DE3025670A1 - OXYGEN SENSOR AND METHOD FOR THE PRODUCTION THEREOF - Google Patents

Description

- 8 HOEGER, STELLRECHi & PARTNER

A 44 234 b Applicant: UOP Inc.

k - 177 Ten UOP Plaza

July 7, 1980 Algonquin & Mt. Prospect

Roads

Des Piaines, Illinois 60016

United States

Oxygen sensor and process for its manufacture

The invention relates to an oxygen sensor with a ceramic tube and one in this transverse to the longitudinal axis sealingly inserted, a reference point j. te and one measuring side, thin disk made of one stabilized, solid electrolyte, as well as a method for the production of such an oxygen sensor.

The invention thus relates to oxygen sensors of the type in which a disk consists of a stabilized solid electrolyte is arranged in a ceramic tube made of a non-electrolytic material. With such sensors, two have mutually Problem areas arise that are to be seen in the fact that on the one hand it presents difficulties, a hermetic To achieve sealing between pipe and disc, and on the other hand associated with problems is to connect leads to the thin platinum electrodes on the main surfaces of the pane. Although adequate solutions have been developed for each of these problems individually, there must be manufacturing a complete sensor assembly is still a significant number of time consuming Operations are performed. For example, US Pat. No. 4,119,513 describes a sensor which delivers extraordinarily accurate measuring voltages and

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in the case of the supply lines made of a metal of the platinum metal group, which lead to the electrodes made of such a metal, extend over the entire length of the tube, namely one on the inner wall and one on the outer wall, the outer supply line over the measuring end of the tube is led away to the measuring electrode. The pulley is held by a seal made of a glass frit, which has proved to be quite satisfactory and which - as experiments have shown - against Tempera door shocks at temperatures up to at least 700 ⁰ C is insensitive. Furthermore, US Pat. No. 4,123,344 describes a disk-shaped electrolyte which is fixed in a ceramic tube while it shrinks during firing. The disk lies in a recess and has an inner and an outer supply line at their connection point! different materials come together, as well as certain additional elements used for assembly. In general, the low shrinkage exhibited by most ceramic materials imposes very tight tolerances on the outside diameter of the disk and the inside diameter of the counterbore in which the disk is held in accordance with the teachings of the cited patent. In addition, when using seals made of a glass frit, there must be practically no material defects whatsoever if a gas-tight seal is to be achieved between the surfaces to be connected to one another in a sealing manner.

The invention is based on the state of the art is based on the task of creating a tubular oxygen

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sensor with a disk made of a solid electrolyte, which can be assembled quickly and economically can be and which in terms of the dimensions of the pipe and the sealing to be determined therein Disc has large tolerances.

This object is achieved according to the invention in an oxygen sensor of the type described at the outset in that the outer diameter of the disc is greater than the inner diameter of the pipe, at least with respect to the axially spaced apart pipe regions that directly adjoin the two sides of the disc, that the outer diameter of the tube is larger in the plane of the disk than in immediately adjacent planes running transversely to the longitudinal axis of the tube and that the differences in the diameters are sufficiently large to hermetically seal ^{the disk in the tube in a temperature range of at least about 260 to 1100 ° C} to be determined.

An additional aim is to establish a connection between the electrodes in a quick and simple manner the disk and the supply lines, which are protected against damage should and which can also be made of the same material as the electrodes in order to the emergence of secondary stresses of undefined size between different, adjacent ones Avoid metals.

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This additional problem is thereby solved in accordance with the invention solved that the predominant part of the measuring side of the disc and a first narrow circumferential area the same is coated with a first continuous porous electrode layer that the predominant part of the reference side of the disc and a second, narrow peripheral area of the same, which in the circumferential direction with respect to the first circumferential area is offset, coated with a second, continuous, porous electrode layer are that the measuring side and the reference side in the areas that directly adjoin the coated peripheral areas do not have any electrode coating that on the inner wall of the ceramic tube a first and a second conductive strip extending in the axial direction are provided is that the conductive strips, starting from the reference end of the tube, at least to the edge of the The measuring side of the disc is enough and that of the two conductive strips one is coated with the second Circumferential area and the other is aligned with the first coated circumferential area such that the conductive strips and the coated peripheral areas in close electrical and mechanical contact stand together.

The invention is also based on the object of a method for producing such an oxygen sensor to specify. This object is achieved according to the invention by the method according to claim 9.

In detail, in an oxygen sensor according to the invention and in the method for its manufacture

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Position according to a preferred embodiment of the invention, a disk is used which is provided on the predominant part of its main surface, both on the measurement side and on the reference side, with a continuous electrode coating, each electrode coating in a narrow band or a strip on the edge or runs out at the periphery of the disc. The narrow contact or electrode strips are provided at a distance from one another and are preferably diametrically opposite one another. In addition, a small area is left free or not coated both on the measurement side and on the reference side of the pane, which area directly adjoins the narrow strip which is integrally connected to the electrode coating on the opposite side. Furthermore, a coating of conductive material, preferably of the same material from which the electrode coatings are made, is applied in the form of two strips to the inner wall of the pipe. The disk is then placed on a base, whereupon the unfired tube is pushed over the disk and base, which can then shrink during firing in order to form an oversized seat together with the disk. The disk is pre-sintered and is preferably made of yttrium-stabilized zirconium, while the tube is preferably made of fosterite, which shrinks by about 25% ^{when fired at a temperature of about 1300 ° C.} Satisfactory results were achieved when the inside diameter of the unfired ceramic tube was about 20% larger than the outside diameter of the disk (inside diameter approx. 11.6 mm; outside diameter approx. 9.65 mm).

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Furthermore, the electrodes and the leads were preferably made of a platinum paste, as The glass frit used as the binder had a melting point that was about 35 to 95 ° C below the firing temperature for the pipe lay. In this configuration, the tube shrinks during the burning so that with the disc a seat with an oversize of about 5% results, which leads to a slight bulge in the area of the disc the pipe wall leads. The pipe is also "glassy" when burning, so that a tight mechanical connection with the pane both due to the "glazing" and due to the pressure of the fit comes.

The oxygen sensor produced according to the method described above can also be a heating device contain. Such a heating device allows the sensor to be at a constant temperature works that is slightly above the maximum temperature in the process in which the sensor is used will. In this embodiment, the sensor output signal is direct with the well-known Nernst equation linked and can display the percentage of oxygen without the need to to provide a complicated circuit, which the influence of the temperature change on the measurement result considered. The heating device can be in the tubular wall of the ceramic tube in the radial direction be arranged adjacent to the disk-shaped solid electrolyte.

In a preferred exemplary embodiment, an oxygen sensor with a solid electrolyte is

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shrinking of a ceramic tube produced, with heating devices installed in a sealing manner in the tube wall are and a sealing connection between the tube and a disk made of the solid electrolyte will.

The ceramic material is preferably fosterite, its thermal expansion closely matched to the thermal expansion of yttrium stabilized zirconia is which is a common solid electrolyte. Of the

Fosterite body has an outside diameter of about 25.4 mm and a central opening of about 9.45 mm extruded, which is surrounded by a number of narrower channels that are about 3.15 mm in diameter and are suitable for receiving heating elements. The number of channels can vary widely Range, for example between about 4 and 12, obviously a larger number of channels leads to more even heating of the plate or disk made of the solid electrolyte. If the fosterite is dry but still unfired and easy to work with, then the pipe will open Cut length. In addition, an annular groove with a width of about 3.15 mm, the depth of which is approximately equal to the depth of the innermost points of the in Circumferential direction of the pipe wall is distributed channels. In addition, the face of the measuring end of the Cut a second groove in the tube which has a diameter which is the diameter of the circle or circular ring, which contains the channels. The two grooves provide space for the arches a heating coil, which is filled into the channels

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after the pipe is burned. The grooves are then filled with a castable ceramic material,
to seal the heating coil. To improve the heat transfer between the heating coil and the
Ceramic tube, the channels are filled with a packing of MgO particles or another material after the annular groove has been sealed. The disc from the
According to the invention, solid electrolyte is tightly fixed in the ceramic tube by the shrinkage of the same during firing, with a mechanical connection
of the elements takes place when the surface of the Phosteritkörpers is glassy at the typical firing temperature of about 1300 ⁰ C.

Further details and advantages of the invention are explained in more detail below with reference to drawings. Show it:

1 shows a longitudinal section through the disk, the tube and supply lines of a preferred embodiment of an oxygen sensor according to the invention after burning;

FIG. 2 shows a cross section through the sensor according to FIG. 1 along the line 2-2 in this figure;

3 shows a longitudinal section through the unfired tube of the sensor according to FIG. 1;

FIG. 4 shows a plan view of the tube according to FIG. 3;

FIG. 5 shows a perspective illustration of the solid electrolyte disk of the sensor according to FIG. 1

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after applying the electrode layers; 6 shows a side view of the disk according to FIG. 5;

7 shows a longitudinal section through a sensor arrangement according to Fig. 1 before firing with a burner insert for mutual positioning of the Sensor elements;

FIG. 8 a plan view of the arrangement according to FIG. 7;

9 shows a perspective illustration of an inventive Oxygen sensor with integrated heating device, with some parts broken away are and

FIG. 10 shows a longitudinal section through the sensor according to FIG.

In detail, Fig. 1 shows an improved oxygen sensor 10 according to the invention, which essentially from a ceramic tube 12 or a ceramic, tubular base body and one therein in the Near the upper end or the sensor end 12 'mounted disc 14 made of a ceramic solid electrolyte consists. Here, the ceramic tube 12 is something at 12 " "bulged" shown in order to illustrate the fact that the directly adjacent to the disk 14 Pipe areas have shrunk during a firing process to a tight interlocking of To reach tube 12 and disk 14. The oxygen sensor 10 is - which is not shown in the drawing - generally mounted in a housing, which allows the measuring end 12 'to enter the gases to be examined, typically exhaust gases or smoke

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gases, while the other end of the sensor, which referred to as reference end 12 '' 'with the ambient air communicates. With such an assembly, the measuring side 14 'and the reference side 14' * of the electrolyte of the disk 14 exposed to gas mixtures in which a different partial pressure of oxygen is present. It is known that these different oxygen partial pressures lead to one Voltage across the disk 14, which represents a solid electrolyte cell, which by means of a circuit (not shown) can be measured, which with connections 16 'and 18' of a reference electrode conductor 16 or a measuring electrode conductor 18 is connected. The conductors 16, 18 are preferably made of platinum and are in firm contact with a reference electrode 20 and a measuring electrode 22, the two Electrodes 20, 22 are also preferably made of platinum, so that there are no different electrodes in the sensor Metals are present, which can lead to the creation of undesirable stresses. The electrodes 20, 22 are also on the reference page 14 '' or on the measuring side 14 'of the disk 14 is provided.

The oxygen sensor 10 is constructed by first performing the method step explained with reference to FIG. In this process step, a sintered plate or disk made of a solid electrolyte, on the main surfaces of which paste-like electrode layers 20, 20 'and 22, 22' have been applied, as shown in FIGS. 5 and 6, is placed on a base 30 which is provided on a ceramic firing insert 32 _? so that the disc 14 in a predetermined axial Lr depending on the

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unfired or raw ceramic tube 12, which is shown in Figs. The disk 14 is arranged in such a way that strip-shaped electrode parts 2O ¹ or 22 ′ are aligned with the strip-shaped conductors 16 and 18 on the inner wall of the tube 12, as FIG. 8 shows. The burner insert 32 with the unfired tube 12 and the disk 14 can now be placed in a furnace, where the tube 12 is fired, whereby it shrinks and comes into firm mechanical contact with the disk 14, as FIG. 1 shows. If fosterite is used as the material for the tube, which shows a shrinkage of about 25% when fired, then the outer diameter of the disk 14 and the inner diameter of the tube 12 can differ in size by 20%, although there is still a fit with an oversize of 5% is achieved. This is a significant advantage as it means that the tolerances of the disks and the extruded unfired ceramic tubes can be set fairly generously. In addition, there is no need to machine the tube to create a seat for the disc. In addition, the fact that the pipe wall now has the same wall thickness throughout improves the resistance of the sensor to sudden changes in temperature.

9 shows a perspective illustration of an oxygen sensor provided with a heating device 10 according to the invention, with some parts broken away. The tube 12 again has a measuring end 12 'and a reference end 12 ··· passing through the disc 14 are separated from a solid electrolyte. The reference electrode conductor 16 and the measuring electrode conductor

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ter 18 are in close contact with strip-shaped Parts of the reference electrode 20 and the measuring electrode 22. The conductors and electrodes are preferably made all made of the same material, preferably platinum, which is first applied as a paste to avoid secondary stresses avoid that can arise when different metals are used. At the Extruding the tube 12 from malleable ceramic material is a central opening 26 as well Number of smaller openings or channels 24 made in the pipe wall. By machining is also in the lateral surface of the tube 12 a Annular groove 28 is produced, which extends approximately to the inside of the channels 24. The annular groove 28 has a Width of about 2 mm, so that it is possible to thread a heating wire 30 into the channels 24 so that it runs through this in a meandering shape, the groove 28 being the heating wire arches at the reference end of the heating device receives, while another groove 32 receives the heating wire arches at the measuring end of the same. The two ends 30 ', 30' 'of the heating wire 30 protrude over the reference end 12' * 'of the sensor 10, where they are connected to a Supply voltage source (not shown) can be connected. As the drawing shows, it stands Heating wire 30 over a length which is slightly larger than the diameter of the disk 14 in the axial direction forward and backward over the washer 14 to ensure that there is even heating the disc 14 and its electrodes takes place. A pack of MgO particles 34 in the channels 24, through which the heating wire 3C is guided, promotes heat conduction through the wall of the tube 12 to the Disk 14. A layer 36 of castable ceramic material serves to seal the annular groove 28

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sen, while a layer 38 of castable ceramic material serves to seal the groove 32 provided on the end face of the tube 12. the Layers 36 and 38 also protect the heating wire 30 from the adjacent atmosphere, for example against smoke gases to which the sensor 10 is normally exposed.

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L e r s e i t e

Claims (1)

y ci L ₁ f sch, Hoeger, STELLRECHT & PARTNER £, ^ ηι PATENTANWÄLTE UHLANDSTRASSE 14 ο D 70OO STUTTGART -. J (Y / Sun / U A 44 234 b Applicant: UOP Inc. k - 177 Ten UOP Plaza July 7, 1980 Algonquin & Mt Prospect Roads Des Piaines, Illinois 60016 United States Claims Oxygen sensor with a ceramic tube and a in this, sealingly inserted transversely to the longitudinal axis, having a reference side and a measuring side, thin disc made of a stabilized, solid electrolyte, characterized in that the outer diameter of the disc (14) is at least with respect to the axially spaced pipe areas that are directly connected to the adjoin both sides (14 ', 14' ') of the disc (14), larger is than the inner diameter of the pipe (12) that the outer diameter of the pipe (12) is larger in the plane of the disc (14) than in immediately adjacent planes and transversely to the longitudinal axis of the tube (12) that the differences in the diameters are large enough to allow the disc (14) to be in the Tube (12) hermetically sealed in a temperature range of at least about 260 to 1100 C. to be determined. An oxygen sensor according to claim 1, characterized in that the predominant part of the Messeite (14 ') is coated of the disc (14) and a first, narrow peripheral portion thereof with a first continuous _t orösen electrode layer (22, 22'), that the majority of the reference side of the disc (14) and a 130012/0617 July 7, 1980 - 2 - second, narrow circumferential area of the same, which is offset in the circumferential direction with respect to the first circumferential area, are coated with a second, continuous, porous electrode layer (20, 20 ') that the measuring side (14 ·) and the reference side (14'') in the Areas that directly adjoin the coated peripheral areas (20 ¹ ) / (22 ') do not have an electrode coating that a first and a second conductive strip (16, 18) running in the axial direction are provided on the inner wall of the ceramic tube (12) is that the conductive strips (16, 18), starting from the reference end (12 ¹¹¹ ) of the tube (12) at least as far as the edge of the measuring side (14 ') of the disc (14) and that from the two conductive strips (16, 18) one (16) is aligned with the second coated peripheral area (2O ¹ ) and the other (18) with the first coated peripheral area (22 ') in such a way that the conductive strips (16, 18) and the coated peripheral areas (20 ¹ , 22 ') are in close electrical and mechanical contact with one another. 3. Oxygen sensor according to claim 2, characterized in that that the electrode layers (20, 20 ', 22, 22') and the conductive strips (16, 18) consist of the same material. 4. Oxygen sensor according to one of claims 1 to 3, characterized in that the ceramic tube (12) has a central opening (26) and in which the central opening (26) surrounding wall at least four 130012/0617 " ³ " July 7, 19 80 - 3 - channels (24) arranged at a distance from one another, that the disc (14) in the central opening (26) is arranged transversely to the longitudinal axis of the tube (12) in such a way that its measuring side (14 ') can be exposed to a gas to be tested while their reference side (14 ¹¹⁾ can be exposed to a reference gas, that (24) electrical Widerstandheizeinrichtungen (30) are provided in the at least four channels, at least, wherein the disc (14) is in a region adjacent the channels (24) and outside this lies that the heating devices (30) are sealingly enclosed in the channels (24) in the area adjoining the pane (24) and that the heating devices (30) have supply lines (30 ', 30'') which pass through at least two of the Channels (24) are passed through to the reference end (12 '") of the tube (12). Oxygen sensor according to claim 4, characterized in that the ceramic tube (12) is provided with an annular groove (28) which extends to the depth of the channels (24), that the annular groove on the reference side (14 ¹¹ ) of the disc (14) is that the resistance heating devices have a heating wire (30) which has a heating section which is threaded into a part of the channels (24) located between the annular groove (28) and a groove (32) on the face of the reference end that the heating wire (30) has end regions which form the feed lines (30 ", 30"), and that the annular groove (28) and the end 1 3001 2 / 0B17 July 7, 1980 - 4 - lateral groove (32) for sealing the heating area in the area between the grooves (28, 32) with a castable ceramic material (36), (38) are sealed. 6. Oxygen sensor according to claim 5, characterized in that that the heating wire (30) receiving parts of the channels (24) with magnesium oxide grains are filled. 7. Oxygen sensor according to claim 6, characterized in that the heating area extends in the axial direction over such a part of the length of the tube (12) that its length starting from the disc (14) both in the direction of the reference end (12 ¹¹¹ JwIe also in the direction of the measuring end (12 ¹ ) of the tube (12) is at least as large as the diameter of the disc (14). 8. Oxygen sensor according to one of claims 2 to 7, characterized in that the ^{conductive strips (16, 18) leading to the reference end (12 '11} J) on the inner wall of the tube (12) are under pressure in electrical contact with the corresponding to the coated peripheral regions strip-shaped electrode parts (20 ", 20 ¹ ') stand and that the tube (12) and the disc (14) together form a seat with oversize. 9. Method of making an oxygen sensor according to one of claims 1 to 8, characterized by the following process steps: 130012/0617 k - 177 July 7, 19 80 - 5 - a sintered disk made of stabilized solid electrolyte ceramic is produced; a first, porous, continuous electrode coating is applied to the larger part the measuring side of the disc and on a narrow first band-shaped area on the narrow circumferential surface of the disk, while the measuring side of the disk is immediately adjacent on a second coated circumferential area, which extends in the circumferential direction at a distance from the first band-shaped coated peripheral area is located, not with a coating provides; a second, porous, continuous electrode coating is applied to the predominant one Part of the reference side of the disc and on a narrow second band-shaped circumferential area same on, while looking at the reference side of the disc in the area that immediately follows adjoining the first narrow coated peripheral region, does not apply an electrode coating; a first and a second conductive strip are placed on at least part of them Length of an unfired ceramic tube, which has an inner diameter that is larger is than the outside diameter of the disc, and a temperature coefficient of expansion, which after dfein burn with that of the disc largely coincides, but when the pipe burns it causes ^ ier ^ s to shrink so 130012 / 06T ⁷ " ⁶ ' July 7, 1980 - 6 - that it forms a hermetically sealed connection with the pane, whereby the conductive Strips are applied in the circumferential direction at a distance equal to the distance between corresponds to the band-shaped coated peripheral areas of the disk; the disc is positioned inside the unfired ceramic tube in such a way that the band-shaped coated circumferential areas are aligned with the conductive strips and these opposite and the arrangement of tube and disk obtained during positioning is fired to shrink it on of the tube on the disk and the coated circumferential areas of the disk mechanically in close contact with the associated conductive strip to press. 10. The method according to claim 9, characterized in that the pipe to be burned by extrusion will be produced. 11. The method according to claim 9 or 10, characterized in that the tube is made of a starting material which shrinks by about 25% when fired. 12. The method according to any one of claims 9 to 11, characterized in that the electrode coatings on the disc and the conductive strips on the inner wall of the tube 130012/0617 k - 177 July 7, 19 80 - 7 - be made of the same material and that the conductive strips up to the reference end of the pipe. 130012/0617 " ⁸ "