# US 5,707,583 A · Method for preparing the zinc oxide base varistor > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 5,707,583 A - Document ID: US5707583A - Status: Granted - Kind: A - Application number: 08/444,578 - Filed: 1995-05-19 - Granted: 1998-01-13 - Earliest claimed: 1994-05-19 - Assignees: TDK Corporation - Inventors: Masatada Yodogawa - Web page: https://patentgrep.com/patent/US5707583A ## CPC - H01C 7/112: ZnO type - C04B 35/453: based on zinc, tin, or bismuth oxides or solid solutions thereof with other oxides, e.g. zincates, stannates or bismuthates - H01C: RESISTORS - C04B: LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE {(roofing granules E04D7/005)}; CERAMICS (devitrified glass-ceramics C03C10/00); REFRACTORIES; TREATMENT OF NATURAL STONE ## Abstract In preparing a zinc oxide base varistor in the form of a sintered body which itself has a voltage-dependent nonlinear resistance, firing is done in an atmosphere containing at least 60% of oxygen at or above the temperature at which additives form a liquid phase, and thereafter the sintered body is heat treated in an atmosphere containing at least 10% of oxygen at a temperature of 600.degree. to 1,000.degree. C. There is obtained a zinc oxide base varistor having a high energy handling capability, a high nonlinearity index .alpha., and satisfactory load life characteristics such as a humid load life. ## Claims ### Claim 1 A method for preparing a zinc oxide based varistor in the form of a sintered body, comprising: firing a composition in an atmosphere comprising at least 60 vol. % oxygen, thereby forming a liquid phase to obtain a sintered body; followed by heat treating said sintered body in an atmosphere comprising at least 10 vol. % oxygen, at a temperature of 600.degree.-1000.degree. C.; wherein said composition comprises zinc, at least one rare earth element, cobalt, Si and at least one element selected from the group consisting of B, Al, Ga and In, and said zinc and said at least one rare earth element are present as oxides, or compounds which convert into oxides upon said firing. ### Claim 2 (depends on 1) The method of claim 1, wherein said at least one rare earth element is present in an amount of 0.02-5 at. %. ### Claim 3 (depends on 1) The method of claim 1, wherein said composition further comprises cobalt in amount of 0.01-10 at. %. ### Claim 4 (depends on 1) The method of claim 1, wherein said composition further comprises at least one element selected from the group consisting of B, Al, Ga and In, in an amount of 1.times.10.sup.-4 to 1.times.10.sup.-1 at. %. ### Claim 5 (depends on 1) The method of claim 1, wherein said composition further comprises Si in an amount of 0.001-0.5 at. %. ### Claim 6 (depends on 1) The method of claim 1, wherein said heating is carried out in an atmosphere comprising 20-50 vol. % oxygen. ### Claim 7 (depends on 1) The method of claim 1, wherein said heating is carried out at a temperature of from 700.degree.-800.degree. C. ### Claim 8 (depends on 1) The method of claim 1, wherein said composition further comprises: 0.1-10 at. % cobalt; 1.times.10.sup.-4 to 1.times.10.sup.-1 at. % of at least one element selected from the group consisting of Ba, Al, Ga and In; 0.001-0.5 at. % of Si; and 0.01-1 at. % of Cr. ### Claim 9 (depends on 1) The method of claim 1, wherein the firing step is performed at a temperature of from 1150.degree. C. to 1500.degree. C. ### Claim 10 A method for preparing a zinc oxide based varistor in the form of a sintered body, comprising: firing a composition in an atmosphere comprising at least 60 vol. % oxygen, thereby forming a liquid phase to obtain a sintered body; followed by heat treating said sintered body in an atmosphere comprising at least 10 vol. % oxygen, at a temperature of 600.degree.-1000.degree. C.; wherein said composition comprises zinc, at least one rare earth element, cobalt, Cr and at least one element selected from the group consisting or B, Al, Ga and In, and said zinc and said at least one rare earth element are present as oxides, or compounds which convert into oxides upon said firing. ### Claim 11 (depends on 10) The method of claim 10, wherein said composition further comprises Cr in an amount of 0.01-1 at. %. ### Claim 12 (depends on 10) The method of claim 10, wherein the firing step is performed at a temperature of from 1150.degree. C. to 1500.degree. C. ### Claim 13 (depends on 12) The method of claim 12, wherein said composition further comprises at least one element selected from the group consisting of K, Rb and Cs, present in an amount of 0.005-1 at. %. ### Claim 14 (depends on 10) The method of claim 10, wherein said at least one rare earth element is present in an amount of 0.02-5 at. %. ### Claim 15 (depends on 10) The method of claim 10, wherein said composition further comprises cobalt in amount of 0.01-10 at. %. ### Claim 16 (depends on 10) The method of claim 10, wherein said composition further comprises at least one element selected from the group consisting or B, Al, Ga and In, in an mount of 1.times.10.sup.-4 to 1.times.10.sup.-1 at. %. ### Claim 17 (depends on 10) The method of claim 10, wherein said heating is carried out in an atmosphere comprising 20-50 vol. % oxygen. ### Claim 18 (depends on 17) The method of claim 17, wherein said heating is carried out at a temperature of from 700.degree.-800.degree. C. ### Claim 19 A method for preparing a zinc oxide based varistor in the form of a sintered body, comprising: firing a composition in an atmosphere comprising at least 60 vol. % oxygen, thereby forming a liquid phase to obtain a sintered body; followed by heat treating said sintered body in an atmosphere comprising at least 10 vol. % oxygen, at a temperature of 600.degree.-1000 .degree. C.; wherein said composition comprises zinc, at least one rare earth element, cobalt, at least one element selected from the group consisting of K, Rb and Cs, and at least one element selected from the group consisting or B, Al, Ga and In, and said zinc and said at least one rare earth element are present as oxides, or compounds which convert into oxides upon said firing. ### Claim 20 (depends on 19) The method of claim 19, wherein said composition further comprises at least on element selected from the group consisting of Mg, Ca, Sr and Ba, in an amount of 0.005-4 at. %. ### Claim 21 (depends on 19) The method of claim 19, wherein the firing step is performed at a temperature of from 1150.degree. C. to 1500.degree. C. ### Claim 22 (depends on 19) The method of claim 19, wherein said at least one rare earth element is present in an amount of 0.02-5 at. %. ### Claim 23 (depends on 19) The method of claim 19, wherein said composition further comprises cobalt in amount of 0.01-10 at. %. ### Claim 24 (depends on 19) The method of claim 19, wherein said composition further comprises at least one element selected from the group consisting or B, Al, Ga and In, in an mount of 1.times.10.sup.-4 to 1.times.10.sup.-1 at. %. ### Claim 25 (depends on 19) The method of claim 19, wherein said heating is carried out in an atmosphere comprising 20-50 vol. % oxygen. ### Claim 26 (depends on 25) The method of claim 25, wherein said heating is carried out at a temperature of from 700.degree.-800.degree. C. ### Claim 27 A method for preparing a zinc oxide based varistor in the form of a sintered body, comprising: firing a composition in an atmosphere comprising at least 60 vol. % oxygen, thereby forming a liquid phase to obtain a sintered body; followed by heat treating said sintered body in an atmosphere comprising at least 10 vol. % oxygen, at a temperature of 600.degree.-1000.degree. C.; wherein said composition comprises zinc, at least one rare earth element, cobalt, at least one element selected from the group consisting of Mg, Ca, Sr and Ba, and at least one element selected from the group consisting of B, Al, Ga and In, and said zinc and said at least one rare earth element are present as oxides, or compounds which convert into oxides upon said firing. ### Claim 28 (depends on 27) The method of claim 27, wherein the firing step is performed at a temperature of from 1150.degree. C. to 1500.degree. C. ### Claim 29 (depends on 27) The method of claim 27, wherein said at least one rare earth element is present in an amount of 0.02-5 at. %. ### Claim 30 (depends on 27) The method of claim 27, wherein said composition further comprises cobalt in amount of 0.01-10 at. %. ### Claim 31 (depends on 22) The method of claim 22, wherein said composition further comprises at least one element selected from the group consisting of B, Al, Ga and In, in an amount of 1.times.10.sup.-4 to 1.times.10.sup.-1 at. %. ### Claim 32 (depends on 27) The method of claim 27, wherein said heating is carried out in an atmosphere comprising 20-50 vol. % oxygen. ### Claim 33 (depends on 32) The method of claim 32, wherein said heating is carried out at a temperature of from 700.degree.-800.degree. C.