• Title/Summary/Keyword: Monoclinic zirconia

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Effect on Mechanical Properties of 3Y-TZP; (II) Addition of Alumina (3Y-TZP의 기계적 물성에 미치는 영향: (II) 알루미나의 첨가)

  • Yang, Seong-Koo;Bae, Kyung-Man;Cho, Bum-Rae;Kang, Jong-Bong
    • Journal of the Korean Ceramic Society
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    • v.42 no.6 s.277
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    • pp.417-424
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    • 2005
  • Although a lot of studies in fracture toughness of Y-TZP ceramics for structural applications have been done, it remains an important challenge to be able to improve fracture toughness of Y-TZP ceramics. In this research, milling method adding monoclinic zirconia and $Al_2O_3$ to 3Y-TZP was introduced to improve the fracture toughness of 3Y-TZP. Experimental results showed that addition of small amount of $Al_2O_3$ causes to make lots of oxygen vacancies (VO) by substituting $Al^{3+}$ for $Zr^{4+}$. It is believed that the produced vacancies provides useful routes far mass transfer. Y-TZP ceramics having higher microhardness and better fracture toughness was fabricated by sintering at $1400^{\circ}C$.

Biotribological Properties of TZP/Al2O3 Ceramics for Biomechanical Applications

  • Lee, Deuk-Yong;Lee, Se-Jong;Jang, Ju-Woong;Kim, Hak-Kwan;Kim, Dae-Joon
    • Journal of the Korean Ceramic Society
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    • v.40 no.6
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    • pp.525-529
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    • 2003
  • Biotribological properties, such as wear rate and friction coefficient, of 3Y-TZP and Low Temperature Degradation (LTD) free materials were investigated via a ball(SiC)-on-plate sliding wear test to evaluate the relationship between wear mechanism and phase transformation. Wear test was conducted with a sliding speed of 0.035 m/s at room temperature and at 25$0^{\circ}C$ in air under a normal load of 49 N, respectively. Although friction coefficient of 3Y-TZP was the lowest due to the fine grain size, the highest wear loss and rate were observed due to the debris of monoclinic grains introduced during sliding and their values increased drastically with raising temperature. However, the biotribological properties of LTD-free materials were insensitive to temperature due to the inertness of the phase transformation, suggesting that they may be applicable to the biomechanical parts.

Synthesis of ZrO2 Gel Dispersed with Au Fine Particles by Sol-Gel Method (졸-겔법에 의한 Au 미립자 분산 ZrO2 겔의 합성)

  • Mun, Chong-Soo;Lee, Seung-Min
    • Korean Journal of Materials Research
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    • v.13 no.4
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    • pp.219-223
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    • 2003
  • Zirconia gels dispersed with fine Au particles have been prepared by the sol-gel method. Starting solution with (OC$Zr_4$$H_{ 9}$)$_4$, $C_4$ $H_{9}$ OH, $H_2$O,$ HNO_3$, $HAuC1_4$ was used to prepare gels in several molar ratio. After hydrolysis, viscosity of solutions as 4∼5 cP and gelling time of sols were spent about 9 days. As the heat-treatment temperature was increased,$ ZrO_2$ had the phase transition from tetragonal to monoclinic at $750^{\circ}C$. Heat-treatments of the gel have performed at 500, 700, 750, 800, 1000 and $1100^{\circ}C$ for 3 hrs, respectively. We have investigated TG-DTA, X-ray diffraction patterns, SEM and EDS. The size of Au fine particles dispersed in the heat-treatmented gel was about 0.15∼0.23 $\mu\textrm{m}$ and the shape was most sphericity.

Preparation of $AI_2O_3/Ca-TZP$ Composites and its Characteristics ($AI_2O_3/Ca-TZP$ 복합체의 제조 및 그 특성)

  • 곽효섭;백용혁;이종국
    • 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.

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Sintering Characteristics of Zircon Nanopowders Fabricated by High Energy Milling Process (고 에너지 밀링 공정으로 제조된 지르콘 나노분말의 소결특성에 관한 연구)

  • Lee, Ju Seong;Kang, Jong Bong
    • Korean Journal of Materials Research
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    • v.26 no.2
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    • pp.95-99
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    • 2016
  • In this study, 5 um sized $ZrSiO_4$ was ground to 1.9 um, 0.3 um, and 0.1 um sized powders by wet high energy milling process, and the sintering characteristics were observed. Pure $ZrSiO_4$ itself can-not be sintered to these levels of theoretical density, but it was possible to sinter $ZrSiO_4$ powder of nano-scale size of, -0.1 um to the theoretical density and to lower the sintering temperature for full density. Also, the decomposition of $ZrSiO_4$ with a size in the micron range resulted in the formation of monoclinic $ZrO_2$; however, in the nano sized range, the decomposition resulted in the tetragonal phase of $ZrO_2$. So, it was possible to improve the sintering characteristics of nano-sized $ZrSiO_4$ powders.

The Effect of Trivalent Cation Doping on the Low Temperature Phase Stability of 2Y-TZP (3가 양이온 산화물이 첨가된 2Y-TZP의 저온 상안정성)

  • Jang, Ju-Woong;Kim, Hak-Kwan;Lee, Deuk-Yong;Kim, Dae-Joon;Park, Sun-Min
    • Journal of the Korean Ceramic Society
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    • v.39 no.11
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    • pp.1055-1062
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    • 2002
  • The phase stability and the Low Temperature Degradation(LTD) mechanism of Tetragonal Zirconia Polycrystals(TZP), sintered specimens of $Y_2O_3$-Stabilized Zirconia(2Y-TZP), doped with trivalent cations, were evaluated by investigating meachnical properties, Raman spectra, lattice parameter variation and the oxygen vacancy behavior under applied electric field. XRD observation was put forward on 2Y-TZP doped with trivalent cation whose ionic radii were larger than $Zr^{4+}(Sc^{3+},\;Yb^{3+},\;Y^{3+},\;Sm^{3+},\;Nd^{3+},\;La^{3+})$ up to 2 mol% and sintered at 1500 h for 1h. For $La^{3+}$ doping, the stability of tetragonal phase was degraded due to the formation of the pyrochlore phase $(La_2Zr_2O_7)$ as the dopant content increased above exceeded 0.5 mol%. As the dosage increased, tetragonal phase maintained for the case of $Sc^{3+}$, whose radius was similar to $Zr^{4+}$, on the other hand, the cubic phase was formed for the cases of $Yb^{3+},\;Y^{3+},\;Sm^{3+},\;Nd^{3+}$. As the radii of dopant cation increased, c/a ratio increased and it was experimentally observed that the amount of monoclinic phase decreased when the specimens were annealed at $220{\circ}C$ for 500 h.

Synthesis of Dimethyl Carbonate from Methanol and Supercritical Carbon Dioxide over K2CO3/ZrO2 Catalysts (메탄올과 초임계 이산화탄소로부터 K2CO3/ZrO2 촉매를 이용한 디메틸카보네이트 (Dimethyl Carbonate) 합성)

  • Hong, Seung Tae;Park, Hyung Sang;Lim, Jong Sung;Yoo, Ki-Pung
    • Korean Chemical Engineering Research
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    • v.46 no.3
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    • pp.550-554
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    • 2008
  • The synthesis of dimethyl carbonate (DMC) from methanol and supercritical carbon dioxide over $K_2CO_3/ZrO_2$ catalysts have been studied. The catalysts were prepared by impregnating $ZrO_2$ with an aqueous $K_2CO_3$ solution. The optimum calcination temperature to disperse K species on the $ZrO_2$ surface was found to be 673 K. Monoclinic $ZrO_2$ was not active, as itself, for the DMC production. However, when the $K_2CO_3$ was impregnated on the $ZrO_2$, the catalytic performance was improved. Besides the catalyst, $CH_3I$ was used as a promoter. The $CH_3I$ promoter as well as the $K_2CO_3/ZrO_2$ catalyst was found to take an important role to improve the production of DMC. The optimum quantities for the catalyst and the promoter were estimated. The effect of the catalyst and the promoter for the DMC synthesis from methanol and supercritical carbon dioxide was investigated and the reaction mechanism was proposed.

A Study on the Alumina Ceramic Composite Dispersed With the Zirconia (지르코니아-알루미나 세라믹 복합재료에 관한 연구)

  • Park, Jae-Sung;Lee, Yeong-Sin
    • 전자공학회논문지 IE
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    • v.49 no.2
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    • pp.1-8
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    • 2012
  • The effects of the addition of either monoclinic $ZrO_2(pure)$ or tetragonal $ZrO_2$ containing 5.35wt% $Y_2O_3(Y-TZP)$ on the mechanical properties and thermal shock resistance of $Al_2O_3$ ceramics were investigated. The addition of $ZrO_2$(m) and Y-TZP increased sintered density of $Al_2O_3$. The Vickers hardness also increased as the volume fraction of Y-TZP increased going through a maximum at 20wt%. The hardness of the specimens was found to be dependent on the sintered density. The higher volume fraction of either $ZrO_2(m)$ or Y-TZP resulted in the higher fracture toughness of the composite was. This result may be taken as evidence that toughening of $Al_2O_3$ can be achieved by not only the transformation toughening but microcrack toughening of $ZrO_2$. The thermal shock property for $Al_2O_3-ZrO_2$ composites was improved by increasing the volume fraction of monoclinic $ZrO_2(pure)$. The grain size increased as the volume fraction of $ZrO_2$ did.

NiO/La2O3-ZrO2/WO3 Catalyst Prepared by Doping ZrO2 with La2O3 and Modifying with WO3 for Acid Catalysis

  • Sohn, Jong-Rack;Choi, Hee-Dong;Shin, Dong-Chul
    • Bulletin of the Korean Chemical Society
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    • v.27 no.6
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    • pp.821-829
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    • 2006
  • A series of catalysts, $NiO/La_2O_3-ZrO_2/WO_3$, for acid catalysis was prepared by the precipitation and impregnation methods. For the $NiO/La_2O_3-ZrO_2/WO_3$ samples, no diffraction lines of nickel oxide were observed, indicating good dispersion of nickel oxide on the catalyst surface. The catalyst was amorphous to X-ray diffraction up to 300 ${^{\circ}C}$ of calcination temperature, but the tetragonal phase of $ZrO_2$ and monoclinic phase of $WO_3$ by the calcination temperatures from 400 ${^{\circ}C}$ to 700 ${^{\circ}C}$ were observed. The role of $La_2O_3$ in the catalyst was to form a thermally stable solid solution with zirconia and consequently to give high surface area and acidity. The high acid strength and high acidity were responsible for the W=O bond nature of complex formed by the modification of $ZrO_2$ with $WO_3$. For 2-propanol dehydration the catalyst calcined at 400 ${^{\circ}C}$ exhibited the highest catalytic activity, while for cumene dealkylation the catalyst calcined at 600 ${^{\circ}C}$ showed the highest catalytic activity. 25-$NiO/5-La_2O_3-ZrO_2/15-WO_3$ exhibited maximum catalytic activities for two reactions due to the effects of $WO_3$ modifying and $La_2O_3$ doping.

Low-temperature phase stability and mechanical properties of $Y-Nb-TZP/Al_2O_3$ compoites ($Y-Nb-TZP/Al_2O_3$ 복합체의 저온 상안정성 및 기계적 특성)

  • 이득용;김대준;조경식;장주웅
    • Journal of the Korean Crystal Growth and Crystal Technology
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    • v.8 no.4
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    • pp.634-639
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    • 1998
  • $Y_2O_3$ and $Nb_2O_5$ co-doped zirconia composites containing 10~30 vol% $Al_2O_3$ with two different particle sizes were sintered for 5 h at $1550^{\circ}C$ to evaluate low-temperature phase stability of the composite using X-ray diffractometry after heat-treatments for 1000 h at $250^{\circ}C$ in air or for 5 h at $180^{\circ}C$ in 0.3 MPa $H_2O$ vapor pressure. No tetragonal to monoclinic phase transformation during degradation, so called enhanced low-temperature phase stability, was observed for all composites. It is concluded that Nb addition to the composite for the phase stability is more effective than $Al_2O_3$ addition. The optimum combination of strength (670 MPa) and fracture toughness ($7.1{\textrm} {MPam}^{1/2}$) were obtained for the composite containing 20 vol% of $Al_2O_3$ with 2.8 $\mu$m to 0.2 $\mu$m, the flexural strength increases but the fracture toughness decreases.

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