Somar Corporation

Zenbee Nakagawa

Akihide Igari

Hideo Ochi

Masaaki Toyoda

A varistor material having a non-linear coefficient of at least 30 and a varistor voltage of at least 800 V/mm is disclosed. The varistor is produced by a method including commingling an admixture of ZnO and a manganese compound while preventing the admixture from contacting with a surface containing an element belonging to group IIIb of the Periodic Table. The resulting mixture is calcined and then pulverized while preventing the contact with a IIIb element-containing surface to obtain a pulverized product having a content of impurity compounds of a IIIb element of not greater than 20 ppm by weight. The pulverized product is molded and sintered at such a temperature as to obtain the varistor formed from particles with an average particle size of not greater than 5 .mu.m.

Sintered varistor material with small particle size

A varistor having a non-linear coefficient of at least 40 and improved stability for DC stress is produced by a method including a step of mixing ZnO powder with a solvent solution of Mn and Pb compounds, a step of calcining the resultig mixture, and a step of pulverizing the calcined product to obtain a pulverized product. These steps are performed while preventing the contamination with a Group IIIb or Ia element, so that the pulverized product has MnO and PbO contents of 3-7 mole % and 0.003-0.01 mole %, respectively, and a content of impurity compounds of a IIIb or Ia element of not greater than 20 ppm by weight. The pulverized product is molded and sintered to obtain the varistor.

Method of producing varistor

A process for the production of a varistor material having a nonlinear index (.alpha.) of at least 20, which comprises adding a manganese compound to zinc oxide; heating the obtained mixture in the form of a powder in the atomosphere at 1050.degree. to 1150.degree. C.; grinding the material to give a particle size of 150 mesh or below; molding the powder into a desired shape; and sintering the same at 1200.degree. to 1350.degree. C.; is disclosed.

Process for production of varistor material

A varistor material comprising two crystalline phases of ZnO and ZnMn.sub.2 O.sub.4, wherein Zn and Mn are present at such a ratio that 3 to 7% by mol of ZnO is contained per 100% by mol of ZnO+MnO and the nonlinear index (.alpha.) of the varistor properties is at least 10; and a process for the production of the same, which comprises adding a manganese compound to ZnO at such a ratio as to give a content of MnO, sintering the mixture at 1100.degree. to 1350.degree. C., and further annealing the obtained sintered material at a temperature lower than the sintering temperature by at least 50.degree. C. and higher than 1000.degree. C. are disclosed.

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Kanagawa, Japan

Zenbee Nakagawa