• Title/Summary/Keyword: ZrO2

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Fabrication and Physical Properties of ZrO2(m)-Al2O3ZrO2(t)-Al2O3 Structural Ceramics (ZrO2(m)-Al2O3ZrO2(t)-Al2O3 세라믹스의 제조와 물리적 특성)

  • Park, Jae-Sung;Park, Ju-Tae;Park, Jung-Rang
    • Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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    • v.24 no.4
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    • pp.140-148
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    • 2010
  • The effects of the addition of either monoclinic $ZrO_2(ZrO_2(m))$ or tetragonal $ZrO_2(ZrO_2(t))$ containing 5.35[wt%] $Y_2O_3$ on the physical properties and electrical conductivity of $Al_2O_3$ were investigated. The addition of $ZrO_2$(m) and $ZrO_2$(t) increased sintered density of $Al_2O_3$. The Vickers hardness also increased as addition of $ZrO_2$(t) increased going through a maximum at 20[wt%] and the hardness of the specimens was found to be dependent on the sintered density. The addition of $ZrO_2$(t) improved the hardness of $Al_2O_3-ZrO_2$ systems and the $ZrO_2$(m) addition showed the better effect on the thermal shock property of $Al_2O_3-ZrO_2$ systems than that of the $ZrO_2$(t) addition. Above 15[wt%] addition of $ZrO_2$(t), the electrical conductivity is gradually increased with increasing applied voltage but not effects by addition of $ZrO_2$(m).

(Effect of Monoclinic Zirconia and Tetragonal Zirconia Addition on Physical Properties and Electrical conductivity of $Al_2O_3$) ($Al_2O_3$의 물리적 성질 및 전기전도도에 미치는 단사정 지르코니아와 정방정 지르코니아의 첨가효과)

  • 박재성;어수해
    • Journal of the Institute of Electronics Engineers of Korea TE
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    • v.39 no.1
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    • pp.1-8
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    • 2002
  • The effects of the addition of either monoclinic $ZrO_2$($ZrO_2$(m)) or tetragonal $ZrO_2$($ZrO_2$(t)) containing 5.35wt% $Y_2O_3$ on the physical properties and electrical conductivity of TEX>$Al_2O_3$ were investigated. The addition of $ZrO_2$(m) and $ZrO_2$(t) increased sintered density of $Al_2O_3$. The Vickers hardness also increased as addition of >($ZrO_2$(t) increased going through a maximum at 20wt% and the hardness of the specimens was found to be dependent on the sintered density. The addition of $ZrO_2$(t) improved the hardness of $Al_2O_3$-$ZrO_2$ systems and the $ZrO_2$(m) addition showed the better effect on the thermal shock property of $Al_2O_3$-$ZrO_2$ systems than that of the $ZrO_2$(t) addition. Above 15wt% addition of $ZrO_2$(t), the electrical conductivity is gradually increased with increasing applied voltage but not effects by addition of $ZrO_2$(m).

Microstructures and Mechanical Properties of $Al_2O_3$-$ZrO_2$ Ceramics Prepared by a Precipitation Method (침전법으로 제조한 $Al_2O_3$-$ZrO_2$계 세라믹스의 미세구조 및 기계적 특성)

  • 홍기곤;이홍림
    • Journal of the Korean Ceramic Society
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    • v.27 no.8
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    • pp.991-1003
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    • 1990
  • A precipitation method, one of the most effective liquid phase reaction methods, was adopted in order to prepare high-tech Al2O3/ZrO2 composite ceramics. Al2(SO4)3.18H2O, ZrOCl2.8H2O and YCl3.6H2O were used as starting materials and NH4OH as a precipitation agent, various types of metal hydroxides were obtained by single precipitation(series A) and co-precipitation(series B) method at the pH condition between 7 and 11. Fine Al2O3-ZrO2 powders were prepared at optimum calcination condition and the effects of ZrO2 on microstructures and mechanical properties of Al2O3 were investigated. The composition of Al2O3/ZrO2 composites wax fixed as Al2O3-15 v/o ZrO2(+3m/o Y2O3). ZrO2 limited the grain growth of Al2O3 and increased grain size homogeneity of Al2O3 more effectively than MgO.Flexural strength values in Al2O3 and Al2O3/ZrO2 composites were 340-430 MPa and 540-820 MPa, respectively, and the effect of strength improvement showed 20-50% by adding ZrO2 to Al2O3. Fracture toughness of Al2O3/ZrO2 composites was improved by stress-induced phase transformation of tetragonal ZrO2 and toughening effect by microcrack was not observed. Also, ZrO2 particles located at Al2O3 grain junction contributed to toughening, while spherical ZrO2 particles located within Al2O3 grain did not contribute to toughening. Weibull moduli of Al2O3 ceramics and Al2O3/ZrO2 composites of series A and series B were 4.34, 5.17 and 9.06, respectively. Above 0.5 of failure probability, strength values in Al2O3 ceramics and Al2O3/ZrO3 composites of series A and series B were above 400 MPa, 700 MPa and 650 MPa, respectively.

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Microstructure and Mechanical Properties of $Al_2$O$_3$/t-ZrO$_2$ Particulate Composites (Al$_2$O$_3$/t-ZrO$_2$ 입자복합체의 미세구조 및 기계적 성질)

  • 심동훈;이윤복;김영우;오기동;박홍채
    • Journal of the Korean Ceramic Society
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    • v.36 no.7
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    • pp.734-741
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    • 1999
  • Al2O3/t-ZrO2 particulate composites were prepared by sintering at 150$0^{\circ}C$ and 1$600^{\circ}C$ for 2h in air and microstructure and mechanical properties of the composites were investigated. Although most ZrO2 particles existed at Al2O3 grain boundaries a few ZrO2 particles within Al2O3 grains. Al2O3 grain growth was depressed due to the pinning effect by ZrO2 particles. During sintering coarsening of intergranular ZrO2 particles occurred as a results of the elimination of ZrO2 intraagglomerate grain boundaries and the coalescence of dragged ZrO2 particles by migrating Al2O3 grain boundries. Changes in mechanical properties of Al2O3 composites were dependant on microstructure of Al2O3 matrix and on size and structure of dispersed ZrO2.

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Control of Microstructures and Properties of Composites of the Al2O3/ZrO2-ZrO2-Spinel System: I. Preparation and Sintering Behavior of Al2O3-ZrO2 Composite Powders (Al2O3/ZrO2-Spinel계 복합체의 미세구조 및 물성제어: I. Al2O3-ZrO2 복합분체의 제조 및 소결특성)

  • 현상훈;송원선
    • Journal of the Korean Ceramic Society
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    • v.29 no.10
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    • pp.797-805
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    • 1992
  • Al2O3-20 wt% ZrO2 composite powders to be used as the starting materials of the Al2O3/ZrO2-Spinel composite system were prepared by the use of the emulsion-hot kerosene drying method. The crystalline phase of ZrO2 in the synthesized Al2O3-ZrO2 composite powders was 100% tetragonal but the small amount of t-ZrO2 was transformed into m-ZrO2 after crushing. The hardness, fracture toughness, and flexural strength of the composite, which was sintered at 1650$^{\circ}C$ for 4 hrs after calcining at 1100$^{\circ}C$ for 2 hrs and had the relative density of 99%, were 15.7 GPa, 4.97 MN/m3/2, and 390 MPa, respectively. The fracture form in the sintered composites was found to be the intergranular fracture.

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Microstructure and Mechanical Properties of $Al_2O_3$-$ZrO_2$-Nb Composites Prepared by Reaction Sintering (반응소결로 얻어진 $Al_2O_3$-$ZrO_2$-Nb 복합체의 미세구조와 기계적 성질)

  • ;;;R.J. Brook
    • Journal of the Korean Ceramic Society
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    • v.28 no.5
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    • pp.422-428
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    • 1991
  • The reaction sintering of Al2O3-ZrO2-Nb composite has been investigated using Al2O3, and ZrAl2 powders. Two kinds of specimens, 78.3Al2O3-14.0Nb2O5-7.7ZrAl2 in wt.% (AZN-5) and 72.3Al2O3-13.8Nb2O5-7.5ZrAl2-6.4ZrO2(AZN-10), were prepared. Powder compacts were sintered at various temperatures between 1$600^{\circ}C$ and 1$700^{\circ}C$ for 30 min in Ar. DTA and X-ray analysis have showen that a reaction between Nb2O5 and ZrAl2 started at 149$0^{\circ}C$ to form Al2O3, ZrO2, and Nb. The sintered density increased with the sintering temperature. AZN-10 specimen showed higher density than AZN-5 specimen for almost all the experimental conditions. Al2O3-ZrO2-Nb composite hot pressed after reaction sintering showed higher toughness and lower hardness than hot pressed Al2O3-ZrO2. The crack propagated through many metallic Nb particles which showed plastic deformation, and this is the cause of the increase in toughness of Al2O3-ZrO2-Nb composite over Al2O3-ZrO2.

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Effect of ZrO2 Addition on the Microstructure and Electrical Properties of Ni-Mn Oxide NTC Thermistors (Ni-Mn 산화물 NTC 서미스터의 미세구조와 전기적 특성에 미치는 ZrO2첨가의 효과)

  • 박경순;방대영;윤성진;최병현
    • Journal of the Korean Ceramic Society
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    • v.40 no.1
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    • pp.11-17
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    • 2003
  • The effect of$ZrO_2$addition on the microstructure and electrical properties of Ni-Mn oxide NTC thermistors was studied. Major phases present in the sintered bodies of $Ni_{1.0}Mn_{2-x}Zr_xO_4$ were the solid solutions of Ni-Mn-Zr oxides with a cubic spinel structure and the $ZrO_2$ with a tetragonal structure. The $ZrO_2$ was formed by the partial decomposition or incomplete formation of the Ni-Mn-Zr oxides during sintering. With increasing the amount of added $ZrO_2$, the $ZrO_2$ phase increased. The relationship between log resistivity (log p) and the reciprocal of absolute temperature (1/T) of the NTC thermistors prepared was linear, indicative of NTC characteristics. The resistivity, B constant and activation energy of the thermistors increased with increasing $ZrO_2$ content.

Preparation of $ZrO_2/Al_2O_3-Mullite$ Composites Using the Silica Sol Infiltration Method (실리카 졸 침투법을 이용한 $ZrO_2/Al_2O_3-Mullite$ 복합체의 제조)

  • 현상훈;최지영
    • Journal of the Korean Ceramic Society
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    • v.29 no.9
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    • pp.719-728
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    • 1992
  • ZrO2/Al2O3-Mullite composites were prepared by infiltration of the silica sol to the porous ZrO2/Al2O3 bodies. The porous ZrO2/Al2O3 bodies for infiltration were fabricated using ZrO2 (20wt%)/Al2O3 composite powders synthesized by the emulsion-hot kerosene drying method. The preparation of silica sols was conducted by the hydrolysis-peptization of an alcoholic TEOS solution. When ZrO2/Al2O3-Mullite and ZrO2/Al2O3 composites were sintered at 1$650^{\circ}C$ for 4 hrs, both of them showed an excellent sinterability. As the amount of mullite added in the composites increased, the ratio of the tetragonal phase of zirconia to the monoclinic phase at the room temperature became higher. It was known that values of the fracture toughness of the ZrO2/Al2O3-Mullite composites were about 5.48 MPa.m1/2 much larger than that of the ZrO2/Al2O3 system.

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A Study of Crystallization and Fracture Toughness of Glass Ceramics in the $ZrO_2.SiO_2$ Systems Prepared by the Sol-Gel Method (졸-겔법으로 제조한 $ZrO_2.SiO_2$계 결정화유리의 결정화 및 파괴인성에 관한 연구)

  • 신대용;한상목;강위수
    • Journal of the Korean Ceramic Society
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    • v.37 no.1
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    • pp.50-56
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    • 2000
  • Precursor gels with the composition of xZrO2·(100-x)SiO2 systems (x=10, 20 and 30 mol%) were prepared by the sol-gel method. Kinetic parameters, such as activation energy, Avrami's exponent, n, and dimensionality crystal growth value, m, have been simultaneously calculated from the DTA data using Kissinger and Matusita equations. The crystallite size dependence of tetragonal to monoclinic transformation of ZrO2 was investigated using XRD, in relation to the fracture toughness. The crystallization of tetragonal ZrO2 occurred through 3-dimensional diffusiion controlled growth(n=m=2) and the activation energy for crystallization was calculated using Kissinger and Matusita equations, as about 310∼325±10kJ/mol. The growth of t-ZrO2, in proportion to the cube of radius, increased with increasing heating temperature and hteat-treatment time. It was suggested that the diffusion of Zr4+ ions by Ostwald ripening was rate-limiting process for thegrowth of t-ZrO2 crystallite size. The fracture toughness of xZrO2·(100-x)SiO2 systems glass ceramics increased with increasing crystallite size of t-ZrO2. The fracture toughness of 30ZrO2·70SiO2 system glass ceramics heated at 1,100℃ for 5h was 4.84 MPam1/2 at a critical crystaliite size of 40 nm.

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Properties of the System $ZrO_2$+3m/o $Y_2O_3$ Powder Prepared by Co-precipitation Method(I) : Stability of Tetragonal ZrO2 Powder (공침법으로 제조한 $ZrO_2$+3m/o $Y_2O_3$계 분체의 특성(I) : 정방정 Zirconia분체의 안정성)

  • 홍기곤;이홍림
    • Journal of the Korean Ceramic Society
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    • v.27 no.3
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    • pp.361-368
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    • 1990
  • The properties of the powder of ZrO2+3m/o Y2O3 system prepared by co-precipitation method at the pH values of 7, 9, 10 and 11 were investigated. ZrOCl2.8H2O and YCl3.6H2O were used as starting materials and NH4OH as a precipitation agent. Zirconium hydroxide near by Zr(OH)4 structure showed more excellent crystallinity and lower formation temperature of tetragonal ZrO2. In the range of this study, cubic ZrO2 was not formed and stability of tetragonal ZrO2 prepared in the conditiion of pH 7 was most excellent. Average particle sizes and specific surface areas of tetragonal ZrO2 powders, prepared as calcining amorphous zirconium hydroxides at $600^{\circ}C$ for 1h, were 0.6-0.8${\mu}{\textrm}{m}$ and 45-70$m^2$/g, respectively.

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