Claims
- 1. A magnesia-based beta alumina sintered body, comprising beta alumina crystals and sodium aluminate crystals, wherein:
- (1) the average crystalline particle diameter of beta alumina crystals, calculated assuming that the beta alumina crystals are of a circular cross-section, is in a range of 1-4 .mu.m;
- (2) the amount of beta alumina crystals having particle diameters not more than 5 .mu.m, when measured in a cross-sectional area of the sintered body, is 85% to 98%;
- (3) the maximum crystalline particle diameter is not more than 300 .mu.m;
- (4) the number of coarse particles having diameters falling in a range of 100 .mu.m to 300 .mu.m is not more than 1, when counted in a 10 mm.times.10 mm cross-sectional area of the sintered body; and
- (5) the content of crystals of sodium aluminate is 0.5 wt % to 6.0 wt %.
- 2. The magnesia-based beta alumina sintered body according to claim 1, further comprising 0.1 wt % to 3.0 wt % ZrO.sub.2 relative to the total weight of the sintered body.
- 3. The magnesia-based beta alumina sintered body according to claim 1, which has a diametrical compression strength of not less than 250 MPa, and a four-terminal electric resistance of not more than 5 .OMEGA.cm at 350.degree. C.
- 4. A process for producing a magnesia-based beta alumina sintered body, comprising the steps of:
- weighing and mixing MgOAl.sub.2 O.sub.3 spinel, alumina and a sodium compound as starting materials in such respective amounts that the resulting magnesia-based beta alumina sintered body is composed of 85.5 to 87.5 wt % of Al.sub.2 O.sub.3, 3.5 to 4.5 wt % of MgO and 9.0 to 10.0 wt % of Na.sub.2 O;
- calcining the resulting mixture to form calcined beta alumina;
- milling and granulating the calcined beta alumina;
- molding the granulated beta alumina;
- firing the molded beta alumina at 1580.degree.-1600.degree. C. for a time period from 30 minutes to 60 minutes; and
- cooling the fired beta alumina in a temperature range from a maximum firing temperature to 1,450.degree. C. at a cooling rate of 300.degree. C./hr to 800.degree. C./hr.
- 5. The process according to claim 4, wherein the starting materials are mixed in such respective amounts that residual crystals of sodium aluminate are present in an amount of 0.5 to 6.0 wt % relative to the total weight of the magnesia-based beta alumina sintered body.
- 6. The process according to claim 4, wherein when the starting materials are mixed, ZrO.sub.2 is so added that the content of ZrO.sub.2 is in a range of 0.1 to 3.0 wt % relative to the total weight of the sintered body.
- 7. The process according to claim 4, wherein the sintered body as a diametrical compression strength of not less than 250 MPa, and a four-terminal electric resistance of not more than 5 .OMEGA.cm at 350.degree. C.
- 8. The process according to claim 6, wherein the sintered body as a diametrical compression strength of not less than 250 MPa, and a four-terminal electric resistance of not more than 5 .OMEGA.cm at 350.degree. C.
- 9. A process for producing a magnesia-based beta alumina sintered body, comprising the steps of:
- weighing and mixing MgOAl.sub.2 O.sub.3 spinel, alumina and a sodium compound as starting materials in such respective amounts that the resulting magnesia-based beta alumina sintered body is composed of 85.5 to 87.5 wt % of Al.sub.2 O.sub.3, 3.5 to 4.5 wt % of MgO and 9.0 to 10.0 wt % of Na.sub.2 O;
- calcining the resulting mixture to form calcined beta alumina;
- milling and granulating the calcined beta alumina;
- molding and granulated beta alumina;
- firing the molded beta alumina, wherein the firing temperature at which the molded beta alumina is fired on a low temperature side in a firing furnace is set at not less than 1580.degree. C., while the beta alumina is kept at the firing temperature for a time period not less than 30 minutes, whereas the firing temperature at which the beta alumina is fired on a higher temperature side in the firing furnace is set at not more than 1650.degree. C., while the beta alumina is kept at the firing temperature for a time period of not more than 60 minutes; and
- cooling the fired beta alumina in a temperature range from a maximum firing temperature to 1,450.degree. C. at a cooling rate of 300.degree. C./hr to 800.degree. C./hr.
- 10. The magnesia-based beta alumina sintered body according to claim 7, which as a diametrical compression strength of not less than 250 MPa, and a four-terminal electric resistance of not more than 5 .OMEGA.cm at 350.degree. C.
- 11. The process according to claim 5, wherein when the starting materials are mixed, ZrO.sub.2 is so added that the content of ZrO.sub.2 is in a range of 0.1 to 3.0 wt % relative to the total weight of the sintered body.
- 12. The process according to claim 5, wherein the sintered body as a diametrical compression strength of not less than 250 MPa, and a four-terminal electric resistance of not more than 5 .OMEGA.cm at 350.degree. C.
Priority Claims (2)
Number |
Date |
Country |
Kind |
3-226551 |
Aug 1991 |
JPX |
|
7-015861 |
Feb 1995 |
JPX |
|
Parent Case Info
This application is CIP application of Ser. No. 08/247,460 filed May 23, 1994, which is a continuation application of Ser. No. 07/925,857 filed Aug. 7, 1992, both now abandoned.
US Referenced Citations (11)
Foreign Referenced Citations (5)
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0013833 |
Aug 1980 |
EPX |
0110712 |
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8251172 |
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2-123671 |
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Continuations (1)
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Number |
Date |
Country |
Parent |
925857 |
Aug 1992 |
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Continuation in Parts (1)
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Number |
Date |
Country |
Parent |
247460 |
May 1994 |
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