ZnO varistors made from powders produced utilizing a urea process

• Main Authors: Sonder, E., Quinby, T.C., Kinser, D.L.
• Language: unknown
• Published: 2017
• Subjects: 42 ENGINEERING; SEMICONDUCTOR RESISTORS; PRODUCTION; ZINC OXIDES; CHEMICAL PREPARATION; DENSITY; GRAIN SIZE; HOT PRESSING; MELAMINE; POWDERS; SINTERED MATERIALS; UREA; AMIDES; AMINES; AZINES; CARBONIC ACID DERIVATIVES; CHALCOGENIDES; CRYSTAL STRUCTURE; ELECTRICAL EQUIPMENT; EQUIPMENT; FABRICATION; HETEROCYCLIC COMPOUNDS; MATERIALS; MATERIALS WORKING; MICROSTRUCTURE; ORGANIC COMPOUNDS; ORGANIC NITROGEN COMPOUNDS; OXIDES; OXYGEN COMPOUNDS; PHYSICAL PROPERTIES; PRESSING; RESISTORS; SEMICONDUCTOR DEVICES; SIZE; SYNTHESIS; TRIAZINES; ZINC COMPOUNDS; Carbonic acid
• Online Access: http://www.osti.gov/servlets/purl/5331308; https://www.osti.gov/biblio/5331308; https://doi.org/10.2172/5331308

Small-grained oxide powders of uniform composition, ideally suited for varistor production, have been prepared as follows: ZnO and other components are dissolved in nitric acid. Urea is added and the mixture is heated to remove water and nitrates and to form solid melamine. The melamine is then calcined to burn off the organics and to produce fine oxide powders. Grain sizes, densities, and electrical characteristics have been measured for varistors fabricated from these powders by sintering or hot pressing. The densities and grain sizes increase with processing temperature, the nonlinearity coefficient depends primarily on composition, and the average voltage per barrier for sintered samples is approximately 2.5 eV. The breakdown field for hot-pressed samples is not uniform for different slices of the same varistor and depends on variables other than the grain size.