Sealing element for sensors

Details Sealing element for sensors Sealing element for sensors

1998-08-07

2001-08-14

Knight, Anthony (Department: 3626)

Seal for a joint or juncture

Seal between fixed parts or static contact against...

Contact seal between parts of internal combustion engine

C277S630000, C277S650000, C277S943000, C204S424000

Reexamination Certificate

active

06273432

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a seal for a sensor element of a gas sensor.
BACKGROUND INFORMATION
A seal for a sensor element of a gas sensor is known, for example, from German Published Patent Application No. 195 32 090 A1, in which the sensor is mounted into a longitudinal bore of a housing by way of at least two sealing members and a deformable auxiliary seal arranged between the sealing members. The two sealing members are made of magnesium aluminum silicate (steatite), and the sealing member mounted between those sealing members is made of the hexagonal allotrope of boron nitride.
SUMMARY OF THE INVENTION
The seal according to the present invention is both gas-tight and impermeable to liquids, in particular to fuels, and moreover possesses very high temperature resistance. This is achieved by way of a mixture of at least one ceramic compound and at least one fluoride compound. In addition, the use of this mixture instead of a seal configuration made up of sealing elements of different chemical compositions yields simplified handling and assembly.
In a particularly advantageous manner, steatite, i.e. the combustion product of soapstone, having the approximate chemical formula 3MgO.4SiO
2
.H
2
O, in a mixture with a fluoride compound, is used as the ceramic compound. This ensures particularly high temperature stability.
In a further preferred embodiment, boron nitride is used as the ceramic compound, the hexagonal allotrope of BN being preferred. The hexagonal allotrope of boron nitride is very fine-grained and similar to its isostere graphite, a highly deformable compound, so that the tightness and flexibility of the sealing element are decisively improved.
Advantageously, a metallic fluoride, in particular a divalent or trivalent metallic fluoride, is used as the fluoride compound. The addition of a metal fluoride of this kind allows an increase in the coefficient of thermal expansion of the powder packet in temperature ranges from 500 to 1000 degrees. The coefficient of thermal expansion of the sealing element is thereby adapted to those of, for example, chromium steel or yttrium-stabilized zirconium dioxide (YSZ).
In a preferred embodiment, the quantitative concentration of the fluoride compound is 15 to 70 wt. %, in particular 20 to 30 wt. %, in terms of the total mass of the seal. By using a fluoride compound in the form of a powder having an average particle diameter &agr;
50
of 0.5 to 10 &mgr;m, in particular 1 to 5 &mgr;m, the coefficient of thermal expansion is adapted particularly well to that of YSZ. As a result of the use of the metal fluoride, the coefficient of thermal expansion (CTE) of the powder packet which is used as the sealing element is, for example, 10 to 18×10
−6
Kelvin
−1
in the temperature range from 500 to 1000 degrees C. The coefficient of thermal expansion of YSZ, in contrast, is 10×10
−6
Kelvin
−1
, so that by appropriately varying the metal fluoride, the coefficient of thermal expansion can be adapted in such a way that no thermally induced stresses occur between the seal and the solid electrolyte body of the gas sensor. This makes it possible, in particular, for the powder packet of the seal to function in consistent and stable fashion even in hot gases and in continuous operation.


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patent: 195 32 090 A1 (1997-03-01), None
patent: 195 32 090 (1997-03-01), None
patent: 59-219697 (1984-12-01), None

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