Comparison of water-based and solvent-based tape casting for preparing multilayer ZnO varistors

Water-soluble acrylic was used as the binder of the water-based (aqueous) slurry while polyvinyl butyral was the binder of the solvent-based (nonaqueous) slurry. Both types of slurry exhibited shear thinning properties suitable for tape casting. The casting parameters for them were different when the same thick green sheets were cast. Thermogravimetric analysis was used to find the binder burnout temperatures of the aqueous and nonaqueous green tape. Scanning electron microscopy (SEM) studies revealed that both types of green tapes have smooth defect-free surfaces but the aqueous green tape is denser than the nonaqueous one. The multilayer ZnO varistors prepared by aqueous tape casting display comparable good electrical properties to those prepared by nonaqueous tape casting because both types of ceramic have a uniform, fine grain microstructure with a homogeneous dopant distribution indicated using SEM and transmission electron microscopy. © 2008 The American Ceramic Society.