Study on the high impulse current withstand properties and failure mechanism of ZnO varistors with different Bi2O3 content
In this work, the effect of Bi 2 O 3 content on the microstructure, mechanical, thermal, and electrical properties of ZnO varistors was investigated, and the high impulse current withstand properties and failure mechanism of ZnO varistors was discussed in detail. When content of Bi 2 O 3 equaled to 0.75 mol%, the varistors possessed excellent mechanical, thermal, and electrical properties, where the value of σ f and E f were 130.77 MPa and 69.60 GPa, K T and λ T were 6.504 W·(m·°C) −1 and 7.00 × 10 –6 °C −1 , E 1mA , α, J L , and K were 272.13 V·mm –1 , 55.96, 1.55 μA·cm –2 , and 1.74, respectively, being due to the highest density and finest uniform grain size distribution. Finite Element Analysis (FEA) showed that the thermal stress decreased first and then increased with the increase of Bi 2 O 3 content, where E f and λ T played a more important role than K T . And the loaded impulse current I p can generate Joule heat to improve the temperature of ZnO varistors, thereby increasing the thermal stress and promoting the migration of dopants ions from ZnO to the Bi 2 O 3 crystal lattice. Hence, J L increased and U 1mA reduced, which further increased the thermal effect generated by I p . When the value of I p equaled to 100 kA, high temperature produced a loose microstructure and broken grains originated from the strong thermal stress. Meanwhile, the enhanced migration increased J L (3.77 μA·cm −2 ) and decreased U 1mA (4.93 kV), resulting in a critical value of Δ U 1 mA (9.88%). A further increase in I p led to the failure of ZnO varistors.
危险品化学品经营许可证（带存储）