Zinc oxide varistor and method for manufacturing same

Patent metadata

Field	Value
Publication number	US-11370712-B2
Application number	US-201716467624-A
Country	US
Kind code	B2
Filing date	Dec 7, 2017
Priority date	Dec 7, 2016
Publication date	Jun 28, 2022
Grant date	Jun 28, 2022

Abstract

Focus is on zinc oxide itself, which is a base material for a zinc oxide varistor (laminated varistor), wherein specified quantities of additives are added to a zinc oxide powder having a crystallite size of 20 to 50 nm, grain diameter of 15 to 60 nm found using the specific surface area BET method, untamped density of 0.38 to 0.50 g/cm3, and tap density of 0.50 to 1.00 g/cm3. This allows securing of uniformity, high compactness, and high electrical conductivity of a zinc oxide sintered body, and provision of a zinc oxide varistor having high surge resistance.

First claim

The invention claimed is:

1. A zinc oxide varistor, comprising zinc oxide (ZnO) as a main component, one or more additives selected as a grain boundary forming component selected from the group consisting of bismuth (Bi) and praseodymium (Pr) and mixtures thereof, and one or more additives selected as a transition metal element selected from the group consisting of cobalt (Co), manganese (Mn) and nickel (Ni) and mixtures thereof;
wherein the zinc oxide has a crystallite size of 20 to 50 nm found by X-ray diffraction, grain diameter of 15 to 60 nm found using a specific surface area BET method, untamped density of 0.38 to 0.50 g/cm 3 , and tap density of 0.50 to 1.00 g/cm 3 .

2. The zinc oxide varistor according to claim 1 , wherein crystallite size when powder of the zinc oxide is sintered at 1000° C. is 70 to 1200 nm, and crystallite size when sintered at 1150° C. is 75 to 170 nm.

3. The zinc oxide varistor according to claim 2 , wherein increasing rate of the crystallite size of the zinc oxide by sintering within the range of 1000° C. and 1150° C. is 10% or less.

4. The zinc oxide varistor according to claim 1 , further comprising one or more donor elements selected from the group consisting of aluminum (Al), boron (B), and gallium (Ga), and mixtures thereof.

5. A zinc oxide varistor, comprising zinc oxide (ZnO) as a main component, one or more additives selected as a grain boundary forming component selected from the group consisting of bismuth (Bi) and praseodymium (Pr) and mixtures thereof, and one or more additives selected as a transition metal element selected from the group consisting of cobalt (Co), manganese (Mn) and nickel (Ni), and mixtures thereof;
wherein the zinc oxide has median diameter of 30 to 60 nm found using a dynamic scattering method, cumulant diameter of 40 to 82 nm, and cumulant polydispersity index of 0.05 to 0.20.

6. The zinc oxide varistor according to claim 5 , wherein crystallite size when powder of the zinc oxide is sintered at 1000° C. is 70 to 1200 nm, and crystallite size when sintered at 1150° C. is 75 to 170 nm.

7. The zinc oxide varistor according to claim 6 , wherein increasing rate of the crystallite size of the zinc oxide by sintering within the range of 1000° C. and 1150° C. is 10% or less.

8. The zinc oxide varistor according to claim 5 , wherein one or more donor elements selected from the group consisting of aluminum (Al), boron (B), and gallium (Ga), and mixtures thereof, is further added.

9. A manufacturing method of a zinc oxide varistor, comprising the steps of:
manufacturing basic zinc carbonate slurry that is a first precursor of zinc oxide (ZnO) powder;
obtaining from the first precursor a dried powder of basic zinc carbonate that is a second precursor of zinc oxide (ZnO) powder;
obtaining zinc oxide (ZnO) through heat treatment of the second precursor;
manufacturing a mixed material resulting from adding a predetermined additive to the zinc oxide (ZnO); and
forming a varistor element for a zinc oxide varistor from the mixed material,
wherein the zinc oxide varistor comprises zinc oxide (ZnO) as a main component, one or more additives selected as a grain boundary forming component selected from the group consisting of bismuth (Bi) and praseodymium (Pr) and mixtures thereof, and one or more additives selected as a transition metal element selected from the group consisting of cobalt (Co), manganese (Mn) and nickel (Ni) and mixtures thereof; and
the zinc oxide has a crystallite size of 20 to 50 nm found by X-ray diffraction, grain diameter of 15 to 60 nm found using the specific surface area BET method, untamped density of 0.38 to 0.50 g/cm 3 , and tap density of 0.50 to 1.00 g/cm 3 .

10. The manufacturing method of a zinc oxide varistor according to claim 9 ,
wherein the zinc oxide varistor comprises zinc oxide (ZnO) as a main component, one or more additives selected as a grain boundary forming component selected from the group consisting of bismuth (Bi) and praseodymium (Pr) and mixtures thereof, and one or more additives selected as a transition metal element selected from the group consisting of cobalt (Co), manganese (Mn) and nickel (Ni), and mixtures thereof; and
the zinc oxide has median diameter of 30 to 60 nm found using a dynamic scattering method, cumulant diameter of 40 to 82 nm, and cumulant polydispersity index of 0.05 to 0.20.

11. The manufacturing method of a zinc oxide varistor according to claim 10 , wherein one or more donor elements selected from the group consisting of aluminum (Al), boron (B), and gallium (Ga), and mixtures thereof, is further added.

12. The manufacturing method of a zinc oxide varistor according to claim 9 , wherein one or more donor elements selected from the group consisting of aluminum (Al), boron (B), and gallium (Ga), and mixtures thereof, is further added.

Assignees

• Koa Corp
• Jfe Mineral Co Ltd
• KOA Corporoation

Inventors

• Gomi Yoji
• Iguchi Kenichi
• UDAGAWA Etsurou
• ECHIZENYA Yuko
• Nakata yoshimi

Classifications

• C01P2002/60

  Compounds characterised by their crystallite size · CPC title

• C04B2235/85

  Intergranular or grain boundary phases · CPC title

• C04B2235/3279

  Nickel oxides, nickalates, or oxide-forming salts thereof · CPC title

• C01P2004/64

  Nanometer sized, i.e. from 1-100 nanometer · CPC title

• C04B2235/781

  Nanograined materials, i.e. having grain sizes below 100 nm · CPC title