4-O_2$ plasma, the etching rate of the yttria film was 1/100 that of quartz, 1/10 that of sintered alumina and comparable to that of sintered yttria.

• Journal of the Korean Society for Heat Treatment
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• v.37 no.1
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• pp.1-8
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• 2024

Phase stability of tetragonal crystals in yttria-stabilized zirconia ceramics is dependent on the content of yttria and the heat-treatment condition, related with mechanical properties. In this study, we fabricated the 1.5 mol% yttria-stabilized zirconia (1.5Y-YSZ) ceramics by cold isostatic pressing (CIP) and post-sintering at temperature range of 1200 to 1350℃ for 2 hours and investigated the sintered properties and microstructural evolution. Sintered and microstructural parameters, i.e, apparent density, grain size and phase composition of 1.5Y-YSZ ceramics were mainly dependent on the sintering temperature. Maximum sintered density of 99.4 % and average grain size of 200-300 nm could be obtained from the heat-treatment condition above sintering temperature at 1300℃ for 2 hours, possessing the superior mechanical hardness with 1200 Hv. However, phase stability of tetragonal grains in 1.5 YSZ ceramics is very low, inducing the phase transformation to monoclinic crystals on specimen surface during cooling after heat-treatment.

• Journal of the Korean Ceramic Society
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• v.34 no.12
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• pp.1247-1253
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• 1997

Sinter-active yttria powders were prepared by a solution precipitation with using a self-decomposing precipitation agent NH2CONH2(urea). The cold-pressed powders can be sintered to full density and the microstructure of grains less than 200 nm at a temperature as low as 120$0^{\circ}C$. The activity of the yttria powder has been controlled by varying nucleation conditions during precipitation and by minimizing formation of aggregates. The type of precursor is decisive in preparation of a sinter-active oxide powder, and urea is desirable as a precipitation agent for an active yttrium oxide powder.

• Journal of the Korean Ceramic Society
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• v.24 no.3
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• pp.263-269
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• 1987

It is investigated that the determination of the correlation between the change of microstructure and electrical properties. Yttria is added to the compositiojn of rhombohedral region in Pb(Mg1/3Nb2./3)O3-PbTiO3-PbZrO3 ternary system. Average grian size, lattice parameters and distribution of yttrium are characterized by XRD, SEM and EDS. Electrical properties are determined by measurement of Curie temperature, piezoelectric properties and hysteresis loops. The results are as follows; 1. Both lattice parameters, a and ${\alpha}$, are changed by addition of yttria to the composition of rhomboheadral region in Pb(Mg1/3Nb2./3)O3-PbTiO3-PbZrO3 ternary system and Curie temperature is proportional to the values at (90-${\alpha}$).

• Journal of the Korean Ceramic Society
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• v.33 no.5
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• pp.495-506
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• 1996

Monodispersed colloidaly yttria(Y2O3) can be used in a variety of applications such as phosphors. IR transparent materials and fine ceramics. For preparing monodispersed yttria homogeneous precipitation has been regarded as a fovorable method that is monodispersed yttria can be obtained through calcining monodispersed colloidal compound of yttrium (eg:Y(OH)CO3.nH2O)which can be prepared by homogeneous precipitation with urea. It is however still required to find out the quantitative effects of important variables of precipitation such as concentration of yttrium and urea reaction temperature and initial pH of reactant even though homogeneous precipitation of Y3+ with urea has been studied extensively. Among the effects of these variables we investiga-ted 1) the effect of yttrium concentration on the shape and size of precipitate and the reation rate 2) range of yttrium concentration required to make monodispersed colloidal particles 3) the reason for limited concentra-tion range of yttrium and 4) the effect of ultrasonic radiation on the limited concentration.

• Journal of the Korean Ceramic Society
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• v.26 no.2
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• pp.228-234
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• 1989

Pressureless-sintering of SiC with additions of yttria and alumina was studied. SiC could be densified to about 97% of its theoretical density at 185$0^{\circ}C$ which is about 20$0^{\circ}C$ below the normal sintering temperature of SiC with boron and carbon. Yttria and alumina formed intergranular liquid phases at the sintering temperature and promoted densification by the liquid phase sintering mechanism. The microstructure of sintered specimens was equiaxed and the liquid phase appeared to wet and dissolve SiC grains. The fracture toughness was measured by indentation method and found to be 5.3MPa.m1/2. Processing flaws near the surface of specimens appeared to be the major fracture origin during 3-point bending tests.