Microstructure and Phase Transition of ZnO Varistor Ceramics

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J. Korean Ceram. Soc. > Volume 28(2); 1991 > Article

Journal of the Korean Ceramic Society 1991;28(2): 160.

ZnO 바리스터 세라믹스의 미세구조와 상전이

김경남, 한상목

강원대학교 재료공학과

Microstructure and Phase Transition of ZnO Varistor Ceramics

ABSTRACT

Microstructure and phase changes during the sintering of ZnO varistors were studied in ZnO-Bi2O3-CoO-Sb2O3 and ZnO-Bi2O3-CoO-Sb2O3-Cr2O3 systems using acanning electron microscopy (SEM) with an energy dispersive X-ray analysis (EDAX), X-ray diffraction (XRD) and differential thermal analysis (DTA). The spinel phase and the Bi2O3 phase were formed by the decomposition of the pyrochlore phase during heating. The spinel particles (2-4$mutextrm{m}$), which were formed both along ther grain boundaries and within the ZnO grain, were always found near the pyrochlore phase. Intergranular phases (Bi2O3 and pyrochlore) were precipitated from the liquid phase during cooling. The Bi2O3 phases were located at the triple (or multiple) point of the ZnO grains. Cr2O3 played a role in decreasing the formation temperature of the spinel phase and Bi2O3 phase during sintering, and inhibited the grain growth.