High field strength varistor material

Patent metadata

Field	Value
Publication number	US-9672964-B2
Application number	US-89475510-A
Country	US
Kind code	B2
Filing date	Sep 30, 2010
Priority date	Oct 1, 2009
Publication date	Jun 6, 2017
Grant date	Jun 6, 2017

Abstract

The present invention relates to a varistor material for a surge arrester with target switching field strength ranging from 250 to 400 V/mm comprising ZnO forming a ZnO phase and Bi expressed as Bi 2 O 3 forming an intergranular bismuth oxide phase, said varistor material further comprising a spinel phase, characterized in that the amount of a pyrochlore phase comprised in the varistor material is such, that the ratio of the pyrochlore phase to the spinel phase is less than 0.15:1.

First claim

The invention claimed is:

1. A varistor material for a surge arrester comprising ZnO forming a ZnO phase and Bi expressed as Bi 2 O 3 forming an intergranular bismuth oxide phase, the varistor material further comprising a mixture of spinel forming components comprising Mn, Co, Ni and Cr expressed as MnO 2 , CoO, NiO and Cr 2 O 3 , respectively, and optionally Si expressed as SiO 2 , the amount of SiO 2 being less than 0.05 mol %, said varistor material further comprising a spinel phase, wherein the amount of a pyrochlore phase comprised in the varistor material is such that the ratio of the pyrochlore phase to the spinel phase is less than 0.15:1.

2. The varistor material according to claim 1 , wherein the ratio of the pyrochlore phase to the spinel phase is less than 0.1:1.

3. The varistor material according to claim 1 , wherein a target switching field strength ranges from 250 to 400 V/mm.

4. The varistor material according to claim 1 , wherein:
the amount of Bi 2 O 3 is at least 0.3 mol %,
the amount of Sb 2 O 3 is less than 1.8 mol %,
the molar ratio of Bi 2 O 3 to Sb 2 O 3 is at least 0.5:1, and
the total amount of MnO 2 , CoO, NiO and Cr 2 O 3 is at least 2.5 mol %.

5. The varistor material according to claim 1 , wherein
the amount of Bi 2 O 3 is less than 0.5 mol %,
the molar ratio of Bi 2 O 3 to Sb 2 O 3 being less than 0.4:1 the total amount of MnO 2 , CoO, NiO and Cr 2 O 3 is at least 4 mol %.

6. The varistor material according to claim 1 , the mixture of spinel forming components additionally comprising at least one additional spinel forming component selected from the group consisting of Fe, Al, Ti, Mg and Cu.

7. The varistor material according to claim 1 , the material additionally comprising at least one dopant selected from the group consisting of Ag and B.

8. A process for preparing a varistor material according to claim 1 , wherein a starting composition comprising Bi 2 O 3 , Sb 2 O 3 , MnO 2 , CoO, NiO and Cr 2 O 3 is mixed with ZnO and optionally remaining dopants, compacted to discs and sintered at a temperature above 1000° C. to obtain the varistor material.

9. A process for preparing a varistor material according to claim 5 , wherein a starting composition comprising Bi 2 O 3 , Sb 2 O 3 , MnO 2 , CoO, NiO and Cr 2 O 3 is mixed with ZnO and optionally remaining dopants, compacted to discs and sintered at a temperature above 1000° C. to obtain the varistor material, and wherein the starting composition of Bi 2 O 3 , Sb 2 O 3 , MnO 2 , CoO, NiO and Cr 2 O 3 is calcinated at a temperature above 600° C. before mixing it with ZnO and optionally remaining dopants.

10. A surge arrester having a target switching field strength ranging from 250 to 400 V/mm, comprising the varistor material according to claim 1 .

11. A varistor material for a surge arrester comprising ZnO forming a ZnO phase and Bi expressed as Bi 2 O 3 forming an intergranular bismuth oxide phase, the varistor material further comprising a mixture of spinel forming components comprising Mn, Co, Ni and Cr expressed as MnO 2 , CoO, NiO and Cr 2 O 3 , respectively, and optionally Si expressed as SiO 2 , the amount of SiO 2 being less than 0.05 mol %, the varistor material additionally comprising at least one dopant selected from the group consisting of Ag and B, the varistor material further comprising a spinel phase, wherein the amount of a pyrochlore phase comprised in the varistor material is such that the ratio of the pyrochlore phase to the spinel phase is less than 0.15:1, and wherein a target switching field strength ranges from 250 to 400 V/mm.

12. A varistor material for a surge arrester comprising ZnO forming a ZnO phase and Bi expressed as Bi 2 O 3 forming an intergranular bismuth oxide phase, wherein an amount of the Bi 2 O 3 is from 0.6 to 0.9 mol %, the varistor material further comprising Sb 2 O 3 in an amount from 0.9 to 1.5 mol %, a mixture of spinel forming components comprising Mn, Co, Ni and Cr expressed as MnO 2 , CoO, NiO and Cr 2 O 3 , respectively, a total amount of MnO 2 , CoO, NiO and Cr 2 O 3 being at least 3 mol %, and optionally Si expressed as SiO 2 in an amount of less than 0.05 mol %, the varistor material further comprising a spinel phase, wherein the amount of a pyrochlore phase comprised in the varistor material is such that the ratio of the pyrochlore phase to the spinel phase is less than 0.15:1.

Assignees

• Greuter Felix
• Hagemeister Michael
• Beck Oliver
• Osterlund Ragnar
• Kessler Reto
• Abb Schweiz Ag

Inventors

• Greuter Felix
• Hagemeister Michael
• Beck Oliver
• Osterlund Ragnar
• Kessler Reto

Classifications

• C04B2235/3275

  Cobalt oxides, cobaltates or cobaltites or oxide forming salts thereof, e.g. bismuth cobaltate, zinc cobaltite · CPC title

• C04B35/453

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

• C04B2235/3294

  Antimony oxides, antimonates, antimonites or oxide forming salts thereof, indium antimonate · CPC title

• H01B1/08

  oxides · CPC title

• C04B2235/3418

  Silicon oxide, silicic acids or oxide forming salts thereof, e.g. silica sol, fused silica, silica fume, cristobalite, quartz or flint · CPC title