Metal oxide varistors, precursor powder compositions and methods

Details Metal oxide varistors, precursor powder compositions and methods Metal oxide varistors, precursor powder compositions and methods

1988-05-13

1991-08-13

Barr, Josephine

Compositions

Electrically conductive or emissive compositions

Metal compound containing

252519, 252520, 252521, 423596, H01B 106

Patent

active

050394525

ABSTRACT:
This invention provides a process for making metal oxide varistor precursor powder comprising (a) dissolving soluble precursors of the additive metal oxides, e.g. bismuth nitrate as precursor for bismuth oxide, in an aqueous solution, (b) forming a suspension or slurry in the aqueous solution of a powder of the desired primary metal oxide, e.g. zinc oxide, having the desired particle size, (c) adding a precipitating reagent to convert the additive metal from the soluble precursor form to the oxide or hydrous oxide form and precipitate the oxide or hydrous oxide in the presence of the primary metal oxide particles, (d) removing water and by-product salts to form a powder. The resulting varistor precursor powder contains smaller particles of the additive metal oxides evenly distributed throughout larger particles of the primary metal oxide. Varistors prepared from the resulting powder can be sintered at temperatures lower than conventionlly used, for example 900.degree. C.-1000.degree. C. and the resulting varistors exhibit properties of volts per grain boundary value higher than conventional varistors for example 3.75 to 4.5 and dielectric constants lower than conventional varistors, e.g., under 1000.

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