Modified Citrate Gel Techniques to Produce ZnO-Based Varistors (Part I—Microstructural Characterisation)

Two novel chemical processing routes were developed for the production of ZnO-based varistor powders and compared with the conventional mixed-oxide route. The central idea behind the new techniques was to separate the minority components in relation to their function and incorporate them into the varistor powders accordingly. The densification of green bodies prepared by the chemical routes proceeded in one or two stages (at 770 °C and 910 °C) compared to many stages for the conventional route. The sintered pellets thus produced from the chemical routes showed smaller grain sizes, higher densities and more evenly distributed intergranular phases than those from the conventional mixed-oxide route.