Zinc oxide based varistor and fabrication method

Patent metadata

Field	Value
Publication number	US-9601244-B2
Application number	US-201214443137-A
Country	US
Kind code	B2
Filing date	Dec 27, 2012
Priority date	Dec 27, 2012
Publication date	Mar 21, 2017
Grant date	Mar 21, 2017

Abstract

A varistor may include a varistor ceramic that includes zinc oxide having a molar percent greater than 90 percent and a set of metal oxides, where the set of metal oxides includes Bi 2 O 3 having a molar fraction between 0.2 and 2.5 percent; Co 3 O 4 having a molar fraction between 0.2 and 1.2 percent; Mn 3 O 4 having a molar fraction between 0.05 and 0.5 percent; Cr 2 O 3 having a molar fraction between 0.05 and 0.5 percent; NiO having a molar fraction between 0.5 and 1.5 percent; Sb 2 O 3 oxide having a molar fraction between 0.05 and 1.5 percent; B 2 O 3 having a molar fraction between 0.001 to 0.03 percent; and aluminum in the form of an oxide having a molar fraction between 0.001 and 0.05 percent.

First claim

What is claimed is:

1. A varistor ceramic comprising:
zinc oxide having a molar percent greater than 90 percent;
a set of metal oxides, the set of metal oxides comprising:
bismuth in oxide form comprising a molar fraction equivalent to between 0.2 and 2.5 percent Bi 2 O 3 ;
cobalt in oxide form comprising a molar fraction equivalent to between 0.2 and 2.0 percent Co 3 O 4 ;
manganese in oxide form comprising a molar fraction equivalent to between 0.05 and 1.5 percent Mn 3 O 4 ;
chromium in oxide form comprising a molar fraction equivalent to between 0.05 and 0.5 percent Cr 2 O 3 ;
nickel in oxide form comprising a molar fraction equivalent to between 0.5 and 1.5 percent NiO;
antimony in oxide form comprising a molar fraction equivalent to between 0.05 and 0.199 percent Sb 2 O 3 ;
boron in oxide form comprising a having a molar fraction equivalent to 0.001 to 0.05 percent B 2 O 3 ; and

aluminum in oxide form comprising a molar fraction equivalent to between 0.001 and 0.05 percent.

2. The varistor of claim 1 , comprising:
bismuth in oxide form comprising a molar fraction equivalent to between 0.8 and 1.0 percent Bi 2 O 3 ;
cobalt in oxide form comprising a molar fraction equivalent to between 0.4 and 0.6 percent Co 3 O 4 ;
manganese in oxide form comprising a molar fraction equivalent to between 0.05 and 0.2 percent Mn 3 O 4 ;
chromium in oxide form comprising a molar fraction equivalent to between 0.1 and 0.2 percent Cr 2 O 3 ;
nickel in oxide form comprising a molar fraction equivalent to between 0.6 and 0.8 percent NiO;
antimony in oxide form comprising a molar fraction equivalent to between 0.05 and 0.15 percent Sb 2 O 3 ; and
titanium in oxide form comprising a molar fraction equivalent to between 0.5 and 0.7 percent TiO 2 .

3. The varistor of claim 1 , comprising:
bismuth in oxide form comprising a molar fraction equivalent to between 2 and 2.2 percent Bi 2 O 3 ;
cobalt in oxide form comprising a molar fraction equivalent to between 0.3 and 0.5 percent Co 3 O 4 ;
manganese in oxide form comprising a molar fraction equivalent to between 0.1 and 0.3 percent Mn 3 O 4 ;
chromium in oxide form comprising a molar fraction equivalent to between 0.05 and 0.2 percent Cr 2 O 3 ;
nickel in oxide form comprising a molar fraction equivalent to between 0.7 and 0.9 percent NiO.

4. The varistor of claim 1 , comprising:
bismuth in oxide form comprising a molar fraction equivalent to between 0.4 and 0.6 percent Bi 2 O 3 ;
cobalt in oxide form comprising a molar fraction equivalent to between 0.3 and 0.4 percent Co 3 O 4 ;
manganese in oxide form comprising a molar fraction equivalent to between 0.2 and 0.4 percent Mn 3 O 4 ;
chromium in oxide form comprising a molar fraction equivalent to between 0.05 and 0.2 percent Cr 2 O 3 ; and
nickel in oxide form comprising a molar fraction equivalent to between 1.0 and 1.2 percent NiO.

5. The varistor of claim 1 , further comprising at least one alkaline earth metal having a molar percent of 0.001 to 0.03.

6. A method of fabricating a varistor ceramic comprising:
forming a varistor slurry comprising:
a solvent mixture;
a set of additives including an aluminum containing species operative to produce a molar fraction of aluminum in the varistor ceramic of 0.001 to 0.1 percent;
a set of metal oxides comprising:
bismuth in oxide form comprising a molar fraction equivalent to between 0.2 and 2.5 percent Bi 2 O 3 ;
cobalt in oxide form comprising a molar fraction equivalent to between 0.2 and 1.2 percent Co 3 O 4 ;
manganese in oxide form comprising a molar fraction equivalent to between 0.05 and 0.5 percent Mn 3 O 4 ;
chromium in oxide form comprising a molar fraction equivalent to between 0.05 and 0.5 percent Cr 2 O 3 ;
nickel in oxide form comprising a molar fraction equivalent to between 0.5 and 1.5 percent NiO;
antimony in oxide form comprising a molar fraction equivalent to between 0.05 and 0.199 percent Sb 2 O 3 ; and
zinc oxide operative to generate a molar fraction greater than 95 percent in the varistor ceramic; and
heat treating the varistor slurry to form a solid varistor granule.

7. The method of claim 6 , wherein the forming the varistor slurry further comprising:
preparing a binder solution containing a polymeric material;
dissolving the binder solution in a set of solvent components to form the solvent mixture before forming the varistor slurry; and
spray drying the varistor slurry wherein a powder is formed from the varistor slurry.

8. The method of claim 7 , further comprising:
forming varistor powder from the varistor slurry;
pressing the varistor powder to form a varistor perform; and
heat treating the varistor powder through at a temperature in the range of 400° C. to 700° C. for a duration effective to remove polymeric material.

9. The method of claim 6 , wherein the heat treating the varistor slurry comprising:
performing a debinder heat treatment on a compacted varistor powder formed from the varistor slurry at a debinder temperature in the range of 500° C. to 600° C.;
sintering the heat treated compacted varistor powder at a maximum sintering temperature between 1000° C. and 1300° C.; and
performing a silver firing at a temperature range of about 500° C. to 700° C.

10. The method of claim 9 , wherein the debinder heat treatment comprising a duration of about 15 to 40 hr.

11. The method of claim 9 , wherein the sintering comprising a duration of about 18 to 25 hrs.

12. The method of claim 9 , wherein the silver firing comprising a duration of about 30 to 200 minutes.

Assignees

• Littelfuse Inc

Inventors

• Liu Shuying

Classifications

• C04B35/638

  Removal thereof · CPC title

• C04B35/453 Primary

  based on zinc, tin, or bismuth oxides or solid solutions thereof with other oxides, e.g. zincates, stannates or bismuthates · CPC title

• H01C7/12 Primary

  Overvoltage protection resistors; Arresters · CPC title

• C04B35/62655

  Drying, e.g. freeze-drying, spray-drying, microwave or supercritical drying · CPC title

• C04B2235/6567

  Treatment time · CPC title