The effect of ZnO particle size on the dynamic mechanical, thermal, and dielectric properties of ZnO varistor-Epoxy composites

In this study, ZnO varistors with different particle sizes were added into the epoxy resin to fabricate ZnO varistor-Epoxy composites. The effect of ZnO filler size on the dynamic mechanical, thermal, and dielectric properties of ZnO varistor-Epoxy composites was investigated. As the temperature ranges from − 60 to 110 °C, 20 vol% ZnO varistor-Epoxy composites with different ZnO particle sizes represent the glassy state, the glass transition state and rubbery state. When ZnO particle size increases from 70 to 255 μm, the storage modulus of ZnO varistor-Epoxy composites is significantly improved from 1681 MPa to 2755 MPa at room temperature, and the maximum value of damping factor fluctuates between 0.55 and 0.60. As the frequency increases from 0.1 to 20 Hz, both the storage modulus and the maximum value of damping factor are raised. In addition, the coefficient of thermal expansion decreases from 5.06 × 10 − 5 K − 1 to 4.45 × 10 − 5 K − 1 , whereas the filler size has little influence on the glass transition temperature of composites. Besides, both the dielectric constant and dielectric loss in the frequency range from 10 3 to 10 6 Hz vary in a small range with the increase of the ZnO filler size. With the increase of frequency, both the dielectric constant and dielectric loss gradually decrease. However, as the temperature increases, the dielectric constant and dielectric loss show an opposite trend.