Grain size and sintering temperatures effects on the mechanical properties of ZnO nanoparticle-based varistor ceramics

Abstract

The grain size impact on the behavior of ZnO–Bi2O3–Mn2O3 varistors was determined in this study. Samples with different sintering temperatures and times were prepared via traditional ceramic methodology, and their properties were described. Results exhibited that various temperatures and times of the sintering process had considerable effects on the varistors. In particular, the growth of ZnO grains was improved at a minimal-temperature sintering process of 900 °C for 1 h. Significant solid-state reaction even at lower sintering temperatures perhaps caused the surface characteristics of ZnO nanoparticles. Vickers indentation analyses were applied to define the fracture toughness and hardness of the samples. Hardness diminished with the growth of ZnO grain. Fracture toughness did not exhibit any change with the increase in grain size (~ 5.1 MPam0.5) up to 1.6 μm for WZ-V and 3.5 μm 20Z-V. Above these grain sizes, a spontaneous conversion from hexagonal to monoclinic phase occurred. WZ-V and 20Z-V samples were used to investigate the analogous bending strength at 1152 and 1148 MPa, respectively. The structural coarsening desired for realizing significant grain size led to increased scattering strength values, as evidenced by lesser Weibull modulus (9.23 vs. 5.10). Variations in the mechanical behavior of the investigated varistors with different grain sizes were demonstrated, and their probable reasons were discussed in brief.