Sintering of surfactant modified ZnO-Bi₂O₃ based varistor nanopowders

Surfactant modified nano-origin ZnO-Bi₂O₃ varistor powder was prepared in presence of cetyltrimethyl ammonium bromide (CTAB) surfactant through an aqueous reflux reaction at 100 °C. The compacted varistor discs made from the nano-origin powders were subjected to step-sintering, microwave sintering and solid-state sintering. The influences of CTAB in different sintering methods were analyzed from the densification characteristics, evolution of sintered microstructures and associated varistor properties (I-V). The conventional solid-state sintering produced 96% theoretical sintered dense samples at 1100 °C. The step and microwave sintered samples showed 93% and 99% sintered densities, respectively, with controlled microstructures having grain sizes in the range of 2-6 μm at the given conditions. The CTAB advantages were clearly seen in grain structuring and grain boundary properties, in addition to the enhanced densification and homogenous microstructures for obtaining high breakdown voltage and non-linearity coefficient.