• Title/Summary/Keyword: ZnO Grain

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The Effect of Additives on Twining in ZnO Varistors

  • Han, Se-Won;Kang, Hyung-Boo
    • The Korean Journal of Ceramics
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    • v.4 no.3
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    • pp.207-212
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    • 1998
  • By comparison of the experimental results in two systems of ZnO varistors, it's appear that Sb2O3 is the indispensable element for twining in ZnO varistors and the Zn7Sb2O12 spinel acts as the nucleus to form twins. Al2O3 is not the origin of twining in ZnO varistor, but it was found that Al2O3 could strengthen the twining and form a deformation twining by ZnAl2O4 dragging and pinning effect. The inhibition ratios of grain and nonuniformity of two systems ZnO varistors increase with the increase of Al2O3 content. The twins affect the inhibition of grain growth, the mechanism could be explained follow as: twins increase the mobility viscosity of ZrO grain and grain boundary, and drag ZrO grain and liquid grain boundary during the sintering, then the grain growth is inhibited and the microstructure becomes more uniform.

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Microstructure Properties of Zinc Oxide Varistor with $Sb_2O_3$ Contents for Low Voltage Application ($Sb_2O_3$함량 변화에 따른 저전압용 ZnO Varistor의 미세구조 특성)

  • 박종주;서정선
    • Korean Journal of Crystallography
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    • v.8 no.2
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    • pp.149-153
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    • 1997
  • ZnO varistor based on ZnO-Bi2O3-Co3O4-MnCO3-Cr2-O3-Sb2O3 system with Sb2O3 contents were studied for grain size variation and microstructure properties. The composition of pure ZnO varistor was observed composition was inhibited owing to formation of Zn7Sb2O12 spinel phase and did not observed abnrmal grain growth. With Sb2O3 contents, the grain sizes of ZnO varistor were remarkably decreased and the microstructure had the distribution of dense and homogeneous grains.

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The Structure and Electrical Characteristics of ZnO Varistors Surface using-Fractal (프랙탈을 이용한 ZnO 바리스터 표면 구조 및 전기적 특성)

  • Oh, Soo-Hong;Hong, Kyung-Jin;Lee, Jin;Lee, Joon-Ung;Kim, Tae-Sung
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.13 no.10
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    • pp.834-839
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    • 2000
  • The structural properties that SEM photograph of ZnO varistors surface studied by fractal mathematics program were investigated to verify the relations of electrical characteristics. The SEM photograph of ZnO varistors surface were changed by binary code and the grain shape of that were analyzed by fractal dimension. The void of ZnO varistors surface was found by fractal program. The relation between grain density and electrical properties depend on fractal dimension. The grain size in ZnO varistors surface was decreased by increasing of Sb$_2$O$_3$ addition. The spinel structure was formed by Sb$_2$O$_3$addition and it was depressed the ZnO grain formation. The grain size of ZnO by Sb$_2$O$_3$addition were from 5 to 10[${\mu}{\textrm}{m}$]. Among of ZnO varistors, fractal dimension of ZnO4 was very high as a 1.764. The density of grain boundary in ZnO2 and ZnO3 varistors surface was 15[%] by formed spinal structure. The breakdown electric field of ZnO2 that fractal dimension has 1.752 was very high to be 8.5[kV/cm]. When the fractal dimensin was high, the grain shape of ZnO varistors was complex and the serial layers of ZnO grain was increased.

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The Effect of Additives on Twins in ZnO Varistors (ZnO 바리스터에서 첨가물이 쌍정에 미치는 영향)

  • 한세원;조한구;강형부
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • 2001.07a
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    • pp.1057-1060
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    • 2001
  • By comparison of the experimental results in two systems of ZnO varistors, its appear that Sb$_2$O$_3$is the indispensable element for twinning in ZnO varistors, and the Zn$_{7}$Sb$_2$O$_{12}$ spinel acts as the nucleus to form twins. A1$_2$O$_3$is not the origin of twinning in ZnO varistor, but it was found that A1$_2$O$_3$could strengthen the twinning and form a deformation twinning by ZnA$_{12}$O$_4$-dragging and pinning effect. The inhibition ratios of grain growth and nonuniformity of two systems ZnO varistors increase with the increase of A1$_2$O$_3$content. The twins affect the inhibition of grain growth, the mechanism could be explained follow as : twins increase the mobility viscosity of ZnO grain and grain boundary, and drag ZnO grain and liquid grain boundary during the sintering, then the grain growth is inhibited, and the microstructure becomes more uniform.orm.m.

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Effects of Grain-Size Distribution on the Breakdown Voltage in ZnO Varistors (입도분포가 ZnO 바리스터의 임계전압에 미치는 영향)

  • 김경남;한상목;김대수
    • Journal of the Korean Ceramic Society
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    • v.30 no.3
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    • pp.199-205
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    • 1993
  • Effects of grain size distribution on the breakdown voltage of ZnO varistors were investigated in the ZnO-Bi2O3-CoO-Sb2O3 and ZnO-Bi2O3-CoO-Sb2O3-Cr2O3 systems, respectively. The grain size was increased with increasing sintering temperature maintaining lognormal distribution in both systems. The width of grain size distribution of ZnO-Bi2O3-CoO-Sb2O3 system was narrower than that of ZnO-Bi2O3-CoO-Sb2O3 system. The breakdown voltage(Vb) was decreased by increasing sintering temperature(1000~135$0^{\circ}C$) and sintering time(0.5~5hr), due to the enhancement of ZnO grain growth. The current path of the ZnO varistor was dependent on the distribution of the largest grains (chains of long grains) between the electrodes.

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A Study on the Initial Stage of Sintering and the Grain Growth of ZnO in ZnO-Bi2O3 System (ZnO-Bi2O3계의 소결초기단계와 입자성장에 관한 연구)

  • 성건용;강을손;김종희
    • Journal of the Korean Ceramic Society
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    • v.26 no.4
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    • pp.505-513
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    • 1989
  • The sintering behavior and grain growth of ZnO in 99.0mol% ZnO-1.0mol% Bi2O3 which are the basic compositions of ZnO varistor were studied. The microstructrual observation confirmed that the final sintered density was mainly determined at the initial stage of sintering, i.e. grain rearrangement and grain growth which were induced by the penetration of eutectic melts formed at eutectic temperature(74$0^{\circ}C$). But when the liquid penetration was terminated, the grain growth did not promote further densification. Activation energy of the grain growth of ZnO in the system of 99.0mol% ZnO-1.0mol% Bi2O3 was 44.8$\pm$1.8Kcal/mol.

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Effects of ${ZnAl_2}{O_4}$ on the Microstructure and Electrical Properties of ZnO Varistor (ZnO 바리스터의 미세구조와 전기적특성에 미치는 ${ZnAl_2}{O_4}$의 영향)

  • 손세구;김경남;한상목
    • Journal of the Korean Ceramic Society
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    • v.37 no.4
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    • pp.314-319
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    • 2000
  • Microstructueral development and electrical properties in ZnO-Bi2O3-ZnAl2O4 system were investigated with ZnAl2O4 content(0.1~1.0 mol%). The shrinakge of specimens started around $700^{\circ}C$ and finished at 110$0^{\circ}C$, reaching a maximum shrinkage rate at 80$0^{\circ}C$. The shrinkage rate is strongly related to the fromation of a Bi-rich liquid. The increase of the ZnAl2O4 content inhibited the grain growth of ZnO. Most of ZnAl2O4 particles located at the grain boundaries were about 2~3${\mu}{\textrm}{m}$. ZnO grain size changed little up to 110$0^{\circ}C$, but increased markedly above 115$0^{\circ}C$, especially at lower ZnAl2O4 content. Drastic decreasing in breakdown voltage(Vb) with increasing temperature is expected to be dependent on the ZnO grain size and the distribution of the largest grains between the electrode. The nonlinear I-V characteristic was significantly influenced by the ZnAl2O4 content, which exhibited a maximum value at about 15${\mu}{\textrm}{m}$ of ZnO grain size.

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Somteromg Behavior and Electrical Characteristics of ZnO Variators Prepared by Pechini Process (Pechini 방법으로 제조된 ZnO 바리스터의 소결 거동 및 전기적 특성)

  • 윤상원;심영재;조성걸
    • Journal of the Korean Ceramic Society
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    • v.35 no.5
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    • pp.499-504
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    • 1998
  • ZnO varistors having a composition of 98.0 mol% ZnO 1.0 mol% $Bi_2O_3$ 0.5 mol% $MnO_2$ were prepared by the Pechini process and the sintering behavior and electrical characteristics were studied. ZnO varis-색 powder with $1.5\mu\textrm{m}$ mean diameter and narow particle size distribution was obtained using the Pechni pro-cess. Typical intermediate stage grain growth of liquid phase sintering was observed by sintering at $1100^{\circ}C$ At this temperature ZnO varistors having uniform grain size and Bi-rich liquid phase distributed uniformly along grain boundaries were prepared. The nonlinear coefficients of the ZnO varistors were in the range of 40-60 The breakdown voltages of the varistors were nearly inversely propeortional to the grain size which reflects that ZnO varistors prepared by the Pechini process have uniform distribution of Bi-rich liquid phase along grain boundaries It is believed that the microstructures of ZnO varistors can be controlled effectively by using the Pechini process which makes the control of the electrical properties of ZnO varistors possible.

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Fabrication of Low Voltage ZnO Varistor by Seed Grain Method (종자 입정을 이용한 저전압용 ZnO 바리스터의 제조)

  • 강을손;성건용;김종희
    • Journal of the Korean Ceramic Society
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    • v.27 no.4
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    • pp.473-480
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    • 1990
  • Low-voltage ZnO-based varistors were made by seed grain method at various sintering conditions. Their microstructure and electrical properties were investigated and comlpared with those of the ZnO varistors made by a conventional method at the same sintering condition. During the sintering process, the added seed ZnO grain rapidly grew to be a gaint grain(above 500$\mu\textrm{m}$) provinding easy current path. Therefore the breakdown voltage was lowered as much as the order of 1/10-1/5 in comparison to that of the varistor made by a conventional method. But the grain size of the giant ZnO was little influenced by sintering condition, so the breakdown voltate was also little influenced. The weight loss was decreased by the addition of the seed grain, because the giant grain decreased the evaporation area. Therefore the nonobmic property of the specimen made by seed grain method was little influencedby sintering condition. In this research the low-voltage varistor made by seed grain method showed the least leakage current when sintered at 1150$^{\circ}C$ for zero hour.

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Influence of NiO additive on electrical properties of ZnO-based ceramic varistors (ZnO세라믹 바리스터에 NiO첨가가 전기적 특성에 미치는 영향)

  • 남춘우
    • Electrical & Electronic Materials
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    • v.9 no.6
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    • pp.542-550
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    • 1996
  • ZnO-based ceramic varistors containing NiO range 0.5 mol% to 4.0 mol% were fabricated by standard ceramic techniques. The influence of NiO on the microstructure and electrical behavior of ZnO varistor was investigated. As the content of NiO additive increases, average grain size decreased from 16.5.mu.m to 13.2.mu.m, and the amount of NiO existing in the grain interior and grain boundary region was approximately equal. NiO acted as an acceptor which decreases donor concentration due to the increase of Zn vacancy in the grain, and as a driver which migrates Zn interstitial in the depletion region toward the interface of grain boundary, which resulted in the decrease of interface state density. As a result, increasing the content of NiO additive, barrier height, nonlinear exponent, and varistor voltage decreased, and leakage current increased. Wholly, the physical and electrical properties of the ZnO varistor can be said to be affected by the NiO additive.

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