• 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.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.

• 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 Society of Manufacturing Technology Engineers
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• v.19 no.1
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• pp.7-14
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• 2010

AE(acoustic emission) sensor has been used for a state monitoring and observation during a ultra-precision machining because AE signal, which has high frequency range, is sensitive enough. In case of ceramic fabrication, a monitoring of machining state is important because of its hard and brittle nature. A machining characteristic of ceramic is susceptibly different in accordance with variable machining conditions. In this study, Yttria($Y_2O_3$) ceramic was fabricated using the ultra-precision lapping process with in-process electrolytic dressing(IED) method. And the surface machining characteristic and AE sensor signal were compared and analyzed.

• Journal of the Korean Ceramic Society
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• v.50 no.3
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• pp.180-185
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• 2013

We investigated the characteristics of hot-pressed pure yttria ceramics, and annealed them in an oxidation atmosphere. Regardless of the heat treatment in the oxidation atmosphere, XRD analysis showed that all the samples had a $Y_2O_3$ phase without structural change. Even though the color variation of the hot-pressed $Y_2O_3$ ceramics was due to the sintering temperatures, the oxidation process turned the color of the $Y_2O_3$ ceramics into white. The color change during oxidation treatment appears to be related to oxygen defects. In addition, oxygen defects also affected the weight change and microstructure of the $Y_2O_3$ ceramics. The $Y_2O_3$ ceramic sintered at $1600^{\circ}C$ had a $5.03g/cm^3$ density, which is close to the theoretical density of $Y_2O_3$. As the sintering temperature increased, small homogeneous grains grew to large grains which affected the Vickers hardness. $Y_2O_3$ ceramics hot-pressed at $1600^{\circ}C$ and annealed at $1200^{\circ}C$ had a flexural strength of 140MPa.

• 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.

• Korean Chemical Engineering Research
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• v.43 no.5
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• pp.627-631
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• 2005

The $(La_{0.8}Sr_{0.2})_{0.95}MnO_3$/yttria-stabilized zirconia (LSM/YSZ) composites were investigated as anode materials for high temperature steam electrolysis using X-ray diffractometry, scanning electron microscopy, galvanodynamic and galvanostatic polarization method. For this purpose, the LSMperovskites were fabricated in powders by co-precipitation method and then were mixed with 8 mol% YSZ powders in different molar ratios. The LSM/YSZ composites were deposited on 8 mol% YSZ electrolyte disks by means of a screen printing method, followed by sintering at temperatures above $1,100^{\circ}C$. From the experimental results, it is concluded that the electrochemical properties of LSM and the LSM/YSZ composites are closely related to their microstructure and operating temperatures.

• 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.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.924-925
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• 2006

In this study, hydroxyapatite (HAp) and hydroxyapatite-yttria stabilized zirconia (HAp-3YSZ) with 20 vol.%-($ZrO_2+3%mol\;Y_2O_3$) nanopowders were consolidated very rapidly to full density by High-frequency induction heat sintering (HFIHS). Effects of temperature and the addition of 3YSZ on the toughness, hardness and microstructure properties have been studied. 3YSZ second phase toughening HAp composites with higher toughness were successfully developed at relatively low temperatures through this technique. Compared with hardness and toughness obtained for pure HAp, the hardness and toughness for HAp-20vol. % 3YSZ were much higher.

• The Korean Journal of Ceramics
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• v.5 no.2
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• pp.131-136
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• 1999

Yttria stabilized zirconia(YSZ) films were deposited on porous NiO substrates and quartz plates by the thermal CVD using $ZrCl_4, YCl_3$ as precursors, and $O_2$ as a reactive gas at atmospheric pressure. The evaporation temperature of $ZrCl_4$ was varied from $250^{\circ}C$ to $550^{\circ}C$ while the temperatures of $YCl_3$ and the substrate were varied from $1000^{\circ}C$ to $1030^{\circ}C$. As the evaporation temperature of $ZrCl_4$ increased, the deposition rate of $ZrO_2$ decreased, contrary to our expectation. As a result of the decreased deposition rate of $ZrO_2$, the yttria content increase. The high evaporation temperature of $ZrCl_4$ makes the well-faceted crystal while the low evaporation temperature leads to the cauliflower-shaped structure. The dependence of the evaporation temperature on the growth rate and the morphological evolution was interpreted by the charged cluster model.