Patent ID: 6620346
Filing Date: 2003-09-16
Classification: H01C

Abstract:
A method for the manufacture of a varistor having a very high breakdown voltage, comprising:(a) mixing powders of zinc oxide (ZnO) and bismuth oxide (Bi2O3) with at least one other powder of an additive capable of influencing the properties of the varistance, said mixing being carried out with such amounts of powders that the zinc oxide represents at least 75 mol % of the resulting mixture; (b) subjecting said powders to an intensive milling before, during, or after their mixing, by means of a high energy ball mill in such a manner that the obtained powders be nanocrystalline; and (c) subjecting the so milled mixture to a consolidation treatment wherein said consolidation treatment includes a sintering and is carried out under time and temperature conditions selected to keep a zinc oxide grain size lower than 3 &mgr;m.