Modified citrate gel techniques to produce ZnO-based varistors (Part I - Microstructural characterisation)

Two novel chemical processing routes were developed for the production of Z nO-based varistor powders and compared with the conventional mixed-oxide ro ute. The central idea behind the new techniques was to separate the minorit y components in relation to their function and incorporate them into the va ristor powders accordingly. The densification of green bodies prepared by t he chemical routes proceeded in one or two stages (at 770 degreesC and 910 degreesC) 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 thos e from the conventional mixed-oxide route.