Microstructural evolution during sintering of Bi2O3-doped ZnO

adZnO based varistors are widely used for overvoltage protection in many electrical and electronic circuits, at voltages ranging from a few to over a million volts. By careful control of the microstructure, through nanostructuring by chemical routes, it should be possible to produce varistors with high breakdown voltage (V c ), as this is proportional to the number of active grain boundaries in the sintered body. This property is particularly important for the production of the small-sized varistors needed for modern electronic instruments such as tablet computers and mobile phones. The current review will outline the recent advances in the chemical processing (e.g. sol-gel, combustion synthesis plasma pyrolysis, micro-emulsion synthesis and precipitation routes) of varistors from ZnO nanomaterials and the properties of these materials. Uncontrolled grain growth at higher temperature is highlighted as a major challenge for obtaining desirable electrical properties for nano-varistors. Various novel sintering techniques such as step-sintering, spark plasma and microwave sintering methods are expected to deliver a varistor with controlled grain growth and optimum electrical characteristics.

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Advances in the synthesis of ZnO nanomaterials for varistor devices

Pillai

et al. 2013

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Microstructural Features of the ZnO-Bi<sub>2</sub>O<sub>3</sub> Binary System

Yongvanich

Visuttipitukul

Kijsiri

et al. 2013

KEM

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Grain growth in ZnO with Bi2O3 addition of up to 1 mol% was examined in great detail for sintering in air. The results are analyzed and compared with previous reports in the context of the simplified phenomenological grain growth kinetics equation along with the physical properties of the sintered ceramics. In spite of the eutectic temperature at 735 °C, high density (> 90%) was not achieved at all Bi2O3 contents; this finding was contradictory to the well-known liquid-phase sintering. At 800 °C, rapid improvement in sintering occurred when increasing the content of Bi2O3 from 0.125mol% to 0.25mol%. Schematic study on weight loss also demonstrated an insignificant level of Bi2O3 volatilization under certain content. Analysis of the grain growth kinetics from isothermal sintering (900 °C - 1,000 °C) revealed strikingly different results in both grain growth exponent (n) and activation energy previously reported in literature. The n values ranged from 3.2 to 5.6 whereas the activation energy from 335 to 598 kJ/mol. Such large disparities were believed to be associated with various mass transport processes. The grain sizes in this study were much smaller than those published in literature (> 10 μm). This size difference, along with other microstructural features, was discussed and correlated in order to explain such anomalies and new findings obtained from the grain growth kinetics results.

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Microstructural evolution during sintering of Bi2O3-doped ZnO

Cited by 2 publications

References 9 publications

Advances in the synthesis of ZnO nanomaterials for varistor devices

Advances in the synthesis of ZnO nanomaterials for varistor devices

Microstructural Features of the ZnO-Bi<sub>2</sub>O<sub>3</sub> Binary System

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