The correlation between surge energy capability and Bi₂O₃ volatilization in ZnO varistors

Abstract

This study investigated the correlation between the surge energy capability and Bi 2 O 3 volatilization in ZnO varistors by analyzing the volatilization phenomenon of Bi 2 O 3. A ZnO varistor is composed mainly of Sb 2 O 3 , Bi 2 O 3. Bi 2 O 3 has the lowest vapor pressure among these components. Bi 2 O 3 play an important role, moreover, in forming it grain boundaries. These grain boundaries have low conductivity in the leakage current region, but, becomes higher in the region. It also determines the surge energy capability of the varistors. Bismuth oxide has four phases, each with intrinsic ion-conductivity. Formation of the bismuth oxide phase depends on the amount of bismuth at the grain boundary. Volatilization of Bi 2 O 3 should therefore be prevented when developing ZnO varistors was conducted using with high energy capabilities. Analysis of the volatilization phenomenon of Bi 2 O 3 X-ray analysis methods such as X-ray fluorescence, X-ray photoelectron spectroscopy and X-ray diffraction. The results confirmed a close correlation among them. Sealed sintering methods were proposed to prevent the volatilization of Bi 2 O 3 by ZnO varistors.

Effects of Dopants and Processing Parameters on the Properties of ZnO-V2O5-Based Varistors Prepared by Powder Metallurgy: A Review

“…Bi 2 O 3 has high volatility and considerable reactivity during LPS above 1000 °C, affecting the microstructure and performance of the ZnO-Bi 2 O 3 systems [ 121 , 122 ]. When the volatilization of Bi 2 O 3 is not prevented (e.g., by sealed sintering with Al 2 O 3 -covered crucibles), unsuitable GB layers can result [ 121 ]. The liquid phase can enhance GB mobility, but the formed intragrain pores can decrease the sintered density of MOVs [ 118 ].…”

“…The δ- and β-Bi 2 O 3 phases are good ionic conductors, promoting the oxygen migration from the GBs, but the γ- and α-Bi 2 O 3 phases are low ionic conductors. The α-Bi 2 O 3 phase yields p-type electronic conductivity at room temperature (RT), while the δ-Bi 2 O 3 phase has ionic conductivity with oxide ions as the majority charged carriers [ 121 ]. The polymorphs of Bi 2 O 3 influence the existence and content of oxygen at the interface across ZnO grains, affecting the behavior of MOVs in service [ 132 ].…”

Nadir Toprak Elementi İlaveli ZnO-Esaslı Varistörlerin Elektriksel Özelliklerinin Karşılaştırılması

“…Bu şekilde çeşitli dalgalanmaların üstesinden gelmenin en ekonomik yolu varistör kullanmaktır. ZnO varistörleri, az miktarda çeşitli metal oksitleri içeren ZnO tozunun sinterlenmesiyle üretilen doğrusal olmayan voltaj (V)-akım (I) özelliklerine sahip seramik cihazlardır [2][3][4].…”