محمد مالکی شهرکی

The aim of this work is to find a proper grinding medium that produce the best suspension of additives in order to fabricated ZnO varistors with excellent comprehensive electrical properties. For this, the effect of various kind of milling media (alumina, zirconia, and agate) in the milling times of 2, 6, and 12 h on particle size distribution, contamination amount, and zeta potential of additives suspensions was explored. Furthermore, the relation between these parameters with the microstructures and electrical properties of ZnO varistors was elaborated. Results showed that, for same milling times, the additives suspension obtained by zirconia medium produced the smallest size of particles with the most absolute value of zeta potential. The contamination amount was minimum in agate samples. In the instrument detection limit, the XRD results reveal that there is no variation in the phase compositions of the all ZnO varistors. The SEM images confirmed that the type of milling medium has a major effect on the morphology and the grain size of varistor samples. The excellent comprehensive electrical performance which are Eb: 325 V/mm, α: 68, JL: 2 µA/cm2, Kr: 1.5 along with an excellent discharge capability was acquired for those samples prepared by the zirconia medium after 6 h milling. Therefore, these results corroborate that the zirconia medium is the best choice for production of ZnO varistors with highly outstanding non-Ohmic characteristics.